Acute Osteomyelitis

Clinical Snapshot

Acute osteomyelitis is a bone infection, most often caused by Staphylococcus aureus, that reaches the bone by one of three distinct routes — hematogenous seeding from bacteremia, spread from a contiguous soft-tissue or joint focus, or direct inoculation from trauma, surgery, or a penetrating wound — and the mechanism strongly predicts both the typical causative organism(s) and the patient population affected.^[1] "Acute" here means a duration of symptoms generally under 2 weeks; symptoms present for longer, especially over several months, should prompt reconsideration of chronic osteomyelitis or an atypical cause such as tuberculosis or brucellosis guided by epidemiologic exposure history (place of birth, travel), and usually warrants infectious diseases consultation rather than the acute-presentation approach covered in this chapter. Cure requires both an adequately dosed, sufficiently prolonged course of antibacterial therapy and — in most cases — surgical debridement or drainage, since antibacterials penetrate poorly into devascularized bone and into any undrained collection of pus. Untreated or inadequately treated acute osteomyelitis can progress to chronic osteomyelitis with bone necrosis (sequestrum formation) and permanent functional loss, which is far harder to cure.

Recognize the Condition

Typical presentation

Symptoms generally develop over a period under 2 weeks: fever, bone pain, redness and swelling over the affected area, and limping or another loss of function or movement in the affected limb.^[2] Tenderness over the affected bone can be exquisite. Erythema and warmth may appear pink or red in light skin tones, or deeper red in darker skin tones — weigh warmth and tenderness alongside colour change rather than relying on redness alone, particularly in darker skin tones.

Examine range of movement in the affected limb: pseudoparalysis, or warmth/erythema overlying an adjacent joint, should raise concern for coexisting septic arthritis and prompt urgent surgical referral rather than management as osteomyelitis alone — this combination is not uncommon in young children under 18 months. If a vertebra is involved, specifically assess for any abnormal neurologic finding.

Pathogenesis: the 3 routes bone infection reaches bone

Mechanism drives both the typical patient population and the typical causative organism(s) — use it to guide the differential and empiric antibiotic selection (see Choose Initial Treatment).

Hematogenous osteomyelitis

The most common type overall. Predominant in children and in adults over 50. Bloodborne bacteria lodge in bone as a nidus of infection — usually a long bone (femur, tibia, or humerus), though vertebral osteomyelitis is not uncommon in adults, with predisposing factors including intravenous drug use, trauma, recent bacteremia, and another infection source such as the urinary tract or infective endocarditis (see the Infective Endocarditis chapter).

Typical organisms by age: neonates — group B streptococcus, gram-negative enteric bacteria, S. aureus. Children — S. aureus (MSSA and MRSA), group A streptococcus, and Kingella kingae in children under 3 years; rarely, H. influenzae (in unimmunized children or areas where invasive disease remains more common) or S. pneumoniae. Adults — S. aureus and gram-negative enteric bacteria. Sickle cell disease — Salmonella species in addition to S. aureus.

Contiguous-focus osteomyelitis

Spread from an adjacent infected site. Common in older adults; predisposing factors include recent surgery and an adjacent soft-tissue infection.

Typical organisms by source: a soft-tissue infection source — S. aureus and streptococci, often polymicrobial in the setting of vascular insufficiency or a diabetic foot ulcer (see the Diabetic Foot Infections chapter for the dedicated approach to this common scenario). A head/neck source — often polymicrobial (S. aureus, anaerobes, gram-negative organisms). A genitourinary source — often polymicrobial, gram-negative enteric bacilli, with potential for a necrotizing infection involving anaerobes; rare in children.

Direct inoculation osteomyelitis

Bacteria introduced directly into bone by trauma, surgery, or a penetrating wound — for example, a puncture wound of the foot (this category excludes animal or human bite wounds, which need separate management).

Typical organisms: Pseudomonas aeruginosa and skin organisms (S. aureus, streptococci); infection may be polymicrobial.

Risk Factors

Age under 5 years or over 50 years — each associated with a different predominant mechanism and organism profile.
Recent bacteremia, or another concurrent infection source such as a urinary tract infection or infective endocarditis (see the Infective Endocarditis chapter).
Intravenous drug use.
Recent trauma, surgery, or a penetrating wound.
Prosthetic material or other implanted foreign material.
Sickle cell disease — specifically predisposes to Salmonella osteomyelitis in addition to S. aureus.
Vascular insufficiency, including peripheral arterial disease.
Immunocompromise — diabetes, HIV infection, immunosuppressive therapy, or malignancy.
A neuropathic diabetic foot ulcer — a common, distinct scenario with its own severity-based management approach (see the Diabetic Foot Infections chapter).
Incomplete immunization against Haemophilus influenzae type b.
Age under 3 years specifically — makes Kingella kingae a relevant pathogen.
Epidemiologic exposure (place of birth, time spent abroad) raising the likelihood of tuberculosis or brucellosis, particularly with a chronic or atypical presentation.

Red Flags & Refer

Any of the following changes management immediately.

Suspected epidural abscess or spinal cord compression in vertebral osteomyelitis — new or progressive motor weakness, sensory loss, bowel or bladder dysfunction, or severe unremitting back pain in a patient with (or at risk for) vertebral osteomyelitis is a true surgical emergency: obtain emergent MRI of the entire spine and immediate neurosurgical/spine surgery consultation without waiting for routine imaging turnaround.^[3]
Signs of sepsis or hemodynamic instability — fever, tachycardia, hypotension, or altered mental status arising from a bone or joint infection needs immediate resuscitation and, in a pediatric patient, should not delay empiric antibacterial therapy.
Pseudoparalysis, warmth, or erythema overlying an adjacent joint — raises concern for coexisting septic arthritis and needs urgent surgical/orthopedic referral for joint aspiration, since septic arthritis needs emergent joint drainage that osteomyelitis alone does not.
Rapidly progressive bone or joint destruction on imaging, or a rapidly spreading soft-tissue component.
Failure to improve despite an appropriate empiric regimen and adequate duration — suggests an undrained focus (abscess, sequestrum), a resistant or unexpected organism, or a missed alternative diagnosis, and needs re-evaluation rather than simply extending or broadening the same regimen.
Subacute presentation, infection associated with prosthetic or implanted material, an immunocompromised host, or suspected fungal or mycobacterial etiology — empiric coverage may differ significantly from the regimens in this chapter; obtain infectious diseases consultation.

Assessment & Diagnosis

History

Duration of symptoms — generally under 2 weeks in acute osteomyelitis; symptoms lasting over 2 weeks, but often months, may warrant infectious diseases consultation and consideration of tuberculosis or brucellosis depending on epidemiologic risk factors (place of birth, time spent abroad).
Any recent surgery, trauma, penetrating wound, or prosthetic/foreign implanted material.
Underlying conditions — sickle cell disease, vascular insufficiency, immunocompromise.
A neuropathic diabetic foot ulcer (see the Diabetic Foot Infections chapter).

Examination

Tenderness over the affected bone, which can be exquisite.
Range of movement in the affected limb — pseudoparalysis, warmth, or erythema overlying an adjacent joint should raise concern for coexisting septic arthritis and prompt urgent surgical referral.
If a vertebra is involved, assess for any abnormal neurologic finding.

Laboratory tests

CBC and acute-phase reactants (ESR, CRP) as a baseline.
Blood cultures — should be obtained before starting antibacterials whenever the patient is stable enough to allow it (see Choose Initial Treatment).

Aspiration and biopsy — get the best specimen you can, before treatment

Send specimens for urgent Gram stain and aerobic and anaerobic bacterial culture; add fungal and mycobacterial culture if host or epidemiologic risk factors are present (an immunocompromised host, a chronic overlying open wound, or a wound with a history of water or soil exposure).

The best specimen is a bone or periosteal aspirate, obtained surgically or by percutaneous biopsy through unaffected skin — involve orthopedic surgery early to help obtain it.^[1] A superficial swab of an overlying ulcer or draining sinus often identifies colonizing organisms rather than the true pathogen and is unreliable; some true pathogens, particularly anaerobes, are also too fastidious to reliably recover from a superficial specimen.

Imaging

If clinical findings suggest osteomyelitis, MRI or a bone scan is not required before starting treatment, so long as appropriate cultures (blood cultures, surgical samples) have already been obtained.

X-ray is not sensitive enough to rule out osteomyelitis, but remains an important, easily accessible test for assessing other causes of limb pain. Radiographs may be normal initially — rarefaction of bone becomes visible only once roughly half of bone density is lost (seen earlier in neonates, later in older children and adults), and bony changes such as periosteal reaction or osteolysis are usually not evident until at least 10 days after the onset of infection. In a diabetic foot infection, chronic osteopathy can complicate radiographic interpretation (see the Diabetic Foot Infections chapter).
Ultrasound cannot evaluate bone marrow and has limited utility for diagnosing osteomyelitis itself, but is a useful adjunct for visualizing a soft-tissue abscess, a subperiosteal collection, or a joint effusion — findings that may require surgical intervention — and can guide aspiration of soft-tissue or joint fluid.
MRI is highly sensitive and is the preferred advanced imaging study when it is necessary to define the extent of infection and any extraosseous complication such as a periosteal abscess; it assesses bone, joint, and soft tissue simultaneously while sparing the patient ionizing radiation. Where MRI access is limited, routine use for an acute, uncomplicated presentation is not necessary — a CT scan is a reasonable alternative in that setting.
Bone scan (technetium-99m-labelled methylene diphosphonate) offers early diagnosis with sensitivity and specificity similar to MRI when paired with a gallium or white blood cell scan, but is less specific overall, since other causes of increased bone turnover (fracture, tumour) also produce a positive result. In a neuropathic foot, small stress fractures may still show uptake despite being difficult to detect clinically or radiographically; vascular insufficiency may attenuate bone-scan changes. A negative bone scan does not rule out osteomyelitis. In neonates, an X-ray may be more reliable than a bone scan.

Vertebral osteomyelitis: a distinct, higher-stakes presentation

Consider vertebral osteomyelitis in an adult, particularly over 50, presenting with back pain and elevated inflammatory markers, with or without fever — predisposing factors include intravenous drug use, trauma, recent bacteremia, and another infection source such as the urinary tract or infective endocarditis (see the Infective Endocarditis chapter). MRI is the preferred imaging modality.^[3] Assess every patient with known or suspected vertebral osteomyelitis for new neurologic findings at presentation and at every subsequent assessment — see Red Flags & Refer for the emergency evaluation this triggers.

Treatment Targets

Cure the acute infection microbiologically, not just resolve symptoms.
Minimize morbidity, including loss of limb function.
Prevent recurrence and progression to chronic osteomyelitis.
Preserve neurologic function in vertebral osteomyelitis.
Identify and treat any coexisting joint infection, abscess, or contiguous soft-tissue infection.
Obtain a microbiologic diagnosis before, or very early in, therapy so that ongoing treatment is culture-directed rather than indefinitely empiric.

Choose Initial Treatment

Direct treatment rule

Diagnosis before treatment

Obtain blood cultures and, whenever the patient is hemodynamically stable enough to tolerate the delay, a bone or periosteal specimen (surgical or percutaneous biopsy) for Gram stain and aerobic/anaerobic culture before starting empiric antibacterial therapy — this single decision is the one most likely to change subsequent antibiotic selection, since a confirmed organism and susceptibilities allow narrowing from broad empiric coverage to directed therapy. Pediatric exception do not delay starting empiric therapy beyond 48-72 hours after presentation, even if the full diagnostic workup is not yet complete, to avoid complications of delayed treatment.^[2]

Empiric antibacterial selection

These infections are generally monomicrobial, so empiric IV therapy should always include activity against S. aureus at minimum; select the specific regimen using the patient's mechanism of infection and age (see the table below).^[1]

When to add empiric MRSA coverage

Add vancomycin (or another MRSA-active agent) when local prevalence of MRSA among invasive staphylococcal infections is ≥10-20%, when the patient has known prior MRSA colonization or infection, or when an initial non-MRSA-active regimen has already failed to produce clinical improvement.^[1] Where local MRSA prevalence is below this threshold and no other risk factor is present, a non-MRSA-active regimen (cloxacillin or cefazolin) is appropriate first-line empiric therapy.

Duration and transition to oral therapy

Maximum duration is 6 weeks of antibacterial therapy for acute osteomyelitis without retained hardware, including vertebral osteomyelitis.^[3] For uncomplicated, adequately débrided osteomyelitis — including the vast majority of pediatric cases — a 4-week course is usually sufficient; extend toward 6 weeks for a more severe initial presentation, extensive bone involvement, slow clinical resolution, or infection with a more resistant organism such as MRSA.^[2] After a penetrating injury with adequate débridement, 10-14 days of treatment is sufficient.

Switch IV to oral therapy once the patient is clinically stable, tolerating oral intake, has adequate source control, and a bioavailable oral option with a spectrum matching the identified (or presumed) organism is available — there is no required minimum duration of IV lead-in before making this switch.^[4] Systemic improvement, resolution of fever, and resolution of local inflammation and tenderness may take several days to appear and should guide timing more than a fixed calendar interval; in children, a falling CRP also helps time the switch. Do not switch to oral step-down in a neonate or in a patient with an underlying immunodeficiency — continue IV therapy for the full course in these groups.

When switching to oral therapy, use a dose materially larger than what would be used for a minor infection, choose an agent with good oral bioavailability (see Drug Tables), and confirm the absence of any GI issue that would impair absorption. If no organism was ever isolated but the patient has clearly improved on the empiric IV regimen, switching to an oral agent with a similar spectrum of activity is still appropriate. Recurrence of symptoms on oral step-down therapy demands immediate reassessment and strong consideration of resuming IV antibacterials.

Empiric IV antibacterial regimens by mechanism, age, and organism

Real regimen and dose for each scenario — narrow to directed therapy once culture results are available.

Hematogenous osteomyelitis

Neonates: if MRSA is unlikely, cloxacillin plus cefotaxime (covers gram-negative enteric bacilli); if MRSA is possible, vancomycin plus cefotaxime or ceftriaxone. If concomitant meningitis is possible, consider meningitic dosing — see the Bacterial Meningitis chapter.

Children: if MRSA is unlikely, cloxacillin or cefazolin; if MRSA is possible, add vancomycin. Replace cefazolin with cefotaxime if the child is not immunized against H. influenzae.

Adults: if MRSA is unlikely, cloxacillin or cefazolin; if MRSA is possible, add vancomycin.

Contiguous-focus osteomyelitis

From a soft-tissue source: cloxacillin or cefazolin; if there is a polymicrobial risk (vascular insufficiency, diabetic foot ulcer), use ceftriaxone plus metronidazole, or piperacillin/tazobactam; add vancomycin if MRSA is possible. Osteomyelitis complicating a diabetic foot ulcer is a distinct, very common scenario with its own severity-based selection approach — see the Diabetic Foot Infections chapter.

From a head/neck source (all ages): ceftriaxone plus metronidazole — this source is often polymicrobial (S. aureus, anaerobes, gram-negative organisms).

From a genitourinary source: ceftriaxone plus metronidazole, given the potential for anaerobic and necrotizing infection; piperacillin/tazobactam, or a fluoroquinolone such as moxifloxacin, is a reasonable alternative when broader antipseudomonal or anaerobic coverage is warranted. Rare in children.

Direct inoculation osteomyelitis

Children: cloxacillin or cefazolin plus ceftazidime (for Pseudomonas coverage); piperacillin/tazobactam is an alternative.

Adults: piperacillin/tazobactam, or cefazolin plus ciprofloxacin (for Pseudomonas coverage). Discuss with infectious diseases.

Do not use routinely

Do not use rifampin as monotherapy for staphylococcal osteomyelitis — resistance develops rapidly when it is used alone. Its role as an adjunctive agent has not been rigorously studied in uncomplicated acute osteomyelitis (non-vertebral, no retained hardware, not associated with a diabetic foot infection) — reserve rifampin-containing combination regimens for infected-hardware or biofilm-associated scenarios under infectious diseases direction rather than using it routinely.

Non-Pharmacologic Treatment

Surgical drainage and debridement — combined antimicrobial and surgical management should be considered in every case, since antibacterials penetrate poorly into a collection of pus or into bone whose blood supply is compromised by infection. Surgical decompression and exploration may be necessary when the patient is septic or clinically unstable, there has been a delay in presentation or diagnosis, pus has been found on aspiration, a surrounding abscess is present, or imaging shows bone destruction or sequestrum formation.^[1]
If swelling, pain, tenderness, and fever do not improve within a few days of starting antibacterials, consider surgical exploration, especially if the initial empiric regimen did not cover MRSA.
Suspected osteomyelitis secondary to a penetrating injury (for example, to the calcaneus) requires bone exploration, debridement, and culture regardless of clinical trajectory.
Osteomyelitis associated with a diabetic foot infection often requires surgical debridement, which should be aggressive and may involve amputation of the infected limb or digit — see the Diabetic Foot Infections chapter for the complete approach to this scenario.
Involve orthopedic surgery early, even when immediate operative intervention is not yet needed — early involvement facilitates a bone/periosteal biopsy for culture and allows surgical planning if debridement becomes necessary later.
For patients requiring a prolonged course of IV therapy, a home IV therapy program is an option to shorten hospital stay — nursing resources, infusion pump availability, and access to an infusion centre may limit specific treatment choices, particularly dosing frequency and the stability of reconstituted antibiotics.

Pharmacologic Treatment Options

Drug / intervention	Role	Dose / use	Important adverse effects	Teaching points
Cloxacillin Preferred	Empiric/definitive therapy, MSSA and streptococci, when MRSA is unlikely	Adults: 2 g IV Q4H. Children: 200 mg/kg/day IV divided Q6H (maximum 6 g/day)	GI upset, hypersensitivity reactions, vein irritation with IV use	First choice when MRSA risk is low; provides reliable anti-staphylococcal and streptococcal coverage.
Cefazolin Preferred	Empiric/definitive therapy, MSSA and streptococci, alternative to cloxacillin	Adults: 2 g IV Q8H (consult infectious diseases if over 120 kg). Children: 100-150 mg/kg/day IV divided Q8H (maximum 6 g/day)	GI upset, phlebitis, hypersensitivity reactions	Interchangeable with cloxacillin for MSSA/streptococcal coverage; replace with cefotaxime in an unimmunized child if H. influenzae coverage is needed.
Vancomycin (IV) Special situation	Add when MRSA is possible or confirmed	Adults: 15 mg/kg/dose IV Q12H, then adjust to levels (target AUC 400-600 mg·h/L). Children: 40 mg/kg/day IV divided Q6H, then adjust to levels	Nephrotoxicity, ototoxicity, infusion-related flushing	Requires level-guided dosing throughout therapy; do not confuse with oral vancomycin capsules, which do not treat osteomyelitis.
Ceftriaxone + metronidazole Alternative	Contiguous-source (head/neck or genitourinary) empiric IV coverage, or polymicrobial risk without MRSA	Combo: ceftriaxone 1-2 g IV once daily + metronidazole 500 mg IV/PO Q8H	Ceftriaxone: hypersensitivity, elevated bilirubin. Metronidazole: GI upset, metallic taste, peripheral neuropathy with cumulative dose	Ceftriaxone alone has poor activity against S. aureus — never rely on it as the only agent when staphylococcal infection is likely; never co-administer with calcium-containing IV solutions.
Metronidazole Preferred	Adjunctive anaerobic coverage for polymicrobial contiguous-source infection	Adults: 500 mg PO/IV Q12H. Children: 10 mg/kg/dose PO/IV Q12H	GI upset, metallic taste, peripheral neuropathy with cumulative use	Always paired with an agent covering aerobic organisms; avoid alcohol during treatment.
Cephalexin Preferred	Oral step-down, MSSA and streptococci	Adults: 1 g PO Q6H. Children: 100 mg/kg/day PO divided Q6H (maximum 4 g/day)	GI upset, hypersensitivity reactions	Better tolerated (taste, dosing frequency) than oral cloxacillin, especially in children.
Clindamycin Alternative	Oral or IV step-down for confirmed susceptible MRSA, or penicillin allergy	Adults: 600 mg PO/IV Q6-8H. Children (confirmed susceptible MRSA): 30 mg/kg/day PO divided Q8H, or 40 mg/kg/day IV divided Q6H (maximum 2 g/day)	Diarrhea, C. difficile-associated colitis	Confirm inducible clindamycin resistance with a D-test before relying on it for MRSA.
Sulfamethoxazole/trimethoprim Alternative	Oral step-down for MRSA	Adults: 2 double-strength (800/160 mg) tablets PO Q12H. Children: 4-6 mg/kg/dose (trimethoprim component) PO Q12H	Nausea, photosensitivity, hyperkalemia	Avoid near term in pregnancy; increases warfarin and phenytoin levels.
Doxycycline Alternative	Oral step-down for MRSA	Adults: 100 mg PO Q12H. Children 8 years and older: 1-2 mg/kg/dose PO Q12H	Photosensitivity, GI upset	Avoid under 8 years of age and in pregnancy; separate administration from antacids/iron/dairy.
Linezolid Special situation	Reserve agent for MRSA when other oral/IV options are unsuitable	Adults and children 12 years and older: 600 mg PO/IV Q12H. Children under 11 years: 30 mg/kg/day PO/IV divided Q8H	Myelosuppression beyond 2 weeks, peripheral/optic neuropathy, serotonin syndrome risk	Reserve antimicrobial — obtain infectious diseases input; monitor CBC weekly if used beyond 2 weeks.
Daptomycin Special situation	Reserve agent for MRSA, in consultation with infectious diseases	Adults (off-label): 6 mg/kg/dose IV once daily. Children over 1 year: 6-10 mg/kg/dose IV once daily	Creatine kinase elevation, rhabdomyolysis	Reserve antimicrobial; monitor CK at least weekly, hold a concomitant statin where possible.
Piperacillin/tazobactam Special situation	Broad empiric coverage after penetrating trauma, or when Pseudomonas coverage is needed	Adults: 4.5 g IV Q8H. Children: 100 mg/kg/dose (piperacillin component) IV Q6H (maximum 16 g/day)	GI upset, hypersensitivity reactions	Does not cover MRSA — add vancomycin if MRSA risk is present.
Ciprofloxacin Special situation	Pseudomonas coverage in adults, always paired with an anti-staphylococcal agent	Adults: 500 mg PO Q12H (750 mg Q12H if the organism is P. aeruginosa), or 400 mg IV Q12H. Children (off-label, Pseudomonas coverage only): 30 mg/kg/day PO divided Q12H (maximum 1500 mg/day)	Tendinopathy, peripheral neuropathy, CNS effects	No reliable gram-positive activity — always paired with a staphylococcal-active agent.
Ampicillin Alternative	Group B streptococcus and gram-negative enteric coverage, especially in neonates	Adults: 2 g IV Q4H. Children: 300-400 mg/kg/day IV divided Q4-6H (maximum 12 g/day)	GI upset, hypersensitivity reactions	Commonly paired with cefotaxime for empiric neonatal hematogenous osteomyelitis.
Penicillin G Preferred	Definitive therapy, confirmed group A or B streptococcus	Adults: 12-24 million units/day IV divided Q4-6H. Children: 200,000 units/kg/day IV divided Q4-6H (maximum 24 million units/day)	GI upset, hypersensitivity, electrolyte disturbance at high dose	Monitor potassium and sodium with high-dose parenteral use.
Amoxicillin Preferred	Oral step-down, confirmed streptococcal osteomyelitis	Adults: 0.5-1 g PO Q8H. Children: 100 mg/kg/day PO divided Q8H (maximum 4 g/day)	GI upset, rash	Good oral bioavailability, well tolerated for the prolonged course required.

Special Populations

Pregnancy

Osteomyelitis in pregnancy is uncommon. When it occurs, favour beta-lactams considered compatible with pregnancy — cloxacillin, cefazolin, ceftriaxone, penicillin G, and ampicillin. Avoid fluoroquinolones (ciprofloxacin, moxifloxacin) and tetracyclines (doxycycline) throughout pregnancy given effects on developing cartilage and bone/teeth. Avoid sulfamethoxazole/trimethoprim near term given a theoretical risk of neonatal hyperbilirubinemia. Vancomycin and clindamycin can be used when specifically indicated (for example, MRSA coverage). Manage jointly with obstetrics and infectious diseases, and favour MRI (without gadolinium contrast where possible) over ionizing-radiation imaging when advanced imaging is needed.

Breastfeeding

Most beta-lactams (cloxacillin, cefazolin, ceftriaxone, penicillin G, ampicillin, amoxicillin, amoxicillin/clavulanate), clindamycin, and vancomycin are considered compatible with breastfeeding. Avoid doxycycline and fluoroquinolones when a suitable alternative exists. Sulfamethoxazole/trimethoprim should be used with caution, particularly with a jaundiced or unwell infant. Metronidazole is compatible with breastfeeding at standard multidose regimens.

Pediatric and neonatal

Organism likelihood shifts meaningfully with age — see Recognize the Condition and the by-mechanism empiric table in Choose Initial Treatment. Do not delay empiric therapy beyond 48-72 hours in a pediatric patient, even if the diagnostic workup is not complete.^[2] Do not switch a neonate to oral step-down therapy — continue IV therapy for the full course. Kingella kingae becomes a relevant pathogen specifically under 3 years of age. Immunization status against H. influenzae changes empiric cephalosporin selection in children (see Choose Initial Treatment). Dosing throughout this chapter is weight-based for children — confirm against a current pediatric dosing reference and the patient's actual weight.

Sickle cell disease

Salmonella species are a specifically relevant additional pathogen in sickle cell disease, alongside S. aureus — factor this into both empiric coverage and interpretation of culture results.

Renal impairment

Dose-adjust cefazolin, cefotaxime, ceftazidime, piperacillin/tazobactam, sulfamethoxazole/trimethoprim, ciprofloxacin, and metronidazole (in severe impairment) for reduced renal function; ceftriaxone requires less adjustment given predominantly biliary excretion. Vancomycin requires level-guided dosing regardless of baseline renal function. Daptomycin and linezolid do not require renal dose adjustment, though daptomycin's dosing interval may still need review in severe impairment. Consult a renal dosing reference or pharmacist for the specific adjustment.

Hepatic impairment

Most agents in this chapter do not require specific hepatic dose adjustment; monitor liver enzymes with prolonged courses of a hepatically metabolized agent (cloxacillin, clindamycin) and review dosing individually with a pharmacist in significant hepatic impairment.

Older adults

Older adults, particularly over 50, make up the predominant population for hematogenous vertebral osteomyelitis (see Assessment & Diagnosis). Review renal function before dosing any renally cleared agent, and review for polypharmacy and interactions — many agents in this chapter (cephalosporins, penicillins, fluoroquinolones, sulfamethoxazole/trimethoprim, metronidazole, doxycycline) can raise INR in a patient on warfarin.

Monitoring & Follow-Up

Judge treatment success clinically, by careful follow-up of systemic signs (fever, overall well-being), local signs of decreasing inflammation and tenderness, and return of full function. ESR gradually returns to normal over several weeks; CRP may normalize within days and is the more useful marker for near-term trend-following, including helping to time the IV-to-oral switch in children.

In vertebral osteomyelitis specifically, consider checking inflammatory markers at approximately 4 weeks of therapy.^[3]

Do not routinely repeat follow-up imaging (MRI) once a patient has achieved appropriate clinical recovery on adequate therapy — there is poor correlation between clinical response and MRI/CT/nuclear-medicine findings, and radiologic resolution may lag well behind clinical resolution.^[5]

Monitor for adverse effects specific to a prolonged antibacterial course: vancomycin trough- or AUC-guided levels alongside renal function; creatine kinase at least weekly with daptomycin; a complete blood count at least weekly if linezolid is continued beyond 2 weeks, plus watch for peripheral or optic neuropathy with more prolonged linezolid or metronidazole use; watch for C. difficile-associated diarrhea with any oral agent, particularly clindamycin; monitor INR closely in a patient on warfarin given the number of interacting agents in this chapter; monitor renal function throughout therapy with any nephrotoxic or renally cleared agent; and monitor the IV access site (or central line, if used for home IV therapy) for signs of phlebitis or line infection.

Treatment Failure / Next Step

Confirm the full prescribed regimen was actually taken at the correct dose, route, and duration, and that GI absorption is not impaired (for oral step-down).
Confirm cultures/organism identification were obtained and that therapy is genuinely matched to susceptibilities — if therapy was started empirically without ever obtaining cultures, consider whether a resistant or unexpected organism (including MRSA, if not initially covered) explains the lack of response.
Re-image (MRI preferred) to look for an undrained abscess, sequestrum, or bone destruction that requires surgical debridement — antibacterials alone cannot resolve infection around dead bone or an undrained collection.
Obtain surgical/orthopedic (and, for vertebral disease, neurosurgical/spine) consultation if not already involved.
Consider a subacute presentation, prosthetic/hardware involvement, immunocompromise, or a fungal or mycobacterial etiology, and obtain infectious diseases consultation.
If recurrent symptoms appear during oral step-down therapy, reassess immediately and strongly consider resuming IV therapy rather than persisting with oral therapy.
If failure persists despite adequate debridement and culture-directed therapy, treat as evolving chronic osteomyelitis and plan for a substantially longer, specialist-directed course.

Common Errors to Avoid

Starting empiric antibacterials before obtaining blood cultures (and, where feasible, a bone/periosteal specimen) in a hemodynamically stable patient — this is the single decision most likely to compromise later culture-directed therapy.
Relying on a superficial wound or sinus-tract swab to guide antibiotic therapy — it identifies colonizing organisms, not the true pathogen, and is specifically unreliable, especially for fastidious organisms such as anaerobes.
Using rifampin as monotherapy for staphylococcal osteomyelitis — resistance develops rapidly.
Treating osteomyelitis with antibacterials alone when surgical drainage or debridement is indicated (sepsis, abscess, sequestrum, delayed diagnosis, or failure to improve).
Choosing too short a treatment duration — osteomyelitis requires weeks, not days, of therapy even when uncomplicated and adequately débrided.
Delaying empiric therapy beyond 48-72 hours in a pediatric patient to complete a full diagnostic workup.
Missing coexisting septic arthritis in a young child with pseudoparalysis or warmth/erythema over an adjacent joint.
Ordering an MRI or bone scan before starting treatment when clinical findings already support the diagnosis and appropriate cultures have been obtained — this delays care without changing the immediate management decision.
Repeating follow-up MRI routinely in a patient who is already showing clear clinical improvement.
Overlooking a coexisting or causative vascular insufficiency/diabetic foot process when contiguous-source osteomyelitis is present.
Forgetting that many of the antibacterials used for osteomyelitis (cephalosporins, penicillins, fluoroquinolones, sulfamethoxazole/trimethoprim, metronidazole, doxycycline) can raise INR in a patient on warfarin.

Clinical Decision Algorithm

Algorithm A — Initial evaluation and empiric therapy

Suspected acute osteomyelitis: fever, bone pain, swelling, or loss of function, generally under 2 weeks duration

Assess hemodynamic stability and, in children, time elapsed since presentation

Hemodynamically stable adult, or pediatric patient within 48-72h of presentation

Obtain blood cultures, CBC, ESR/CRP, and — whenever feasible — a bone/periosteal specimen (surgical or percutaneous biopsy) for Gram stain and culture before starting antibacterials

Septic, hemodynamically unstable, or a pediatric patient approaching the 48-72h limit

Obtain blood cultures immediately but do not delay empiric IV antibacterial therapy any further

Determine mechanism — hematogenous, contiguous-focus, or direct inoculation — and assess MRSA risk factors (local prevalence ≥10-20%, known colonization, or prior treatment failure)

Start empiric IV antibacterial therapy matched to mechanism, age, and MRSA risk — see Choose Initial Treatment and Drug Tables

Obtain early surgical/orthopedic consultation; proceed to urgent surgical drainage/debridement if septic, pus on aspiration, an abscess, bone destruction/sequestrum on imaging, or no improvement within a few days — especially if MRSA was not covered

Algorithm B — Vertebral osteomyelitis

Suspected vertebral osteomyelitis: back pain and elevated inflammatory markers, with or without fever, typically in a patient over 50 with IV drug use, recent bacteremia, or another infection source

Obtain MRI of the spine (preferred imaging modality) and blood cultures; obtain an image-guided or open biopsy for culture if blood cultures are negative and the organism is not yet known

New motor/sensory deficit, bowel/bladder dysfunction, or severe unremitting pain

Treat as epidural abscess or cord compression until proven otherwise — emergent MRI of the entire spine plus immediate neurosurgical/spine surgery consultation

No neurologic deficit

Manage as for other acute osteomyelitis: empiric or culture-directed IV antibacterial therapy for up to 6 weeks; consider checking inflammatory markers at approximately 4 weeks

Involve infectious diseases early, and spine surgery when relevant, given the higher stakes and frequently prolonged course of vertebral disease

Algorithm C — Duration and IV-to-oral step-down

Patient responding clinically to empiric or culture-directed IV therapy

Confirm clinical stability, tolerance of oral intake, adequate source control, and availability of a bioavailable oral agent matching the organism's susceptibility

Neonate, or underlying immunodeficiency

Continue IV therapy for the full course — do not switch to oral step-down in these groups

All other patients meeting the switch criteria

Switch to oral step-down at a full treatment dose, larger than a minor-infection dose — no minimum IV lead-in is required

Total duration: 4 weeks for uncomplicated, adequately débrided osteomyelitis (most pediatric cases); up to 6 weeks for a severe presentation, extensive bone involvement, slow resolution, or a resistant organism, including vertebral osteomyelitis; 10-14 days after a penetrating injury with adequate débridement

Recurrence of symptoms during oral step-down: reassess immediately and strongly consider resuming IV therapy

Drug Tables

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Cephalosporins

A patient with a prior IgE-mediated penicillin reaction (anaphylaxis, immediate urticaria, angioedema) should avoid a cephalosporin given potential cross-reactivity; a prior non-immediate rash allows cautious cephalosporin use.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Cefazolin	Adults: 2 g IV Q8H (consult infectious diseases if body weight is over 120 kg — an increased dose or frequency may be required) Children: 100-150 mg/kg/day IV divided Q8H (maximum 6 g/day)	GI effects (especially diarrhea), phlebitis, hypersensitivity reactions (rash, fever, eosinophilia, elevated liver enzymes and creatinine), cytopenias, false-positive Coombs test	May increase INR with warfarin	First-line for hematogenous and contiguous-source empiric/definitive MSSA coverage.
Cefotaxime	Adults: 2 g IV Q4-8H Children: 150 mg/kg/day IV divided Q8H (maximum 12 g/day)	GI effects (especially diarrhea), phlebitis, hypersensitivity reactions, cytopenias, false-positive Coombs test	May increase INR with warfarin	Adds gram-negative enteric coverage — used in neonates and in unimmunized children in place of cefazolin.
Ceftazidime	Adults: 2 g IV Q8H Children: 150 mg/kg/day IV divided Q8H (maximum 6 g/day)	GI effects (especially diarrhea), phlebitis, hypersensitivity reactions, cytopenias, false-positive Coombs test	May increase INR with warfarin	Adds Pseudomonas aeruginosa coverage for direct-inoculation osteomyelitis; limited gram-positive activity — pair with a staphylococcal-active agent.
Ceftriaxone	Adults: 1-2 g IV once daily (maximum 2 g/day) Children: 100 mg/kg/day IV Q24H (maximum 2 g/day)	GI effects (especially diarrhea), phlebitis, hypersensitivity reactions, cytopenias, false-positive Coombs test, elevated bilirubin	May increase INR with warfarin. Do not reconstitute or co-administer with calcium-containing IV solutions — risk of precipitation, particularly in neonates; if sequential administration is unavoidable, flush the infusion line thoroughly between infusions.	Convenient once-daily dosing; poor activity against S. aureus alone — pair with an anti-staphylococcal agent when staphylococcal infection is likely.
Cephalexin	Adults: 1 g PO Q6H Children: 100 mg/kg/day PO divided Q6H (maximum 4 g/day)	GI effects (especially diarrhea), hypersensitivity reactions, cytopenias, false-positive Coombs test	May increase INR with warfarin	Oral step-down agent; better tolerated than oral cloxacillin, especially in children.

Fluoroquinolones

Reserve for Pseudomonas aeruginosa coverage or an anaerobic-coverage alternative — neither agent provides reliable gram-positive (staphylococcal) coverage on its own.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Ciprofloxacin	Adults: 500 mg PO Q12H (750 mg PO Q12H if the organism is P. aeruginosa), or 400 mg IV Q12H Children (off-label, Pseudomonas coverage only): 30 mg/kg/day PO divided Q12H (maximum 1500 mg/day)	Abdominal pain, nausea, vomiting, rash, dizziness, headache, drowsiness, diarrhea (including C. difficile infection), tendinopathy and tendon rupture, peripheral neuropathy, CNS effects, possible hyper- or hypoglycemia in patients with diabetes	Absorption decreased by antacids, iron salts, and sucralfate; decreases theophylline and caffeine elimination; increases INR with warfarin	Preferred fluoroquinolone specifically for Pseudomonas aeruginosa coverage; always paired with a staphylococcal-active agent.
Moxifloxacin	Adults: 400 mg PO or IV once daily Children: Not established for routine pediatric use in osteomyelitis — specialist-directed only.	GI upset, tendinopathy and tendon rupture, peripheral neuropathy, CNS effects, QTc prolongation	Absorption decreased by antacids and metal cations; avoid with Class IA/III antiarrhythmics or a prolonged baseline QTc	Unlike ciprofloxacin, possesses genuine anaerobic activity — a reasonable alternative for genitourinary-source contiguous osteomyelitis; not a reliable Pseudomonas or gram-positive choice.

Glycopeptides

Drug	Dosage	Adverse effects	Drug interactions	Comments
Vancomycin (IV)	Adults: 15 mg/kg/dose IV Q12H (round to the nearest 250 mg, maximum 1500 mg/dose), then adjust to levels; target AUC 400-600 mg·h/L for susceptible MRSA, or a trough of 10-15 mg/L if using trough-only monitoring Children: 40 mg/kg/day IV divided Q6H (maximum 4 g/day) prior to therapeutic drug monitoring, then adjust to levels	Infusion-related flushing and hypotension if infused too quickly, nephrotoxicity, ototoxicity, drug fever, eosinophilia	Increased nephrotoxicity and ototoxicity with other nephrotoxic or ototoxic drugs (for example, aminoglycosides)	Active against gram-positive organisms including MRSA; requires level-guided dosing. Do not confuse with oral vancomycin capsules, which treat only Clostridioides difficile infection and do not achieve therapeutic bone or blood levels.

Lincosamides

Drug	Dosage	Adverse effects	Drug interactions	Comments
Clindamycin	Adults, confirmed susceptible MRSA: 600 mg IV or PO Q6-8H Children, confirmed susceptible MRSA: 40 mg/kg/day IV divided Q6H, or 30 mg/kg/day PO divided Q8H (maximum 2 g/day)	Rash, diarrhea (including C. difficile infection and pseudomembranous colitis), rarely elevated liver transaminases and alkaline phosphatase	May potentiate neuromuscular blocking agents; may increase INR with warfarin	Reserve for confirmed susceptible MRSA — confirm inducible clindamycin resistance with a D-test before relying on it, since an erythromycin-resistant strain can develop clindamycin resistance during treatment despite appearing susceptible initially.

Lipopeptides

Drug	Dosage	Adverse effects	Drug interactions	Comments
Daptomycin	Adults (off-label): 6 mg/kg/dose IV once daily Children (over 1 year): 6-10 mg/kg/dose IV once daily	Creatine kinase elevation, myopathy, rhabdomyolysis	HMG-CoA reductase inhibitors (statins) may increase the risk of skeletal muscle toxicity — monitor creatine kinase closely and consider holding a concomitant statin	Reserve antimicrobial per Health Canada's Reserve list — use in consultation with infectious diseases.

Nitroimidazoles

Active exclusively against anaerobic organisms — always paired with an agent covering aerobic pathogens.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Metronidazole	Adults: 500 mg PO or IV Q12H Children: 10 mg/kg/dose PO or IV Q12H	GI upset, headache, dizziness, metallic taste, darkened urine, peripheral neuropathy with prolonged use (cumulative doses over roughly 4 weeks)	Disulfiram-like reaction with ethanol; may increase INR with warfarin

Oxazolidinones

Drug	Dosage	Adverse effects	Drug interactions	Comments
Linezolid	Adults and children 12 years and older: 600 mg PO or IV Q12H Children under 11 years: 30 mg/kg/day PO or IV divided Q8H (maximum 600 mg/dose)	Headache, diarrhea, lactic acidosis, optic neuropathy (consider a baseline ophthalmologic assessment with prolonged use), cytopenias (monitor if used beyond 2 weeks), peripheral neuropathy with prolonged use	Contraindicated within 2 weeks of an MAOI; has monoamine oxidase inhibitor activity itself — use caution with serotonergic medications including SSRIs given serotonin syndrome risk, and avoid tyramine-rich foods	Reserve antimicrobial per Health Canada's Reserve list — use in consultation with infectious diseases.

Penicillins

A semisynthetic, penicillinase-resistant penicillin such as cloxacillin provides reliable coverage against S. aureus and streptococci, but not against gram-negative or anaerobic organisms.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Cloxacillin	Adults: 2 g IV Q4H Children: 200 mg/kg/day IV divided Q6H, or 150-200 mg/kg/day PO divided Q6H (maximum 6 g/day)	GI effects, rash; rarely hypersensitivity reactions, false-positive Coombs test, drug fever, interstitial nephritis, cytopenias; can cause vein irritation with IV use, especially in young children	May increase methotrexate levels; may increase INR with warfarin	First-line agent across all 3 mechanisms when MRSA is unlikely.
Penicillin G	Adults: 12-24 million units/day IV divided Q4-6H Children: 200,000 units/kg/day IV divided Q4-6H (maximum 24 million units/day)	GI effects, rash; rarely hypersensitivity reactions, false-positive Coombs test, drug fever, interstitial nephritis, cytopenias, electrolyte disturbance at high dose	May increase methotrexate levels; may increase INR with warfarin	Definitive therapy for confirmed group A or B streptococcus; monitor potassium and sodium with high-dose parenteral use.
Ampicillin	Adults: 2 g IV Q4H Children: 300-400 mg/kg/day IV divided Q4-6H (maximum 12 g/day)	GI effects, rash; rarely hypersensitivity reactions, false-positive Coombs test, drug fever, interstitial nephritis, cytopenias	May increase methotrexate levels; may increase INR with warfarin	Commonly paired with cefotaxime for empiric neonatal hematogenous osteomyelitis (group B streptococcus and gram-negative enteric coverage).
Amoxicillin	Adults: 0.5-1 g PO Q8H Children: 100 mg/kg/day PO divided Q8H (maximum 4 g/day)	GI effects, rash; rarely hypersensitivity reactions, false-positive Coombs test, drug fever, interstitial nephritis, cytopenias	May increase methotrexate levels; may increase INR with warfarin	Oral step-down for confirmed streptococcal osteomyelitis.
Amoxicillin/clavulanate	Adults: 500/125 mg PO Q8H, or 875/125 mg PO Q12H Children: 100 mg/kg/day (amoxicillin component) PO divided Q8H (maximum 1750 mg/day, using the 7:1 ratio suspension)	GI effects, diarrhea (more common than with amoxicillin alone), rash; rarely hypersensitivity reactions, false-positive Coombs test, drug fever, interstitial nephritis, cytopenias	May increase methotrexate levels; may increase INR with warfarin	Oral formulation only — for IV combination coverage of a similar polymicrobial spectrum, use ceftriaxone plus metronidazole instead (see Choose Initial Treatment).
Piperacillin/tazobactam	Adults: 4.5 g IV Q8H Children: 100 mg/kg/dose (piperacillin component) IV Q6H (maximum 16 g/day)	GI effects, hypersensitivity reactions	May increase methotrexate levels	Broad empiric coverage including Pseudomonas aeruginosa for direct-inoculation osteomyelitis; does not cover MRSA — add vancomycin when indicated.

Sulfonamide combinations

Drug	Dosage	Adverse effects	Drug interactions	Comments
Sulfamethoxazole/trimethoprim	Adults: 2 double-strength (800/160 mg) tablets PO Q12H Children: 4-6 mg/kg/dose (trimethoprim component) PO Q12H	Nausea, vomiting, diarrhea; hypersensitivity reactions, leukopenia, thrombocytopenia, rarely hepatitis	Increases phenytoin levels; increases INR with warfarin; increases hypoglycemia risk with sulfonylureas; increases nephrotoxicity with cyclosporine	Oral step-down option for MRSA; avoid near term in pregnancy.

Tetracyclines

Drug	Dosage	Adverse effects	Drug interactions	Comments
Doxycycline	Adults: 100 mg PO Q12H Children, 8 years and older: 1-2 mg/kg/dose PO Q12H (avoid under 8 years unless no other oral option exists)	Nausea, dyspepsia, photosensitivity	May increase INR with warfarin and increase digoxin levels. Ethanol, carbamazepine, phenytoin, and phenobarbital may decrease doxycycline concentrations. Aluminum, bismuth, iron, and magnesium reduce absorption.	Oral step-down option for MRSA; avoid under 8 years of age and in pregnancy.

Evidence note: Drug inventory, dosing, adverse effects, and comments reflect standard Canadian practice, cross-checked against the current WikiGuidelines osteomyelitis update, the IDSA native vertebral osteomyelitis guideline, and the PIDS/IDSA pediatric acute hematogenous osteomyelitis guideline.^[1]^[3]^[2]^[6]

References

2025 Update to WikiGuidelines for the management of pyogenic osteomyelitis in adults — The American Journal of Medicine, WikiGuidelines Group (Spellberg B, Ghanem B, Russell CD, et al.). Am J Med 2026;139(4):395-398
Clinical Practice Guideline by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America: 2021 Guideline on Diagnosis and Management of Acute Hematogenous Osteomyelitis in Pediatrics — Pediatric Infectious Diseases Society / Infectious Diseases Society of America, Journal of the Pediatric Infectious Diseases Society (Woods CR, Bradley JS, Chatterjee A, et al.). J Pediatr Infect Dis Soc 2021;10(8):801-844
2015 Infectious Diseases Society of America (IDSA) Clinical Practice Guidelines for the Diagnosis and Treatment of Native Vertebral Osteomyelitis in Adults — Infectious Diseases Society of America, Clinical Infectious Diseases (Berbari EF, Kanj SS, Kowalski TJ, et al.). Clin Infect Dis 2015;61(6):e26-e46
Oral versus intravenous antibiotics for bone and joint infection — New England Journal of Medicine (Li HK, Rombach I, Zambellas R, et al., OVIVA Trial Collaborators). N Engl J Med 2019;380(5):425-436
Choosing Wisely Canada — top five list in infectious diseases: an official position statement of the Association of Medical Microbiology and Infectious Disease (AMMI) Canada — Journal of the Association of Medical Microbiology and Infectious Disease Canada (Leis JA, Evans GA, Ciccotelli W, et al.). J Assoc Med Microbiol Infect Dis Can 2016;1(1):5-11
Reserve list for antimicrobial drugs — Public Health Agency of Canada. Government of Canada, antimicrobial resistance resources

Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.