Appendicitis
Clinical Snapshot
Acute appendicitis is inflammation of the vermiform appendix, most often triggered by luminal obstruction — a fecalith or appendicolith, lymphoid hyperplasia (frequently post-viral in children and adolescents), or, less commonly, a tumour — that leads to distension, bacterial overgrowth, venous congestion, and, if untreated, ischemia and perforation. It is one of the most common causes of the acute abdomen, with a lifetime risk of roughly 8-9% in North America and Europe and a peak incidence between ages 10 and 30, though it occurs at any age.[1]
Two genuinely different, both guideline-endorsed management paths exist side by side. Appendectomy — laparoscopic, wherever available — remains the standard of care and the only option once disease is complicated (perforation, gangrene, abscess, or peritonitis). But a substantial and growing body of randomized trial evidence now supports antibiotics-alone (non-operative) management as a safe, guideline-endorsed alternative for carefully selected adults and children with uncomplicated appendicitis and no appendicolith on imaging.[1][2][3] The diagnostic pathway itself is built around an index of clinical suspicion — history, examination, and selective imaging — rather than reflexive cross-sectional imaging in every patient.[4] This is a chapter where the pharmacist's role runs from perioperative antibiotic-prophylaxis stewardship (a single pre-incision dose, and no more, for uncomplicated disease) through to being a genuine partner in the antibiotics-alone decision and the multi-day regimen that follows it.
Recognize the Condition
The classic pattern — and why it is only a pattern
The textbook presentation is vague periumbilical or epigastric pain that migrates over roughly 12-24 hours to the right lower quadrant, accompanied by anorexia, nausea and vomiting (typically after the pain begins, not before), and a low-grade fever. On examination, look for localized right lower quadrant tenderness and specifically for McBurney's point tenderness — maximal tenderness 1.5-2 cm from the anterior superior iliac spine along a line drawn to the umbilicus (sensitivity 50-94%, specificity 75-86%) — and Rovsing's sign, right lower quadrant pain elicited by palpating the left lower quadrant (sensitivity 22-68%, specificity 75-86%).[4]
Presentation varies with the appendix's anatomic position
Position-specific signs
Retrocecal appendix
Often produces flank or back pain with fewer anterior peritoneal signs. Test for the psoas sign — pain with passive extension or active flexion of the right hip (sensitivity 13-42%, specificity 79-97%).
Pelvic appendix
Often produces suprapubic pain and urinary or rectal urgency that can mimic a urinary or gynecologic source. Test for the obturator sign — passive flexion and internal rotation of the right hip (sensitivity 8%, specificity 94%).
Atypical presentation is common, not rare
A meaningful share of patients — especially women, older adults, pregnant patients, and young children — present without the classic migratory pattern, and clinicians should not wait for a textbook history before considering the diagnosis.
- Women have a broader differential for right lower quadrant pain than men, since imaging is used partly to rule out ovarian torsion, an ovarian mass, uterine fibroids, or pelvic inflammatory disease before attributing pain to appendicitis.[4]
- Older adults more often present later, with a blunted inflammatory response, less pronounced fever, and a presentation that can be mistaken for a bowel obstruction, diverticulitis, or a perforating colonic malignancy — perforation rates are higher in this group at presentation.
- Pregnant patients have the appendix displaced progressively upward and laterally by the enlarging uterus as pregnancy advances, so pain can present well above McBurney's point, particularly in the third trimester — see Special Populations.
- Young children often cannot localize or describe pain reliably, tend to present later, and have a correspondingly higher perforation rate at diagnosis.
Risk Factors
- Age 10-30 years is the peak incidence, though appendicitis occurs at any age.
- Luminal obstruction from a fecalith or appendicolith — also the strongest known predictor of both perforation and of failure if antibiotics-alone management is chosen.
- Lymphoid hyperplasia of the appendiceal wall, frequently following a viral illness — a common mechanism in children and adolescents.
- An appendiceal or cecal tumour (carcinoid, mucocele, adenocarcinoma) as the obstructing lesion — uncommon overall but meaningfully more frequent in adults 40 years and older presenting with complicated appendicitis.
- A family history of appendicitis.
- Cystic fibrosis, through abnormally thick intraluminal mucus.
- Male sex — a modestly higher lifetime incidence than in women, though the gap narrows once pregnancy-related and gynecologic mimics are accounted for.
Red Flags & Refer
Any of the following changes the plan from "confirm the diagnosis" to "arrange urgent surgical or interventional-radiology involvement":
- Diffuse abdominal tenderness, guarding, or rigidity — suggests perforation with generalized peritonitis rather than localized disease.
- Hemodynamic instability, high fever, or marked tachycardia — evaluate for perforation, abscess, or evolving sepsis; see the Sepsis and Septic Shock chapter if these criteria are met.
- Any suspicion of appendicitis in pregnancy — this needs prompt assessment and imaging; current guidance specifically advises against non-operative management in this group.[1]
- Imaging showing a well-formed abscess or phlegmon — this changes management to drainage plus antibiotics (see Choose Initial Treatment), not simple appendectomy scheduling.
- A normal-appearing appendix found at surgery — evaluate for an alternative cause (terminal ileitis, a Meckel diverticulum, gynecologic pathology, or a perforating cecal or sigmoid malignancy) rather than closing without an explanation.[4]
- Complicated appendicitis in a patient 40 years or older — arrange colonoscopy and an interval contrast-enhanced CT scan even if the acute course resolves uneventfully, since an appendiceal or cecal neoplasm is found in 3-17% of complicated appendicitis in this age group.[1]
Assessment & Diagnosis
History and examination
Characterize the pain (onset, location, migration), and ask specifically about anorexia, the sequence of nausea/vomiting relative to pain onset, and fever. Examine for McBurney's point tenderness, Rovsing's sign, and — depending on the suspected anatomic position — the psoas and obturator signs described in Recognize the Condition. In women of reproductive age, always also assess for a gynecologic cause and check a pregnancy test.
The Alvarado score — a bedside aid, not a stand-alone diagnostic test
The Alvarado score combines 3 symptoms, 3 signs, and 2 laboratory findings into a 10-point score.[5]
| Finding | Points |
|---|---|
| Migration of pain to the right lower quadrant | 1 |
| Anorexia | 1 |
| Nausea or vomiting | 1 |
| Right lower quadrant tenderness | 2 |
| Rebound tenderness in the right lower quadrant | 1 |
| Elevated temperature (over 37.5°C) | 1 |
| Leukocytosis (white cell count over 10,000/mm³) | 2 |
| Left shift on the differential | 1 |
- 0-4 points — appendicitis unlikely (low clinical suspicion).
- 4-6 points — equivocal; imaging (CT) is recommended.
- 7 points or more — high suspicion; obtain surgical consultation.
Use the score as a structured aid to risk-stratify, not as a stand-alone diagnostic test. Current WSES guidance specifically suggests against relying on the Alvarado score alone to positively confirm appendicitis in adults, given only moderate specificity, and notes it performs less reliably in older adults and in patients with HIV — the newer Appendicitis Inflammatory Response (AIR) score and Adult Appendicitis Score (AAS) currently have better discriminating power for confirming the diagnosis and are preferred where available. Clinical scores in general remain genuinely useful for excluding low-risk patients and for deciding who actually needs imaging.[1]
Laboratory testing
White cell count is typically mildly elevated with a left shift (sensitivity approximately 80%, specificity approximately 55% for this pattern alone) — a normal white cell count does not exclude appendicitis, and CRP is a useful adjunct, particularly in children.[4][1]
Imaging
| Modality | Sensitivity | Specificity | Role and practical notes |
|---|---|---|---|
| Point-of-care/graded-compression ultrasound | 67-100% | 83-96% | Recommended first-line imaging in both adults and children when imaging is indicated. No radiation; most accurate in patients with a lower body mass index; results are operator-dependent.[1][4] |
| MRI | 94% | 97% | No radiation. Preferred second-line study in pregnancy after an inconclusive ultrasound. Slower to organize and less widely available than CT.[4] |
| Contrast-enhanced CT | 90.4-100% | 94% | Some ionizing radiation; widely available and easily interpreted; more accurate than ultrasound in patients with a higher body mass index. Use a low-dose contrast-enhanced protocol over a standard-dose protocol in adolescents and young adults with a negative ultrasound.[1][4] |
A practical stepwise pathway: ultrasound first in both adults and children; if non-diagnostic, move to CT (adults) or, depending on local availability and expertise, a second-line study chosen case by case (children).[4][1] In patients younger than 40 with a high-risk clinical score (for example, Alvarado 9-10), cross-sectional imaging may reasonably be skipped altogether in favour of proceeding directly to diagnostic-and-therapeutic laparoscopy.[1] If imaging is non-diagnostic, manage by clinical suspicion: high suspicion warrants diagnostic laparoscopy; intermediate or low suspicion supports admission and observation.[4]
The CAGS pathway further stratifies the decision to image at all by patient group: a young man (under 30) with a high index of clinical suspicion may reasonably proceed straight to diagnostic laparoscopy without imaging first, while men 30 and older are imaged first specifically because increasing age raises the incidence of appendiceal masses, abscesses, and other alternative diagnoses — including colon cancer — that pre-operative imaging can identify before committing to surgery. In non-pregnant women, imaging is used primarily to rule out gynecologic causes of right lower quadrant pain.[4]
Treatment Targets
- Confirm the diagnosis efficiently while minimizing unnecessary radiation exposure, especially in children and in pregnancy.
- Decide between appendectomy and antibiotics-alone management through genuine shared decision-making for every eligible patient with uncomplicated appendicitis.
- Achieve definitive source control for complicated disease — perforation, gangrene, or an abscess — through surgery, percutaneous drainage, or both.
- Use antibiotics precisely: a single pre-incision dose only for uncomplicated appendicitis undergoing surgery, a defined 3-5 day postoperative course for complicated disease with adequate source control, and a real, finite multi-day regimen (not an indefinite one) when antibiotics are the primary treatment.
- Avoid unnecessary broad-spectrum coverage or unnecessarily prolonged courses while never undertreating perforated or abscessed disease.
- Recognize and refer promptly for signs of perforation, abscess, or sepsis.
- Screen for an underlying appendiceal or cecal neoplasm in patients 40 years or older managed non-operatively for complicated appendicitis.
- Set patients choosing antibiotics-alone management up for a safe outcome with explicit return precautions and follow-up.
Choose Initial Treatment
Operative vs. non-operative — the core decision
All patients with complicated appendicitis — perforation, gangrene, diffuse peritonitis, or a well-formed abscess — need surgical or interventional management; antibiotics alone are not definitive therapy here. For uncomplicated appendicitis (no perforation, abscess, peritonitis, or appendicolith on imaging), two guideline-endorsed paths exist. Standard of care laparoscopic appendectomy, planned for the next available operating list within 24 hours of admission — delaying surgery beyond 24 hours is linked to worse outcomes and should be avoided.[1] Antibiotics-first (non-operative) a genuine, guideline-endorsed alternative to discuss with the patient, appropriate specifically in the absence of an appendicolith on imaging — an appendicolith independently predicts both perforation and antibiotics-alone treatment failure.[1][2] Patients choosing this path need to understand the trade-off up front: roughly 1 in 4 will need appendectomy within the first year, and cumulative recurrence reaches about 39% by 5 years — but among this group overall, the 5-year complication rate is substantially lower than in patients randomized straight to surgery (6.5% vs 24.4%).[1]
Perioperative antibiotic prophylaxis for appendectomy
Every patient undergoing appendectomy a single dose of broad-spectrum antibiotic prophylaxis, given within 60 minutes before the skin incision — this alone measurably reduces wound infection and postoperative intra-abdominal abscess, regardless of how inflamed the appendix turns out to be.[1] Uncomplicated appendicitis confirmed at surgery do not continue antibiotics afterward — this is a strong recommendation, not a judgment call; unnecessary continuation adds cost and resistance pressure without any demonstrated benefit, in adults or children.[1]
Complicated appendicitis — postoperative antibiotics
Perforation, gangrene, or an abscess/peritonitis found at surgery changes the plan: continue broad-spectrum antibiotics postoperatively, particularly if source control was incomplete.[1] Adults with adequate source control a fixed postoperative course of about 3-5 days performs as well as a longer course guided by resolution of fever, leukocytosis, and ileus — do not extend therapy chasing normal labs once source control is adequate.[1][6] Children with complicated appendicitis switch to oral antibiotics once clinically stable, generally by 48 hours, to complete a total course under 7 days — this is as safe and effective as a longer intravenous course, with a shorter stay and lower cost.[1]
Antibiotics-alone (non-operative) management — selection and regimen
Appropriate candidates are adults or children with imaging-confirmed uncomplicated appendicitis, no appendicolith, and no signs of perforation, abscess, peritonitis, or sepsis, who understand and accept the recurrence risk above and can return promptly if symptoms worsen.[1][2] Not appropriate pregnancy — current guidance specifically recommends against non-operative management here until stronger evidence is available, given the higher stakes of a missed complicated course for both mother and fetus.[1] Give initial intravenous antibiotics with a switch to oral therapy once the patient is clinically improving; published regimens generally total 7-10 days.[1]
Representative regimens from the randomized trials
APPAC protocol
Ertapenem 1 g IV once daily for 3 days, then a 7-day oral course of levofloxacin 500 mg once daily plus metronidazole 500 mg 3 times daily (10 days total).[2]
CODA protocol
At least 24 hours of intravenous antibiotics (agent chosen locally — commonly a cephalosporin plus metronidazole, or piperacillin-tazobactam) followed by a 10-day total oral course individualized to the patient and local susceptibility patterns.[3]
Community-acquired intra-abdominal infection regimens
Amoxicillin-clavulanate 1.2-2.2 g IV every 6 hours alone; or ceftriaxone 2 g IV once daily plus metronidazole 500 mg IV every 6 hours; or cefotaxime 2 g IV every 8 hours plus metronidazole 500 mg IV every 6 hours. Beta-lactam allergy ciprofloxacin 400 mg IV every 8 hours plus metronidazole 500 mg IV every 6 hours, or moxifloxacin 400 mg IV once daily. Risk factors for an ESBL-producing organism ertapenem 1 g IV once daily, or tigecycline 100 mg IV as a loading dose then 50 mg IV every 12 hours.[1]
Appendiceal phlegmon or abscess
1st line non-operative management — intravenous antibiotics as for complicated appendicitis, plus image-guided percutaneous drainage of any drainable collection — is the preferred initial approach; primary laparoscopic appendectomy in experienced hands is a reasonable alternative where advanced laparoscopic expertise is available.[1] Do not perform routine interval appendectomy afterward in patients younger than 40 or in children who recover fully — the number needed to treat to prevent one recurrence is roughly 8, which current guidance judges does not justify routine surgery; reserve interval appendectomy for patients with recurrent symptoms.[1] Age 40 or older arrange colonoscopy and an interval contrast-enhanced CT scan even without recurrent symptoms — an appendiceal or cecal neoplasm, not simple appendicitis, is the actual diagnosis in 3-17% of complicated appendicitis in this age group.[1]
Non-Pharmacologic Treatment
- Laparoscopic appendectomy is preferred over open surgery for both uncomplicated and complicated disease wherever laparoscopic equipment and expertise are available — less pain, lower surgical-site infection, shorter hospital stay, and better quality-of-life scores.[1]
- Absolute contraindications to a laparoscopic approach: inability to tolerate a general anesthetic, hemodynamic instability, advanced cardiopulmonary disease, and uncorrected coagulopathy; relative contraindications include inability to tolerate pneumoperitoneum and extensive expected adhesions from prior abdominal surgery.[4]
- Image-guided percutaneous drainage of a drainable abscess is core therapy, not an adjunct, alongside antibiotics — it measurably reduces length of stay and complication rates compared with antibiotics alone.[4]
- Correct any coagulopathy and resuscitate with IV fluids before surgery; keep the patient NPO pending the operative or interventional plan.
- Drains are not routinely beneficial after appendectomy for complicated disease in either adults or children — they do not prevent intra-abdominal abscess and are linked to a longer hospital stay.[1]
- Outpatient (same-day) laparoscopic appendectomy is feasible and safe for uncomplicated appendicitis where a well-defined enhanced-recovery pathway and patient education are in place.[1]
- Send every appendectomy specimen for routine histopathology — unexpected findings, though uncommon, do occur and change follow-up.[1]
- For patients choosing antibiotics-alone management: clear, specific return precautions (worsening pain, new or higher fever, inability to tolerate oral intake) and a confirmed follow-up plan are as essential as the antibiotic prescription itself.
Special Populations
Pregnancy
Appendicitis is the most common non-obstetric surgical emergency of pregnancy, suspected in roughly 1 in 500-1,000 pregnancies and confirmed in about 1 in 800-1,500; it occurs across all trimesters (reported at roughly 25% in the first, 40% in the second, and 24% in the third).[4] As pregnancy advances, the enlarging uterus progressively displaces the appendix upward and laterally, so pain can present well above McBurney's point, especially in the third trimester — maintain suspicion even with an atypical location. Imaging graded compression trans-abdominal ultrasound first; published series report the appendix itself going unvisualized on ultrasound in a substantial proportion of second- and third-trimester patients, so proceed to MRI if the ultrasound is inconclusive — though even MRI fails to visualize the appendix in up to about 30% of pregnant patients, and a negative or inconclusive study does not exclude the diagnosis if clinical suspicion remains high.[4][1] Do not manage appendicitis non-operatively in pregnancy — current guidance specifically recommends against this until stronger evidence is available.[1] Surgery laparoscopic appendectomy is preferred over open surgery across all trimesters where expertise is available, with a shorter stay and lower infection risk.[1] Time matters more here than almost anywhere else in this chapter: a 24-hour delay to surgery after presentation is linked to a 66% relative increase in perforation rate, and while uncomplicated appendicitis carries under a 5% chance of fetal loss, perforated appendicitis with peritonitis carries a fetal loss rate as high as 35%.[4] For antibiotic selection, beta-lactams (penicillins, cephalosporins, carbapenems) are generally preferred and considered compatible throughout pregnancy; avoid fluoroquinolones and tetracyclines.
Breastfeeding
Cefazolin, cefoxitin, ceftriaxone, piperacillin-tazobactam, ertapenem, and metronidazole at standard multidose regimens are all considered compatible with breastfeeding; confirm specifics against each drug's own Drug Database entry. Avoid fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin) when a suitable alternative exists.
Pediatrics
Fewer than 1 in 5 children have complicated appendicitis at presentation, so most children with uncomplicated disease are candidates for either surgery or antibiotics-alone management, decided with the family.[1] Do not base the diagnosis on a clinical score alone in children — the Alvarado score and Pediatric Appendicitis Score are useful for excluding appendicitis, but current guidance suggests against using either to confirm the diagnosis without supporting imaging or labs.[1] Imaging ultrasound first-line; current guidance suggests against routine CT as the first-line study in children, since the population with an equivocal CT still has a meaningful rate of true appendicitis.[1] Appendicolith present antibiotics-alone failure rates run high (45-60% in several series) — surgery is generally preferred in this specific situation.[1] Uncomplicated, undergoing surgery no postoperative antibiotics — a single perioperative dose is the complete course, exactly as in adults.[1] Complicated appendicitis a single broad-spectrum agent (a second- or third-generation cephalosporin such as cefoxitin) for milder complicated disease; for perforated appendicitis, either the classic triple regimen (ampicillin plus clindamycin or metronidazole plus gentamicin) or dual therapy (ceftriaxone plus metronidazole) — dual therapy is equally effective and more cost-effective. Broader agents (piperacillin-tazobactam, ampicillin-sulbactam, ticarcillin-clavulanate, or imipenem-cilastatin) are reasonable for higher-severity disease, but extended-spectrum coverage has not been shown to outperform narrower regimens for most surgically managed children — reach for it by specific indication, not by default.[1] Switch to oral therapy once stable, generally by 48 hours, to complete a total course under 7 days.[1]
Older adults
Presentation is more often atypical and delayed, and perforation rates at diagnosis are correspondingly higher — maintain a lower threshold for imaging. Laparoscopic appendectomy is still preferred in this group and is linked to reduced mortality and morbidity compared with an open approach.[1] Any patient 40 years or older with complicated appendicitis managed non-operatively needs colonoscopy and an interval contrast-enhanced CT scan, since an underlying appendiceal or cecal neoplasm — not simple appendicitis — turns out to be the actual diagnosis in a meaningful minority.[1]
Immunocompromised patients
The inflammatory response can be blunted, masking severity on exam and in routine labs — maintain a lower threshold for imaging and for early surgical involvement, and do not let a reassuring white cell count or modest fever delay assessment.
Renal impairment
Dose-adjust piperacillin-tazobactam, the carbapenems (ertapenem, imipenem-cilastatin), cefazolin, cefoxitin, ciprofloxacin, levofloxacin, and ketorolac (avoid in significant impairment) for reduced renal function; ceftriaxone typically needs no adjustment. Consult a renal dosing reference or pharmacist for the specific adjustment.
Hepatic impairment
Reduce the metronidazole dose in severe hepatic impairment given reduced clearance of active metabolites, and use acetaminophen cautiously (lower total daily dose) in significant hepatic impairment. Most beta-lactams and cephalosporins do not require specific hepatic dose adjustment.
Monitoring & Follow-Up
After appendectomy for uncomplicated disease, routine postoperative monitoring (vitals, wound check, tolerance of oral intake) is generally all that is needed, and same-day or next-day discharge is standard where an enhanced-recovery pathway is in place. After surgery for complicated disease, watch specifically for fever, worsening or new abdominal pain, and distension in the days following discharge — these suggest a residual or new intra-abdominal abscess rather than simply "slow recovery," and warrant reimaging before assuming the antibiotic course simply needs to run longer.
For patients managed with antibiotics-alone: confirm the full course is understood and completed (initial IV, then oral, typically to 7-10 days total), and schedule a specific follow-up contact rather than leaving return solely to the patient's discretion — non-operative management can fail during the index admission in roughly 8% of patients, with an additional 20% needing a second hospitalization for recurrence within the first year.[1] Counsel clearly that recurrence remains possible even after full apparent resolution, with cumulative recurrence reaching about 39% by 5 years, and confirm the patient knows exactly what to watch for and where to seek care.[1]
In every patient 40 years or older who had complicated appendicitis managed non-operatively (antibiotics with or without percutaneous drainage), explicitly schedule the interval colonoscopy and contrast-enhanced CT at the time of discharge rather than leaving it to a future visit to remember — this step is easy to lose once the acute illness has resolved.[1] Confirm routine histopathology results are reviewed on every appendectomy specimen. Complete medication reconciliation at discharge, including confirming any antibiotic course end date and any analgesic taper.
Common Errors to Avoid
- Continuing antibiotics after appendectomy for uncomplicated appendicitis "just in case" — this is a strong recommendation against in both adults and children, not a judgment call.
- Offering antibiotics-alone management to a patient with an appendicolith on imaging without discussing the substantially higher failure rate — surgery is generally preferred here.
- Treating pregnancy as eligible for non-operative management — current guidance specifically recommends against it.
- Relying on the Alvarado score alone to positively confirm appendicitis in an adult — current guidance suggests against this specific use, given only moderate specificity; it remains genuinely useful for excluding low-risk patients and for deciding who needs imaging.
- Ordering CT reflexively in every patient — point-of-care or graded-compression ultrasound is the recommended first-line study in both adults and children, with CT reserved for an inconclusive ultrasound or specific higher-risk situations.
- Using a standard-dose CT protocol in an adolescent or young adult when a low-dose contrast-enhanced protocol is available and appropriate.
- Extending complicated-appendicitis antibiotics past 5 days by default once adequate source control has been achieved, rather than stopping on schedule.
- Reaching for extended-spectrum antibiotics (piperacillin-tazobactam, a carbapenem, or similar) as a default choice rather than a narrower regimen in surgically managed appendicitis — evidence shows no added benefit for most patients and adds unnecessary resistance pressure.
- Performing routine interval appendectomy in every patient under 40 after successful non-operative management of a phlegmon or abscess — reserve it for patients with recurrent symptoms.
- Missing the possibility of an underlying appendiceal or cecal neoplasm in a patient 40 or older with complicated appendicitis — arrange colonoscopy and interval imaging even if the acute course resolves uneventfully.
- Assuming a normal-appearing appendix at surgery ends the workup — evaluate for an alternative cause rather than closing without an explanation.
Clinical Decision Algorithm
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.
Perioperative Antibiotic Prophylaxis (Appendectomy)
A single dose within 60 minutes before skin incision is the complete course for uncomplicated appendicitis confirmed at surgery — no postoperative doses.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Cefazolin | Adults: 2 g IV single dose (3 g if 120 kg or heavier) | Hypersensitivity, rare interstitial nephritis | Possible increased INR with warfarin | Combine with metronidazole for anaerobic coverage; use 3 g instead of 2 g in patients 120 kg or heavier. |
| Cefoxitin | Adults: 2 g IV single dose | GI upset, hypersensitivity reactions | May increase aminoglycoside nephrotoxicity | A single second-generation cephalosporin covering both gram-negatives and anaerobes without a second agent. |
| Metronidazole | Adults: 500 mg IV single dose | GI upset, metallic taste, peripheral neuropathy with prolonged use | Disulfiram-like reaction with alcohol | Added to cefazolin (or another agent without reliable anaerobic activity) for single-dose prophylaxis. |
Complicated Appendicitis — Postoperative Therapy
Continue for about 3-5 days with adequate source control in adults; switch children to oral therapy by 48 hours to complete under 7 days total.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Ceftriaxone | Adults: 2 g IV once daily | Hypersensitivity, biliary sludging, transient LFT elevation | Do not co-administer with calcium-containing IV solutions | Combine with metronidazole; dual therapy is as effective as, and more cost-effective than, triple-agent regimens. |
| Piperacillin-tazobactam | Adults: 4.5 g IV every 6-8 hours, renally adjusted | GI upset, rash, interstitial nephritis | May increase methotrexate levels | Single-agent broader coverage; reserve for higher-severity or resistance-risk disease. |
| Ertapenem | Adults: 1 g IV once daily | Diarrhea, hypersensitivity reactions | May decrease valproic acid levels | Convenient once-daily dosing; does not cover Pseudomonas. |
| Ampicillin | Children: Per weight-based pediatric dosing reference | Hypersensitivity, GI upset, rash | May reduce efficacy of estrogen-containing contraceptives (theoretical) | Combined with clindamycin (or metronidazole) plus gentamicin as the classic perforated-appendicitis triple regimen, particularly in children. |
| Gentamicin | Adults: 5-7 mg/kg IV once daily, adjusted to levels and renal function | Nephrotoxicity, ototoxicity | Additive nephro/ototoxicity with vancomycin or other nephrotoxins | Added for gram-negative synergy within the classic triple regimen; monitor levels and renal function closely. |
| Clindamycin | Adults: 600-900 mg IV every 8 hours | Clostridioides difficile-associated diarrhea, GI upset | None significant at standard doses | An alternative to metronidazole within the classic triple regimen for anaerobic and toxin-suppression coverage. |
Antibiotics-Alone (Non-Operative) Regimens — Uncomplicated Appendicitis
Initial IV therapy with a switch to oral once clinically improving; total course generally 7-10 days. Confirm no appendicolith and no signs of perforation, abscess, or peritonitis before selecting this pathway.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Levofloxacin | Adults: 500 mg PO once daily for 7 days | GI upset, headache; rare tendinopathy, peripheral neuropathy, QTc prolongation | Antacids/sucralfate/metal cations/dairy reduce absorption; avoid with other QTc-prolonging drugs | Oral component of the APPAC protocol, paired with metronidazole, after 3 days of IV ertapenem. |
| Amoxicillin-clavulanate | Adults: 1.2-2.2 g IV every 6 hours, or an equivalent oral dose for step-down | GI upset, diarrhea, hypersensitivity | May increase methotrexate levels; may increase INR with warfarin | A single-agent oral or IV option that already covers anaerobes. |
| Moxifloxacin | Adults: 400 mg IV or PO once daily | GI upset, QTc prolongation; rare tendinopathy, hepatotoxicity | Avoid with other QTc-prolonging drugs | A single-agent alternative in beta-lactam allergy — already covers anaerobes, so metronidazole is not required alongside it. |
| Tigecycline | Adults: 100 mg IV loading dose, then 50 mg IV every 12 hours | GI upset (nausea common), hepatotoxicity | May reduce efficacy of concurrent oral contraceptives (theoretical) | Reserve for confirmed or strongly suspected risk of an ESBL-producing organism. |
| Ciprofloxacin | Adults: 400 mg IV every 8 hours | GI upset, tendinopathy risk, QTc prolongation | Chelation with antacids/metal cations reduces absorption; avoid with other QTc-prolonging drugs | Paired with metronidazole in beta-lactam allergy. |
Postoperative Analgesia and Antiemesis
Scheduled multimodal analgesia (acetaminophen plus an NSAID where appropriate) is preferred over an opioid-first approach; reserve opioids for breakthrough pain.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Acetaminophen | Adults: 975-1000 mg PO/IV every 6 hours, maximum 4 g/day (lower in hepatic impairment) | Hepatotoxicity with overdose or in significant hepatic impairment | None significant at standard doses | First-line, scheduled — not only as-needed. |
| Ketorolac | Adults: 15-30 mg IV every 6 hours | GI bleeding, renal impairment, platelet inhibition | Increased bleeding risk with anticoagulants; avoid with other NSAIDs | Limit to 5 days total; avoid in significant renal impairment or active GI bleeding risk. |
| Morphine | Adults: 2-4 mg IV every 3-4 hours PRN | Respiratory depression, sedation, constipation, nausea | Additive CNS/respiratory depression with other sedatives | Reserve for breakthrough pain on top of scheduled multimodal analgesia. |
| Hydromorphone | Adults: 0.2-0.5 mg IV every 3-4 hours PRN | Respiratory depression, sedation, constipation, nausea | Additive CNS/respiratory depression with other sedatives | Preferred over morphine in significant renal impairment given more predictable metabolite handling. |
| Ondansetron | Adults: 4 mg IV/PO, may repeat per the product monograph | Headache, QTc prolongation at higher/repeated doses | Additive QTc prolongation with other QTc-prolonging drugs | First-line for postoperative nausea and vomiting. |
References
- Diagnosis and treatment of acute appendicitis: 2020 update of the WSES Jerusalem guidelines — World Journal of Emergency Surgery, World Society of Emergency Surgery (Di Saverio S, Podda M, De Simone B, et al.). World J Emerg Surg 2020;15:27
- Antibiotic Therapy vs Appendectomy for Treatment of Uncomplicated Acute Appendicitis: The APPAC Randomized Clinical Trial — JAMA (Salminen P, Paajanen H, Rautio T, et al.). JAMA 2015;313(23):2340-2348
- A Randomized Trial Comparing Antibiotics with Appendectomy for Appendicitis — New England Journal of Medicine, CODA Collaborative. N Engl J Med 2020;383(20):1907-1919
- Acute Appendicitis — Dynamic Practice Guidelines for Emergency General Surgery, Committee on Acute Care Surgery, Canadian Association of General Surgeons (Ward M, Visser R, Gillman LM). CAGS Dynamic Practice Guidelines for Emergency General Surgery, Chapter 7, 2018
- A practical score for the early diagnosis of acute appendicitis — Annals of Emergency Medicine (Alvarado A). Ann Emerg Med 1986;15(5):557-564
- Trial of Short-Course Antimicrobial Therapy for Intraabdominal Infection — New England Journal of Medicine (Sawyer RG, Claridge JA, Nathens AB, et al.). N Engl J Med 2015;372(21):1996-2005
Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.