Preeclampsia
Clinical Snapshot
Preeclampsia is a multisystem disorder specific to pregnancy, defined by new-onset hypertension developing after 20 weeks' gestation together with evidence of maternal end-organ dysfunction — most classically proteinuria, but proteinuria is not required for the diagnosis if another marker of end-organ involvement is present. It complicates roughly 2-8% of pregnancies globally and is one of the leading causes of maternal and perinatal death, both directly (eclampsia, stroke, HELLP syndrome, placental abruption) and through the downstream effects of medically indicated preterm delivery.[1] Preeclampsia sits within a broader family of hypertensive disorders of pregnancy — chronic hypertension, gestational hypertension, preeclampsia, and chronic hypertension with superimposed preeclampsia — that share overlapping management principles (see Recognize the Condition).
For a community or prenatal pharmacist, the single highest-yield interaction with this condition is low-dose aspirin prophylaxis: a large proportion of pregnant patients meet at least one risk-factor threshold for aspirin, the drug is available without a prescription, and the timing window (started by 16 weeks, ideally by 12 weeks) is easy to miss if it is not raised proactively at an early prenatal counselling visit. The second major pharmacist-relevant thread in this chapter is recognizing that ACE inhibitors and ARBs are contraindicated in pregnancy — a genuinely common and dangerous prescribing/dispensing error when a patient with treated chronic hypertension becomes pregnant.[2]
Recognize the Condition
Often silent until a routine check finds it
Mild-to-moderate preeclampsia is frequently asymptomatic — it is found on a routine blood pressure check or routine prenatal urinalysis, not because the patient feels unwell. Symptoms, when present, more often signal progression toward severe disease (see Red Flags & Refer) than early or mild disease, so a well-appearing, asymptomatic patient cannot be assumed to be at low risk on that basis alone.
The hypertensive disorders of pregnancy
Four overlapping categories, plus 2 severe presentations that can complicate any of them.
Chronic hypertension
Hypertension present before pregnancy, diagnosed before 20 weeks' gestation, or persisting beyond 12 weeks postpartum.
Gestational hypertension
New-onset hypertension after 20 weeks' gestation, without proteinuria or any other feature of preeclampsia. Up to half of these patients go on to develop proteinuria or another marker of end-organ dysfunction and are then reclassified as preeclampsia — this progression is more likely the earlier gestational hypertension is diagnosed. Gestational hypertension presenting with severe-range blood pressure is managed the same way as preeclampsia with severe features.[1]
Preeclampsia (with or without severe features)
New-onset hypertension after 20 weeks' gestation plus proteinuria, or — in the absence of proteinuria — another new marker of maternal end-organ dysfunction (see Assessment & Diagnosis).
Chronic hypertension with superimposed preeclampsia
Pre-existing hypertension plus new or worsening proteinuria, a sudden increase in previously well-controlled blood pressure, new thrombocytopenia, or a new rise in liver enzymes developing after 20 weeks.
Eclampsia
The convulsive manifestation of the hypertensive disorders of pregnancy — new-onset tonic-clonic, focal, or multifocal seizures in a preeclamptic patient, in the absence of another cause (epilepsy, intracranial hemorrhage, drug use). A significant minority of eclamptic seizures occur with no prior documented hypertension or proteinuria, and eclampsia can occur before, during, or after labour, including several days postpartum.[1]
HELLP syndrome
Hemolysis, elevated liver enzymes, and low platelet count — one of the more severe presentations of preeclampsia, associated with higher maternal morbidity. Up to 15% of HELLP cases lack either hypertension or proteinuria at presentation, and the main presenting symptoms are often right-upper-quadrant pain and malaise rather than classic preeclampsia symptoms — a genuinely easy diagnosis to miss on symptoms alone.[1]
Symptoms that suggest progression toward severe disease
- New, persistent headache unresponsive to usual-dose acetaminophen.
- Visual disturbances — blurred vision, scotomata (flashing lights or spots), or transient vision loss.
- Right-upper-quadrant or epigastric pain, with or without nausea and vomiting — easy to mistake for heartburn or gallbladder pain in the third trimester, but a genuine red flag in this context.
- Shortness of breath, or rapidly worsening edema out of proportion to normal late-pregnancy swelling.
- Hyperreflexia or clonus on examination.
Risk Factors
High-risk factors
Any single high-risk factor is enough on its own to recommend low-dose aspirin prophylaxis (see Choose Initial Treatment).
- Preeclampsia in a previous pregnancy, especially when it was accompanied by an adverse outcome (early-onset disease, preterm delivery, growth restriction).
- Multifetal gestation (twins or higher order).
- Chronic hypertension.
- Pregestational diabetes mellitus (type 1 or type 2).
- Renal disease.
- Autoimmune disease associated with an elevated preeclampsia risk — systemic lupus erythematosus, antiphospholipid antibody syndrome.
Moderate-risk factors
More than one moderate-risk factor is needed before aspirin prophylaxis is recommended — evidence does not clearly separate individual moderate factors from one another, but risk rises with the number present.
- Nulliparity.
- Obesity (pre-pregnancy BMI over 30 kg/m²).
- Family history of preeclampsia (mother or sister).
- Maternal age 35 years or older.
- Personal history factors — a previous low-birth-weight or small-for-gestational-age infant, a previous adverse pregnancy outcome, or a pregnancy interval of more than 10 years.
- Assisted reproductive technology.
- Obstructive sleep apnea.
Low risk
A previous uncomplicated full-term delivery, on its own, does not warrant aspirin prophylaxis.
[1][2]Red Flags & Refer
Escalate immediately — same-day urgent obstetric assessment, or emergency services for the items marked as such — for any of the following. These define preeclampsia with severe features, eclampsia, or an acute complication, and are not managed as routine prenatal follow-up.
- Systolic BP ≥160 mmHg or diastolic BP ≥110 mmHg, confirmed on repeat measurement — urgent antihypertensive treatment is needed, typically within 30-60 minutes of confirmation.
- New-onset headache unresponsive to usual-dose acetaminophen and not accounted for by an alternative diagnosis.
- Visual disturbances — blurred vision, scotomata, or transient vision loss.
- Severe or persistent right-upper-quadrant or epigastric pain unresponsive to analgesics, with or without nausea and vomiting — suspect HELLP syndrome or hepatic involvement, not simple heartburn, especially in the third trimester.
- Shortness of breath or signs suggesting pulmonary edema.
- A tonic-clonic, focal, or multifocal seizure in a pregnant or postpartum patient — this is eclampsia until proven otherwise. Call emergency services immediately.
- Any of the above occurring in the postpartum period — preeclampsia and eclampsia can newly develop, or a previously controlled case can worsen, after delivery, most often within the first week but occasionally later. Discharge from obstetric care does not mean the risk has ended.
Assessment & Diagnosis
Diagnostic criteria for preeclampsia
| Criterion | Definition |
|---|---|
| Blood pressure | Systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg, on 2 occasions at least 4 hours apart, after 20 weeks' gestation in a patient with previously normal blood pressure. Once BP reaches the severe range (≥160/110 mmHg), a confirmatory reading can be taken within a short interval (minutes) rather than waiting 4 hours, to allow timely treatment. |
| Proteinuria | 300 mg or more per 24-hour urine collection, or a protein-to-creatinine ratio of 30 mg/mmol (0.3 mg/dL) or more, or a dipstick reading of 2+ (used only when quantitative testing is not available, given its high false-positive and false-negative rate). |
Or, in the absence of proteinuria, new-onset hypertension together with any one of the following new findings after 20 weeks:
- Thrombocytopenia — platelet count under 100 × 10⁹/L.
- Renal insufficiency — serum creatinine over 97 μmol/L (1.1 mg/dL), or a doubling of the serum creatinine in the absence of other renal disease.
- Impaired liver function — liver transaminases elevated to twice the upper limit of normal.
- Pulmonary edema.
- New-onset headache unresponsive to usual-dose acetaminophen and not accounted for by an alternative diagnosis, or new visual disturbances.
Severe features
Any one of the following, present alongside the diagnosis above, makes this preeclampsia with severe features — a materially higher-risk state that changes management (see Choose Initial Treatment):
- Systolic BP ≥160 mmHg or diastolic BP ≥110 mmHg on 2 occasions at least 4 hours apart (unless antihypertensive therapy was already started, in which case the interval requirement is relaxed).
- Thrombocytopenia — platelet count under 100 × 10⁹/L.
- Impaired liver function not accounted for by an alternative diagnosis — liver transaminases more than twice the upper limit of normal, or severe, persistent right-upper-quadrant or epigastric pain unresponsive to medication.
- Renal insufficiency — serum creatinine over 97 μmol/L (1.1 mg/dL), or a doubling of the serum creatinine, in the absence of other renal disease.
- Pulmonary edema.
- New-onset headache unresponsive to usual-dose acetaminophen and not accounted for by an alternative diagnosis.
- Visual disturbances.
HELLP syndrome
Diagnosed with all 3 of: hemolysis (abnormal peripheral blood smear, elevated LDH ≥600 IU/L, or elevated bilirubin), elevated liver enzymes (AST or ALT more than twice the upper limit of normal), and thrombocytopenia (platelet count under 100 × 10⁹/L). Deteriorates in an insidious, sometimes atypical pattern — as noted in Recognize the Condition, up to 15% of cases lack hypertension or proteinuria at presentation, so maintain suspicion in any pregnant or postpartum patient with new right-upper-quadrant pain and malaise even with a reassuring blood pressure.[1]
Distinguishing superimposed preeclampsia from worsening chronic hypertension
In a patient with pre-existing chronic hypertension, suspect superimposed preeclampsia when any of the following develops after 20 weeks: new proteinuria (or a sudden increase in previously stable proteinuria), a sudden increase in blood pressure that had previously been well controlled, new thrombocytopenia, or a new rise in liver enzymes. Because both conditions share the same baseline finding — hypertension — this diagnosis rests on a genuine change from the patient's own baseline, not on an isolated reading.
Investigations
- CBC with platelet count.
- Serum creatinine.
- AST and ALT.
- LDH and uric acid if HELLP or hepatic involvement is suspected.
- Urinalysis and a urine protein-to-creatinine ratio (or 24-hour urine collection where a rapid ratio is not available).
- Fetal assessment — ultrasound for growth and amniotic fluid volume, and antenatal fetal testing, guided by gestational age and severity.
Treatment Targets
- Prevent progression to eclampsia, stroke, HELLP syndrome, placental abruption, and pulmonary edema.
- Control severe-range blood pressure promptly enough to prevent maternal stroke and cardiac complications, without lowering it so aggressively that placental perfusion is compromised.
- Prevent an eclamptic seizure in every patient with severe features, using magnesium sulfate — and treat one promptly if it occurs.
- Support a safely timed delivery — the only definitive treatment for preeclampsia — balancing maternal risk of continuing the pregnancy against fetal risk of early delivery.
- In patients at increased risk, reduce the incidence and severity of preeclampsia in the first place through correctly timed aspirin prophylaxis.
- Provide adequate postpartum surveillance and treatment, since preeclampsia and eclampsia can newly appear or worsen after delivery.
- Counsel every affected patient on the associated long-term cardiovascular risk once the pregnancy has ended.
Choose Initial Treatment
Recommend low-dose aspirin to every patient with 1 or more high-risk factors, or more than 1 moderate-risk factor (see Risk Factors).
Dose: acetylsalicylic acid (ASA) 81-162 mg PO once daily, taken at bedtime.[2]
Timing: start once pregnancy is confirmed, by 16 weeks' gestation, and ideally before 12-16 weeks — the benefit on severe and preterm preeclampsia is substantially greater when aspirin is started before 16 weeks than after.[3][1]
Duration: continue once daily until delivery.[2]
Start oral antihypertensive therapy for sustained BP over 140/90 mmHg, targeting roughly 120-140/80-90 mmHg — treating too aggressively toward a much lower target risks reducing placental perfusion.[2]
Preferred labetalol 100 mg PO BID, titrated up to 800 mg PO TID as needed (maximum 2400 mg/day); or nifedipine extended-release 30 mg PO once daily, titrated up to 60 mg PO BID.
Alternative methyldopa 250 mg PO BID, titrated up to 1000 mg PO TID — an acceptable option, chosen less often given lower potency and a higher side-effect burden than labetalol or nifedipine.
Treat within 30-60 minutes of confirming persistent severe-range BP — do not wait for a scheduled reassessment.[1]
1st line IV labetalol 10-20 mg, then 20-80 mg IV every 10-30 minutes as needed to a maximum cumulative dose of 300 mg; or a continuous infusion of 1-2 mg/min. Avoid in asthma, pre-existing myocardial disease, decompensated cardiac function, heart block, or bradycardia.
Alternative IV or IM hydralazine 5 mg, then 5-10 mg IV every 20-40 minutes as needed to a maximum cumulative dose of 20 mg; or a continuous infusion of 0.5-10 mg/hr.
Oral alternative, when IV access is not yet available immediate-release nifedipine 10-20 mg PO, repeated in 20 minutes if needed, then 10-20 mg every 2-6 hours (maximum 180 mg/day).[1]
Start magnesium sulfate for every patient diagnosed with preeclampsia with severe features or eclampsia — it is the drug of choice for seizure prevention and treatment, more effective than phenytoin, diazepam, or nimodipine for this purpose.[4][5]
Loading dose: 4-6 g IV over 20-30 minutes.
Maintenance: continuous IV infusion of 1-2 g/hour.
Duration: continue through labour and delivery, and for 24 hours after delivery (or 24 hours after the last seizure, whichever is later).
Magnesium sulfate is not an antihypertensive — it treats and prevents seizures only; blood pressure must still be controlled separately with the agents in Step 3.
ACE inhibitors, ARBs, and direct renin inhibitors are contraindicated throughout pregnancy — fetotoxic in the 2nd and 3rd trimesters (oligohydramnios, fetal growth restriction, fetal/neonatal renal failure, skull hypoplasia) and associated with teratogenic effects on first-trimester exposure. Switch any patient of childbearing potential on one of these agents before conception, or immediately on discovering an unplanned pregnancy.[2]
Avoid atenolol specifically — associated with fetal growth restriction, unlike other beta-blockers. Avoid diuretics for routine blood pressure control — preeclampsia already involves a contracted intravascular volume, and diuretics can worsen placental perfusion; reserve them for treating pulmonary edema specifically.
Delivery is the only definitive treatment. Without severe features deliver at 37 0/7 weeks rather than continuing expectant management.[1]
With severe features, at or beyond 34 0/7 weeks deliver after maternal stabilization, or with labour or prelabour rupture of membranes — do not delay delivery to complete a course of antenatal corticosteroids in the late preterm period.
With severe features, before 34 0/7 weeks expectant management may be considered under strict selection criteria (stable maternal and fetal status, resources appropriate for both), with antenatal corticosteroids for fetal lung maturation and close inpatient maternal/fetal monitoring — but deliver immediately, regardless of gestational age, if any condition precluding expectant management develops (uncontrolled severe-range BP, refractory headache, refractory epigastric/right-upper-quadrant pain, visual disturbance, altered sensorium or motor deficit, stroke, myocardial infarction, HELLP syndrome, worsening renal function, pulmonary edema, eclampsia, suspected abruption, abnormal fetal testing, or fetal death).[1]
Non-Pharmacologic Treatment
- Bed rest, with or without hospitalization, has not been shown to reduce the risk or severity of preeclampsia and should not be routinely recommended.
- Sodium restriction has not been shown to reduce preeclampsia risk and is not routinely recommended for this purpose.
- For patients with low dietary calcium intake, calcium supplementation of at least 1 g/day reduces the risk of preeclampsia and related hypertensive complications — the benefit is most pronounced in populations with low baseline calcium intake.[2]
- Vitamins C and E, fish oil, garlic, vitamin D, and folic acid supplementation have not shown sufficient evidence of benefit for preeclampsia prevention specifically and should not be recommended for this indication.[1]
- Educate every patient — at the first prenatal visit, and again at every visit thereafter — on the warning symptoms in Red Flags & Refer, and to seek care immediately if any occur, including in the postpartum period.
- For gestational hypertension or preeclampsia without severe features managed as an outpatient, arrange frequent blood pressure and symptom checks (a combination of in-clinic and home monitoring, at least once weekly in-clinic) and serial laboratory monitoring — this is not a "wait until the next routine visit" condition.
- Smoking cessation and standard healthy-pregnancy counselling (diet, weight management as appropriate) remain relevant for overall pregnancy risk, though neither has been shown to specifically prevent preeclampsia.
Special Populations
Postpartum
Continue magnesium sulfate for 24 hours after delivery (or 24 hours after the last seizure) in every patient who required it antepartum or intrapartum — stopping early raises the risk of a postpartum eclamptic seizure.[1]
Preeclampsia and eclampsia can develop for the first time after delivery, most often within the first week postpartum, and a patient with no antepartum hypertension is not exempt. Take new severe headache, visual change, epigastric pain, or hypertension seriously in any postpartum patient, not only those with a known antepartum diagnosis.
NSAIDs are preferred over opioids for routine postpartum analgesia, even in patients with preeclampsia with severe features — randomized and cohort data have not shown that NSAID use lengthens the duration of severe-range blood pressure or changes antihypertensive requirements in the postpartum period, so avoiding NSAIDs on this basis alone is outdated practice.[1]
Blood pressure follow-up: check BP within 72 hours of delivery (inpatient if the patient is still admitted, or a dedicated office/virtual visit if already discharged), and again at 7-10 days postpartum — blood pressure typically falls in the first 48 hours after delivery but rebounds around days 3-6, which is exactly the window a standard 6-week postpartum visit would miss entirely. Support home blood pressure monitoring in between these visits and give explicit written warning-symptom education at discharge.[6]
HELLP syndrome
Delivery is generally recommended regardless of gestational age once HELLP syndrome is diagnosed, given its progressive and sometimes sudden clinical course; patients remote from term should be cared for at a centre with neonatal and obstetric intensive-care resources. Monitor platelet count and liver enzymes at least every 12 hours until a clear improving trend is established — the platelet nadir typically occurs about 23 hours after delivery, and a rebound thrombocytosis by day 4-7 postpartum is a normal recovery pattern, not a new problem.[1]
Breastfeeding
Labetalol, nifedipine extended-release, methyldopa, and magnesium sulfate are all considered compatible with breastfeeding.
Renal impairment
In mild renal impairment (serum creatinine 88-133 μmol/L [1.0-1.5 mg/dL]) or oliguria (urine output under 30 mL/hr for more than 4 hours), give the standard magnesium sulfate loading dose but reduce the maintenance infusion to 1 g/hour, and check serum magnesium levels every 4 hours — magnesium is cleared almost entirely by the kidney, so impaired clearance raises toxicity risk substantially at a standard maintenance rate.[1]
Obesity / higher body mass index
A higher volume of distribution in patients with a BMI over 35 kg/m² can leave magnesium levels subtherapeutic for several hours after a standard loading dose — some protocols use a higher loading dose (e.g., 4.5 g followed by a 1.8 g/hr maintenance infusion) in this group; follow local hospital protocol.[1]
When IV access is difficult
Magnesium sulfate can be given intramuscularly: 4 g IV as a loading dose, immediately followed by 10 g IM (5 g deep IM into each buttock), then 5 g IM every 4 hours. Mixing the IM dose with 1 mL of 2% lidocaine reduces injection-site pain; the IM route carries a higher rate of local adverse effects than the IV route.[1]
Monitoring & Follow-Up
During a magnesium sulfate infusion: assess deep tendon reflexes, respiratory rate, and urine output at least hourly. Loss of deep tendon reflexes is the earliest clinical sign of impending toxicity and should prompt an immediate serum magnesium level and consideration of stopping the infusion.
| Serum magnesium | Effect |
|---|---|
| 2-3.5 mmol/L (4-7 mEq/L; 5-9 mg/dL) | Therapeutic range for seizure prophylaxis. |
| >3.5 mmol/L (>7 mEq/L; >9 mg/dL) | Loss of patellar (deep tendon) reflexes. |
| >5 mmol/L (>10 mEq/L; >12 mg/dL) | Respiratory paralysis. |
| >12.5 mmol/L (>25 mEq/L; >30 mg/dL) | Cardiac arrest. |
Deep tendon reflexes are lost before respiratory depression occurs at a higher level still — provided reflexes are present, more serious toxicity has been avoided. If renal function is impaired, levels rise faster and monitoring should be more frequent (see Special Populations).[1]
Blood pressure and severity monitoring: for hospitalized severe disease, monitor blood pressure and symptoms continuously through labour and delivery, and immediately postpartum, watching specifically for progression to severe features. For outpatient gestational hypertension or preeclampsia without severe features, weekly platelet count, creatinine, and liver enzymes, with blood pressure and symptom checks in-clinic at least weekly supplemented by home monitoring.[1]
Long-term: counsel every patient with a history of preeclampsia that it roughly doubles the future risk of cardiovascular disease (hypertension, myocardial infarction, heart failure, stroke), with a graded relationship — the more severe the preeclampsia, the higher the later cardiovascular risk. Recommend ongoing primary-care follow-up and cardiovascular risk-factor management well beyond the postpartum period, not only the standard 6-week check.[1]
Common Errors to Avoid
- Continuing an ACE inhibitor or ARB after conception, or failing to switch a patient with treated chronic hypertension before a planned pregnancy — genuinely contraindicated, not merely "preferably avoided."
- Missing the aspirin-prophylaxis window — starting after 16 weeks meaningfully reduces the benefit on severe and preterm preeclampsia compared with starting before 16 weeks.[3]
- Treating non-severe hypertension in pregnancy toward an aggressively low target — over-lowering blood pressure can compromise placental perfusion; the target is roughly 120-140/80-90 mmHg, not the tightest number achievable.
- Assuming magnesium sulfate is an antihypertensive — it prevents and treats seizures only; blood pressure still needs separate, active management.
- Stopping a magnesium sulfate infusion before the full 24-hour postpartum course is complete, particularly around the stress of a caesarean delivery, when the seizure threshold may be lowest.
- Missing HELLP syndrome because hypertension or proteinuria is absent — up to 15% of cases present without either, with right-upper-quadrant pain and malaise as the dominant symptoms instead.
- Withholding NSAIDs from a postpartum patient with a history of severe features out of outdated concern — current evidence supports their preferential use over opioids for postpartum analgesia in this group.
- Discharging a patient with a hypertensive disorder of pregnancy without a scheduled blood pressure check in the 72-hour and 7-10-day window, missing the well-documented days-3-to-6 rebound in blood pressure.
- Treating delivery as the end of the condition — new-onset postpartum preeclampsia and eclampsia are real, and long-term cardiovascular risk counselling is easy to skip once the pregnancy itself has ended.
- Not keeping calcium gluconate readily available at the bedside whenever a magnesium sulfate infusion is running.
Clinical Decision Algorithm
Drug Tables
How to use this table: doses are adult obstetric doses for preeclampsia specifically and require patient-specific confirmation. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.
Aspirin — Preeclampsia Prophylaxis
The only prevention strategy with strong supporting evidence in patients meeting the risk-factor threshold.[3]
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Acetylsalicylic acid (ASA) | 81-162 mg PO once daily at bedtime; start by 16 weeks (ideally before 12-16 weeks); continue until delivery | GI upset, dyspepsia; small increase in bleeding risk | Theoretical additive bleeding risk with other antiplatelets or anticoagulants | Confirm the patient is using a true 81 mg low-dose product, not attempting to split a higher-strength tablet; taking it at bedtime is the studied regimen. |
Oral Antihypertensives — Non-Severe Hypertension Maintenance Therapy
1st-line maintenance options once BP is sustained over 140/90 mmHg; target roughly 120-140/80-90 mmHg.[2]
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Labetalol | 100 mg PO BID initially, titrate to 800 mg PO TID (max 2400 mg/day) | Dizziness (especially postural), fatigue, nausea, nasal stuffiness, scalp tingling | Cimetidine increases bioavailability; additive hypotension with other antihypertensives | Preferred oral agent; avoid in asthma, significant bradycardia, or heart block. |
| Nifedipine, extended-release | 30 mg PO once daily, titrate to 60 mg PO BID | Headache, flushing, peripheral edema, reflex tachycardia | CYP3A4 substrate — strong inhibitors (azole antifungals, macrolides) raise levels | Extended-release formulation only for maintenance — do not crush, chew, or split. |
| Methyldopa | 250 mg PO BID initially, titrate to 1000 mg PO TID | Sedation, dry mouth, orthostatic hypotension, rare drug-induced hepatitis or hemolytic anemia | Additive sedation with other CNS depressants; may interact with MAOIs | Longest-established pregnancy safety record; reserved as an alternative given lower potency and more sedation than labetalol or nifedipine. |
Parenteral / Acute-Onset Antihypertensives — Severe Hypertension (≥160/110 mmHg)
Treat within 30-60 minutes of confirming persistent severe-range BP.[1]
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Labetalol, IV | 10-20 mg IV, then 20-80 mg IV every 10-30 min (max cumulative 300 mg); or infusion 1-2 mg/min | Bradycardia, bronchospasm, hypotension | Additive bradycardia with non-dihydropyridine calcium channel blockers | 1st-line parenteral agent; avoid in asthma, decompensated cardiac function, or heart block. |
| Hydralazine, IV/IM | 5 mg IV or IM, then 5-10 mg IV every 20-40 min (max cumulative 20 mg); or infusion 0.5-10 mg/hr | Reflex tachycardia, headache, hypotension | Additive hypotension with other antihypertensives | Alternative when labetalol is contraindicated or ineffective. |
| Nifedipine, immediate-release | 10-20 mg PO, repeat in 20 min if needed, then 10-20 mg every 2-6 hours (max 180 mg/day) | Reflex tachycardia, headache, marked hypotension | Additive neuromuscular blockade and hypotension with concurrent magnesium sulfate — monitor more closely | Oral option when IV access is not yet available; observe for reflex tachycardia. |
Magnesium Sulfate — Eclamptic Seizure Prophylaxis and Treatment
The drug of choice for preventing and treating eclamptic seizures — more effective than phenytoin, diazepam, or nimodipine for this purpose.[4]
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Magnesium sulfate, IV | Load 4-6 g IV over 20-30 min, then 1-2 g/hr IV continuous infusion; continue 24 hours postpartum or 24 hours after the last seizure | Flushing, warmth, nausea; dose-related loss of deep tendon reflexes, respiratory depression, cardiac arrest | Additive neuromuscular blockade with calcium channel blockers and neuromuscular blocking agents; potentiates non-depolarizing anesthetic muscle relaxants | Not an antihypertensive — treat blood pressure separately. Reduce the maintenance rate to 1 g/hr in renal impairment or oliguria (see Special Populations). Recurrent seizure: additional 2-4 g IV over 5 minutes. |
| Magnesium sulfate, IM (when IV access is difficult) | 4 g IV loading dose, then 10 g IM (5 g deep IM into each buttock), then 5 g IM every 4 hours | Same as IV; injection-site pain and higher local adverse-effect rate than IV | Same as IV | Mix each IM dose with 1 mL of 2% lidocaine to reduce injection pain. |
| Calcium gluconate (antidote) | 10 mL of 10% solution IV over 3 minutes | Hypercalcemia with rapid or excessive administration; local irritation with extravasation | None specific to this indication | Give for clinical signs of magnesium toxicity (absent deep tendon reflexes, respiratory depression) — do not wait for a serum magnesium level to result. Keep available at the bedside for every magnesium sulfate infusion. |
Contraindicated in pregnancy
| Drug | Dosage | Reason avoided | Drug interactions | Comments |
|---|---|---|---|---|
| Ramipril (ACE inhibitor, example agent) Avoid | N/A | Fetotoxic in the 2nd/3rd trimester (oligohydramnios, fetal growth restriction, fetal/neonatal renal failure, skull hypoplasia); teratogenic on 1st-trimester exposure | — | Switch to labetalol, nifedipine, or methyldopa before conception or immediately on discovering an unplanned pregnancy. |
| Losartan / Irbesartan (ARBs, example agents) Avoid | N/A | Same fetotoxic and teratogenic profile as ACE inhibitors — the entire class is contraindicated | — | Same switching principle as ACE inhibitors; never combine an ACE inhibitor with an ARB even outside pregnancy. |
| Atenolol Avoid | N/A | Associated specifically with fetal growth restriction, unlike other beta-blockers, which carry only a weak association | — | Use labetalol instead if a beta-blocker is needed. |
Evidence note: drug inventory, dosing, adverse effects, and comments reflect standard Canadian obstetric practice, cross-checked against current SOGC and ACOG guidance.[2][1]
References
- Gestational Hypertension and Preeclampsia: ACOG Practice Bulletin, Number 222 — Obstetrics & Gynecology, American College of Obstetricians and Gynecologists (Committee on Practice Bulletins-Obstetrics). Obstet Gynecol 2020;135(6):e237-e260
- Guideline No. 426: Hypertensive Disorders of Pregnancy: Diagnosis, Prediction, Prevention, and Management — Journal of Obstetrics and Gynaecology Canada, Society of Obstetricians and Gynaecologists of Canada (Magee LA, Smith GN, Bloch C, Côté AM, Jain V, Nerenberg K, von Dadelszen P, Helewa M, Rey E). J Obstet Gynaecol Can 2022;44(5):572-597
- Aspirin versus Placebo in Pregnancies at High Risk for Preterm Preeclampsia — New England Journal of Medicine (Rolnik DL, Wright D, Poon LC, O'Gorman N, Syngelaki A, de Paco Matallana C, et al.). N Engl J Med 2017;377(7):613-622
- Do women with pre-eclampsia, and their babies, benefit from magnesium sulphate? The Magpie Trial: a randomised placebo-controlled trial — The Lancet (Magpie Trial Collaborative Group). Lancet 2002;359(9321):1877-1890
- Magnesium sulphate and other anticonvulsants for women with pre-eclampsia — Cochrane Database of Systematic Reviews (Duley L, Gülmezoglu AM, Henderson-Smart DJ, Chou D). Cochrane Database Syst Rev 2010;(11):CD000025
- Society for Maternal-Fetal Medicine Special Statement: Checklist for postpartum discharge of women with hypertensive disorders — American Journal of Obstetrics and Gynecology (Gibson KS, Hameed AB). Am J Obstet Gynecol 2020;223(4):B18-B21
Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.