METHYLDOPA AND CHLOROTHIAZIDE
Clinical safety rating: safe
Lithium may cause increased lithium toxicity Can cause hemolytic anemia and positive Coombs test.
Methyldopa is a centrally acting alpha-2 adrenergic agonist that reduces sympathetic outflow, lowering peripheral vascular resistance; chlorothiazide is a thiazide diuretic that inhibits sodium reabsorption in the distal convoluted tubule, reducing blood volume.
| Metabolism | Methyldopa is metabolized via catecholamine pathways (e.g., decarboxylation, sulfation); chlorothiazide is not extensively metabolized and is excreted unchanged in urine. |
| Excretion | Methyldopa: ~70% renal (unchanged and conjugates), ~25% biliary/fecal. Chlorothiazide: ~95% renal (tubular secretion, unchanged), ~5% biliary/fecal. |
| Half-life | Methyldopa: Terminal half-life ~1.8 hours (range 1.4-2.1 h) in normal renal function; prolonged to 4-6 h in renal impairment. Chlorothiazide: Biphasic; terminal half-life ~6-15 hours (renal impairment prolongs). |
| Protein binding | Methyldopa: ~15% bound to albumin; Chlorothiazide: ~20-30% bound to albumin. |
| Volume of Distribution | Methyldopa: Vd ~0.2-0.4 L/kg (confined to extracellular fluid). Chlorothiazide: Vd ~0.1-0.2 L/kg (restricted to plasma and extracellular space). |
| Bioavailability | Methyldopa: Oral bioavailability ~25% (range 8-50%) due to first-pass metabolism. Chlorothiazide: Oral bioavailability ~20-30% (variable, dose-dependent). |
| Onset of Action | Methyldopa: Oral onset 3-6 hours, IV 1-2 hours. Chlorothiazide: Oral diuresis within 2 hours, peak at 4 hours. |
| Duration of Action | Methyldopa: Antihypertensive effect lasts 12-24 hours (single oral dose); trough effect requires twice-daily dosing. Chlorothiazide: Diuretic effect lasts 6-12 hours following oral dose. |
Oral: 1 tablet (250 mg methyldopa / 250 mg chlorothiazide) twice daily; maximum 2 tablets/day.
| Dosage form | TABLET |
| Renal impairment | eGFR 30-50 mL/min: reduce dose by 50%; eGFR <30 mL/min: contraindicated. |
| Liver impairment | Child-Pugh class B: reduce dose by 50%; class C: contraindicated due to methyldopa hepatotoxicity. |
| Pediatric use | Not recommended in children; safety and efficacy not established. |
| Geriatric use | Start with lowest dose (0.5 tablet daily); monitor for hypotension and electrolyte imbalance; avoid in patients with significant renal impairment. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Lithium may cause increased lithium toxicity Can cause hemolytic anemia and positive Coombs test.
| FDA category | Human |
| Breastfeeding | Methyldopa is excreted in breast milk (M/P ratio ~1.0), but infant doses are low (~1-2% of maternal weight-adjusted dose). Chlorothiazide is excreted in breast milk (M/P ratio unknown), may suppress lactation. Use caution, monitor infant for jaundice, electrolyte imbalance, and hypotension. |
| Teratogenic Risk | First trimester: Methyldopa is considered low risk; chlorothiazide exposure may increase risk of neural tube defects. Second and third trimesters: Methyldopa is generally safe; chlorothiazide may cause fetal electrolyte disturbances, hypoglycemia, and thrombocytopenia. Avoid chlorothiazide after 20 weeks due to risk of oligohydramnios and fetal renal anomalies. |
■ FDA Black Box Warning
None
| Common Effects | Sedation |
| Serious Effects |
["Hypersensitivity to methyldopa, chlorothiazide, or sulfonamides","Active hepatic disease (e.g., acute hepatitis, cirrhosis) due to methyldopa","Anuria due to chlorothiazide","Previous methyldopa therapy associated with liver disorders or hemolytic anemia"]
| Precautions | ["Hepatic dysfunction: methyldopa may cause liver damage; perform liver function tests periodically.","Hemolytic anemia: rare but severe; check Coombs test.","Electrolyte imbalance: chlorothiazide may cause hypokalemia, hyponatremia, hypomagnesemia.","Sulfonamide allergy: chlorothiazide is a sulfonamide derivative.","Systemic lupus erythematosus exacerbation: methyldopa.","Parkinsonism: methyldopa may worsen symptoms.","Renal impairment: dose adjustment may be needed."] |
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| Fetal Monitoring | Maternal: Blood pressure, serum electrolytes (especially potassium), renal function, liver function, and CBC. Fetal: Ultrasound for growth and amniotic fluid volume (chlorothiazide risk of oligohydramnios); consider fetal monitoring in third trimester. |
| Fertility Effects | No known adverse effects on fertility from either component. Methyldopa may cause reversible menstrual irregularities or galactorrhea in some women. |