METHYLDOPA AND HYDROCHLOROTHIAZIDE
Clinical safety rating: safe
Lithium may cause increased lithium toxicity Can cause hemolytic anemia and positive Coombs test.
Methyldopa is converted to alpha-methylnorepinephrine, which stimulates central alpha-2 adrenergic receptors, reducing sympathetic outflow and lowering blood pressure. Hydrochlorothiazide inhibits the sodium-chloride symporter in the distal convoluted tubule, increasing sodium, chloride, and water excretion, reducing plasma volume and blood pressure.
| Metabolism | Methyldopa is metabolized via sulfate conjugation and O-methylation; hydrochlorothiazide is not metabolized, excreted unchanged in urine. |
| Excretion | Methyldopa: ~70% renal (unchanged and sulfate conjugate), ~30% biliary/fecal. Hydrochlorothiazide: >95% renal (unchanged). |
| Half-life | Methyldopa: 1.8-8 hours (terminal), prolonged in renal impairment; clinical context: requires dose adjustment in renal failure. Hydrochlorothiazide: 6-15 hours (terminal), prolonged in renal impairment. |
| Protein binding | Methyldopa: <15% bound to plasma proteins. Hydrochlorothiazide: 40-68% bound to serum albumin. |
| Volume of Distribution | Methyldopa: 0.3-0.6 L/kg (distributes into total body water). Hydrochlorothiazide: 0.8-1.5 L/kg (extensively distributed, crosses placenta). |
| Bioavailability | Methyldopa: oral ~25% (range 20-50%), with significant first-pass metabolism. Hydrochlorothiazide: oral ~65-75% (well absorbed). |
| Onset of Action | Methyldopa: oral onset 3-6 hours, peak effect 6-8 hours. Hydrochlorothiazide: oral onset 2 hours, peak effect 4 hours. |
| Duration of Action | Methyldopa: 12-24 hours (antihypertensive effect) after single dose, accumulates with repeated dosing. Hydrochlorothiazide: 6-12 hours (diuretic effect), but antihypertensive effect may persist for 24 hours with chronic use. |
Oral: 1 tablet (250 mg methyldopa / 15 mg hydrochlorothiazide) twice daily, increased as needed to max 3 tablets/day.
| Dosage form | TABLET |
| Renal impairment | GFR 30-60 mL/min: reduce dose by 50%; GFR <30 mL/min: avoid use. |
| Liver impairment | Child-Pugh class B: reduce methyldopa dose by 50%; Child-Pugh class C: contraindicated. |
| Pediatric use | Oral: methyldopa 10 mg/kg/day in 2-4 divided doses, max 65 mg/kg/day or 3 g/day; hydrochlorothiazide 1-2 mg/kg/day in 2 doses, max 2 mg/kg/day. Weight-based combination not standard. |
| Geriatric use | Start at lowest dose (half tablet once daily), increase slowly; monitor for orthostatic hypotension, electrolyte disturbances, and renal function. |
| 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 | M/P ratio unknown. Methyldopa is excreted in breast milk in small amounts; hydrochlorothiazide is also excreted in low levels. Generally considered compatible with breastfeeding, but monitor infant for hypotonia, drowsiness, and electrolyte disturbances. Use with caution in preterm or ill infants. |
| Teratogenic Risk |
■ FDA Black Box Warning
None
| Common Effects | Sedation |
| Serious Effects |
["Active hepatic disease (e.g., acute hepatitis, cirrhosis)","Prior methyldopa-induced liver disease","Concomitant MAO inhibitor therapy","Anuria","Known hypersensitivity to sulfonamide-derived drugs or thiazides"]
| Precautions | ["Sedation and dizziness may occur, impairing ability to drive or operate machinery","May cause positive Coombs test and hemolytic anemia","Sulfonamide hypersensitivity cross-reactivity","Electrolyte disturbances (hypokalemia, hyponatremia) due to thiazide","Monitor for hypotension, especially in patients with cerebrovascular disease","Abrupt withdrawal may cause rebound hypertension","Hepatotoxicity and hepatic failure reported with methyldopa","Thiazides may exacerbate systemic lupus erythematosus"] |
Loading safety data…
| First trimester: Methyldopa is considered low risk; hydrochlorothiazide is associated with increased risk of neural tube defects and oral clefts. Second and third trimesters: Methyldopa is generally safe; hydrochlorothiazide may cause fetal electrolyte abnormalities, jaundice, and placental insufficiency. Avoid thiazide diuretics for pregnancy-induced hypertension due to decreased maternal plasma volume and placental perfusion. |
| Fetal Monitoring | Monitor maternal blood pressure, electrolytes (especially potassium and sodium), renal function, and complete blood count. Fetal monitoring includes ultrasound for fetal growth, amniotic fluid index, and non-stress testing in high-risk pregnancies. |
| Fertility Effects | Limited data. Methyldopa may cause amenorrhea or gynecomastia in males; hydrochlorothiazide may have minimal effects. No significant impact on female fertility reported. |