MINIZIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MINIZIDE (MINIZIDE).
Prazosin is a selective alpha-1 adrenergic antagonist that inhibits vascular smooth muscle contraction, reducing peripheral vascular resistance and blood pressure. Polythiazide is a thiazide diuretic that inhibits the Na+/Cl- cotransporter in the distal convoluted tubule, increasing sodium and water excretion, and reducing intravascular volume.
| Metabolism | Prazosin is extensively metabolized in the liver via O-demethylation and conjugation, primarily by CYP3A4. Polythiazide is not extensively metabolized; it is excreted unchanged in the urine. |
| Excretion | Renal: 90% (unchanged drug and metabolites); biliary/fecal: <10% |
| Half-life | 2-3 hours (prazosin component); prolonged in heart failure or renal impairment |
| Protein binding | 97% (prazosin bound to alpha-1 acid glycoprotein and albumin) |
| Volume of Distribution | 0.6 L/kg (prazosin); reflects extensive tissue distribution |
| Bioavailability | Oral: 50-70% (prazosin); first-pass metabolism reduces systemic availability |
| Onset of Action | Oral: 1-2 hours (first-dose syncope possible within 30-90 minutes) |
| Duration of Action | 10-24 hours (antihypertensive effect); tolerability to first-dose orthostasis may persist beyond 24 hours |
1-2 capsules orally twice daily; each capsule contains prazosin 0.5 mg and polythiazide 0.5 mg. Titrate based on blood pressure response.
| Dosage form | CAPSULE |
| Renal impairment | Contraindicated in patients with GFR <30 mL/min. For GFR 30-60 mL/min: use with caution, reduce dose by 50%, monitor electrolytes. No adjustment for GFR >60 mL/min. |
| Liver impairment | Child-Pugh A: no adjustment necessary. Child-Pugh B: reduce dose by 50%. Child-Pugh C: avoid use due to risk of hepatic encephalopathy. |
| Pediatric use | Not recommended for pediatric use due to lack of safety and efficacy data. |
| Geriatric use | Initiate therapy at the lower end of the dosing range (1 capsule daily) due to increased sensitivity to orthostatic hypotension and electrolyte disturbances. Titrate slowly. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MINIZIDE (MINIZIDE).
| Breastfeeding | Prazosin: low levels in breast milk; M/P ratio 0.75-1.0. Polythiazide: may suppress lactation; M/P ratio unknown. Use caution, monitor infant for diuretic effects or hypotension. |
| Teratogenic Risk | Prazosin-polythiazide combination. First trimester: Risk category C; limited human data. Second and third trimesters: potential fetal/neonatal effects include hypotension, electrolyte imbalance, and decreased placental perfusion. Avoid use unless clearly needed. |
| Fetal Monitoring |
■ FDA Black Box Warning
None.
| Serious Effects |
["Anuria","Hypersensitivity to prazosin, polythiazide, or sulfonamide-derived drugs (thiazides)","Concomitant use with phosphodiesterase-5 inhibitors (e.g., sildenafil) due to risk of severe hypotension"]
| Precautions | ["First-dose syncope (orthostatic hypotension) can occur, especially with initial use or dose escalation","Sodium and water depletion may occur with thiazide, leading to hypokalemia, hyponatremia, and hypomagnesemia","May exacerbate renal impairment; monitor renal function","May increase serum uric acid and precipitate gout","May cause hypersensitivity reactions, including anaphylaxis and angioedema"] |
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| Maternal: blood pressure, serum electrolytes, renal function. Fetal: growth ultrasound, amniotic fluid index (due to diuretic effects), and fetal heart rate monitoring if used near term. |
| Fertility Effects | No well-controlled studies. Prazosin may rarely cause priapism; polythiazide may affect spermatogenesis in animal studies. Clinical significance unknown. |