THEROXIDIL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for THEROXIDIL (THEROXIDIL).
Theroxidil is a vasodilator that acts by opening potassium channels in vascular smooth muscle, leading to hyperpolarization and relaxation. It also inhibits platelet aggregation and reduces peripheral vascular resistance.
| Metabolism | Primarily metabolized by hepatic CYP3A4 and CYP2D6; undergoes glucuronidation. Metabolites are excreted renally. |
| Excretion | Approximately 60% renal (15% unchanged, 45% as glucuronide metabolites), 40% fecal/biliary as metabolites |
| Half-life | Terminal elimination half-life 24-30 hours; steady-state reached after 4-5 days; clinically significant for once-daily dosing |
| Protein binding | 92-95% primarily to albumin and alpha-1-acid glycoprotein |
| Volume of Distribution | Vd 1.2-1.5 L/kg, indicating extensive extravascular distribution |
| Bioavailability | Oral: 45-55% (first-pass effect); Topical: <5% systemic absorption |
| Onset of Action | Oral: 2-3 hours; Intravenous: 15-30 minutes; Topical: 4-6 weeks (hair regrowth) |
| Duration of Action | 24 hours per dose; requires continuous daily therapy; clinical effects persist for several weeks after discontinuation |
5 mg orally once daily, increased to 10 mg after 4 weeks as tolerated.
| Dosage form | SOLUTION |
| Renal impairment | GFR 30-89 mL/min: 5 mg daily; GFR 15-29 mL/min: 2.5 mg daily; GFR <15 mL/min: not recommended. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: 2.5 mg daily; Child-Pugh C: not recommended. |
| Pediatric use | 0.1 mg/kg orally once daily, maximum 5 mg; titrate after 4 weeks to 0.2 mg/kg, maximum 10 mg. |
| Geriatric use | Initiate at 2.5 mg orally once daily; consider renal function and comorbidities. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for THEROXIDIL (THEROXIDIL).
| Breastfeeding | Excretion into breast milk is unknown. Due to potential for serious adverse effects in nursing infants, breastfeeding is not recommended. M/P ratio not determined. |
| Teratogenic Risk | THEROXIDIL is contraindicated in pregnancy. Animal studies indicate teratogenicity including cardiovascular and skeletal malformations. First trimester exposure carries highest risk for major congenital anomalies; second and third trimester exposure may cause fetal growth restriction and oligohydramnios. |
| Fetal Monitoring |
■ FDA Black Box Warning
May cause severe hypotension and reflex tachycardia. Use with caution in patients with coronary artery disease or history of stroke.
| Serious Effects |
Hypersensitivity to theroxidil or any excipients. Concomitant use with strong CYP3A4 inducers. Severe aortic stenosis or obstructive cardiomyopathy. Uncorrected hypotension (systolic BP < 90 mmHg).
| Precautions | Risk of symptomatic hypotension, especially when initiating therapy. May exacerbate angina. Monitor heart rate and blood pressure regularly. Abrupt discontinuation can cause rebound hypertension. |
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| Monitor maternal blood pressure, renal function, and electrolytes. Perform serial fetal ultrasound for growth, amniotic fluid volume, and anatomy. Nonstress test or biophysical profile in third trimester. |
| Fertility Effects | THEROXIDIL may impair fertility in both sexes. In males, reversible sperm motility reduction. In females, possible anovulation based on animal data. |