PROSCAR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PROSCAR (PROSCAR).
Finasteride inhibits 5α-reductase type II, preventing conversion of testosterone to dihydrotestosterone (DHT) in the prostate, reducing prostate volume and improving urinary symptoms.
| Metabolism | Primarily metabolized by CYP3A4 to t-butyl side-chain hydroxylated metabolites; minor metabolism by other CYP enzymes. |
| Excretion | Primarily hepatic metabolism (CYP3A4), metabolites excreted renally (39%) and fecally (57%) as unchanged drug and metabolites. |
| Half-life | Terminal elimination half-life is 6-8 hours (range 4-12 hours) in young adults; prolonged to 8-10 hours in elderly (≥70 years), but no dose adjustment required. Steady-state reached after 2 weeks dosing. |
| Protein binding | Approximately 90% bound to plasma proteins (albumin and alpha-1-acid glycoprotein). |
| Volume of Distribution | Apparent volume of distribution is 1.4 L/kg (range 0.8-2.0 L/kg), indicating extensive tissue distribution (including prostate, seminal vesicles, and skin). |
| Bioavailability | Oral bioavailability is approximately 63-80% (mean 65% from tablet formulation); food does not significantly affect absorption (Cmax decreased by 8%, AUC unchanged). |
| Onset of Action | Oral: Reduction in serum DHT detectable within 24 hours; maximal effect on DHT (65-80% reduction) at 2 weeks; clinical effect on urinary symptoms may take 3-6 months; effect on prostate volume significant at 6-12 months. |
| Duration of Action | Once-daily dosing maintains therapeutic effect. After discontinuation, serum DHT returns to baseline within 2 weeks, but clinical benefit (e.g., reduced prostate volume, improved urinary flow) may persist for several months before regressing. |
5 mg orally once daily.
| Dosage form | TABLET |
| Renal impairment | No adjustment required for renal impairment; dose adjustment not studied in GFR < 30 mL/min. |
| Liver impairment | No specific guidelines for Child-Pugh A or B; use with caution in severe hepatic impairment. |
| Pediatric use | Not indicated for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | No specific dose adjustment required; normal adult dosing recommended. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PROSCAR (PROSCAR).
| Breastfeeding | Finasteride is excreted in breast milk in very low amounts (M/P ratio 0.52). Limited data; use caution. Consider alternative therapy, especially in nursing mothers of male infants due to theoretical risk of antiandrogenic effects. |
| Teratogenic Risk | Finasteride is contraindicated in pregnancy (Category X). In first trimester, exposure may cause hypospadias in male fetuses due to inhibition of 5α-reductase; second and third trimester risks include ambiguous genitalia in male fetuses. Avoid handling crushed tablets if pregnant. |
■ FDA Black Box Warning
Not approved for use in women or children; finasteride is contraindicated in women who are or may become pregnant due to risk of hypospadias in male fetuses.
| Serious Effects |
Hypersensitivity to finasteride or any component, women who are or may become pregnant, pediatric patients (not indicated).
| Precautions | Increased risk of high-grade prostate cancer (Gleason score 8-10) reported in clinical trials; monitor for urinary obstruction; evaluate for other urological diseases; potential for decreased serum PSA levels; sexual dysfunction (decreased libido, erectile dysfunction, ejaculation disorder) may persist after discontinuation; mood changes including depression; breast cancer risk not established. |
Loading safety data…
| Fetal Monitoring |
| Monitor for signs of prostate cancer in male patients; no specific maternal-fetal monitoring required as drug is contraindicated in pregnancy. For accidental exposure during pregnancy, fetal ultrasound for genital development. |
| Fertility Effects | Finasteride reduces serum DHT and may impair spermatogenesis. Reversible decrease in sperm count and motility reported. Discontinuation may restore fertility within months. |