PROSCAR
Clinical safety rating
cautionComprehensive 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. |
| Molecular Weight | 372.55 |
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 | Contraindicated in pregnancy. Finasteride (PROSCAR) is a 5α-reductase inhibitor that can inhibit the conversion of testosterone to dihydrotestosterone (DHT) and may cause abnormal development of external genitalia in male fetuses. Its use is contraindicated in women who are or may become pregnant. |
| 2nd trimester | Contraindicated in pregnancy. Finasteride (PROSCAR) is a 5α-reductase inhibitor that can inhibit the conversion of testosterone to dihydrotestosterone (DHT) and may cause abnormal development of external genitalia in male fetuses. Its use is contraindicated in women who are or may become pregnant. |
| 3rd trimester | Contraindicated in pregnancy. Finasteride (PROSCAR) is a 5α-reductase inhibitor that can inhibit the conversion of testosterone to dihydrotestosterone (DHT) and may cause abnormal development of external genitalia in male fetuses. Its use is contraindicated in women who are or may become pregnant. |
Clinical note
Comprehensive clinical and safety monograph for PROSCAR (PROSCAR).
| Placental transfer | Finasteride crosses the placenta in animal studies and is expected to cross the human placenta based on its molecular weight and lipophilicity. In pregnant rats, finasteride produced hypospadias in male offspring at maternal doses less than the human therapeutic dose of 5 mg/day. |
| Breastfeeding | Finasteride is excreted in human milk. However, no data are available on the effects of finasteride on the breastfed infant or on milk production. Because of the potential for adverse effects on the nursing infant, breastfeeding is not recommended during finasteride therapy. The manufacturer recommends that women should not handle crushed or broken tablets if they are pregnant or may become pregnant due to potential transdermal absorption. |
| Lactation Rating | L4 (Possibly Hazardous) - or 'Avoid' according to some sources. |
| 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. |
| 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. |
■ 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 |
Pregnancy or women who may become pregnantHypersensitivity to finasteride or any component of the formulation
| 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. |
| Food/Dietary | No significant food interactions. Can be taken with or without meals. |
| Clinical Pearls | Proscar (finasteride 5 mg) is indicated for benign prostatic hyperplasia (BPH); not interchangeable with Propecia (1 mg) for alopecia. Onset of symptom improvement may take 6-12 months. Monitor serum PSA (multiply by 2 for first 2 years). May cause reversible decrease in libido, ejaculatory dysfunction. Avoid in women of childbearing potential due to teratogenicity (risk of hypospadias). |
| Patient Advice | Take once daily with or without food. · Do not crush or split tablets. · Symptom improvement may take 6 months or longer. · Possible side effects include decreased libido, erectile dysfunction, or decreased semen volume. · Women who are pregnant or may become pregnant should not handle crushed or broken tablets. · Regular monitoring of PSA levels is required during treatment. · Do not donate blood while taking this medication. · Report any breast lumps or testicular pain to your healthcare provider. |
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