Finasteride (5 brand names, 2 dosage forms, 1 route)
Available dosage forms: TABLET, CAPSULE.
Routes of administration: ORAL.
Brand Names
- ENTADFI
- FINASTERIDE
- FINASTERIDE AND TADALAFIL
- PROPECIA
- PROSCAR
Indications and Usage
Finasteride tablets are indicated for the treatment of male pattern hair loss (androgenetic alopecia) in MEN ONLY. Efficacy in bitemporal recession has not been established. Finasteride tablets are not indicated for use in women.
Dosage and Administration
Finasteride tablets may be administered with or without meals. The recommended dose of finasteride is one tablet (1 mg) taken once daily. In general, daily use for three months or more is necessary before benefit is observed. Continued use is recommended to sustain benefit, which should be re-evaluated periodically. Withdrawal of treatment leads to reversal of effect within 12 months.
Contraindications
Finasteride tablets are contraindicated in the following: Pregnancy. Finasteride use is contraindicated in women when they are or may potentially be pregnant. Because of the ability of Type II 5α-reductase inhibitors to inhibit the conversion of testosterone to 5α-dihydrotestosterone (DHT), finasteride may cause abnormalities of the external genitalia of a male fetus of a pregnant woman who receives finasteride. If this drug is used during pregnancy, or if pregnancy occurs while taking this drug, the pregnant woman should be apprised of the potential hazard to the male fetus. [See Warnings and Precautions (5.1), Use in Specific Populations (8.1), How Supplied/Storage and Handling (16)and Patient Counseling Information (17).] In female rats, low doses of finasteride administered during pregnancy have produced abnormalities of the external genitalia in male offspring. Hypersensitivity to any component of this medication.
Mechanism of Action
Finasteride is a competitive and specific inhibitor of Type II 5α-reductase, an intracellular enzyme that converts the androgen testosterone into DHT. Two distinct isozymes are found in mice, rats, monkeys, and humans: Type I and II. Each of these isozymes is differentially expressed in tissues and developmental stages. In humans, Type I 5α-reductase is predominant in the sebaceous glands of most regions of skin, including scalp, and liver. Type I 5α-reductase is responsible for approximately one-third of circulating DHT. The Type II 5α-reductase isozyme is primarily found in prostate, seminal vesicles, epididymides, and hair follicles as well as liver, and is responsible for two-thirds of circulating DHT. In humans, the mechanism of action of finasteride is based on its preferential inhibition of the Type II isozyme. Using native tissues (scalp and prostate), in vitrobinding studies examining the potential of finasteride to inhibit either isozyme revealed a 100-fold selectivity for the human Type II 5α-reductase over Type I isozyme (IC 50=500 and 4.2 nM for Type I and II, respectively). For both isozymes, the inhibition by finasteride is accompanied by reduction of the inhibitor to dihydrofinasteride and adduct formation with NADP+. The turnover for the enzyme complex is slow (t 1/2approximately 30 days for the Type II enzyme complex and 14 days for the Type I complex). Inhibition of Type II 5α-reductase blocks the peripheral conversion of testosterone to DHT, resulting in significant decreases in serum and tissue DHT concentrations. In men with male pattern hair loss (androgenetic alopecia), the balding scalp contains miniaturized hair follicles and increased amounts of DHT compared with hairy scalp. Administration of finasteride decreases scalp and serum DHT concentrations in these men. The relative contributions of these reductions to the treatment effect of finasteride have not been defined. By this mechanism, finasteride appears to interrupt a key factor in th
Overdosage
In clinical studies, single doses of finasteride up to 400 mg and multiple doses of finasteride up to 80 mg/day for three months did not result in adverse reactions. Until further experience is obtained, no specific treatment for an overdose with finasteride can be recommended. Significant lethality was observed in male and female mice at single oral doses of 1500 mg/m 2(500 mg/kg) and in female and male rats at single oral doses of 2360 mg/m 2 (400 mg/kg) and 5900 mg/m 2(1000 mg/kg), respectively.