Finasteride is a medicine used for the symptoms of an enlarged prostate (benign prostatic hyperplasia). It shrinks the prostate by blocking the conversion of testosterone to its more active form. Effects take several months to appear.
Also known as: Proscar, Propecia
Ketoconazole may slightly raise finasteride blood levels, but the clinical impact is considered of little significance.
Finasteride is mainly metabolised by CYP3A4 but does not significantly affect this system. CYP3A4 inhibitors and inducers may alter its plasma concentrations; however, based on established safety margins, they are unlikely to be clinically significant.
CYP3A4: finasteride is metabolised by CYP3A4, but the label states that any increase from inhibitors is unlikely to be clinically significant (wide safety margins).
Finasteride CYP3A4 metabolism, with clinical impact unlikely.
No specific monitoring.
No specific red flags.
No special precaution needed; maintain usual surveillance.
DailyMed/FDA (NIH/NLM) — approved Finasteride label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=350b2bdb-84a1-4465-b0ad-175b8f720400 ; approved Ketoconazole label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f162e616-21b4-49b1-b437-15e21001a6f0 ; EMC-UK (MHRA) — approved Finasteride SmPC: https://www.medicines.org.uk/emc/product/100132/smpc ; Prontuário Terapêutico do INFARMED (11th ed., 2012)
Finasteride may be taken with or without food, with no relevant documented food interactions.
Take with or without food, as preferred.
DailyMed/FDA (NIH/NLM) — approved Finasteride label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=350b2bdb-84a1-4465-b0ad-175b8f720400
Finasteride reduces serum PSA by about 50% and may increase the risk of high-grade prostate cancer; it is not approved for prostate cancer prevention.
Screen for prostate cancer (digital rectal examination and PSA) before and periodically during treatment; interpret PSA with the adjustment factor (double the value after 6 months of treatment).
DailyMed/FDA (NIH/NLM) — approved Finasteride label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=350b2bdb-84a1-4465-b0ad-175b8f720400 ; Prontuário Terapêutico do INFARMED (11th ed., 2012)
Contraindicated in pregnant women or those who may become pregnant: type II 5-alpha reductase inhibitors can cause abnormalities of the external genitalia of a male fetus.
Contraindicated at any stage of pregnancy; pregnant women or those who may become pregnant must not handle crushed or broken tablets.
Not indicated in women; no data on milk excretion.
Women of child-bearing age must use effective contraception; men have no specific contraception restriction.
DailyMed/FDA (NIH/NLM) — approved Finasteride label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=350b2bdb-84a1-4465-b0ad-175b8f720400 ; Prontuário Terapêutico do INFARMED (11th ed., 2012)
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Type II 5-alpha-reductase inhibitor used in benign prostatic hyperplasia and androgenetic alopecia. At 5 mg/day it reduces serum DHT by about 70% (maximum effect 8 hours after the first dose) and prostatic tissue DHT by about 80%. The effect is reversible: DHT returns to baseline about 2 weeks after discontinuation.
Competitively and specifically inhibits type II 5-alpha-reductase, blocking the conversion of testosterone to 5-alpha-dihydrotestosterone (DHT) in the prostate, liver and skin. It has no affinity for the androgen receptor.
Mean bioavailability is 63% (34 to 108%), with peak plasma concentrations 1 to 2 hours after dosing; bioavailability is not affected by food. About 90% of circulating finasteride is bound to plasma proteins and the volume of distribution is about 76 L.
Extensively metabolised in the liver, mainly by the CYP3A4 subfamily. The identified metabolites have no more than 20% of the 5-alpha-reductase inhibitory activity. About 39% of the dose is excreted in urine as metabolites and 57% in faeces.
The mean elimination half-life is about 6 hours (3 to 16 hours); in subjects aged 70 years or older it is approximately 8 hours.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
