Finasteride in Special Populations: Transplant, HIV, Hepatic Impairment, and Beyond

What the labels cover, and what they leave out

The 1 mg tablet (finasteride 1 mg, Propecia) is indicated for male pattern hair loss in men only; the label states it is not indicated for women and that efficacy in bitemporal recession has not been established [1]. The 5 mg tablet (Proscar) is indicated for symptomatic benign prostatic hyperplasia in men with an enlarged prostate, to improve symptoms and reduce the risk of acute urinary retention and of surgery [3]. Proscar is not approved for the prevention of prostate cancer [3].

Finasteride is a competitive inhibitor of type II 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT). The label reports 65% suppression of serum DHT within 24 hours of a 1 mg tablet, with mean testosterone and estradiol rising about 15% but staying within the normal range [1].

Both labels handle other medicines in a single interaction section. It states that no drug interactions of clinical importance have been identified, that finasteride does not appear to affect the cytochrome P450 system, and that antipyrine, digoxin, propranolol, theophylline and warfarin produced no clinically meaningful interactions [1][3]. A second part lists drugs used alongside finasteride in clinical studies — acetaminophen, aspirin, alpha-blockers, ACE inhibitors, anticonvulsants, benzodiazepines, beta blockers, calcium channel blockers, nitrates, diuretics, H2 antagonists, HMG-CoA reductase inhibitors, NSAIDs and quinolone anti-infectives — without evidence of clinically significant adverse interactions [1][3].

The gap that matters for this page: that section does not discuss CYP3A4 inhibitors or inducers, even though finasteride is extensively metabolized in the liver, mainly by CYP3A4 [1].

Transplant recipients and people living with HIV

The label's contraindications are pregnancy and hypersensitivity to a component, so having a transplant is not itself a listed contraindication [1]. Neither interaction section, nor its list of medicines used with finasteride in clinical trials, names a calcineurin inhibitor, an mTOR inhibitor, mycophenolate or an antiretroviral [1][3]. We found no published measurement of how these medicines change finasteride levels.

Kidney function after transplant falls under the renal data below: the Propecia label says no dosage adjustment is necessary in renal impairment, and a pharmacokinetic review states the same, because the metabolites that accumulate are relatively inactive and well tolerated and because fecal excretion of metabolites rises in these patients [1][2].

Liver disease

The liver is where finasteride is handled. The label describes extensive hepatic metabolism, mainly by CYP3A4, with two metabolites carrying no more than 20% of the parent drug's activity; about 57% of a dose leaves in feces and about 39% in urine as metabolites [1]. The Propecia label says the effect of hepatic impairment on finasteride pharmacokinetics has not been studied and that caution should be exercised in patients with liver function abnormalities because finasteride is metabolized extensively in the liver [1]. A published pharmacokinetic review likewise states that the effect of hepatic dysfunction on finasteride metabolism is unknown [2]. Neither gives a liver-specific exposure result or dose.

Kidney disease

The Propecia label states that no dosage adjustment is necessary in renal impairment. In its single-dose study in chronic renal impairment (creatinine clearance 9.0 to 55 mL/min), finasteride AUC, peak concentration, half-life and protein binding were similar to healthy volunteers, but plasma metabolite concentrations were significantly higher [1]. The pharmacokinetic review states that the metabolites which accumulate are relatively inactive and well tolerated, and that greater fecal excretion of metabolites occurs in these patients [2]. Kidney function is the one comorbidity in this group with a clear, drug-specific answer.

Older men

The label gives a mean terminal half-life of about 5 to 6 hours in men aged 18 to 60 and about 8 hours in men over 70 [1]. The Propecia label says that, based on the pharmacokinetics of finasteride 5 mg, no dosage adjustment is necessary in the elderly, but that its efficacy studies did not include subjects aged 65 and over [1]. The pharmacokinetic review likewise notes higher half-lives in elderly men and no need for dose adjustment [2].

For BPH, the four-year PLESS trial randomized 3,040 men aged 45 to 78 to finasteride 5 mg or placebo: surgery for BPH was 5% vs 10% (55% risk reduction, 95% CI 41 to 65) and acute urinary retention 3% vs 7% (57% reduction, 95% CI 40 to 69) [4]. The hair-loss trials that support the 1 mg dose enrolled men aged 18 to 41 [5].

Women, pregnancy, and children

Propecia is not indicated for women, and pregnancy is a contraindication: the label warns that finasteride may cause abnormal development of the external genitalia of a male fetus [1]. The label states that women who are pregnant or may become pregnant should not handle crushed or broken tablets, and that intact coated tablets prevent contact with the active ingredient during normal handling [1]. Finasteride is not indicated in pediatric patients [1].

PSA after finasteride

Propecia lowered mean PSA from 0.7 to 0.5 ng/mL at month 12 in men aged 18 to 41 [1]. The 5 mg label states that PSA falls by approximately 50% within six months, that a new baseline should be set at least six months after starting, that an isolated value in a man treated for six months or more should be doubled for comparison with normal ranges, and that any confirmed increase from the lowest value on treatment should be evaluated for prostate cancer even if it is still within the normal range [3]. Percent free PSA is unchanged and needs no adjustment [3].