Restarting Finasteride After Acute Illness: A Clinical Guide

What the labels say about dosing and starting again

Propecia's dosing section is one tablet (1 mg) once daily, with or without meals [1]. Proscar's is one tablet (5 mg) once a day, alone or with doxazosin [2]. Neither section contains a loading dose, a titration step or a taper [1][2]. HealthRX.com offers finasteride 1 mg by prescription.

The Propecia label says daily use for three months or more is necessary before benefit is observed, that continued use is recommended to sustain benefit, and that withdrawal leads to reversal of effect within 12 months [1]. The same label's postmarketing section lists sexual dysfunction that continued after discontinuation of treatment, including erectile dysfunction, libido disorders, ejaculation disorders and orgasm disorders [1]. Acute illness, fever, surgery and hospitalization are not listed as reasons to stop; the contraindications are pregnancy and hypersensitivity to a component of the tablet [1][2].

How long the drug's effect lasts

Finasteride's mean terminal half-life is about 5 to 6 hours in men aged 18 to 60 and about 8 hours in men over 70 [1]. The effect on DHT outlasts that because the enzyme complex turns over slowly, roughly 30 days for Type II, and a single 1 mg tablet suppresses serum DHT by 65% within 24 hours [1]. Neither label gives guidance on gaps in treatment.

Medicines started during the illness

Propecia's interactions section states that no drug interactions of clinical importance have been identified and that antipyrine, digoxin, propranolol, theophylline and warfarin were tested with no clinically meaningful interactions [1]. Quinolone anti-infectives were used alongside finasteride in clinical studies without clinically significant adverse interactions [1]. Finasteride is metabolized mainly by CYP3A4, but the section does not discuss CYP3A4 inhibitors or inducers [1].

PSA if the prescription is the 5 mg tablet

Proscar lowers serum PSA by approximately 50% within six months; the label advises a new baseline at least six months after starting and doubling an isolated value in a man treated for six months or more [2]. Propecia's label records mean PSA falling from 0.7 to 0.5 ng/mL at month 12 in men aged 18 to 41 [1]. Both labels say non-compliance may affect PSA results [1][2].