Finasteride dosing

Finasteride is well absorbed from the gastrointestinal tract (95%), and its absorption is unaffected by food. Peak serum concentrations are reached 1 to 2 hours after the dose. Finasteride is highly protein bound. The liver extensively metabolizes finasteride to inactive metabolites, which are largely excreted in stool. The plasma half-life is 4.7 to 7.1 hours, but its biologic half-life is probably longer, because decreased serum DHT levels persist for up to 2 weeks after finasteride dosing is stopped. ... 

Approximately 90% is bound to plasma proteins. The half-life of finasteride is 4.8 to 6 hours following 1 and 5 mg/day dosing, respectively. 

In the normal daily dose of 1 mg, which is sufficient to treat male pattern hair loss, finasteride is well tolerated over long periods. There is a very slightly higher incidence of impaired sexual function in users compared with placebo (17). In women too, low doses of finasteride (2.5 mg/day) are well tolerated when used to treat hirsutism (18). However, many of the problems seen... 

In women with hirsutism low doses of finasteride (2.5 mg/ day) are generally well tolerated (19). However, in a randomized study in 38 hirsute women finasteride 2.5 mg every 3 days was as effective as 2.5 mg/day and better tolerated (20). 

The effect of adding finasteride 5 mg/day to high-dose bicalutamide 150 mg/ day has been studied in 41 men with advanced prostate cancer treated over a mean of 3.9 years (21). The serum prostate-specific antigen (PSA) concentration was measured every 2 weeks until disease progression. At the first nadir of PSA, the median fall from baseline was 96.5% a second nadir occurred in 30 of 41 patients, with a median fall of 98.5% from baseline. The median times to each nadir were 3.7 and 5.8 weeks respectively. The median time to treatment failure was 21 months. Adverse effects were minor, including gynecomastia. Sex drive was normal in 17 of 29 men at baseline and in 12 of 24 men at the second PSA nadir, but one-third of the men had spontaneous erections at both times. The authors concluded that finasteride provided additional intracellular androgen blockade when added to bicalutamide. The duration of control was comparable to that achieved with castration, with preserved sexual function in some patients. 

In a Spanish systematic review of the world literature there were firm conclusions about the value of finasteride in reducing the symptoms of benign prostatic hyperplasia in doses that are well tolerated in all respects (36). 

At an oral dose of 1 mg/day finasteride has no major adverse effects on measures of semen production or quality (57), although it can cause a slight reduction in the volume of ejaculate (15). 

Reversible painful gynecomastia has been reported as an adverse effect of finasteride in a dose as low as 1 mg/day (67) it can be unilateral (68) or bilateral (69). Some reports of gynecomastia in users of finasteride relate to doses as low as 1 mg/day (70). 

Many of the problems seen with finasteride have undoubtedly been due to its use in unnecessarily high doses. Particularly when used for cosmetic ends there has been doubt as to how far dosage can be reduced while maintaining an acceptable effect. Finasteride continues to be used to treat hirsutism in women and is effective, although long-term information on safety is sparse, and in principle it might adverse affect an unborn child (81). The dose should certainly be kept as low as possible. 

Bayram F, Muderris I, Guven M, Ozcelik B, Kelestimur F. Low-dose 2.5 mg/day) finasteride treatment in hirsutism. Gynecol Endocrinol 2003 17 419-22. 

Tartagni M, Schonauer MM, Cicinelli E, Petruzzelli F, De Pergola G, De Salvia MA, Loverro G. Intermittent low-dose finasteride is as effective as daily administration for the treatment of hirsute women. Fertil Steril 2004 82 752-5. 

Wade MS, Sinclair RD. Reversible painful gynaecomastia induced by low dose finasteride (1 mg/day). Australas J Dermatol 2000 41 55. 

Clinical studies have reported very few adverse effects that are of a mild nature (usually gastric distress or headache) following saw palmetto administration at normal doses. One randomized, double-blind study of finasteride, tamsulosin, and saw palmetto for 3 months observed no differences among the three treatments in terms of the effectiveness measures and no change in sexual function in those individuals receiving saw palmetto, though ejaculation disorders were noted as the most common side effect in those individuals receiving either tamsulosin or finasteride (26). 

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