Adverse Effects
Both dutasteride and finasteride were well tolerated in this phase II study, and no new safety concerns have arisen in any of the phase II and phase III studies of dutasteride given at doses up to 5 mg daily (the 5-mg dose was used in a phase II study for BPH).
There were no significant differences in side effects, serious adverse events, or withdrawals due to adverse events among any of the treatment groups, including placebo. In total, 11 subjects withdrew because of adverse events: 3 were in the placebo group (irritable bowel syndrome and impotency), 7 in the dutasteride 0.1 mg group (decreased libido, malaise and fatigue, mood disorders, skin disorders, injuries caused by trauma, and gastrointestinal- and neurology-related complaints) and 1 in the dutasteride 0.5 mg group (gastrointestinal discomfort and pain).
Decreased libido was noted in:
2 subjects in the placebo group
2 subjects in each of the 0.05-mg and 0.1-mg dutasteride groups
1 subject in the 0.5-mg dutasteride group
9 subjects in the 2.5 mg dutasteride group
3 subjects in the finasteride group
Of the 9 subjects with decreased libido in the 2.5-mg dutasteride group:
4 resolved while receiving therapy
1 resolved within 3 weeks
1 resolved within 8 weeks of stopping drug therapy
1 subject, decreased libido continued after therapy had been stopped and was presumed by the subject to be unrelated to the trial or drug therapy
Concerning possible sexual adverse events, there was no evidence in the present study that either dutasteride or finasteride was associated with impotence. However, 9 men in the 2.5-mg dutasteride group complained of decreased libido, compared with 1 man in the 0.5-mg dutasteride group and 3 men in the finasteride group. As with previous studies with finasteride, this adverse event was characterized as either mild or moderate in severity and often resolved with continuation of the medication. In the 4-year follow-up of the phase III trials in BPH, dutasteride (0.5 mg) was well tolerated and the incidence of the most common sexual adverse events was low and tended to decrease over time.
