Dutasteride

Use with caution in patients taking potent, chronic cytochrome P450 (CYP)3A4 enzyme inhibitors (e.g., ritonavir). ( 7 )

7.1 Cytochrome P450 3A Inhibitors Dutasteride is extensively metabolized in humans by the cytochrome P450 (CYP)3A4 and CYP3A5 isoenzymes. The effect of potent CYP3A4 inhibitors on dutasteride has not been studied. Because of the potential for drug-drug interactions, use caution when prescribing dutasteride capsules to patients taking potent, chronic CYP3A4 enzyme inhibitors (e.g., ritonavir) [see Clinical Pharmacology ( 12.3 )] .

7.2 Alpha-adrenergic Antagonists The administration of dutasteride in combination with tamsulosin or terazosin has no effect on the steady-state pharmacokinetics of either alpha-adrenergic antagonist. The effect of administration of tamsulosin or terazosin on dutasteride pharmacokinetic parameters has not been evaluated.

7.3 Calcium Channel Antagonists Coadministration of verapamil or diltiazem decreases dutasteride clearance and leads to increased exposure to dutasteride. The change in dutasteride exposure is not considered to be clinically significant. No dose adjustment is recommended [see Clinical Pharmacology ( 12.3 )] .

7.4 Cholestyramine Administration of a single 5-mg dose of dutasteride followed 1 hour later by 12 g of cholestyramine does not affect the relative bioavailability of dutasteride [see Clinical Pharmacology ( 12.3 )] .

7.5 Digoxin Dutasteride does not alter the steady-state pharmacokinetics of digoxin when administered concomitantly at a dose of 0.5 mg/day for 3 weeks [see Clinical Pharmacology ( 12.3 )] .

7.6 Warfarin Concomitant administration of dutasteride 0.5 mg/day for 3 weeks with warfarin does not alter the steady-state pharmacokinetics of the S- or R-warfarin isomers or alter the effect of warfarin on prothrombin time [see Clinical Pharmacology ( 12.3 )] .

8.1 Pregnancy Risk Summary Dutasteride is contraindicated for use in pregnancy because it may cause harm to the male fetus [see Contraindications (4)] . Dutasteride is not indicated for use in women. Dutasteride is a 5 alpha-reductase inhibitor that prevents conversion of testosterone to dihydrotestosterone (DHT), a hormone necessary for normal development of male genitalia. Abnormalities in the genitalia of male fetuses is an expected physiological consequence of inhibition of this conversion. These results are similar to observations in male infants with genetic 5 alpha-reductase deficiency. In the U.S.

general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively. In animal reproduction studies, dutasteride inhibited normal development of external genitalia in male offspring when given to rats or rabbits during organogenesis at less than the maximum recommended human dose (MRHD) of 0.5 mg daily, in the absence of maternal toxicity. At 15 times the MRHD, prolonged pregnancy, decreased reproductive organ weights, and delayed puberty in male offspring were observed in rats, with no-effect levels less than the MRHD of 0.5 mg daily.

Increased placental weights in rabbits were also observed, with no-effect levels less than the MRHD of 0.5 mg daily (see Data) . Although dutasteride is secreted into human semen, the drug concentration in the human female partner is approximately 100 times less than concentrations producing abnormalities of male genitalia in animal studies (see Data) . In monkeys dosed during organogenesis at blood concentrations comparable to or above levels to which a human female partner is estimated to be exposed, male offspring external genitalia was not adversely affected.

No feminization occurred in male offspring of untreated female rats mated to treated male rats even though detectable blood levels of dutasteride were observed in the female rats [see Nonclinical Toxicology (13.1)] . Data Human Data: The highest measured semen concentration of dutasteride in treated men was 14 ng/mL. Although dutasteride is detected in semen, assuming exposure of a 50-kg woman to 5 mL of semen and 100% absorption, the woman's expected dutasteride blood concentration through semen would be about 0.0175 ng/mL. This concentration is approximately 100 times less than blood concentrations producing abnormalities of male genitalia in animal studies.

Dutasteride is highly protein bound in human semen (greater than 96%), which may reduce the amount of…

8.3 Females and Males of Reproductive Potential Infertility Males: The effects of dutasteride 0.5 mg/day on semen characteristics were evaluated in normal volunteers aged 18 to 52 years (n = 27 dutasteride, n = 23 placebo) throughout 52 weeks of treatment and 24 weeks of post-treatment follow-up. At 52 weeks, the mean percent reductions from baseline in total sperm count, semen volume, and sperm motility were 23%, 26%, and 18%, respectively, in the dutasteride group when adjusted for changes from baseline in the placebo group. Sperm concentration and sperm morphology were unaffected.

After 24 weeks of follow-up, the mean percent change in total sperm count in the dutasteride group remained 23% lower than baseline. While mean values for all semen parameters at all timepoints remained within the normal ranges and did not meet predefined criteria for a clinically significant change (30%), 2 subjects in the dutasteride group had decreases in sperm count of greater than 90% from baseline at 52 weeks, with partial recovery at the 24-week follow-up. The clinical significance of dutasteride's effect on semen characteristics for an individual patient's fertility is not known [see Warnings and Precautions (5.6)] .