Propecia and Pregnancy - Part 1 Topics: What defect is caused by Finasteride? | Conceiving while on Propecia | Propecia and Genital Development

Since the sensitive period of development of the external genitalia in the human embryo is the 7th to 9th weeks of gestation, there can be no danger to the child if the father is taking finasteride at the time of conception. Originally, Merck decided to err on the side of caution and warned against the possible problem of finasteride transfer in semen. This warning has since been removed from the package insert. Considering the medical/legal implications of a theoretically possible link of finasteride treatment to birth defects, it is reasonable to assume that Merck & Co. must be very confident in knowing that impregnating a woman while taking finasteride absolutely does not cause birth defects.

Intercourse During Pregnancy

Nor is there any evidence of birth defects when the father taking finasteride has intercourse with the pregnant mother during the critical periods of sexual development. The in utero effects of finasteride exposure during the period of embryonic and fetal development (gestation days 20-100) were evaluated in the rhesus monkey, a species fairly predictive of human development. Intravenous administration of finasteride to pregnant monkeys at doses as high as 800ng/day (at least 60 to 120 times the highest estimated exposure of pregnant women to finasteride from semen of men taking 5mg/day) caused no abnormalities in male fetuses.

Still, Merck retains this admonition: “Women should not handle crushed or broken Propecia tablets when they are pregnant or may be potentially pregnant because of the possibility of absorption of finasteride and the subsequent potential risk to a male fetus. Propecia tablets are coated and will prevent contact with the active ingredient during normal handling, provided that the tablets have not been broken or crushed.”

In Conclusion

Considering that intravenous administration of finasteride to pregnant experimental animals during the critical periods of sexual development didn’t cause birth defects, there is no reason to believe that transdermal absorption of finasteride from handling broken tablets could cause birth defects in the male child. But, since Propecia has not been approved by the FDA for use by women, Merck has nothing to lose by retaining this warning. In fact, it has good p.r. value.

So, can finasteride cause birth defects? Yes, there is a theoretical possibility that it can, but the probability is close to nil, when finasteride is taken in the recommended dosages. Since Propecia was approved by the FDA on 22 December 1997 and Proscar on 28 August 1996, millions of doses of finasteride have been taken and there has not been a single case report of a birth defect. Now that’s reassuring information.

Richard Lee, M.D.

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Imperato-McGinley, J.; Gautier, T.: Inherited 5-alpha-reductase deficiency in man. Trends Genet. 2: 130-133, 1986
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Thigpen, A. E.; Davis, D. L.; Milatovich, A.; Mendonca, B. B.; Imperato-McGinley, J.; Griffin, J. E.; Francke, U.; Wilson, J. D.; Russell, D. W.: The molecular genetics of steroid 5-alpha-reductase 2 deficiency. J. Clin. Invest. 90: 799-809, 1992
http://encarta.msn.com/encyclopedia_761580700/Human_Sexuality.html#endads
http://science.howstuffworks.com/human-reproduction5.htm
Sex-organ development is determined by the third month of development.
http://www.people.virginia.edu/~rjh9u/sexdev.html
http://www.lindasy.com/cgi-local/SoftCart.100.exe/skin411/411_dec01.html?E+scstore

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