Pregnancy and isotretinoin therapy

We read with interest the article by Choi and colleagues on isotretinoin therapy and the importance of a multilevel approach to ensure adequate contraception in women taking potentially teratogenic medications.1 We agree that it is essential that health care providers know the failure rates of various contraceptive methods when counselling patients. However, we encourage health care providers to become familiar with the more recent and accepted perfect and typical use failure rates reported by Trussell and colleagues in Appendix 1, available at www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.1132111/-/DC1,2 which in some instances are quite different than the ones the cited by Choi and colleagues.3

The rates reported by Trussell and colleagues are referred to in numerous contraception guidelines including those from the Society of Obstetricians and Gynaecologists of Canada,4 the Centers for Disease Control and Prevention,5 and the World Health Organization.6

Prescribers must also understand the difference between perfect-use and typical-use failure rates. Failure rates are reported as the percentage of women who will have an unintended pregnancy during the first year of use of a method. Perfect use may be hard to achieve, particularly with more compliance-demanding methods, which explains why typical-use failure rates are much higher than perfect-use failure rates with methods such as condoms and oral contraceptives. Long-acting reversible contraceptive methods such as intrauterine contraceptive devices and implants are not as reliant on user compliance and hence typical-use failure rates approach those of perfect-use rates. Long-acting reversible contraceptives also have lower discontinuation rates at one year.2

We encourage contraceptive prescribers to be familiar with Trussell’s reported failure rates,2 and reiterate that women of reproductive age who use teratogenic medications should be counselled about all contraceptive options — particularly long-acting reversible contraceptives given their low typical- and perfect-use failure rates and their increased adherence.