We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
from Part IV - Drug interactions in specific patient populations and special conditions
Published online by Cambridge University Press: 07 September 2009
Background
In 1972 Kenyon sent a letter to the British Medical Journal describing a patient with epilepsy treated with phenytoin (PHT) who became pregnant despite taking usual amounts of oral contraceptive (OC) pills (Kenyon, 1972). She astutely attributed the contraceptive failure to an inductive effect of the PHT on the metabolism of the sex steroid hormones. This observation was soon confirmed by others (Coulam and Annegers, 1979; Janz and Schmidt, 1974) and the underlying mechanisms were further elucidated (Back, 1980). All the older antiepileptic drugs (AEDs), carbamazepine (CBZ), phenobarbital (PB), PHT and primidone (PRM) except valproate (VPA) (Crawford 1986; Sonnen, 1983) were found to have similar effects (Mattson et al., 1986; Schmidt, 1981). In contrast most of the new AEDs with the exception of felbamate (FBM), oxcarbazepine (OXC) and topiramate (TPM) do not change the metabolism of the OCs. Parenteral formulations (intramuscular (i.m.) depot, subcutaneous implant and dermal patch) of contraceptive female sex hormones have also been reported to be subject to increased clearance.
The effect of the AEDs on testosterone metabolism has also indicated changes occur although the evidence of clinical effects is less easily assessed than an unplanned pregnancy. Conversely, except for lamotrigine (LTG) the OCs do not appear to change the pharmacokinetics of AEDs.
Frequency and importance of interactions
Following the initial case report by Kenyon, three other cases of OC failure were cited by Janz and Schmidt (1974). By 1983 Sonnen found that 52 cases had been reported.
To save this book to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.
