Ethinyl estradiol, not progestogens, reduces lamotrigine serum concentrations

Area of Science:

• Pharmacology
• Clinical Pharmacy
• Neuroscience

Background:

• Lamotrigine (LTG) is an antiepileptic drug with a narrow therapeutic index.
• Hormonal contraception is widely used by women of childbearing age, including those with epilepsy.
• Potential drug interactions between LTG and hormonal contraceptives require investigation to ensure treatment efficacy and safety.

Purpose of the Study:

• To investigate the pharmacokinetic interaction between lamotrigine (LTG) and hormonal contraception.
• To determine if ethinyl estradiol (EE) or progestogen (PG) components of hormonal contraceptives affect LTG serum concentrations.

Main Methods:

• Prospective analysis of LTG serum concentrations in female patients using no hormonal contraception, EE-containing, or PG-only contraception.
• Measurement of LTG serum concentration-to-dose ratio (CDR) using gas chromatography/mass spectrometry.
• Statistical comparison between groups using the Mann-Whitney U test, with some patients serving as their own controls.

Main Results:

• LTG serum concentration-to-dose ratio (CDR) was significantly lower in women using EE-containing contraception compared to controls (p=0.003).
• CDR was not significantly different in women using progestogen-only contraception compared to controls.
• Women switching from no contraception to EE showed reduced CDR, while those switching from EE to PG showed increased CDR.

Conclusions:

• The ethinyl estradiol (EE) component of oral contraceptives interacts with lamotrigine (LTG), reducing its serum concentrations.
• Progestogen-only contraceptives did not demonstrate a significant interaction with LTG serum concentrations in this study.
• These findings are crucial for counseling women with epilepsy of childbearing age using both LTG and hormonal contraception.