Oral contraceptives reduce lamotrigine plasma levels

The mean steady-state plasma concentration of lamotrigine (LTG) was 13 mumol/L in 22 women taking LTG in combination oral contraceptives (OC) compared with 28 mumol/L among 30 women on LTG who did not take OC ( p < 0.0001). The LTG dose/body weight/plasma concentration was 2.1 L/kg/day in women on OC compared with 0.8 L/kg/day in women without OC ( p < 0.0001), indicating that LTG plasma levels are reduced by > 50% during OC co-medication. It is advisable to monitor LTG plasma levels in conjunction with initiation or withdrawal of OC in women on LTG therapy.