Interactions of Topamax with other medications
Effects of Topamax on other drugs
Topamax may increase phenytoin plasma concentrations when phenytoin metabolism is near saturation, such as when phenytoin serum levels are in the upper teens.
Women taking an oral contraceptive for purposes of contraception should consider a barrier method or take a higher-strength pill. Topamax accelerates the metabolism of hormonal contraceptives, lessening their effectiveness.
Effects of other drugs on Topamax
Because the metabolism of Topamax is dependent on the hepatic P450 microsomal enzymes, its clearance is increased in the setting of enzyme-inducing AEDs, resulting in decreased Topamax concentrations.
Therefore, some AEDs may decrease the blood level of Topamax:
- carbamazepine (Tegretol, Tegretol XR, Carbatrol)
- phenytoin (Dilantin, Phenytek)
- phenobarbital
- primidone (Mysoline)
