Felbamate Antacids

Pharmacokinetics. Felbamate is rapidly and well absorbed. The absorption is unaffected by food or antacids. About 40% to 50% of a dose of felbamate is metabolized by hydroxylation and conjngation pathways in the liver, with the remainder being excreted imchanged in the mine. Felbamate displays linear pharmacokinetics. ... 

Therefore, plasma concentrations for drugs metabolized by these isoforms will be affected (see Chapter 10). Thus, the addition of phenytoin to an AED regimen can reduce their plasma levels by inducing their CYP3A4 metabolism for carbamazepine, felbamate, lamotrigine, oxcarbazepine, tiagabine, valproate, and zonisamide. Other drugs for which metabolism is induced by phenytoin include methadone, theophylline, warfarin, and oral contraceptives. On the other hand, plasma phenytoin levels are increased by carbamazepine, felbamate, cimetidine, warfarin, chloramphenicol, isoniazid, and disulfiram. Plasma phenytoin levels are decreased by rifampin, antacids, and valproate (free phenytoin levels remain the same). 

An aluminium/magnesium hydroxide-containing antacid had no effect on the absorption of felbamate. 

Felbamate 2.4 g daily was given to 9 epileptic women for 2 weeks. For a third week the felbamate was taken with an antacid containing alumini-um/magnesium hydroxide (Maalox Plus). No significant changes in the plasma levels or AUC were seen. No special precautions would seem to be needed if felbamate is taken with this or any other similar antacid. 

Sachdeo RC, Narang-Sachdeo SK, Howard IR, Dix RK, Shumaker RC, Perhach JL, Rosenberg A Effect of antacid on die absorptionof felbamate in subjects with epilep. E/jffepiia (1993) 34 (Suppl 6), 79-80,... 

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