Methadone Lamotrigine

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). 

It is unclear whether the methadone or the liver impairment contributed to the lamotrigine-associated rash and blood dyscrasias and therefore this isolated cases is of unknown significance. 

Uleyne S, Alao A, Batki SL. Lamotrigine-associated rash and blood dyscrasias in a methadone-treatment patient witii hepatitis C. Psychosomatics (2006) 47, 257-8. 

Methadone levels can be reduced by carbamazepine, phenobarbital or phenytoin. Valproate appears not to interact. An isolated report describes lamotrigine-associated rash and blood dyscrasias, which may have been associated with methadone use. 

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