Drug-Drug Interaction

VALPROIC ACID/FELBAMATE

MECHANISM OF ACTION
Felbamate may inhibit the metabolism of valproic acid.

DISCUSSION
Administration of felbamate to 10 epileptic patients stabilized on valproic acid resulted in a dose related increase in felbamate area-under-curve (AUC) and maximum concentration (Cmax).(2)

CLINICAL EFFECTS
The addition of felbamate may result in elevated levels and toxicity from valproic acid.(1,2)

SEVERITY LEVEL
3-Moderate Interaction: Assess the risk to the patient and take action as needed.

PATIENT MANAGEMENT
The US manufacturer of felbamate recommends decreasing the dosage of valproic acid by 20% during the initiation of felbamate therapy.(1)

PREDISPOSING FACTORS
None determined.

REFERENCES

1. Felbatrol (felbamate) US prescribing information. MedPoint Pharmaceuticals .Felbatrol (felbamate) US prescribing information. MedPoint Pharmaceuticals Inc. April 23, 2009.
2. Wagner ML, Graves NM, Leppik IE, Remmel RP, Ward DL, Shumaker RC. The .Wagner ML, Graves NM, Leppik IE, Remmel RP, Ward DL, Shumaker RC. The effect of felbamate on valproate disposition. Epilepsia 1991;32(3):15.