[Unexpected loss of therapeutic effect of oxcarbazepine]

After months of successful analgesic therapy with oxcarbazepine, a 52-year old woman with trigeminal neuralgia suddenly experienced episodes of heavy trigeminal attacks regularly in the evening at about the same time. Asked about changes in daily life or eating habits, she reported the ingestion of healing earth daily in the morning. After stopping the ingestion of healing earth, analgesic control of trigeminal neuralgia was restored without any changes of the initial pharmacotherapy. In daily practice, interactions which significantly influence the absorption of drugs are often overlooked. The documentation of these interactions in drug interaction databases, in the prescribing information, and in the literature is sparse though clinically relevant. Separating the ingestion of interacting substances by a time interval may not sufficiently avoid the interaction in every case. Particular caution is warranted when slow-release cation containing drugs or substances with entero-hepatic circulation are used.