Carbamazepine toxicity following Oxybutynin and Dantrolene administration: A case report

Objective: To report a case of Carbamazepine toxicity following the administration of Oxybutynin and Dantrolene. Study design: A case report. Setting: The Spinal Rehabilitation Department, Loewenstein Hospital, Raanana, Israel. Methods: A patient with C₆D tetraplegia who sustained intoxication because of drug interaction is presented. She had been treated by Carbamazepine 1000 mg/day for neuropathic pain for 2 years without clinical or laboratory signs of toxicity. After administration of Oxybutynin concomitantly with an increase in the dose of Dantrolene, she presented the clinical symptoms and laboratory finding of Carbamazepine intoxication. Trying to adjust the treatment to the patient's requirements, Carbamazepine together with Oxybutynin and Dantrolene was readministrated in lower doses. Results: The combination of these drugs, even small doses, caused toxicity. Adding Dantrolene and Oxybutynin elevated the blood level of Carbamazepine, possibly by inhibition of cytochrome P450. Conclusion: A possible pharmacokinetic interaction between Dantrolene and Oxybutynin should be borne in mind when considering Carbamazepine medication for a patient with a spinal cord lesion.