Appropriateness of requests for therapeutic drug monitoring of antiepileptic drugs: the experience in southwestern Saudi Arabia.

The purpose of this study was to evaluate request forms of therapeutic drug monitoring of antiepileptic drugs for appropriateness criteria according to published data. Request forms received by the laboratory were sampled as all requests in one day per week on an alternating basis. Drugs monitored were phenytoin (PHT), phenobarbital (PB), carbamazepine (CBZ) and valproic acid (VPA). A total of 420 request forms were collected. Age, gender and weight were provided in 95.5%, 97.1% and 56.9% of request forms, respectively. The diagnosis, seizure type and the indication for therapeutic drug monitoring were provided in 81.6%, 3.2% and 55.5%, respectively. Sampling times were provided in 45% and were considered appropriate in 25.2% of the request forms. The indications for therapeutic drug-monitoring were considered appropriate in 28.6% of the request forms, and only 19.2% of these were appropriately sampled. Only 37.9% of all samples were drawn at steady-state. Serum albumin and creatinine concentrations were lacking in 93.6% and 53.3% of requests, respectively. The potential for drug-drug interactions was detected in 28.6% of all requests. Thus, the information needed for the proper interpretation of therapeutic drug monitoring results and that was provided in the request forms was surprisingly scarce. Most of the appropriateness criteria for therapeutic drug monitoring were not met.