Described is a method to perform drug utilization review retrospectively by using mutually exclusive categories. Drug use criteria were developed and structured in such a manner so that a patient's drug use experience could be readily and appropriately classified by medical records technicians during the routine medical record abstraction. Utilizing a contract abstracting service format, a summary by category of drug use experiences for the patients audited is provided monthly and used as the preliminary audit summary. The system represents an efficient and cost-conscious means of effectively monitoring selected portions of the drug utilization process.