Experience with a two-tiered therapeutic interchange policy

A university hospital's formulary policy for therapeutic interchange is described in which pharmacists can routinely interchange some drugs but must contact the prescribers before interchanging other drugs. For drugs that are not automatically interchanged by the pharmacy, the formulary contains a "class representative," which pharmacy may change as relative prices of drug products change. When a non-formulary drug for which there is a designated class representative is prescribed, pharmacy contacts the prescriber. When a class representative for injectable histamine H2-receptor antagonists was being selected, previous positive and negative experiences with establishing therapeutic equivalence for antimicrobial agents were considered. The implementation of H2 antagonist therapeutic equivalence included the following steps: determining potential cost savings, reviewing the literature, consulting with specialty practitioners, presenting the information to the pharmacy and therapeutics committee, distributing formal bids, and educating hospital staff. Before cimetidine was designated the class representative, 84% of orders for injectable H2 antagonists were for ranitidine; one year later, 90% were for cimetidine. Orders for oral H2 antagonists also changed from predominantly ranitidine to predominantly cimetidine. The hospital's total costs for H2 antagonists decreased 8.4% in one year. The two-tiered approach to therapeutic interchange can reduce drug costs and increase the scope of agents deemed therapeutic equivalents in a manner that is acceptable to physicians and pharmacists.