Therapeutic substitution in the health maintenance organization outpatient environment.

Health maintenance organizations (HMO) are growing in number as a cost-effective way of providing health care. In some, stringent formulary management policies including programs authorizing therapeutic substitution are practiced. Under this concept a drug that has been previously determined to be therapeutically equivalent to a second drug, even though it is not chemically equivalent to the prescribed drug, is automatically dispensed without contacting the prescriber. This study was undertaken to learn the extent and conditions under which therapeutic substitution is being practiced in the HMO setting. A survey was sent to all HMO in the U.S. inquiring into the operation of the pharmacy services. Specific focus was on the operation of the formulary and the policies and procedures being followed. The main goal was to learn how many programs authorize therapeutic substitution, what drugs are allowed, and what procedures are followed once the substitution is made. Of the 481 surveys sent out, 192 (40 percent) usable responses were received. Results indicate that 30.5 percent of HMO pharmacy plans allow therapeutic substitution. These programs were most likely to be of the staff-model or the group-model and least likely to be of the independent practice association type. HMO with an inhouse pharmacy more frequently had policies allowing therapeutic substitution than those using outside pharmacy services.