Trends of generic substitution in community pharmacies.

The purpose of this study is to measure the rate of genetic drug substitution by pharmacists, and factors influencing generic substitution, such as the extent of drugs listed on the formulary as well as physicians' and patients' acceptance rate of generic substitutes. A total of 9,328 prescription orders were retrospectively reviewed from 94 pharmacies which were selected at random. The substitution rate by pharmacists, which is the rate using the number of prescriptions eligible for substitution as the denominator, has risen from 47% in 1979 to 96% in 1997; double the rate over the past 20 years. The net substitution rate, which uses all prescriptions as the denominator, was 30% in 1997; over 4 times greater than the rate in 1979. Physicians wrote most prescriptions (86%) using the brand name of the drug, which has been the trend for the past 20 years. Of the prescriptions ordered by brand name, 47% were substitutable according to the New Jersey formulary. Of these prescriptions, prescribers allowed generic substitution 77% of the time. Out of these prescriptions, 97% of patients agreed to use a generic substitute if the physician approved of substitution. Generic substitution rates have increased, probably due to greater acceptance of generics by physicians and pharmacists as well as encouragement from external sources such as third party payers. Health care professionals, third parties, and patients all have an important role to play in order to increase the use of generics, and therefore reduce drug expenditures.