Survey of potential drug interaction incidence in an outpatient clinic population.

A study was conducted at a large VA outpatient facility to determine the total number of potential drug interactions resulting from outpatient clinic prescribing. Interactions classified as of moderate or major clinical significance were tabulated. No attempt was made to ascertain whether patients taking digoxin and a thiazide diuretic without a potassium supplement were having their serum potassium levels monitored or if patients had been instructed to space their antacid dosages away from potential reacting drugs. Of the 3028 patients studied, 710 received drugs which had the potential to interact. A dramatic increase of potential interactions was seen as the number of prescriptions received per patient increased. Drug combinations which had potential for interaction and frequency of prescription are listed.