Drug interactions and long-term antidiabetic therapy.

A study has been carried out on a representative sample (709 patients) of the Aberdeen Diabetic Clinic. The aims were to measure the occurrence and attempt to assess the clinical significance of drug interactions involving antidiabetic agents. In the month before interview, 63% of the patients were taking between one and nine additional prescribed medicines. Fifty-one per cent of the patients had been exposed to one to five drugs with a potential to interact with their anti-diabetic therapy. Only 22% of the patients had taken no drugs other than their anti-diabetic medication. The degree of control of diabetes, based on arbitrary criteria on data from seven consecutive out-patient visits, was significantly worse for sulphonylurea-treated patients exposed to drugs with the potential to interact compared to patients not taking such drugs. In particular, control was adversely affected in older patients taking concurrent barbiturate or diuretic therapy. No such influence of interacting drugs on control was evident in patients on insulin or biguanide therapy. A system designed to prevent the unintentional initiation of drug interactions in patients on hypoglycaemic agents is described.