Drug Assay Services and Therapeutic Drug Use in a General Hospital

A prospective audit was conducted in the Alfred Hospital, Melbourne, on the use of drug assay services with digoxin, phenytoin, phenobarbital, theophylline, gentamicin, and quinidine as model therapeutic drugs. The efficiency of drug administration was judged by comparison of plasma assay results with therapeutic concentration ranges. Study drugs were prescribed to 1586 patients out of a total of 5921 patients who were admitted to the hospital during the study. Assays were performed on 786 samples drawn from 538 (34%) of these persons. Drug use appeared to be suboptimal, as 60% of the over-all assay results were demonstrated to be outside the therapeutic range. However, repeat assays were performed in only 56 (12%) of those instances in which assay results were above or below the therapeutic range, and successful dosage adjustments were made in only 39% (22 of 56) of the cases reassayed. The results indicate that in the Alfred Hospital: (i) the drug assay services are used inefficiently, and are not consistently employed to guide drug usage; (ii) the delivery of drug-related health care could be improved in consequence; and (iii) significant savings in costs can be projected if drug usage is improved. Consultative services and educational efforts related to therapeutic drug usage within our hospital appear to be indicated.