Experience with a specific request form for antidepressant drug monitoring

With the introduction of an antidepressant drug monitoring service in this hospital, it became necessary to have a completed request form prior to analysis. The importance of ordering these tests selectively and of basic pharmacokinetics for antidepressants was stressed through special lectures and a newsletter. This study was undertaken to assess whether the use of this form assisted in optimizing drug monitoring of antidepressants. Information provided on the form was used to assist in interpretative reporting and to improve clinical use of the results. Requested information included the name, age, sex, height, and weight of the patient; time of last dose; date therapy started at present dose; reason for the request; and a list of concurrent medications. Results obtained for 600 specimens in 18 months showed that the form was completed fully, sampling time was appropriate, and drug concentration was at steady state 82, 73, and 95% of the time, respectively. Major reasons for requesting analysis were suspicion of subtherapeutic (52%), uncertain (20%), above therapeutic (15%), and toxic (10%) ranges. The most popular monitoring requests were for imipramine (40%), doxepin (28%), amitriptyline (14%), and desipramine (11%). Clinical impression of efficacy in the treatment of endogenous depression agreed with plasma levels 60% of the time in the subtherapeutic range, but agreement was only 32% above the therapeutic range. It was concluded that a special request form helps to assure appropriate sampling, explain observed drug interactions, and facilitate interpretative reporting for the medical and nursing staff.