Therapeutic drug and biochemical monitoring in a community pharmacy: Part 2

Abstract

Abstract Opportunistic blood samples, at appropriate times post-dose, were taken from patients presenting prescriptions at a community pharmacy. Measurement and interpretation of carbamazepine (19 patients), digoxin (23), phenytoin (13) and theophylline (51) plasma concentrations indicated that 63.1 per cent (12 patients), 47.8 (11), 84.6 (11) and 58.6 (30), respectively, of the patients could benefit from a change to their therapeutic management to provide plasma concentrations with the highest probability of efficacy and the smallest possibility of side effects. Changes in the therapeutic management of 22 out of 46 patients (47.8 per cent) were necessary because of their plasma potassium concentrations. Of these, 13 (28.3 per cent of the total) were hypokalaemic and their medication included diuretics with no potassium assistance. Nine patients (19.6 per cent) were hyperkalaemic and were taking either a potassium sparing diuretic or potassium supplements with their diuretics. Thirty three (70.2 per cent) of the 47 patients whose creatinine clearance was determined required a change to their therapy. These patients had some degree of renal impairment and, according to the British National Formulary, a dosage adjustment was justified. We have previously shown (in part 1) that accurate measurements of these therapeutic drugs and biochemical parameters can be made in a community pharmacy from plasma samples. The study reported here shows that community pharmacists can use clinical pharmacokinetic and therapeutic knowledge to recommend optimal therapeutic regimens. Liaison between community pharmacists and general practitioners could provide a therapeutic drug and biochemical monitoring service with patient and economic benefits.