Enalapril to lisinopril: economic impact of a voluntary angiotensin-converting enzyme-inhibitor substitution program in a staff-model health maintenance organization.
OBJECTIVE: The cost-effectiveness of a voluntary program that switched enalapril to lisinopril therapy in patients with benign essential hypertension in a staff-model health maintenance organization (HMO) was evaluated. DESIGN: The one-year nonrandomized, controlled trial was performed from November 1989 through October 1990. PARTICIPANTS: One hundred twenty-seven patients were entered into the study: 75 who converted from enalapril to lisinopril and 52 who remained on enalapril throughout the study period. Patients were excluded from analysis because of diagnosis (not benign essential hypertension) or insufficient data collection. INTERVENTIONS: Patients taking enalapril were asked by staff pharmacists if they were willing to consider switching from enalapril to lisinopril. To encourage patients, the HMO agreed to waive the drug rider copayment for three months. If patients were willing, their physicians were contacted and they established the lisinopril dosage. MAIN OUTCOME MEASURES: Total direct cost and savings resulting from converting patients from enalapril to lisinopril were measured and compared with costs of therapy for patients who remained on enalapril. RESULTS: The control and study groups were evenly matched according to demographics and concomitant drug therapy. Drug acquisition costs, costs associated with waiving drug rider copayment, pharmacy administrative costs, costs of managing adverse events, costs of visits to physicians, and laboratory test costs were assessed. Depending on the cost of capital assumed, net savings ranged from $85 to $110 per patient converted from enalapril to lisinopril. Monthly net savings that ranged from $2.04 to $2.61 per patient were required to result in overall net savings within the first two years. CONCLUSIONS: In a regular practice setting, a net savings is realized in less than 12 months when patients are converted from enalapril to lisinopril for treatment of benign essential hypertension. The voluntary therapeutic interchange program provided a good means for achieving cost controls for pharmacy expenses.