The effect of prescription size on acquisition of maintenance medications

Abstract

Objective: To determine whether large prescriptions (> or = 90 days' supplies) enhance the acquisition of maintenance medications by patients.

Design: Study 1: multisite, retrospective cohort study evaluating outpatient digoxin use. Study 2: single-site, retrospective cohort study to confirm Study 1.

Setting: Study 1: Ten Veterans Affairs Medical Centers in the Rocky Mountain region. Study 2: The only facility from Study 1 (site C) that dispensed large prescriptions of maintenance medications.

Patients: Randomly selected outpatients receiving two or more digoxin prescriptions (n = 176 in Study 1, n = 114 in Study 2).

Intervention: None.

Results: The main outcome measure was the proportion of prescribed doses of maintenance medications obtained. In Study 1, patients who received at least one large digoxin prescription obtained a mean of 137.2% of their prescribed digoxin doses over a mean of nine months, compared with 91.3% for patients who received only small prescriptions of < 90 days' supplies (p = 0.02). Patients receiving large prescriptions were more likely to obtain at least 100% of their prescribed amounts of digoxin (adjusted OR = 11.4, 95% CI = 1.3-96.8, p = 0.03). At site C, patients in Study 1 obtained a mean of 129.0% of all maintenance drugs given in large supplies, compared with 95.2% of drugs prescribed only in small supplies (p = 0.006). In Study 2, acquisition of digoxin increased progressively from 89.7% among individuals who received only small digoxin prescriptions to 113.0% for those who received only large supplies (p = 0.002), over a mean of 14 months.

Conclusions: Large prescriptions facilitate the acquisition of maintenance medications but may lead to oversupplies, while small prescriptions impose a barrier to obtaining these drugs.