The effect of prescription size on acquisition of maintenance medications

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

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

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.

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

None.

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.

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