Prescription of topical antiglaucoma agents for patients with contraindications to ß-blockers

Abstract

Background: In Canada, public drug plans may restrict the use of newer topical antiglaucoma agents. The goals of this retrospective study were to estimate the proportion of patients who, at the initiation of topical glaucoma therapy, had contraindications to the use of topical ß-blockers and to identify whether changes in formulary listing status (from restricted-drug list to generally available drug list) influenced the use of topical glaucoma agents in patients with contraindications to ß-blockers.Methods: Claims databases administered by the Régie de l'assurance maladie du Québec were used to identify incident users of ß-blockers (betaxolol and timolol) and newer antiglaucoma agents (brimonidine, dorzolamide and latanoprost) among patients aged 35 years or older. Drug claims and physician diagnoses were used to determine the prevalence of the following contraindications to the use of ß-blockers (including warnings and precautions): asthma or chronic bronchitis, diabetes, dysrhythmia and heart failure, all in the year preceding the initiation of therapy; or use of systemic ß-blockers at the time glaucoma therapy was started. The observation period was divided into 2 phases: the time during which newer agents were on the restricted-drug list (first-line use being limited to patients with contraindications to the use of ß-blockers; January 1997 to March 1999) and the time during which these agents were on the generally available drug list (that is, after reimbursement restrictions were relaxed; April 1999 to June 2000).Results: Of the 20 309 eligible patients, 59.8% were female, and the mean age was 72 years. Contraindications to topical ß-blocker therapy were significantly more frequent among the patients using newer antiglaucoma agents than among those using ß-blockers (71.5% vs. 55.5%, p < 0.0001). Asthma and chronic bronchitis were also more frequent among the patients using the newer agents than among those using ß-blockers (43.1 % vs. 22.5%, p < 0.0001). Among the patients without contraindications to topical ß-blocker therapy, the overall proportions started on therapy with a newer agent were 22.7% when there were reimbursement restrictions and 30.0% when the restrictions were relaxed (p < 0.000 1).Conclusions: Among patients with contraindications to the use of ß-blockers, newer topical antiglaucoma agents were used more often than ß-blockers. Among patients without such contraindications, the use of the newer agents increased modestly when reimbursement restrictions were relaxed.