Association Between Copayment and Adherence to Medications for Pulmonary Arterial Hypertension

Background Pharmacologic treatment for pulmonary arterial hypertension (PAH) improves exercise capacity, functional class, and hemodynamic indexes. However, monthly prescription costs often exceed $4000. We examined associations between (1) medication copayment and (2) annual household income with adherence to pulmonary vasodilator therapy among individuals with PAH. Methods and Results We used administrative claims data from an insured population in the United States to identify individuals diagnosed with PAH between 2015 and 2020. All individuals had ≥1 medication claim for endothelin receptor antagonists, phosphodiesterase type-5 inhibitors, prostanoids or prostacyclin receptor agonists, or the soluble guanylate cyclase stimulator riociguat. We defined copayments as low, medium, or high, as determined by their distributions for each medication class. Annual household income was categorized as <$40 000, $40 000 to $74 999, and ≥$75 000. The primary outcome was medication adherence, defined by proportion of days covered ≥80%. We studied 4025 adults (aged 65.9±13.3 years; 71.2% women). Compared with those with annual household income ≥$75 000, individuals in the <$40 000 and $40 000 to $74 999 categories had no significant differences in medication adherence. Compared with those with low copayments, individuals with high copayments had decreased adherence to prostanoids (odds ratio [OR], 0.36 [95% CI, 0.20-0.65]; P<0.001) and combination therapy with endothelin receptor antagonist and phosphodiesterase type-5 inhibitor (OR, 0.61 [95% CI, 0.38-0.97]; P=0.03). Conclusions We identified associations between copayment and adherence to prostanoids and combination therapy among individuals with PAH. Copayment may be a structural barrier to medication adherence and merits inclusion in studies examining access to pharmacotherapy among individuals with PAH.