Background: Pulmonary arterial hypertension (PAH) is described by proliferation of small pulmonary arteries leading to increased pulmonary vascular resistance, right ventricular failure, and death. Research confirms long-term improvement in composite morbidity and mortality endpoints on some endothelin receptor antagonists alone and in combination with phosphodiesterase type 5 inhibitors (PDE-5is) but not with PDE-5i monotherapy. While current treatment guidelines incorporate these findings, a substantial number of patients are started or maintained on PDE-5i monotherapy. Objectives: This study describes real-world clinical practice and treatment patterns with PDE-5i monotherapy including events indicative of clinical worsening, treatment modifications, adherence, allcause healthcare resource utilization, and costs. Methods: This retrospective study analyzed PharMetrics Plus claims data including 150 million lives; study period was January 1, 2009 through December 31, 2013. Eligible patients were ≥18 years with ≥1 inpatient or ≥2 outpatient claims ≥30 days apart, a diagnosis of pulmonary hypertension or other chronic pulmonary heart disease, and an initial PDE-5i prescription. To include only World Health Organization group 1 PAH patients, ≥1 encounter for right-heart catheterization or Doppler echocardiogram was required during the pre-index period. Results: PDE-5i monotherapy for PAH treatment was associated with high treatment modification rates, low adherence, increased healthcare resource utilization, and high costs. At 12 months post index, 41.5% of patients experienced treatment modification. For the index therapy, 47% of patients had ≥80% adherence to therapy. Almost 50% of patients had ≥1 hospitalization, with costs increased three fold to $197 111 compared to $59 164 for non-hospitalized patients. Conclusions: Initial treatment with PDE-5i monotherapy was associated with substantial direct medical costs, including hospitalizations and emergency department visits, low therapy adherence and a high rate of treatment modifications.

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