A pilot study of oral treprostinil pharmacogenomics and treatment persistence in patients with pulmonary arterial hypertension

Differential drug response in pulmonary arterial hypertension: The potential for precision medicine

Pulmonary arterial hypertension (PAH) is a rare, complex, and deadly cardiopulmonary disease. It is characterized by changes in endothelial cell function and smooth muscle cell proliferation in the pulmonary arteries, causing persistent vasoconstriction, resulting in right heart hypertrophy and failure. There are multiple drug classes specific to PAH treatment, but variation between patients may impact treatment response. A small subset of patients is responsive to pulmonary vasodilators and can be treated with calcium channel blockers, which would be deleterious if prescribed to a typical PAH patient. Little is known about the underlying cause of this important difference in vasoresponsive PAH patients. Sex, race/ethnicity, and pharmacogenomics may also factor into efficacy and safety of PAH-specific drugs. Research has indicated that endothelin receptor antagonists may be more effective in women and there have been some minor differences found in certain races and ethnicities, but these findings are muddled by the impact of socioeconomic factors and a lack of representation of non-White patients in clinical trials. Genetic variants in genes such as CYP3A5, CYP2C9, PTGIS, PTGIR, GNG2, CHST3, and CHST13 may influence the efficacy and safety of certain PAH-specific drugs. PAH research faces many challenges, but there is potential for new methodologies to glean new insights into PAH development and treatment.

Pharmacogenomics in the Management of Pulmonary Arterial Hypertension: Current Perspectives

Pulmonary arterial hypertension (PAH) is a rare disease with heterogeneous causes that can lead to right ventricular (RV) failure and death if left untreated. There are currently 10 medications representative of five unique pharmacologic classes that are approved for treatment. These have led to significant improvements in overall clinical outcome. However, substantial variability in dosing requirements and treatment response is evident, leading to suboptimal outcome for many patients. Furthermore, dosing is empiric and iterative and can lead to delays in meeting treatment goals and burdensome adverse effects. Pharmacogenomic (PGx) associations have been reported with certain PAH medications, such as treprostinil and bosentan, and can explain some of the variability in response. Relevant genes associated with treprostinil include CYP2C8, CYP2C9, CAMK2D, and PFAS. CYP2C8 and CYP2C9 are the genes encoding the major metabolizing liver enzymes for treprostinil, and reduced function variants (*2, *3) with CYP2C9 were associated with lower treatment persistence. Additionally, a higher CYP2C9 activity score was associated with a significantly less risk of treatment discontinuation. Other genes of interest that have been explored with treprostinil include CAMK2D, which is associated with right ventricular dysfunction and significantly higher dose requirements. Similarly, PFAS is associated with lower concentrations of cyclic adenosine monophosphate and significantly higher dose requirements. Genes of interest with the endothelin receptor antagonist (ERA) class include GNG2 and CYP2C9. A genetic variant in GNG2 (rs11157866) was linked to a significantly increased rate of clinical improvement with ERAs. The *2 variant with CYP2C9 (encoding for the major metabolizing enzyme for bosentan) was significantly associated with a higher risk for elevations in hepatic aminotransferases and liver injury. In summary, this article reviews the relevant pharmacogenes that have been associated to date with dosing and outcome among patients who received PAH medications.

Adherence and Discontinuation of Disease-Specific Therapies for Pulmonary Arterial Hypertension: A Systematic Review and Meta-Analysis

BACKGROUND

In patients with pulmonary arterial hypertension (PAH), the use of disease-specific therapies (i.e., endothelin receptor antagonists, phosphodiesterase type-5 inhibitors, soluble guanylate cyclase stimulators, prostacyclins, and prostanoids) has been associated with disease improvement and decreased mortality risk. We aimed to quantify the adherence and discontinuation rates for patients prescribed PAH-specific therapies.

METHODS

We performed a systematic review via searching MEDLINE, EMBASE, and the Cochrane Library from their inception to 4 March 2022 for observational studies published in English that reported data on adherence to and persistence with PAH-targeted therapies. Random-effects meta-analysis was performed to explore average adherence and discontinuation rates.

RESULTS

In all, 14 studies involving 14,861 individuals prescribed PAH-targeted therapies were included. The overall pooled proportion of patients adherent to their PAH-targeted medications was 60.9% (95% confidence interval [CI] 52.3-69.1%). The pooled proportions of patients adherent in questionnaire-based studies and in studies using prescription/dispensing data were 52.9% (95% CI 48.9-56.9%) and 62.9% (95% CI 53.1-72.2%), respectively. The pooled proportion of patients who discontinued their PAH-targeted medications was 42.3% (95% CI 31.6-53.3). Factors reported to impact adherence included administration frequency, length of time on treatment, co-payment, and occurrence of adverse events.

CONCLUSIONS

In the real world, a considerable proportion of patients prescribed PAH-specific therapies were non-adherent or discontinued. As diverse factors may influence treatment adherence, multifaceted interventions are needed to address this trend in order to improve patient outcomes.

REGISTRATION

The systematic review protocol was registered in the PROSPERO database (CRD42022316638).