Pulmonary Arterial Hypertension Medications Studied for Drug Interactions

According to a study published by researchers at Novartis Pharma, common medications for severe pulmonary arterial hypertension interact, increasing one another’s levels when taken at the same time. However, co-administration of the medications does not appear to impact their effectiveness or increase the risk of liver problems.

The study, entitled, “Pharmacokinetic interactions among imatinib, bosentan and sildenafil, and their clinical implications in severe pulmonary arterial hypertension,” appeared in the January 7th issue of the British Journal of Clinical Pharmacology.

Pulmonary arterial hypertension (PAH) is a condition that worsens over time and can be potentially fatal, since pressure in the pulmonary arteries can strain the heart. Although PAH currently has no cure, several medications are used to control PAH symptoms.

The current study examined three medications commonly prescribed for people with PAH, including imatinib, bosentan and sildenafil.

Imatinib (also called Gleevec) is a treatment for leukemia that is sometimes used as an add-on therapy in PAH. The drug can improve exercise capacity in patients with advanced PAH and improve blood capacity, possibly due to inhibitory effects on platelet-derived growth factor.

Bosetan (also called Tracleer) is a PAH medication that also can improve exercise capacity and acts by blocking the activity of endothelin, a molecule that causes blood vessel narrowing and interruption of blood flow.

Sildenafil, (called Viagra and other brand names) is a medication used to treat pulmonary arterial hypertension and erectile dysfunction by inducing blood vessel dilation.

The investigators measured blood levels of medications in 21 patients with severe PAH when they were taking imatibnib together with bosentan or imatinib along with sildenafil. The participants in this study were already taking stable doses of bosentan and sildenafil and were given either imatinib or placebo in addition to their current medication.

Sildenafil concentrations increased by an average of 64% and bosentan by 51% when taken together with imatinib. However, despite elevations in blood levels of the medications, the drugs appeared to remain as effective and did not appear to have increased risk for liver toxicity.

The researchers noted that “treatment differences between imatinib and placebo for change in 6-min walk distance and pulmonary vascular resistance were relatively constant across the entire concentration range for sildenafil and bosentan. Overall, higher concentrations of imatinib and bosentan were not associated with increasing liver enzymes (serum glutamic oxaloacetic transaminases [SGOT]/serum glutamic-pyruvic transaminase [SGPT]).”

According to the researchers, “Imatinib was found effective regardless of the co-medications and showed intrinsic efficacy beyond merely elevating the concentrations of the co-medications due to [drug-drug interactions]. There was no evidence of increased risk of liver toxicity upon co-administration with bosentan.”