Following two cases of fatal liver injury, Pfizer has voluntarily withdrawn Thelin from the worldwide market and discontinued all ongoing trials. The drug had been approved in the EU, Canada and Australia for the treatment of pulmonary arterial hypertension (PAH).

The withdrawal was based on a review of emerging safety information from clinical trials and post-marketing reports. Thelin belongs to a class of drugs of which liver toxicity is a known complication. As such, the treatment has been contraindicated in patients with mild to severe hepatic impairment and elevated aminotransferases prior to initiation of treatment. In a press statement, however, Pfizer said: “Given the availability of alternate treatments, Pfizer has concluded that the overall benefit of Thelin no longer outweighs the risk in the general population of PAH patients.”

The company has recommended that no new patients be prescribed Thelin and that current patients be transitioned to alternate therapies as soon as safely possible. In a statement, the EMA also added that patients currently taking Thelin are advised not to stop the treatment and to consult their physician to review their treatment at their next scheduled appointment.

Pfizer acquired Thelin after buying Encysive Pharmaceuticals in 2008. The treatment has been authorized for use in the EU in 2006. On the other side of the Atlantic, however, the FDA has refused to approve the drug on three different occasions because of safety concerns. Pfizer had been trying to alleviate these with new clinical studies, which have now been discontinued.