United Therapeutics Corp has received approval from regulators in the USA for tadalafil, the active ingredient in Eli Lilly’s erectile dysfunction drug Cialis, for the treatment of pulmonary arterial hypertension (PAH).

United will market the drug under the brand name Adcirca as a once-daily oral treatment for PAH with a 40mg dose. The company, which acquired the US marketing rights for this indication of Cialis from Lilly in November 2008, expects to launch the drug at the beginning of August.

The approval from the US Food and Drug Administration is based on a Phase III trial where patients took Adcirca 40mg (administered as two 20mg tablets) once-daily and achieved a 33 metre improvement in six-minute walk distance compared to the placebo group. In addition, patients on tadalafil, experienced “less clinical worsening” (defined as death, lung transplantation, atrial septostomy, hospitalisation because of worsening PAH, initiation of new therapy, or worsening functional class) compared to placebo.

The approval means that tadalafil is the first once-daily phosphodiesterase type 5 (PDE5) inhibitor for the treatment of PAH. United chief executive Martine Rothblatt noted that “thanks to the clinical development efforts” led by Lilly, “we are thrilled to make available an effective, convenient and economical therapy for PAH patients." She added that the FDA's go-ahead “is a big plus for all three P's: patients, physicians and payors”.

The approval has gone down well with investors (United’s shares climbed 10%) and analysts. Terence Flynn at Lazard Capital Markets issued a research note saying that he expects Adcirca to capture market share from Pfizer's PAH drug Revatio (sildenafil), the same active ingredient as Viagra.

Adcirca should flourish, he said, due to its more convenient dosing than Revatio, a lower price and easier reimbursement when the dosage has to be adjusted. Mr Flynn is predicting peak US Adcirca sales of more than $150 million.