Encysive Pharmaceuticals has designed and developed a small molecule sodium salt which blocks the action of Endothelin – ET on the Endothelin-A [ETA] selective receptor, to be known and marketed as Thelin formulated from the popular ingredients called Sitaxsentan or Sitaxsentan Sodium. It is the sulfonamide class Endothelin receptor agonist – ERA and is undergoing the Food and Drugs Administration – FDA of the United States, reviews for use in the treatment of pulmonary hypertension.

The basis for benefit as compared with the non selective Endothelin - ET blocker bosentan, is slightly inhibition of the beneficial effects of ETB stimulation, for instance, the production of nitric oxide as well as the clearance of Endothelin – ET from the circulation. While the efficiency of Thelin or Sitaxsentan is found to be almost similar to that of bosentan as per the clinical trials, but the liver toxicity was noticed to have improved. Hence Thelin or Sitaxsentan is believed to be marketed as the safer drug option as compared to bosentan; however it may not be necessarily proving better efficacy.

Several adverse effects of the drug Thelin – Sitaxsentan have been reported to incorporate: typical dysfunction of liver like enhanced ALT and AST; headaches; edema; constipation; congestion in the nasal passageway; infections in the upper respiratory tract; giddiness; insomnia and flushing. Several symptoms other than mentioned here may also be experienced in some typical cases for which the physician should be consulted on priority and the medication use should be averted unless doctor further advises.

It is recommended to conjoin a reduced dose of warfarin with Thelin as Thelin slows down the metabolism of warfarin.