Treatment of COVID-19 pneumonia and acute respiratory distress with ramatroban, a thromboxane A2 and prostaglandin D2 receptor antagonist: A 4-Patient Case Series Report

COVID-19 associated pneumonia and acute respiratory distress syndrome are accompanied by a massive and sustained increase in lung and systemic thromboxane (Tx) A2. TxA2 is a short-lived, potent vasoconstrictor of pulmonary veins > arteries, and thereby selectively increases pulmonary venous resistance, promoting an increase in pulmonary capillary pressure. TxA2 also increases vascular permeability which, in the lungs, exaggerates pressure-mediated transudation into the alveolar space, causing pulmonary edema and ARDS. Also relevant to COVID-19 pathophysiology, TxA2 contracts bronchial smooth muscle, triggers and amplifies platelet activation, mediates apoptosis of immature thymocytes, and promotes a procoagulant state, all of which are mediated by TxA2 receptor (TPr) activation. The stable TxA2 metabolite, 11-dehydro-TxB2, is elevated in direct proportion to COVID-19 severity. Though inactive at TPr, 11-dehydro-TxB2 activates PGD2 / DP2 receptors (DPr2) which promote a Th2 immune response that is atypical for viral infections and inhibits antiviral defense by suppressing interferon λ expression. Ramatroban is an orally bioavailable, potent, dual antagonist of TPr and DPr2 receptors. We report use of ramatroban (Baynas®, Bayer Yakuhin Ltd., Japan) in 4 COVID-19 outpatients, 22 to 87 years of age, with acute onset / worsening of respiratory distress and hypoxemia. All four patients experienced a decrease in respiratory distress and increase in SpO2, within hours of the first dose of ramatroban and, thereby, avoided hospitalization. By the 5th day all 4 patients had complete resolution of respiratory distress and hypoxemia. Ramatroban has an established safety profile, having been indicated in Japan for the treatment of allergic rhinitis for over 20 years. As an anti-vasospastic, broncho-relaxant, anti-thrombotic and immunomodulator, ramatroban addresses the fundamental host response mechanisms underlying respiratory and critical organ failure in COVID-19, and merits urgent clinical trials that might impact the ongoing pandemic.