Hello Ankur, You have asked quite a difficult yet pertinent question. The GPIIb/IIIa def is functional, and can affect platelet function, and as far as studies are concerned with platelet and antihistamines it is usually a decrease in number (though rare). Fexofenadine is a long acting 2nd generation antihistamine and the SPC of fexofenadine does not mention any such platelet problem. You are advised to discuss with your Haematologist if still in doubt. Thanks.