<prompt> In cotrimoxazole, sulphamethoxazole and trimethoprim are in the ratio of-2:011:015:011:05  <response>: Ans. is c i.e., 5 : 1 o Optimal synergy in case of most organism is exhibited at a concentration ratio of Sulphamethoxazole 20: Trimethoprim 1 This ratio is obtained in plasma when two are given in a dose ratio of 5:1. 