001-410-576-2000 Fax. 001-410-576-2221 Ingredients CAS Quantity Cephalexin USP 15686-71-2 250 mg and 500 mg Fire and Explosion Expected to be non-combustible Health Cephalexin is contraindicated in patients with known allergy to the cephalosporin group of antibiotics.ests to determine the mutagenic potential of cephalexin have not been performed. In male and female rats, fertility and reproductive performance were not affected by cephalexin oral doses up to 1.5 times the highest recommended human dose based upon mg/m 2. No relevant studies identified.