Pharmacology All India exam 675c4561 Longest acting oral sulphonamide is A Sulphadoxine B Sulphadiazine C Sulphacetamide D Mafenide High-Yield Explanation Sulphadoxine is the longest acting orally absorbable drug. Mafenide is a topical drug.sulphadiazine and sulfacetamide are sho-acting oral drugsRef: KD Tripathi 6th ed .pg: 684