<prompt> Longest acting oral sulphonamide isSulphadoxineSulphadiazineSulphacetamideMafenide  <response>: 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 