The antibacterial activity of dyes was first reported in 1913. Interestingly, the discovery of sulfonamides as chemotherapeutic agents ensued from the antibacterial activity observed in the dye prontosil.
Azo dyes (eg, scarlet red and phenazopyridine HCl) are most active in an acidic medium and are effective against gram-negative organisms. Scarlet red is often used as a 5% ointment on sores, ulcers, and wounds. Pyridium is often incorporated as an analgesic with sulfonamides to treat urinary tract infections.
Acridine dyes (eg, acriflavine, proflavine, aminacrine) are more active against gram-positive bacteria. Their activity is enhanced in alkaline medium and antagonized by hypochlorites. Impregnated bandages and gauze and acriflavine jelly have been used extensively for treatment of burns.