Sulfonamides drug interactions/adverse effect

Celecoxib is associated with fewer endoscopic ulcers than most other NSAIDs. Probably because it is a sulfonamide, celecoxib may cause rashes. It does not affect platelet aggregation at usual doses. It interacts occasionally with warfarin—as would be expected of a drug metabolized via CYP2C9. Adverse effects are the common toxicities listed above. 

A woman who had been taking phenelzine 15 mg three times daily for about 3 weeks eomplained of weakness, ataxia, vertigo, tinnitus, musele pains and paraesthesias within 7 days of starting to take sulfafurazole 1 g four times daily. These adverse effeets eontinued until the 10-day sulfonamide eourse was eompleted, and did not oeeur again in the following 8 weeks. The reasons are not understood, but as these adverse effeets are a combination of the adverse effects of both drugs, it seems possible that a mutual interaction (perhaps saturation of the acelylating mechanisms in the liver) was responsible. This appears to be an isolated report, but bear it in mind in the event of an unexpected response to treatment. 

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