I saw a seriously recurrent UTI patient who has allergies to abx like bactrim, penicillin, cipro, rocephine and augmentin in an ICU ward recently.

He was given tramadol and citravescent for this time admission.

Unfortunately, he acquired a bad face rash and was itching badly until it swelled and scorched. A piriton was given together with a moisturiser to minimise the effect.

Upon query, he said he has no issue with tramadol for his other maladies but citravescent is the only new thing that made him itch immediately upon consumption.

When he brought up the issues to his medical-in-charge, his claim was dismissed outrightly. The next day the same thing happened, he decided to stop taking it totally and the itch, swell and scorching face returned to normal.

He is on Nitrofurontoin and has since been discharged.

Judging by his experience, while some patients or doctors found citravescent "safe", why others still feel the danger lurks everytime it is consumed?

Could it be that his immune system was very down then?

Or is it true citravescent is resistant to some patients, UTIs' especially?