Fixed drug eruption: topical provocation and subsequent phenomena.

Objective: To determine the usefulness of topical provocation in detecting the incriminated drug causing fixed eruption.

Design: Quasi-experimental study.

Place And Duration Of Study: Department of Dermatology, Shaikh Zayed FPGMI, Lahore, from November 2002 to December 2005.

Patients And Methods: Three hundred and five, clinically diagnosed cases of Fixed Drug Eruption (FDE) of either gender and of any age were subjected to topical provocation with different drugs by using concentration of 1% (n=203), 2% (n=210) and 5% (n=235) in white soft paraffin. Drug ointment of one strength was applied one at a time on normal skin of flexor surface of right or left forearm. The effects of tests on involved and uninvolved skin were observed for 48 hours. The changes in lesions like erythema, hyperpigmentation, itching, burning or appearance of new lesion were considered a positive response. In case of no change, the patients (n=5) were subjected to oral provocation test, by giving half to full therapeutic dose of the suspected drug depending upon the severity of the initial attack. A patient who exhibited see-sawing phenomenon with 5% metamizole TPT was given oral challenge with same drug. Control topical tests were repeated in equal number of normal persons with various drug ointments and in patients of FDE with white soft paraffin on normal and affected skin.

Results: One hundred and thirty-seven patients were males and one hundred and sixty-eight patients were females. Maximum number of patients belonged to third decade. With 1% drug preparations 12 out of 316, with 2% drug preparations 28 out of 422 and with 5% drug preparations, 312 out of 523 TPTs were positive. The comparison revealed a highly significant association (Chi-square 448.1 and p < 0.000) among various strengths of preparations and positive response. Sulphamethoxazole was found to be the most commonly incriminated cause of FDE applied in 5% concentration yielded sensitivity rate of 91% compared to 4% with lower concentrations. Positive patch test was also observed with oxytetracycline. Five patients who were given oral provocation with different drugs were found to be positive to tinidazole, dapsone, propylphenazone, belladonna and phenobarbitone. Interesting phenomena like earlier reactivation of lesion situated distal to site of application of preparation, marching, see-sawing (with oral metamizole) and lightening observed, are not yet reported in literature.

Conclusion: Topical provocation test with 5% drug concentration applied on normal skin of patient with FDE is a possible first line investigation in finding the incriminated drug.