Cutaneous adverse drug eruption: the role of drug patch testing

Drug patch testing has been proposed as a helpful investigation upon suspecting drug allergy. We evaluated the value of drug patch testing in Cutaneous Adverse Drug Reactions (CADRs).All patients with a diagnosis of CADRs were patch tested with suspected drugs.Of 122 patients with CADRs, 44.3% had at least one positive result after drug patch testing, P value = 0.312. Drug rash with eosinophilia and systemic symptom (DRESS) rendered the highest positive patch testing at 53.9%, followed by a maculopapular rash (MP) at 49.0%, fixed drug eruption (FDE) at 48.3%, lichenoid drug eruption and Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) at 25.0% each. Lichenoid drug eruption had the longest mean onset of almost 2.5 years. One hundred and twenty-eight drugs and herbal medicines were tested. About 32.8% of these drugs gave a positive result, P value = 0.041. Nonsteroidal anti-inflammatory drugs (NSAIDs) were the most common positive drug especially for fixed drug eruption (FDE), followed by antiretroviral and antibiotics, which were the most common positive drugs for MP. While anti-Tuberculosis (anti-TB) drugs and antihypertensives together with lipid-lowering drugs were the most common for DRESS and lichenoid eruption, respectively. Subgroup analysis among HIV patients showed a 61.5% positive patch test. The median CD4 count in the positive group was 43.5 cells/mm3 .We recommend drug patch testing as a safe method to identify the culprit drug in CADRs, especially DRESS, MP, and FDE. In HIV patients, the positive test was associated with low CD4 count and copositive reaction.