Rannakoe J Lehloenya1, Rudzani Muloiwa2, Sipho Dlamini3, Nomphelo Gantsho4, Gail Todd4, Keertan Dheda5. 1. Division of Dermatology, Department of Medicine, University of Cape Town, Cape Town, South Africa Lung Infection and Immunity Unit, Department of Medicine, University of Cape Town, Cape Town, South Africa. 2. Department of Paediatrics and Child Health, University of Cape Town, Cape Town, South Africa. 3. Division of Infectious Disease and HIV Medicine, Department of Medicine, University of Cape Town, Cape Town, South Africa. 4. Division of Dermatology, Department of Medicine, University of Cape Town, Cape Town, South Africa. 5. Lung Infection and Immunity Unit, Department of Medicine, University of Cape Town, Cape Town, South Africa keertan.dheda@uct.ac.za.
Abstract
BACKGROUND:Isoniazid and ethionamide are important first- and second-line anti-TB drugs (FLDs and SLDs), respectively. Ethionamide is a structural analogue of isoniazid and the two drugs share other similarities, including their metabolism, therapeutic targets, hepato-toxicity patterns and drug resistance. As a result, there has always been concern about possible cross-reactivity between them. METHODS: Among 69 patients with drug rash with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN) to FLDs, FLDs were stopped and SLDs added when the skin and laboratory parameters had settled. This was followed by sequential and additive rechallenge with FLDs. We report 25 consecutive cases that developed confirmed cutaneous adverse drug reactions (CADRs) toisoniazid or ethionamide used as FLD and SLD, respectively. RESULTS:Sixty-nine participants who developed CADRs on FLDs were enrolled in the study. Twenty developed a rechallenge reaction to isoniazid and five reacted to ethionamide. Four of the 20 isoniazid cases were patch test positive, 3/20 were skin prick test positive and 13/20 reacted to oral rechallenge. All seven cases that were patch and skin prick test positive were associated with systemic reactions. Twenty of the 25 cases had DRESS and 5 had SJS/TEN. Twenty-three of the 25 cases with rechallenge reactions were HIV infected. Importantly, none of the cases that reacted to ethionamide during the rechallenge reacted to isoniazid and none who subsequently reacted to isoniazid reacted to ethionamide. CONCLUSIONS: Our findings strongly suggest that the risk of cross-reactivity of isoniazid and ethionamide in DRESS syndrome and SJS/TEN is low. These findings have implications for clinical management.
RCT Entities:
BACKGROUND:Isoniazid and ethionamide are important first- and second-line anti-TB drugs (FLDs and SLDs), respectively. Ethionamide is a structural analogue of isoniazid and the two drugs share other similarities, including their metabolism, therapeutic targets, hepato-toxicity patterns and drug resistance. As a result, there has always been concern about possible cross-reactivity between them. METHODS: Among 69 patients with drug rash with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN) to FLDs, FLDs were stopped and SLDs added when the skin and laboratory parameters had settled. This was followed by sequential and additive rechallenge with FLDs. We report 25 consecutive cases that developed confirmed cutaneous adverse drug reactions (CADRs) to isoniazid or ethionamide used as FLD and SLD, respectively. RESULTS: Sixty-nine participants who developed CADRs on FLDs were enrolled in the study. Twenty developed a rechallenge reaction to isoniazid and five reacted to ethionamide. Four of the 20 isoniazid cases were patch test positive, 3/20 were skin prick test positive and 13/20 reacted to oral rechallenge. All seven cases that were patch and skin prick test positive were associated with systemic reactions. Twenty of the 25 cases had DRESS and 5 had SJS/TEN. Twenty-three of the 25 cases with rechallenge reactions were HIV infected. Importantly, none of the cases that reacted to ethionamide during the rechallenge reacted to isoniazid and none who subsequently reacted to isoniazid reacted to ethionamide. CONCLUSIONS: Our findings strongly suggest that the risk of cross-reactivity of isoniazid and ethionamide in DRESS syndrome and SJS/TEN is low. These findings have implications for clinical management.