What are SCARs?
Adverse drug reactions (ADRs) affect up to 25% of outpatients and 20% of inpatients, nearly 1 in 300 inpatient ADRs result in death. Severe cutaneous adverse reactions (SCARs) are a subset of severe immunologic ADRs that includes Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome.
SCARs involve skin and mucous membranes of various body parts such as the eyes, lips and mouth. These severe reactions may also involve serious damage to internal organs such as the liver and kidneys. SCARs are infrequent, affecting 0.1 to 1.0 in 1000 hospitalized patients, but result in substantial morbidity, long term disability, and a mortality of 10-50%.
Current SCAR Research and Limitations
Over the last decade, significant promise for prediction and prevention has come from the discovery that many SCARs are associated with genetic markers. For example, researchers identified a genetic variation (called HLA-B*15:02) associated with SCARs caused by a drug called carbamazepine. This has led to routine pre-prescription screening for carbamazepine in many Southeast Asian countries which has significantly reduced the cases of carbamazepine related SCARs. Despite this progress, there is little known about the clinical and genetic risk factors for SCARs related to commonly used drugs such as antibiotics. There is also limited information about genetic risk for SCARs across the diverse populations present in the United States (US).
SCAR research in the US has been limited by challenges to case identification. Traditional methods using diagnostic codes from claims data have shown poor specificity, as SCARs may be coded using a variety of different International Classification of Disease (ICD) 9/10 codes, and some SCARs have no specific codes available to date. Although electronic health record (EHR) systems have an allergy list to record adverse and allergic reactions, SCARs are not available as coded entries (i.e., the reactions would exist only in free text). International registries have improved our understanding of the epidemiology of SCARs; in the US, however, there is no mandatory reporting by clinicians, and voluntary reporting to the Food and Drug Administration’s adverse event reporting system is inconsistent and has limited data. SCAR prevalence, causative drugs, predictors, and sequelae in the US remain poorly described, especially for antibiotic-associated SCARs.