[Risk assessment for clinical external application of calomel]

Calomel is a common traditional Chinese medicine (TCM) containing mercury in clinical external application. Although the toxicity of calomel has attracted concern, there is no unified standard yet in clinical external application. Risk assessment is used for evaluating the potential health effects of hazardous substances. The purpose of this article was to evaluate the health risk of calomel in clinical external application on the basis of toxicity data, to ensure safe and rational application of TCM containing calomel. The toxicity data of transdermal administration of calomel or mercurous chloride were collected by searching the literature. The daily maximum exposure dosage of calomel in clinical external application was estimated by following the four procedures of risk assessment, and Margin of Safety (MOS) as an evaluation indicator was then calculated to evaluate the safety of calomel on clinical application. It has been reported that the adult in single transdermal administration of calomel at 1. 5 g was lethal. Based on the LOAEL of calomel for long-term transdermal exposure (1 month) in rats was 0.096 g · kg(-1) · d(-1), the NOAEL of calomel for patients (about 60 kg) by external application within 2 weeks was estimated to be 1.46 mg · kg(-1) · d(-1). When MOS value equals to 1, the daily maximum exposure of calomel in clinical external application within 2 weeks was calculated to be 1.1 g. The results suggest that daily single dose of calomel in clinical external application should be lower than 1.5 g for adults, and more attention should be paid to changes in hepatic and renal function of patients when repeated dose more than 1.1 g within 2 weeks. The approach of risk assessment could be helpful in rational application of TCM containing mercury.