Introduction
Chloroquine and hydroxychloroquine are being repurposed for use as treatment options for coronavirus disease 2019 (COVID-19) (Ferner and Aronson, 2020). The Food and Drug Administration sanctioned their emergency use in the USA (FDA, 2020), and clinical guidelines in Belgium, China, France, India, Iran, Italy, South Korea, and The Netherlands make recommendations for uses ranging from prophylaxis (Indian Council of Medical Research, 2020) to the treatment of the most severely affected patients.
Case reports of cardiotoxicity and fatal poisoning relating to the use of chloroquine and hydroxychloroquine for COVID-19 have emerged (Binding, 2020; Agence Régionale de Santé, 2020; Xuan, 2020; Busari and Adebayo, 2020; SimpliCity, 2020). The acute toxic effects of these drugs are well recognised (WHO, 2016), and relate to their cardiotoxic effects of widening of the QRS complex, atrioventricular block, ventricular arrhythmias, negative inotropy, hypotension and severe hypokalaemia, which occur within 1-3 hours of ingesting doses >2g in adults. Without intensive, supportive treatment, circulatory collapse and death can rapidly follow acute overdose. Mortality due to acute toxicity is high, with 134 of the 387 cases reported in the literature between 1955 and 1975 (Bondurand et al., 1980), and a further 135 from 335 suicide attempts (Weniger and World Health Organization, 1979) resulting in death.
Current recommendations for the management of acute toxicity include ensuring adequate ventilation, gastric lavage, administration of activated charcoal, adrenaline for its inotropic and vasoconstrictor effects, diazepam, and correction of metabolic acidosis and hypokalaemia (Jones, 2015). The observation in 1976 of a patient who took 5g of chloroquine together with 500mg of diazepam, and survived without symptoms of chloroquine toxicity (Djelardje, 1976), drew attention to the possible role of diazepam in chloroquine poisoning. Subsequent case reports (Jaeger et al., 1987; Rajah, 1990; Meeran and Jacobs, 1993) and a prospective non-randomised trial (Riou et al., 1988a), in which the odds of survival significantly favoured diazepam therapy, led to the recommendation of diazepam in the management of acute chloroquine toxicity. However, there remains controversy given some conflicting evidence of benefit (Damaziere et al., 1992; Clemessy et al., 1996) and limitations in study designs (Yanturali, 2004).
Experimental toxicity studies are also inconclusive. Crouzette et al., (1983) demonstrated that an intraperitoneal injection of diazepam caused a significant decrease in the mortality of rats treated with chloroquine. Riou et al., (1988b) observed an improvement in haemodynamics and a correction of the QRS interval prolongation when diazepam was administered to chloroquine-intoxicated pigs. Gnassounou et al., (1988) observed that clonazepam protected anaesthetized rats against chloroquine toxicity, and that diazepam – but not the translocator protein (TSPO) agonist Ro5-4864 (4’-chlorodiazepam) – protected against the decrease in contractions observed when guinea-pig atria were exposed to chloroquine. In other studies, however, diazepam failed to improve the mechanical performance of rat cardiac papillary muscle exposed to chloroquine (Riou et al., 1989); and was ineffective in reversing chloroquine toxicity in anaesthetized rats (Buckley et al., 1996).
It would therefore appear that the effectiveness of diazepam in reversing chloroquine toxicity is equivocal and that the mechanism(s) by which diazepam may exert its effects remain unclear. Due to the resurgence in the use of chloroquine and its structural analogue hydroxychloroquine for COVID-19, the aim of the present study was to investigate the potential cardioprotective effects of diazepam in experimental models of chloroquine toxicity.