Hypotension and bradycardia following varenicline overdose

Objective: To report a case of symptomatic varenicline overdose in an adult. Case report: Varenicline is a new drug for smoking cessation. It is both a partial agonist and antagonist to the nicotine receptor. Trials have shown safety and efficacy at doses of 1 mg BD.¹ Adverse effects have included nausea, vomiting, headache, fatigue and drowsiness.² There are few reports of overdoses involving varenicline. A 14 year old female developed lethargy after ingesting 21 milligrams.³ Hypotension, tachycardia and coma have occurred when varenicline has been ingested in combination with unknown amounts of valproic acid and quetiapine.⁴ We report the case of a 48 year old male who ingested 12.5 milligrams of varenicline. Alcohol was co-ingested. The patient presented to hospital four hours after ingestion. On admission he was drowsy, hypotensive and experiencing hyperhidrosis. In accordance with TOXBASE (the primary clinical toxicology database of the National Poisons Information Service), the management plan for the patient included monitoring blood pressure, pulse, respiratory rate and temperature. A twelve lead ECG was recommended. Subsequently the patient become bradycardic and was given atropine and ephedrine. IV fluids were administered. Over a six hour period his condition improved and he made a complete recovery. Conclusion: Varenicline is a new drug and very little is known about its effects in overdose. This case suggests that toxicity may be seen at a dose which is relatively small compared to previously reported cases. References: 1. Faessel HM, Gibbs MA, Clark DJ, et al. Multiple-dose pharmacokinetics of the selective nicotinic receptor partial agonist, varenicline, in healthy smokers. J Clin Pharmacol 2006; 46:1439–1448. 2. SPC for Champix, Pfizer Limited. From http://emc.medicines.org.uk. Cited 10th November 2008. 3. Feng S, Goto CS, Velez LI, et al. Varenicline (Chantix) overdose in an adolescent female (abstract). Clin Toxicol 2008; 46:362. 4. Goto CS, Feng S, Velez LI, et al. Spectrum of toxicity due to varenicline (Chantix) exposure (abstract). Clin Toxicol 2008; 46:365