Tetrahydrozoline: Death by Eyedrops

Abstract

Tetrahydrozoline (THZ) is an alpha-adrenergic receptor agonist most commonly used in eyedrops to reduce redness. Reported plasma concentrations are less than 1 ng/mL after normal use. Adverse effects following oral ingestion include drowsiness, tremors, irregular heartbeat and respiratory depression. Several cases of individuals surviving accidental THZ exposure and drug facilitated crimes victims rendered unconscious by the drug have been reported. The purpose of this study is to summarize THZ concentrations from cases submitted to a reference laboratory and examine its role in death cases. Data were extracted from NMS Labs’ (Horsham, PA, USA) Laboratory Information Management System for all cases received from December 2010 to December 2021. Cases with a reported blood THZ concentration were classified as postmortem (PM), driving under the influence of drugs (DUID), drug facilitated crime (DFC) or unknown. The mean, median and concentration ranges for each group were determined. The number and types of other drugs reported were also examined in cases which underwent comprehensive testing. 129 cases were positive for THZ. The reported concentrations are summarized below: – Case Type N Mean (ng/mL) Median (ng/mL) Range (ng/mL) – PM 112 20 1.7 0.19–290, – DUID 1 0.64 0.64 -, – DFC 3 0.35 0.35 <0.10–0.52, – UNKNOWN 13 18 1.2 0.27–130. Comprehensive testing was performed on approximately 100 cases. The most commonly detected other drugs were ethanol, Delta-9 THC), diphenhydramine, fentanyl, amphetamine, and morphine. THZ concentrations ≥100 ng/mL were reported in 10 cases. One case (THZ = 100 ng/mL) was from a living individual and the status of the patient could not be determined in another case (THZ = 130 ng/mL). The remaining cases included a dual suicide, one sudden death, one “suspected poisoning”, one homicide and one case still under active investigation. A woman admitted to lacing her boyfriend's water with tetrahydrozoline on multiple occasions from 2009–2012 to get him to pay more attention to her. The man, who survived, sought medical attention for trouble breathing, irregular blood pressure and nausea and had a blood THZ concentration of 49 ng/mL. The THZ concentration in cardiac blood from a decedent whose death was originally believed to be due to natural causes was 68 ng/mL. THZ, an uncommon finding in toxicology testing, has been reported in multiple homicide, suicide and drug facilitated crimes highlighting the importance of its inclusion in comprehensive post-mortem toxicology testing.