QJM Advance Access originally published online on November 28, 2008
QJM 2009 102(2):123-131; doi:10.1093/qjmed/hcn153
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Promethazine overdose: clinical effects, predicting delirium and the effect of charcoal
From the 1Department of Clinical Toxicology and Pharmacology, Calvary Mater Newcastle Hospital, Newcastle, NSW, Australia, 2School of Pharmacy, University of Otago, Dunedin, New Zealand, 3Discipline of Clinical Pharmacology, Faculty of Health, University of Newcastle, Newcastle, NSW and 4Tropical Toxinology Unit, Menzies School of Health Research, Charles Darwin University, Darwin, Australia
Address correspondence to Dr C.B. Page, Department of Clinical Toxicology and Pharmacology, Calvary Mater Newcastle, NSW 2310, Australia. email: cpage{at}bigpond.net.au
Received 8 August 2008 and in revised form 27 October 2008
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Abstract |
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Objective: The aim of this study was to describe the clinical effects of promethazine in overdose and explore the relationship between delirium and possible predictor variables.
Methods: A case series of promethazine poisonings was identified from a prospective database of poisoning admissions to a regional toxicology service. Data were extracted including demographics, details of ingestion, clinical features including delirium, complications and medical outcomes. In addition to descriptive statistics, a fully Bayesian approach using logistic regression was undertaken to investigate the relationship between predictor variables and delirium.
Results: There were 199 patients with 237 presentations, including 57 patients with 78 promethazine alone overdoses. Of these 57 patients who ingested promethazine alone the median age was 22 years [interquartile range (IQR): 17–31] and 42 were female (74%). The median dose ingested was 625 mg (IQR: 350–1250 mg). Median length of stay was 19 h (IQR: 13–27 h), ten were admitted to the intensive care unit (ICU) and four were ventilated. Delirium occurred in 33 patients (42%), tachycardia (HR>100) occurred on 44 occasions (56%) and hypotension only twice. There were no seizures, dysrhythmias or deaths. Multivariate analysis of 215 presentations (in 181 patients) where dose of promethazine ingested was known demonstrated that dose, administration of charcoal within 2 h and co-ingestants predicted whether patients developed delirium. No relationship was shown for sex and age. A plot of probability that a patient will develop delirium vs. dose was constructed which showed the probability of delirium for 250 mg was 31%, 500 mg was 42% and for 1 g was 55% for promethazine alone overdoses.
Conclusion: The main feature of promethazine toxicity is delirium, the probability of which can be predicted from the dose ingested. The administration of charcoal and the presence of co-ingestants appears to reduce the probability of delirium in a predictable manner.