Gamma-Hydroxybutyrate – GHB has many names including: Cherry meth, liquid Fanta, Easy Lay, Fantasy, Georgia Homeboy, Liquid Ecstasy, Liquid G and most annoyingly…water. GHB is the opposite of Amphetamine, instead of making you angry and hypervigilant it depresses your CNS. It is a precursor and metabolite of gamma-aminobutyric acid (GABA – the inhibitory neurotransmitter).
- GHB causes rapid onset of CNS and respiratory depression.
- In overdose the classic presentation is of euphoria followed by coma. Patients can be roused by external stimulus and often briefly difficult to manage before rapidly dropping back into a coma.
- It has a rapid absorption with peak plasma concentrations within 25-60 minutes.
- Metabolism requires alcohol dehydrogenase in the liver, hence the presence of alcohol can inhibit and delay the onset of action.
- The elimination half life is usually less than 1 hour and complete within 4-8 hours. Classically they can go from a GCS of 3 to 14 within minutes. Periods of agitation and delirium can occur during recovery.
The show notes are presented as a ‘show and reveal‘ mini quiz.
- Respiratory depression
- Loss of protective airway reflexes.
- GHB has a short half life which in some ways makes management difficult as you maybe reluctant to intubate the patient knowing they will wake in 2-3 hours. A thorough assessment of their airway and breathing needs to be made. If these are at risk or inadequate it is safer to intubate and ventilate for a number of hours than cause increase morbidity or mortality from a soiled airway.
Resus: What co-ingestions would increase the risk of respiratory depression?
- CNS depressants (e.g Benzodiazepines)
- Average strength is 1 g/ml
- Average dose is 30 mg/kg = 2.1g for a 70kg adult
- Lethal = >50 mg/kg = 3.5g for a 70kg adult
- Of course everyone is different and the chronic user will have required some tolerance.
- Bradycardia is common. If asymptomatic and they are maintaining adequate perfusion atropine or catecholamine infusions are rarely required.
- BSL – particularly if they have a reduced GCS
- ECG, paracetamol and ethanol levels for screening
- If the diagnosis is unclear or the patient has not recovered in an expected time a CT brain and metabolic screen should be considered.
- No – it is too rapidly absorbed. By the time the patient has presented to an emergency service they will have reached peak serum levels. Also if it was possible to give them a charcoal chaser they is a high risk of aspiration with coma.
- Features of withdrawal such as hallucinations, paranoia, insomnia, agitation and anxiety can last anywhere from 3 – 21 days.
- Allen L, Alsalim W. Gammahydroxybutyrate overdose and physostigmine. Emergency Medicine Journal 2006; 23(4):300-301.
- Traub SJ, Nelson LS, Hoffman RS. Physostigmine as treatment for Gamma Hydroxybutyrate toxicity: A Review. Journal of Toxicology-Clinical Toxicology 2002; 40(6):781-787.
- Chin RL, Sporer KA, Cullison B, Dyer JE, Wu TD. Clinical course of gamma-hydroxybutyrate overdose. Annals of Emergency Medicine 1998; 31:716-722.
- Murray L, Little M, Pascu O, Hoggett K. Toxicology Handbook 3rd Edition. Elsevier 2015. ISBN 9780729542241