GHB toxicity
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.
Tox Tute AUDIO – GHB
The show notes are presented as a ‘show and reveal‘ mini quiz.
Question 1
Resus: What are the potential early life threats with GHB?
Reveal the Answer
- Coma
- 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.
Question 2
Resus: What co-ingestions would increase the risk of respiratory depression?
Reveal the Answer
- Ethanol
- CNS depressants (e.g Benzodiazepines)
Question 3
Risk assessment: Although each supplier will have a unique brew, what is the average strength in grams per ml and what is the standard dose compared to potentially lethal dose?
Reveal the Answer
- 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.
Question 4
Supportive care: While you are providing supportive care for a GHB patient that is not intubated the nurse informs you they have a HR of 45. An ECG is done and it shows sinus bradycardia with no conduction delays. What do you do?
Reveal the Answer
Bradycardia is common. If asymptomatic and they are maintaining adequate perfusion atropine or catecholamine infusions are rarely required.
Question 5
Investigations: What would you consider important?
Reveal the Answer
- 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.
Question 6
Decontamination: Is there a role for activated charcoal?
Reveal the Answer
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.
Question 7
Disposition: You are handed over a recovering GHB patient and told that if they have remained well for 2 hours they can go home. They have unfortunately developed a psychosis. You appropriately refer to your psychiatric team who ask you how many days do you think his psychosis will last. What is the answer?
Reveal the Answer
Features of withdrawal such as hallucinations, paranoia, insomnia, agitation and anxiety can last anywhere from 3 – 21 days.
References
- 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, et al. Clinical course of gamma-hydroxybutyrate overdose. Annals of Emergency Medicine 1998; 31:716-722.
Toxicology Library
DRUGS and TOXICANTS
Dr Neil Long BMBS FACEM FRCEM FRCPC. Emergency Physician at Kelowna hospital, British Columbia. Loves the misery of alpine climbing and working in austere environments (namely tertiary trauma centres). Supporter of FOAMed, lifelong education and trying to find that elusive peak performance.