Half-life of GHB
The half-life of Gamma-Hydroxybutyric acid (GHB) is short, ranging from 20 to 60 minutes in the body. 1
Pharmacokinetic Properties of GHB
GHB has several important pharmacokinetic characteristics:
- Absorption: Rapid gastric absorption (5-45 minutes) 1
- Distribution: Volume of distribution is approximately 0.49 ± 0.9 L/kg 1
- Elimination half-life: 20-60 minutes 1, 2
- Detection window:
Clinical Significance of GHB's Short Half-life
The short half-life of GHB has several important clinical implications:
- Rapid onset of action: Effects begin within 15 minutes of ingestion 3
- Duration of effects: 3-6 hours when taken alone, but can be prolonged to 36-72 hours when combined with alcohol or other drugs 3
- Forensic considerations: The short detection window (3-10 hours) necessitates rapid sample collection in suspected cases 2
Metabolism and Elimination
GHB follows complex elimination kinetics:
- At recreational or abuse doses, GHB appears to follow zero-order kinetics rather than first-order kinetics 4
- This means the body eliminates GHB at a constant rate (approximately 18 mg/L per hour) rather than a constant proportion 4
- Only about 1-5% of the GHB dose is recoverable in urine 2
Clinical Toxicology Considerations
When managing potential GHB intoxication, it's important to understand:
- Toxic effects: GHB can cause dose-dependent CNS depression, with lethal doses reported at approximately 60 mg/kg 1
- Sampling timing: Due to the short half-life, expeditious sampling is critical when evidence of GHB use is required 2
- Back-calculation limitations: Using first-order kinetics to back-calculate GHB levels can lead to unrealistic estimates; zero-order kinetics are more appropriate for abuse doses 4
Common Pitfalls in GHB Testing and Management
- Misidentification: GHB is often misidentified as alcohol intoxication due to similar symptoms
- Missed detection: The short half-life means GHB may be undetectable in biological samples if collection is delayed
- Precursor drugs: GHB precursors (GBL and 1,4-butanediol) are rapidly converted to GHB in the body (t½ ~1 min) and should be considered in testing 2
- Combined intoxication: When GHB is combined with alcohol, its effects and detection window are significantly prolonged 3
Understanding GHB's short half-life is crucial for appropriate clinical management, forensic investigation, and interpretation of toxicology results in cases of suspected use or intoxication.