- Design
- Single-patient pharmacokinetic modelling with simulations
- Population
- One adult woman with severe caffeine intoxication in ICU
- Primary outcome
- Caffeine elimination kinetics and predicted duration of toxic exposure
- Effect
- Half-life 42.6 h early vs 11.2 h late; Vmax 27.2 mg/h, Km 17.7 mcg/mL
This short communication analysed serial serum caffeine concentrations in one woman admitted to intensive care with severe caffeine intoxication. The first level was 140.6 mcg/mL; it took 163 hours to fall to 1.7 mcg/mL.
Elimination was concentration-dependent: the apparent half-life was 42.6 hours early on and 11.2 hours later, fitting a Michaelis–Menten model with Vmax 27.2 mg/h and Km 17.7 mcg/mL. Simulations predicted that starting concentrations of 300, 200 and 100 mcg/mL would take 248, 154 and 55 hours to fall below 50 mcg/mL.
Caffeine tablets and energy-product overdoses are a growing cause of toxic presentations. The pharmacological point is that at high concentrations the enzyme is saturated, so clearance is fixed and slow — the toxic period is much longer than the textbook half-life of a few hours suggests. That affects decisions about how long to monitor and when extracorporeal removal is worth it.
- Expect prolonged toxicity in severe caffeine overdose; the usual 3–6-hour half-life does not apply at toxic levels.
- Measure serial caffeine levels where available and plan monitoring for days, not hours.
- Consider haemodialysis early in life-threatening caffeine toxicity, since natural clearance is slow.
- Monitor for arrhythmias, hypokalaemia and seizures throughout the prolonged exposure.
Why it matters
It corrects the intuition that caffeine clears quickly, which can lead to premature step-down of monitoring.
Don't overread it
The model is fitted to one patient; the predicted times are illustrative, not a validated nomogram.
The statistics, in plain English
Michaelis–Menten elimination means that above the Km (here about 18 mcg/mL) the body removes a roughly fixed amount per hour rather than a fixed fraction, so the higher the level, the disproportionately longer it takes to fall.
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