- Design
- Case report with nonlinear pharmacokinetic modelling
- 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 case report from an ICU modelled serial caffeine levels in a woman with severe caffeine intoxication. Her initial serum level was 140.6 mcg/mL and took 163 hours to fall to 1.7 mcg/mL.
The apparent half-life was 42.6 hours early on and 11.2 hours later, consistent with saturable (Michaelis-Menten) metabolism. Simulations predicted that, from starting levels of 300, 200 and 100 mcg/mL, it would take about 248, 154 and 55 hours respectively to fall below 50 mcg/mL.
The usual half-life of caffeine — a few hours — does not apply in overdose. When metabolism saturates, elimination slows sharply, so toxicity lasts much longer than expected. That has a bearing on how long to monitor, and on early discussion of extracorporeal removal when levels are very high.
- In severe caffeine overdose, expect elimination to be much slower than the normal half-life suggests.
- Plan monitoring for days, not hours, when the initial level is very high.
- Repeat caffeine levels to track the fall rather than extrapolating from one value.
- Discuss extracorporeal removal with toxicology early when levels and toxicity are severe.
Why it matters
Caffeine overdose from tablets and energy products is rising, and the standard half-life badly underestimates how long toxicity lasts.
Don't overread it
This model rests on a single patient; the predicted times are estimates, not population norms.
The statistics, in plain English
Michaelis-Menten elimination means the body clears a fixed maximum amount per hour when enzymes are saturated, so the higher the level, the longer the apparent half-life.
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