Caffeine and its metabolites in caffeine overdose cause falsely elevated serum theophylline measurements.

In two cases of caffeine overdose, the elimination of caffeine appeared to be non-linear. Measurements of theophylline concentrations after caffeine overdose were method-dependent. After caffeine overdose, quantitation of caffeine is not clinically indicated, because of the variable correlation between concentration and toxic effects. Our data suggest that the measurement of theophylline concentrations after caffeine overdose is also not clinically indicated, and may be misleading if a nonspecific method is used.