Hypokalemia after theophylline intoxication. The effects of acute vs chronic poisoning.

To characterize the frequency and pattern of hypokalemia (serum potassium level less than 3.5 mmol/L) after theophylline poisoning, we prospectively evaluated 88 consecutive patients with theophylline intoxication (serum theophylline concentration greater than or equal to 0.165 mmol/L). This mean admission serum theophylline concentration of this cohort was 0.331 mmol/L, with a range of 0.165 to 0.982 mmol/L. The simultaneous mean serum potassium concentration was 3.36 mmol/L (range, 2.20 to 5.80 mmol/L). Fifty-three patients (60%) were hypokalemic on hospital arrival. When, on the basis of recent ingestion, patients were separated into acute, chronic, or acute-on-chronic categories of theophylline intoxication, significant differences in serum potassium were found: Patients with acute theophylline intoxication had a mean serum potassium concentration of 2.94 mmol/L; 85% were hypokalemic. In contrast, patients with chronic theophylline intoxication had a mean serum potassium concentration of 3.83 mmol/L, with a 32% frequently of hypokalemia. These data demonstrate that hypokalemia is common after theophylline intoxication and has a significantly higher incidence after acute overdose. The difference in the frequency of hypokalemia between patients with acute vs chronic intoxication has unclear origins but may be related to the disparities in clinical course (particularly the appearance of seizures and cardiac arrhythmias) that have been observed after acute vs chronic theophylline intoxication.