Severe oral phenytoin overdose does not cause cardiovascular morbidity

To evaluate the potential for cardiovascular toxicity from severe oral phenytoin overdose.

Fifty-seven patients admitted during a two-year period to an inner-city hospital for severe oral phenytoin overdose, which is defined as a peak level of 40 micrograms/mL or more.

Case records were reviewed retrospectively for symptoms and signs of phenytoin toxicity, especially circulatory effects. Baseline and toxic 12-lead ECGs, when available, were reviewed in detail. Continuous variables were compared using either paired or unpaired t tests, as appropriate. Significance was taken as P less than or equal to .05.

Mean peak phenytoin level was 49.4 +/- 7.7 micrograms/mL. Continuous single-lead ECG monitoring in 36 patients (63%) for a mean of 26.5 +/- 21.6 hours revealed no incidents of dysrhythmia requiring treatment. ECGs recorded during toxicity in 52 cases (91%) revealed no clinically significant abnormalities attributable to phenytoin. ECGs during toxic and baseline states were available for detailed analysis in 15 cases. Ten patients exhibited an increase in PR interval (mean, 19 +/- 10 ms) when toxic, whereas five had a decrease (mean, 18 +/- 11 ms) compared with nontoxic records. No change in heart rate, QRS duration, or corrected QT interval was observed. There were no circulatory complications and no deaths.

Cardiovascular toxicity is rarely a manifestation of oral phenytoin overdose. Routine management of stable patients with severe phenytoin overdose in a monitored setting is not mandatory.