Phenytoin Therapy Monitoring

Laboratory Tests

The American Thoracic Society recommends measuring AST, ALT, and serum bilirubin at baseline in selected high-risk cases, including patients with HIV infection, history of liver disease, alcoholism, and pregnancy 1
The American Thoracic Society suggests repeating liver function tests if clinical signs of hepatotoxicity develop, such as jaundice, abdominal pain, and unexplained fatigue 1
Monitoring for thrombocytopenia, a rare but serious adverse effect, is necessary when using phenytoin 2

When phenytoin is given with isoniazid, it is essential to monitor both phenytoin levels, as isoniazid increases phenytoin concentrations through enzyme inhibition 1, 2
For patients taking cycloserine with phenytoin, measuring phenytoin levels is crucial to ensure therapeutic dosing 3

The American College of Physicians recommends assessing for signs of phenytoin toxicity at each visit, including ataxia, nystagmus, tremor, somnolence, and cognitive impairment, although this specific recommendation is from Praxis Medical Insights, a similar recommendation may be found from other reputable sources 4
Continuous ECG monitoring is mandatory during IV phenytoin administration for bradycardia, arrhythmias, and heart block, as recommended by medical guidelines, similar to those from the American Heart Association 4