Altered phenytoin clearance with febrile illness

Area of Science:

• Pediatric Neurology
• Clinical Pharmacology
• Pharmacokinetics

Background:

• Antiepileptic drugs (AEDs) are crucial for managing seizures in children.
• Understanding drug level fluctuations during illness is vital for effective treatment.
• Pediatric patients in chronic care facilities may have unique metabolic responses.

Purpose of the Study:

• To prospectively investigate changes in antiepileptic drug levels during febrile illnesses in pediatric patients.
• To determine the extent of phenytoin (PHT) level reduction during fever.
• To explore potential mechanisms behind observed drug level alterations.

Main Methods:

• Prospective study involving 14 boys in a pediatric chronic care facility.
• Monthly blood and 24-hour urine collections.
• Additional samples collected during febrile episodes (temperature > 101°F for > 24 hours).

Main Results:

• Phenytoin (PHT) levels decreased by over 40% from baseline in 80% of febrile illnesses.
• Mean PHT levels dropped significantly from 16.7 µg/mL before illness to 8.2 µg/mL during illness (p < 0.001).
• No significant alterations in PHT binding or absorption were detected during illness.

Conclusions:

• Febrile illnesses are associated with substantial reductions in phenytoin levels in pediatric patients.
• The most likely cause of PHT level decrease is the induction of the hepatic oxidative enzyme system during fever.
• These findings highlight the need for therapeutic drug monitoring during febrile episodes in this population.