(39) A 55- year old man begins taking phenytoin a seizure disorder that devel;oped following cerebral infections. At a dose of 300mg daily , his serum phenytoin concentration is 12 micrograms( normal therapeutic range is 10-20) and breakthrough seizures occur. AT a dose of 400 mg daily, serum phenytoin concentration is 28 microgram/mL and he has a symptom of toxicity, including ataxia and somnolence. Which of the following best explains the large increase in the patients serum phenytoin concentration? (A) Accidental ingestion of excess medication (B) Age-related decrease in cytochrome P450-enzyme activity (C) Age-related decrease in liver cell mass (D) Decreased glucuronidation in the liver (E) Saturation of an enzyme pathway that metabolizes phenytoin
(39) A 55- year old man begins taking phenytoin a seizure disorder that devel;oped following cerebral infections. At a dose of 300mg daily , his serum phenytoin concentration is 12 micrograms( normal therapeutic range is 10-20) and breakthrough seizures occur. AT a dose of 400 mg daily, serum phenytoin concentration is 28 microgram/mL and he has a symptom of toxicity, including ataxia and somnolence. Which of the following best explains the large increase in the patients serum phenytoin concentration?
(A) Accidental ingestion of excess medication
(B) Age-related decrease in cytochrome P450-enzyme activity
(C) Age-related decrease in liver cell mass
(D) Decreased glucuronidation in the liver
(E) Saturation of an enzyme pathway that
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