A nurse is teaching a client who has a seizure disorder and has a new prescription for phenytoin. Which of the following client statements indicates an understanding of the teaching?

Choice A rationale Dark urine while taking phenytoin is not an expected finding and may indicate hepatotoxicity. Phenytoin is metabolized by the liver, and liver damage can alter bilirubin metabolism, leading to a buildup of conjugated bilirubin in the blood. This can result in dark, tea-colored urine and jaundice, which are signs of a serious adverse drug reaction. Choice B rationale Taking an extra dose of phenytoin after a breakthrough seizure is unsafe and can lead to phenytoin toxicity. The therapeutic index of phenytoin is narrow, meaning the range between a therapeutic dose and a toxic dose is small. Increasing the dose without a physician's guidance can cause severe central nervous system depression, ataxia, and nystagmus. Choice C rationale Phenytoin has a narrow therapeutic range (10-20 mcg/mL), making it crucial to monitor blood levels to ensure efficacy while avoiding toxicity. Regular blood tests are essential to confirm the medication is within this range. Monitoring helps to prevent sub-therapeutic levels that could lead to seizures or toxic levels that could cause adverse effects. Choice D rationale Antacids can decrease the absorption of phenytoin from the gastrointestinal tract, thereby reducing its therapeutic effectiveness. The antacid's calcium and magnesium ions can chelate with the phenytoin molecule, forming an insoluble complex. This reduces the amount of drug available to be absorbed, potentially leading to a sub-therapeutic level and an increased risk of seizures.