A nurse in a primary care clinic is caring for a 40-year-old male client who was diagnosed with asthma during childhood.

Complete the following sentence by using the lists of options: The client is most at risk for developing

________

, due to their

________

.

Requires Immediate Follow-Up

• Alcohol use While not a strict contraindication, alcohol can interfere with phenytoin metabolism, increasing the risk of toxicity or subtherapeutic levels. It also lowers the seizure threshold. This pattern of alcohol use warrants counseling and follow-up.
• Amenorrhea (last menstrual period 3 months ago) This may indicate pregnancy, which is critical to assess because phenytoin is teratogenic (FDA Pregnancy Category D). Immediate follow-up is needed to evaluate for pregnancy and consider alternative treatment options or additional supplementation (e.g., folic acid).
• Diazepam use Diazepam and phenytoin are both central nervous system depressants and can interact pharmacokinetically. Diazepam may increase phenytoin levels and vice versa, requiring close monitoring for sedation or toxicity.

Not Concerning

• Vegetarian diet and multivitamin use This is not a contraindication and does not require immediate follow-up. However, long-term phenytoin use can affect folate and vitamin D metabolism, so continued multivitamin use may be beneficial.

Take-home points

• Phenytoin has a narrow therapeutic index and interacts with many substances, including alcohol and benzodiazepines.
• Women of childbearing age should be screened for pregnancy before initiating phenytoin due to its teratogenic potential.
• Amenorrhea in a client on antiseizure medication should prompt evaluation for pregnancy or endocrine dysfunction.
• Nutritional status and supplementation should be monitored in clients on long-term phenytoin, especially for folate and vitamin D.

Choice A rationale: A temperature of 36.4°C (97.6°F) is within the normal oral temperature range (36.1°C to 37.2°C). Phenytoin does not have contraindications related to normal body temperature. Fever or hypothermia may influence drug metabolism in extreme cases, but this client’s temperature is stable and does not interfere with phenytoin pharmacokinetics or safety. Therefore, this finding does not require immediate follow-up as it poses no contraindication to phenytoin therapy.

Choice B rationale: Being vegetarian and taking a multivitamin daily is not a contraindication to phenytoin. However, phenytoin may interfere with the absorption of certain vitamins, particularly folic acid, vitamin D, and vitamin K. While vegetarians may have lower dietary intake of some nutrients, this is not an absolute contraindication. Monitoring for deficiencies is prudent, but this finding does not necessitate immediate follow-up or discontinuation of phenytoin.

Choice C rationale: Alcohol consumption significantly affects phenytoin metabolism. Chronic alcohol use induces hepatic enzymes, reducing phenytoin levels and risking seizure recurrence. Conversely, acute alcohol intake inhibits metabolism, increasing phenytoin levels and toxicity risk. This bidirectional interaction complicates seizure control and increases adverse effects such as ataxia, nystagmus, and CNS depression. Therefore, regular alcohol use requires immediate follow-up to assess risk and reinforce abstinence during phenytoin therapy3.

Choice D rationale: A missed menstrual period for three months raises concern for possible pregnancy. Phenytoin is teratogenic and associated with fetal hydantoin syndrome, including craniofacial anomalies and developmental delays. It also reduces the efficacy of hormonal contraceptives by inducing CYP450 enzymes. Therefore, pregnancy must be ruled out before initiating phenytoin, and non-hormonal contraception should be advised. This finding requires immediate follow-up due to potential fetal harm5.

Choice E rationale: Diazepam, a benzodiazepine, interacts with phenytoin by altering its serum concentration. Diazepam may increase or decrease phenytoin levels unpredictably, leading to toxicity or subtherapeutic effects. Symptoms of phenytoin toxicity include nystagmus, ataxia, and confusion. Co-administration requires close monitoring of phenytoin levels and possible dose adjustments. This interaction is clinically significant and warrants immediate follow-up to ensure safe concurrent use7.

Choice F rationale: A soft, nontender abdomen with normoactive bowel sounds is a normal physical finding and does not interfere with phenytoin absorption or metabolism. Gastrointestinal status is relevant if there is malabsorption or vomiting, which could affect oral drug bioavailability. However, in this case, the GI exam is unremarkable and does not present a contraindication to phenytoin therapy. No follow-up is required for this finding.

Choice G rationale: Full range of motion and the ability to maintain flexion against resistance in all extremities indicate intact neuromuscular function. Phenytoin does not have contraindications related to baseline muscle strength or motor function. Neurological assessment is important for monitoring phenytoin toxicity, but normal strength and coordination do not require follow-up. This finding supports the client’s current functional status and is not a contraindication.