A 60-year-old epileptic woman who has been on the same dose of phenytoin for 20 years develops cerebellar ataxia with nystagmus. Her other medication consists of folic acid, hormone replacement therapy (HRT) and furosemide prescribed by the GP for ankle swelling and mild hypertension. She is referred to A&E. Routine investigations reveal an elevated plasma creatinine, normal plasma potassium and calcium, hypoalbuminaemia and proteinuria. The phenytoin concentration is 15 mg/L (therapeutic reference range 10-20 mg/L). A diagnosis of nephrotic syndrome is made and the cerebellar signs are attributed to phenytoin toxicity. Which of the following is likely to be correct?

Correct Answer: D

Rationale: Phenytoin toxicity (ataxia, nystagmus) occurs despite a ‘normal' total plasma level (15 mg/L) due to nephrotic syndrome's hypoalbuminemia. Normally, phenytoin is 90% protein-bound, with 10% free (active). Low albumin increases the free fraction (e.g., to 20%), raising CNS exposure despite a therapeutic total level. Creatinine doesn't typically interfere with phenytoin assays; they're reliable unless specific lab issues exist. Furosemide doesn't alter the blood-brain barrier for phenytoin; no evidence supports this. Oestrogen in HRT doesn't directly enhance phenytoin's CNS toxicity; it may affect metabolism, but not here. Cerebrovascular events don't fit the drug-related context. The increased free fraction explains toxicity, necessitating free level monitoring in hypoalbuminemia.

Correct Answer: C

Rationale: Valproate belongs to the category class of anticonvulsants, which means it is primarily used to treat seizures and epilepsy. Additionally, valproate also has properties that make it effective in the treatment of vascular headaches, such as migraines. It is not an anticoagulant, antianxiety medication like benzodiazepines, or a mood stabilizer.

Correct Answer: C

Rationale: Codeine sulfate, a narcotic analgesic, commonly causes constipation as a side effect. It works by binding to opioid receptors in the central nervous system, which can slow down gastrointestinal motility, leading to constipation. Clients taking codeine sulfate should be advised to increase their fluid intake, eat high-fiber foods, and possibly use stool softeners to prevent or alleviate constipation. Monitoring for constipation and providing appropriate interventions are essential to improve the client's comfort and prevent complications.

Correct Answer: B

Rationale: Sedatives and hypnotics are drugs that act as depressants on the central nervous system. They slow down brain activity, leading to relaxation, drowsiness, and in higher doses, inducing sleep. These drugs are commonly used to reduce anxiety, promote sleep, or induce anesthesia. Therefore, the correct classification for sedatives and hypnotics is as depressants.

Correct Answer: B

Rationale: Metformin (Glucophage) is a biguanide medication used to manage type 2 diabetes. While it is generally well-tolerated, one of its rare but serious adverse effects is lactic acidosis, a condition characterized by the buildup of lactic acid in the bloodstream. This can occur in patients with renal impairment or other risk factors. Hypoglycemia is uncommon with metformin alone, and GI distress, though common, is not life-threatening. Somnolence is not typically associated with metformin. Therefore, lactic acidosis is the most specific and serious adverse effect.