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: A

Rationale: Finasteride, a 5-alpha reductase inhibitor, is prescribed as Proscar for benign prostatic hyperplasia (BPH) but also as Propecia for male pattern baldness, reducing dihydrotestosterone levels to slow hair loss. Without a prostate disorder, baldness becomes a plausible alternative indication. Erectile dysfunction isn't treated by finasteride-it may even cause it as a side effect-making that question irrelevant. Stomach ulcers and high blood pressure have no connection to finasteride's mechanism, which targets androgen pathways, not gastrointestinal or cardiovascular systems. Asking about baldness aligns with finasteride's dual use, probing a condition tied to its action on hair follicles, offering a logical explanation for its prescription in the absence of BPH, and guiding the nurse's understanding of the client's treatment rationale.

Correct Answer: C

Rationale: Chronic renal failure impairs kidney excretion, critical for drugs cleared renally-like metformin-raising toxicity risk if doses aren't adjusted, a targeted concern. Liver compensation aids metabolism, not excretion, so effectiveness isn't assured. Toxicity from all drugs assumes universal renal clearance, too broad. Decreased effectiveness ignores accumulation risks. Assessing for renal-excreted drugs' toxicity aligns with kidney function's role, ensuring safety by checking specific drug profiles.

Correct Answer: D

Rationale: Teratogenic drugs (e.g., thalidomide) cause fetal harm, absolute no-go in pregnancy, per safety. Category A is safe (e.g., levothyroxine). Category B has no human risk (e.g., metformin). ‘Cautionary' isn't a class-teratogenic fits X or known risks. Refusing teratogens protects the fetus, a clear rule.

Correct Answer: B

Rationale: Methylphenidate boosts dopamine in prefrontal cortex, enhancing focus/attention in ADHD-per neuroscience-not blocking PNS, reducing levels, or deactivating areas. Activation explains efficacy, per mechanism.