A nurse is caring for a client who has Parkinson's disease and a new prescription for levodopa. The nurse should identify which of the following medications can interact with levodopa to cause a life-threatening complication?

Levodopa is a dopamine precursor that crosses the blood-brain barrier to treat Parkinson's disease by replenishing depleted striatal dopamine. When combined with non-selective monoamine oxidase inhibitors (MAOIs), it can trigger a massive release of catecholamines, leading to a dangerous hypertensive crisis. This sympathomimetic surge results from the simultaneous increase in dopamine synthesis and the inhibition of its metabolic breakdown. Rationale: A. Phenelzine is a non-selective MAOI that, when taken with levodopa, can lead to a life-threatening hypertensive crisis. This occurs because levodopa increases dopamine levels while phenelzine prevents the enzymatic breakdown of monoamines, resulting in excessive systemic vasoconstriction. The nurse must ensure a washout period of at least 14 days between these two specific pharmacological agents. B. Ibuprofen is a non-steroidal anti-inflammatory drug that does not typically have a life-threatening interaction with levodopa. While all medications should be monitored for general side effects, ibuprofen does not interfere with the dopaminergic pathways or metabolic breakdown of levodopa. It is generally considered safe for managing mild musculoskeletal pain in patients with Parkinson's disease. C. Diphenhydramine is an antihistamine with anticholinergic properties that is sometimes used as an adjunct in Parkinson's therapy to reduce tremors. It does not cause a life-threatening complication when paired with levodopa; in fact, it may provide synergistic benefits for motor symptoms. However, the nurse should monitor the patient for increased sedation and urinary retention. D. Vitamin B12 is a water-soluble vitamin essential for neurological health and does not interact dangerously with levodopa. It is often pyridoxine (Vitamin B6) that is of concern, as B6 can increase the peripheral conversion of levodopa, reducing its efficacy. Vitamin B12 supplementation is generally safe and does not pose a risk for hypertensive or catecholamine-related emergencies.