A patient with Parkinson's disease is prescribed Carbidopa/Levodopa. Which of the following statements by the nurse is most accurate regarding this medication?

A. Avoid caffeine while taking this medication: Theophylline is a methylxanthine, similar in structure and effect to caffeine. Concurrent use can increase CNS stimulation and risk of side effects such as insomnia, tachycardia, and tremors. Avoiding caffeine helps prevent toxicity and unwanted stimulation.
B. Crush your extended-release tablet and mix it with apple sauce for easier consumption: Extended-release formulations should never be crushed, as this can lead to rapid absorption and potentially toxic drug levels. Theophylline has a narrow therapeutic index, and proper dosing is critical.
C. Take this medication as needed when you are not feeling well: Theophylline is a maintenance medication meant to be taken on a regular schedule. Taking it only as needed undermines its therapeutic effectiveness and can lead to inconsistent symptom control.
D. Consume a high-protein diet: While diet can influence drug metabolism, there is no routine recommendation for a high-protein diet with Theophylline. In fact, sudden dietary changes can alter its metabolism, requiring careful monitoring of serum drug levels.

A. It increases the metabolism of drugs in the liver: Grapefruit juice actually inhibits, rather than increases, the activity of liver enzymes particularly CYP3A4 resulting in slower drug metabolism and higher plasma concentrations of certain medications.
B. It decreases the absorption of medications: Grapefruit juice does not generally reduce drug absorption. In fact, by inhibiting intestinal enzymes, it can increase the absorption and bioavailability of some drugs, potentially raising them to toxic levels.
C. It only affects medications taken in the morning: The interaction is not time-specific. Grapefruit juice can affect drug metabolism even when consumed hours apart from the medication, as enzyme inhibition can persist for up to 24–72 hours.
D. It blocks the action of enzymes, leading to increased drug levels in the blood: Grapefruit juice inhibits cytochrome P450 enzymes especially CYP3A4 in the intestinal wall. This results in decreased drug breakdown and higher systemic concentrations, increasing the risk of adverse effects and toxicity.