A client taking a calcium channel blocker is seen in the clinic and receives a diagnosis of drug toxicity. When collecting the nursing history, consumption of what product would indicate the likely cause of this drug toxicity?

A. One to two alcoholic drinks daily: While alcohol can interact with many medications, including calcium channel blockers, moderate alcohol consumption is less likely to cause drug toxicity compared to grapefruit juice, which directly affects the metabolism. B. Dairy products in the morning: Dairy products do not typically interact with calcium channel blockers in a way that would lead to drug toxicity. This dietary habit is unlikely to be the cause of the client's symptoms. C. Grapefruit juice with meals: Grapefruit juice is known to inhibit the CYP3A4 enzyme, which plays a significant role in the metabolism of many calcium channel blockers. This interaction can increase the concentration of the drug in the bloodstream, leading to toxicity. D. Aged cheese several times a week: Aged cheese contains tyramine, which can interact with certain medications like monoamine oxidase inhibitors (MAOIs), but it is not a concern for calcium channel blockers.