LAS VEGAS — Dietary risks among patients with hypertension that take calcium channel blockers are widely underappreciated by clinicians, according to a researcher at the American Academy of Nurse Practitioners 26th Annual NP meeting.

Potentially deadly interactions can result from seemingly benign substances like grapefruit, warned Amelie Hollier, DNP, FNP-BC, president and CEO of Advanced Practice Education Associates in Lafayette, Louisiana.

Calcium channel blockers require CYP3A4 enzymes for metabolism, but it is easy to miss a patient’s use of CYP3A4 inhibitors like macrolides, some statins and even grapefruit juice when obtaining a clinical history.

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“The greatest effects seen in CYP3A4 tends to be the DHP calcium agonists,” Hollier said. “Patients on amlodipine (Norvasc) need to worry about grapefruit juice.”

Grapefruit juice can inhibit CYP3A4 for several days or even weeks, Hollier said. Yet there is a widely held and dangerous belief among clinicians that it is safe to have grapefruit or grapefruit juice in the morning and to take calcium channel blockers in the evening.

That can cause a 35% unmetabolized ‘remainder’ of calcium channel blocker in the patient after one day, Hollier explained, and by day four an intended 60 mg dose may really be 140 mg. “An elderly lady will not be able to stand at this dose,” she said.

Hollier added that levels of felodipine (Plendil), another calcium channel blocker, higher 300% of the intended dose could result in death. “These patients should not be drinking grapefruit.”

Orange marmalade poses a similar drug interaction risk, Hollier added, though most other citrus fruits, including oranges, appear to be safe for patients on calcium agonists.

“There’s a lot of data coming out now about cranberries and cherries, but we are not at a point where we can say patients should stop [consuming these fruits],” Hollier said.

Hollier reported no financial conflicts of interest.

Hollier A. “Hypertension management: developing treatment strategies in primary care.” Presented at: 26th Annual American Academy of Nurse Practitioners Conference, 2011: Las Vegas, Nevada.

Bryant Furlow is a medical writer and award-winning investigative healthcare journalist based in Albuquerque, New Mexico.