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Carbamazepine decreases antihypertensive effect of nilvadipine
Norio Yasui-Furukori1, Tomonori Tateishi
1Department of Clinical Pharmacology, Hirosaki University School of Medicine, Japan.
Insights
Carbamazepine can reduce the effectiveness of the antihypertensive drug nilvadipine by lowering its plasma concentration. This drug interaction may lead to dangerously high blood pressure, requiring careful monitoring.
Area of Science:
- Pharmacology
- Clinical Medicine
- Drug Interactions
Background:
- Hypertension management requires effective antihypertensive agents.
- Psychiatric conditions often necessitate psychotropic medications.
- Concomitant administration of multiple drugs can lead to complex interactions.
Observation:
- A patient with hypertension and psychiatric symptoms was treated with haloperidol, nilvadipine, and subsequently carbamazepine.
- Abnormally high blood pressure occurred during coadministration of carbamazepine and nilvadipine.
- Nilvadipine plasma concentrations were undetectable during carbamazepine treatment.
Findings:
- Carbamazepine coadministration led to a significant decrease in nilvadipine plasma concentrations.
- The antihypertensive effect of nilvadipine was diminished during concurrent carbamazepine use.
- Carbamazepine likely induced cytochrome P450 3A (CYP3A), leading to increased nilvadipine metabolism.
Implications:
- Clinicians should be aware of the potential interaction between carbamazepine and nilvadipine.
- Monitoring blood pressure is crucial when these drugs are used together.
- This interaction highlights the importance of considering drug metabolism pathways in polypharmacy.
Abstract:
A 59-year-old male who had suffered from hypertension for 21 years was admitted because of manic and delusional symptoms. He was treated with 12 mg/day of haloperidol for psychotic symptoms and 8 mg/day of nilvadipine for hypertension. Due to insufficient effect of haloperidol on the patient's manic symptoms, carbamazepine was added to these medications. Abnormally high blood pressure was observed during carbamazepine coadministration, and it returned gradually to normal range after its discontinuation. Retrospective analyses revealed that the plasma concentrations of nilvadipine were undetectable during carbamazepine treatment. The clinical course and laboratory findings suggest that carbamazepine decreased the plasma concentration and hence the antihypertensive effect of nilvadipine probably via CYP3A induction. This interaction between nilvadipine and carbamazepine should be kept in mind when these drugs are administered concomitantly.