A man with previously well-controlled hypertension developed sudden loss of blood pressure control 2 weeks after starting rifampin therapy, attributed to rifampin-induced CYP3A4 enzyme induction reducing plasma concentrations of amlodipine by up to approximately 80%.
Key Findings
Background
A patient with previously well-controlled hypertension experienced sudden deterioration in blood pressure control temporally associated with rifampin initiation.
The patient was a man in his early 60s with a history of well-controlled essential hypertension.
Blood pressure deterioration occurred approximately 2 weeks after starting isoniazid-rifampin therapy for latent tuberculosis infection.
The patient presented with headache and newly uncontrolled hypertension.
Prior to rifampin initiation, blood pressure had been stable on an angiotensin receptor blocker and a calcium channel blocker.
Background
Rifampin is a potent inducer of CYP3A4 and can reduce plasma concentrations of calcium channel blockers such as amlodipine by up to approximately 80%.
Rifampin-induced cytochrome P450 enzyme induction was identified as the likely mechanism for the loss of antihypertensive effect.
The reduction in plasma concentrations of amlodipine attributed to CYP3A4 induction was reported as up to approximately 80%.
This substantial reduction in drug concentration was considered to have substantially diminished the antihypertensive effect of the calcium channel blocker.
Results
Blood pressure improved after escalation of antihypertensive therapy while antituberculosis treatment was continued without interruption.
Management involved increasing the intensity of antihypertensive therapy rather than discontinuing rifampin.
Antituberculosis treatment was continued without interruption, indicating that the drug-drug interaction was managed pharmacologically.
The case demonstrates that this interaction can be managed without compromising tuberculosis treatment.
Discussion
This case highlights the importance of structured medication review when evaluating sudden loss of blood pressure control in primary care.
The sudden deterioration in blood pressure was initially at risk of being misattributed to progression of essential hypertension rather than a drug-drug interaction.
The temporal association between rifampin initiation and loss of blood pressure control was key to identifying the interaction.
A structured medication review is recommended as a clinical approach when patients present with unexplained loss of blood pressure control.
What This Means
This research describes the case of a man in his early 60s whose blood pressure had been well-controlled for some time on two blood pressure medications — a type called an angiotensin receptor blocker and another called a calcium channel blocker (amlodipine). About two weeks after he started a standard antibiotic combination (isoniazid and rifampin) to treat a latent tuberculosis infection, his blood pressure suddenly became uncontrolled and he developed headaches. Rather than his underlying high blood pressure getting worse on its own, the culprit turned out to be rifampin interfering with his blood pressure medication.
Rifampin is known to strongly activate a liver enzyme called CYP3A4, which is responsible for breaking down many medications in the body. When this enzyme is activated, it breaks down drugs like amlodipine much faster than normal — reducing the amount of the drug in the bloodstream by as much as 80%. With so little amlodipine remaining active in his system, the medication was essentially unable to do its job of lowering blood pressure. Once doctors recognized this drug-drug interaction, they increased his blood pressure medications, and his blood pressure improved — all while continuing the tuberculosis treatment without interruption.
This research suggests that when patients who are taking certain blood pressure medications (particularly calcium channel blockers) start rifampin, healthcare providers should be alert to the possibility of a clinically significant drop in blood pressure medication effectiveness. Rather than assuming the patient's underlying condition has worsened, clinicians should consider reviewing all medications for potential interactions. This is especially relevant in primary care settings, where rifampin may be prescribed for latent tuberculosis and patients may also be on long-term medications for chronic conditions like hypertension.
Park J. (2026). Loss of blood pressure control after rifampin initiation: a clinically significant antihypertensive drug-drug interaction.. BMJ case reports. https://doi.org/10.1136/bcr-2026-273417