[Drug interactions with calcium inhibitors in man]
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Insights
Calcium antagonists (CA) and beta-blockers offer combined benefits for angina and hypertension but increase side effect risks. Verapamil and diltiazem notably interact with digoxin and other drugs, impacting patient safety.
Area of Science:
- Pharmacology and Cardiovascular Therapeutics
- Drug Interactions and Pharmacokinetics
Context:
- Cardiovascular drugs, particularly calcium antagonists (CA) and beta-blockers, are frequently used for stable effort angina and hypertension.
- Combined therapy with CA and beta-blockers can enhance efficacy but poses risks for patients with specific cardiac dysfunctions.
- Understanding drug interactions is crucial for optimizing cardiovascular treatment and preventing adverse events.
Purpose:
- To review and summarize the pharmacokinetic and pharmacodynamic interactions of primary calcium antagonists (verapamil, diltiazem, nifedipine) with commonly prescribed cardiovascular and other medications.
- To highlight the clinical significance of these interactions, particularly concerning digoxin, quinidine, and immunosuppressants.
Summary:
- Calcium antagonists (CA) like verapamil (VE) and diltiazem (DTZ) can increase bioavailability and alter elimination half-life (T1/2) of drugs such as propranolol and digoxin, increasing intoxication risk.
- Nifedipine (NF) shows less significant interactions with digoxin compared to VE and DTZ, especially in heart failure patients.
- VE and DTZ also affect the metabolism of other drugs, decreasing clearance of antipyrine and carbamazepine, and significantly increasing ciclosporin levels.
Impact:
- Highlights the potential for serious adverse events, such as digitalis intoxication, due to drug-drug interactions involving cardiovascular medications.
- Informs clinical practice regarding the careful selection and monitoring of patients on combined cardiovascular therapies, especially those with pre-existing cardiac conditions.
- Emphasizes the need for healthcare professionals to be aware of the complex pharmacokinetic profiles of calcium antagonists and their implications for co-administered drugs.
Abstract:
The most common interactions concern cardiovascular drugs. The combination of calcium antagonists (CA) and beta-blockers is more effective than single-agent therapy in stable effort angina and hypertension. But there is an increased risk of hemodynamic or electrophysiological side effects in patients with left ventricular or sinus dysfunction, or disturbances of conduction. Pharmacokinetic interactions have been observed in particular with verapamil (VE) which increases propranolol bioavailability. VE increases the T1/2 of elimination and plasma digoxin concentration following single or prolonged administration. The primary mechanism appears to be renal. These modifications increase the risk of digitalis intoxication. Diltiazem (DTZ) inconsistently increases steady state plasma digoxin levels. In healthy subjects, nifedipine (NF) increases plasma digoxin concentrations and decreases digoxin renal clearance. These findings have not been observed in patients with heart failure. NF therefore leads to less marked modifications in digitalis pharmacokinetics than do VE and DTZ. Nitrendipine and nicardipine interact only slightly with digoxin, and consequently there are no pharmacodynamic effects. In healthy subjects, VE increases quinidine t1/2 and markedly decreases its metabolic clearance. Conversely, quinidine increases plasma NF levels. The primary CA are extensively metabolized by liver microsome oxidases. These result in interactions with the drugs that are also metabolized by these enzymes, or able to modify their activity. VE and DTZ decrease antipyrine and carbamazepine clearance. VE, DTZ and nicardipine lead to a marked increase in plasma ciclosporin levels. Cimetidine, but not ranitidine, increases plasma NF levels. The effects on VE are controversial. Prolonged rifampicin treatment decreases plasma VE levels.