Related Experiment Video
Updated: Apr 20, 2026
Cell-based Calcium Assay for Medium to High Throughput Screening of TRP Channel Functions using FlexStation 3
Published on: August 17, 2011
Calcium channel blocker-clarithromycin drug interaction did not increase the risk of nonvertebral fracture: a
Lisa-Ann Fraser1, Salimah Z Shariff2, Eric McArthur2
1Western University, London, ON, Canada LisaAnn.Fraser@sjhc.london.on.ca.
Insights
In elderly patients on calcium channel blockers (CCBs), clarithromycin coprescription did not increase nonvertebral fracture risk compared to azithromycin. This finding is crucial for medication safety in older adults.
Area of Science:
- Geriatric Medicine
- Pharmacology
- Cardiology
Background:
- Elderly patients using calcium channel blockers (CCBs) face risks of falls and fractures.
- CCBs are metabolized by cytochrome P450 3A4 (CYP3A4).
- Clarithromycin inhibits CYP3A4, potentially increasing CCB levels, while azithromycin does not.
Purpose of the Study:
- To investigate the association between clarithromycin vs. azithromycin coprescription and fracture risk in elderly CCB users.
- To assess medication safety concerning drug interactions and fracture outcomes.
Main Methods:
- Population-level retrospective cohort study in Ontario, Canada (2003-2012).
- Included older adults (mean age 76) on CCBs, newly prescribed clarithromycin or azithromycin.
- Assessed nonvertebral fracture risk within 30 days of new coprescription.
Main Results:
- No significant baseline characteristic differences between clarithromycin and azithromycin groups.
- Amlodipine was the most common CCB used.
- Coprescribing clarithromycin was not associated with a higher 30-day risk of nonvertebral fracture (OR 1.23, 95% CI 0.94-1.60).
Conclusions:
- Concurrent use of clarithromycin with CCBs in older adults did not significantly increase the 30-day risk of nonvertebral fracture compared to azithromycin.
- This suggests a potentially safer interaction profile than initially hypothesized based on CYP3A4 inhibition.
Background:
Calcium channel blocker (CCB) use in elderly patients lowers blood pressure and can increase the risk of falls and fractures. These drugs are metabolized by the cytochrome P450 3A4 (CYP3A4) enzyme, and blood concentrations of these drugs may rise to harmful levels when CYP3A4 activity is inhibited. Clarithromycin is an inhibitor of CYP3A4, whereas azithromycin is not.
Objective:
In older patients taking a CCB, we investigated whether coprescription of clarithromycin, compared with azithromycin, was associated with a higher risk of fracture.
Methods:
This was a population-level retrospective cohort study in Ontario, Canada, from 2003 to 2012 of older adults (mean age = 76 years) newly prescribed clarithromycin (n = 96 226) or azithromycin (n = 94 083) while taking a CCB (amlodipine, nifedipine, felodipine, verapamil, diltiazem). The outcome assessed within 30 days of a new coprescription was a nonvertebral fracture.
Results:
There were no differences in measured baseline characteristics between the clarithromycin and azithromycin groups. Amlodipine was the most commonly prescribed CCB (more than 50% of patients). Coprescribing clarithromycin, versus azithromycin, was not associated with a higher 30-day risk of nonvertebral fracture (124 patients of 96 226 taking clarithromycin [0.13%] vs 98 patients of 94 083 taking azithromycin [0.10%]; odds ratio = 1.23 [95% CI = 0.94-1.60]; P = 0.134).
Conclusions:
Among older adults taking a CCB, concurrent use of clarithromycin, compared with azithromycin, was not associated with a statistically significantly greater 30-day risk of nonvertebral fracture.
Related Concept Videos
01:17Antiepileptic Drugs: Calcium Channel Blockers
Calcium channel blockers exert their antiepileptic effects by targeting T-type calcium channels, which are integral to transmitting nerve signals in the central nervous system. These channels allow the passage of calcium ions, which are vital for neuronal communication. By inhibiting T-type calcium channels, calcium channel blockers effectively reduce the release of neurotransmitters and...
01:18Antihypertensive Drugs: Action of Calcium Channel Blockers
01:20Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers
Verapamil, a calcium channel blocker, inhibits calcium movement across myocardial cell membranes and vascular smooth muscle. This results in the dilation of coronary and...
01:25Antianginal Drugs: Calcium Channel Blockers and Ranolazine
CCBs, a diverse class that includes dihydropyridines (nifedipine) and diphenylalkylamines (verapamil and diltiazem), exert their effect by blocking calcium channels in cardiac and smooth muscle cells. This...
01:22Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers
Class 1A Antiarrhythmic Drugs: These drugs work by moderately blocking sodium channels,...
01:30Drug toxicity: Drug–Drug Interaction