Amlodipine interactions with other medications
Amlodipine is rarely taken in isolation: it is combined with statins, other antihypertensive medications, and antibiotics, and people who train — also with sports supplements. Most such combinations are safe, but a few interactions have real clinical significance. The editorial team examines exactly how amlodipine interacts with other substances and where one should be attentive.
Two types of interactions
All drug interactions can be conditionally divided into pharmacokinetic and pharmacodynamic. Pharmacokinetic ones change the concentration of a drug in the blood — through an effect on absorption, metabolism, or excretion. Pharmacodynamic ones do not change the concentration but enhance or weaken the effect when two substances act in the same or opposite directions.
For amlodipine the key pharmacokinetic mechanism is metabolism in the liver by the enzyme CYP3A4. Substances that suppress this enzyme raise the concentration of amlodipine; substances that activate it lower it. At the same time, amlodipine itself is a weak inhibitor of CYP3A4 and is able to raise the level of some other drugs.
The pharmacodynamic interactions of amlodipine concern mainly blood pressure: other agents that lower pressure enhance its effect, and substances that raise pressure or retain fluid weaken it.
Because of the long half-life, changes in the concentration of amlodipine develop gradually, over days. This means that the consequences of an interaction may appear not immediately after starting a new drug but several days later.
CYP3A4 inhibitors and inducers
Strong CYP3A4 inhibitors — some azole antifungals (ketoconazole, itraconazole), HIV protease inhibitors (ritonavir), the macrolide antibiotics clarithromycin and erythromycin — can substantially raise the concentration of amlodipine. The FDA label recommends monitoring the patient for hypotension and edema in such cases.
The clinical significance of this interaction was shown by the population study of Gandhi and colleagues (2013), published in JAMA. In elderly people taking calcium channel blockers, the prescription of clarithromycin was associated with a higher risk of hospitalization with acute kidney injury and hypotension compared with azithromycin, which does not suppress CYP3A4. The greatest risk was observed precisely for the dihydropyridines, in particular amlodipine.
The opposite effect is produced by CYP3A4 inducers: rifampicin, carbamazepine, phenytoin, St. John's wort preparations. They accelerate the metabolism of amlodipine, lower its concentration and, as a result, its antihypertensive effect. If a person starts or stops taking such a drug, blood pressure should be monitored more often.
| Group | Examples | Effect on amlodipine | Possible consequence |
|---|---|---|---|
| Strong CYP3A4 inhibitors | Clarithromycin, itraconazole, ritonavir | ↑ concentration | Hypotension, edema, kidney damage |
| Moderate CYP3A4 inhibitors | Diltiazem, erythromycin | ↑ concentration | Enhancement of the effect |
| CYP3A4 inducers | Rifampicin, carbamazepine, St. John's wort | ↓ concentration | Insufficient blood pressure control |
| Grapefruit juice | Large amounts | Moderate ↑ | Usually little clinical significance |
Grapefruit juice suppresses CYP3A4 in the intestine. For amlodipine, unlike felodipine or nifedipine, this effect is small, because the drug's bioavailability is high to begin with. The instructions usually advise not to consume grapefruit in large amounts, but moderate consumption is rarely a problem.
Statins and immunosuppressants
Amlodipine itself weakly suppresses CYP3A4, and this is important for drugs with a narrow therapeutic range or a high risk of dose-dependent complications. The best-known example is simvastatin.
In 2011 the FDA updated its recommendations on simvastatin because of the risk of myopathy and rhabdomyolysis, which rises with an increase in its concentration. For patients taking amlodipine, the daily dose of simvastatin was limited to 20 mg. Atorvastatin, rosuvastatin, and pravastatin have fewer restrictions in this context, so a doctor can choose another statin if needed.
The FDA label also indicates that amlodipine may raise the concentration of cyclosporine and tacrolimus — immunosuppressants taken after organ transplantation. For these drugs, monitoring of the blood concentration is recommended after starting, changing the dose, or discontinuing amlodipine.
- Simvastatin— dose restriction because of the risk of myopathy.
- Lovastatin— also metabolized by CYP3A4, requires caution.
- Cyclosporine, tacrolimus— concentration monitoring.
- mTOR inhibitors(sirolimus, everolimus) — a possible increase in exposure.
People who combine statins with intense training should know that muscle pain and weakness are grounds for seeing a doctor and taking a creatine kinase test, rather than attributing everything to soreness.
Medications that affect blood pressure
The pharmacodynamic interactions of amlodipine are mostly predictable. Other antihypertensive agents — ACE inhibitors, ARBs, diuretics, beta-blockers, alpha-blockers — enhance the lowering of blood pressure. In most cases this is the very goal of combination therapy, but at the start or with dose changes episodes of hypotension are possible.
Phosphodiesterase type 5 inhibitors (sildenafil, tadalafil) also dilate blood vessels. The FDA label describes an additive lowering of pressure when combined with amlodipine. Nitrates and alpha-blockers combined with vasodilators can cause orthostatic hypotension, especially in elderly people.
On the other hand, the effect of amlodipine can be weakened by nonsteroidal anti-inflammatory drugs (which retain sodium and water), glucocorticoids, some decongestants with pseudoephedrine, and also substances with a pronounced sympathomimetic action.
Separately, the instructions of some countries mention intravenous dantrolene: in animal experiments the combination of verapamil with dantrolene caused fatal arrhythmias and hyperkalemia, so the combination of calcium channel blockers with intravenous dantrolene is recommended to be avoided.
Sports supplements and stimulants
People who train are often interested in how amlodipine combines with popular supplements. Protein, creatine, amino acids, vitamins, and most minerals have no clinically significant interactions with amlodipine. However, there are a few categories worth paying attention to.
Pre-workout complexes with stimulants — high doses of caffeine, synephrine, yohimbine — raise blood pressure and heart rate, effectively working against antihypertensive therapy. People with hypertension should discuss their use with a doctor.
Licorice extract (glycyrrhizin) in significant amounts causes sodium retention, potassium loss, and elevated blood pressure. Herbal supplements with St. John's wort can lower the concentration of amlodipine through induction of CYP3A4. «Drainage» and diuretic complexes can enhance dehydration and hypotension after training.
It is also worth remembering nonsteroidal anti-inflammatory drugs, which athletes often take for injuries. Regular intake of NSAIDs can raise blood pressure and reduce the effectiveness of antihypertensive therapy.
We also recommend reading our articles on the side effects of amlodipine, on why athletes need amlodipine, and on tests during its use.
Editorial conclusions
Most interactions of amlodipine are predictable and associated with two mechanisms: metabolism through CYP3A4 and an additive effect on blood pressure.
The greatest clinical significance belongs to strong CYP3A4 inhibitors, in particular clarithromycin, the dose restriction of simvastatin, and the increase in the levels of cyclosporine and tacrolimus.
For people who train, the main risks are stimulants in pre-workout complexes, NSAIDs, and diuretic supplements, which can either weaken the drug's effect or enhance hypotension.
References
- Norvasc (amlodipine besylate) tablets. Prescribing information. U.S. Food and Drug Administration.
- Gandhi S, Fleet JL, Bailey DG, et al. Calcium-channel blocker–clarithromycin drug interactions and acute kidney injury and hypotension in older adults. JAMA. 2013;310(23):2544–2553.
- U.S. Food and Drug Administration. FDA Drug Safety Communication: New restrictions, contraindications, and dose limitations for Zocor (simvastatin) to reduce the risk of muscle injury. 2011.
- Williams B, Mancia G, Spiering W, et al. 2018 ESC/ESH Guidelines for the management of arterial hypertension. Eur Heart J. 2018;39(33):3021–3104.
- Brunton LL, Knollmann BC (eds). Goodman & Gilman's The Pharmacological Basis of Therapeutics. 14th ed. McGraw Hill; 2023.
Andriy Melnyk
A strength-sports coach and author of programs for beginner and intermediate levels. Writes about training planning.
