Effects of erythromycin on other medicinal products
Erythromycin is an inhibitor of CYP3A4 and the transport protein P-glycoprotein. The extent of inhibition with different CYP3A4 substrates is difficult to predict. Erythromycin should therefore not be used during treatment with CYP3A4 substrates unless the plasma concentrations, effects or side effects of the substrate can be closely followed. A dose reduction of other medicinal products that are metabolised by CYP3A4 can be necessary and combination with erythromycin should take place with caution (e.g. acenocoumarol, alfentanil, bromocriptine, cilostazole, cyclosporine, hexobarbiton, colchicine, methylprednisolone, midazolam, omeprazole, tacrolimus, valproate, vinblastine, antimycotics such as fluconazole, ketoconazole and itraconazole). Alternatively, the treatment with CYP3A4 substrates should be discontinued during treatment with erythromycin.
Medicinal products that may prolong the QT interval
Erythromycin affects the metabolism of terfenadine, astemizole and pimozide during concomitant administration. Rare cases of severe, potentially fatal cardiovascular events such as cardiac arrest, torsades de pointes and other ventricular arrhythmias have been observed and therefore concomitant administration of these medicinal products is contraindicated (see section 4.3).
Elevated cisapride levels have been reported in patients receiving erythromycin and cisapride concomitantly. This may result in QT prolongation and cardiac arrhythmias including ventricular tachycardia, ventricular fibrillation and torsades de pointes. Similar effects have been observed with concomitant administration of disopyramide and erythromycin and may be expected also in patients taking astemizole or pimozide. Concomitant administration with astemizole, cisapride, disopyramide and pimozide is contraindicated (see section 4.3).
Erythromycin may inhibit the metabolism of quinidine resulting in a 40% increase in Cmax in healthy volunteers. There are case reports of increased plasma concentrations and torsades de pointes. In case of concomitant treatment with erythromycin the plasma levels of quinidine should be controlled.
Caution is recommended when erythromycin is given to patients treated with other medicinal products that may prolong the QT interval (see section 4.4).
Sildenafil
Data suggest that erythromycin inhibits the metabolism of sildenafil. A starting dose of 25 mg sildenafil should be considered.
Benzodiazepines
Erythromycin has been reported to decrease clearance of triazolam, alprazolam, clozapine and related benzodiazepines and thereby increasing the pharmacological effect of these medicinal products. In healthy volunteers pretreated with erythromycin the absorption of zopiclone is faster resulting in higher plasma concentrations and more pronounced hypnotic effect compared to controls.
Theophylline
Concomitant treatment with erythromycin and high doses of theophylline may result in increased plasma theophylline levels and potential theophylline toxicity, probably due to inhibition of metabolism. In case of concomitant treatment plasma levels of theophylline should be followed in order to avoid toxic plasma levels (dose reduction). The erythromycin plasma concentrations may be reduced in case oral erythromycin is given together with theophylline, possibly resulting in subtherapeutic erythromycin levels.
Oral anticoagulants
There have been reports of increased anticoagulant effects when erythromycin and oral anticoagulants (e.g. warfarin, rivaroxaban) are used concomitantly
Fexofenadine
In case of concomitant treatment with erythromycin and fexofenadine plasma concentrations of fexofenadine increase 2-3-fold, probably due to increased absorption.
Statins
Erythromycin inhibits the metabolism of several HMG-CoA reductase inhibitors resulting in increased plasma concentrations of these medicinal products. Erythromycin also increases the plasma concentrations of simvastatin acid (5-fold). Rare cases of rhabdomyolysis, associated with elevated plasma levels, have been reported during concomitant treatment with clarithromycin and lovastatin or simvastatin. Erythromycin must not be used concomitantly with simvastatin, atorvastatin or lovastatin. Treatment with these medicinal products must be discontinued during treatment with erythromycin.
Lomitapide
Concomitant administration of erythromycin with lomitapide is contraindicated due the potential for markedly increased transaminases (see section 4.3).
Ergot alkaloids (e g ergotamine and dihydroergotamine)
There are case reports of clinical ergotism, characterised by vasospasm and ischaemia in CNS, extremities and other tissues, due to elevated plasma levels of ergot alkaloids during concomitant treatment with macrolide antibiotics. The combination is contraindicated (see section 4.3).
Digoxin
Concomitant treatment with erythromycin and digoxin may result in elevated plasma digoxin levels. Control of plasma levels should be considered during initiation and termination of erythromycin treatment. Dose adjustment may be necessary.
Corticosteroids
Caution should be exercised in concomitant use of erythromycin with systemic and inhaled corticosteroids that are primarily metabolised by CYP3A due to the potential for increased systemic exposure to corticosteroids. If concomitant use occurs, patients should be closely monitored for systemic corticosteroid undesirable effects.
Hypotension, bradyarrhythmia and lactic acidosis has been observed in patients concomitantly treated with the calcium channel blocker verapamil.
Effects of other medicinal products on the pharmacokinetics of erythromycin
Erythromycin is metabolised by CYP3A4. Thus, strong inhibitors of this enzyme may inhibit the metabolism of erythromycin resulting in elevated plasma levels.
Medicinal products that induce CYP3A4 (such as rifampin, phenytoin, carbamazepine, Phenobarbital, St. John's Wort (Hypericum perforatum)) can induce the metabolism of erythromycin. This may lead to subtherapeutic levels of erythromycin and consequently may reduce the effect. The induction is gradually reduced over a period of 2 weeks following discontinuation of treatment with CYP3A4 inducers. Erythromycin should not be used during treatment with CYP3A4 inducers and 2 weeks following discontinuation of therapy.
Cimetidine may inhibit the metabolism of erythromycin resulting in elevated plasma levels.
During concomitant treatment with erythromycin and protease inhibitors inhibition of erythromycin metabolism has been observed.
Observational data have shown that co-administration of azithromycin with hydroxychloroquine in patients with rheumatoid arthritis is associated with an increased risk of cardiovascular events and cardiovascular mortality. Because of the potential for a similar risk with other macrolides when used in combination with hydroxychloroquine or chloroquine, careful consideration should be given to the balance of benefits and risks before prescribing erythromycin for any patients taking hydroxychloroquine or chloroquine. Erythromycin should be used with caution in patients receiving these medicines known to prolong the QT interval due to the potential to induce cardiac arrhythmia and serious adverse cardiovascular events.