Erythromycin is an antibiotic (macrolide) used for respiratory and skin infections and other infections caused by susceptible bacteria, especially in patients allergic to penicillin. It can affect the heart rhythm and interacts with several medicines.
Also known as: Eritrocina, Erythrocin
Loratadine + erythromycin: possible increased loratadine concentrations.
Loratadine is metabolised in the liver by CYP3A4 (and CYP2D6) and erythromycin is a known CYP3A4 inhibitor — the combination raises loratadine and its active metabolite desloratadine concentrations, potentially potentiating somnolence (especially in the elderly and with high loratadine doses). The erythromycin label states that "erythromycin has been associated with prolongation of the QT interval and infrequent cases of arrhythmia", with class IA/III antiarrhythmics contraindicated and caution in hypokalaemia/hypomagnesaemia — although loratadine at therapeutic doses does not significantly prolong the QT, the arrhythmogenic risk of erythromycin itself must be respected. In practice, watch for sedation and cardiovascular symptoms, use the lowest effective loratadine dose and monitor the QT interval in at-risk patients (long QT, hypokalaemia, elderly).
Erythromycin + loratadine: erythromycin (CYP3A4 inhibitor) reduces loratadine metabolism, raising its levels. Watch for somnolence and erythromycin QT risk.
Erythromycin (CYP3A4 inhibitor) reduces loratadine metabolism.
Symptoms of antihistamine excess.
Drowsiness, headache, palpitations.
Watch for sedation and adverse effects; most tolerate without dose adjustment.
DailyMed (FDA) — approved Loratadine label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=569a35be-d653-181c-e063-6294a90a6eb9 ; approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c05e1f7-a3d4-8e69-e063-6394a90aecc3 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Erythromycin inhibits the CYP3A4 that metabolizes Atorvastatin, raising atorvastatin levels and the risk of myopathy and rhabdomyolysis.
Erythromycin is an inhibitor of CYP3A4, the enzyme that metabolises atorvastatin, and can raise statin concentrations and the risk of myopathy/rhabdomyolysis, especially in prolonged courses, high doses or with renal impairment. The atorvastatin label lists erythromycin among the CYP3A4 inhibitors whose combination requires a risk/benefit consideration (the 20 mg limit is explicit only for clarithromycin and itraconazole). During an erythromycin course, consider the lowest statin dose or temporary suspension, monitor muscle symptoms and CK, and inform the patient.
Atorvastatin + erythromycin: the macrolide inhibits CYP3A4 and can raise statin levels, with a risk of myopathy. Monitor and consider stopping.
Erythromycin is a CYP3A4 inhibitor; Atorvastatin is a substrate of this CYP. Enzymatic inhibition raises statin levels and the risk of muscle toxicity, especially at higher doses.
Watch for muscle symptoms (pain, weakness, cramps), CPK and dark urine during and after the combination.
Severe myalgia, muscle weakness, dark urine or markedly elevated CPK require immediate statin discontinuation.
Avoid the combination; if needed, choose a macrolide that does not inhibit CYP3A4 (e.g. azithromycin, when appropriate) or temporarily hold the statin.
DailyMed/FDA (NIH/NLM) — approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=49b3ca93-43cc-439c-8f5d-e3ea2e87ad2f ; approved Atorvastatin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=86841382-4229-4e03-958e-3ac22639efd4 — with additional reference: Prontuário Terapêutico do INFARMED, INFARMED (11th ed., 2012)
Fexofenadine + erythromycin: increased fexofenadine exposure (OATP/P-gp transport).
Fexofenadine is eliminated essentially unchanged, without relevant CYP450 metabolism; the interaction with erythromycin occurs at the level of intestinal transporters (P-gp/OATP), which erythromycin inhibits, raising fexofenadine plasma concentrations. The mechanism is documented in the fexofenadine prescribing information (Allegra), which describes increased exposure with erythromycin coadministration (AUC increase of about 100%) without clinically relevant QT changes — unlike terfenadine (its precursor), fexofenadine does not prolong the QT interval. Erythromycin, in turn, "has been associated with prolongation of the QT interval and infrequent cases of arrhythmia" (erythromycin label). In practice, watch for fexofenadine adverse effects (headache, dizziness, mild somnolence) and, for erythromycin, respect the QT contraindications; routine dose adjustment is not needed, but avoid supratherapeutic doses.
Erythromycin + fexofenadine: erythromycin interferes with intestinal transport (P-gp/OATP) and raises fexofenadine levels. Watch for adverse effects (headache, dizziness).
Erythromycin interferes with intestinal transport (P-gp/OATP), raising fexofenadine levels.
Antihistamine adverse effects.
Nausea, dizziness, drowsiness.
Watch for adverse effects; not clinically significant for most.
DailyMed (FDA) — approved Fexofenadine label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=dd0da52b-fc82-4ec9-854c-0d7c52e926fb ; approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c05e1f7-a3d4-8e69-e063-6394a90aecc3 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Desloratadine + erythromycin: possible increased desloratadine concentrations.
The desloratadine label documents that coadministration with "erythromycin... resulted in increased plasma concentrations of desloratadine and 3-hydroxydesloratadine, but there were no clinically relevant changes in the safety profile of desloratadine" — desloratadine is metabolised by CYP3A4 (and CYP2D6), which erythromycin inhibits. The combination is generally well tolerated; the main concerns are potentiation of somnolence/CNS effects (especially in the elderly) and the QT risk of erythromycin itself, which "should be avoided in patients with known QT prolongation, uncorrected hypokalaemia or hypomagnesaemia, clinically significant bradycardia, and with class IA/III antiarrhythmics" (erythromycin label). Routine dose adjustment of desloratadine is not needed; watch for somnolence and inform the patient.
Erythromycin + desloratadine: erythromycin (CYP3A4 inhibitor) raises desloratadine levels, without clinically relevant safety changes. Watch for somnolence.
Erythromycin reduces desloratadine metabolism (CYP3A4).
Antihistamine adverse effects.
Drowsiness, dry mouth, headache.
Watch for sedation; dose adjustment is usually not required.
DailyMed (FDA) — approved Desloratadine label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=2a90b899-7746-43dc-ac8a-e754428eb30c ; approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c05e1f7-a3d4-8e69-e063-6394a90aecc3 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Erythromycin may potentiate the anticoagulant effect of Warfarin, raising the INR and the bleeding risk.
Erythromycin inhibits CYP3A4, the enzyme that metabolises R-warfarin, and reduces the gut flora producing vitamin K. This dual action increases the anticoagulant effect, with INR elevation and bleeding risk documented in clinical reports and mentioned in approved labels. The effect can be rapid (days) and persist after the antibiotic ends. Monitor the INR frequently during and after treatment and adjust the warfarin dose; consider an alternative antibiotic when possible.
Erythromycin inhibits CYP3A4 and reduces gut flora, potentially raising the INR markedly. Monitor the INR during and after the antibiotic.
Erythromycin inhibits CYP3A4 and CYP1A2, reducing Warfarin metabolism (mainly the active isomer); higher anticoagulant levels raise the INR.
Monitor the INR more frequently and watch for bleeding signs (bruising, gum bleeding, melena).
Bleeding, a very high INR or signs of hemorrhage require discontinuation/adjustment and urgent medical evaluation.
Monitor the INR and adjust the warfarin dose during and after antibiotic therapy; inform the patient of the bleeding risk.
DailyMed/FDA (NIH/NLM) — approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=49b3ca93-43cc-439c-8f5d-e3ea2e87ad2f ; approved Warfarin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=541c9a70-adaf-4ef3-94ba-ad4e70dfa057 — with additional reference: Prontuário Terapêutico do INFARMED, INFARMED (11th ed., 2012)
Erythromycin may raise plasma Digoxin levels, with a risk of digitalis toxicity (arrhythmias, nausea, visual disturbances).
Erythromycin raises digoxin concentrations through two mechanisms: P-glycoprotein inhibition (reduces intestinal and renal digoxin excretion) and elimination of the gut bacterial flora that metabolises digoxin to inactive metabolites. Studies show 40–100% increases in digoxin levels in patients treated with erythromycin, with a risk of digitalis toxicity. Monitor digoxin levels and the ECG during and after the antibiotic course, watch for toxicity symptoms and reduce the digoxin dose if needed.
Erythromycin inhibits P-gp and reduces the flora that inactivates digoxin, potentially raising its levels. Monitor for digitalis toxicity signs.
Erythromycin inhibits P-glycoprotein and CYP3A4, reducing Digoxin elimination and increasing its effect; electrolyte disturbances (hypokalemia) may potentiate digitalis toxicity.
Watch for bradycardia, arrhythmias, nausea, anorexia, visual disturbances and potassium levels.
Arrhythmias, marked bradycardia, persistent nausea or blurred vision require urgent evaluation and a digoxin level.
Monitor serum digoxin levels and signs of toxicity; a digoxin dose reduction or an alternative macrolide may be needed.
DailyMed/FDA (NIH/NLM) — approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=49b3ca93-43cc-439c-8f5d-e3ea2e87ad2f ; approved Digoxin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5886e233-b2da-4acb-be05-9bf40fb8e7f4 — with additional reference: Prontuário Terapêutico do INFARMED, INFARMED (11th ed., 2012)
Food may reduce absorption of some erythromycin formulations; taking on an empty stomach maximises levels.
Prefer taking on an empty stomach unless the formulation advises otherwise.
DailyMed/FDA (NIH/NLM) — approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ca65a48f-5fe6-4b31-8359-51dbc31f6d4e
Grapefruit inhibits CYP3A4 and can raise erythromycin concentrations, increasing the risk of QT prolongation.
Avoid grapefruit juice during treatment.
DailyMed/FDA (NIH/NLM) — approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ca65a48f-5fe6-4b31-8359-51dbc31f6d4e
Erythromycin use in neonates is associated with infantile hypertrophic pyloric stenosis.
Avoid in neonates when alternatives exist; watch for projectile vomiting.
DailyMed/FDA (NIH/NLM) — approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ca65a48f-5fe6-4b31-8359-51dbc31f6d4e
Erythromycin prolongs the QT interval and increases the risk of torsades de pointes, especially in at-risk patients.
Avoid in QT prolongation, hypokalaemia or with QT-prolonging drugs.
DailyMed/FDA (NIH/NLM) — approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ca65a48f-5fe6-4b31-8359-51dbc31f6d4e
Erythromycin is the first-choice macrolide in pregnancy when indicated; no major malformations have been associated.
May be used in pregnancy when indicated (e.g. Legionella, pertussis, chlamydia).
Excreted into breast milk; compatible with breastfeeding.
No specific additional contraception.
DailyMed/FDA (NIH/NLM) — approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ca65a48f-5fe6-4b31-8359-51dbc31f6d4e
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Macrolide antibacterial. It diffuses into most body fluids; it concentrates in the liver and is excreted in the bile; 12 to 15% of the intravenous dose is excreted in active form in the urine. Low CSF concentrations without meningeal inflammation, increasing with meningitis. Prolongs the QT interval (torsades de pointes reported, mainly with the intravenous route).
Inhibition of bacterial protein synthesis by binding to the 50S ribosomal subunits of susceptible organisms; it does not affect nucleic acid synthesis. Resistance in S. aureus may emerge during therapy; many Haemophilus influenzae isolates are resistant.
Well absorbed orally; after a 500 mg intravenous infusion, mean serum levels of about 10 mcg/mL at 1 hour and 2.6 mcg/mL at 2.5 hours. It crosses the placenta and is excreted in breast milk; not removed by dialysis.
Mainly hepatic (biliary) elimination; 12 to 15% of the intravenous dose in active form in the urine; not removed by peritoneal dialysis or haemodialysis. CYP3A4 inhibitor — interactions with statins (lovastatin, simvastatin), colchicine, carbamazepine, digoxin, theophylline and oral anticoagulants.
Erythromycin concentrates in the liver and is excreted in the bile; with normal hepatic function, serum levels fall to about 1 mcg/mL at 6 hours after a 500 mg infusion. The half-life may be prolonged with hepatic dysfunction; doses ≥4 g/day increase the risk of reversible hearing loss in the elderly.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
