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)
Erythromycin, a moderate CYP3A4 inhibitor, may reduce Vardenafil clearance and increase its exposure, potentiating adverse effects such as hypotension and headache.
Vardenafil is metabolized primarily by the CYP3A4/5 isoenzymes and, to a lesser extent, by CYP2C9 of the cytochrome P450 system. Erythromycin, a moderate CYP3A4 inhibitor, reduces vardenafil clearance, increasing its plasma concentrations and potentiating vasodilatory and adverse effects. The vardenafil label states that inhibitors of these enzymes reduce drug clearance, so an increase in exposure is expected. The combination should be used with caution, considering initiation at the lowest vardenafil dose and monitoring for hypotension, dizziness and headache. With strong CYP3A4 inhibitors (ketoconazole, ritonavir), the maximum permitted dose is substantially lower.
Vardenafil + erythromycin: erythromycin, a moderate CYP3A4 inhibitor, reduces vardenafil clearance and increases exposure. Use with caution and consider the lowest dose.
Vardenafil is metabolized primarily by CYP3A4/5 isoforms (and to a lesser extent by CYP2C9); inhibitors of these enzymes, such as erythromycin, reduce its clearance and increase plasma concentrations.
Monitor blood pressure, dizziness and headache after dosing.
Orthostatic hypotension, severe dizziness or syncope.
Use with caution; consider starting with the lowest vardenafil dose and monitor for adverse effects. With strong CYP3A4 inhibitors the maximum dose is lower.
DailyMed/FDA (NIH/NLM) — approved Vardenafil label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=2782efed-6198-47b9-81ac-3e255e2ab7f6 ; approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c05e1f7-a3d4-8e69-e063-6394a90aecc3
Erythromycin increases Sildenafil exposure (Cmax +160%, AUC +182%), with a higher risk of hypotension, flushing and headache. Consider a starting dose of 25 mg.
Sildenafil is metabolized by CYP3A4 and, to a lesser extent, by CYP2C9. In a clinical study, erythromycin, a moderate CYP3A4 inhibitor, increased sildenafil Cmax by 160% and AUC by 182%, values that raise the risk of vasodilatory effects such as hypotension, flushing, headache and nasal congestion. The sildenafil label therefore recommends considering a starting dose of 25 mg when given with erythromycin or other moderate CYP3A4 inhibitors. In patients with cardiovascular disease, the elderly or the poly-medicated, blood pressure monitoring should be reinforced and the patient informed of the symptoms to watch for.
Sildenafil + erythromycin: erythromycin increases sildenafil Cmax (+160%) and AUC (+182%). Consider a 25 mg starting dose and monitor for hypotension.
Erythromycin is a moderate CYP3A4 inhibitor; since sildenafil is metabolized by this isoenzyme, concomitant administration increases sildenafil peak concentration and total exposure.
Monitor blood pressure and symptoms of vasodilation (flushing, headache, nasal congestion).
Symptomatic hypotension, dizziness or syncope.
Consider a starting sildenafil dose of 25 mg when used with erythromycin and monitor for adverse effects.
DailyMed/FDA (NIH/NLM) — approved Sildenafil label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1b1ab00d-de9c-4614-e063-6394a90afcde ; approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c05e1f7-a3d4-8e69-e063-6394a90aecc3
Erythromycin, a CYP3A4 inhibitor, predictably increases Tadalafil exposure, with a higher risk of hypotension, flushing and headache.
Tadalafil is a substrate predominantly metabolized by CYP3A4, so inhibitors of this isoenzyme increase its exposure. Although no specific studies were conducted with erythromycin, the tadalafil label states that CYP3A4 inhibitors such as erythromycin would likely increase exposure to the drug, similar to ketoconazole (which increased AUC by 107–312% depending on the dose). The increased exposure potentiates hypotension, flushing and headache. Caution is recommended, considering a reduction in the tadalafil dose, and monitoring of vasodilatory effects, particularly in patients with cardiovascular disease.
Tadalafil + erythromycin: a CYP3A4 inhibitor predictably increases tadalafil exposure. Use with caution and consider dose reduction.
Tadalafil is a substrate predominantly metabolized by CYP3A4; inhibitors of this isoenzyme, such as erythromycin, increase its exposure (the label states that CYP3A4 inhibitors such as erythromycin would likely increase exposure).
Monitor blood pressure, headache, dizziness and flushing.
Symptomatic hypotension, dizziness or syncope.
Use with caution; consider reducing the tadalafil dose and monitor for adverse effects.
DailyMed/FDA (NIH/NLM) — approved Tadalafil label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c3409762-3b2b-1cfc-e053-2995a90ab91b ; approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c05e1f7-a3d4-8e69-e063-6394a90aecc3
Erythromycin, a moderate CYP3A4 inhibitor, may increase Tamsulosin exposure, with a higher risk of orthostatic hypotension. Use with caution, particularly at doses higher than 0.4 mg.
Tamsulosin is extensively metabolized, mainly by CYP3A4 and CYP2D6. The label recommends caution when it is used with moderate CYP3A4 inhibitors, such as erythromycin, particularly at doses higher than 0.4 mg (e.g., 0.8 mg), given the risk of increased exposure. With ketoconazole, a strong CYP3A4 inhibitor, tamsulosin Cmax and AUC increased 2.2- and 2.8-fold, respectively, illustrating the effect of this drug class. The clinical risk is orthostatic hypotension, especially at treatment initiation, with dizziness, lightheadedness and falls. In patients taking both drugs, blood pressure on standing should be monitored and the patient advised to rise slowly.
Tamsulosin + erythromycin: caution with moderate CYP3A4 inhibitors (increased exposure and risk of orthostatic hypotension), especially at doses > 0.4 mg.
Tamsulosin is extensively metabolized by CYP3A4 and CYP2D6; inhibitors of these isoenzymes increase its plasma concentrations (the label advises caution with moderate CYP3A4 inhibitors such as erythromycin).
Monitor dizziness, blood pressure drop on standing and syncope.
Syncope, symptomatic orthostatic hypotension or falls.
Use with caution; monitor for orthostatic hypotension, especially at treatment initiation or when increasing the dose above 0.4 mg.
DailyMed/FDA (NIH/NLM) — approved Tamsulosin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e4202c52-be9d-41d9-b5ff-122740298544 ; approved Erythromycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0c05e1f7-a3d4-8e69-e063-6394a90aecc3
Statin + macrolide: CONTRAINDICATED — simvastatin levels significantly increased.
Erythromycin is a moderate CYP3A4 inhibitor. Combination with simvastatin increases simvastatin levels 2-4 fold. Although the increase is less than with ketoconazole, the risk of myopathy and rhabdomyolysis remains significant. The FDA withdrew the 80 mg simvastatin dose precisely due to rhabdomyolysis risk with CYP3A4 inhibitors. CONTRAINDICATED — use azithromycin (does not inhibit CYP3A4) as macrolide alternative.
Statin + macrolide: CONTRAINDICATED. Erythromycin inhibits CYP3A4, significantly increasing simvastatin levels. Risk of myopathy and rhabdomyolysis.
Erythromycin inhibits CYP3A4, increasing simvastatin levels and the risk of myopathy and rhabdomyolysis. CONTRAINDICATED.
DailyMed/FDA (NIH/NLM) — approved Simvastatin (Zocor) label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8f55d5de-5a4f-4a39-8c84-c53976dd6af9
Lincosamide + macrolide: bacteriological antagonism. Both bind to the 50S subunit — competition for the same site.
Clindamycin and erythromycin compete for the same binding site on the 70S bacterial ribosomal 50S subunit. Erythromycin (macrolide) is bacteriostatic and may reduce the bactericidal efficacy of clindamycin in concentration-dependent situations (synergistic combination). Documented exception: in Pneumocystis jirovecii, the combination may have synergy (both inhibit protein synthesis at different sites). In conventional clinical practice, the combination is avoided.
Lincosamide + macrolide: antagonism — competition for 50S subunit. Avoid.
Clindamycin and erythromycin compete for the same binding site on the 50S ribosomal subunit. Erythromycin (bacteriostatic) may reduce clindamycin efficacy (also bacteriostatic). Clinically, the combination is generally avoided, except in Pneumocystis (documented synergy).
Clinical response, cultures if available.
Avoid the combination for conventional bacterial infections. Exception: Pneumocystis jirovecii prophylaxis (synergy).
DailyMed/FDA (NIH/NLM) — approved Clindamycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3f6b2c5a-e581-414f-bc9e-eaf66a5685cd
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 ; Prontuário Terapêutico do INFARMED (11th ed., 2012) — Annex 1, Drugs and Pregnancy: It is unknown whether it is harmful. ; Prontuário Terapêutico do INFARMED (11th ed., 2012) — Annex 2, Drugs and Breastfeeding: Avoid; present in milk in animal studies.
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.
