Erythromycin

Erythromycin is an antibiotic available in multiple oral, intravenous, and topical formulations, each with specific approved uses.

• Oral forms (ERY-TAB, erythromycin delayed-release tablets/capsules, erythromycin film-coated and coated tablets): upper respiratory tract infections; lower respiratory tract infections; pertussis (whooping cough); listeriosis; Legionnaires' disease; skin and skin-structure infections; primary syphilis (in penicillin-allergic patients); gonorrhea (as an alternative); chlamydial infections (including during pregnancy); non-gonococcal urethritis; intestinal amebiasis
• Erythromycin ethylsuccinate oral suspension and tablets (E.E.S., Ery-Ped, generic forms): same indications as other oral erythromycin forms, including upper respiratory infections, skin infections, pertussis, chlamydia, intestinal amebiasis, Legionnaires' disease, and more
• Erythrocin Lactobionate IV and erythromycin lactobionate injection: used when oral treatment is not possible, or when the severity of infection requires immediate high blood levels — same infection types as oral forms; IV therapy should be transitioned to oral erythromycin as soon as clinically appropriate
• Erythromycin topical solution 2% and Ery 2% Pads (topical swabs): topical treatment of acne vulgaris only — not for systemic infections

Erythromycin is a macrolide antibiotic that works by binding to the 50S ribosomal subunit inside susceptible bacteria — essentially jamming the bacteria's protein-building machinery. Without the ability to make essential proteins, bacteria cannot grow or reproduce. Erythromycin does not affect human cells' protein synthesis or DNA, making it selective for bacteria.

Resistance can develop when bacteria modify the target site (the 23S rRNA within the 50S subunit) so erythromycin can no longer bind effectively, or by actively pumping the drug out of the bacterial cell. Erythromycin also antagonizes (works against) certain other antibiotics — including clindamycin, lincomycin, and chloramphenicol — meaning these combinations may be less effective than either drug alone.

Erythromycin is available in several forms and the dosing approach differs by product and route.

• ERY-TAB (delayed-release tablets): taken orally, multiple times daily; works best on an empty stomach (at least 30 minutes before meals), though it can be taken with food
• Erythromycin ethylsuccinate tablets, suspensions, and granules (E.E.S., Ery-Ped, generics): taken orally with or without food; ethylsuccinate tablets should not be chewed due to unpleasant taste
• IV forms (Erythrocin Lactobionate, erythromycin lactobionate injection): given only by slow continuous or intermittent IV infusion in a healthcare setting — never by rapid IV injection; IV should be switched to oral as soon as appropriate
• Ery 2% Pads / erythromycin topical solution: applied to clean, dry skin twice daily (morning and evening); for topical acne treatment only

Children's oral doses are determined by weight, age, and infection severity — always follow your prescriber's instructions and your product's label directions.

The most common side effects of erythromycin are stomach-related, especially with oral forms, and tend to be worse at higher doses.

• Nausea
• Vomiting
• Stomach pain or cramping
• Diarrhea
• Loss of appetite
• Abnormal liver function tests or symptoms of hepatitis (yellowing of skin or eyes)
• Skin rash, hives, or rarely severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis)
• Reversible hearing loss (mainly at high doses or in patients with kidney problems)

Seek immediate medical help if you experience irregular or fast heartbeat, severe skin blistering or peeling, signs of a serious allergic reaction, persistent or severe diarrhea, or yellowing of the skin or eyes.

• Heart rhythm (QT prolongation): Erythromycin can prolong the QT interval and, rarely, trigger a life-threatening arrhythmia called torsades de pointes. Avoid it if you have a known long QT interval, slow heart rate, or low potassium or magnesium levels, or if you take Class IA or Class III antiarrhythmics. Older adults are at higher risk.
• Liver toxicity: Hepatitis, elevated liver enzymes, and jaundice have been reported with oral erythromycin. Report any yellowing of skin or eyes or unusual fatigue to your doctor promptly.
• C. difficile colitis: Like all antibiotics, erythromycin can cause C. diff overgrowth in the gut, leading to diarrhea that ranges from mild to severe (even fatal colitis). This can occur up to two months after stopping the antibiotic.
• Drug interactions — serious risks: Combining erythromycin with certain statins (lovastatin, simvastatin), colchicine, or ergot drugs can cause life-threatening reactions including rhabdomyolysis, colchicine toxicity, and dangerous blood vessel spasm.
• Syphilis in pregnancy: Oral erythromycin does not reach the fetus at levels adequate to prevent congenital syphilis — babies born to mothers treated this way for syphilis need additional penicillin treatment.

Erythromycin is both a substrate and an inhibitor of the CYP3A4 liver enzyme, meaning it can raise the blood levels of many other drugs to potentially dangerous levels — and some combinations are outright contraindicated.

• Terfenadine, astemizole, cisapride, pimozide — CONTRAINDICATED: can cause fatal cardiac arrhythmias including torsades de pointes
• Ergotamine / dihydroergotamine — CONTRAINDICATED: risk of acute ergot toxicity — dangerous blood vessel spasm affecting the limbs and brain
• Lovastatin, simvastatin — CONTRAINDICATED: serious risk of rhabdomyolysis (severe muscle breakdown)
• Colchicine (gout medication): potentially life-threatening toxicity even at normal doses — use with caution; dose adjustment may be needed
• Atorvastatin and other CYP3A4-metabolized statins: increased muscle-damage risk
• Calcium channel blockers (verapamil, amlodipine, diltiazem): risk of low blood pressure, slow heart rate, and lactic acidosis
• Oral anticoagulants (e.g., warfarin): erythromycin increases their blood-thinning effect, raising bleeding risk — especially in older adults
• Theophylline: erythromycin raises theophylline levels (toxicity risk) and theophylline lowers erythromycin levels (reduced effectiveness)
• Digoxin: erythromycin can raise digoxin levels, increasing toxicity risk
• Triazolam, midazolam, alprazolam: erythromycin slows clearance of these sedatives, intensifying their effects
• Sildenafil (Viagra): erythromycin increases sildenafil exposure — dose reduction of sildenafil may be needed
• Cyclosporine, tacrolimus, carbamazepine, and others: CYP3A4-based interactions can raise blood levels of these drugs significantly

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Do not take erythromycin if you are allergic to it or have had a prior reaction to it
• Tell your doctor about all medications you take — especially statins, heart-rhythm drugs, blood thinners, colchicine, theophylline, or digoxin
• Tell your doctor if you have liver disease; erythromycin is processed in the liver and can worsen liver function
• Tell your doctor if you have or have had a prolonged QT interval, irregular heart rhythms, or low potassium or magnesium levels
• If you are pregnant, especially being treated for syphilis: oral erythromycin alone is not adequate to protect the baby from congenital syphilis — your doctor will need to plan additional treatment
• Erythromycin passes into breast milk — discuss risks and benefits with your doctor if breastfeeding
• Older adults face a higher risk of heart-rhythm effects, hearing changes at high doses, and stronger interactions with blood thinners
• Children's doses must be calculated based on weight and infection severity — never adjust doses without guidance from a prescriber
• Patients with kidney or liver impairment receiving high doses are at increased risk for reversible hearing loss

If too much erythromycin is taken, it should be stopped immediately and steps taken to remove any unabsorbed drug from the body. Standard supportive measures should be started right away. Erythromycin is not removed by dialysis (peritoneal or hemodialysis), so those methods are not useful in an overdose situation.

Erythromycin stops susceptible bacteria from growing by blocking their ability to build the proteins they need to survive. It binds specifically to the bacterial 50S ribosomal subunit, halting protein synthesis without interfering with human cells' own protein production or DNA. It is active against a broad range of gram-positive and gram-negative bacteria, as well as other organisms including Mycoplasma, Chlamydia, and Treponema pallidum.

When taken by mouth, erythromycin base and its salts are readily absorbed in an active form, though absorption varies between individuals — some people do not reach optimal blood levels. The drug binds extensively to plasma proteins and distributes widely into body fluids. It crosses the placenta (though fetal levels remain low) and is excreted in breast milk. Erythromycin is concentrated in the liver and excreted primarily in bile; less than 5% of an oral dose appears unchanged in the urine, and dialysis does not remove it from the body.

ERY-TAB and other delayed-release oral formulations use a pH-dependent coating that resists dissolving in the acidic stomach environment, releasing the drug in the small intestine for better absorption. These formulations have been shown to deliver adequate drug levels in both fasting and fed states, though blood levels tend to be higher when taken on an empty stomach.

Store Erythromycin Ethylsuccinate 200 and Erythromycin Ethylsuccinate 400, prior to mixing, below 86°F (30°C). stored at or below 77°F (25°C) and used within 35 days; refrigeration is not required.