Erythromycin is an antibiotic useful for the treatment of a number of bacterial infections. This includes respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used during pregnancy to prevent Group B streptococcal infection in the newborn. Erythromycin may be used to improve delayed stomach emptying.

Molecular Structure


Class of Drug

Antibiotic, Macrolide.

Mechanism of Action

Inhibits RNA-dependent protein synthesis at the level of the 50S ribosome.

Susceptible organisms in vivo:

> Gram-positive organisms: Group A Streptococcus and Streptococcus pneumoniae (increasing resistance especially outside the United States); MSSA (not MRSA) with limited activity, viridans streptococci, Corynebacterium diphtheriae, Listeria monocytogenes.

> Gram-negative organisms: Neisseria gonorrhoeae (some resistant strains), Neisseria meningitidis, Bordetella pertussis, Campylobacter jejuni, Treponema pallidum, Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia trachomatis,Bartonella sp. Less active against Hemophilus influenzae.

Indications / Dosage / Route

Routes of Administration: Oral, IV.

Condition: Streptococcal upper respiratory tract infections (pharyngitis, tonsillitis)

Dose: Adults: 250 mg q.i.d. 10 or more days. Maximum: 4 g/d.

Children: 30-50 mg/kg/d, equally divided doses, >10 days. Maximum: 4 g/d.

Condition: Prophylaxis of recurring attacks of rheumatic fever in patients allergic to penicillin and sulfonamides.

Dose: Adults: 250 mg b.i.d.

Condition: Prophylaxis against bacterial endocarditis in patients allergic to penicillin

Dose: Adults: 1 g 1 hour prior to procedure, then 500 mg 6 hours later.

Condition: Conjunctivitis caused by C. trachomatis

DoseNewborn: 50 mg/kg/d, 4 divided doses, >2 weeks.

Condition: Pneumonia of infancy caused by C. trachomatis

DoseInfants: 50 mg/kg/d, 4 divided doses, >3 weeks.

Condition: GU infections during pregnancy

Dose: Adults: 500 mg/d q.i.d. >7 days

Condition: Uncomplicated urethral, endocervical, or rectal infections caused by C. trachomatis and other nongonococcal urethritis (Ureaplasma and Mycoplasma genitalium) when a tetracycline cannot be tolerated.

Dose: Adults: 500 mg q.i.d., > 7 days.

Condition: Primary syphilis

Dose: Adults: 30-10 g in divided doses, 10-15 days.

Condition: Acute pelvic inflammatory disease (in combination therapy)

Dose: Adults: IV 500 mg (Erythrocin Lactobionate) q4h, 3 days.
Then 500 mg Erythromycin Base PO ql2h, 7 days.

Condition: Pertussis

Dose: Children: PO 40-50 mg/kg/d, divided doses, 5-14 days.

Condition: Legionnaires’ disease

Dose: Adults: 2-4 g/d, divided doses

Condition: Respiratory tract infections caused by M. pneumoniae and C. pneumoniae’.

Dose: Adults: 500 PO mg q6h 5-10 days (up to 3 weeks if severe).

Condition: Upper respiratory tract infections (mild to moderate) caused by S. pyogenes and S. pneumoniae

Dose: Adults: PO 250-500 mg q.i.d. 10 days.

Children: PO 20-50 mg/kg/d, in divided doses, 10 days.

Condition: Lower respiratory tract infections (mild to moderate) caused by S. pyogenes and S. pneumoniae

Dose: Adults: 250-500 PO mg q.i.d. (or 20-50 mg/kg/d in divided doses), 10 days.

Adjustment of Dosage


Food and Drug Interactions

Food: Take on empty stomach.

Pregnancy: Category B.

Lactation: Appears in breast milk. Considered compatible by American Academy of Pediatrics.

Contraindications: Hypersensitivity to macrolide antibiotics, concomitant administration of pimozide.

Warnings / Precautions

> Use with caution in patients with liver and kidney disease, long QT syndrome or prolonged QT interval.

Clinically Important Drug Interactions

> Drugs that decrease effects/toxicity of macrolides: rifampin, aluminum or magnesium containing antacids.

> Macrolides increase effects/toxicity of following drugs: oral anticoagulants, astemizole, benzodiazepines, bromocriptine, buspirone, carbamazepine, cisapride, cyclosporine, digoxin, ergot alkaloids, felodipine, grepafloxacin, statins, pimozide, sparfloxacin, tacrolimus.

Adverse Reactions

> Common: Nausea, Diarrhea, Abdominal pain.

> Serious: pseudomembranous colitis, ventricular arrhythmias, nephritis, cholestatic jaundice, angioedema.

Parameters to Monitor

> Signs and symptoms of superinfection, in particular pseudomembranous colitis.

> Signs and symptoms of renal toxicity.

> Signs and symptoms of hearing impairment. Patients with kidney or liver disease are at highest risk.

Further Useful Info

> Erythromycin is used in penicillin allergic patients to treat streptococcal tonsillitis (resistance is increasing outside the United States.

> It is used to treat S. pneumoniae, M. catarrhalis and H. influenzae infections (acute otitis media, sinusitis).

> It is the drug of choice in atypical pneumonia caused by Legionella, M. pneumoniae, andC. trachomatis.

> It is first choice for diphtheria and whooping cough.

> It is often used to treat acne.

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