Erythromycin is widely effective in treating a broad range of clinical infections, including:

• Upper respiratory tract infections: Tonsillitis, peritonsillar abscess, pharyngitis, laryngitis, sinusitis, and secondary infections associated with colds and influenza
• Lower respiratory tract infections: Tracheitis, acute and chronic bronchitis
• Ear infections: Otitis media, otitis externa, mastoiditis
• Eye infections: Blepharitis, established trachoma
• Skin and soft tissue infections: Boils, carbuncles, impetigo, abscesses, pustular acne, paronychia, cellulitis, erysipelas
• Gastrointestinal tract infections: Cholecystitis, staphylococcal enterocolitis
• Prophylaxis: Pre- and post-operative use, trauma, burns, rheumatic fever prevention
• Other infections: Osteomyelitis, diphtheria, scarlet fever, whooping cough

Erythromycin belongs to the macrolide class of antibiotics. It acts by interfering with bacterial protein synthesis at the ribosomal level, producing either bacteriostatic or bactericidal effects depending on the organism and drug concentration. It is commonly used for infections caused by penicillinase-producing staphylococci. The microorganisms particularly susceptible to erythromycin include Gram-positive cocci and bacilli; Gram-negative organisms such as Neisseria catarrhalis, Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilus influenzae, Bordetella species, and Haemophilus pertussis; as well as other organisms including Mycoplasma pneumoniae, Legionella pneumophila, Bacteroides fragilis, Bacteroides oralis, Bacteroides melaninogenicus, Fusobacterium species, Chlamydia trachomatis, and Treponema pallidum.

Erythromycin inhibits microsomal protein synthesis in susceptible organisms by blocking the translocation process. It binds specifically to the 50S subunit of the bacterial ribosome or the 70S ribosome. It does not bind to the stable 80S mammalian ribosome. Erythromycin is active against many gram-positive bacteria, some gram-negative bacteria, and also against mycoplasma and chlamydia.

Absorption: Erythromycin base is destroyed by gastric acid and is therefore administered in the form of a stable ester. The absorption of both the base and the ester forms may be reduced by the presence of food. Erythromycin stearate is hydrolyzed in the intestine, and the free erythromycin is then absorbed.

Blood Concentration: After an oral dose of 500 mg of erythromycin base or stearate, peak serum concentrations of approximately 0.9 to 1.4 mg/ml and 0.4 to 1.8 mg/ml, respectively, are reached within 1 to 4 hours.

Half-life: The serum half-life of erythromycin ranges from 1.2 to 4 hours. In patients with oliguria, the half-life may be approximately 5 hours.

Distribution: Erythromycin is widely distributed throughout body tissues and fluids, with some retention in the liver and spleen. The protein binding of erythromycin base is about 73%. It may enter the cerebrospinal fluid when the meninges are inflamed. Erythromycin also crosses the placenta and is excreted in breast milk.

Excretion: Approximately 5% to 15% of an erythromycin dose is excreted in the urine, while a large amount of the unchanged active drug is excreted in the bile.

Adult and Children over 8 years: 250-500 mg every six hours for mild to moderate infections. This may be increased upto 4 gm. or more daily in severe cases.

Elderly: No special dosage recommendation. Erythromycin may be administered if desired, three times daily or twice daily by giving one-third or half of the total daily requirement 8 hourly or 12 hourly respectively.

Children aged 2 to 8 years: 250 mg. every six hours or 30-50 mg/kg body weight per day divided into four equal dosage.

Infants and Children upto 2 years: 500 mg. in divided doses or 30-50 mg/kg body weight in divided doses.

Recent studies show that using erythromycin together with high doses of theophylline may increase the level of theophylline in the blood and raise the risk of theophylline toxicity. In such situations, the dose of theophylline should be reduced.

Erythromycin should not be used in patients who are known to be hypersensitive or allergic to it.

Allergic reactions are uncommon and usually mild, although anaphylaxis has been reported in rare cases. After oral use, some patients may experience abdominal discomfort, sometimes accompanied by nausea and vomiting. These symptoms usually improve after a few days without needing to reduce the dose.

Clinical and laboratory studies have not shown evidence of teratogenic effects or toxicity in humans. However, caution should be used when prescribing erythromycin during pregnancy and breastfeeding, because it can cross the placenta and is excreted into breast milk.

Erythromycin should be used cautiously in patients with impaired liver function, because it is mainly excreted through the bile.

In the event of an overdose, erythromycin should be stopped immediately. Management should include prompt removal of any unabsorbed drug and other appropriate supportive measures. Erythromycin cannot be removed by peritoneal dialysis or haemodialysis.

Antidiarrhoeal antimicrobial drugs, Macrolides.

Store below 25°C in a cool, dry place, protected from light and moisture. Keep out of the reach of children.