Etrocin

Approved Indications:

• Respiratory Tract Infections:
• Acute bacterial exacerbations of chronic bronchitis
• Community-acquired pneumonia
• Pharyngitis and tonsillitis caused by Streptococcus pyogenes (as an alternative to penicillin)
• Skin and Soft Tissue Infections:
• Impetigo, cellulitis, erysipelas
• Ear Infections:
• Otitis media, otitis externa
• Eye Infections:
• Neonatal conjunctivitis caused by Chlamydia trachomatis or Neisseria gonorrhoeae
• Gastrointestinal Infections:
• Campylobacter enteritis
• Helicobacter pylori eradication (part of combination therapy)
• Sexually Transmitted Infections:
• Chlamydial urethritis and cervicitis
• Syphilis (penicillin allergy alternative)
• Gonorrhea (alternative regimen)
• Diphtheria:
• Treatment and prophylaxis in close contacts
• Pertussis:
• Treatment and post-exposure prophylaxis
• Legionnaires’ Disease
• Rheumatic Fever Prophylaxis:
• Long-term prevention in penicillin-allergic individuals

Clinically Accepted Off-Label Uses:

• Gastroparesis (prokinetic agent)
• Acne vulgaris (topical or systemic)
• Chronic prostatitis (as part of combination therapy)
• Rosacea (topical erythromycin gel)

Adults (Oral):

• Typical dose: 250–500 mg every 6–12 hours depending on infection severity
• Maximum: 4 g/day in divided doses
• For H. pylori eradication: 500 mg 3–4 times daily (with other agents)

Pediatric Dosing (Oral):

• Neonates: 10–15 mg/kg every 6–12 hours
• Children >1 month: 30–50 mg/kg/day in divided doses every 6–8 hours

Intravenous Use (Adults):

• 15–20 mg/kg/day in divided doses (q6h); not to exceed 4 g/day
• Used when oral route is not feasible

Topical Formulations:

• Applied 1–2 times daily for acne or rosacea

Ophthalmic (Eye Ointment):

• Apply 1 cm ribbon into conjunctival sac up to 6 times daily

Rectal Suppository (limited use):

• 500 mg every 6 hours (when oral/IV not possible)

Dose Adjustments:

• Renal impairment: No significant adjustment required
• Hepatic impairment: Use with caution; monitor LFTs
• Elderly: No routine dose adjustment but monitor for toxicity

Administration Notes:

• Administer on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption
• Do not crush enteric-coated tablets
• IV formulation must be diluted and infused slowly to avoid phlebitis

Erythromycin is a macrolide antibiotic that exerts its antibacterial effect by binding to the 50S ribosomal subunit of susceptible microorganisms. This binding inhibits the translocation steps of protein synthesis, leading to inhibition of bacterial growth (bacteriostatic) and, at higher concentrations or against highly susceptible organisms, it may be bactericidal. The drug interferes with the elongation of the peptide chain during translation, effectively blocking the production of essential proteins required for bacterial survival and replication.

• Absorption: Variable oral bioavailability (~30–65%); improved in enteric-coated or esterified forms (e.g., erythromycin ethylsuccinate)
• Distribution: Widely distributed into most tissues and fluids, except cerebrospinal fluid (CSF); crosses the placenta; moderate protein binding (~70–90%)
• Metabolism: Extensively metabolized in the liver; major enzyme: CYP3A4
• Active Metabolites: None
• Half-life: 1.5–2.5 hours (may be prolonged in hepatic impairment)
• Elimination: Primarily via bile/feces; small fraction excreted unchanged in urine

• Pregnancy:
• Former FDA category: Category B
• Human studies have not demonstrated fetal harm; generally considered safe during pregnancy
• Lactation:
• Excreted in human breast milk in low concentrations
• Generally safe; however, infants may experience GI disturbances (e.g., diarrhea, pyloric stenosis risk in neonates)
• Caution advised in breastfeeding premature or newborn infants

• Primary Class: Macrolide Antibiotic
• Subclass: First-generation macrolide (bacteriostatic class)
• Other Classifications: Prokinetic agent (off-label use for gastroparesis)

• Known hypersensitivity to erythromycin or other macrolides
• History of cholestatic jaundice or hepatic dysfunction associated with prior erythromycin use
• Concurrent use with drugs highly dependent on CYP3A4 for clearance (e.g., ergotamine, cisapride, pimozide, simvastatin)
• Known prolonged QT interval or ventricular arrhythmias
• Significant liver dysfunction (relative contraindication)

• QT Prolongation & Arrhythmia: Risk of torsades de pointes; avoid in patients with known QT prolongation or electrolyte abnormalities
• Hepatotoxicity: May cause cholestatic hepatitis; monitor liver function during prolonged use
• Clostridioides difficile-associated diarrhea (CDAD): May occur; evaluate if patient develops persistent diarrhea
• Drug Interactions via CYP3A4 Inhibition: May increase serum levels of other drugs (e.g., warfarin, theophylline, carbamazepine)
• Infants <6 weeks: Risk of infantile hypertrophic pyloric stenosis (IHPS); monitor for vomiting or feeding intolerance
• Resistance Risk: Avoid unnecessary use to limit resistance development

Common Side Effects:

• Gastrointestinal: Nausea, vomiting, diarrhea, abdominal pain, anorexia
• Hepatic: Transient LFT elevation, cholestatic hepatitis
• Dermatologic: Rash, pruritus
• Local (IV): Phlebitis, pain at injection site

Serious and Rare Adverse Effects:

• QT prolongation and arrhythmias (e.g., torsades de pointes)
• Severe hepatotoxicity
• Anaphylaxis or Stevens-Johnson syndrome (rare)
• Hearing loss (reversible; high IV doses or prolonged therapy)

Dose-Dependence: GI effects more common with higher oral doses
Onset Timing: GI symptoms may appear within hours; liver toxicity may take days to weeks

• Major Drug-Drug Interactions:
• CYP3A4 substrates: Increased levels of carbamazepine, theophylline, warfarin, statins (e.g., simvastatin), ergotamine
• QT-prolonging agents: Additive risk (e.g., amiodarone, fluoroquinolones)
• Colchicine: Risk of colchicine toxicity
• Digoxin: Increases digoxin serum levels (via gut flora alteration)
• Drug-Food Interaction: Food may delay absorption; ideally taken on an empty stomach
• Drug-Alcohol: No direct interaction but alcohol may worsen GI side effects
• Enzyme Involvement: Strong inhibitor of CYP3A4

• Macrolide resistance trends have led to restricted use for certain indications in recent guidelines, especially for Streptococcus pneumoniae
• EMA and FDA recommend close QT monitoring when used with other QT-prolonging drugs
• Updated acne guidelines in dermatology recommend short-course erythromycin use to limit resistance development
• New warnings added regarding risk of infantile hypertrophic pyloric stenosis in neonates

• Oral tablets/capsules: Store at 20°C to 25°C (68°F to 77°F); protect from moisture and heat
• Suspensions (reconstituted):
• Erythromycin ethylsuccinate: Stable for 10–14 days at room temperature; do not refrigerate unless stated
• Shake well before use
• IV solution:
• Store powder vials below 25°C
• Reconstituted solution stable for 8 hours at room temperature or 24 hours refrigerated
• Topical/Ophthalmic:
• Store below 25°C
• Protect from light; do not freeze