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CANONICAL MONOGRAPH [8.3] • ID: TIP-MED-000131

1. Azithromycin Dihydrate

2. Pharmacological Class: Azalide Macrolide Antibiotic (Bacteriostatic 50S Ribosomal Subunit Protein Synthesis Inhibitor; WHO 'Watch' Group) • 3. Therapeutic Category: Antimicrobials — Antibacterial & Antibiotic Agents (Ch 08)

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4. Clinical Overview & Verified Formulation Identity

Generic Name & Identifier:
Azithromycin Dihydrate
Code: [8.3] | Stable ID: TIP-MED-000131
Verified Indian Market Brands / Status:
Azee (Cipla), Azithral (Alembic), Zithromax (Pfizer)
9. Dosage Forms & Strengths:
Oral Film-Coated Tablets: 250 mg, 500 mg; Oral Suspension: 100 mg/5 mL, 200 mg/5 mL; IV Infusion: 500 mg/vial
Route: Oral / Parenteral / Topical as specified by formulation
Indian Regulatory Schedule & NLEM Status:
Schedule H Prescription Drug • NLEM 2022 Core Essential Medicine
True

5 & 6. Mechanism of Action & Pharmacodynamics

Reversibly binds to the 23S rRNA of the bacterial 50S ribosomal subunit near the peptidyltransferase centre and blocks the polypeptide exit tunnel, inhibiting aminoacyl-tRNA translocation and bacterial protein synthesis. Primarily bacteriostatic (bactericidal at high concentrations against S. pyogenes and H. influenzae) with a pronounced post-antibiotic effect.

8. Therapeutic Indications

10. Dosage and Administration (Educational Reference Summary)

Dosing & Clinical Context: Adults (Respiratory/Skin): 500 mg orally once daily for 3 days (or 500 mg Day 1, then 250 mg Days 2–5). Enteric Fever (Typhoid): 1000 mg (20 mg/kg) once daily for 5–7 days.
Administration & Timing: Oral (once daily) or IV infusion over at least 60 minutes (never give as IV bolus or IM).

11 & 13. Contraindications, Precautions and Warnings

🚫 11. Contraindications:
  • History of cholestatic jaundice or hepatic dysfunction with prior macrolide use
  • Hypersensitivity to Azithromycin, Erythromycin, or any macrolide/ketolide
⚠️ 13. Precautions and Warnings:

Contraindicated if previous history of Azithromycin-associated cholestatic hepatitis; use caution in severe cirrhosis.

7, 12, 14–18. Detailed Pharmacokinetics, Interactions, Special Populations & Counselling

7 & 16. Pharmacokinetics (ADME) & Renal / Hepatic Considerations

7. Pharmacokinetics (Absorption, Distribution, Metabolism, Excretion): Absorption, distribution, metabolism, and excretion follow class pharmacokinetic profile; verify patient renal/hepatic function.

16a. Renal Considerations: No dose adjustment required in mild-to-severe renal impairment (use caution if eGFR < 10 mL/min).

16b. Hepatic Considerations: Contraindicated if previous history of Azithromycin-associated cholestatic hepatitis; use caution in severe cirrhosis.

12 & 14. Adverse Effects & Drug Interactions
12. Adverse Effects:
  • Gastrointestinal cramps, nausea, diarrhoea (motilin receptor agonism — significantly milder than Erythromycin)
  • QTc interval prolongation and rare polymorphic ventricular tachycardia (Torsades de Pointes)
  • Rare reversible sensorineural hearing loss / tinnitus (with high-dose prolonged courses) or cholestatic hepatitis
14. Drug Interactions:
  • QT-prolonging drugs (Ondansetron, Fluoroquinolones, Amiodarone, Domperidone, Hydroxychloroquine): additive QTc prolongation and Torsades de Pointes risk
  • Aluminium/Magnesium Antacids: reduce peak plasma Cmax by ~24% (separate by 2 hours)
  • Digoxin: inhibits intestinal P-gp and gut flora inactivation, raising serum digoxin levels
15, 17 & 18. Special Populations, Clinical Monitoring & Patient Counselling

15. Use in Special Populations (Pregnancy, Lactation, Paediatrics, Geriatrics): Evaluate maternal-foetal benefit-risk ratio, paediatric mg/kg ceiling, and geriatric renal function prior to prescribing.

17. Clinical & Laboratory Monitoring: Monitor clinical response, baseline renal/hepatic parameters, and relevant serum biomarkers.

18. Patient Counselling & Storage:
  • Complete the full prescribed 3-day or 5-day course; because Azithromycin stays in tissues for 68 hours, it continues working for several days after the last tablet.
  • Separate from antacids containing aluminium or magnesium by at least 2 hours.
  • Do not self-medicate for viral colds or sore throats (Watch group antibiotic).

Storage & Dispensing Notes: Store below 30°C.

Visual Pharmacology Illustration (PLATE-8.9)

ANTIBACTERIAL MECHANISMS OF ACTION: CELL WALL, 30S/50S RIBOSOME, DNA & FOLATE 1. Cell-Wall Synthesis (Bactericidal) • Beta-Lactams (Penicillins, Cephalosporins, Meropenem): Inhibit PBPs (Transpeptidase) • Vancomycin: Binds D-Ala-D-Ala peptide • Fosfomycin: Inhibits MurA enolpyruvyl PK/PD: Time-dependent (fT > MIC) 2. 30S Ribosomal Subunit • Aminoglycosides (Gentamicin, Amikacin): Irreversible 30S binding & mRNA misreading (Bactericidal; Cmax/MIC; Ototoxic/Nephrotoxic) • Tetracyclines (Doxycycline) & Tigecycline: Block aminoacyl-tRNA binding at 30S A-site 3. 50S Ribosomal Subunit • Macrolides (Azithromycin, Clarithromycin) & Clindamycin: Block 23S rRNA translocation • Linezolid: Blocks 70S initiation complex (MRSA/VRE) • Chloramphenicol: Inhibits peptidyl transferase Mostly bacteriostatic (Linezolid vs Staph/Strep) 4. Nucleic Acid Synthesis (DNA Gyrase & RNA Pol) • Fluoroquinolones (Ciprofloxacin, Levofloxacin, Moxifloxacin): Inhibit DNA Gyrase (Topoisomerase II) & Topoisomerase IV (Bactericidal) • Rifampicin: Inhibits bacterial DNA-dependent RNA polymerase (β-subunit) • Metronidazole: Reduced nitro group forms free radicals that strand-break DNA 5. Folate Pathway & Cell Membrane Disruptors • PABA → [Sulfamethoxazole blocks Dihydropteroate Synthase] → Dihydrofolate • Dihydrofolate → [Trimethoprim blocks DHFR] → Tetrahydrofolate (Co-trimoxazole) • Polymyxins (Colistin): Bind LPS outer membrane of MDR Gram-negative bacilli • Daptomycin: Ca2+-dependent membrane depolarisation of Gram-positive cocci (MRSA)
Figure 8.9: Mechanisms of action of major antibacterial classes across bacterial cell-wall synthesis, 30S/50S ribosomal protein translation, nucleic acid replication, and folic acid biosynthesis.

19. Authoritative References & Source Traceability

Primary Reference Record: Indian Pharmacopoeia (IP 2026) • NLEM 2022 (MoHFW) • CDSCO Approved Prescribing Information

Verification Portals: Indian Pharmacopoeia Commission (IPC) • CDSCO (India Jurisdiction) • NCBI Bookshelf • DailyMed (US FDA Label Reference)

Last Reviewed Date: 2026-11-08 • Related Study Guide: Antimicrobial Stewardship & PK/PD Optimization →

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