Azithromycin Dihydrate

1. Pharmacology

Azithromycin Dihydrate is a macrolide antibiotic of the azalide group. It binds to the 50S ribosomal subunit of susceptible bacteria, thereby inhibiting RNA-dependent protein synthesis. It has a long half-life and extensive tissue distribution, allowing for once-daily dosing and short-course therapy. Azithromycin is bacteriostatic but can be bactericidal at high concentrations against certain organisms.

2. Indication

Azithromycin is indicated for the treatment of infections caused by susceptible organisms, including:

Upper respiratory tract infections (e.g., pharyngitis, tonsillitis)
Lower respiratory tract infections (e.g., bronchitis, pneumonia)
Acute otitis media
Skin and soft tissue infections
Sexually transmitted infections (e.g., chlamydia, gonorrhea)
Mycobacterial infections (in combination therapy for MAC in HIV patients)

3. Dosage & Administration

Adults:

Community-acquired pneumonia, Pharyngitis, Skin infections: 500 mg once daily on day 1, then 250 mg once daily for 4 more days
Sexually transmitted infections (e.g., Chlamydia): 1 g single dose
MAC prophylaxis: 1.2 g once weekly

Children:

Acute otitis media: 10 mg/kg once daily on day 1, then 5 mg/kg for 4 more days (or 10 mg/kg/day for 3 days)
Pharyngitis/tonsillitis: 12 mg/kg/day for 5 days

Route: Oral or intravenous (IV for serious infections)

IV Dose (Adults):

500 mg once daily for 2 days, followed by oral therapy to complete 7–10 days.

4. Interaction

Antacids (especially aluminum and magnesium): Reduce absorption; take azithromycin 1 hour before or 2 hours after.
Warfarin: Enhanced anticoagulant effects; monitor INR.
Cyclosporine, Digoxin, Theophylline, Ergot derivatives: Increased plasma levels or risk of toxicity.
Nelfinavir: May increase azithromycin concentrations.
QT-prolonging agents (e.g., amiodarone, sotalol): Risk of additive QT prolongation.

5. Contraindications

Hypersensitivity to azithromycin, erythromycin, or other macrolides
History of cholestatic jaundice/hepatic dysfunction associated with prior azithromycin use

6. Side Effects

Common: Diarrhea, nausea, abdominal pain, vomiting
Less common: Headache, dizziness, rash, photosensitivity
Serious (rare): QT prolongation, hepatotoxicity, anaphylaxis, Stevens-Johnson syndrome, Clostridioides difficile-associated diarrhea

7. Pregnancy & Lactation

Pregnancy: Category B (no evidence of risk in humans). Use if clearly needed.
Lactation: Excreted in breast milk in small amounts. Use with caution; monitor for gastrointestinal disturbances in infant.

8. Precautions & Warnings

Use with caution in patients with:
- Liver disease
- Renal impairment
- Myasthenia gravis (may worsen symptoms)
- Cardiac arrhythmias or prolonged QT interval
May mask or delay symptoms of other infections.
Risk of secondary infections with long-term use.

9. Overdose Effects

Symptoms may include:

Nausea, vomiting, diarrhea
Temporary hearing loss (reported in high doses)
No specific antidote; supportive care and symptomatic treatment recommended

10. Therapeutic Class

Macrolide Antibiotic
Subclass: Azalides

11. Storage Conditions

Oral formulation (tablets, suspension): Store at 15°C to 30°C (59°F to 86°F)
Reconstituted suspension: Store below 25°C; discard after 10 days
IV formulation: Store as per manufacturer’s instructions; protect from light and use immediately after reconstitution

12. Chemical Structure

Chemical Name:
(2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13-[(2,6-Dideoxy-3-C-methyl-3-O-methyl-α-L-ribo-hexopyranosyl)oxy]-2-ethyl-3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl-11-[[3,4,6-trideoxy-3-(dimethylamino)-β-D-xylo-hexopyranosyl]oxy]-1-oxa-6-azacyclopentadecan-15-one dihydrate

Molecular Formula:
C₃₈H₇₂N₂O₁₂ · 2H₂O

Molecular Weight:
785.0 g/mol (anhydrous base)

Molecular Formula :	C₃₈H₇₂N₂O₁₂
Chemical Structure :