Azithromycin: Uses, Dosage, Side Effects, & Interactions

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Description of Azithromycin

Azithromycin is a macrolide antibacterial antibiotic that is derived from erythromycin. It comes in different dosage forms which include capsules, injections, and powder for suspension. It had broad-spectrum of activity against bacteria which it stops their growth by inhibiting protein synthesis in them.

Pharmacodynamics of Azithromycin

How does Azithromycin work?

Azithromycin exhibits antimicrobial activity by binding to the 50S subunit of bacterial ribosome. This leads to protein synthesis and translation inhibition.

Microbiology of Azithromycin

Azithromycin prevents bacteria from growing by interfering with their protein synthesis. Azithromycin binds to the 50S subunit of the bacterial ribosome, and thus inhibits translation of mRNA. Nucleic acid synthesis is not affected. Azithromycin has similar antimicrobial spectrum as erythromycin where it is derived from, but is more effective against certain gram-negative bacteria, particularly Haemophilus influenzae.

Azithromycin has been proven to be most effective against the most isolates of the following microorganisms:

  • Staphylococcus aureus
  • Streptococcus agalactiae
  • Streptococcus pneumoniae
  • Streptococcus pyogenes
  • Haemophilus ducreyi
  • Haemophilus influenzae
  • Moraxella catarrhalis
  • Neisseria gonorrhoeae
  • Chlamydia pneumoniae
  • Chlamydia trachomatis
  • Mycoplasma pneumoniae

Azithromycin has been shown to be effective against malaria when used in combination with artesunate or quinine; the optimal dose for this is not yet known.

Indications and Uses of Azithromycin

  1. Infections of upper respiratory tracts (bacterial pharyngitis, laryngitis, tonsilitis, sinusitis etc.)
  2. Infections of lower respiratory tracts (bacterial bronchitis, alveolar & krupps pneumoniae, chronicle obstructive lung disease) nose, ear throat infections (otitis, rhinitis, tonsilitis etc.)
  3. Skin & skin structure infections: furunculosis of varied origin, pyoderma and impetigo.

Dosage of Azithromycin

1. Community Acquired Pneumonia

Indicated for treatment of community-acquired pneumonia due to Chlamydophila pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, or Streptococcus pneumoniae in patients appropriate for oral therapy

Adult: As dihydrate: Initially, 500 mg on day one followed by 250 mg daily for the remaining 4 days or 500 mg daily as a single dose for 3 days.

2. Pharyngitis or Tonsillitis

Indicated for treatment of pharyngitis/tonsillitis caused by Streptococcus pyogenes as an alternative therapy in individuals who cannot use first-line therapy

Adult: As dihydrate: Initially, 500 mg on day one followed by 250 mg daily for the remaining 4 days or 500 mg daily as a single dose for 3 days.

3. Uncomplicated Skin and Skin Structure Infection

Indicated for treatment of uncomplicated skin and skin structure infections due to Staphylococcus aureus, Streptococcus pyogenes, or Streptococcus agalactiae

Adult: As dihydrate: Initially, 500 mg on day one followed by 250 mg daily for the remaining 4 days or 500 mg daily as a single dose for 3 days.

4. Acute bacterial exacerbations of chronic obstructive pulmonary disease

Indicated for treatment of acute bacterial exacerbations of chronic bronchitis due to Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae

Adult: 500 mg PO daily for 3 days

OR

Alternatively, 500 mg on day one followed by 250 mg daily for the remaining 4 days or 500 mg daily as a single dose for 3 days.

4. Acute Bacterial Sinusitis

Indicated for treatment of acute bacterial sinusitis due to Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae

Adult: 500 mg PO daily for 3 days

5. Chancroid in Men

Indicated for treatment of genital ulcer disease in men due to Haemophilus ducreyi (chancroid)

1 g PO once.

6. Nongonococcal or Gonococcal Urethritis and Cervicitis

Indicated for treatment of urethritis and cervicitis due to Chlamydia trachomatis or Neisseria gonorrhoeae

1 g PO once

7. Pelvic Inflammatory Disease

Indicated for treatment of pelvic inflammatory disease due to Chlamydia trachomatis, Neisseria gonorrhoeae, or Mycoplasma hominis in patients who require initial IV therapy.

See CDC for more on this.

The usual dose for children is 10 mg/kg body weight orally per day for 3 days (3 days treatment course)

OR

10 mg/kg body weight stat followed by 5 mg/kg body weight for 4 remaining days (five days treatment course)

Pharmacokinetics of Azithromycin

Azithromycin is acid-stable and can therefore be taken orally with no need of protection from gastric acids. It is readily absorbed, and diffused into most tissues and phagocytes. Due to the high concentration in phagocytes, azithromycin is actively transported to the site of infection. During active phagocytosis, large concentrations of azithromycin are released. The concentration of azithromycin in the tissues can be over 50 times higher than in plasma. This is due to ion trapping and the high lipid solubility.

Absorption

Bioavailability of azithromycin is 37% following oral administration. Absorption is not affected by food.

Volume of distribution

After oral administration, azithromycin is widely distributed in tissues with an apparent steady-state volume of distribution of 31.1 L/kg

Metabolism:

Following a single 500 mg dose, plasma concentrations of azithromycin declined in a polyphasic pattern with a mean apparent plasma clearance of 630 mL/min and a terminal elimination half-life of 68 hours. The prolonged terminal half life is thought to be due to extensive uptake and subsequent release of drug from tissues.

Excretion

Biliary excretion of azithromycin, predominantly unchanged, is a major route of elimination. Over the course of a week, approximately 6% of the administered dose appears as unchanged drug in urine.

Half-life

Terminal elimination half-life: 68 hours

Side effects of Azithromycin

Most common side effects are gastrointestinal:

  • diarrhea (4-5%),
  • nausea (3%),
  • abdominal pain (2-3%) and
  • vomiting.

Fewer than 1% of patients stop taking the drug due to side effects. Serious allergic reactions, dermatologic reactions, and fatalities have been reported but are extremely rare. As with all antimicrobial agents, pseudomembranous colitis can occur during and up to several weeks after azithromycin therapy.

Allergic reaction

Patients who suffer from an allergic reaction to Azithromycin will often experience blood in the stool 4-10 days after ingestion, although cases of this have been recorded as early as after the first day of ingestion. These allergies are usually non-severe if the treatment is immediatley stopped.

Contraindication of Azithromycin

Azithromycin is contraindicated in patients with high sensitivity to the macrolide group, or with kidney & liver insufficiency.

Drug interaction with Azithromycin

Azithromycin interacts with cimetidine, theophylline, warfarin, carbamazepine and methylprednisolone.

Azithromycin Use in Pregnancy and Breastfeeding

Pregnancy Category B

Azithromycinin should only be given in pregnancy when the benefit outweighs the risk. It is excreted in breast milk and as such the manufacturer recommends that caution be used when administering to nursing mothers.

How to Store Azithromycin

Store below 30°C. Protect from light

KEEP MEDICINE OUT OF REACH OF CHILDREN

Chemical Structure of Azithromycin

 

Azithromycin

References

  1. Drug Bank
  2. Science Direct
  3. PharmGKB

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