Introduction
Azithromycin is a broad-spectrum macrolide antibiotic with a long half-life and a high degree of tissue penetration .
It is primarily used for the treatment of respiratory, enteric and genitourinary infections and may be used instead of other macrolides for some sexually transmitted and enteric infections. It is structurally related to erythromycin .
Azithromycin is a part of the azalide subclass of macrolides, and contains a 15-membered ring, with a methyl-substituted nitrogen instead of a carbonyl group at the 9a position on the aglycone ring, which allows for the prevention of its metabolism. This differentiates azithromycin from other types of macrolides .
Uses
Azithromycin is a macrolide antibiotic used to treat a variety of bacterial infections.
Azithromycin should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria in order to prevent the development antimicrobial resistance and maintain the efficacy of azithromycin .
Azithromycin is indicated for the treatment of patients with mild to moderate infections caused by susceptible strains of the microorganisms listed in the specific conditions below. Recommended dosages, duration of therapy and considerations for various patient populations may vary among these infections. Refer to the FDA label and "Indications" section of this drug entry for detailed information .
Adults:
Acute bacterial exacerbations of chronic obstructive pulmonary disease due to Haemophilus influenzae, Moraxella catarrhalis or Streptococcus pneumoniae
Acute bacterial sinusitis due to Haemophilus influenzae, Moraxella catarrhalis or Streptococcus pneumoniae
Community-acquired pneumonia due to Chlamydophila pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae or Streptococcus pneumoniae in patients appropriate for oral therapy
Pharyngitis/tonsillitis caused by Streptococcus pyogenes as an alternative to first-line therapy in individuals who cannot use first-line therapy. Uncomplicated skin and skin structure infections due to Staphylococcus aureus, Streptococcus pyogenes, or Streptococcus agalactiae. Abscesses usually require surgical drainage.
Urethritis and cervicitis due to Chlamydia trachomatis or Neisseria gonorrhoeae.
Genital ulcer disease in men due to Haemophilus ducreyi (chancroid). Due to the small number of women included in clinical trials, the efficacy of azithromycin in the treatment of chancroid in women has not been established.
Pediatric Patients
Acute otitis media caused by Haemophilus influenzae, Moraxella catarrhalis or Streptococcus pneumoniae
Community-acquired pneumonia due to Chlamydophila pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae or Streptococcus pneumoniae in patients appropriate for oral therapy.
Pharyngitis/tonsillitis caused by Streptococcus pyogenes as an alternative to first-line therapy in individuals who cannot use first-line therapy.
Associated Conditions
Pharmacodynamics
Macrolides stop bacterial growth by inhibiting protein synthesis and translation, treating bacterial infections . Azithromycin has additional immunomodulatory effects and has been used in chronic respiratory inflammatory diseases for this purpose .
Mechanism of Action
In order to replicate, bacteria require a specific process of protein synthesis, enabled by ribosomal proteins . Azithromycin binds to the 23S rRNA of the bacterial 50S ribosomal subunit. It stops bacterial protein synthesis by inhibiting the transpeptidation/translocation step of protein synthesis and by inhibiting the assembly of the 50S ribosomal subunit , . This results in the control of various bacterial infections , . The strong affinity of macrolides, including azithromycin, for bacterial ribosomes, is consistent with their broad‐spectrum antibacterial activities .
Azithromycin is highly stable at a low pH, giving it a longer serum half-life and increasing its concentrations in tissues compared to erythromycin .
Absorption
Bioavailability of azithromycin is 37% following oral administration. Absorption is not affected by food. Macrolide absorption in the intestines is believed to be mediated by P-glycoprotein (ABCB1) efflux transporters, which are known to be encoded by the ABCB1 gene .
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 . Significantly greater azithromycin concentrations have been measured in the tissues rather than in plasma or serum , . The lung, tonsils and prostate are organs have shown a particularly high rate of azithromycin uptake .
This drug is concentrated within macrophages and polymorphonucleocytes, allowing for effective activity against Chlamydia trachomatis . In addition, azithromycin is found to be concentrated in phagocytes and fibroblasts, shown by in vitro incubation techniques. In vivo studies demonstrate that concentration in phagocytes may contribute to azithromycin distribution to inflamed tissues .
Protein Binding
The serum protein binding of azithromycin varies in humans, decreasing from 51% at 0.02 g/mL to 7% at 2 g/mL .
Route of Elimination
Biliary excretion of azithromycin, primarily as unchanged drug, is a major route of elimination. Over a 1 week period, approximately 6% of the administered dose is found as unchanged drug in urine .
Half Life
Terminal elimination half-life: 68 hours
Clearance
Mean apparent plasma cl=630 mL/min (following single 500 mg oral and i.v. dose)
Toxicity
Rat Oral LD50: >2000 mk/kg
Possible major adverse effects include cardiovascular arrhythmias and hearing loss. Macrolide resistance is also an ongoing issue. Hepatotoxicity has been observed in rare cases.
A note on the risk of liver toxicity:
Due to the act that azithromycin is mainly eliminated by the liver, caution should be observed when azithromycin is given to patients with decreased hepatic function .
A note on potential renal toxicity:
Because limited data in patients with renal GFR Label.
Use in Pregnancy:
This drug is categorized as a pregnancy category B drug. Reproduction studies have been done in rats and mice at doses up to moderately maternally toxic doses (for example, 200 mg/kg/day). These doses, based on a mg/m2 basis, are approximately 4 and 2 times, respectively, the human daily dose of 500 mg. In the animal studies, no harmful effects to the fetus due to azithromycin were observed. There are, at this time, no conclusive and well-controlled studies that have been done in pregnant women. Because animal reproduction studies do not always predict human response, azithromycin should be used during pregnancy only if clearly needed .
Nursing Mothers:
It is unknown at this time whether azithromycin is excreted in human milk. Because many other drugs are excreted in human milk, caution should be observed when azithromycin is given to a nursing woman .
Carcinogenesis, Mutagenesis, Impairment of Fertility:
Long-term studies in animals have not been performed to study carcinogenic potential. Azithromycin has demonstrated no potential to be mutagenic in standard laboratory tests. No evidence of negative effects on fertility due to azithromycin was found .
Food Interactions
- Take on an empty stomach. Take at least 1 hour before or 2 hours after meals.
Dosage
Adult: 500 mg once daily orally for 3 days or 500 mg once on day 1, then 250 mg once on days 2-5 for 4 days. For sexually transmitted diseases caused by Chlamydia trachomatis in adults, the dose is 1 gm given as a single dose or 500 mg once on day 1, followed by 250 mg once daily for next 2 days may also be given.
Children:
- 10 mg/kg body weight once daily for 3 days for child over 6 months
- 200 mg (1 teaspoonful) for 3 days if body weight is 15-25 kg
- 300 mg (1½ teaspoonfuls) for 3 days if body weight is 26-35 kg; 400 mg (2 teaspoonfuls) for 3 days if body weight is 36-45 kg.
- In typhoid fever, 500 mg (2½ teaspoonfuls) once daily for 7-10 days is given.
Azithromycin Injection (For IV Infusion only): The recommended dose of Azithromycin for injection for the treatment of adult patients with community-acquired pneumonia due to the indicated organisms is:
- 500 mg as a single daily dose by the intravenous route for at least two days. Intravenous therapy should be followed by Azithromycin by the oral route at a single, daily dose of 500 mg, administered as two 250-mg tablets to complete a 7 to 10-day course of therapy. The timing of the switch to oral therapy should be done at the discretion of the physician and in accordance with clinical response.
- The recommended dose of Azithromycin for the treatment of adult patients with pelvic inflammatory disease due to the indicated organisms is: 500 mg as a single daily dose by the intravenous route for one or two days. Intravenous therapy should be followed by Azithromycin by the oral route at a single, daily dose of 250 mg to complete a 7-day course of therapy. The timing of the switch to oral therapy should be done at the discretion of the physician and in accordance with clinical response. If anaerobic microorganisms are suspected of contributing to the infection, an antimicrobial agent with anaerobic activity should be administered in combination with Azithromycin.
- Safety and effectiveness of azithromycin for injection in children or adolescents under 16 years have not been established.
