Azithromycin is acid-stable and can therefore be taken orally with no need of protection from gastric acids. It is readily absorbed; its absorption is greater on an empty stomach. Time to peak concentration in adults is 2.1 to 3.2 hours for oral dosage forms. 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.

Azithromycin's half-life allows a large single dose to be administered and yet maintain bacteriostatic levels in the infected tissue for several days. 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. 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.

Microbiology: Azithromycin acts by binding to the 50S ribosomal subunit of susceptible microorganisms and, thus, interfering with microbial protein synthesis. Nucleic acid synthesis is not affected. Azithromycin has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections:

• Aerobic and facultative gram-positive microorganisms: Staphylococcus aureus, Streptococcus agalactiae, Streptococcus pneumoniae, Streptococcus pyogenes
• Aerobic and facultative gram-negative microorganisms: Haemophilus ducreyi, Haemophilus influenzae, Moraxella catarrhalis, Neisseria gonorrhoeae
• Other microorganisms: Chlamydia pneumoniae, Chlamydia trachomatis , Mycoplasma pneumoniae , Betalactamase production should have no effect on azithromycin activity.
• Aerobic and facultative gram-positive microorganisms: Streptococci (Groups C,F,G), Viridans group streptococci
• Aerobic and facultative gram-negative microorganisms: Bordetella pertussis, Legionella pneumophila
• Anaerobic microorganisms: Peptostreptococcus species, Prevotella bivia

Azithromycin is indicated for infections (caused by susceptible organisms) in lower respiratory tract infections including bronchitis and pneumonia, in upper respiratory tract infections including sinusitis and pharyngitis/tonsillitis, in otitis media, and in skin and soft tissue infections. In sexually transmitted diseases in men and women, Azithromycin is indicated in the treatment of non-gonococcal urethritis and cervicitis due to Chlamydia trachomatis.

Oral-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.

Reconstitution procedure of suspension-

• Step 01: Shake the bottle well to loosen the powder.
• Step 02: Add boiled and cooled water up to the water mark of the bottle label.
• Step 03: Shake until powder is completely mixed with water.

Azithromycin should be taken at least 1 hour before or 2 hours after meal.

Azithromycin is contraindicated in patients hypersensitive to Azithromycin or any other macrolide antibiotic. Co-administration of ergot derivatives and Azithromycin is contraindicated. Azithromycin is contraindicated in patients with hepatic diseases.

Azithromycin is well tolerated with a low incidence of side effects. The side effects include nausea, vomiting, abdominal discomfort (pain/cramps), flatulence, diarrhoea, headache, dizziness, and skin rashes and are reversible upon discontinuation of therapy.

Overdose Effects

There is no data on overdosage with Azithromycin. Typical symptoms of overdosage with macrolide antibiotics include hearing loss, severe nausea, vomiting and diarrhoea. Gastric lavage and general supportive measures are indicated.

As with any antibiotic, observation for signs of superinfection with non-susceptible organisms, including fungi, is recommended. No dose adjustment is needed in patients with renal impairment.

Pregnancy & Lactation

Pregnancy Category of Azithromycin is B. Animal reproduction studies have demonstrated that Azithromycin has no evidence of harm to the fetus. There are no adequate and well controlled studies in pregnant women. Since animal reproduction studies are not always predictive of human response, Azithromycin should be used during pregnancy only if adequate alternatives are not available. It is not known whether Azithromycin is secreted in breast milk. So, caution should be exercised when Azithromycin is administered to nursing women.