Azithromycin is an azalide, a subclass of macrolide antibiotics.

Azystate-500 Tablets	Azithromycin 500 mg.
Azystate-250 Tablets	Azithromycin 250 mg.

 

Microbiology

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, but is more effective against certain gram-negative bacteria, particularly Haemophilus influenzae.

Azithromycin resistance has been described and is common in many areas.

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

Helicobacter pylori

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.

Pharmacokinetics

Unlike erythromycin, 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.

Azithromycin's half-life allows a large single dose to be administered and yet maintain bacteriostatic levels in the infected tissue for several days. The new "Zmax" formulation of azithromycin is an enteric-coated suspension that releases the drug in a single 2g dose once it has cleared the stomach, reducing the GI side-effects of high-dose azithromycin.

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.

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.

Side effects

Most common side effects are gastrointestinal; diarrhea (5%), nausea (3%), abdominal pain (3%) and vomiting. Fewer than 1% of patients stop taking the drug due to side effects. Serious allergic reactions, nervousness, dermatologic reactions, and fatalities have been reported but are extremely rare. Increased appetite may or may not occur in the patient. As with all antimicrobial agents, pseudomembranous colitis can occur during and up to several weeks after azithromycin therapy. This drug may interfere with the effectiveness of birth control pills; other forms of contraception may be required during the treatment period. Although mild diarrhea is normal, if it is moderate to severe, or if it continues or is bothersome, check with your doctor. If you experience vomiting, unable to process food, or hearing loss or ringing in the ears, contact your doctor as soon as possible.

Allergic reaction

Allergic reaction to this medicine is unlikely, but seek immediate medical attention if it occurs. Patients who suffer from an allergic reaction to Azithromycin can 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 immediately stopped. A severe reaction includes a severe rash, hives, breathing difficulties, or dizziness. If experiencing difficulty breathing; tightness of chest; swelling of eyelids, face, legs, hands, eyes, throat, tongue or lips; or you develop a rash or hives, tell your doctor immediately. If you notice other effects not listed above, contact your doctor, nurse, or pharmacist.