Azithromycin

Azithromycin is a semi-synthetic 15-membered azalide antibiotics derived from erythromycin. Azithromycin is a macrolide antibiotic suitable for the management of a number of bacterial infections. This comprises respiratory tract infections, skin infections, chlamydia infections, and syphilis. It may also be used during pregnancy to prevent Group B streptococcal infection in the new-born. It can be given intravenously and by mouth. Azithromycin displays bacteriostatic activity or inhibits growth of bacteria, principally at higher concentration, however the mechanism is not completely understood. By binding to the 50s subunit of the bacterial rRNA complex, protein synthesis and subsequent structure and function processes critical for life or replication are inhibited. Azithromycin is very rapidly absorbed, and diffuses into most tissues and phagocytes. Usual dosage range: -Oral: 500 mg once daily. Azithromycin has pharmacokinetics that allows shorter dosing schedules because of prolonged tissue levels. The bioavailability of azithromycin is approximately 37 % in humans. Tissue concentrations exceed serum concentrations by as far as 100-fold after a single 500 mg oral dose. Macrophages and polymorphonuclear leucocytes concentrate azithromycin at levels greater than those found in tissues themselves. High concentrations of drug are found in tissues such as tonsil, lung, prostate, liver and lymph nodes with relatively low concentrations in fat and muscle. As with all antimicrobial agents, pseudomembranous colitis can occur during and up to several weeks after azithromycin therapy. However, it has a few side effects like mild diarrhoea, nausea, vomiting, abdominal pain. Azithromycin can cause abnormal changes in the electrical activity of the heart that may lead to a potentially fatal irregular heart rhythm. Evidence indicates that azithromycin is largely excreted in the faeces unchanged, with a small percentage appearing in the urine. Exacerbations of myasthenia gravis have also been reported with the use of azithromycin. Azithromycin’s pharmacokinetics and tolerability make it particularly useful in the treatment of sexually transmitted infections, intracellular enteric pathogens and for prophylaxis of mycobacterial infection. It is furthermore beneficial for treating a variety of respiratory diseases. Unfettered use of azithromycin, particularly for its immunomodulatory properties, is of concern in light of macrolide resistance.

Two simple, rapid, accurate, sensitive and economical visible spectrophotometric (direct, indirect) methods (A and B) for the determination of azithromycin (AZT) in bulk sample and in dosage forms are described. The first method (A) is based on the oxidation of the drug by ammonium metavanadate in sulfuric acid medium and the absorbance is measured at 750 nm. The absorbance concentration plot is linear over the range (0.3-29.7 μg/ml). The second method (B) is based on oxidation of AZT by iodine solution in acidic medium, and determination of the unreacted oxidant by measuring the decrease in absorbance using methylene blue dye (MB) at a suitable λmax (662 nm), respectively. Regression analysis of Beer's law plots showed good correlation in the concentration ranges (0.4-36.1 μg/ml). The quality control/assurance parameters such as limits of detection (LOD), quantification (LOQ), molar absorptivity and Sandelle’s sensitivity values are also reported. The accuracy and precision of the methods were studied on intra-day and inter-day basis. No interference was observed from common pharmaceutical additives. The methods are used successfully to assay AZT in its pharmaceutical dosage forms viz. tablets, capsules and spiked human plasma.