Azithromycin belongs to a group of medicines called macrolide antibiotics. Antibiotics are used to treat infections caused by micro-organisms like bacteria. Azithromycin is prescribed to treat acute bacterial infections, such as respiratory infections, ear infections, skin infections and some genital infections.
Why is this medication prescribed?Azithromycin is an antibiotic medicine taken once a day to treat the following types of infections in adults: bronchitis, certain types of skin infections, strep throat (pharyngitis, tonsillitis), and pneumonia.
Azithromycin helps stop the growth of the bacteria that cause infection. It gets into infected tissue where it is released slowly over time. The medicine fights the infection for several days after the last dose is taken.
Indications and Usage
It can be taken by adults and children. It works by stopping the bacteria causing the infection from multiplying. Azithromycin is used for the treatment of certain infections caused by bacteria that are sensitive to it, such as:
- Chest, throat or nasal infections (such as bronchitis, pneumonia, tonsillitis, sore throat (pharyngitis) and sinusitis)
- Ear infections
- Skin and soft tissue infections, with exception of infected burn wounds e.g. - infection of the tube that carries urine from the bladder (urethra) or the neck of the womb (cervix) caused by Chlamydia trachomatis (bacteria)
You have severe liver or kidney problems.
You have severe heart problems or problems with your heart beat such as long QT syndrome (shown on an electro-cardiogram or ECG machine).
Your blood levels of potassium or magnesium are too low.
You develop signs of another infection.
you are taking any ergot derivatives such as ergotamine (to treat migraine) as these medicines should not be taken together with azithromycin.
Mechanism of Action:Azithromycin is a macrolide antibacterial drug. Azithromycin concentrates in phagocytes and fibroblasts as demonstrated byin vitro incubation techniques. Using such methodology, the ratio of intracellular to extracellular concentration was > 30 after one hour of incubation. In vivo studies suggest that concentration in phagocytes may contribute to drug distribution to inflamed tissues.
Pharmacodynamics:Based on animal models of infection, the antibacterial activity of azithromycin appears to correlate with the ratio of area under the concentration-time curve to minimum inhibitory concentration (AUC/MIC) for certain pathogens (S. pneumoniae and S. aureus). The principal pharmacokinetic/pharmacodynamic parameter best associated with clinical and microbiological cure has not been elucidated in clinical trials with azithromycin.
Pharmacokinetics:Following oral administration of a single 500 mg dose (two 250 mg tablets) to 36 fasted healthy male volunteers, the mean (SD) pharmacokinetic parameters were AUC0-72 = 4.3 (1.2) mcgâ€¢h/ml; Cmax = 0.5 (0.2) mcg/mL; Tmax = 2.2 (0.9) hours. With a regimen of 500 mg (two 250 mg tablets*) on day 1, followed by 250 mg daily (one 250 mg capsule) on days 2 through 5, the pharmacokinetic parameters of azithromycin in plasma in healthy young adults (18 to 40 years of age) are portrayed in the chart below. Cmin and Cmax remained essentially unchanged from day 2 through day 5 of therapy.
Absorption: The absolute bioavailability of azithromycin 250 mg tablets is 38%.In a two-way crossover study in which 12 healthy subjects received a single 500 mg dose of azithromycin (two 250 mg tablets) with or without a high fat meal, food was shown to increase Cmax by 23% but had no effect on AUC. When azithromycin suspension was administered with food to 28 adult healthy male subjects, Cmax increased by 56% and AUC was unchanged.The AUC of azithromycin was unaffected by coadministration of an antacid containing aluminum and magnesium hydroxide with azithromycin tablets; however, the Cmax was reduced by 24%. Administration of cimetidine (800 mg) two hours prior to azithromycin had no effect on azithromycin absorption.
Distribution: The serum protein binding of azithromycin is variable in the concentration range approximating human exposure, decreasing from 51% at 0.02 mcg/ml to 7% at 2 mcg/ml. Following oral administration, azithromycin is widely distributed throughout the body with an apparent steady-state volume of distribution of 31.1 l/kg. Greater azithromycin concentrations in tissues than in plasma or serum were observed. High tissue concentrations should not be interpreted to be quantitatively related to clinical efficacy. The antimicrobial activity of azithromycin is pH related and appears to be reduced with decreasing pH. However, the extensive distribution of drug to tissues may be relevant to clinical activity.
Metabolism: In vitro and in vivo studies to assess the metabolism of azithromycin have not been performed.
Elimination: Plasma concentrations of azithromycin following single 500 mg oral and i.v. doses declined in a polyphasic pattern with a mean apparent plasma clearance of 630 ml/min and 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 as unchanged drug, is a major route of elimination. Over the course of a week, approximately 6% of the administered dose appears as unchanged drug in urine.
Drug interaction studies were performed with azithromycin and other drugs likely to be coadministered .When used in therapeutic doses, azithromycin had a modest effect on the pharmacokinetics of atorvastatin, carbamazepine, cetirizine, didanosine, efavirenz, fluconazole, indinavir, midazolam, rifabutin, sildenafil, theophylline (intravenous and oral), triazolam, trimethoprim/sulfamethoxazole or zidovudine. Coadministration with efavirenz or fluconazole had a modest effect on the pharmacokinetics of azithromycin. No dosage adjustment of either drug is recommended when azithromycin is coadministered with any of the above agents.
Interactions with the drugs listed below have not been reported in clinical trials with azithromycin; however, no specific drug interaction studies have been performed to evaluate potential drug-drug interaction. Nonetheless, they have been observed with macrolide products. Until further data are developed regarding drug interactions when azithromycin and these drugs are used concomitantly, careful monitoring of patients is advised:
Digoxin elevated digoxin concentrations.
Ergotamine or dihydroergotamine acute ergot toxicity characterized by severe peripheral vasospasm and dysesthesia.
Terfenadine, cyclosporine, hexobarbital and phenytoin concentrations.
If you are pregnant or breast-feeding.
If you have any problems with the way your liver works or the way your kidneys work.
If you know you have an unusual heart rhythm.
If you have a muscle disorder called myasthenia gravis.
If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
If you have ever had an allergic reaction to a medicine.
Swelling of the hands, feet, ankles, face, lips, mouth or throat Problems with swallowing or breathing
Serious skin reactions including Stevens-Johnson Syndrome (a severe skin rash) and other severe skin rashes which may involve blistering or peeling (these may be severe allergic reactions)
Severe, persistent diarrhoea especially if it has blood or mucus in it (this may be Pseudo membranous colitis).
Oral:This is a Prefered Dosage:
Always take Azithromycin 250 mg exactly as your doctor has prescribed you. You should check with your doctor or pharmacist if you are not sure.
Adults: Respiratory tract and skin or soft tissue infections: 500 mg once daily for three days.
Sexually transmitted diseases: 1000 mg as a single dose.
Elderly: The usual adult doses may be used.
Children: Azithromycin 250mg tablets are not recommended for use in children weighing less than 45 kg. For children weighing more than 45 kg the usual adult dose may be used.
Disclaimer:To be taken only after consulting with the doctor.
• Store in a cool, dry place, away from direct heat and light.
• If you have been given liquid medicine, it will have been made up by the pharmacy and it lasts for a limited number of days only. Check the expiry date on the bottle and do not use it after this date.