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Azithromycin (Pfizer’s Zithromax/Zitromax) is widely used for treatment of RTIs, including community-acquired pneumonia, AECB, otitis media and pharyngitis. The agent was launched in the early 1990s. Azithromycin (Zithromax) can also be used to treat skin infections and some sexually transmitted diseases in adults. In children, Azithromycin (Zithromax) is used to treat ear infections and pharyngitis/tonsillitis. This agent is available in oral and IV formulations. Azithromycin (Zithromax) is recognized for its broad efficacy, dosing advantages, favorable side-effect profile, and good-tasting liquid formulation for children. It has become the leading macrolide in the United States, owing primarily to its safety, long-half life (which allows an abbreviated five-day treatment course), and excellent promotion by Pfizer.
Azithromycin (Zithromax) acts by binding to the 50S ribosomal subunit of susceptible microorganisms and interfering with microbial protein synthesis. It demonstrates activity in vitro against a wide range of bacteria, including gram-positive bacteria such as S. aureus, S. pneumoniae, and other streptococci, and gram-negative bacteria such as H. influenzae and H. parainfluenzae. Azithromycin (Zithromax) demonstrates cross-resistance with erythromycin-resistant, gram-positive strains and most strains of methicillin-resistant staphylococci.
Azithromycin (Zithromax) is indicated for community-acquired pneumonia due to S. pneumoniae, H. influenzae, C. pneumoniae, or M. pneumoniae in patients for whom oral therapy is appropriate.
Data summarized from eight comparative studies and two noncomparative studies of patients with pneumonia demonstrate that a standard course of Azithromycin (Zithromax) delivered overall clinical response rates similar to response rates for comparators in patients of varying ages: 88% for both groups. The comparators used were cefaclor (Lilly’s Ceclor, generics); amoxicillin (GSK’s Amoxil, generics); erythromycin (generics); amoxicillin/clavulanate (generics); and josamycin (Bayer’s Josacine), dosed three times a day or twice a day for seven to ten days as appropriate.
The summarized data also demonstrate comparable clinical response rates in the subset of patients aged 16 to 60 years (92% for Azithromycin (Zithromax) and 95% for comparatives agents) and in the subset of patients older than 60 years of age (82% and 78%, respectively). Bacteriologic response rates (i.e., eradication of the susceptible pathogen present at baseline), compared with the other agents used, were as follows: S. pneumoniae (93% for Azithromycin (Zithromax), 95% for comparative agents) and H. influenzae (100% for Azithromycin (Zithromax), 85% for comparative agents).
Azithromycin (Zithromax) is rapidly and extensively taken up by leukocytes, which deliver the drug to the site of infection, where the drug maintains high sustained concentrations. In addition, Azithromycin (Zithromax) has a long half-life (68 hours), thus allowing a convenient five-day dosing regimen. It offers excellent tolerability, with a low incidence of adverse events. Azithromycin (Zithromax) compares favorably with amoxicillin/clavulanate and other competitive agents from a side-effect and tolerability standpoint. The most common side effects are diarrhea/loose stools (4-5%), nausea (3%), and abdominal pain (2-3%); the overall discontinuation rate is 0.7%.
Azithromycin: Organs and Systems
Cardiovascular
Torsade de pointes and cardiorespiratory arrest have been reported in a patient with congenital long QT syndrome who took azithromycin. In a prospective study of 47 previously healthy people, there was a modest statistically insignificant prolongation of the QTC interval without clinical consequences after the end of a course of azithromycin 3 g/day for 5 days.
Sensory systems
Ears
Azithromycin can cause ototoxicity. In one study, 8 (17%) of 46 HIV-positive patients had probable (n = 6) or possible (n = 2) ototoxicity with azithromycin. The effects were hearing loss (88%), tinnitus (37%), plugged ears (37%), and vertigo (25%), developing at a mean of 7.6 weeks (1.5-20 weeks) after the start of long-term azithromycin therapy for Mycobacterium avium infection. The symptoms resolved in a mean of 4.9 weeks (2-11 weeks) after withdrawal.
Sensorineural hearing loss has been attributed to azithromycin.
A 35-year old Caucasian man with AIDS and multiple opportunistic infections, including Mycobacterium kansasii and Mycobacterium avium complex (MAC) disease developed moderate to severe primary sensorineural hearing loss after 4-5 months of therapy with oral azithromycin 500 mg/day. Other medications included ethambutol, isoniazid, rifabutin, ciprofloxacin, co-trimoxazole, fluconazole, zidovudine (later switched to stavudine), lamivudine, indinavir, methadone, modified-release oral morphine, pseudoephedrine, diphenhydramine, megestrol acetate, trazodone, sorbitol, salbutamol by metered-dose inhaler and nebulizer, ipratropium, and oral morphine solution as needed. Significant improvement of the hearing impairment was documented 3 weeks after drug withdrawal.
A literature review identified several cases of ototoxicity in HIV-positive patients treated with azithromycin for Mycobacterium avium complex infection. In four series, 14-41% of such patients had some degree of hearing loss. However, some patients were also taking other potentially ototoxic drugs, which may have contributed to the high frequency of hearing loss reported. Hearing loss improved markedly after withdrawal of azithromycin. Hearing loss may be more common and probably more severe with high-dose azithromycin than with high-dose clarithromycin.
A 47-year-old woman who had a left lung transplantation 3 months earlier and who was taking ticarcillin + -clavulanate and aztreonam for sinusitis, was given co-trimoxazole, ticarcillin + clavulanate, azithromycin (500 mg/day intravenously), and ganciclovir for presumed pneumonia. Other drugs included tacrolimus, mycophenolate, prednisone, lansoprazole, diltiazem, itraconazole, warfarin, alendronate, ipratropium bromide, folic acid, and nystatin. The next day, rimantadine and vancomycin were added, and co-trimoxazole was reduced. A neurological examination to assess symptoms of peripheral neuropathy noted no hearing deficit. On day 3, vancomycin, ticarcillin + – clavulanate, and ganciclovir were withdrawn. On the fifth day, mild tinnitus and reduced hearing developed and gradually progressed to complete deafness. After eight doses, azithromycin was withdrawn, and 20 days later her hearing was back to baseline.
Low-dose exposure to azithromycin has been associated with irreversible sensorineural hearing loss in otherwise healthy subjects. Even a single oral dose of azithromycin altered the conjunctival bacterial flora of children from a trachoma endemic area. However, the clinical significance is not yet clear.
Psychological, psychiatric
Azithromycin can cause delirium.
Hematologic
The effects of combining azithromycin and rifabutin have been studied in 50 subjects with or without HIV infection, of whom 19 took azithromycin 1200 mg/day and rifabutin 600 mg/day, and 31 took azithromycin 600 mg/day and rifabutin 300 mg/day. Neutropenia was the most common adverse event, in 33 of 50 subjects. Low-grade nausea, diarrhea, fatigue, and headache were also common, and most subjects had more than one type of event. There was no significant pharmacokinetic interaction between the two drugs.
Gastrointestinal
In a review of 12 clinical studies most of the adverse events in those taking azithromycin affected the gastrointestinal system, and were reported in 138 (8.5%) azithromycin-treated patients. Abdominal pain, diarrhea, nausea, and vomiting were the most frequently reported gastrointestinal adverse events.
Gastrointestinal symptoms were the most common adverse effects reported in a trial of azithromycin in disseminated Mycobacterium avium complex in 62 patients with AIDS. Erythromycin is a motilin receptor agonist. This mechanism may be at least partly responsible for the gastrointestinal adverse effects of macrolides. Azithromycin may act on gastrointestinal motility in a similar way to erythromycin, as it produces a significant increase in postprandial antral motility.
Liver
Azithromycin can cause intrahepatic cholestasis.
A 33-year-old woman and a 72-year-old man developed cholestasis after they had taken a 5-day course of azithromycin. The woman was given colestyramine and underwent six courses of plasmapheresis; 2 months later, her total bilirubin and serum transaminases were back to normal. After withdrawal of azithromycin, the man’s symptoms resolved within 1 month and his liver enzymes returned to normal.
Skin
A 19-year-old man with infectious mononucleosis developed a maculopapular, non-pruritic rash after one dose of azithromycin 500 mg.
Immunologic
Occupational allergic contact dermatitis has been attributed to azithromycin.
A 32-year-old pharmaceutical worker had been loading reactors at three different stages of azithromycin synthesis for the past 3 years and had been exposed to airborne powders. He wore overalls and latex gloves. His symptoms had persisted for 1 year in the form of pruritus, erythema, vesicles, and scaling of the face and forearms. A positive patch test and a positive workplace challenge were considered reliable in the diagnosis of occupational allergic contact dermatitis induced by azithromycin. After transfer to another work station that excluded exposure to azithromycin, he had no further work-related symptoms.
Hypersensitivity to azithromycin has been reported.
A 79-year-old man developed fever, mental changes, a rash, acute renal insufficiency, and hepatitis after he had completed a 5-day course of oral azithromycin (500 mg initially then 250 mg/day). With intravenous hydration only, his fever abated and his urinary output and renal and hepatic function returned to normal over the next 4 days. His mental status improved significantly. The skin rash was followed by extensive desquamation.
Azithromycin has been associated with Churg-Strauss syndrome in a patient with atopy.
Generic Zithromax (Azithromycin): Side Effects
Observational studies
In 3995 patients who took azithromycin 1.5 g in divided doses over 5 days or who took 1 g as a single dose for urethritis/cervicitis adverse events occurred in 12%. In patients over 65 years the rate was 9.3%, and in children under 14 years of age it was 5.4%. The most common adverse effects were gastrointestinal (9.6%); central nervous system and peripheral nervous system effects were reported in 1.3%. Overall, 59% of the adverse events were considered mild, 34% moderate, and only 6% severe, involving mainly the gastrointestinal tract. Adverse events resulted in withdrawal in 0.7% of patients, lower than the rate reported with other macrolides. Treatment-related rises in liver enzymes were uncommon (under 2%), as was leukopenia (1.1-1.5%).
Phase II/III clinical trials in the USA have yielded data on 1928 children aged 6 months to 15 years who took azithromycin for infections that included acute otitis media (n = 1150) and streptococcal pharyngitis (n = 754). Most took a 5-day course of azithromycin (5-12 mg/kg/day). There were adverse effects in 190 patients (9.9%): diarrhea (3.1%), vomiting (2.5%), abdominal pain (1.9%), loose stools (1%), and rash (2.5%). In three comparisons with co-amoxiclav, the overall incidence of adverse effects was significantly lower with azithromycin (7.7 versus 29%), with withdrawal rates of 0.3 versus 3.6%. However, the incidence of adverse effects was significantly greater with azithromycin than with penicillin V in comparisons in patients with streptococcal pharyngitis (13 versus 6.7%). In conclusion, it appears that the safety and tolerability of azithromycin is similar in children and adults.
In an open study, children with end-stage lung disease or chronic airflow limitation unresponsive to conventional therapy were treated with long-term azithromycin. Seven children (mean age 12 years), all of whom were colonized with Pseudomonas aeruginosa and who took azithromycin for more than 3 months, were studied. There was a significant improvement in FVC and FEV1.
The mechanism whereby azithromycin works is unknown, but it may be other than antibacterial. It has been hypothesized that the effect may be due to upregulation of a P glycoprotein, a member of the family of multidrug resistant proteins, since erythromycin upregulates P glycoprotein expression in a monkey model. Multidrug resistance (MDR) is homologous to cystic fibrosis transmembrane conductance regulator (cystic fibrosis transmembrane conductance regulator), and previous in vitro experiments have shown that the multidrug resistance and cystic fibrosis transmembrane conductance regulator genes can complement each other. However, direct proof of this hypothesis is lacking at the moment.
Of 42 adult HIV-positive patients with confirmed or presumed acute toxoplasmic encephalitis who received azithromycin 900, 1200, or 1500 mg/day plus pyrimethamine, 28 responded to therapy during the induction period. Six patients withdrew during the induction period because of reversible toxic effects (three with raised liver enzymes, two with hearing loss, one with neutropenia). Treatment-terminating adverse events occurred most often among the patients who took 1500 mg/day.
In an open, prospective trial gingival hyperplasia due to ciclosporin was successfully treated with azithromycin 250 mg/day for 5 days in 30 of 35 patients, who reported esthetic satisfaction and disappearance of bleeding and pain. There was no change in ciclosporin concentration or renal function after azithromycin.
Comparative studies
The tolerability of azithromycin oral suspension, 10 mg/ kg od for 3 days, has been assessed in children in a review of 16 multicenter studies. Of 2425 patients, 1213 received azithromycin and 1212 received other drugs. The incidence of treatment-related adverse events was significantly lower in those who took azithromycin, while withdrawal rates were similar. There were significantly fewer gastrointestinal events with azithromycin and their duration was significantly shorter.
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In a multicenter, parallel-group, double-blind trial in 420 evaluable patients aged 6 months to 16 years with community-acquired pneumonia, the therapeutic effect of azithromycin (once-daily for 5 days) was similar to that of co-amoxiclav in children under 5 years and to that of erythromycin tds for 10 days. Treatment-related adverse events occurred in 11% of those given azithromycin and 31% in the comparator group.
Azithromycin (500 mg/day for 3 days) has been used to treat acute periapical abscesses. Of 150 patients treated with azithromycin 18 reported a total of 26 adverse events. Slightly more (24 out of 153) treated with co-amoxiclav reported 34 adverse events, but this difference did not reach statistical significance. Most of the adverse events (44/60) were gastrointestinal, mostly diarrhea or abdominal pain. There were no significant differences between the two groups in the severity of adverse events or in the number of withdrawals because of adverse events.
Fluoroquinolones
In a multicenter, open, randomized comparison of levofloxacin 500 mg/day orally or intravenously and azithromycin 500 mg/day intravenously for up to 2 days plus ceftriaxone 1 g/day intravenously for 2 days in 236 patients, the most common drug-related adverse events in those given azithromycin were diarrhea (4.2%), vein disorders (2.5%), and pruritus (1.7%).
Other macrolides
The incidence of disseminated MAC (Mycobacterium avium complex) infection has increased dramatically with the AIDS epidemic. Treatment regimens for patients with a positive culture for MAC from a sterile site should include two or more drugs, including clarithromycin. Prophylaxis against disseminated Mycobacterium avium complex should be considered for patients with a CD4 cell count of less than 50 x 106/1. In a randomized, open trial in 37 patients with HrV-associated disseminated Mycobacterium avium complex infection, treatment with clarithromycin + ethambutol produced more rapid resolution of bacteremia, and was more effective at sterilization of blood cultures after 16 weeks than azithromycin + ethambutol.
Tetracyclines
Compared with tetracycline, azithromycin had a favorable short-term effect on childhood morbidity in a mass trial for trachoma in rural Gambian villages, and adverse effects were limited.
Treatment of facial comedonic and papulopustular acne with azithromycin (500 mg/day for 4 days in four cycles every 10 days) may be at least as effective as minocycline (100 mg/day for 6 weeks). Both were well tolerated and mild adverse effects were reported in 10% of patients given azithromycin and 12% of those given minocycline.
Placebo-controlled studies
In 169 patients with acute infective rhinitis, azithromycin (500 mg/day for 3 days) resulted in a better cure rate after 11 days than placebo; however, after 25 days the results for both improvement and cure were equal.
In a randomized, double-blind, placebo-controlled multicenter trial in 174 HIV-infected patients with CD4 cell counts of under 100 x 106/1, azithromycin (1200 mg once a week) was safe and effective in preventing disseminated mycobacterium avium complex infection, death due to MAC (Mycobacterium avium complex) infection, and respiratory tract infections.
In a triple-masked, randomized, placebo-controlled study in 1867 women, prophylaxis with azithromycin 500 mg 1 hour before intrauterine contraceptive device insertion did not affect the rate of intrauterine contraceptive device removal, the frequency of medical attention after insertion, or the risk of upper genital tract infection at 90 days. Women were at low risk of sexually transmitted disease according to self-reported medical history. Gastrointestinal adverse effects were infrequent (3% azithromycin; 2% placebo). Fewer women taking azithromycin (0.7%) than those taking placebo (1.3%) were treated with antibiotics for pelvic tenderness; however, this difference was not statistically significant. Since cervical infections increase the risk of pelvic infection in women who use intrauterine contraceptive devices (IUCDs), generalization of these results may be difficult.
In a meta-analysis of randomized, controlled trials of 3-5 days of azithromycin or other antibiotics that are typically given in longer courses for upper respiratory tract infections, there were no significant differences in bacteriological outcomes. Azithromycin was withdrawn because of adverse events in only 37 (0.8%) of 4870 patients.
Second-Generation Effects
Pregnancy
In two randomized trials in pregnant women with cervical Chlamydia trachomatis infection, women were randomized to oral amoxicillin 500 mg tds for 7 days or oral azithromycin 1 g in a single dose. The two drugs had similar efficacy. Adverse effects were common in both groups: 40% of those who took azithromycin reported moderate to severe gastrointestinal adverse effects compared with 17% of those who took amoxicillin.
Susceptibility Factors
Renal disease
In eight patients a single 500 mg oral dose of azithromycin was not substantially removed by continuous ambulatory peritoneal dialysis in the absence of peritonitis. Azithromycin cannot be recommended for widespread use in CAPD at present. However, the successful use of azithromycin in treating peritonitis, perhaps because of an intracellular drug transport mechanism, has been reported.
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Preparations
International Brand Drug Names
The information about drugs around the world. Many drugs are marketed under different names in different countries.
The United States Pharmacopeia 31, 2008: Azithromycin Capsules.
Proprietary Preparations
Australia: Zithromax;
Austria: Zithromax;
Canada: Z-Pak; Zithromax;
France: Azadose; Zithromax;
Germany: Ultreon; Zithromax;
India: Azee; Azibact; Azifast; Azithral; Aziwok; Zithrocin; Zycin;
Philippines: Zithromax; ZMax;
France: Zithrogen; Zithromax;
UK : Zithromax;
US : AzaSite; Zithromax; Zmax.
Azithromycin: Drug-Drug Interactions
Antacids
Owing to interference by antacids, azithromycin should be given at least 1 hour before or 2 hours after antacids. Antacids containing aluminium and magnesium reduce peak serum concentrations, but the total extent of azithromycin absorption is not altered.
Antihistamines
The effects of azithromycin 250 mg/day on the pharmacokinetics of desloratadine 5 mg/day and fexofenadine 60 mg bd have been studied in a parallel-group, third-party-blind, multiple-dose, randomized, placebo-controlled study. There were small increases (under 15%) in the mean plasma concentrations of desloratadine. In contrast, peak fexofenadine concentrations were increased by 69% and the AUC by 67%. There were no changes in the electrocardiogram.
Carbamazepine
A retrospective analysis of 3995 patients treated with azithromycin did not show any pharmacokinetic interactions in patients who were also taking various other drugs, including carbamazepine.
Ciclosporin
When azithromycin is used concomitantly with ciclosporin, blood ciclosporin concentrations need to be monitored.
Cimetidine
A retrospective analysis of 3995 patients treated with azithromycin did not show any pharmacokinetic interactions in patients who were also taking various other drugs, including cimetidine.
Cytochrome P450
Azithromycin has a 15-membered ring and does not induce or inhibit cytochrome P450 in rats.
Digoxin
When azithromycin is used concomitantly with digoxin, serum digoxin concentrations need to be monitored. While data on the effects of azithromycin on the intestinal metabolism of digoxin have not been reported so far, it is likely that it will affect Eubacterium lentum, like other macrolides.
Methylprednisolone
A retrospective analysis of 3995 patients treated with azithromycin did not show any pharmacokinetic interactions in patients who were also taking various other drugs, including methylprednisolone.
Midazolam
In an open, randomized, crossover, pharmacokinetic and pharmacodynamic study in 12 healthy volunteers who took clarithromycin 250 mg bd for 5 days, azithromycin 500 mg/day for 3 days, or no pretreatment, followed by a single dose of midazolam (15 mg), clarithromycin increased the AUC of midazolam by over 3.5 times and the mean duration of sleep from 135 to 281 minutes. In contrast, there was no change with azithromycin, suggesting that it is much safer for co-administration with midazolam.
Piroxicam
In 66 patients undergoing oral surgery, treatment with azithromycin impaired the periodontal disposition of piroxicam.
Rifamycins
An interaction involving azithromycin with rifabutin, and less commonly rifampicin, was observed in patients with Mycobacterium avium complex infections.
Terfenadine
The potential interaction of azithromycin with terfenadine has been evaluated in a randomized, placebo-controlled study in 24 patients who took terfenadine plus azithromycin or terfenadine plus placebo. Azithromycin did not alter the pharmacokinetics of the active carboxylate metabolite of terfenadine or the effect of terfenadine on the QT interval.
Theophylline and other xanthines
A retrospective analysis of 3995 patients treated with azithromycin did not show any pharmacokinetic interactions in patients who were also taking various other drugs, including theophylline.
In two double-blind, randomized, placebo-controlled studies there was no inhibition of the metabolism of theophylline by azithromycin. However, there has been a report of reduced theophylline concentrations after withdrawal of azithromycin. The authors concluded that the mechanism of interaction was best explained by concomitant induction and inhibition of theophylline metabolism by azithromycin, followed by increased availability of unbound enzyme sites as azithromycin was cleared from the system.
Warfarin
A retrospective analysis of 3995 patients treated with azithromycin did not show any pharmacokinetic interactions in patients who were also taking various other drugs, including warfarin.
Zidovudine
Zidovudine does not affect azithromycin concentrations and azithromycin does not affect zidovudine concentrations.
Food-Drug Interactions
Owing to interference by food, azithromycin should be given at least 1 hour before or 2 hours after food.