Azithromycin (Zithromax®) versus Clarithromycin (Biaxin®)

Based on "Antibiotic and Chemotherapy"
written by Roger G. Finch

Main differences between Azithromycin and Clarithromycin

	Azithromycin	Clarithromycin
Drug class	Macrolide antibiotic
Dosing schedule	more convenient once a day dosing	twice-a-day dosing
Spectrum of activity	More rapid killing and longer postantibiotic effect against H. influenzae	Significantly longer postantibiotic effect against S. pneumonia
	Better in vitro activity against M catarrhalis and M pneumoniae	More active in vitro against the atypical respiratory pathogens (e.g., against Legionella pneumophila and Chlamydia pneumoniae)
	Has activity against enteric pathogens, including Escherichia coli, Salmonella spp, Yersinia enterocolitica, and Shigella spp4	Has no in vitro activity against these enteric pathogens
	More active against Campylobacter jejuni	More active against Helicobacter pylori
Adverse effects & Toxicity	Small risk of QT interval prolongation	Greater risk of QT interval prolongation 5
Drug interactions	Does not affect CYP isoenzymes	Clarithromycin is an inhibitor of cytochrome CYP3A4 isoenzymes and may cause drug interactions with medications that require CYP3A4 enzyme for their metabolism.
Other notes	Azithromycin distributes less well across bronchial membranes than clarithromycin

Pneumonia

Azithromycin (3-day, once-daily course) is as effective and well tolerated as clarithromycin (10-day, twice-daily course) in the treatment of mild to moderate community-acquired pneumonia2.

Results of randomized, multicentre study comparing azithromycin versus clarithromycin in adults with mild to moderate community-acquired pneumonia 2	Azithromycin	Clarithromycin
Regimen	500 mg once daily for 3 days	250 mg twice daily for 10 days
Satisfactory clinical response, number of patients (%)	83 of 88 (94%)	84 of 88 (95%)
Number (%) of eradicated pathogens which were isolated from patients before treatment	31 of 32 (97%)	32 of 35 (91%)
Incidences of adverse events	similar
Relapsed patients	1	1
Number of patients who discontinued therapy due to severe adverse events	0	2 (2%)

Acute exacerbation of chronic bronchitis

Azithromycin is equivalent to clarithromycin for the treatment of acute exacerbation of chronic bronchitis (AECB) in adults1.

Results of randomized, double-blind, double-dummy, multicenter study comparing azithromycin versus clarithromycin for acute exacerbation of chronic bronchitis 1	Azithromycin	Clarithromycin
Regimen	500 mg once daily for 3 days	250 mg twice daily for 10 days
The clinical cure (based on direct observation of the patient) rates	85%	82%
Clinical success rates on day 10-12	93%	94%
Bacteriologic success rates at test of cure: S. pneumoniae H. influenzae M. catarrhalis	90.6% 71.4% 100%	85.2% 81.3% 86.7%
Incidence of adverse events abdominal cramps diarrhea nausea	20.9% 6.3% 4.4% 4.4%	26.8% 6.1% 5.5% 3.7%

Otitis media

Both azithromycin and clarithromycin are effective for the treatment of children with acute otitis media (infection of the middle ear)3.

Results of randomized, open clinical trial comparing azithromycin and clarithromycin in children aged 6 months to 12 years of age with acute otitis media with effusion 3	Azithromycin	Clarithromycin
Regimen	10 mg/kg once daily for 3 days	15 mg/kg day divided into 2 equal doses for 10 days
Satisfactory clinical response, number of patients (%)	50 (100%)	45 (95.7%)
Rates of persistence of middle ear effusion and possible side effects	comparable

References

1. Swanson RN, Lainez-Ventosilla A, De Salvo MC, Dunne MW, Amsden GW. Azithromycin compared with clarithromycin for acute exacerbation of chronic bronchitis. Treat Respir Med. 2005;4(1):31-9. PubMed
2. O'Doherty B, Muller O. Randomized, multicentre study of the efficacy and tolerance of azithromycin versus clarithromycin in the treatment of adults with mild to moderate community-acquired pneumonia. Eur J Clin Microbiol Infect Dis. 1998 Dec;17(12):828-33. PubMed
3. Arguedas A, Loaiza C, Rodriguez F, Herrera ML, Mohs E. Comparative trial of 3 days of azithromycin versus 10 days of clarithromycin in the treatment of children with acute otitis media with effusion. J Chemother. 1997 Feb;9(1):44-50. PubMed
4. Retsema J, Girard A, Schelkly W, et al. Spectrum and mode of action of azithromycin (CP-62,993), a new 15-membered-ring macrolide with improved potency against gram- negative organisms. Antimicrob Agents Chemother 1987;31:1939–47.
5. Guo D, Cai Y, Chai D, Liang B, Bai N, Wang R. The cardiotoxicity of macrolides: a systematic review. Pharmazie. 2010 Sep;65(9):631-40. PubMed