From the Guidelines
Azithromycin is preferred over clarithromycin due to its better tolerance, fewer drug interactions, lower pill burden, and single daily dosing, despite equal efficacy, as suggested by the 2020 clinical practice guideline published in Clinical Infectious Diseases 1. When considering the treatment of macrolide-susceptible MAC pulmonary disease, the choice between clarithromycin and azithromycin is crucial. Key differences between the two antibiotics include:
- Dosing frequency: Azithromycin is typically taken once daily, while clarithromycin is taken twice daily.
- Treatment duration: Azithromycin courses are often shorter, lasting 3-5 days, compared to clarithromycin, which may be prescribed for 7-14 days.
- Spectrum of activity: Both antibiotics are effective against various respiratory pathogens, but azithromycin has better coverage against certain bacteria, such as Haemophilus influenzae.
- Side effect profiles: Clarithromycin is more likely to cause metallic taste and has more significant drug interactions through the CYP3A4 enzyme system, whereas azithromycin has fewer drug interactions and may be better tolerated.
- Specific uses: Clarithromycin is often preferred for H. pylori eradication and has better activity against Mycobacterium avium complex, but azithromycin is preferred for MAC pulmonary disease due to its advantages, as stated in the guideline 1. It is essential to consider these factors when choosing between clarithromycin and azithromycin, prioritizing the patient's specific needs and potential interactions with other medications.
From the FDA Drug Label
Clarithromycin is a semi-synthetic macrolide antimicrobial for oral use. Chemically, it is 6- 0-methylerythromycin. Azithromycin has the chemical name (2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13-[(2,6-dideoxy-3-C-methyl-3-O-methyl-α-L-ribo-hexopyranosyl) oxy]-2-ethyl-3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl-11-[[3,4,6-trideoxy-3- (dimethylamino)-β-D-xylo-hexopyranosyl]oxy]-1-oxa-6-azacyclopentadecan-15-one The main difference between clarithromycin and azithromycin is their chemical structure.
- Clarithromycin is a semi-synthetic macrolide antimicrobial, chemically known as 6-0-methylerythromycin 2.
- Azithromycin is an azalide, a subclass of macrolide antibiotics, with a methyl-substituted nitrogen atom incorporated into the lactone ring 3. Key differences include:
- Molecular formula: clarithromycin (C38H69NO13) vs azithromycin (C38H72N2O12)
- Molecular weight: clarithromycin (747.96) vs azithromycin (749)
From the Research
Comparison of Clarithromycin and Azithromycin
- Both clarithromycin and azithromycin are new macrolide antibiotics with several advantages over erythromycin, including improved oral bioavailability, longer half-life, and higher tissue concentrations 4, 5.
- Azithromycin has an expanded spectrum against gram-negative bacilli, while clarithromycin is more active than erythromycin against gram-positive cocci 4, 6.
- Clarithromycin and azithromycin have been effective in treating various infections, including streptococcal pharyngitis, acute sinusitis, acute lower respiratory tract infections, skin and soft-tissue infections, and sexually transmitted diseases 4, 5, 6.
- Azithromycin has been shown to be effective for the treatment of genital chlamydial infections with a single dose 4, 7.
- Both agents have fewer gastrointestinal adverse effects compared to erythromycin, with the most frequently reported adverse effects being nausea, diarrhea, and abdominal pain 5, 6.
Pharmacokinetics and Antimicrobial Activity
- Clarithromycin and azithromycin have good oral bioavailability, excellent tissue penetration and persistence, and long elimination half-lives, allowing for once-daily or twice-daily dosing 5, 6, 8.
- Azithromycin has increased gram-negative activity compared to erythromycin, including activity against Haemophilus influenzae, while maintaining activity against gram-positive organisms 6.
- Clarithromycin has in vitro activity against Mycobacterium avium complex (MAC) and Toxoplasma gondii, and has been used to treat MAC and Toxoplasma infections in patients with acquired immunodeficiency syndrome 6, 7.
Clinical Use and Adverse Effects
- The clinical efficacy of clarithromycin and azithromycin has been similar to erythromycin for the treatment of upper and lower respiratory tract and skin and soft tissue infections 5.
- New therapeutic roles include the use of azithromycin for C. trachomatis infections and the inclusion of clarithromycin or azithromycin as part of therapeutic regimens for disseminated MAC infections in HIV-infected patients 5, 7.
- Further clinical trials are needed to determine the optimal roles for and uses of these new macrolides 5, 7.