Dirithromycin

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Cat Number

API62013041

CAS Number

62013-04-1

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CAS Number

62013-04-1

EINECS

624-080-7

Storage

Store at room temperature

Synonyms

Dirithromycine; Dynabac; Diritromicina; Dirithromycinum; LY-237216; 1801D76STL

Molecular Formula

C42H78N2O14

Molecular Weight

835.1

Smiles

CC[C@@H]1[C@@]([C@H]2[C@H]([C@H]([C@@H](C[C@@]([C@@H]([C@H]([C@@H]([C@H](C(=O)O1)C)O[C@H]3C[C@@]([C@H]([C@@H](O3)C)O)(C)OC)C)O[C@H]4[C@@H]([C@H](C[C@H](O4)C)N(C)C)O)(C)O)C)N[C@H](O2)COCCOC)C)(C)O

Appearance

White to almost white powder to crystal

Melting Point

185-189°C

Boiling Point

871.8±65.0°C at 760 mmHg

Relative Density

1.2±0.1

General Description

Dirithromycin is a semisynthetic macrolide antibiotic derived from erythromycin, featuring a 14-membered lactone ring with a 9-amine substituent that forms a cyclic carbamate. This structural modification confers acid stability and improved oral absorption. The molecule is a white crystalline powder, practically insoluble in water but soluble in organic solvents.

Mechanism of Action

Dirithromycin binds reversibly to the 50S ribosomal subunit of susceptible bacteria, specifically the 23S rRNA, inhibiting protein synthesis by blocking the translocation step of peptide chain elongation. The drug is bacteriostatic at therapeutic concentrations. Unlike erythromycin, dirithromycin is inactive until hydrolyzed to its active metabolite, erythromycylamine, which retains the same ribosomal binding site and spectrum of activity.

Application

Dirithromycin is indicated for the treatment of mild to moderate respiratory tract infections, including acute exacerbations of chronic bronchitis, community-acquired pneumonia, and pharyngitis/tonsillitis caused by susceptible organisms such as Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. It is also used for skin and soft tissue infections.

Dirithromycin (37.75–250 µg/mL, 24–48 h) significantly increased sister chromatid exchanges, chromosome aberrations, and micronucleus frequency in cultured human lymphocytes, with no effect on mitotic, replication, or nuclear division indices. The antibiotic induced dose- and time-dependent genotoxic and mutagenic damage in vitro.

Fig. 1 Chromosome break (67.50 μg/mL dirithromycin, 24 h treatment, ♀). (Kayraldız A, et al., 2015)

References

Kayraldız A, et al. Evaluation of Possible Genotoxic Activity of Dirithromycin in Cultured Human Lymphocytes. J Toxicol. 2015;2015:535490.

A network meta‑analysis of 19 RCTs (5,906 AECOPD patients) found dirithromycin had the highest clinical cure rate with fewest adverse effects. Ofloxacin, ciprofloxacin, and trimethoprim‑sulfamethoxazole also had high cure rates with moderate adverse effects. Only doxycycline significantly improved microbiological response vs placebo (OR 3.84). No differences were found in recurrence or mortality.

Fig. 2 Network of comparisons for the clinical cure rate included in the analysis. (Zhang HL, et al., 2017)

References

Zhang HL, et al. Antibiotics for treatment of acute exacerbation of chronic obstructive pulmonary disease: a network meta-analysis. BMC Pulm Med. 2017;17(1):196.

Does Dirithromycin require protection from moisture during long-term storage?

Yes, it is hygroscopic and susceptible to hydrolysis of the macrolactone ring. Store in tightly sealed, moisture-proof containers with desiccant.

What is the recommended storage temperature for Dirithromycin?

Store at controlled room temperature (15-25°C). Avoid temperatures above 30°C, which accelerate degradation of the macrolactone ring.

Is Dirithromycin stable in tablet formulations with standard excipients?

Yes, when formulated with moisture-protective packaging.

How is the impurity erythromycylamine (a hydrolysis product) monitored?

This primary degradation product is specifically quantified using a stability-indicating HPLC method, ensuring it remains within pharmacopoeial limits.