Macrolide
Dirithromycin is a macrolide antibiotic derived from erythromycin. Its antibacterial action, like erythromycin, is through inhibition of bacterial protein synthesis by binding to the 50S ribosomal subunit.

Similar to erythromycin, dirithromycin has an antimicrobial activity spectrum in vitro.
With MICs of approximately 1.0 and <0.25 μg/mL at pH values of 7.1 and 7.4, respectively, dirithromycin demonstrates good in vitro activity against a number of strains of Legionella.
With MICs of less than 0.5 μg/mL, dirithromycin exhibits strong activity against a number of Helicobacter pytori strains[2].

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The antimicrobial spectrum of Dirithromycin is similar to that of erythromycin. It is active against gram-positive bacteria (e.g., Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus pneumoniae), Legionella spp., Helicobacter pylori, and Chlamydia trachomatis.
Against susceptible staphylococci and streptococci, MICs of Dirithromycin are generally within the same range as erythromycin, though its potency is slightly reduced. For example, against S. aureus X1.1, the MIC is 0.5 μg/mL; against S. epidermidis 222, MIC is 0.5 μg/mL; against S. pyogenes C203, MIC is 0.12 μg/mL; against S. pneumoniae Park I, MIC is 0.06 μg/mL.
Bacterial strains resistant to erythromycin are cross-resistant to Dirithromycin.
Dirithromycin is less active than erythromycin against Haemophilus influenzae strains (MICs ranging from 1.0 to 32 μg/mL).
It has no significant activity against gram-negative bacteria of the Enterobacteriaceae family or Pseudomonas spp. (MICs ≥ 64 μg/mL).
Against Legionella strains, Dirithromycin exhibited excellent activity comparable to erythromycin (MICs from <0.12 to 1.0 μg/mL at pH 7.4).
Against Helicobacter pylori strains, Dirithromycin showed potent activity (MICs ≤ 0.06 to 0.5 μg/mL).
Against Chlamydia trachomatis, Dirithromycin was slightly less active (MIC 4.0 μg/mL) than erythromycin (MIC 0.25 μg/mL).
Against anaerobic bacteria, Dirithromycin was generally less active than erythromycin.
The bacteriostatic or bactericidal properties (MBCs) of Dirithromycin were very similar to those of erythromycin. It acted primarily as a bacteriostatic agent against most staphylococci and streptococci, but was bactericidal against S. pneumoniae, Streptococcus sanguis, and Streptococcus intermedius.
Increasing the bacterial inoculum size from 10³ to 10⁸ CFU/ml led to increased MICs for Dirithromycin, similar to erythromycin.
The addition of human serum (0-40%) did not increase the MICs for Dirithromycin.
Different susceptibility testing methodologies (agar dilution, macrodilution, microdilution) and growth media yielded comparable results for Dirithromycin and erythromycin, with typically two- to fourfold differences in MICs.
In vitro resistance development studies showed that strains made resistant to either Dirithromycin or erythromycin exhibited cross-resistance to the other macrolide.

With ED50s of 1.0, 0.6, and <0.6 mg/kg, dirithromycin (s.c. for two times) is effective against experimental infections in mice caused by S. aureus, S. pyogenes, and S. pneumoniae[2].
With ED50s of 27, 34, and 23 mg/kg, respectively, dirithromycin (p.o. for two times) is effective against experimental infections in mice caused by S. aureus, S. pyogenes, and S. pneumoniae[2].

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In standard mouse protection tests against experimental infections caused by S. aureus, S. pyogenes, and S. pneumoniae, subcutaneous administration of Dirithromycin showed greater efficacy (lower ED50 values) than erythromycin. For example, against S. aureus, the subcutaneous ED50 for Dirithromycin was 1.0 mg/kg x2, compared to 1.6 mg/kg x2 for erythromycin.
When administered orally in solution by gavage (without protective formulation), neither Dirithromycin nor its metabolite erythromycinylamine was as effective as erythromycin. Oral efficacy was generally improved by administering two doses rather than one.
In a rat experimental endocarditis model caused by Enterococcus faecium X66, treatment with Dirithromycin (20 mg/kg/day for 8 days) was significantly more efficacious in eradicating the pathogen from heart vegetations than treatment with erythromycin at the same dose.

Aerobic Susceptibility Testing (Agar Dilution): Antibiotic susceptibility was determined by an agar dilution technique using Mueller-Hinton agar, supplemented for certain organisms. Antibiotics were incorporated into melted agar before pouring plates. Inocula of about 10⁴ CFU, prepared from overnight broth cultures, were applied using a multi-prong inoculator. Plates were incubated at 37°C for 18-20 hours before examining for growth. The MIC was the lowest concentration inhibiting visible growth.
Anaerobic Susceptibility Testing (Agar Dilution): Activity against anaerobic bacteria was evaluated by agar dilution according to a standard manual. Cultures were grown in supplemented broth, adjusted to a McFarland 0.5 standard. Antibiotic dilutions were incorporated into Wilkins-Chalgren agar. An inoculum of 10⁵ CFU per spot was applied with a calibrated replicator. Plates were incubated anaerobically at 35°C for 42-48 hours. The MIC was the lowest concentration yielding no growth, one discrete colony, or a barely visible haze.
Broth MIC and MBC Determinations: Broth MICs were determined using microdilution procedures in supplemented Mueller-Hinton broth. To determine MBCs, a 10-μl sample from non-turbid wells on the MIC plate was subcultured onto Mueller-Hinton agar without antibiotic. Plates were incubated at 37°C for 72 hours. The lowest antibiotic dilution yielding no growth on the subculture was the MBC.
Effect of Inoculum Size: Tests were done by broth microdilution. Actively growing cultures were diluted to match a McFarland 0.5 standard (~10⁸ CFU/ml) and then serially diluted (10-fold steps to 10³ CFU/ml). Aliquots of each dilution were added to broth containing antibiotic dilutions. Plates were incubated at 37°C for 16-20 hours. The MIC was the lowest concentration with no visible growth compared to the drug-free control.
Effect of Human Serum: Tests were done by broth microdilution. Cultures were diluted to ~5 x 10⁵ CFU/ml. Aliquots were added to broth containing antibiotic and human serum (final concentration 0-40%). Plates were incubated and read as above.
Methodology Comparison: Susceptibility was determined concurrently using agar dilution, macrodilution broth, and microdilution broth methods with the same inoculum.
Special Pathogen Tests: For Legionella, BCYE agar was used with an inoculum of 10⁶ CFU/spot, incubation at 35°C for 18h. For Helicobacter pylori, brain heart infusion agar with blood and supplement was used, incubation at 37°C for 72h under microaerophilic conditions. For Chlamydia trachomatis, cell culture using McCoy cells was employed.

Mouse Protection Tests: ICR mice (19-21 g) were infected intraperitoneally with 0.5 ml of a bacterial suspension (S. aureus, S. pyogenes, or S. pneumoniae) adjusted to give 50-500% LD50. Antibiotics (Dirithromycin, erythromycin, erythromycinylamine) were administered subcutaneously or orally (by gavage in solution) at 1 and 5 hours post-infection. Animals were observed for 7 days. ED50 values were calculated by the Reed and Muench method. Untreated infected control groups were included to titrate the LD50.
Rat Endocarditis Model: Female Sprague-Dawley rats (200-220 g) were anesthetized. A polyethylene catheter was inserted via the right carotid artery into the left ventricle and secured to induce sterile vegetations. After 48 hours, rats were infected intravenously via the tongue vein with 0.5 ml of an Enterococcus faecium X66 suspension (~5 x 10⁸ CFU/ml). Rats were divided into groups (n=5). Treatment groups received Dirithromycin or erythromycin at 20 mg/kg twice daily for 9 days subcutaneously; one group was untreated. Rats were sacrificed at 5 and 9 days post-infection. Heart vegetations and tissue were harvested, homogenized, serially diluted, and plated to determine CFU/g of tissue.
Pharmacokinetic Studies in Rodents: Mice or rats were administered Dirithromycin, erythromycin, or erythromycinylamine subcutaneously or orally (by gavage in solution) at a dose of 20 mg/kg. Blood samples were collected at various time points post-dose. Concentrations of antibiotics in serum and tissues were determined by a microbiological assay using agar plates seeded with Micrococcus luteus. Zone sizes were measured, and concentrations were calculated from standard curves.

Absorption, Distribution and Excretion
Orally administered erythromycin is rapidly absorbed, with an absolute bioavailability of approximately 10%. Dietary fat has little effect on the bioavailability of erythromycin. Metabolism/Metabolites During absorption, erythromycin is converted to the active compound erythromycinamine via non-enzymatic hydrolysis. Within 35 minutes of administration, 60% to 90% of the dose is hydrolyzed to erythromycinamine, and the conversion is almost complete after 1.5 hours. Erythromycinamine undergoes minimal hepatic biotransformation. No other metabolites of erythromycin have been detected in serum. Biological Half-Life In patients with normal renal function, the mean plasma half-life of erythromycinamine is estimated to be approximately 8 hours (2 to 36 hours), and the mean urinary terminal elimination half-life is approximately 44 hours (16 to 65 hours). Erythromycin Under acidic conditions or in vivo, it is hydrolyzed to its major active metabolite, 9(S)-erythromycinamine.
In rats, subcutaneous injection of 20 mg/kg erythromycin resulted in a longer duration of serum concentration of erythromycin and its metabolite erythromycinamine over 12 hours compared to erythromycin.
In mice, subcutaneous injection of 20 mg/kg erythromycin also resulted in higher serum concentrations of erythromycin and erythromycinamine, with a longer duration of concentration.
In rats and mice, oral administration (gavage) of 20 mg/kg solution resulted in extremely low or undetectable serum concentrations of erythromycin, erythromycinamine, and erythromycin.
In rats, oral administration of erythromycin (20 mg/kg) resulted in significantly higher antibiotic concentrations in the lungs, liver, kidneys, and urine within 30 minutes to 4 hours after administration compared to serum concentrations at the same timeframe, indicating that the drug can penetrate and accumulate in tissues.
The lipophilicity of erythromycin, as determined by reversed-phase high-performance liquid chromatography (RP-HPLC), is higher than that of erythromycin and erythromycinamine, which may explain its higher tissue permeability and larger volume of distribution.

Protein Binding
The protein binding rate of the active compound erythromycin is 15% to 30%.

[1]. J Antimicrob Chemother. 1999 Apr;43(4):541-8.

[2]. Antimicrob Agents Chemother. 1991 Jun;35(6):1116-26.

[3]. Ann Pharmacother, 1996. 30(10): p. 1141-9.

Dierythromycin is a hemiacetal formed by the condensation of erythromycin derivative (9S)-erythromycin cycloamine and 2-(2-methoxyethoxy)acetaldehyde. Because the oxazine ring containing the hemiacetal group is unstable under both acidic and alkaline conditions, erythromycin can be used as a lipid-soluble prodrug of (9S)-erythromycin cycloamine. Dierythromycin is formulated as enteric-coated tablets to prevent acid-catalyzed hydrolysis in the stomach and is used to treat respiratory, skin, and soft tissue infections caused by susceptible bacteria. It is a prodrug. Dierythromycin is a macrolide glycopeptide antibiotic used to treat various bacterial infections, such as bronchitis, pneumonia, tonsillitis, and even skin infections. Dierythromycin is a semi-synthetic macrolide antibiotic prodrug. During intestinal absorption, erythromycin is hydrolyzed to erythromycin amine, which has microbial activity. Erythromycin amine binds to the 50S subunit of the 70S ribosome of susceptible microorganisms, thereby inhibiting bacterial RNA-dependent protein synthesis. This antibiotic is used to treat respiratory, skin, and soft tissue infections caused by Gram-positive bacteria (including Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes) and Gram-negative bacteria (including Haemophilus influenzae, Legionella pneumophila, Moraxella catarrhalis, and Mycoplasma pneumoniae). Indications: For the treatment of mild to moderate infections caused by susceptible strains of the following: acute bacterial exacerbations of chronic bronchitis, secondary bacterial infections of acute bronchitis, community-acquired pneumonia, pharyngitis/tonsillitis, and uncomplicated skin and skin/soft tissue infections. Mechanism of Action: Dierythromycin inhibits bacterial growth by interfering with bacterial protein synthesis. Dierythromycin binds to the 50S subunit of the bacterial 70S ribosome, thereby inhibiting peptide transport. Dierythromycin has a more than 10-fold higher affinity for the 50S subunit than erythromycin. Furthermore, erythromycin can simultaneously bind to both domains of the 50S subunit and 23S RNA of the ribosomal, while older macrolide antibiotics can only bind to one domain. Erythromycin also inhibits the formation of the 50S and 30S subunits of the ribosomal. Erythromycin (AS-E 136; LY237216) is a 9-N-11-O-oxazine derivative of erythromycin, formed by the condensation of 9(S)-erythromycinamine with 2-(2-methoxyethoxy)acetaldehyde. Its development aimed to overcome some limitations of erythromycin, such as acid instability, unstable oral absorption, and short half-life. The synthetic method involves preparing 2-(2-methoxyethoxy)acetaldehyde and 9(S)-erythromycinamine, which are then reacted in acetonitrile to generate erythromycin, which crystallizes from solution. Its structure has been determined by nuclear magnetic resonance spectroscopy and X-ray crystallography. Although its in vitro activity is slightly lower than that of erythromycin against certain strains, its pharmacokinetic advantages (high and sustained tissue concentrations) make it more effective in vivo against certain infections in animal models. Erythromycin, erythromycinamide, and erythromycin have the same pKa value for their basic amino groups (9.0).

C42H78N2O14

835.0737

834.545

C, 60.41; H, 9.42; N, 3.35; O, 26.82

62013-04-1

6473883

Solid powder

1.2±0.1 g/cm3

871.8±65.0 °C at 760 mmHg

185 - 189ºC

481.0±34.3 °C

0.0±0.6 mmHg at 25°C

1.533

2.84

5

16

12

58

1300

20

O1[C@]([H])(C([H])([H])OC([H])([H])C([H])([H])OC([H])([H])[H])N([H])[C@@]2([H])[C@]([H])(C([H])([H])[H])C([H])([H])[C@](C([H])([H])[H])([C@@]([H])([C@@]([H])(C([H])([H])[H])[C@@]([H])([C@@]([H])(C([H])([H])[H])C(=O)O[C@]([H])(C([H])([H])C([H])([H])[H])[C@](C([H])([H])[H])([C@]1([H])[C@@]2([H])C([H])([H])[H])O[H])O[C@@]1([H])C([H])([H])[C@](C([H])([H])[H])([C@]([H])([C@]([H])(C([H])([H])[H])O1)O[H])OC([H])([H])[H])O[C@@]1([H])[C@@]([H])([C@]([H])(C([H])([H])[C@@]([H])(C([H])([H])[H])O1)N(C([H])([H])[H])C([H])([H])[H])O[H])O[H]

WLOHNSSYAXHWNR-DWIOZXRMSA-N

InChI=1S/C42H78N2O14/c1-15-29-42(10,49)37-24(4)32(43-30(56-37)21-52-17-16-50-13)22(2)19-40(8,48)36(58-39-33(45)28(44(11)12)18-23(3)53-39)25(5)34(26(6)38(47)55-29)57-31-20-41(9,51-14)35(46)27(7)54-31/h22-37,39,43,45-46,48-49H,15-21H2,1-14H3/t22-,23-,24+,25+,26-,27+,28+,29-,30-,31+,32+,33-,34+,35+,36-,37-,39+,40-,41-,42-/m1/s1

(1R,2R,3R,6R,7S,8S,9R,10R,12R,13S,15R,17S)-9-(((2S,3R,4S,6R)-4-(dimethylamino)-3-hydroxy-6-methyltetrahydro-2H-pyran-2-yl)oxy)-3-ethyl-2,10-dihydroxy-7-(((2R,4R,5S,6S)-5-hydroxy-4-methoxy-4,6-dimethyltetrahydro-2H-pyran-2-yl)oxy)-15-((2-methoxyethoxy)methyl)-2,6,8,10,12,17-hexamethyl-4,16-dioxa-14-azabicyclo[11.3.1]heptadecan-5-one

LY237216; LY 237216; LY-237216;Antibiotic AS-E 136;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Ethanol : 100~50 mg/mL(59.88 mM)
DMSO : 11~33.33 mg/mL ( 13.17~39.91 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (2.99 mM) (saturation unknown) in 10% EtOH + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear EtOH stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (2.99 mM) (saturation unknown) in 10% EtOH + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear EtOH stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (2.99 mM) (saturation unknown) in 10% EtOH + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear EtOH stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 10% EtOH+40% PEG300+5% Tween-80+45% Saline: ≥ 2.5 mg/mL (2.99 mM)

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 (Please use freshly prepared in vivo formulations for optimal results.)