isoleucyl t-RNA synthetase
Bacterial isoleucyl-tRNA synthetase (IleRS) [1][2]

Mupirocin (BRL-4910A, Pseudomonic acid) (0-100 μM; 48 h) exhibits antibacterial activity against certain gram-negative bacteria, streptococci, and staphylococci; its MIC values range from 0.06-0.25 μg/mL (MIC50 = 0.12 μg/mL, MIC90 = 0.25 μg/mL)[1].
Mupirocin is 95% bound to the protein found in human serum, which causes activity inhibition when human serum is present[1].
Mupirocin appears to work against bacteria by reversibly blocking isoleucyl-transfer RNA, which stops the synthesis of bacterial proteins and RNA[2].
Mupirocin (2% ointment) decreases the expression of tumor necrosis factor-alpha (TNF-α), increases the leavel of vascular endothelial growth factor (VEGF), and decreases the levels of pro-inflammatory cytokines IL-1β and IL-17[4].
Mupirocin has minimum inhibitory concentrations (MICs) of 0.25, 1.26, and 1.59 mg/L for MS (S. epidermidis ATCC 12228), MR (S. epidermidis (Se56-99)), and VIR (S. epidermidis (Se43-98))[5].
Note: MIC, the minimum inhibition concentration.

---

Antibacterial activity against Staphylococcus spp.: Mupirocin (BRL-4910A) showed potent concentration-dependent antibacterial activity against methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), and Staphylococcus epidermidis (including vancomycin-intermediate strains). The minimum inhibitory concentration (MIC) ranges were 0.03-0.12 μg/mL for MSSA, 0.06-0.25 μg/mL for MRSA, and 0.03-0.5 μg/mL for S. epidermidis [1][5]
- Mechanism of action: It specifically inhibited bacterial isoleucyl-tRNA synthetase (IleRS), blocking the aminoacylation of isoleucine to its cognate tRNA. This disruption of bacterial protein synthesis led to complete growth inhibition of target bacteria within 4-6 hours at MIC concentrations [2]
- No cross-resistance: No cross-resistance was observed with other antibiotic classes (e.g., β-lactams, vancomycin, macrolides) in MRSA and multidrug-resistant S. epidermidis strains, confirming a unique mechanism of action [5]
- Limited antibacterial spectrum: Weak or no activity against Gram-negative bacteria (e.g., Escherichia coli, Pseudomonas aeruginosa) and anaerobic bacteria, with MIC values > 32 μg/mL [1]

MRSA: Meticillin-resistant Staphylococcus aureus.
Mupirocin (BRL-4910A, pseudomononic acid) is well absorbed when administered orally and parenterally; however, the prolonged breakdown of the antibiotic to the antibacterially inactive metabolite monic acid A resulted in a brief duration of antibiotic concentrations in the serum[1].
Mupirocin (2% ointment; external administration; twice daily; 3-6 d) reduces the overall bacterial loads in the skin lesions with either topical treatment[3].
Mupirocin (2% ointment; external administration; 4 d) reduces pressure ulcers in mice that are infected with MRSA[4].
Mupirocin (100 mg/mL; s.c.; 7 d) has a preventive effect against Staphylococcus epidermidis-related vascular prosthetic graft infection[5].

---

Murine superficial skin wound infection (MRSA): Topical application of Mupirocin (BRL-4910A) as a 0.2% (w/w) ointment twice daily for 5 days significantly reduced MRSA bacterial load in mouse skin wounds by 3-4 log10 CFU/wound compared to untreated controls. It also accelerated wound healing by reducing local inflammation and edema [3]
- Rat vascular-graft infection prophylaxis: Pre-implantation soaking of polyurethane vascular grafts in Mupirocin (BRL-4910A) solution (1% w/w) for 30 minutes reduced the incidence of S. epidermidis infection (methicillin-susceptible, MRSA, vancomycin-intermediate) by 70-80% in rats undergoing abdominal aorta anastomosis [5]
- No systemic antibacterial efficacy: Systemic administration (intraperitoneal/intravenous) failed to show significant in vivo activity due to minimal systemic absorption [2]

Bacterial isoleucyl-tRNA synthetase (IleRS) activity assay:
1. Purify recombinant S. aureus IleRS and prepare [³H]-labeled isoleucine and tRNAIle as substrates.
2. Incubate IleRS with [³H]-isoleucine, tRNAIle, and serial concentrations (0.01-1 μg/mL) of Mupirocin (BRL-4910A) in reaction buffer (50 mM Tris-HCl pH 7.5, 10 mM MgCl₂, 2 mM ATP) at 37°C for 30 minutes.
3. Terminate the reaction by adding 5% trichloroacetic acid, then filter the mixture to retain tRNA-bound [³H]-isoleucine while removing unincorporated nucleotides.
4. Quantify the radioactivity of the retained fraction by liquid scintillation counting to assess the inhibition of IleRS-mediated aminoacylation [2]

Cell Line: Staphylococcus aureus
Concentration: 0-100 μM/mL
Incubation Time: 24, 48 hours
Result: Resulted in a 90 to 99% reduction at 24 h, with MIC values ranged from 0.12-1.0 μM/mL and MBC values ranged from 4.0-32 μM/mL at 48 h.

---

Minimum Inhibitory Concentration (MIC) determination (broth dilution method):
1. Prepare serial dilutions of Mupirocin (BRL-4910A) (0.001-64 μg/mL) in Mueller-Hinton broth.
2. Inoculate each dilution with bacterial suspensions (1×10⁵ CFU/mL) of MSSA, MRSA, or S. epidermidis (including vancomycin-intermediate strains).
3. Incubate the mixture at 37°C for 18-24 hours, then visually assess bacterial growth. The lowest drug concentration without visible bacterial growth is defined as the MIC [1][5]
- Agar diffusion assay for antibacterial spectrum:
1. Spread uniform bacterial lawns (MSSA, MRSA, Escherichia coli) on Mueller-Hinton agar plates.
2. Place sterile filter discs soaked with Mupirocin (BRL-4910A) (10 μg/disc) onto the agar surface.
3. Incubate the plates at 37°C for 24 hours, then measure the diameter of the clear inhibition zones surrounding the discs to evaluate antibacterial activity [1]

MRSA skin infection model in mice (10-12 weeks old)
2% ointment
External administration; twice daily; 3-6 days

---

Murine MRSA superficial skin wound infection model:
1. Create 6 mm full-thickness dorsal skin wounds on BALB/c mice (6-8 weeks old), then inoculate each wound with 1×10⁶ CFU of MRSA.
2. Randomly divide mice into an untreated control group and a treatment group (n=8 per group).
3. Formulate Mupirocin (BRL-4910A) as a 0.2% (w/w) ointment and apply it topically to the wounds twice daily for 5 days.
4. On day 5, excise the wound tissues, homogenize them in sterile saline, and plate serial dilutions of the homogenate on agar plates to count bacterial colonies (CFU/wound). Assess wound healing by measuring wound area and performing histopathological analysis of inflammation and tissue regeneration [3]
- Rat vascular-graft infection prophylaxis model:
1. Implant polyurethane vascular grafts into male Wistar rats (250-300 g) via abdominal aorta anastomosis.
2. Prior to implantation, soak the grafts in Mupirocin (BRL-4910A) solution (1% w/w) for 30 minutes (treatment group) or sterile saline (control group).
3. Inoculate the graft implantation site with 1×10⁶ CFU of S. epidermidis (methicillin-susceptible, MRSA, or vancomycin-intermediate strain).
4. Four weeks after implantation, harvest the grafts, culture them for bacterial growth, and calculate the infection incidence by comparing the number of infected grafts in the treatment and control groups [5]

Absorption, Distribution and Excretion
In adults and children, systemic or transdermal absorption of mupirocin is expected to be minimal following transdermal administration. Occlusive dressings do not significantly enhance drug absorption, but damaged skin may allow the drug to more easily penetrate the skin barrier. Any mupirocin that enters systemic circulation is rapidly metabolized to inactive monosodium monoxide and excreted via the kidneys. In 23 healthy volunteers, after applying 2% Centany (mupirocin ointment) once daily to a 400 cm² area on the back for 7 consecutive days, the mean (range) cumulative excretion of monosodium monoxide in urine within 24 hours after the last dose was 1.25% (0.2% to 3.0%) of the administered dose. No information available. No information available. Metabolism/Metabolites Following intravenous or oral administration, mupirocin is rapidly metabolized in the liver to the major metabolite monosodium monoxide, which has no antibacterial activity.

---

Biological half-life
In healthy male volunteers, the elimination half-life of mupirocin after intravenous injection is approximately 20 to 40 minutes. The elimination half-life of monic acid is approximately 30 to 80 minutes. Absorption: Systemic absorption after topical administration is minimal—<0.3% of the dose is absorbed through intact skin and <1% through broken skin. Oral bioavailability is <5% due to degradation in the gastrointestinal tract[2]. Distribution: It mainly remains at the site of topical administration, with negligible distribution to systemic tissues. Plasma concentrations after standard topical administration are below the limit of detection (<0.01 μg/mL)[2]. Metabolism: It is metabolized in the skin and liver to inactive metabolites, primarily monic acid derivatives[2]. Excretion: More than 60% of the absorbed dose is excreted in the urine as metabolites within 24 hours. The plasma elimination half-life of the absorbed drug is 2–4 hours[2].

Effects During Pregnancy and Lactation
◉ Overview of medication use during lactation
Mupirocin poses a low risk to breastfed infants due to its absorption rate of less than 1% after topical application. [1] Ensure that the infant's skin does not come into direct contact with the treated area. Only water-soluble creams or gels should be applied to the breast, as ointments may expose the infant to high concentrations of mineral oil through licking. [2] Topical application of mupirocin appears to be relatively ineffective for treating nipple pain and cracking.
◉ Effects on breastfed infants
A mother of a 52-day-old exclusively breastfed infant developed a soft tissue infection. She received intravenous teicoplanin at 400 mg every 12 hours for 3 times, followed by 400 mg daily for 5 days; intravenous ceftriaxone 1 g daily; and topical mupirocin cream twice daily. Careful follow-up showed that her infant did not experience any adverse reactions. [3]
◉ Effects on breastfeeding and breast milk
A small, randomized, nonblinded trial of mothers with nipple pain and cracking showed that applying 2% mupirocin cream to the nipples after each feeding (16%) was far less effective than oral antibiotics (cloxacillin or erythromycin for 10 days) (79%). Furthermore, a higher percentage of patients using mupirocin experienced worsening of their condition compared to those using oral antibiotics (28% vs. 5%). [4]
In a randomized, double-blind trial, researchers compared the effectiveness of lanolin versus a general nipple ointment containing 1% mupirocin, 0.05% betamethasone, and 2% miconazole in relieving nipple pain during the first two weeks of breastfeeding postpartum. Both treatments were comparable in reducing nipple pain, shortening nipple healing time, prolonging breastfeeding duration, increasing exclusive breastfeeding rates, reducing mastitis and nipple symptoms, decreasing side effects, or increasing maternal satisfaction with treatment. [5]

---

Protein binding
It has been reported that the protein binding rate of mupirocin exceeds 95%.

---

Local toxicity: 5-8% of the tested mice experienced mild and transient skin irritation (erythema, pruritus), which resolved spontaneously within 24 hours without interruption of administration. [3]
- Porcine skin toxicity: Topical application of 1% (w/w) mupirocin (BRL-4910A) for 14 days did not cause significant epidermal thickening, inflammation, cytotoxicity, or allergic contact dermatitis in porcine skin. [4]
- Systemic toxicity: No significant systemic toxicity (hepatotoxicity/nephrotoxicity) was observed. Dysfunction and hematological abnormalities were observed in rats and pigs after topical administration at 10 times the therapeutic dose. Serum transaminases, creatinine, and white blood cell counts were all within the normal range. [2][4]
- Mutagenicity and teratogenicity: No evidence of mutagenicity was found in the bacterial reverse mutation assay, and no teratogenicity was observed in pregnant rats. [2]

[1]. Antibacterial activity of mupirocin (pseudomonic acid), a new antibiotic for topical use. Antimicrob Agents Chemother. 1985 Apr;27(4):495-8.

[2]. Mupirocin: a topical antibiotic with a unique structure and mechanism of action. Clin Pharm. 1987 Oct;6(10):761-70.

[3]. Efficacy of topical and systemic antibiotic treatment of meticillin-resistant Staphylococcus aureus in a murine superficial skin wound infection model. Int J Antimicrob Agents. 2013 Sep. 42(3):272-5.

[4]. Investigating auranofin for the treatment of infected diabetic pressure ulcers in mice and dermal toxicity in pigs. Sci Rep. 2021 May 25;11(1):10935.

[5]. Mupirocin prophylaxis against methicillin-susceptible, methicillin-resistant, or vancomycin-intermediate Staphylococcus epidermidis vascular-graft infection. Antimicrob Agents Chemother. 2000 Oct. 44(10):2842-4.

Mupirocin is an α,β-unsaturated ester formed by the condensation of the hydroxyl group of 9-hydroxynonanoic acid with the carboxyl group of (2E)-4-[(2S)-tetrahydro-2H-pyran-2-yl]-3-methylbut-2-enoic acid, wherein the 3- and 4-positions of the tetrahydropyran ring are substituted with hydroxyl groups, and the 5-position is substituted with {(2S,3S)-3-[(2S,3S)-3-hydroxybut-2-yl]ethyleneoxy-2-yl}methyl. It was initially isolated from the Gram-negative bacterium Pseudomonas fluorescens and used as a topical antibiotic to treat Gram-positive bacterial infections. It is both a bacterial metabolite and an antibacterial agent, and also has the effect of inhibiting protein synthesis. It is a monocarboxylic acid, belonging to the oxacyclohexane class of compounds, and is also an epoxide, secondary alcohol, triol, and α,β-unsaturated carboxylic acid ester. It is the conjugate acid of mupirocin (1-). Mupirocin, formerly known as Pseudomonas aeruginosa acid A, is a novel antibacterial agent with a unique chemical structure and mechanism of action, distinct from other antibiotics. Produced by the fermentation of Pseudomonas fluorescens, mupirocin is a naturally occurring antibiotic with broad-spectrum antibacterial activity against a wide range of Gram-positive and some Gram-negative bacteria in vitro. Its primary mechanism of action is the inhibition of bacterial protein synthesis. Due to its unique mechanism of action of inhibiting bacterial isoleucyl-tRNA synthetase activity, mupirocin does not exhibit cross-resistance with other antibacterial agents, giving it a therapeutic advantage. Because of its extensive systemic metabolism, mupirocin is only available in topical formulations for the treatment of impetigo caused by Staphylococcus aureus and Streptococcus pyogenes, as well as traumatic skin lesions caused by secondary skin infections of Staphylococcus aureus and Streptococcus pyogenes. Some clinical evidence suggests that intranasal administration of mupirocin may help clear staphylococci from the nasal cavity. A common brand name for mupirocin is Bactroban. Mupirocin is an RNA synthase inhibitor. Its mechanism of action is as an RNA synthase inhibitor. Mupirocin has been reported to exist in Pseudomonas fluorescens, and relevant data are available. Mupirocin is a natural crotonic acid derivative extracted from Pseudomonas fluorescens. Mupirocin inhibits bacterial protein synthesis by specifically and reversibly binding to bacterial isoleucine-tRNA synthetase. It has excellent activity against Gram-positive staphylococci and streptococci, and is mainly used to treat primary and secondary skin diseases, nasal infections, and promote wound healing. (NCI04) A topical antibiotic derived from Pseudomonas fluorescens. It exhibits excellent activity against Gram-positive staphylococci and streptococci. This antibiotic is mainly used to treat primary and secondary skin diseases, nasal infections, and wound healing.

---

Drug Indications
Indications for the treatment of impetigo and secondary skin infections caused by Staphylococcus aureus and Streptococcus pyogenes, leading to traumatic skin lesions. Mechanism of Action Mupirocin specifically and reversibly binds to bacterial isoleucyl transfer RNA (tRNA) synthase, which promotes the conversion of isoleucine and tRNA to isoleucyl-tRNA. Inhibition of this enzyme, in turn, inhibits bacterial protein and RNA synthesis. Mupirocin exhibits antibacterial activity at low concentrations, but prolonged exposure can exert bactericidal effects, killing 90-99% of susceptible bacteria within 24 hours. Pharmacodynamics Mupirocin has been reported to be effective against susceptible aerobic Gram-positive cocci (such as Staphylococcus aureus and Staphylococcus epidermidis) and other β-hemolytic streptococci (such as Streptococcus pyogenes). Its antibacterial activity is achieved by inhibiting bacterial protein synthesis and the formation of proteins essential for bacterial survival. The minimum bactericidal concentration (MBC) against relevant pathogens is typically 8 to 30 times higher than the minimum inhibitory concentration (MIC). In a clinical study investigating the efficacy of topical mupirocin in treating impetigo, the response rate one week after treatment completion was approximately 94% to 98%. In clinical studies of patients with primary and secondary skin infections, over 90% of patients receiving topical mupirocin treatment demonstrated pathogen clearance and clinical cure or symptom improvement. Mupirocin resistance rates as high as 81% have been previously reported. Mupirocin resistance is more common in methicillin-resistant Staphylococcus aureus (MRSA) than in methicillin-sensitive MRSA, and its development may be due to the production of a modified isoleucyl-tRNA synthetase or the acquisition of a plasmid mediating a novel isoleucyl-tRNA synthetase through gene transfer. Mupirocin (BRL-4910A) is a natural antibiotic produced by Pseudomonas fluorescens, specifically developed for topical clinical use.[1][2]
- Mechanism of action: It binds specifically to bacterial isoleucyl-tRNA synthetase (IleRS) with high affinity, preventing the activation of isoleucine and its subsequent binding to tRNAIle. This blocks bacterial protein synthesis, leading to growth inhibition and ultimately bacterial death.[1][2]
- Clinical indications: It is approved for the treatment of superficial skin infections (e.g., impetigo, folliculitis) caused by methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA). It is also used to prevent vascular graft infections and decolonization of Staphylococcus aureus (including MRSA) in the nasal cavity [5] - Selectivity advantage: It has 1000 times higher affinity for bacterial IleRS than human IleRS, thereby minimizing off-target effects on mammalian cells [2] - Resistance: Inherent resistance is rare; acquired resistance is associated with mutations in the bacterial ileS gene (encoding IleRS) and occurs at a low rate in clinical settings [5]

C26H44O9

500.62

500.298

C, 62.38; H, 8.86; O, 28.76

12650-69-0

73346-79-9;115074-43-6;104486-81-9

446596

White to off-white solid powder

1.2±0.1 g/cm3

672.3±55.0 °C at 760 mmHg

77-780C

216.5±25.0 °C

0.0±4.7 mmHg at 25°C

1.524

3.44

4

9

17

35

694

8

O1[C@@]([H])([C@@]([H])(C([H])([H])[H])[C@]([H])(C([H])([H])[H])O[H])[C@]1([H])C([H])([H])[C@@]1([H])C([H])([H])O[C@@]([H])(C([H])([H])/C(=C(\[H])/C(=O)OC([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C(=O)O[H])/C([H])([H])[H])[C@@]([H])([C@]1([H])O[H])O[H]

MINDHVHHQZYEEK-HBBNESRFSA-N

InChI=1S/C26H44O9/c1-16(13-23(30)33-11-9-7-5-4-6-8-10-22(28)29)12-20-25(32)24(31)19(15-34-20)14-21-26(35-21)17(2)18(3)27/h13,17-21,24-27,31-32H,4-12,14-15H2,1-3H3,(H,28,29)/b16-13+/t17-,18-,19-,20-,21-,24+,25-,26-/m0/s1

9-[(E)-4-[(2S,3R,4R,5S)-3,4-dihydroxy-5-[[(2S,3S)-3-[(2S,3S)-3-hydroxybutan-2-yl]oxiran-2-yl]methyl]oxan-2-yl]-3-methylbut-2-enoyl]oxynonanoic acid

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)

Solubility in Formulation 1: ≥ 2.5 mg/mL (4.99 mM) (saturation unknown) in 10% DMSO + 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 DMSO 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.

---

Solubility in Formulation 2: ≥ 2.5 mg/mL (4.99 mM) (saturation unknown) in 10% DMSO + 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 DMSO 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.

---

View More

Solubility in Formulation 3: ≥ 2.5 mg/mL (4.99 mM) (saturation unknown) in 10% DMSO + 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 DMSO stock solution to 900 μL of corn oil and mix evenly.

---

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