Mupirocin
Antimicrobial / TopicalAlso known as: Bactroban, Centany, Pseudomonic Acid A
Mechanism
The gold standard for MRSA nasal decolonization and a frontline treatment for impetigo. Derived from the bacterium Pseudomonas fluorescens, it has a completely unique mechanism — it blocks an enzyme (isoleucyl-tRNA synthetase) that no other antibiotic targets, meaning there is zero cross-resistance with any other antibiotic class. Applied intranasally to eliminate MRSA carriage or topically for skin infections.
Technical detail
Pseudomonic acid A — a C9 fatty acid linked to monic acid via an ester bond, produced by Pseudomonas fluorescens (NCIMB 10586). Unique mechanism: reversible competitive inhibitor of bacterial isoleucyl-tRNA synthetase (IleRS). Binds to both the isoleucine and tRNA binding sites simultaneously, preventing isoleucyl-adenylate formation and blocking protein synthesis. Selectivity: 8000x higher affinity for bacterial IleRS vs. mammalian IleRS. Active against S. aureus (including MRSA — MIC 0.12-0.5 µg/mL), S. pyogenes. Resistance: mutations in ileS (low-level, MIC 8-256 µg/mL) or acquisition of mupA gene (plasmid-mediated, high-level MIC >512 µg/mL). FDA-approved: 2% ointment (impetigo), 2% nasal ointment (S. aureus nasal decolonization — applied BID x 5 days). Metabolized to inactive monic acid on skin.
Effects
## Detailed Effects — Mupirocin ### Dermatological System [Tier 1] - Bactericidal against Staphylococcus aureus (including MRSA), Streptococcus pyogenes, and most gram-positive skin pathogens at concentrations achieved topically (>256 mcg/mL in skin). - Reversible inhibition of bacterial isoleucyl-tRNA synthetase — blocks protein synthesis at the translational level. Unique mechanism unrelated to other antibiotics, minimizing cross-resistance. - MRSA nasal decolonization: 2% nasal ointment eliminates nasal carriage in 80-93% of patients within 5 days (Tier 1 RCT data from the REDUCE MRSA trial, Huang et al., NEJM 2013). - Impetigo clearance rates 88-97% in RCTs vs 52% for vehicle (Tier 1). - Secondarily infected dermatoses (eczema, traumatic wounds): clinical cure rates 90%+ in controlled trials. ### Immune / Infection Control [Tier 1] - ICU decolonization protocols with mupirocin nasal ointment + chlorhexidine bathing reduced MRSA clinical cultures by 37% and all bloodstream infections by 44% (REDUCE MRSA trial, NEJM 2013). - Pre-surgical prophylaxis: nasal mupirocin before cardiac and orthopedic surgery reduces S. aureus surgical site infections by 45-58% (Tier 1 meta-analysis, Bode et al., NEJM 2010). - Peritoneal dialysis exit-site application reduces S. aureus peritonitis by 60-73% (Bernardini et al., JASN 2005). ### Resistance Considerations [Tier 1-2] - Low-level resistance (mupA gene, MIC 8-256 mcg/mL) increasing in some hospital settings — prevalence 5-15% in surveillance studies. - High-level resistance (mupA plasmid-mediated, MIC >512 mcg/mL) remains relatively uncommon (<5%) but is concerning when detected. - Resistance more common with prolonged or repeated use; institutional surveillance recommended.
Practitioner Guide
## Practitioner Guide — Mupirocin ### Formulations & Practical Selection - **Mupirocin 2% ointment (Bactroban Ointment)**: polyethylene glycol base — use for impetigo, skin infections. Do NOT use on large open wounds or burns (PEG absorption → potential nephrotoxicity). - **Mupirocin 2% cream (Bactroban Cream)**: oil-in-water emulsion — cosmetically elegant, better for secondarily infected traumatic lesions and eczema. - **Mupirocin 2% nasal ointment (Bactroban Nasal)**: paraffin base, specifically designed for nasal application — this is the ONLY formulation for nasal decolonization. Do not substitute the skin ointment intranasally. ### MRSA Nasal Decolonization Protocol (Gold Standard) - Apply a small ribbon (~1 cm) to each anterior nare BID x 5 days. - Press nostrils together and massage for 1 minute to distribute. - Combine with chlorhexidine 2% or 4% daily body washes for full decolonization. - Repeat nasal swab culture 48 hours after completing the course to confirm clearance. - If recolonization occurs: can repeat one additional 5-day course. Beyond that, consider alternative agents (retapamulin, photodynamic therapy) or accept chronic carriage. - Institutional protocols: universal decolonization on ICU admission is now preferred over screening-and-treating (REDUCE MRSA trial finding). ### Surgical Prophylaxis Application - Start nasal mupirocin BID x 5 days before elective surgery (cardiac, orthopedic, neurosurgical). - Combine with pre-operative chlorhexidine shower the night before and morning of surgery. - Particularly valuable for known S. aureus carriers identified by pre-op nasal swab. ### Wound Application Tips - Apply to affected area TID x 10 days maximum. Do not exceed 10 days to minimize resistance selection. - For impetigo: gently remove crusts with warm water before application for better drug penetration. - Cover with a light gauze if area is prone to rubbing — occlusion is not necessary but improves compliance. - If no improvement in 3-5 days, obtain wound culture and sensitivity — consider resistance. ### Storage & Compounding Notes - Store at room temperature (20-25°C). Do not refrigerate. - Shelf life: 24 months unopened; use within 30 days of opening. - Not typically compounded — commercially available formulations are the standard. - For large-scale institutional decolonization: mupirocin nasal ointment comes in single-use 1g tubes, which is cost-effective for universal protocols. ### Key Cautions for Practitioners - Do NOT use mupirocin ointment (PEG base) on large burns or open wounds — risk of PEG-associated nephrotoxicity (rare but documented). - Avoid prolonged or repeated courses — resistance develops. If needed chronically (e.g., recurrent MRSA), alternate with other topical agents. - Not effective against gram-negative organisms. If mixed infection suspected, add appropriate coverage. - Mupirocin has NO systemic bioavailability when applied topically to intact skin — purely local action.
Research Summary
## Research Summary — Mupirocin ### Tier 1: Randomized Controlled Trials - **REDUCE MRSA Trial (Huang et al., NEJM 2013, n=74,256 ICU patients)**: Universal decolonization with mupirocin nasal ointment + chlorhexidine bathing was superior to targeted decolonization and screening-isolation strategies. Reduced MRSA clinical cultures by 37% and all-cause bloodstream infections by 44%. - **Bode et al., NEJM 2010 (n=6,771 surgical patients)**: Nasal mupirocin + chlorhexidine wash before surgery reduced S. aureus surgical site infections by 58% in S. aureus carriers. - **Multiple impetigo RCTs (Cochrane Review, 2012)**: Mupirocin was superior to placebo (NNT ~2) and equivalent to oral erythromycin for non-bullous impetigo, with fewer GI side effects. - **Peritoneal dialysis prophylaxis (Bernardini et al., JASN 2005, n=267)**: Exit-site mupirocin reduced S. aureus exit-site infections and peritonitis by 60-73%. ### Tier 2: Systematic Reviews & Meta-Analyses - Cochrane Review of topical antibiotics for impetigo (2012): mupirocin and fusidic acid were the two most effective topical agents. - Van Rijen et al., J Antimicrob Chemother 2008: meta-analysis of mupirocin for nasal MRSA decolonization — eradication rates 80-93% at 1 week, declining to 50-60% at 6 months without adjunctive measures. - Phillips et al., Infect Control Hosp Epidemiol 2014: meta-analysis of chlorhexidine bathing + mupirocin for ICU decolonization — 56% reduction in MRSA acquisition. ### Tier 3: Case Reports & Practitioner Protocols - Widespread institutional adoption of universal decolonization protocols following REDUCE MRSA. - Some burn centers report using mupirocin cream (not ointment) on partial-thickness burns with good results, though formal RCT data in burns is limited. - Increasing practitioner concern about mupirocin resistance — some institutions now perform mupirocin susceptibility testing before decolonization protocols. ### Gaps - No large RCTs comparing mupirocin to newer alternatives (retapamulin, ozenoxacin) for decolonization. - Long-term resistance trends in community MRSA with widespread decolonization use poorly characterized. - Optimal re-decolonization strategy for recurrent carriers is not standardized. ### Active Trials - Several ongoing trials examining alternatives to mupirocin for decolonization in the setting of rising resistance (alcohol-based nasal antiseptics, photodynamic therapy).