Mupirocin

Mupirocin is a unique RNA synthetase inhibitor antibacterial used topically to treat skin infections like impetigo and to eliminate MRSA colonization in the nasal passages.

For the treatment of Impetigo and other Secondary Skin Infections, the standard adult dosage involves applying a small amount of mupirocin 2% ointment or cream to the affected area three times daily. This is typically continued for 5 to 10 days, depending on the severity of the infection and the clinical response. If no improvement is seen within 3 to 5 days, the patient should re-consult their healthcare provider.

For MRSA Nasal Decolonization, the nasal ointment (mupirocin calcium) is used. Approximately one-half of the ointment from a single-use tube (or a matchstick-sized amount) is applied into each nostril twice daily (morning and evening) for 5 days. After application, the nostrils should be pressed together and massaged to ensure even distribution of the medication.

Mupirocin is approved for use in pediatric patients. For Impetigo, the dosage for children aged 2 months to 16 years is the same as the adult dose: application to the affected area three times daily for 5 to 10 days. The safety and efficacy of the cream formulation have been established in children as young as 3 months for infected traumatic lesions.

For Nasal Decolonization, the nasal ointment is approved for use in children aged 12 years and older. Use in younger children for nasal decolonization must be strictly supervised and directed by a pediatric specialist.

Renal Impairment

No dosage adjustment is typically required for the cream or nasal ointment. However, caution is advised when using the topical ointment (which contains polyethylene glycol) over large areas of broken skin in patients with moderate to severe renal impairment, as PEG can be absorbed and cause kidney toxicity.

Hepatic Impairment

Since mupirocin is not significantly absorbed systemically, no dosage adjustments are required for patients with liver disease.

Elderly Patients

No specific dosage adjustments are recommended for geriatric patients, provided their skin integrity is relatively intact and renal function is monitored if large-scale application of the PEG-based ointment is required.

1. 1Preparation: Wash your hands thoroughly before and after application. Clean the affected skin area with mild soap and water and pat dry.
2. 2Application: Apply a thin layer of the ointment or cream to the lesion. You may use a cotton swab or gauze pad to avoid touching the infection directly.
3. 3Covering: The treated area may be covered with a sterile gauze dressing if desired or if the infection is in an area prone to friction.
4. 4Avoidance: Do not apply mupirocin to the eyes, mouth, or inside the nose (unless using the specific nasal formulation). If the medication gets into the eyes, rinse thoroughly with water.
5. 5Storage: Store the medication at room temperature (20°C to 25°C or 68°F to 77°F). Do not freeze.

If you miss a dose of mupirocin, apply it as soon as you remember. If it is almost time for your next scheduled application, skip the missed dose and return to your regular dosing schedule. Do not apply extra medication to 'make up' for a missed dose, as this may increase the risk of local irritation.

Systemic overdose via topical application is highly unlikely due to low absorption. However, if the medication is accidentally ingested, contact a poison control center or seek emergency medical attention immediately. Signs of ingestion might include nausea or gastrointestinal upset. If the PEG-based ointment is applied excessively to large open wounds in a patient with kidney issues, signs of renal distress (changes in urination, swelling) should be monitored.

> Important: Follow your healthcare provider's dosing instructions exactly. Even if the skin looks better, complete the full course of treatment to prevent the bacteria from returning or developing resistance.

Mupirocin is generally well-tolerated because it acts locally rather than systemically. The most common side effects are localized to the site of application. Approximately 1% to 3% of patients may experience:

• Burning or Stinging: A transient sensation of heat or sharp stinging immediately after application. This usually subsides within a few minutes.
• Pruritus (Itching): A mild to moderate urge to scratch the treated area. This is often a sign of local irritation rather than an allergy.
• Dryness: The skin at the application site may become slightly flaky or dry, particularly with the cream formulation.

Some patients may experience slightly more pronounced local reactions, including:

Mupirocin is for external use only. It should never be swallowed, injected, or applied to the eyes. If the medication is used on the face, care must be taken to avoid the conjunctiva (the lining of the eyelids). If accidental contact with the eyes occurs, they should be rinsed thoroughly with cool water. Furthermore, mupirocin should not be used for extended periods beyond what is prescribed, as this significantly increases the risk of developing antibiotic-resistant 'superbugs.'

No FDA black box warnings for Mupirocin. Unlike some systemic antibiotics that carry warnings for tendon rupture or severe nerve damage, mupirocin's localized application limits its systemic toxicity profile.

• Allergic Reactions / Anaphylaxis Risk: Patients with a known history of hypersensitivity to mupirocin or any components of the formulation (such as polyethylene glycol) must avoid this drug. A small 'test patch' is sometimes recommended if a patient has sensitive skin.

There are no documented 'absolute' contraindications for drug-drug interactions involving systemic medications, primarily because mupirocin does not enter the bloodstream in significant amounts. However, mupirocin should never be mixed with other topical creams or ointments in the same application area unless specifically directed by a physician. Mixing products can dilute the mupirocin, reducing its concentration below the level needed to kill bacteria, or it may alter the stability of the antibiotic.

• Other Topical Antibacterials: Using mupirocin simultaneously with other topical antibiotics (like neomycin or bacitracin) on the same lesion is generally discouraged. This can increase the risk of skin sensitization and makes it difficult to determine which agent is causing a side effect if an adverse reaction occurs.
• Topical Corticosteroids: While sometimes used together for infected eczema, applying a high-potency steroid and mupirocin simultaneously can sometimes mask the signs of a spreading infection. Healthcare providers usually recommend applying them at different times of the day.

Mupirocin is strictly contraindicated in the following circumstances:

1. 1Hypersensitivity to Mupirocin: Any patient who has experienced a previous severe allergic reaction (anaphylaxis, angioedema, or severe rash) to mupirocin must never use the drug again. The mechanism involves an IgE-mediated immune response that can escalate in severity upon re-exposure.
2. 2Hypersensitivity to Polyethylene Glycol (PEG): This applies specifically to the ointment formulation. PEG is a common excipient in many medications and cosmetics. In sensitive individuals, it can cause contact dermatitis or systemic allergic reactions.
3. 3Ophthalmic Use: Mupirocin is not for use in the eyes. The formulations can cause severe corneal irritation or chemical conjunctivitis.

FDA Pregnancy Category B: Animal reproduction studies (conducted in rats and rabbits with systemic doses many times higher than human topical doses) have failed to demonstrate a risk to the fetus. There are, however, no adequate and well-controlled studies in pregnant women. Because animal studies are not always predictive of human response, mupirocin should be used during pregnancy only if clearly needed. Most experts consider it low-risk due to the negligible systemic absorption when applied to intact skin. It is not known to affect fertility.

It is not known whether mupirocin is excreted in human milk. However, because systemic absorption is so low, it is unlikely that a nursing infant would be exposed to significant amounts of the drug. If mupirocin is applied to the breast or nipple area to treat an infection, the area should be washed thoroughly before breastfeeding to prevent the infant from direct oral ingestion of the medication.

Mupirocin is widely used and FDA-approved for pediatric patients. The ointment is approved for children as young as 2 months for impetigo. The cream is approved for children aged 3 months and older. Clinical trials have shown that the safety profile in children is similar to that in adults. Care should be taken to prevent infants from rubbing the treated area and then touching their eyes or putting their hands in their mouths.

Mupirocin (pseudomonic acid A) is a unique antibacterial agent. Its molecular mechanism involves the inhibition of bacterial protein synthesis by reversibly and specifically binding to bacterial isoleucyl-transfer RNA (tRNA) synthetase. This enzyme catalyzes the formation of isoleucyl-tRNA from isoleucine and tRNA. By competing with isoleucine for the binding site on the enzyme, mupirocin prevents the loading of isoleucine onto the tRNA. This leads to a depletion of isoleucyl-tRNA, which halts the incorporation of isoleucine into peptide chains, effectively stopping bacterial protein production. Because this mechanism is distinct from other antibiotics, mupirocin shows no cross-resistance with other classes.

Mupirocin is primarily active against Gram-positive aerobic bacteria. It is highly effective against Staphylococcus aureus (including MRSA) and Streptococcus pyogenes. It also has some activity against Gram-negative bacteria like Haemophilus influenzae and Neisseria gonorrhoeae, though it is not used clinically for these. The drug's effect is concentration-dependent. At the 2% concentration found in topical products, the levels of mupirocin far exceed the Minimum Inhibitory Concentration (MIC) for susceptible bacteria, resulting in bactericidal action.