Usage
Retapamulin is a topical antibiotic indicated for the short-term treatment of impetigo due to Staphylococcus aureus (methicillin-susceptible isolates only) or Streptococcus pyogenes in patients aged 9 months or older. It can also be used for infected small lacerations, abrasions, or sutured wounds. Its pharmacological classification is antibacterial, specifically a pleuromutilin antibiotic.
Retapamulin exerts its effect by binding to the L3 ribosomal protein of the bacterial 50S subunit, inhibiting protein synthesis. This binding interaction blocks peptidyl transferase activity, preventing the formation of functional ribosomes and thus halting bacterial growth. At clinically relevant concentrations, retapamulin is primarily bacteriostatic (inhibits growth); however, at significantly higher concentrations, it can exhibit bactericidal activity (kills bacteria).
Alternate Names
Generic Name: Retapamulin
Brand Name: Altabax, Altargo
How It Works
Pharmacodynamics: Retapamulin inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, specifically at the peptidyl transferase center involving ribosomal protein L3. This action disrupts the formation of peptide bonds and prevents the elongation of polypeptide chains, ultimately leading to bacterial growth inhibition or death.
Pharmacokinetics: After topical administration, minimal systemic absorption occurs. About 94% of the absorbed drug is bound to plasma proteins. It undergoes extensive hepatic metabolism via mono-oxygenation and di-oxygenation, resulting in multiple metabolites. Elimination pathways have not been fully elucidated, but given the low systemic absorption, the contribution of renal or hepatic excretion is expected to be minimal.
Mode of Action: Retapamulin binds to the bacterial 50S ribosomal subunit, specifically protein L3 within the peptidyl transferase center. This interaction sterically hinders substrate binding, effectively inhibiting peptidyl transferase activity, which is essential for bacterial protein synthesis.
Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Retapamulin’s primary mechanism involves binding to bacterial ribosomes, not human receptors or enzymes. It does not modulate neurotransmitter activity.
Dosage
Standard Dosage
Adults: Apply a thin layer of 1% retapamulin ointment to the affected area (up to 100 cm²) twice daily for 5 days.
Children: For patients aged 9 months and older, apply a thin layer of 1% retapamulin ointment to the affected area (up to 2% of total body surface area) twice daily for 5 days. Safety and efficacy have not been established in children younger than 9 months.
Special Cases:
- Elderly Patients: No dosage adjustment is typically necessary.
- Patients with Renal Impairment: No dosage adjustment is typically necessary due to minimal systemic absorption.
- Patients with Hepatic Dysfunction: No dosage adjustment is typically necessary due to low systemic exposure.
- Patients with Comorbid Conditions: Exercise caution and consider individual patient factors.
Clinical Use Cases
Retapamulin is not systemically administered and is not indicated for clinical scenarios like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations. It is exclusively for topical application on impetigo, small lacerations, abrasions or sutured wounds.
Dosage Adjustments
Due to low systemic absorption, dose adjustments are generally not needed for renal/hepatic dysfunction or metabolic disorders. However, concomitant administration with strong CYP3A4 inhibitors is not recommended in children younger than 2 years of age.
Side Effects
Common Side Effects:
Application site irritation (e.g., itching, burning, stinging), headache.
Rare but Serious Side Effects:
Severe allergic reactions (hives, difficulty breathing, swelling), severe skin reactions at the application site (blistering, swelling, oozing), worsening skin infection.
Long-Term Effects:
Prolonged or repeated use of antibiotics, including retapamulin, can potentially lead to the development of new infections, such as fungal infections, due to disruption of normal skin flora.
Adverse Drug Reactions (ADR)
Significant skin reactions, including Stevens-Johnson Syndrome and toxic epidermal necrolysis, have been reported rarely but warrant prompt intervention if suspected.
Contraindications
Hypersensitivity to retapamulin or any component of the formulation.
Drug Interactions
Concomitant use of retapamulin with strong CYP3A4 inhibitors (e.g., ketoconazole) may increase retapamulin exposure, although dosage adjustments are usually unnecessary in adults and children older than 2 years due to low systemic absorption. Co-administration with other topical products to the same skin area has not been extensively studied.
Pregnancy and Breastfeeding
Pregnancy Category B: Animal studies have not shown evidence of fetal harm. No controlled studies in pregnant women are available. Use only if clearly needed and potential benefit outweighs any risk.
Limited information suggests that retapamulin is not significantly excreted in breast milk, and breastfeeding poses minimal risk to the infant due to negligible systemic absorption.
Drug Profile Summary
- Mechanism of Action: Inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit.
- Side Effects: Application site reactions (itching, burning), headache; rarely, severe allergic reactions or skin reactions.
- Contraindications: Hypersensitivity to retapamulin.
- Drug Interactions: Concomitant use with strong CYP3A4 inhibitors may increase exposure.
- Pregnancy & Breastfeeding: Category B; use with caution. Breastfeeding considered safe due to limited systemic absorption.
- Dosage: Apply a thin layer twice daily for 5 days.
- Monitoring Parameters: Monitor the affected area for improvement or signs of adverse reactions.
Popular Combinations
Retapamulin is typically used as monotherapy. Combination therapy with other topical or systemic agents is not routinely recommended.
Precautions
- Discontinue use if sensitization or severe local irritation occurs.
- Not for oral, intranasal, ophthalmic, or intravaginal use.
- Monitor for signs of superinfection.
- Exercise caution in patients younger than 2 years using concomitant strong CYP3A4 inhibitors.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Retapamulin?
A: Adults and children 9 months and older: Apply a thin layer to the affected area (up to 100 cm² for adults or 2% BSA for children) twice daily for 5 days.
Q2: How does Retapamulin work?
A: Retapamulin inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit.
Q3: What are the common side effects of Retapamulin?
A: Common side effects include application site irritation (itching, burning, stinging) and headache.
Q4: Is Retapamulin safe for use during pregnancy?
A: Pregnancy Category B. Use only if clearly needed and the potential benefit outweighs the risk.
Q5: Can Retapamulin be used in breastfeeding mothers?
A: Limited data suggest minimal risk due to low systemic absorption. However, it is advisable to exercise caution.
Q6: What are the contraindications for Retapamulin use?
A: Hypersensitivity to retapamulin is a contraindication.
Q7: Are there any drug interactions I should be aware of with Retapamulin?
A: Concomitant use of strong CYP3A4 inhibitors may increase retapamulin exposure.
Q8: How long should Retapamulin be used?
A: Treatment duration is typically 5 days.
Q9: What should I do if the infection worsens or does not improve with Retapamulin?
A: Consult a physician to re-evaluate the diagnosis and consider alternative treatment options.
Q10: Can Retapamulin be used on open wounds?
A: Retapamulin is indicated for infected small lacerations, abrasions, or sutured wounds. It is not recommended for deep or extensive wounds without consulting a physician.
