5.1 Local Irritation

In the event of sensitization or severe local irritation from ALTABAX, usage should be discontinued, the ointment wiped off, and appropriate alternative therapy for the infection instituted [see Patient Counseling Information (17)].

5.2 Not for Systemic or Mucosal Use

ALTABAX is not intended for ingestion or for oral, intranasal, ophthalmic, or intravaginal use. The efficacy and safety of ALTABAX on mucosal surfaces have not been established. Epistaxis has been reported with the use of ALTABAX on nasal mucosa.

5.3 Potential for Microbial Overgrowth

The use of antibiotics may promote the selection of nonsusceptible organisms. Should superinfection occur during therapy, appropriate measures should be taken.

Prescribing ALTABAX in the absence of a proven or strongly suspected bacterial infection is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

6.1 Clinical Studies Experience

Because clinical trials are conducted under varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice. The adverse reaction information from the clinical trials does, however, provide a basis for identifying the adverse events that appear to be related to drug use and for approximating rates.

The safety profile of ALTABAX was assessed in 2,115 adult and pediatric subjects 9 months and older who used at least one dose from a 5-day, twice-a-day regimen of retapamulin ointment. Control groups included 819 adult and pediatric subjects who used at least one dose of the active control (oral cephalexin), 172 subjects who used an active topical comparator (not available in the US), and 71 subjects who used placebo.

Adverse events rated by investigators as drug-related occurred in 5.5% (116/2,115) of subjects treated with retapamulin ointment, 6.6% (54/819) of subjects receiving cephalexin, and 2.8% (2/71) of subjects receiving placebo. The most common drug-related adverse events (greater than or equal to 1% of subjects) were application site irritation (1.4%) in the retapamulin group, diarrhea (1.7%) in the cephalexin group, and application site pruritus (1.4%) and application site paresthesia (1.4%) in the placebo group.

Adults

The adverse events, regardless of attribution, reported in at least 1% of adults (aged 18 years and older) who received ALTABAX or comparator are presented in Table 1.

Pediatrics

The adverse events, regardless of attribution, reported in at least 1% of pediatric subjects aged 9 months to 17 years who received ALTABAX are presented in Table 2.

Other Adverse Events

Application site pain, erythema, and contact dermatitis were reported in less than 1% of subjects in clinical trials.

6.2 Postmarketing Experience

In addition to reports in clinical trials, the following events have been identified during postmarketing use of ALTABAX. Because these events are reported voluntarily from a population of uncertain size, it is not possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

General Disorders and Administration Site Conditions

Application site burning.

Immune System Disorders

Hypersensitivity including angioedema.

8.1 Pregnancy

Risk Summary

There are no available data on ALTABAX use in pregnant women to inform any drug associated risk for major birth defects, miscarriage or adverse maternal or fetal outcomes. Retapamulin is negligibly absorbed systemically following topical administration and maternal use is not expected to result in fetal exposure to the retapamulin [see Clinical Pharmacology (12.3)]. Animal reproduction studies were not conducted with ALTABAX. However, in animal studies where retapamulin was administered by oral gavage or intravenous infusion to pregnant rats and rabbits, respectively, during organogenesis, maternal toxicity was seen at doses greater than or equal to 150 mg/kg/day and 7.2 mg/kg/day (8-fold the maximum achievable human exposure based on AUC) for oral and intravenous routes, respectively. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population the background risk of major birth defects in clinically recognized pregnancies is 2% to 4% and of miscarriage is 15% to 20%, respectively.

8.2 Lactation

Risk Summary

There are no data available on the presence of retapamulin in human milk, its effects on the breastfed infant or its effects on milk production. However, breastfeeding is not expected to result in exposure of the child to the drug due to the negligible systemic absorption of retapamulin in humans following topical administration of ALTABAX [see Clinical Pharmacology (12.3)].

The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for ALTABAX and any potential adverse effects on the breastfed infant from ALTABAX or from the underlying maternal condition.

8.4 Pediatric Use

The safety and effectiveness of ALTABAX in the treatment of impetigo have been established in pediatric patients aged 9 months to 17 years. Use of ALTABAX in pediatric patients (9 months to 17 years of age) is supported by evidence from adequate and well-controlled trials of ALTABAX in which 588 pediatric subjects received at least one dose of retapamulin ointment, 1% [see Adverse Reactions (6.1), Clinical Studies (14)]. The magnitude of efficacy and the safety profile of ALTABAX in pediatric subjects 9 months and older were similar to those in adults.

The safety and effectiveness of ALTABAX in pediatric patients younger than 9 months have not been established. An open-label clinical trial of topical treatment with ALTABAX (twice daily for 5 days) was conducted in subjects aged 2 to 24 months. Plasma samples were obtained from 79 subjects. In these pediatric subjects, systemic exposure of retapamulin was higher compared with subjects aged 2 to 17 years. Furthermore, a higher proportion of pediatric subjects aged 2 to 9 months had measurable concentrations (greater than 0.5 ng per mL) of retapamulin compared with subjects aged 9 to 24 months [see Pharmacokinetics (12.3)]. The highest levels were seen in subjects aged 2 to 6 months [see Pharmacokinetics (12.3)]. The use of retapamulin is not indicated in pediatric patients younger than 9 months.

8.5 Geriatric Use

Of the total number of subjects in the adequate and well-controlled trials of ALTABAX, 234 subjects were aged 65 years and older, of whom 114 subjects were aged 75 years and older. No overall differences in effectiveness or safety were observed between these subjects and younger adult subjects.

12.1 Mechanism of Action

ALTABAX is an antibacterial agent [see Clinical Pharmacology (12.4)].

12.2 Pharmacodynamics

In post-hoc analyses of manually over-read 12-lead ECGs from healthy subjects (N = 103), no significant effects on QT/QTc intervals were observed after topical application of retapamulin ointment on intact and abraded skin. Due to the low systemic exposure to retapamulin with topical application, QT prolongation in patients is unlikely [see Clinical Pharmacology (12.3)].

12.3 Pharmacokinetics

Absorption

In a trial of healthy adult subjects, retapamulin ointment, 1% was applied once daily to intact skin (800 cm2 surface area) and to abraded skin (200 cm2 surface area) under occlusion for up to 7 days. Systemic exposure following topical application of retapamulin through intact and abraded skin was low. Three percent of blood samples obtained on Day 1 after topical application to intact skin had measurable retapamulin concentrations (lower limit of quantitation 0.5 ng per mL); thus Cmax values on Day 1 could not be determined. Eighty-two percent of blood samples obtained on Day 7 after topical application to intact skin and 97% and 100% of blood samples obtained after topical application to abraded skin on Days 1 and 7, respectively, had measurable retapamulin concentrations. The median Cmax value in plasma after application to 800 cm2 of intact skin was 3.5 ng per mL on Day 7 (range: 1.2 to 7.8 ng per mL). The median Cmax value in plasma after application to 200 cm2 of abraded skin was 11.7 ng per mL on Day 1 (range: 5.6 to 22.1 ng per mL) and 9.0 ng per mL on Day 7 (range: 6.7 to 12.8 ng per mL).

Plasma samples were obtained from 380 adult subjects and 136 pediatric subjects (aged 2 to 17 years) who were receiving topical treatment with ALTABAX topically twice daily. Eleven percent had measurable retapamulin concentrations (lower limit of quantitation 0.5 ng per mL), of which the median concentration was 0.8 ng per mL. The maximum measured retapamulin concentration in adults was 10.7 ng per mL and in pediatric subjects (aged 2 to 17 years) was 18.5 ng per mL.

A single plasma sample was obtained from 79 pediatric subjects (aged 2 to 24 months) who were receiving topical treatment with ALTABAX twice daily. Forty-six percent had measurable retapamulin concentrations greater than 0.5 ng per mL) compared with 7% in pediatric subjects aged 2 to 17 years. A higher proportion (69%) of pediatric subjects aged 2 to 9 months had measurable concentrations of retapamulin compared with subjects aged 9 to 24 months (32%). Among pediatric subjects aged 2 to 9 months (n = 29), 4 subjects had retapamulin concentrations that were higher (greater than or equal to 26.9 ng per mL) than the maximum concentration observed in pediatric subjects aged 2 to 17 years (18.5 ng per mL). Among pediatric subjects aged 9 to 24 months (n = 50), 1 subject had a retapamulin concentration that was higher (95.1 ng per mL) than the maximum level observed in pediatric subjects aged 2 to 17 years.

Distribution

Retapamulin is approximately 94% bound to human plasma proteins, and the protein binding is independent of concentration. The apparent volume of distribution of retapamulin has not been determined in humans.

Metabolism

In vitro studies with human hepatocytes showed that the main routes of metabolism were mono-oxygenation and di-oxygenation. In vitro studies with human liver microsomes demonstrated that retapamulin is extensively metabolized to numerous metabolites, of which the predominant routes of metabolism were mono-oxygenation and N-demethylation. The major enzyme responsible for metabolism of retapamulin in human liver microsomes was cytochrome P450 3A4 (CYP3A4).

Elimination

Retapamulin elimination in humans has not been investigated due to low systemic exposure after topical application.

12.4 Microbiology

Retapamulin is a semisynthetic derivative of the compound pleuromutilin, which is isolated through fermentation from Clitopilus passeckerianus (formerly Pleurotus passeckerianus). In vitro activity of retapamulin against isolates of Staphylococcus aureus as well as Streptococcus pyogenes has been demonstrated.

Antimicrobial Mechanism of Action

Retapamulin selectively inhibits bacterial protein synthesis by interacting at a site on the 50S subunit of the bacterial ribosome through an interaction that is different from that of other antibiotics. This binding site involves ribosomal protein L3 and is in the region of the ribosomal P site and peptidyl transferase center. By virtue of binding to this site, pleuromutilins inhibit peptidyl transfer, block P-site interactions, and prevent the normal formation of active 50S ribosomal subunits. Retapamulin is bacteriostatic against Staphylococcus aureus and Streptococcus pyogenes at the retapamulin in vitro minimum inhibitory concentration (MIC) for these organisms. At concentrations 1,000 times the in vitro MIC, retapamulin is bactericidal against these same organisms. Although cross-resistance between retapamulin and other antibacterial classes (such as clindamycin and oxazolidones) exist, isolates resistant to these classes may be susceptible to retapamulin.

Mechanisms of Decreased Susceptibility to Retapamulin

In vitro, 2 mechanisms that cause reduced susceptibility to retapamulin have been identified, specifically, mutations in ribosomal protein L3, the presence of Cfr rRNA methyltransferase or the presence of an efflux mechanism. Decreased susceptibility of S. aureus to retapamulin (highest retapamulin MIC was 2 mcg per mL) develops slowly in vitro via multistep mutations in L3 after serial passage in sub-inhibitory concentrations of retapamulin. There was no apparent treatment-associated reduction in susceptibility to retapamulin in the Phase 3 clinical program. The clinical significance of these findings is not known.

Other

Based on in vitro broth microdilution susceptibility testing, no differences were observed in susceptibility of S. aureus to retapamulin whether the isolates were methicillin-resistant or methicillin-susceptible. Retapamulin susceptibility did not correlate with clinical success rates in patients with methicillin-resistant S. aureus. The reason for this is not known but may have been influenced by the presence of particular strains of S. aureus possessing certain virulence factors, such as Panton-Valentine Leukocidin (PVL). In the case of treatment failure associated with S. aureus (regardless of methicillin susceptibility), the presence of strains possessing additional virulence factors (such as PVL) should be considered.

Retapamulin has been shown to be active against the following microorganisms, both in vitro and in clinical trials [see Indications and Usage (1)].

Aerobic and Facultative Gram-Positive Bacteria: Staphylococcus aureus (methicillin-susceptible isolates only); Streptococcus pyogenes.

Susceptibility Testing

The clinical microbiology laboratory should provide cumulative results of the in vitro susceptibility test results for antimicrobial drugs used in local hospitals and practice areas to the physician as periodic reports that describe the susceptibility profile of nosocomial and community-acquired pathogens. These reports should aid the physician in selecting the most effective antimicrobial.

Susceptibility Testing Techniques:

Dilution Techniques: Quantitative methods can be used to determine the MIC of retapamulin that will inhibit the growth of the bacteria being tested. The MIC provides an estimate of the susceptibility of bacteria to retapamulin. The MIC should be determined using a standardized procedure.1,2 Standardized procedures are based on a dilution method (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of retapamulin powder.

Diffusion Techniques: Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure requires the use of standardized inoculum concentrations.2,3 This procedure uses paper disks impregnated with 2 mcg of retapamulin to test the susceptibility of microorganisms to retapamulin.

Susceptibility Test Interpretive Criteria: In vitro susceptibility test interpretive criteria for retapamulin have not been determined for this topical antimicrobial. The relation of the in vitro MIC and/or disk diffusion susceptibility test results to clinical efficacy of retapamulin against the bacteria tested should be monitored.

Quality Control Parameters for Susceptibility Testing: In vitro susceptibility test quality control parameters were developed for retapamulin so that laboratories that test the susceptibility of bacterial isolates to retapamulin can determine if the susceptibility test is performing correctly. Standardized dilution techniques and diffusion methods require the use of laboratory control microorganisms to monitor the technical aspects of the laboratory procedures. Standard retapamulin powder should provide the following MIC and a 2-mcg retapamulin disk should produce the following zone diameters with the indicated quality control strains in Table 3.

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term studies in animals to evaluate carcinogenic potential have not been conducted with retapamulin.

Retapamulin showed no genotoxicity when evaluated in vitro for gene mutation and/or chromosomal effects in the mouse lymphoma cell assay, in cultured human peripheral blood lymphocytes, or when evaluated in vivo in a rat micronucleus test.

No evidence of impaired fertility was found in male or female rats given retapamulin 50, 150, or 450 mg per kg per day orally.