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12 CLINICAL PHARMACOLOGY

12.1Mechanism of Action Daptomycin is an antibacterial drug [see Clinical Pharmacology (12.4) ].

12.2Pharmacodynamics Based on animal models of infection, the antimicrobial activity of daptomycin appears to correlate with the AUC/MIC (area under the concentration-time curve/minimum inhibitory concentration) ratio for certain pathogens, including S. aureus . The principal pharmacokinetic/pharmacodynamic parameter best associated with clinical and microbiological cure has not been elucidated in clinical trials with daptomycin.

12.3Pharmacokinetics Daptomycin Administered over a 30-Minute Period in Adults The mean and standard deviation (SD) pharmacokinetic parameters of daptomycin at steady-state following intravenous administration of daptomycin over a 30-minute period at 4 to 12 mg/kg every 24h to healthy young adults are summarized in Table 11. Table 11: Mean (SD) Daptomycin Pharmacokinetic Parameters in Healthy Adult Volunteers at Steady-State * Daptomycin was administered by intravenous infusion over a 30-minute period. † Doses of daptomycin in excess of 6 mg/kg have not been approved. ‡ AUC 0-24 , area under the concentration-time curve from 0 to 24 hours; t 1/2 , elimination half-life; V ss , volume of distribution at steady-state; CL T , total plasma clearance; C max , maximum plasma concentration.

Dose *† (mg/kg) Pharmacokinetic Parameters ‡ AUC 0-24 (mcg.h/mL) t 1/2 (h) V ss (L/kg) CL T (mL/h/kg) C max (mcg/mL) 4 (N=6) 494 (75) 8.1 (1.0) 0.096 (0.009) 8.3 (1.3) 57.8 (3.0) 6 (N=6) 632 (78) 7.9 (1.0) 0.101 (0.007) 9.1 (1.5) 93.9 (6.0) 8 (N=6) 858 (213) 8.3 (2.2) 0.101 (0.013) 9.0 (3.0) 123.3 (16.0) 10 (N=9) 1,039 (178) 7.9 (0.6) 0.098 (0.017) 8.8 (2.2) 141.1 (24.0) 12 (N=9) 1,277 (253) 7.7 (1.1) 0.097 (0.018) 9.0 (2.8) 183.7 (25.0) Daptomycin pharmacokinetics were generally linear and time-independent at daptomycin doses of 4 to 12 mg/kg every 24h administered by intravenous infusion over a 30-minute period for up to 14 days.

Steady-state trough concentrations were achieved by the third daily dose. The mean (SD) steady-state trough concentrations attained following the administration of 4, 6, 8, 10, and 12 mg/kg every 24h were 5.9 (1.6), 6.7 (1.6), 10.3 (5.5), 12.9 (2.9), and 13.7 (5.2) mcg/mL, respectively. Daptomycin Administered over a 2-Minute Period in Adults Following intravenous administration of daptomycin over a 2-minute period to healthy adult volunteers at doses of 4 mg/kg (N=8) and 6 mg/kg (N=12), the mean (SD) steady-state systemic exposure (AUC) values were 475 (71) and 701 (82) mcg.h/mL, respectively.

Values for maximum plasma concentration (C max ) at the end of the 2-minute period could not be determined adequately in this study. However, using pharmacokinetic parameters from 14 healthy adult volunteers who received a single dose of daptomycin 6 mg/kg intravenous administered over a 30-minute period in a separate study, steady-state C max values were simulated for daptomycin 4 and 6 mg/kg intravenous administered over a 2-minute period. The simulated mean (SD) steady-state C max values were 77.7 (8.1) and 116.6 (12.2) mcg/mL, respectively.

Distribution Daptomycin is reversibly bound to human plasma proteins, primarily to serum albumin, in a concentration-independent manner. The overall mean binding ranges from 90 to 93%. In clinical studies, mean serum protein binding in adult subjects with creatinine clearance (CL CR ) ≥30 mL/min was comparable to that observed in healthy adult subjects with normal renal function.

However, there was a trend toward decreasing serum protein binding among subjects with CL CR <30 mL/min (88%), including those receiving hemodialysis (86%) and continuous ambulatory peritoneal dialysis (CAPD) (84%). The protein binding of daptomycin in adult subjects with moderate hepatic impairment (Child-Pugh Class B) was similar to that in healthy adult subjects. The volume of distribution at steady-state (V ss ) of daptomycin in healthy adult subjects was approx… [Excerpted — this section continues on DailyMed.]

12.1Mechanism of Action Daptomycin is an antibacterial drug [see Clinical Pharmacology (12.4) ].

12.3Pharmacokinetics Daptomycin Administered over a 30-Minute Period in Adults The mean and standard deviation (SD) pharmacokinetic parameters of daptomycin at steady-state following intravenous administration of daptomycin over a 30-minute period at 4 to 12 mg/kg every 24h to healthy young adults are summarized in Table 11. Table 11: Mean (SD) Daptomycin Pharmacokinetic Parameters in Healthy Adult Volunteers at Steady-State * Daptomycin was administered by intravenous infusion over a 30-minute period. † Doses of daptomycin in excess of 6 mg/kg have not been approved. ‡ AUC 0-24 , area under the concentration-time curve from 0 to 24 hours; t 1/2 , elimination half-life; V ss , volume of distribution at steady-state; CL T , total plasma clearance; C max , maximum plasma concentration.

Dose *† (mg/kg) Pharmacokinetic Parameters ‡ AUC 0-24 (mcg.h/mL) t 1/2 (h) V ss (L/kg) CL T (mL/h/kg) C max (mcg/mL) 4 (N=6) 494 (75) 8.1 (1.0) 0.096 (0.009) 8.3 (1.3) 57.8 (3.0) 6 (N=6) 632 (78) 7.9 (1.0) 0.101 (0.007) 9.1 (1.5) 93.9 (6.0) 8 (N=6) 858 (213) 8.3 (2.2) 0.101 (0.013) 9.0 (3.0) 123.3 (16.0) 10 (N=9) 1,039 (178) 7.9 (0.6) 0.098 (0.017) 8.8 (2.2) 141.1 (24.0) 12 (N=9) 1,277 (253) 7.7 (1.1) 0.097 (0.018) 9.0 (2.8) 183.7 (25.0) Daptomycin pharmacokinetics were generally linear and time-independent at daptomycin doses of 4 to 12 mg/kg every 24h administered by intravenous infusion over a 30-minute period for up to 14 days.

Steady-state trough concentrations were achieved by the third daily dose. The mean (SD) steady-state trough concentrations attained following the administration of 4, 6, 8, 10, and 12 mg/kg every 24h were 5.9 (1.6), 6.7 (1.6), 10.3 (5.5), 12.9 (2.9), and 13.7 (5.2) mcg/mL, respectively. Daptomycin Administered over a 2-Minute Period in Adults Following intravenous administration of daptomycin over a 2-minute period to healthy adult volunteers at doses of 4 mg/kg (N=8) and 6 mg/kg (N=12), the mean (SD) steady-state systemic exposure (AUC) values were 475 (71) and 701 (82) mcg.h/mL, respectively.

Values for maximum plasma concentration (C max ) at the end of the 2-minute period could not be determined adequately in this study. However, using pharmacokinetic parameters from 14 healthy adult volunteers who received a single dose of daptomycin 6 mg/kg intravenous administered over a 30-minute period in a separate study, steady-state C max values were simulated for daptomycin 4 and 6 mg/kg intravenous administered over a 2-minute period. The simulated mean (SD) steady-state C max values were 77.7 (8.1) and 116.6 (12.2) mcg/mL, respectively.

Distribution Daptomycin is reversibly bound to human plasma proteins, primarily to serum albumin, in a concentration-independent manner. The overall mean binding ranges from 90 to 93%. In clinical studies, mean serum protein binding in adult subjects with creatinine clearance (CL CR ) ≥30 mL/min was comparable to that observed in healthy adult subjects with normal renal function.

However, there was a trend toward decreasing serum protein binding among subjects with CL CR <30 mL/min (88%), including those receiving hemodialysis (86%) and continuous ambulatory peritoneal dialysis (CAPD) (84%). The protein binding of daptomycin in adult subjects with moderate hepatic impairment (Child-Pugh Class B) was similar to that in healthy adult subjects. The volume of distribution at steady-state (V ss ) of daptomycin in healthy adult subjects was approximately

0.1L/kg and was independent of dose. Metabolism In in vitro studies, daptomycin was not metabolized by human liver microsomes. In 5 healthy adults after infusion of radiolabeled 14 C-daptomycin, the plasma total radioactivity was similar to the concentration determined by microbiological assay.

Inactive metabolites were detected in urine, as determined by the difference between total radioactive concentrations and microbiologically active concentrations. In a separate study, no metabolites were observed in plasma on Day 1 following the adminis… [Excerpted — this section continues on DailyMed.]

12.2Pharmacodynamics Based on animal models of infection, the antimicrobial activity of daptomycin appears to correlate with the AUC/MIC (area under the concentration-time curve/minimum inhibitory concentration) ratio for certain pathogens, including S. aureus . The principal pharmacokinetic/pharmacodynamic parameter best associated with clinical and microbiological cure has not been elucidated in clinical trials with daptomycin.

14 CLINICAL STUDIES

14.1Complicated Skin and Skin Structure Infections Adults with cSSSI Adult patients with clinically documented complicated skin and skin structure infections (cSSSI) (Table 15) were enrolled in two randomized, multinational, multicenter, investigator-blinded trials comparing daptomycin (4 mg/kg intravenous every 24h) with either vancomycin (1 g intravenous q12h) or an anti-staphylococcal semi-synthetic penicillin (i.e., nafcillin, oxacillin, cloxacillin, or flucloxacillin; 4 to 12 g intravenous per day). Patients could switch to oral therapy after a minimum of 4 days of intravenous treatment if clinical improvement was demonstrated.

Patients known to have bacteremia at baseline were excluded. Patients with creatinine clearance (CL CR ) between 30 and 70 mL/min were to receive a lower dose of daptomycin as specified in the protocol; however, the majority of patients in this subpopulation did not have the dose of daptomycin adjusted. Table 15: Investigator’s Primary Diagnosis in the cSSSI Trials in Adult Patients (Population: ITT) *Comparator: vancomycin (1 g intravenous q12h) or an anti-staphylococcal semi-synthetic penicillin (i.e., nafcillin, oxacillin, cloxacillin, or flucloxacillin; 4 to 12 g/day intravenous in divided doses). †The majority of cases were subsequently categorized as complicated cellulitis, major abscesses, or traumatic wound infections.

Primary Diagnosis Adult Patients (Daptomycin / Comparator*) Study 9801 N=264 / N=266 Study 9901 N=270 / N=292 Pooled N=534 / N=558 Wound Infection 99 (38%) / 116 (44%) 102 (38%) / 108 (37%) 201 (38%) / 224 (40%) Major Abscess 55 (21%) / 43 (16%) 59 (22%) / 65 (22%) 114 (21%) / 108 (19%) Ulcer Infection 71 (27%) / 75 (28%) 53 (20%) / 68 (23%) 124 (23%) / 143 (26%) Other Infection † 39 (15%) / 32 (12%) 56 (21%) / 51 (18%) 95 (18%) / 83 (15%) One trial was conducted primarily in the United States and South Africa (study 9801), and the second was conducted at non-US sites only (study 9901).

The two trials were similar in design but differed in patient characteristics, including history of diabetes and peripheral vascular disease. There were a total of 534 adult patients treated with daptomycin and 558 treated with comparator in the two trials. The majority (89.7%) of patients received intravenous medication exclusively.

The efficacy endpoints in both trials were the clinical success rates in the intent-to-treat (ITT) population and in the clinically evaluable (CE) population. In study 9801, clinical success rates in the ITT population were 62.5% (165/264) in patients treated with daptomycin and 60.9% (162/266) in patients treated with comparator drugs. Clinical success rates in the CE population were 76.0% (158/208) in patients treated with daptomycin and 76.7% (158/206) in patients treated with comparator drugs.

In study 9901, clinical success rates in the ITT population were 80.4% (217/270) in patients treated with daptomycin and 80.5% (235/292) in patients treated with comparator drugs. Clinical success rates in the CE population were 89.9% (214/238) in patients treated with daptomycin and 90.4% (226/250) in patients treated with comparator drugs. The success rates by pathogen for microbiologically evaluable patients are presented in Table 16.

Table 16: Clinical Success Rates by Infecting Pathogen in the cSSSI Trials in Adult Patients (Population: Microbiologically Evaluable) *Comparator: vancomycin (1 g intravenous q12h) or an anti-staphylococcal semi-synthetic penicillin (i.e., nafcillin, oxacillin, cloxacillin, or flucloxacillin; 4 to 12 g/day intravenous in divided doses). †As determined by the central laboratory. Pathogen Success Rate n/N (%) Daptomycin Comparator* Methicillin-susceptible Staphylococcus aureus (MSSA)† 170/198 (86%) 180/207 (87%) Methicillin-resistant Staphylococcus aureus (MRSA)† 21/28 (75%) 25/36 (69%) Streptococcus pyogenes 79/84 (94%) 80/88 (91%) Streptococcus agalactiae 23/27 (85%) 22/29 (76%) Streptococcus dysgalactiae subsp. equ… [Excerpted — this section continues on DailyMed.]

13 NONCLINICAL TOXICOLOGY

13.1Carcinogenesis, Mutagenesis, Impairment of Fertility Long-term carcinogenicity studies in animals have not been conducted to evaluate the carcinogenic potential of daptomycin. However, neither mutagenic nor clastogenic potential was found in a battery of genotoxicity tests, including the Ames assay, a mammalian cell gene mutation assay, a test for chromosomal aberrations in Chinese hamster ovary cells, an in vivo micronucleus assay, an in vitro DNA repair assay, and an in vivo sister chromatid exchange assay in Chinese hamsters.

Daptomycin did not affect the fertility or reproductive performance of male and female rats when administered intravenously at doses of 25, 75, or 150 mg/kg/day, which is approximately up to 9 times the estimated human exposure level based upon AUCs (or approximately up to 4 times the recommended human dose of 6 mg/kg based on body surface area comparison).

13.2Animal Toxicology and/or Pharmacology Adult Animals In animals, daptomycin administration has been associated with effects on skeletal muscle. However, there were no changes in cardiac or smooth muscle. Skeletal muscle effects were characterized by microscopic degenerative/regenerative changes and variable elevations in creatine phosphokinase (CPK).

No fibrosis or rhabdomyolysis was evident in repeat-dose studies up to the highest doses tested in rats (150 mg/kg/day) and dogs (100 mg/kg/day). The degree of skeletal myopathy showed no increase when treatment was extended from 1 month to up to 6 months. Severity was dose-dependent.

All muscle effects, including microscopic changes, were fully reversible within 30 days following the cessation of dosing. In adult animals, effects on peripheral nerve (characterized by axonal degeneration and frequently accompanied by significant losses of patellar reflex, gag reflex, and pain perception) were observed at daptomycin doses higher than those associated with skeletal myopathy. Deficits in the dogs’ patellar reflexes were seen within 2 weeks after the start of treatment at 40 mg/kg/day (9 times the human C max at the 6 mg/kg/day dose), with some clinical improvement noted within 2 weeks after the cessation of dosing.

However, at 75 mg/kg/day for 1 month, 7 of 8 dogs failed to regain full patellar reflex responses within a 3-month recovery period. In a separate study in dogs receiving doses of 75 and 100 mg/kg/day for 2 weeks, minimal residual histological changes were noted at 6 months after the cessation of dosing. However, recovery of peripheral nerve function was evident.

Tissue distribution studies in rats showed that daptomycin is retained in the kidney but appears to penetrate the blood-brain barrier only minimally following single and multiple doses. Juvenile Animals Target organs of daptomycin-related effects in 7-week-old juvenile dogs were skeletal muscle and nerve, the same target organs as in adult dogs. In juvenile dogs, nerve effects were noted at lower daptomycin blood concentrations than in adult dogs following 28 days of dosing.

In contrast to adult dogs, juvenile dogs also showed evidence of effects in nerves of the spinal cord as well as peripheral nerves after 28 days of dosing. No nerve effects were noted in juvenile dogs following 14 days of dosing at doses up to 75 mg/kg/day. Administration of daptomycin to 7-week-old juvenile dogs for 28 days at doses of 50 mg/kg/day produced minimal degenerative effects on the peripheral nerve and spinal cord in several animals, with no corresponding clinical signs.

A dose of 150 mg/kg/day for 28 days produced minimal degeneration in the peripheral nerve and spinal cord as well as minimal to mild degeneration of the skeletal muscle in a majority of animals, accompanied by slight to severe muscle weakness evident in most dogs. Following a 28-day recovery phase, microscopic examination revealed recovery of the skeletal muscle and the ulnar nerve effects, but nerve degeneration in the sciatic nerve and spinal cord was… [Excerpted — this section continues on DailyMed.]