Daptomycin pharmacokinetics are generally linear and time-independent at doses of 4 to 12 mg/kg administered as a single daily dose by 30-minute intravenous infusion for up to 14 days in healthy adult volunteers. Steady-state concentrations are achieved by the third daily dose.
Daptomycin administered as a 2-minute intravenous injection also exhibited dose proportional pharmacokinetics in the approved therapeutic dose range of 4 to 6 mg/kg. Comparable exposure (AUC and Cmax) was demonstrated in healthy adult subjects following administration of daptomycin as a 30-minute intravenous infusion or as a 2-minute intravenous injection.
Animal studies showed that daptomycin is not absorbed to any significant extent after oral administration.
Distribution
The volume of distribution at steady state of daptomycin in healthy adult subjects was approximately 0.1 l/kg and was independent of dose. Tissue distribution studies in rats showed that daptomycin appears to only minimally penetrate the blood-brain barrier and the placental barrier following single and multiple doses.
Daptomycin is reversibly bound to human plasma proteins in a concentration independent manner. In healthy adult volunteers and adult patients treated with daptomycin, protein binding averaged about 90% including subjects with renal impairment.
Biotransformation
In in vitro studies, daptomycin was not metabolised by human liver microsomes. In vitro studies with human hepatocytes indicate that daptomycin does not inhibit or induce the activities of the following human cytochrome P450 isoforms: 1A2, 2A6, 2C9, 2C19, 2D6, 2E1 and 3A4. It is unlikely that daptomycin will inhibit or induce the metabolism of medicinal products metabolised by the P450 system.
After infusion of 14C-daptomycin in healthy adults, the plasma radioactivity was similar to the concentration determined by microbiological assay. Inactive metabolites were detected in urine, as determined by the difference in total radioactive concentrations and microbiologically active concentrations. In a separate study, no metabolites were observed in plasma, and minor amounts of three oxidative metabolites and one unidentified compound were detected in urine. The site of metabolism has not been identified.
Elimination
Daptomycin is excreted primarily by the kidneys. Concomitant administration of probenecid and daptomycin has no effect on daptomycin pharmacokinetics in humans suggesting minimal to no active tubular secretion of daptomycin.
Following intravenous administration, plasma clearance of daptomycin is approximately 7 to 9 ml/hr/kg and its renal clearance is 4 to 7 ml/hr/kg.
In a mass balance study using radiolabelled material, 78% of the administered dose was recovered from the urine based on total radioactivity, whilst urinary recovery of unchanged daptomycin was approximately 50% of the dose. About 5% of the administered radiolabel was excreted in the faeces.
Special populations
Elderly
Following administration of a single 4 mg/kg intravenous dose of daptomycin over a 30-minute period, the mean total clearance of daptomycin was approximately 35% lower and the mean AUC0-∞ was approximately 58% higher in elderly subjects (≥ 75 years of age) compared with those in healthy young subjects (18 to 30 years of age). There were no differences in Cmax. The differences noted are most likely due to the normal reduction in renal function observed in the geriatric population.
No dose adjustment is necessary based on age alone. However, renal function should be assessed and the dose should be reduced if there is evidence of severe renal impairment.
Children and adolescents (1 to 17 years of age)
The pharmacokinetics of daptomycin in paediatric subjects was evaluated in 3 single-dose pharmacokinetic studies. After a single 4 mg/kg dose of daptomycin, total clearance normalised by weight and elimination half-life of daptomycin in adolescents (12-17 years of age) with Gram-positive infection were similar to adults. After a single 4 mg/kg dose of daptomycin, total clearance of daptomycin in children 7-11 years of age with Gram-positive infection was higher than in adolescents, whereas elimination half-life was shorter. After a single 4, 8, or 10 mg/kg dose of daptomycin, total clearance and elimination half-life of daptomycin in children 2-6 years of age were similar at different doses; total clearance was higher and elimination half-life was shorter than in adolescents. After a single 6 mg/kg dose of daptomycin, the clearance and elimination half-life of daptomycin in children 13-24 months of age were similar to children 2-6 years of age who received a single 4-10 mg/kg dose. The results of these studies show that exposures (AUC) in paediatric patients across all doses are generally lower than those in adults at comparable doses.
Paediatric patients with cSSTI
A Phase 4 study (DAP-PEDS-07-03) was conducted to assess safety, efficacy, and pharmacokinetics of daptomycin in paediatric patients (1 to 17 years old, inclusive) with cSSTI caused by Gram-positive pathogens. Daptomycin pharmacokinetics in patients in this study are summarised in Table 2. Following administration of multiple doses, daptomycin exposure was similar across different age groups after dose adjustment based on body weight and age. Plasma exposures achieved with these doses were consistent with those achieved in the adult cSSTI study (following 4 mg/kg once daily in adults).
Table 2 Mean (Standard Deviation) of Daptomycin Pharmacokinetics in Paediatric cSSTI Patients (1 to 17 Years of Age) in Study DAP-PEDS-07-03
| Age Range | 12-17 years (N=6) | 7-11 years (N=2)a | 2-6 years (N=7) | 1 to <2 years (N=30)b |
| Dose Infusion Time | 5 mg/kg 30 minutes | 7 mg/kg 30 minutes | 9 mg/kg 60 minutes | 10 mg/kg 60 minutes |
| AUC0-24hr (µg×hr/ml) | 387 (81) | 438 | 439 (102) | 466 |
| Cmax (µg/ml) | 62.4 (10.4) | 64.9, 74.4 | 81.9 (21.6) | 79.2 |
| Apparent t1/2 (hr) | 5.3 (1.6) | 4.6 | 3.8 (0.3) | 5.04 |
| CL/wt (ml/hr/kg) | 13.3 (2.9) | 16.0 | 21.4 (5.0) | 21.5 |
Pharmacokinetic parameter values estimated by noncompartmental analysis.
a Individual values reported as only two patients in this age group provided pharmacokinetic samples to enable pharmacokinetic analysis; AUC, apparent t1/2 and CL/wt could be determined for only one of the two patients.
b Pharmacokinetic analysis conducted on the pooled pharmacokinetic profile with mean concentrations across subjects at each time point.
Paediatric patients with SAB
A Phase 4 study (DAP-PEDBAC-11-02) was conducted to assess safety, efficacy, and pharmacokinetics of daptomycin in paediatric patients (1 to 17 years old, inclusive) with SAB. Daptomycin pharmacokinetics inpatients in this study are summarised in Table 3. Following administration of multiple doses, daptomycin exposure was similar across different age groups after dose adjustment based on body weight and age. Plasma exposures achieved with these doses were consistent with those achieved in the adult SAB study (following 6 mg/kg once daily in adults).
Table 3 Mean (Standard Deviation) of Daptomycin Pharmacokinetics in Paediatric SAB Patients (1 to 17 Years of Age) in Study DAP-PEDBAC-11-02
| Age Range | 12-17 years (N=13) | 7-11 years (N=19)a | 1 to 6 years (N=19)* |
| Dose Infusion Time | 7 mg/kg 30 minutes | 9 mg/kg 30 minutes | 12 mg/kg 60 minutes |
| AUC0-24hr (µg×hr/ml) | 656 (334) | 579 (116) | 620 (109) |
| Cmax (µg/ml) | 104 (35.5) | 104 (14.5) | 106 (12.8) |
| Apparent t1/2 (hr) | 7.5 (2.3) | 6.0 (0.8) | 5.1 (0.6) |
| CL/wt (ml/hr/kg) | 12.4 (3.9) | 15.9 (2.8) | 19.9 (3.4) |
Pharmacokinetic parameter values estimated using a model-based approach with sparsely collected pharmacokinetic samples from individual patients in the study.
*Mean (Standard Deviation) calculated for patients 2 to 6 years of age, since no patients 1 to <2 years of age were enrolled in the study. Simulation using a population pharmacokinetic model demonstrated that the AUCss (area under the concentration time curve at steady state) of daptomycin in paediatric patients 1 to <2 years of age receiving 12 mg/kg once daily would be comparable to that in adult patients receiving 6 mg/kg once daily.
Obesity
Relative to non-obese subjects daptomycin systemic exposure measured by AUC was about 28% higher in moderately obese subjects (Body Mass Index of 25-40 kg/m2) and 42% higher in extremely obese subjects (Body Mass Index of > 40 kg/m2). However, no dose adjustment is considered to be necessary based on obesity alone.
Gender
No clinically significant gender-related differences in daptomycin pharmacokinetics have been observed.
Race
No clinically significant differences in daptomycin pharmacokinetics have been observed in Black or Japanese subjects relative to Caucasian subjects.
Renal impairment
Following administration of a single 4 mg/kg or 6 mg/kg intravenous dose of daptomycin over a 30- minute period to adult subjects with various degrees of renal impairment, total daptomycin clearance (CL) decreased and systemic exposure (AUC) increased as renal function (creatinine clearance) decreased.
Based on pharmacokinetic data and modelling, the daptomycin AUC during the first day after administration of a 6 mg/kg dose to adult patients on HD or CAPD was 2-fold higher than that observed in adult patients with normal renal function who received the same dose. On the second day after administration of a 6 mg/kg dose to HD and CAPD adult patients the daptomycin AUC was approximately 1.3-fold higher than that observed after a second 6 mg/kg dose in adult patients with normal renal function. On this basis, it is recommended that adult patients on HD or CAPD receive daptomycin once every 48 hours at the dose recommended for the type of infection being treated (see section 4.2).
The dosage regimen for daptomycin in paediatric patients with renal impairment has not been established.
Hepatic impairment
The pharmacokinetics of daptomycin is not altered in subjects with moderate hepatic impairment (Child-Pugh B classification of hepatic impairment) compared with healthy volunteers matched for gender, age and weight following a single 4 mg/kg dose. No dosage adjustment is necessary when administering daptomycin in patients with moderate hepatic impairment. The pharmacokinetics of daptomycin in patients with severe hepatic impairment (Child-Pugh C classification) have not been evaluated.