Tigecycline

12 CLINICAL PHARMACOLOGY 12.1 Mechanism of Action Tigecycline is a tetracycline class antibacterial [see Microbiology ( 12.4 )] . 12.2 Pharmacodynamics Cardiac Electrophysiology No significant effect of a single intravenous dose of tigecycline for injection 50 mg or 200 mg on QTc interval was detected in a randomized, placebo-and active-controlled four-arm crossover thorough QTc study of 46 healthy subjects. 12.3 Pharmacokinetics The mean pharmacokinetic parameters of tigecycline after single and multiple intravenous doses based on pooled data from clinical pharmacology studies are summarized in Table 3 . Intravenous infusions of tigecycline were administered over approximately 30 to 60 minutes. Table 3. Mean (CV%) Pharmacokinetic Parameters of Tigecycline Single Dose Multiple Dose a 100 mg 50 mg every 12h (N=224) (N=103) a 100 mg initially, followed by 50 mg every 12 hours b 30-minute infusion c 60-minute infusion C max (mcg/mL) b 1.45 (22%) 0.87 (27%) C max (mcg/mL) c 0.90 (30%) 0.63 (15%) AUC (mcg·h/mL) 5.19 (36%) - - AUC 0-24h (mcg·h/mL) - - 4.70 (36%) C min (mcg/mL) - - 0.13 (59%) t ½ (h) 27.1 (53%) 42.4 (83%) CL (L/h) 21.8 (40%) 23.8 (33%) CL r (mL/min) 38.0 (82%) 51.0 (58%) V ss (L) 568 (43%) 639 (48%) Distribution The in vitro plasma protein binding of tigecycline ranges from approximately 71% to 89% at concentrations observed in clinical studies (0.1 to 1 mcg/mL). The steady-state volume of distribution of tigecycline averaged 500 to 700 L (7 to 9 L/kg), indicating tigecycline is extensively distributed beyond the plasma volume and into the tissues. Following the administration of tigecycline 100 mg followed by 50 mg every 12 hours to 33 healthy volunteers, the tigecycline AUC 0-12h (134 mcg·h/mL) in alveolar cells was approximately 78-fold higher than the AUC 0-12h in the serum, and the AUC 0-12h (2.28 mcg·h/mL) in epithelial lining fluid was approximately 32% higher than the AUC 0-12h in serum. The AUC 0-12h (1.61 mcg·h/mL) of tigecycline in skin blister fluid was approximately 26% lower than the AUC 0-12h in the serum of 10 healthy subjects. In a single-dose study, tigecycline 100 mg was administered to subjects prior to undergoing elective surgery or medical procedure for tissue extraction. Concentrations at 4 hours after tigecycline administration were higher in gallbladder (38-fold, n=6), lung (3.7-fold, n=5), and colon (2.3-fold, n=6), and lower in synovial fluid (0.58-fold, n=5), and bone (0.35-fold, n=6) relative to serum. The concentration of tigecycline in these tissues after multiple doses has not been studied. Elimination Metabolism Tigecycline is not extensively metabolized. In vitro studies with tigecycline using human liver microsomes, liver slices, and hepatocytes led to the formation of only trace amounts of metabolites. In healthy male volunteers receiving 14 C-tigecycline, tigecycline was the primary 14 C-labeled material recovered in urine and feces, but a glucuronide, an N-acetyl metabolite, and a tigecycline epimer (each at no more than 10% of the administered dose) were also present. Tigecycline is a substrate of P-glycoprotein (P-gp) based on an in vitro study using a cell line overexpressing P-gp. The potential contribution of P-gp-mediated transport to the in vivo disposition of tigecycline is not known. Excretion The recovery of total radioactivity in feces and urine following administration of 14 C‑tigecycline indicates that 59% of the dose is eliminated by biliary/fecal excretion, and 33% is excreted in urine. Approximately 22% of the total dose is excreted as unchanged tigecycline in urine. Overall, the primary route of elimination for tigecycline is biliary excretion of unchanged tigecycline and its metabolites. Glucuronidation and renal excretion of unchanged tigecycline are secondary routes. Specific Populations Hepatic Impairment In a study comparing 10 patients with mild hepatic impairment (Child Pugh A), 10 patients with moderate hepatic impairment (Child Pugh B), and 5 patients with severe hepatic impairment (Child Pugh C) to 23 age and weight matched healthy control subjects, the single-dose pharmacokinetic disposition of tigecycline was not altered in patients with mild hepatic impairment. However, systemic clearance of tigecycline was reduced by 25% and the half-life of tigecycline was prolonged by 23% in patients with moderate hepatic impairment (Child Pugh B). Systemic clearance of tigecycline was reduced by 55%, and the half-life of tigecycline was prolonged by 43% in patients with severe hepatic impairment (Child Pugh C). Dosage adjustment is necessary in patients with severe hepatic impairment (Child Pugh C) [see Use in Specific Populations ( 8.6 ) and Dosage and Administration ( 2.2 )] . Renal Impairment A single dose study compared 6 subjects with severe renal impairment (creatinine clearance <30 mL/min), 4 end stage renal disease (ESRD) patients receiving tigecycline 2 hours before hemodialysis, 4 ESRD patients receiving tigecycline 1 hour after hemodialysis, and 6 healthy control subjects. The pharmacokinetic profile of tigecycline was not significantly altered in any of the renally impaired patient groups, nor was tigecycline removed by hemodialysis. No dosage adjustment of tigecycline for injection is necessary in patients with renal impairment or in patients undergoing hemodialysis. Geriatric Patients No significant differences in pharmacokinetics were observed between healthy elderly subjects (n=15, age 65 to 75; n=13, age >75) and younger subjects (n=18) receiving a single 100-mg dose of tigecycline for injection. Therefore, no dosage adjustment is necessary based on age [see Use in Specific Populations ( 8.5 )] . Pediatric Patients A single-dose safety, tolerability, and pharmacokinetic study of tigecycline in pediatric patients aged 8 to 16 years who recently recovered from infections was conducted. The doses administered were 0.5, 1, or 2 mg/kg. The study showed that for children aged 12 to 16 years (n = 16) a dosage of 50 mg twice daily would likely result in exposures comparable to those observed in adults with the approved dosing regimen. Large variability observed in children aged 8 to 11 years of age (n = 8) required additional study to determine the appropriate dosage. A subsequent tigecycline dose-finding study was conducted in 8 to 11 year old patients with cIAI, cSSSI, or CABP. The doses of tigecycline studied were 0.75 mg/kg (n = 17), 1 mg/kg (n = 21), and 1.25 mg/kg (n=20). This study showed that for children aged 8 to 11 years, a 1.2 mg/kg dose would likely result in exposures comparable to those observed in adults resulting with the approved dosing regimen [see Dosage and Administration ( 2.3 )]. Gender In a pooled analysis of 38 women and 298 men participating in clinical pharmacology studies, there was no significant difference in the mean (±SD) tigecycline clearance between women (20.7±6.5 L/h) and men (22.8±8.7 L/h). Therefore, no dosage adjustment is necessary based on gender. Race In a pooled analysis of 73 Asian subjects, 53 Black subjects, 15 Hispanic subjects, 190 White subjects, and 3 subjects classified as “other” participating in clinical pharmacology studies, there was no significant difference in the mean (±SD) tigecycline clearance among the Asian subjects (28.8±8.8 L/h), Black subjects (23±7.8 L/h), Hispanic subjects (24.3±6.5 L/h), White subjects (22.1±8.9 L/h), and “other” subjects (25±4.8 L/h). Therefore, no dosage adjustment is necessary based on race. Drug Interaction Studies Digoxin Tigecycline for injection (100 mg followed by 50 mg every 12 hours) and digoxin (0.5 mg followed by 0.25 mg, orally, every 24 hours) were co-administered to healthy subjects in a drug interaction study. Tigecycline slightly decreased the C max of digoxin by 13%, but did not affect the AUC or clearance of digoxin. This small change in C max did not affect the steady-state pharmacodynamic effects of digoxin as measured by changes in ECG intervals. In addition, digoxin did not affect the pharmacokinetic profile of tigecycline. Therefore, no dosage adjustment of either drug is necessary when tigecycline for injection is administered with digoxin. Warfarin Concomitant administration of tigecycline for injection (100 mg followed by 50 mg every 12 hours) and warfarin (25 mg single-dose) to healthy subjects resulted in a decrease in clearance of R‑warfarin and S‑warfarin by 40% and 23%, an increase in C max by 38% and 43% and an increase in AUC by 68% and 29%, respectively. Tigecycline did not significantly alter the effects of warfarin on INR. In addition, warfarin did not affect the pharmacokinetic profile of tigecycline. However, prothrombin time or other suitable anticoagulation test should be monitored if tigecycline is administered with warfarin. In vitro studies in human liver microsomes indicate that tigecycline does not inhibit metabolism mediated by any of the following 6 cytochrome P450 (CYP) isoforms: 1A2, 2C8, 2C9, 2C19, 2D6, and 3A4. Therefore, tigecycline for injection is not expected to alter the metabolism of drugs metabolized by these enzymes. In addition, because tigecycline is not extensively metabolized, clearance of tigecycline is not expected to be affected by drugs that inhibit or induce the activity of these CYP450 isoforms. In vitro studies using Caco-2 cells indicate that tigecycline does not inhibit digoxin flux, suggesting that tigecycline is not a P-glycoprotein (P-gp) inhibitor. This in vitro information is consistent with the lack of effect of tigecycline on digoxin clearance noted in the in vivo drug interaction study described above. Tigecycline is a substrate of P-gp based on an in vitro study using a cell line overexpressing P-gp. The potential contribution of P-gp-mediated transport to the in vivo disposition of tigecycline is not known. Coadministration of P-gp inhibitors (e.g., ketoconazole or cyclosporine) or P-gp inducers (e.g., rifampicin) could affect the pharmacokinetics of tigecycline. 12.4 Microbiology Mechanism of Action Tigecycline inhibits protein translation in bacteria by binding to the 30S ribosomal subunit and blocking entry of amino-acyl tRNA molecules into the A site of the ribosome. This prevents incorporation of amino acid residues into elongating peptide chains. In general, tigecycline is considered bacteriostatic; however, tigecycline for injection has demonstrated bactericidal activity against isolates of S. pneumoniae and L. pneumophila . Resistance To date there has been no cross-resistance observed between tigecycline and other antibacterial drugs. Tigecycline is less affected by the two major tetracycline-resistance mechanisms, ribosomal protection and efflux. Additionally, tigecycline is not affected by resistance mechanisms such as beta-lactamases (including extended spectrum beta-lactamases), target-site modifications, macrolide efflux pumps or enzyme target changes (e.g., gyrase/topoisomerases). However, some ESBL-producing isolates may confer resistance to tigecycline via other resistance mechanisms. Tigecycline resistance in some bacteria (e.g., Acinetobacter calcoaceticus-Acinetobacter baumannii complex) is associated with multi-drug resistant (MDR) efflux pumps. Interaction with Other Antimicrobials In vitro studies have not demonstrated antagonism between tigecycline and other commonly used antibacterial drugs. Antimicrobial Activity Tigecycline has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections [see Indications and Usage ( 1 )] . Gram-positive bacteria Enterococcus faecalis (vancomycin-susceptible isolates) Staphylococcus aureus (methicillin-susceptible and -resistant isolates) Streptococcus agalactiae Streptococcus anginosus group (includes S. anginosus, S. intermedius, and S. constellatus ) Streptococcus pneumoniae (penicillin-susceptible isolates) Streptococcus pyogenes Gram-negative bacteria Citrobacter freundii Enterobacter cloacae Escherichia coli H