Pharmacotherapeutic Group: Antibacterials for systemic use, tetracyclines. ATC Code: J01AA12.
Pharmacology: Pharmacodynamics: Mechanism of Action: Tigecycline, a glycylcycline antibiotic, 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. At 4 times the minimum inhibitory concentration (MIC), a 2-log reduction in colony counts was observed with tigecycline against Enterococcus spp., Staphylococcus aureus, and Escherichia coli.
Pharmacokinetics: Absorption: Tigecycline is administered intravenously and therefore has 100 % bioavailability.
Distribution: The in vitro plasma protein binding of tigecycline ranges from approximately 71 % to 89 % at concentrations observed in clinical studies (0.1 to 1.0 mcg/ml). Animal and human pharmacokinetic studies have demonstrated that tigecycline readily distributes to tissues.
In rats receiving single or multiple doses of 14C-tigecycline, radioactivity was well distributed to most tissues, with the highest overall exposure observed in bone marrow, salivary glands, thyroid gland, spleen, and kidney. In humans, the steady-state volume of distribution of tigecycline averaged 500 to 700 L (7 to 9 L/kg), indicating that tigecycline is extensively distributed beyond the plasma volume and concentrates into tissues.
No data are available on whether tigecycline can cross the blood-brain barrier in humans.
In clinical pharmacology studies using the therapeutic dosage regimen of 100 mg followed by 50 mg q12h, serum tigecycline steady-state Cmax was 866±233 ng/ml for 30-minute infusions and 634±97 ng/ml for 60-minute infusions. The steady-state AUC0-12h was 2349±850 ng•h/ml.
Biotransformation: On average, it is estimated that less than 20 % of tigecycline is metabolised before excretion. In healthy male volunteers, following the administration of 14C-tigecycline, unchanged tigecycline was the primary 14C-labelled material recovered in urine and faeces, but a glucuronide, an N-acetyl metabolite and a tigecycline epimer were also present.
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 by competitive inhibition. In addition, tigecycline did not show NADPH-dependency in the inhibition of CYP2C9, CYP2C19, CYP2D6 and CYP3A, suggesting the absence of mechanism-based inhibition of these CYP enzymes.
Elimination: The recovery of the total radioactivity in faeces and urine following administration of 14C-tigecycline indicates that 59 % of the dose is eliminated by biliary/faecal excretion, and 33 % is excreted in urine. Overall, the primary route of elimination for tigecycline is biliary excretion of unchanged tigecycline. Glucuronidation and renal excretion of unchanged tigecycline are secondary routes.
The total clearance of tigecycline is 24 L/h after intravenous infusion. Renal clearance is approximately 13 % of total clearance. Tigecycline shows a polyexponential elimination from serum with a mean terminal elimination half-life after multiple doses of 42 hours although high interindividual variability exists.
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. Co-administration of P-gp inhibitors (e.g., ketoconazole or cyclosporine) or P-gp inducers (e.g., rifampicin) could affect the pharmacokinetics of tigecycline.
Special populations: Hepatic impairment: 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 55 % and the half-life of tigecycline was prolonged by 23 % and 43 % in patients with moderate or severe hepatic impairment (Child Pugh B and C), respectively.
Renal impairment: The single dose pharmacokinetic disposition of tigecycline was not altered in patients with renal insufficiency (creatinine clearance < 30 ml/min, n=6). In severe renal impairment, AUC was 30 % higher than in subjects with normal renal function.
Elderly: No overall differences in pharmacokinetics were observed between healthy elderly subjects and younger subjects.
Paediatric population: Tigecycline pharmacokinetics was investigated in two studies. The first study enrolled children aged 8-16 years (n=24) who received single doses of tigecycline (0.5, 1, or 2 mg/kg, up to a maximum dose of 50 mg, 100 mg, and 150 mg, respectively) administered intravenously over 30 minutes. The second study was performed in children aged 8 to 11 years who received multiple doses of tigecycline (0.75, 1, or 1.25 mg/kg up to a maximum dose of 50 mg) every 12 hours administered intravenously over 30 minutes. No loading dose was administered in these studies. Pharmacokinetic parameters are summarised in the table as follows. (See Table 1.)
Click on icon to see table/diagram/image
The target AUC0-12h in adults after the recommended dose of 100 mg loading and 50 mg every 12 hours, was approximately 2500 ng•h/mL.
Population PK analysis of both studies identified body weight as a covariate of tigecycline clearance in children aged 8 years and older. A dosing regimen of 1.2 mg/kg of tigecycline every 12 hours (to a maximum dose of 50 mg every 12 hours) for children aged 8 to <12 years and of 50 mg every 12 hours for adolescents aged 12 to <18 years would likely result in exposures comparable to those observed in adults treated with the approved dosing regimen.
Higher Cmax values than in adult patients were observed in several children in these studies. As a consequence, care should be paid to the rate of infusion of tigecycline in children and adolescents.
Gender: There were no clinically relevant differences in the clearance of tigecycline between men and women. AUC was estimated to be 20 % higher in females than in males.
Race: There were no differences in the clearance of tigecycline based on race.
Weight: Clearance, weight-normalised clearance, and AUC were not appreciably different among patients with different body weights, including those weighing≥ 125 kg. AUC was 24 % lower in patients weighing ≥ 125 kg. No data is available for patients weighing 140 kg and more.
Microbiology: Mechanism of resistance: Tigecycline is able to overcome the two major tetracycline resistance mechanisms, ribosomal protection and efflux. Cross-resistance between tigecycline and minocycline-resistant isolates among the Enterobacteriaceae due to multi-drug resistance (MDR) efflux pumps has been shown. There is no target-based cross-resistance between tigecycline and most classes of antibiotics.
Tigecycline is vulnerable to chromosomally-encoded multi-drug efflux pumps of Proteeae and Pseudomonas aeruginosa. Pathogens of the family Proteeae (Proteus spp., Providencia spp., and Morganella spp.) are generally less susceptible to tigecycline than other members of the Enterobacteriaceae. Decreased susceptibility in both groups has been attributed to the overexpression of the non-specific AcrAB multi-drug efflux pump. Decreased susceptibility in Acinetobacter baumannii has been attributed to the overexpression of the AdeABC efflux pump.
Breakpoints: Minimum inhibitory concentration (MIC) breakpoints established by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) are as follows: Staphylococcus spp. S ≤ 0.5 mg/L and R > 0.5 mg/L.
Streptococcus spp. other than S. pneumoniae S ≤ 0.25 mg/L and R > 0.5 mg/L.
Enterococcus spp. S ≤ 0.25 mg/L and R > 0.5 mg/L.
Enterobacteriaceae S ≤ 1(^) mg/Land R > 2 mg/L
(^)Tigecycline has decreased in vitro activity against Proteus, Providencia, and Morganella spp.
For anaerobic bacteria there is clinical evidence of efficacy in polymicrobial intra-abdominal infections, but no correlation between MIC values, PK/PD data and clinical outcome. Therefore, no breakpoint for susceptibility is given. It should be noted that the MIC distributions for organisms of the genera Bacteroides and Clostridium are wide and may include values in excess of 2 mg/L tigecycline.
There is limited evidence of the clinical efficacy of tigecycline against enterococci. However, polymicrobial intra-abdominal infections have shown to respond to treatment with tigecycline in clinical trials.
Susceptibility: The prevalence of acquired resistance may vary geographically and with time for selected species, and local information on resistance is desirable, particularly when treating severe infections. As necessary, expert advice should be sought when the local prevalence of resistance is such that the utility of the agent in at least some types of infections is questionable. (See Table 2.)
Click on icon to see table/diagram/image
Cardiac Electrophysiology: No significant effect of a single intravenous dose of tigecycline 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.
Paediatric population: In an open-label, ascending multiple-dose study, 39 children aged 8 to 11 years with cIAI or cSSTI were administered tigecycline (0.75, 1, or 1.25 mg/kg). All patients received IV tigecycline for a minimum of 3 consecutive days to a maximum of 14 consecutive days, with the option to be switched to an oral antibiotic on or after day 4.
Clinical cure was assessed between 10 and 21 days after the administration of the last dose of treatment. The summary of clinical response in the modified intent-to-treat (mITT) population results is shown in the following table. (See Table 3.)
Click on icon to see table/diagram/image
Efficacy data previously shown should be viewed with caution as concomitant antibiotics were allowed in this study. In addition, the small number of patients should also be taken into consideration.