Stability studies with tigecycline in bacterial growth medium and impact of stabilizing agents

Pharmacokinetic/pharmacodynamic evaluation of tigecycline dosing in a hollow fiber infection model against clinical bla-KPC producing Klebsiella Pneumoniae isolates

The FDA announced a boxed warning for tigecycline due to progression of infections caused by Gram-negative bacteria and increased risk of mortality during treatment. Plasma exposure of tigecycline might not prevent bacteraemia in these cases from the focuses. Hence, we evaluated intensified dosing regimens and breakpoints that might suppress bloodstream infections, caused by progression of infection by e.g., Gram-negatives. A pharmacometric model was built from tigecycline concentrations (100-600 mg daily doses) against clinical Klebsiella pneumoniae isolates (MIC 0.125-0.5 mg/L). Regrowth occurred at clinically used doses and stasis was only achieved with 100 mg q8h for the strain with the lowest studied MIC of 0.125 mg/L. Stasis at 24 h was related to fAUC/MIC of 38.5. Our study indicates that even intensified dosing regimens might prevent bloodstream infections only for MIC values ≤0.125 mg/L for tigecycline. This indicates an overly optimistic breakpoint of 1 mg/L for Enterobacterales, which are deemed to respond to the tigecycline high dose regimen (EUCAST Guidance Document on Tigecycline Dosing 2022).

Omadacycline, Eravacycline, and Tigecycline Express Anti-Mycobacterium abscessus Activity In Vitro

Mycobacterium abscessus infections are increasing worldwide necessitating the development of new antibiotics and treatment regimens. The utility of third-generation tetracycline antibiotics was reestablished; their anti-M. abscessus activity needs further study. The activities of omadacycline (OMC), eravacycline (ERC), tigecycline (TGC), and sarecycline (SAC) were tested against two reference strains and 193 clinical M. abscessus isolates at different temperatures (30°C and 37°C). The minimum bactericidal concentrations (MBCs) of the four drugs were determined to distinguish between their bactericidal and bacteriostatic activities. The MICs of OMC, ERC, and TGC for the reference strains and clinical isolates were summarized and compared. OMC, ERC, and TGC exhibited a high level of bacteriostatic activity against M. abscessus. The MICs of OMC and ERC for M. abscess remained stable, while the MICs of TGC for the isolates/strains increased with increasing temperature. Notably, the MICs of OMC for M. abscessus isolates obtained in the United States are lower than for those obtained in China. IMPORTANCE The antimicrobial activities of four third-generation tetracycline-class drugs, omadacycline (OMC), eravacycline (ERC), tigecycline (TGC), and sarecycline (SAC), were determined for 193 M. abscessus isolates. The activities of the four drugs at two different temperatures (30°C and 37°C) were also tested. OMC, ERC, and TGC exhibited significant activity against M. abscessus. The anti-M. abscessus activity of TGC increased when the temperature was increased from 30°C to 37°C; the activities of OMC and ERC, on the other hand, remained the same. We found that in vitro MICs of OMC against Chinese and American isolates were distinct. Evaluations in in vivo models of M. abscessus disease or in the clinical setting will provide more accurate insight into potency of OMC against distinct isolates.

Exploring kinetics, removal mechanism and possible transformation products of tigecycline by Chlorella pyrenoidosa

The accumulation of antibiotics in wastewater leads to broad antibiotic resistance, threating human health. Microalgae have been receiving attention due to their ability to remove antibiotics from wastewater. Tigecycline (TGC) is a broad-spectrum glycylcycline antibiotic. It has not been investigated for removal by microalgae. The removal kinetics of TGC by Chlorella pyrenoidosa were evaluated under different initial dry cell densities, TGC concentrations, temperatures and light intensity conditions. Approximately 90% of TGC could be removed when the TGC concentration was 10 mg∙L^-1 and the initial dry cell density was more than 0.2 g∙L^-1. A low value of TGC per g dry cell weight ratio led to a high removal efficiency of TGC. The initial dry cell density of microalgae was also critical for the removal of TGC. A high initial dry cell density is better than a low initial dry cell density to remove TGC when the ratio of the TGC concentration to dry cell weight are the same at the beginning of the cultivation. The removal mechanisms were investigated. Photolysis was a slow process that did not lead to removal at the beginning. Adsorption, hydrolysis, photolysis and biodegradation by microalgae were the main contributors to the removal of TGC. TGC was easily hydrolyzed under high -temperature conditions. Three transformation products of TGC by microalgae were identified. The stability of TGC was evaluated in water and salt solutions of citric acid, K₂HPO₄·3H₂O and ferric ammonium citrate. TGC was stable in ultrapure water and citric acid solution. TGC was hydrolyzed in K₂HPO₄·3H₂O and ferric ammonium citrate solutions.