Pharmacokinetic-Pharmacodynamic Target Attainment Analyses as Support for Meropenem-Vaborbactam Dosing Regimens and Susceptibility Breakpoints.

Meropenem-vaborbactam is a fixed-dose beta-lactam/beta-lactamase inhibitor with potent in vitro and in vivo activity against Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacterales. Pharmacokinetic-pharmacodynamic (PK-PD) target attainment analyses were undertaken using population pharmacokinetic models, nonclinical PK-PD targets for efficacy, in vitro surveillance data, and simulation to provide support for 2 g meropenem-2 g vaborbactam every 8 h (q8h) administered as a 3-h intravenous (i.v.) infusion, and dosing regimens adjusted for patients with renal impairment. Simulated patients varying by renal function measure (estimated glomerular filtration rate [eGFR], mL/min/1.73 m2 and absolute eGFR, mL/min) and resembling the clinical trial population (complicated urinary tract infection, including acute pyelonephritis) were generated. The PK-PD targets for meropenem, the percentage of time on day 1 that free-drug plasma concentrations were above the MIC (%T>MIC), and vaborbactam, the ratio of free-drug plasma area under the concentration-time curve (AUC) on day 1 to the MIC (AUC:MIC ratio), were calculated. Percent probabilities of achieving meropenem free-drug plasma %T>MIC and vaborbactam free-drug plasma AUC:MIC ratio targets were assessed. MIC distributions for Enterobacterales, KPC-producing Enterobacterales, and Pseudomonas aeruginosa were considered as part of an algorithm to assess PK-PD target attainment. For assessments of free-drug plasma PK-PD targets associated with a 1-log10 CFU reduction from baseline, percent probabilities of PK-PD target attainment ranged from 81.3 to 100% at meropenem-vaborbactam MIC values of 4 or 8 µg/mL among simulated patients. The results of these PK-PD target attainment analyses provide support for a dosing regimen of 2 g meropenem-2 g vaborbactam q8h administered as a 3-h i.v. infusion, with dosing regimens adjusted for patients with renal impairment and a meropenem-vaborbactam susceptibility breakpoint of ≤8 µg/mL (tested with a fixed vaborbactam concentration of 8 µg/mL) for Enterobacterales and P. aeruginosa based on these dosing regimens.

Population Pharmacokinetics of Meropenem and Vaborbactam Based on Data from Noninfected Subjects and Infected Patients.

Meropenem-vaborbactam is a broad-spectrum carbapenem-beta-lactamase inhibitor combination approved in the United States and Europe to treat patients with complicated urinary tract infections and in Europe for other serious bacterial infections, including hospital-acquired and ventilator-associated pneumonia. Population pharmacokinetic (PK) models were developed to characterize the time course of meropenem and vaborbactam using pooled data from two phase 1 and two phase 3 studies. Multicompartment disposition model structures with linear elimination processes were fit to the data using NONMEM 7.2. Since both drugs are cleared primarily by the kidneys, estimated glomerular filtration rate (eGFR) was evaluated as part of the base structural models. For both agents, a two-compartment model with zero-order input and first-order elimination best described the pharmacokinetic PK data, and a sigmoidal Hill-type equation best described the relationship between renal clearance and eGFR. For meropenem, the following significant covariate relationships were identified: clearance (CL) decreased with increasing age, CL was systematically different in subjects with end-stage renal disease, and all PK parameters increased with increasing weight. For vaborbactam, the following significant covariate relationships were identified: CL increased with increasing height, volume of the central compartment (Vc) increased with increasing body surface area, and CL, Vc, and volume of the peripheral compartment were systematically different between phase 1 noninfected subjects and phase 3 infected patients. Visual predictive checks demonstrated minimal bias, supporting the robustness of the final models. These models were useful for generating individual PK exposures for pharmacokinetic-pharmacodynamic (PK-PD) analyses for efficacy and Monte Carlo simulations to evaluate PK-PD target attainment.

Effect of food and antacids on the pharmacokinetics of pirfenidone in older healthy adults.

Pirfenidone is a small, synthetic molecule under investigation for treatment of idiopathic pulmonary fibrosis. In an open-label, single-dose crossover study, the pharmacokinetics (PK) of pirfenidone were investigated with or without food and antacids in healthy adult volunteers. Concentrations of pirfenidone and its metabolites in plasma and urine were determined by liquid chromatography with tandem mass spectrometry, and candidate pharmacokinetic models were fit to plasma data using weighted, non-linear regression. The effect of food and antacids on pirfenidone exposure was evaluated by determining 'equivalence' using FDA guidelines. Adverse events were recorded by site personnel and classified by investigators on the basis of severity and relationship to study drug. Sixteen subjects yielded 64 pharmacokinetic profiles. The best fit was achieved using a five-compartment, linear model with an allowance for direct conversion to the primary metabolite (5-carboxy-pirfenidone). Coadministration with food decreased the rate and, to a lesser degree, the extent of pirfenidone absorption of absorption. Analysis of adverse events revealed a correlation between pirfenidone C(max) and the risk of gastrointestinal (GI) adverse events, suggesting that food may reduce the risk of certain adverse events associated with pirfenidone. Administration of pirfenidone with food has a modest effect on overall exposure but results in lower peak concentrations, which may improve tolerability.

Bartonella infections: diverse and elusive.

Children with young cats, HIV-infected patients with low CD4 counts, and lice-infested homeless people are among those with an increased risk. Clinical presentation varies with the infecting Bartonella species and the host. Treatment for cat-scratch disease is supportive; macrolide therapy is an appropriate choice for other Bartonella infections.

Restriction enzyme and Southern hybridization analyses of Pseudomonas aeruginosa strains from patients with cystic fibrosis.

Conventional typing schemes for Pseudomonas aeruginosa may not discriminate strains. P. aeruginosa isolates from patients with cystic fibrosis were examined by restriction enzyme analysis and Southern hybridization. There was marked diversity of restriction enzyme analysis patterns among P. aeruginosa DNAs from cystic fibrosis isolates; however, sequential isolates obtained from individual patients showed very little variation over an 8-year period. DNA fragments from the alginate biosynthesis gene complex, the exotoxin A gene, and the elastase gene of P. aeruginosa were used in Southern hybridization analysis. The patterns of hybridization to the elastase and algD gene probes were highly conserved in all isolates, therefore, these DNA fragments are not useful in discriminating strains, in contrast to the exotoxin A gene probe.

FP2 plasmid curing in Pseudomonas aeruginosa.

A procedure for the elimination of the IncP-8 plasmid FP2 from Pseudomonas aeruginosa strain 1 was developed. The procedure consists of freezing cells, competent for transformation, in 15% glycerol at -70 degrees C for at least 48 h and screening survivors for loss of mercuric chloride resistance. Curing frequencies of 0.5% were achieved only in host cells carrying a dht mutation (unable to convert thymine to dihydrothymine).

Isolation of multiple mutants of Pseudomonas aeruginosa capable of efficient thymine salvage.

Mutants of Pseudomonas aeruginosa strain 1 which incorporate relatively large amounts of thymine into their DNA were isolated. Three steps were required to produce this phenotype. First, strains constitutive for thymine uptake and catabolism were isolated, followed by selection for mutants which could not catabolize thymine. The double mutant was then used to isolate a strain exhibiting greater sensitivity to the thymine analog 5-bromouracil. Efficient DNA-specific pulse labelling with isotopic thymine was successfully carried out with this strain.

Transformation and transfection of Pseudomonas aeruginosa: effects of metal ions.

The ability of different metal ions to promote transformation of Pseudomonas aeruginosa by deoxyribonucleic acid of the plasmid RP1 was examined. CaCl2, MgCl2, and MnCl2 were found to promote such transformation, although at different frequencies and with the optimum response at different concentrations. Only MgCl2 promoted transfection of P. aeruginosa by the linear deoxyribonucleic acid of phage F116. CaCl2 was demonstrated to allow adsorption and entry into the cell of F116 deoxyribonucleic acid such that it became resistant to exogenous deoxyribonuclease, but phage production occurred only when MgCl2 was provided. Inactivation of linear phage deoxyribonucleic acid taken up in the absence of MgCl2 was observed. The transfection frequencies at various concentrations of MgCl2 were compared, and the optimum response occurred at the concentration which promoted the highest frequency of transformation by RP1 deoxyribonucleic acid.

Exonuclease activity from Pseudomonas aeruginosa which is missing in phenotypically restrictionless mutants.

A phenotypically restrictionless strain of Pseudomonas aeruginosa was found to lack a deoxyribonuclease specific for linear duplex DNA. The purified enzyme had an optimum pH of 8.5, required MgCl2 (10 mM) for maximum activity, and did not require ATP. Neither the degradation of heat-denatured DNA nor the degradation of bacteriophage F116 DNA was detected. The genome of bacteriophage F116 was shown to possess single-stranded terminal regions, which account for the resistance to degradation and for the ability of the phage to transfect restriction-proficient strains.

Thymine metabolism in Pseudomonas aeruginosa strain 1: the presence of a salvage pathway.

Exogenous thymine was found to be taken up very slowly by Pseudomonas aeruginosa in comparison to other pyrimidines, and most of it was catabolized by the cell. The existence of a functional, although inefficient, thymine salvage pathway was demonstrated and this pathway operated more effectively when de novo thymidine nucleotide biosynthesis was inhibited by trimethoprim or methotrexate. The mechanism of thymine salvage by P. aeruginosa appears to be different from that of Escherichia coli and Pseudomonas acidovorans as thymidine was not incorporated into the DNA. Like P. acidovorans, P. aeruginosa lacked thymidine phosphorylase activity. Unsuccessful attempts were made to isolate thymine auxotrophs.

Bartonella henselae and Bartonella quintana adherence to and entry into cultured human epithelial cells.

Bartonella henselae expresses pili phenotypically similar to type 4 pili. B. henselae pilus expression undergoes phase variation with multiple passages. Low-passage-number, piliated B. henselae adhered to and invaded HEp-2 cells to a greater extent than did multiply passaged B. henselae with reduced pilus expression. Pili may be a pathogenic determinant for Bartonella species.

Lemierre's syndrome.

Lemierre's syndrome is an acute medical condition characterized by anaerobic oropharyngeal infection leading to septic thrombophlebitis of the internal jugular vein. The illness is often complicated by septic pulmonary emboli and distant metastatic infections. Treatment consists of surgical drainage of purulent collections and long-term intravenous antibiotic therapy. Although Lemierre's syndrome is rare, it is potentially fatal and remains an important entity for clinicians to recognize and treat appropriately.

The agent of bacillary angiomatosis. An approach to the identification of uncultured pathogens.

BACKGROUND: Bacillary angiomatosis is an infectious disease causing proliferation of small blood vessels in the skin and visceral organs of patients with human immunodeficiency virus infection and other immunocompromised hosts. The agent is often visualized in tissue sections of lesions with Warthin-Starry staining, but the bacillus has not been successfully cultured or identified. This bacillus may also cause cat scratch disease. METHODS: In attempting to identify this organism, we used the polymerase chain reaction. We used oligonucleotide primers complementary to the 16S ribosomal RNA genes of eubacteria to amplify 16S ribosomal gene fragments directly from tissue samples of bacillary angiomatosis. The DNA sequence of these fragments was determined and analyzed for phylogenetic relatedness to other known organisms. Normal tissues were studied in parallel. RESULTS: Tissue from three unrelated patients with bacillary angiomatosis yielded a unique 16S gene sequence. A sequence obtained from a fourth patient with bacillary angiomatosis differed from the sequence found in the other three patients at only 4 of 241 base positions. No related 16S gene fragment was detected in the normal tissues. These 16S sequences associated with bacillary angiomatosis belong to a previously uncharacterized microorganism, most closely related to Rochalimaea quintana. CONCLUSIONS: The cause of bacillary angiomatosis is a previously uncharacterized rickettsia-like organism, closely related to R. quintana. This method for the identification of an uncultured pathogen may be applicable to other infectious diseases of unknown cause.