Pharmacokinetics and safety of a new parenteral carbapenem antibiotic, biapenem (L-627), in elderly subjects

Pharmacokinetics of Antibacterial Agents in the Elderly: The Body of Evidence

Infections are important factors contributing to the morbidity and mortality among elderly patients. High rates of consumption of antimicrobial agents by the elderly may result in increased risk of toxic reactions, deteriorating functions of various organs and systems and leading to the prolongation of hospital stay, admission to the intensive care unit, disability, and lethal outcome. Both safety and efficacy of antibiotics are determined by the values of their plasma concentrations, widely affected by physiologic and pathologic age-related changes specific for the elderly population. Drug absorption, distribution, metabolism, and excretion are altered in different extents depending on functional and morphological changes in the cardiovascular system, gastrointestinal tract, liver, and kidneys. Water and fat content, skeletal muscle mass, nutritional status, use of concomitant drugs are other determinants of pharmacokinetics changes observed in the elderly. The choice of a proper dosing regimen is essential to provide effective and safe antibiotic therapy in terms of attainment of certain pharmacodynamic targets. The objective of this review is to perform a structure of evidence on the age-related changes contributing to the alteration of pharmacokinetic parameters in the elderly.

Pharmacokinetics and Target Attainment of ß-lactam Antibiotics in Older People: A Systematic Review of Current Literature

BACKGROUND AND OBJECTIVE

(Patho)physiological changes in older people may influence the pharmacokinetics (PK), and consequently the target attainment, of ß-lactam antibiotics using standard dosing regimens. This systematic review compiles the current knowledge on the PK and target attainment of ß-lactam antibiotics in older people, with the aim to identify priorities for dose optimization in this patient population.

METHODS

A systematic literature search of the PubMed and EMBASE databases was conducted. Relevant articles published prior to 1 December 2021 were identified as eligible when they included data on the PK of ß-lactam antibiotics in adults ≥ 65 years of age. Extracted information included reported PK parameters (volume of distribution, clearance [CL], elimination rate constant, intercompartmental CL, elimination half-life, area under the concentration-time curve, maximum and trough concentration), covariates on PK parameters, target attainment rate, and dosing recommendations.

RESULTS

Ninety-one relevant articles were included in this review. Four main ß-lactam subclasses were represented: 59.3% on cephalosporins + cephamycins, 25.3% on penicillins, 15.4% on carbapenems, and 3.3% on monobactams; 65.9% of articles involved intravenous administration, 16.5% mixed administration routes, 12.1% oral administration, and 5.5% intramuscular administration. The majority of studies had a small sample size, often did not include detailed information on the study population and methods, and were fairly old. CL was, on average, decreased, while elimination half-life was prolonged in aged subjects compared with young subjects. Volume of distribution was generally similar between age groups. Most studies identified renal function as the most important contributor to altered drug CL. In only 30.8% of the articles, target attainment was studied, and in 35.7% of these articles, target attainment was found to be suboptimal. Dosing recommendations were incorporated in 87.9% of articles.

CONCLUSION

Studies frequently fail to provide an evidence-based dosing recommendation for this diverse patient population. Model-based PK studies that address both physiological and disease-related changes are urgently needed. This review identified gaps of knowledge to set priorities for further research.

Role of organic anion transporter 3 in the renal excretion of biapenem and potential drug-drug interactions

Biapenem is a carbapenem antibiotic. It is excreted predominantly through the kidney as unchanged forms. However, the molecular mechanism of renal excretion of biapenem and potential drug-drug interactions (DDIs) were still unknown. In the present study, the role of organic anion transporters (OAT) 1/3 and organic cation transporters (OCT) 2 in the renal excretion of biapenem, and the potential DDIs between biapenem and six clinical commonly prescribed antibiotics and antiviral drugs that acted as substrates or inhibitors of OAT3 were evaluated in vitro. Further, the effect of probenecid on the pharmacokinetics of biapenem was explored in the rats. We observed that biapenem could not inhibit the transport activities of OAT1 or OCT2, while mildly inhibited OAT3 (IC₅₀ >500 μM). Among the tested antibiotics and antiviral drugs, the relatively high DDI index values (maximal unbound plasma concentration over IC₅₀, I_max,u/IC₅₀) were found for piperacillin, linezolid and benzylpenicillin, which were 2.84, 1.7 and 0.62, respectively. Although probenecid had the highest DDI index (27.1) in vitro, no significant impact of it on the pharmacokinetics of biapenem was observed in the rats. Our results indicated that biapenem was primarily eliminated by the glomerular filtration, while OAT3-mediated renal tubular secretion was a minor route. Biapenem is not a clinically relevant substrate or inhibitor because of its low affinity to OAT3. According to current results, it would be safe to use biapenem with other antibiotics and antiviral drugs that acted as substrates or inhibitors of OAT3.

Efficacy and safety of biapenem against lower respiratory tract infections in elderly Chinese patients and optimal dosing regimen based on pharmacokinetic/pharmacodynamic analysis

The present study evaluated the efficacy and safety of biapenem in elderly Chinese patients with lower respiratory tract infections (LRTIs) and proposed optimal dosage regimen on the basis of pharmacokinetic/pharmacodynamic (PK/PD) analysis. The clinical efficacy, bacterial eradication and comprehensive therapeutic effect rates of biapenem were 70.3 (78/111), 68.5 (37/54) and 61.1% (33/54), respectively. Drug-related adverse reactions were seen in 12.6% of patients (14/111). The total protein level, Acute Physiology and Chronic Health Evaluation (APACHE) II score, %fT>MIC, fAUC24/MIC and fCmax/MIC values of patients had significant impacts (P < 0.05) on clinical and bacteriological efficacy. However, logistic regression analysis showed that only %fT>MIC independently influenced comprehensive therapeutic effect (P < 0.01, odds ratio = 1.064). The cut-off value for predicting comprehensive therapeutic effect using %fT>MIC was 75.0%; the sensitivity and specificity were 87.9 and 85.7%, respectively. Monte Carlo simulations revealed that the usual dosage regimen (300 mg every 12 hours, 0.5 hour infusion) was considered to be insufficient to obtain satisfactory therapeutic outcomes against low susceptible pathogens for elderly Chinese patients with LRTIs (CLcr = 70 ml/min).

Clinical effect of biapenem on nursing and healthcare-associated pneumonia (NHCAP)

The clinical effect of Biapenem (BIPM) on Nursing and Healthcare-associated pneumonia (NHCAP) was evaluated. One hundred and three NHCAP patients (Group B: 52 patients, Group C: 51 patients) to whom BIPM was administered were included in this study. Clinical effect, bacteriological effect, and adverse events were examined. Results revealed efficacy in 45 of 52 patients (efficacy rate: 86.5%) of NHCAP Group B, and 43 of 51 patients (efficacy rate: 84.3%) of NHCAP Group C, 88 of 103 patients (efficacy rate: 85.4%) as a whole. As for bacteriological effect, 10 (76.9%) of 13 Pseudomonas aeruginosa strains, 9 (90.0%) of 10 Klebsiella pneumoniae strains, 7 (87.5%) of 8 methicillin-sensitive Staphlococcus aureus strains, and 7 (100%) of 7 Streptococcus pneumonia strains were eradicated. As a whole, 38 (80.9%) of 47 strains were eradicated. Adverse events included drug fever and drug eruption in one patient each, and abnormal laboratory findings, including mild hepatic dysfunction in 18 patients and mild renal dysfunction in 5 patients. Based on the above, it was concluded that BIPM shows excellent clinical effect on NHCAP with fewer adverse events.

Structure of apo- and monometalated forms of NDM-1--a highly potent carbapenem-hydrolyzing metallo-β-lactamase

The New Delhi Metallo-β-lactamase (NDM-1) gene makes multiple pathogenic microorganisms resistant to all known β-lactam antibiotics. The rapid emergence of NDM-1 has been linked to mobile plasmids that move between different strains resulting in world-wide dissemination. Biochemical studies revealed that NDM-1 is capable of efficiently hydrolyzing a wide range of β-lactams, including many carbapenems considered as "last resort" antibiotics. The crystal structures of metal-free apo- and monozinc forms of NDM-1 presented here revealed an enlarged and flexible active site of class B1 metallo-β-lactamase. This site is capable of accommodating many β-lactam substrates by having many of the catalytic residues on flexible loops, which explains the observed extended spectrum activity of this zinc dependent β-lactamase. Indeed, five loops contribute "keg" residues in the active site including side chains involved in metal binding. Loop 1 in particular, shows conformational flexibility, apparently related to the acceptance and positioning of substrates for cleavage by a zinc-activated water molecule.

Clinical efficacy of carbapenems on hospital-acquired pneumonia in accordance with the Japanese Respiratory Society Guidelines for management of HAP

Hospital-acquired pneumonia (HAP) is the second most common cause of hospital-acquired infection and is the leading cause of death. In 2002, the Japanese Respiratory Society (JRS) published guidelines for the diagnosis and treatment of HAP (JRS GL 2002). In these guidelines, treatment with carbapenems is recommended for all disease types of HAP, excluding cases of mild or moderate pneumonia with no risk factors, and cases with early-onset ventilation-acquired pneumonia. To evaluate the efficacy of carbapenems on HAP in accordance with JRS GL 2002, we conducted a prospective study of HAP patients treated with carbapenems based on JRS GL 2002. The results of this study were also analyzed based on the revised guidelines published in June 2008 (JRS GL 2008), and the validity of the new guidelines was examined. Of the 33 subjects, 19 were judged as responders to the treatment, corresponding to a response rate of 57.6%. There were 3 deaths, corresponding to a mortality rate of 9.1%. The efficacy of carbapenems for the treatment of HAP based on JRS GL 2002 was confirmed. The severity rating system in JRS GL 2002 has a tendency to overestimate the severity of the cases and may lead to overtreatment in some cases. On the other hand, the severity rating system by JRS GL 2008 seemed to be more accurate and closely correlated with the efficacy of the treatment. It is suggested that JRS GL 2008 is more useful in clinical practice for accurately judging the severity of the disease and initiating appropriate subsequent antibiotic therapy.

Pharmacokinetic modeling and dosage adaptation of biapenem in Japanese patients during continuous venovenous hemodiafiltration

The present study examined the pharmacokinetics of biapenem during continuous venovenous hemodiafiltration (CVVHDF) and assessed the pharmacodynamic exposure, based on a pharmacokinetic model, to consider biapenem dosage adaptation in CVVHDF. Biapenem (300 mg) was administered by 2-h infusion to seven critically ill patients receiving CVVHDF. The flow rates were 60 ml/min for blood, 800 ml/h for filtrate, and 600 ml/h for dialysate. The drug concentrations in plasma and filtrate-dialysate were determined by high-performance liquid chromatography and analyzed pharmacokinetically. The sieving coefficient was 0.92 +/- 0.06 (mean +/- SD). The simulation curves, using a multicompartment model, were well fitted to the measurements in plasma and filtrate-dialysate. The clearance by CVVHDF and the clearance by non-CVVHDF routes were 1.29 +/- 0.08 and 6.14 +/- 1.89 l/h, respectively. The multicompartment model was used to assess the pharmacodynamic exposure (time above the minimum inhibitory concentration of 4 microg/ml) in plasma. When the total daily dose was 600 mg, the duration of time was greater at 300 mg every 12 h than at 600 mg every 24 h. The minimum dosages needed to achieve more than 30% of the dosing interval at filtrate-dialysate flow rates of 1.4, 2.8, and 5.6 l/h were 300 mg every 12 h, 600 mg every 12 h, and 600 mg every 12 h, respectively. These results suggested that low doses or increased dosing intervals should be avoided in patients receiving this renal replacement technique. Information on pharmacodynamic exposure obtained from this model may help us to determine the appropriate biapenem dosage for CVVHDF. Moreover, our pharmacokinetic model may be useful for further pharmacokinetic studies of biapenem.

Biapenem

Biapenem is a new parenteral carbapenem antibacterial agent with a broad spectrum of in vitro antibacterial activity encompassing many Gram-negative and Gram-positive aerobic and anaerobic bacteria, including species producing beta-lactamases. Biapenem is more stable than imipenem, meropenem and panipenem to hydrolysis by human renal dihydropeptidase-I (DHP-I), and therefore does not require the coadministration of a DHP-I inhibitor. After intravenous administration, biapenem is widely distributed and penetrates well into various tissues (e.g. lung tissue) and body fluids (e.g. sputum, pleural effusion, abdominal cavity fluid). In randomised, nonblind or double-blind clinical trials, biapenem showed good clinical and bacteriological efficacy (similar to that of imipenem/ cilastatin) in the treatment of adult patients with intra-abdominal infections, lower respiratory infections or complicated urinary tract infections. Biapenem is generally well tolerated. The most common adverse events in clinical trials were skin eruptions/rashes, nausea and diarrhoea.

Comparative pharmacokinetics of the carbapenems: clinical implications

During the last few decades, several carbapenems have been developed. The major characteristic of the newer drugs, such as MK-826, is a prolonged half-life. Alternatively, some carbapenems have been developed that can be given orally, such as CS-834 and L-084. Although imipenem and panipenem have to be administered with a co-drug to prevent degradation by the enzyme dehydropeptidase-1 and reduce nephrotoxicity, the newer drugs such as meropenem, biapenem and lenapenem are relatively stable towards that enzyme. Structural modifications have, besides changes in pharmacology, also led to varying antimicrobial properties. For instance, meropenem is relatively more active against Gram-negative organisms than most other carbapenems, but is slightly less active against Gram-positive organisms. Except for half-life and bioavailability, the pharmacokinetic properties of the carbapenems are relatively similar. Distribution is mainly in extracellular body-water, as observed both from the volumes of distribution and from blister studies. Some carbapenems have a better penetration in cerebrospinal fluid than others. In patients with renal dysfunction, doses have to be adjusted, and special care must be taken with imipenem/cilastatin and panipenem/betamipron to prevent accumulation of the co-drugs, as the pharmacokinetic properties of the co-drugs differ from those of the drugs themselves. However, toxicity of the co-drugs has not been shown. The carbapenems differ in proconvulsive activity. Imipenem shows relatively the highest proconvulsive activity, especially at higher concentrations. Pharmacodynamic studies have shown that the major surrogate parameter for antimicrobial efficacy is the percentage of time of the dosage interval above the minimum inhibitory concentration (MIC). The minimum percentage percentage of time above the MIC (TaM) needed for optimal effect is known in animals (30 to 50%), but not in humans. It is probably less than 100%, but may be higher than 50%. Dosage regimens currently in use result in a TaM of about 50% at 4 mg/L, which is the current 'susceptible' breakpoint determined by the National Committee for Clinical Laboratory Standards (NCCLS) for most micro-organisms. Dosage regimens in patients with reduced renal clearance should be based on the TaM. The increased half-life of the newer carbapenems will probably lead to less frequent administration, although continuous infusion may still be the optimal mode of administration for these drugs. The availability of oral carbapenems will have a profound effect on the use of carbapenems in the community.

What's new in the antibiotic pipeline

Many advances have recently been made in the development of chemotherapeutic agents for bacterial infections. As a consequence of problematic antimicrobial-resistant bacteria, research is now directed towards narrow-spectrum agents rather than broad-spectrum agents. Further, orally active agents have always been desirable, but today's cost-saving environment, in line with a desire to minimize treatment costs, values reduced administration costs and keeping patients out of the hospital. There has been a recent increase in research into orally active antibacterial agents, such as carbapenems and cephalosporins, and non-glycopeptide natural products.