Applying Cefepime Population Pharmacokinetics to Critically Ill Patients Receiving Continuous Renal Replacement Therapy.

Patients admitted to the intensive care unit (ICU) may need continuous renal replacement therapy (CRRT) due to acute kidney injury or worsening of underlying chronic kidney disease. This will affect their antimicrobial exposure and may have a significant impact on the treatment. We aim to develop a cefepime pharmacokinetic (PK) model in CRRT ICU patients and generate the posterior predictions for a group and assess their therapy outcomes. Adult patients, who were admitted to the ICU, received cefepime, and had its concentration measured while on CRRT were included from three different data sets. In two data sets, samples were collected from the predialyzer, postdialyzer ports, and effluent fluid at different times within the same dosing interval. The third data set had only cefepime plasma concentration measured as part of clinical service. Patients' demographics, cefepime regimens and concentration, CRRT parameters, and therapy outcomes were recorded. NPAG was used for population PK and posterior predictions. A total of 125 patients were included. Cefepime was described by a five-compartment model, and the CRRT flow rates described the rates of cefepime transfer between compartments. The posterior predictions were generated for the third data set and the median (range) fT>MIC was 100% (27%-100%) and fT>4×MIC was 64% (0%-100%). The mortality rate was 53%. There was no difference in target attainment in terms of clinical cure and 30-day mortality. This model can be used as a precision dosing tool in CRRT patients. Future studies may address other PK/PD targets in a larger population.

Cefepime Population Pharmacokinetics and Target Attainment in Critically Ill Patients on Continuous Renal Replacement Therapy.

Sepsis causes half of acute kidney injuries in the intensive care unit (ICU). ICU patients may need continuous renal replacement therapy (CRRT), which will affect their antimicrobial exposure. We aimed to build a cefepime population pharmacokinetic (PK) model in CRRT ICU patients and perform simulations to assess target attainment. Patients who were ≥18 years old, were admitted to the ICU, and received cefepime 2 g every 8 h as a 4-h infusion while on CRRT were enrolled prospectively. Samples were collected from the predialyzer ports, postdialyzer ports, and effluent fluid at 1, 2, 3, 4, and 8 h after the first dose and at steady state. Age, sex, weight, urine output, and CRRT parameters were recorded. Pmetrics was used for population PK and simulations. The target exposure was 100% of the dosing interval during which the free beta-lactam concentration is above the MIC (fT>MIC). Ten patients were included; their mean age was 53 years, and mean weight was 119 kg. Seventy percent were males. Cefepime was described by a five-compartment model. The downtime was applied to the CRRT flow rates, which were used to describe the rates of transfer between the compartments. At MICs of ≤8 mg/liter, intermittent infusion of 2 g cefepime every 8 h achieved good target attainment both early in therapy and at steady state. Only extended- and continuous-infusion regimens achieved good target attainment at MICs of 16 mg/liter. In conclusion, 2 g cefepime infused over 30 min followed by extended infusion of 2 g every 8 h achieved good target attainment at MICs of ≤16 mg/liter with different CRRT flow rates and may be considered in resistant bacterial infections.

Pharmacokinetics of bedaquiline, delamanid and clofazimine in patients with multidrug-resistant tuberculosis.

BACKGROUND: Pharmacokinetic data are needed for newly implemented anti-tuberculosis drugs to help optimize their use. OBJECTIVES: To help fill existing knowledge gaps, we evaluated the pharmacokinetic parameters of novel and repurposed anti-tuberculosis drugs among patients with drug-resistant pulmonary tuberculosis. METHODS: A prospective cohort study among patients ≥16 years with confirmed pulmonary drug-resistant TB was conducted in Tbilisi, Georgia. Patients receiving bedaquiline, delamanid and/or clofazimine were included. Blood samples were collected 4-6 weeks after drug initiation, and serum concentrations were measured using validated liquid chromatography tandem mass spectrometry assays. A non-compartmental analysis was performed, and the association of exposure parameters with covariates was explored. RESULTS: Among 99 patients, the average age and weight were 40 years and 65 kg, respectively. The median Cmin was 0.68 mg/L for bedaquiline, 0.17 mg/L for delamanid, and 0.52 mg/L for clofazimine. The median AUC0-24 was 30.6 mg·h/L for bedaquiline, 16.1 mg·h/L for clofazimine, and the AUC0-12 was 2.9 mg·h/L for delamanid. Among the significant covariates associated with drug exposure parameters were weight and sex for bedaquiline, alcohol use for delamanid, and weight for clofazimine. CONCLUSIONS: We found a strong association of weight with bedaquiline and clofazimine exposure parameters, suggesting the need for weight-based dosing for those agents.

Population Pharmacokinetics of Linezolid in Tuberculosis Patients: Dosing Regimen Simulation and Target Attainment Analysis.

The prolonged treatment duration for multidrug-resistant tuberculosis (MDR-TB) makes linezolid dosing difficult because of adverse effects associated with long-term use. We sought to find the optimal dosing regimen for linezolid across different MIC values. Pharmacokinetic (PK) data from TB patients were included from Brazil, Georgia, and two U.S. sites. Population PK modeling and simulation were performed. We used an fAUC (area under the unbound drug concentration-time curve)/MIC ratio of >119 as the PK/pharmacodynamic (PD) target and minimum (trough) concentrations of drug (Cmins) of 2 and 7 mg/liter as thresholds for toxicity. The PK/PD breakpoint was defined as the highest MIC at which the probability of target attainment is >90%. A total of 104 patients with pulmonary TB were included, with a median age and weight of 37 years and 60 kg. Eighty-one percent had drug-resistant TB. The PK data were best described by a one-compartment model. The PK/PD breakpoint was 0.125 mg/liter for a total daily dose of 300 mg, while daily doses of 450 to 600 mg and 900 to 1,200 mg had PK/PD breakpoints of 0.25 and 0.50 mg/liter, respectively. The probability of achieving a Cmin of ≤2 mg/liter was higher when the dose was given at once than when dividing it into 2 doses. Linezolid at a daily dose of 300 mg may not be optimal. We predicted an excellent and comparable efficacy of linezolid using total daily doses of 900 and 1,200 mg for MICs of ≤0.5 mg/liter but with the potential for more toxicity than with 600 mg daily. The increase in Cmin was noticeable when the daily dose was divided and may incur greater toxicity.

Population Pharmacokinetics and Target Attainment of Cefepime in Critically Ill Patients and Guidance for Initial Dosing.

Cefepime is commonly used in the intensive care unit (ICU) to treat bacterial infections. The time during which the free cefepime concentration is above the MIC (fT>MIC) should be optimized to increase the efficacy of the regimen. We aim to optimize the exposure of cefepime in ICU patients by using population pharmacokinetic (PK) modeling and simulations. Two data sets were included in this study. The first was a prospective study of pediatric patients who received cefepime at 50 mg/kg of body weight and had extensive PK sampling. The second study comprised retrospective data for adult ICU patients admitted to UF Health Shands Hospital who received cefepime and had their cefepime concentrations measured. The population PK model was developed, and simulations were performed, using Pmetrics. The target exposures were 100% fT>MIC and 100% fT>4×MIC The studies included a total of 266 patients, and the mean ages were 3.9 years in the pediatric group and 55 years in adult group. More than half of the patients were males. The mean (standard deviation [SD]) creatinine clearance (CrCl) was 125 (93) ml/min. The mean (SD) daily dose for adults was 4.9 (1.6) g. Cefepime was well described by a two-compartment model with weight as a covariate on the volume of distribution and elimination rate constant (kel), and CrCl and age group as covariates on kel At a MIC of 8 mg/liter, a cefepime loading dose of 4 g as an extended infusion followed by a 6-g continuous infusion was needed for good target attainment. In conclusion, prolonged or continuous infusions will be needed to achieve optimal cefepime exposure for ICU patients. Given the observed variability, therapeutic drug monitoring can help individualize therapy.

Ethionamide Population Pharmacokinetic Model and Target Attainment in Multidrug-Resistant Tuberculosis.

Ethionamide (ETA), an isonicotinic acid derivative, is part of the multidrug-resistant tuberculosis (MDR-TB) regimen. The current guidelines have deprioritized ETA because it is potentially less effective than other agents. Our aim was to develop a population pharmacokinetic (PK) model and simulate ETA dosing regimens in order to assess target attainment. This study included subjects from four different sites, including healthy volunteers and patients with MDR-TB. The TB centers included were two in the United States and one in Bangladesh. Patients who received ETA and had at least one drug concentration reported were included. The population PK model was developed, regimens with a total of 1,000 to 2,250 mg daily were simulated, and target attainment using published MICs and targets of 1.0-log kill and resistance suppression was assessed with the Pmetrics R package. We included 1,167 ethionamide concentrations from 94 subjects. The final population model was a one-compartment model with first-order elimination and absorption with a lag time. The mean (standard deviation [SD]) final population parameter estimates were as follows: absorption rate constant, 1.02 (1.11) h-1; elimination rate constant, 0.69 (0.46) h-1; volume of distribution, 104.16 (59.87) liters; lag time, 0.43 (0.32) h. A total daily dose of 1,500 mg or more was needed for ≥90% attainment of the 1.0-log kill target at a MIC of 1 mg/liter, and 2,250 mg/day led to 80% attainment of the resistance suppression target at a MIC of 0.5 mg/liter. In conclusion, we developed a population PK model and assessed target attainment for different ETA regimens. Patients may not be able to tolerate the doses needed to achieve the predefined targets supporting the current recommendations for ETA deprioritization.

Early therapeutic monitoring of ß-lactams and associated therapy outcomes in critically ill patients.

BACKGROUND: In the ICU, early and appropriate antimicrobial therapy is important to lower infection-related mortality. OBJECTIVES: Assess whether achieving early ß-lactam free concentration above the MIC 100% of the time (fT>MIC) is associated with positive outcomes in the ICU. METHODS: This retrospective study was conducted in ICU patients admitted to UF Health Shands Hospital between 2016 and 2018. Adult patients who received ß-lactam therapy and had drug concentration measured were included. Data collected included demographics, ß-lactam regimens and concentrations, sources of infection, cultures and susceptibilities, mortality, length of stay, resistance acquisition for 30 days and clinical outcome at end of therapy. Multiple regression and time-to-event (TTE) analyses were performed. RESULTS: Two-hundred and six patients were included. Clinical cure occurred in 71%, microbial eradication occurred in 58% and new resistance to the ß-lactam received developed in 8% of patients. Hospital and 30 day mortalities were 17% and 14%, respectively. fT>MIC and fT>4×MIC were associated with clinical cure (P = 0.0303), microbial eradication (P = 0.0476) and suppression of resistance (P = 0.0043). Delay in measuring ß-lactam concentration was associated with clinical failure (P = 0.0072), longer ICU stay (P < 0.0001) and higher mortality (P = 0.0387). In the TTE analysis, patients with 100% fT>MIC had a significantly shorter ICU stay (P = 0.0297). Patients who had clinical cure and microbial eradication had drug concentrations measured earlier (P = 0.0025 and 0.0254, respectively). CONCLUSIONS: This study highlights the importance of early measurement of ß-lactam concentration and confirms the association between fT>MIC and clinical cure, microbial eradication and emergence of resistance.

Meropenem, Cefepime, and Piperacillin Protein Binding in Patient Samples.

BACKGROUND: The mortality rate of patients with a drug-resistant bacterial infection is high, as are the associated treatment costs. To overcome these issues, optimization of the available therapeutic options is required. Beta-lactams are time-dependent antibiotics and their efficacy is determined by the amount of time the free concentration remains above the minimum inhibitory concentration. Therefore, the aim of this study was to assess the extent and variability of protein binding for meropenem, cefepime, and piperacillin. METHODS: Plasma samples for the analysis of meropenem, cefepime, and piperacillin were collected from patients admitted to a tertiary care hospital as part of the standard care. The bound and unbound drug fractions in the samples were separated by ultrafiltration. Validated liquid chromatography-tandem mass spectrometry assays were used to quantify the total and free plasma concentrations, and the protein binding was determined. RESULTS: Samples from 95 patients were analyzed. The median (range) age of patients was 56 years (17-87) and the median (range) body mass index was 25.7 kg/m (14.7-74.2). Approximately 59% of the patients were men. The median (range) unbound fraction (fu) was 62.5% (41.6-99.1) for meropenem, 61.4% (51.6-99.2) for cefepime, and 48.3% (39.4-71.3) for piperacillin. In the bivariate analysis, as the total meropenem concentration increased, the fu increased (r = 0.37, P = 0.045). A decrease in piperacillin fu was observed as the albumin concentration increased (r = -0.56, P = 0.005). CONCLUSIONS: The average fu values were lower than those reported in the literature. There was also a large variability in fu; hence, it should be considered when managing patients administered with these drugs through direct measurements of free drug concentrations.

A Pharmacology Perspective of Simultaneous Tuberculosis and Hepatitis C Treatment.

Tuberculosis (TB) and hepatitis C virus (HCV) infection are both major public health problems. Despite high rates of co-infection there is scarce literature addressing the convergence of the two diseases. One particularly unexplored area is the potential for simultaneous treatment of TB and HCV which would allow for leveraging an extensive global TB treatment infrastructure to help scale up HCV treatment. We review the drug metabolism of anti-TB and HCV drugs and the known and potential drug-drug interactions between recommended HCV regimens and individual anti-TB drugs. Rifampin is the only anti-TB drug to have been formally studied for potential drug interactions with anti-HCV direct-acting antivirals (DAAs) and existing data precludes these combinations. However, based on known pathways of drug metabolism and enzyme effects, the combination of HCV DAA regimens with all other anti-TB drugs may be feasible. Pharmacokinetic studies are needed next to help move co treatment regimens forward for clinical use among patients coinfected with TB and HCV.

Cycloserine Population Pharmacokinetics and Pharmacodynamics in Patients with Tuberculosis.

Limited pharmacokinetic/pharmacodynamic (PK/PD) data exist on cycloserine in tuberculosis (TB) patients. We pooled several studies into a large PK data set to estimate the population PK parameters for cycloserine in TB patients. We also performed simulations to provide insight into optimizing the dosing of cycloserine. TB patients were included from Georgia, Bangladesh, and four U.S. sites. Monolix and mlxR package were used for population PK modeling and simulation. We used PK/PD targets for time above MIC of ≥30% and ≥64%, representing bactericidal activity and 80% of the maximum kill, to calculate the probability of target attainment (PTA). Optimal PK/PD breakpoints were defined as the highest MIC to achieve ≥90% of PTA. Data from 247 subjects, including 205 patients with drug-resistant TB, were included. The data were best described by a one-compartment model. In most cases, the PK/PD breakpoints for the simulated regimens were similar for both PK/PD targets. Higher PTA were achieved as the total daily dose was increased. The highest PK/PD breakpoint that resulted from the use of 250 mg dosages was 16 mg/liter. For MICs of >16 mg/liter, doses of at least 500 mg three times daily or 750 mg twice daily were needed. In conclusion, the current dosing for cycloserine, 250 to 500 mg once or twice daily, is not sufficient for MICs of >16mg/liter. Further studies are needed regarding the efficacy and tolerability of daily doses of >1,000 mg. Dividing the dose minimally affected the PK/PD breakpoints while optimizing exposure, which can potentially reduce adverse drug effects.

Fluoroquinolones in Drug-Resistant Tuberculosis: Culture Conversion and Pharmacokinetic/Pharmacodynamic Target Attainment To Guide Dose Selection.

Fluoroquinolones are group A drugs in tuberculosis guidelines. We aim to compare the culture conversion between new-generation (levofloxacin and moxifloxacin) and old-generation (ciprofloxacin and ofloxacin) fluoroquinolones, develop pharmacokinetic models, and calculate target attainment for levofloxacin and moxifloxacin. We included three U.S. tuberculosis centers. Patients admitted between 1984 and 2015, infected with drug-resistant tuberculosis, and who had received fluoroquinolones for ≥28 days were included. Demographics, sputum cultures and susceptibility, treatment regimens, and serum concentrations were collected. A time-to-event analysis was conducted, and Cox proportional hazards model was used to compare the time to culture conversion. Using additional data from ongoing studies, pharmacokinetic modelling and Monte Carlo simulations were performed to assess target attainment for different doses. Overall, 124 patients received fluoroquinolones. The median age was 40 years, and the median weight was 60 kg. Fifty-six patients (45%) received old-generation fluoroquinolones. New-generation fluoroquinolones showed a faster time to culture conversion (median 16 versus 40 weeks, P = 0.012). After adjusting for isoniazid and clofazimine treatment, patients treated with new-generation fluoroquinolones were more likely to have culture conversion (adjusted hazards ratio, 2.16 [95% confidence interval, 1.28 to 3.64]). We included 178 patients in the pharmacokinetic models. Levofloxacin and moxifloxacin were best described by a one-compartment model with first-order absorption and elimination. At least 1,500 to 1,750 mg levofloxacin and 800 mg moxifloxacin may be needed for maximum kill at the current epidemiologic cutoff values. In summary, new-generation fluoroquinolones showed faster time to culture conversion compared to the old generation. For optimal target attainment at the current MIC values, higher doses of levofloxacin and moxifloxacin may be needed.

Protein Binding of First-Line Antituberculosis Drugs.

The 4-drug regimen of rifampin, isoniazid, pyrazinamide, and ethambutol is an inexpensive, reliable option for treating patients with drug-susceptible tuberculosis (TB). Its efficacy could be further improved by determining the free drug concentrations in plasma, knowing that only the unbound drug can freely penetrate to the tissues. Using an ultrafiltration technique, we determined the protein binding (PB) extent and variability of the first-line anti-TB drugs when given simultaneously to TB patients, representing a real-life case scenario. We used clinical samples routinely received by our laboratory. Plasma proteins were also measured. A protein-free medium was used to determine the nonspecific binding. Plasma samples from 22 patients were included, of which plasma proteins were measured for 18 patients. The median PB was determined for rifampin (88%; range, 72 to 91%), isoniazid (14%; range, 0 to 34%), pyrazinamide (1%; range, 0 to 7%), and ethambutol (12%; range, 4 to 24%). Plasma proteins were not found to be significant predictors for the PB of first-line anti-TB drugs. Rifampin PB was positively correlated with its plasma concentration (P value = 0.0051). Conversely, isoniazid PB was negatively correlated with its plasma concentration (P value = 0.0417). Age was found to have a significant effect on isoniazid PB (P value = 0.0376). No correlations were observed in pyrazinamide or ethambutol. In conclusion, we have determined variable PB of rifampin, isoniazid, pyrazinamide, and ethambutol in patient plasma samples, with median values of 88, 14, 1, and 12%, respectively. In this small study, PB of rifampin and that of isoniazid are dependent on their plasma concentrations.

Fixed-dose combination associated with faster time to smear conversion compared to separate tablets of anti-tuberculosis drugs in patients with poorly controlled diabetes and pulmonary tuberculosis in Qatar.

BACKGROUND: Diabetes is associated with increased risk of tuberculosis (TB) treatment failure, death, and relapse compared to patients without diabetes. Current TB regimens are available as fixed dose combination (FDC) and separate tablets (ST), in which using the former is purported to make it easier to adhere and complete treatment. So far there are no studies assessing the performance of FDC compared to ST in diabetic patients with pulmonary TB. METHODOLOGY: A retrospective cohort study was conducted, and included eight hospitals in Qatar in which patients diagnosed with pulmonary TB received rifampin, isoniazid, pyrazinamide, and ethambutol (as FDC or ST) given as directly observed therapy. Sputum smears for acid fast bacilli were tested weekly. We included patients admitted between December 2012 and December 2015, ≥18 years old, diagnosed with TB with pretreatment positive sputum smears, and having diabetes. Patients with Mycobacterium tuberculosis that was resistant to any first-line drug were excluded. Blood glucose was monitored closely and controlled to < 180 md/dL using oral hypoglycemic agents and/or insulin. We assessed the effectiveness of TB regimens by comparing time to confirmed negative smears between those treated with FDC or ST, and the impact of adding metformin. RESULTS: 103 patients met inclusion criteria. Mean age and body mass index were 45.6 ± 9.1 years and 22.1 ± 3.6 kg/m2, respectively. Fifty-four (52%) patients received the FDC. There was no difference between groups in baseline characteristics and sputum bacillary loads. Patients prescribed FDC showed faster times to sputum smear conversion compared to ST (32 ± 19 vs. 46 ± 31 days, p = 0.01). The difference was greater among patients with pretreatment bacillary load of 3+ (FDC 36.6 ± 19.5 vs. ST 56.1 ± 28.8, p = 0.008). Receipt of metformin≥2000 mg/day altered the difference in time to smear conversion (FDC 30.7 ± 13.4 vs. ST 62 ± 35.5, p = 0.016), which was of greatest difference in those with pretreatment bacillary load 3+ and who received metformin≥2000 mg/day (FDC 36 ± 12.1 vs. ST 92.2 ± 26 days, p = 0.001). CONCLUSION: Patients with diabetes and prescribed FDC showed faster smear conversion during treatment for pulmonary TB compared to ST which was more pronounced in those with 3+ bacillary load pretreatment and which appeared to be modified by higher dose metformin.

Treatment outcomes of fixed-dose combination versus separate tablet regimens in pulmonary tuberculosis patients with or without diabetes in Qatar.

BACKGROUND: Tuberculosis is considered the second most common cause of death due to infectious agent. The currently preferred regimen for treatment of pulmonary tuberculosis (PTB) is isoniazid, rifampin, pyrazinamide, and ethambutol, which has been used either as separate tablets (ST) or as fixed-dose combination (FDC). To date, no studies have compared both regimens in Qatar. We aim to evaluate the safety and effectiveness of FDC and ST regimen for treating PTB, in addition to comparing safety and efficacy of FDC and ST regimens in patients with diabetes treated for TB. METHODS: A retrospective observational study was conducted in two general hospitals in Qatar. Patients diagnosed with PTB received anti-tuberculosis medications (either as FDC or ST) administered by the nurse. Sputum smears were tested weekly. We assessed the time to negative sputum smear and incidence of adverse events among FDC and ST groups. RESULTS: The study included 148 patients. FDC was used in 90 patients (61%). Effectiveness was not different between FDC and ST regimens as shown by mean time to sputum conversion (29.9 ± 18.3 vs. 35.6 ± 23 days, p = 0.12). Similarly, there was no difference in the incidence of adverse events, except for visual one that was higher in ST group. Among the 33 diabetic patients, 19 received the FDC and had faster sputum conversion compared to those who received ST (31 ± 12 vs. 49.4 ± 30.9 days, p = 0.05). Overall, diabetic patients needed longer time for sputum conversion and had more hepatotoxic and gastric adverse events compared to non-diabetics. CONCLUSION: ST group had higher visual side effects compared to FDC. FDC may be more effective in diabetic patients; however, further studies are required to confirm such finding.

Safety and Efficacy of Fondaparinux in Renal Impairment.

Objective: To evaluate the cumulative evidence regarding the efficacy and safety of using fondaparinux in renal impairment, manifested by preventing new or recurrent thrombosis and the incidence of bleeding, respectively. Data Sources: We searched the MEDLINE and Cochrane databases for relevant studies from 1966 until November 2014, using the terms "fondaparinux" and "renal failure" or "dialysis." Additional references were identified from review of literature citations. Study Selection and Data Extraction: Inclusion criteria were articles in English language and patients with creatinine clearance (CrCl) less than 50 mL/min. Exclusion criteria were using fondaparinux as an anticoagulant for dialyzer circuit patency, abstracts, case reports, case series, pediatrics (<18 years), and pharmacokinetic studies with no clinical efficacy and safety results. Data Synthesis: Our search retrieved 4 cohort studies, 1 clinical trial, and 1 randomized clinical trial (RCT) subgroup analysis. A total of 3237 patients received fondaparinux with a dose ranging from 1.25 mg to 2.5 mg daily. Three studies investigated fondaparinux as a prophylactic agent, 2 as a treatment agent, and 1 study investigated both. The only study with control group was the RCT subgroup analysis, which compared fondaparinux to enoxaparin. A total of 470 patients developed thromboembolic complications or death and 169 developed major bleeding. The composite outcome of safety and efficacy in the RCT subgroup analysis was significantly lower in fondaparinux group compared with the enoxaparin group (P = .001). Conclusions: Current evidence regarding the safety and efficacy of fondaparinux in renally impaired patients is limited and does not support its use in such population.