Application of Population Pharmacokinetic Analysis to Characterize CYP2C19 Mediated Metabolic Mechanism of Voriconazole and Support Dose Optimization

Purpose: The aims of this study were to establish a joint population pharmacokinetic model for voriconazole and its N-oxide metabolite in immunocompromised patients, to determine the extent to which the CYP2C19 genetic polymorphisms influenced the pharmacokinetic parameters, and to evaluate and optimize the dosing regimens using a simulating approach.Methods: A population pharmacokinetic analysis was conducted using the Phoenix NLME software based on 427 plasma concentrations from 78 patients receiving multiple oral doses of voriconazole (200 mg twice daily). The final model was assessed by goodness of fit plots, non-parametric bootstrap method, and visual predictive check. Monte Carlo simulations were carried out to evaluate and optimize the dosing regimens.Results: A one-compartment model with first-order absorption and mixed linear and concentration-dependent-nonlinear elimination fitted well to concentration-time profile of voriconazole, while one-compartment model with first-order elimination well described the disposition of voriconazole N-oxide. Covariate analysis indicated that voriconazole pharmacokinetics was substantially influenced by the CYP2C19 genetic variations. Simulations showed that the recommended maintenance dose regimen would lead to subtherapeutic levels in patients with different CYP2C19 genotypes, and elevated daily doses of voriconazole might be required to attain the therapeutic range.Conclusions: The joint population pharmacokinetic model successfully characterized the pharmacokinetics of voriconazole and its N-oxide metabolite in immunocompromised patients. The proposed maintenance dose regimens could provide a rationale for dosage individualization to improve clinical outcomes and minimize drug-related toxicities.

Effects of Dexmedetomidine on Perioperative Serum Potassium and Postoperative Rehabilitation of Patients Undergoing Radical Resection of Gastrointestinal Malignancy

Background: To investigate the effects of dexmedetomidine on perioperative potassium and postoperative rehabilitation. Methods: Totally 124 patients scheduled for elective radical resection of gastrointestinal malignant tumor under general anesthesia were included. and randomly assigned to four groups (n=31): groups D1, D2 and D3 received dexmedetomidine loading dose 1, 1 and 0.5 μg/kg and maintenance dose 0.25, 0.5 and 0.5 μg/kg/h, respectively, group C received normal saline 50 ml/h for 10 min and maintenance dose 10 ml/h. Serum potassium and lactate changes were recorded at 5 min after arteriovenous puncture (T1), 1 h after surgery beginning (T6), surgery ending (T7) and 1 h into the post-anesthesia care unit (PACU) (T10). Serum potassium was examined at 48 h after surgery (T11). Perioperative rehabilitation indicators were recorded.Results: Compared with basal values, serum potassium concentration in groups C, D1 and D2 increased significantly at T11 (P=0.003, 0.002, and ˂0.001, respectively) and at T7 (P=0.008), T10 (P=0.015) and T11 (P˂0.001) in group D3. Serum potassium at T11 in group D2 was significantly lower than group C (P=0.032). Serum potassium at T7 in group D3 was significantly higher than group D2 (P=0.036). There were no significant differences in perioperative rehabilitation indicators in all groups. Conclusions: Dexmedetomidine did not decrease perioperative potassium significantly in patients undergoing radical resection of gastrointestinal malignancy, while its loading dose 0.5 μg/kg and maintenance dose 0.5 μg/kg/h can elevate potassium slightly with no adverse effect on perioperative rehabilitation.Trial registration: This study was retrospectively registered on the clinicaltrials.gov website (registration number: NCT04771637).

Factors Affecting Voriconazole Trough Concentration and Optimal Maintenance Voriconazole Dose in Chinese Children

Voriconazole is a triazole antifungal agent commonly used for the treatment and prevention of invasive aspergillosis (IA). However, the study of voriconazole's use in children is limited. The present study was performed to explore maintenance dose to optimize voriconazole dosage in children and the factors affecting voriconazole trough concentration. This is a non-interventional retrospective clinical study conducted from 1 January 2016 to 31 December 2020. The study finally included 94 children with 145 voriconazole trough concentrations. The probability of achieving a targeted concentration of 1.0–5.5 µg/mL with empiric dosing increased from 43 (45.3%) to 78 (53.8%) after the TDM-guided adjustment. To achieve targeted concentration, the overall target maintenance dose for the age group of less than 2, 2 to 6, 6 to 12, and 12 to 18 years old was approximately 5.71, 6.67, 5.08 and 3.31 mg·kg−1/12 h, respectively (p < 0.001). Final multivariate analysis found that weight (p = 0.019), dose before sampling (p < 0.001), direct bilirubin (p < 0.001), urea nitrogen (p = 0.038) and phenotypes of CYP2C19 were influencing factors of voriconazole trough concentration. These factors can explain 36.2% of the variability in voriconazole trough concentration. Conclusion: In pediatric patients, voriconazole maintenance doses under the target concentration tend to be lower than the drug label recommended, but this still needs to be further studied. Age, body weight, dose, direct bilirubin, urea nitrogen and phenotypes of CYP2C19 were found to be influencing factors of voriconazole concentration in Chinese children. The influence of these factors should be taken into consideration during voriconazole use.

Exploring population pharmacokinetic models in patients treated with vancomycin during continuous venovenous haemodiafiltration (CVVHDF)

Background Therapeutic antibiotic dose monitoring can be particularly challenging in septic patients requiring renal replacement therapy. Our aim was to conduct an exploratory population pharmacokinetic (PK) analysis on PK of vancomycin following intermittent infusion in critically ill patients receiving continuous venovenous haemodiafiltration (CVVHDF); focussing on the influence of dialysis-related covariates. Methods This was a retrospective single-centre tertiary level intensive care unit (ICU) study, which included patients treated concurrently with vancomycin and CVVHDF between January 2015 and July 2016. We extracted clinical, laboratory and dialysis data from the electronic healthcare record (EHR), using strict inclusion criteria. A population PK analysis was conducted with a one-compartment model using the PMetrics population PK modelling package. A base structural model was developed, with further analyses including clinical and dialysis-related data to improve model prediction through covariate inclusion. The final selected model simulated patient concentrations using probability of target attainment (PTA) plots to investigate the probability of different dosing regimens achieving target therapeutic concentrations. Results A total of 106 vancomycin dosing intervals (155 levels) in 24 patients were examined. An acceptable 1-compartment base model was produced (Plots of observed vs. population predicted concentrations (Obs–Pred) R2 = 0.78). No continuous covariates explored resulted in a clear improvement over the base model. Inclusion of anticoagulation modality and vasopressor use as categorical covariates resulted in similar PK parameter estimates, with a trend towards lower parameter estimate variability when using regional citrate anti-coagulation or without vasopressor use. Simulations using PTA plots suggested that a 2 g loading dose followed by 750 mg 12 hourly as maintenance dose, commencing 12 h after loading, is required to achieve adequate early target trough concentrations of at least 15 mg/L. Conclusions PTA simulations suggest that acceptable trough vancomycin concentrations can be achieved early in treatment with a 2 g loading dose and maintenance dose of 750 mg 12 hourly for critically ill patients on CVVHDF.

Dose Optimization of Colistin: A Systematic Review

Colistin is considered a last treatment option for multi-drug and extensively resistant Gram-negative infections. We aimed to assess the available data on the dosing strategy of colistin. A systematic review was performed to identify all published studies on the dose optimization of colistin. Grey literature and electronic databases were searched. Data were collected in a specified form and the quality of the included articles was then assessed using the Newcastle-Ottawa scale for cohort studies, the Cochrane bias tool for randomized clinical trials (RCT), and the Joanna Briggs Institute (JBI) critical checklist for case reports. A total of 19 studies were included, of which 16 were cohort studies, one was a RCT, and two were case reports. A total of 18 studies proposed a dosing regimen for adults, while only one study proposed a dosing schedule for pediatric populations. As per the available evidence, a loading dose of 9 million international units (MIU) of colistin followed by a maintenance dose of 4.5 MIU every 12 h was considered the most appropriate dosing strategy to optimize the safety and efficacy of treatment and improve clinical outcomes. This review supports the administration of a loading dose followed by a maintenance dose of colistin in severe and life-threatening multi-drug Gram-negative bacterial infections.

Influence of CYP2C9 Polymorphisms on Plasma Concentration of Warfarin and 7-Hydroxy Warfarin in South Indian Patients

Background: Warfarin is primarily metabolized by cytochrome P450 2C9 (CYP2C9), which is encoded by the CYP2C9 gene. CYP2C9*2 and CYP2C9*3 variants significantly influence warfarin metabolism and subsequently the required dose of warfarin. Objective: The current retrospective study was aimed to determine the influence of CYP2C9 variants on warfarin metabolic ratio (MR, warfarin/7-hydroxy warfarin) and warfarin maintenance therapy in 210 patients (mean age 44.6±11.6 (SD) years; male to female ratio 81:129). Method: High-performance liquid chromatography (HPLC) with UV detector was used to measure plasma concentrations of warfarin and 7-hydroxy warfarin. Plasma samples were collected 12 h after the previous dose of warfarin was administered. CYP2C9 variants (rs1799853 and rs1057910) were identified using real-time polymerase chain reaction allele-discrimination method. Results: The mean daily maintenance dose of warfarin was 4.6±1.8 (SD) mg. The mean plasma warfarin and 7-hydroxy warfarin concentrations were 3.7±1.6 (SD) µg/mL and 1.1±0.54 (SD) µg/mL, respectively. Patients carrying other CYP2C9 variants required 39% lower warfarin maintenance dose (3.3±1.2 mg) than CYP2C9*1*1 carrier (4.9±1.8 mg), (p<0.0001). MRs differed significantly between CYP2C9 variant carriers (8.1±5.1) and normal genotype carriers (4.8±3.9) (p<0.0001). Probit analysis identified an MR value of 7.6 as the anti-mode (sensitivity of 55% and specificity of 84%) to differentiate poor and intermediate metabolizers (carriers of any *2 or *3 variant allele) from normal metabolizers (CYP2C9*1*1 genotype). Conclusion : The present study results provide, insights on effect of CYP2C9 genetic polymorphisms on inter-individual variability in warfarin metabolism and emphasizes utility of phenotyping in a setting of genotype-guided dosing of warfarin in the South Indian population.

Population Pharmacokinetic Analysis and Dosing Optimization of Prophylactic Fluconazole in Japanese Patients with Hematological Malignancy

We conducted population pharmacokinetic (PPK) analysis and Monte Carlo simulations to determine the appropriate prophylactic dose of fluconazole to prevent invasive candidiasis in patients with hematological malignancies. Patients receiving chemotherapy or hematopoietic stem cell transplantation at Yokohama City University Hospital between November 2018 and March 2020 were included. Additionally, patients receiving oral fluconazole for prophylaxis were recruited. We set the free area under the curve/minimum inhibitory concentration (MIC) = 50 as the target and determined the largest MIC (breakpoint MIC) that could achieve more than 90% probability of target attainment. The blood fluconazole concentration of 54 patients (119 points) was used for PPK analysis. The optimal model was the one-compartment model with first-order administration and first-order elimination incorporating creatinine clearance (CLcr) as a covariate of clearance and body weight as a covariate of distribution volume. We conducted Monte Carlo simulation with fluconazole at 200 mg/day or 400 mg/day dosing schedules and patient body weight and CLcr ranging from 40 to 70 kg and 40–140 mL/min, respectively. The breakpoint MICs on the first dosing day and at steady state were 0.5–1.0 μg/mL and 1.0–2.0 μg/mL for 200 mg/day and 1.0–2.0 μg/mL and 2.0–4.0 μg/mL for 400 mg/day, respectively. The recommended dose was 400–700 mg/day for the loading dose and 200–400 mg/day for the maintenance dose. Our findings suggest that the optimal prophylactic dose of fluconazole in hematological malignancy patients depends on CLcr and body weight, and a sufficient loading and maintenance dose may be needed to completely prevent invasive candidiasis.

Investigating the Potential Impact of Dosing Tolerance to Facilitate Use of Nplate Self-Administration in Adult Patients with ITP

Background and Objective: Romiplostim, is a TPO agonist approved for the treatment for adult ITP. It follows a weight-based and platelet response-guided dose titration algorithm to maintain patients' platelet counts (PC) between 50 and 200x10 9/L, after which a maintenance dose is administered once weekly to keep platelet counts within the target range. While self-administration of romiplostim maintenance dose has been approved in EU for adult patients, in the US romiplostim is only approved for weekly administration by a healthcare provider (HCP) using an 0.01 mL graduation syringe to ensure dosing accuracy; a dose tolerance margin of romiplostim has never been investigated before. The following work explores the impact of dosing tolerance on PC to assess the feasibility of romiplostim self-administration in adult ITP patients. Methods: The analysis was based on a previously developed pharmacodynamic model of romiplostim in ITP patients (Perez-Ruixo et al, 2012, Gibiansky et al, 2021). Previous romiplostim clinical studies in patients with ITP were leveraged to develop an updated model of 475 ITP patients (&gt;50 kg, weekly romiplostim total dose &gt; 100 µg and between 1 and 10 µg/kg stable maintenance dose for at least 1 month, self-administration) and assess potential differences in PC between ITP patients who qualify for self-administration and the general adult ITP population. Comparison of observed and model predicted PC and romiplostim dose over time confirmed the adequacy of the model to assess the impact of varying dose tolerances on PC that may occur with self-administration. Under the proposed guidelines for romiplostim self-administration eligibility, an adult patient would self-administer up to 4 weekly stable maintenance doses of romiplostim between two platelet measurements 1 month apart. To evaluate the impact on PC over 1 month when patients self-administered all four weekly doses versus patients receiving the same prescribed dose by a healthcare provider, three dosing scenarios were considered: (1) exact titrated dose (no dose deviation), (2) titrated dose plus 0.03 mL or 15 µg of romiplostim, and (3) titrated dose minus 0.03 mL or 15 µg of romiplostim. To further characterize the number of ITP patients with clinically meaningful platelet deviations, the predicted number of virtual patients with a PC below 30 x10 9/L or above 400 x10 9/L were also summarized for each simulated scenario. Lastly, the simulated population was divided into four groups based on the magnitude of their prescribed dose and used to evaluate whether the prescribed romiplostim dose influences platelet excursion rates following the investigated dose scenarios. Results: Simulations suggest that 4 successive weekly doses of ± 0.03 mL (or ± 15 µg) the prescribed romiplostim dose is unlikely to cause a significant change in platelet excursion rates relative to continuous administration of the exact prescribed dose. No meaningful increase (0.1 - 0.4%) was observed in the predicted excursion rates across these thresholds for either the under- or overdosing scenarios (Figure 1). This results also show that while there is a slight trend between the magnitude of the prescribed dose and the fraction of subjects that experience a platelet excursion, it does not result in a meaningful increase (&lt;4%) in platelet excursions in any of the evaluated subgroups. Specifically, we observed minimal changes in the fraction of patients with a platelet excursion outside the potentially clinically meaningful thresholds across all simulated dose groups and dosing scenarios (Table 1). The results from this analysis suggest that possible dosing variance expected from the self-administration of romiplostim by an eligible lay person (± 0.03 mL or 15 μg) with monthly PC evaluation will not lead to a significant increase in the rate of platelet count excursions for patients who achieve a stable romiplostim dose and meet the proposed eligibility criteria. Figure 1 Figure 1. Disclosures Serrano Castillo: Amgen: Current Employment, Current equity holder in publicly-traded company. Saad: Amgen: Current Employment, Current equity holder in publicly-traded company. Wang: Amgen Inc: Current Employment, Current equity holder in publicly-traded company. Zhang: Amgen: Current Employment, Current equity holder in publicly-traded company. Chow: Amgen: Current Employment, Current equity holder in publicly-traded company. Doshi: Amgen: Current equity holder in publicly-traded company; Amgen: Current Employment.

Real-World Data of Tigecycline-Associated Drug-Induced Liver Injury Among Patients in China: A 3-year Retrospective Study as Assessed by the Updated RUCAM

Background: Tigecycline, a glycylcycline antibiotic, is increasingly used clinically for the treatment of severe infections caused by multidrug-resistant bacteria, but it is also associated with hepatotoxicity. However, the incidence and risk factors of tigecycline-associated drug-induced liver injury (DILI) are unclear. We conducted this study to investigate the incidence, characteristics and risk factors of tigecycline-associated DILI in the real-world clinic setting.Patients and Methods: A retrospective analysis was conducted in inpatients who received tigecycline treatment from January 2018 to January 2020. Based on the biochemical criteria of DILI and the causality assessment by Roussel Uclaf Causality Assessment Method (RUCAM) using cases with a probable or highly probable causality grading, two clinical pharmacists and one clinician worked together to screen patients for tigecycline-associated DILI. Then patients with DILI were randomly matched by gender in a ratio of 1:2 to the remaining patients in the tigecycline cohort without biochemical abnormalities to identify risk factors.Results: A total of 973 patients from 1,250 initial participants were included. The incidence of tigecycline-associated DILI was 5.7% (55/973). Among 55 DILI patients, 10 cases presented with the hepatocellular pattern, 4 cases belonged to the mixed pattern, and 41 presented with the cholestatic pattern. Most cases reached the severity of grade 1 and 2. The rate of recovery in hepatocellular pattern, mixed pattern, and cholestatic pattern was 70.0, 50.0, and 41.5%, respectively. The proportion of the DILI cases treated with high dose (100 mg) and prolonged duration (&gt;14 days) was significantly higher than standard dose and routine duration (100.0% vs. 18.1%, p &lt; 0.05). Logistic regression analysis showed that high maintenance dose (OR = 1.028, p = 0.002), prolonged duration (OR = 1.208, p = 0.000), and number of hepatotoxic drugs (OR = 2.232, p = 0.000) were independent factors of tigecycline-associated DILI.Conclusion: Tigecycline was associated with liver injury, with a slightly higher incidence (5.7%) than the frequency of “frequent” (5%) defined by the Medical Dictionary for Regulatory Activities. Patients with a high maintenance dose and prolonged tigecycline regimen, as well as concomitant use of multiple hepatotoxic drugs should be paid more attention.