Clinical pharmacokinetic study of COVID-19 patients
An open-label, single-center study (ethical review approval number: PJ-NBEY-KY-2020-063-01) was conducted to assess the safety, efficacy, and pharmacokinetics of CQ in patients with COVID-19. The study was approved by the Ethics Committee of Ningbo Hwamei Hospital, University of Chinese Academy of Sciences (Ningbo, China), and was performed in accordance with the Declaration of Helsinki.
Patients who met the inclusion criteria but did not have any of the exclusion criteria were included in this study. Inclusion criteria included:
1) Being aged 18 years old or older
2) Having been diagnosed with COVID-19 and meeting all of the following criteria: (A) had an epidemiological history, (B) had clinical manifestations (met any two of the following — fever; normal or decreased white blood cell count or lymphopenia in the early stage of onset; and chest radiology in the early stage showing multiple small patchy shadowing and interstitial changes, which is especially significant in periphery pulmonary (furthermore, this develops into bilateral multiple ground-glass opacity and infiltrating shadowing. Pulmonary consolidation occurs in severe cases. Pleural effusion is rare), and (C) suspected cases who had one of the following etiological evidence and had consequently been confirmed as COVID-19: respiratory or blood specimens testing positive for novel coronavirus nucleic acid by real-time fluorescent RT-PCR; respiratory or blood specimen virus gene sequencing had shown them to be highly homologous with the known novel coronavirus.
These patients received CQ phosphate administration unless they had one or more of the following exclusion criteria: 1) female patients in pregnancy, 2) patients with a clear history of allergies to chloroquine, 3) patients suffering from diseases of the blood system, 4) patients suffering from chronic liver or kidney diseases and reaching the terminal stage, 5) patients suffering from arrhythmia or chronic heart disease patients, 6) patients with known retinal diseases or hearing loss, 7) patients with known mental illness, and 8) patients who have to use digitalis drugs for existing underlying diseases.
All enrolled subjects signed the Informed Consent Form (ICF) before the study was conducted. Subjects received 500 mg CQ phosphate (300 mg CQ) twice a day for 7 days continuously. Blood samples of 4 ml on days 1, 3, 7, and 14 were collected prior to dose administration. Additional sparse blood samples were collected. Anticoagulation of ethylene diamine tetraacetic acid (EDTA) was used to separate plasma after centrifugation for 5 min at 3000 rpm. The collected plasma samples were stored at −80 °C before analysis. The plasma concentrations of CQ were determined using a validated high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method (see details in supplementary file). The lower limit of quantitation (LLOQ) was 2.00 ng/ml. The accuracy was within the range of ± 15%, and the precision was less than 15%.
All subjects receiving at least one dose were incorporated into the analysis. The patient demographics, baseline characteristics (including laboratory examination), and drug combination information were also collected and included in the analysis.
Literature data collection
All published literature on clinical PK of CQ was collected from PubMed and Embase databases. The keywords used for searching were: “Clinical Pharmacokinetic and Chloroquine”. Publications from January 1, 1940, to February 29, 2020, were reviewed. Inclusion criteria of publications for PK model development were: 1) the study drug was chloroquine phosphate or chloroquine, 2) human, as the research subjects had participated in clinical trials, 3) the literature reported the plasma CQ concentration-time profiles. Exclusion criteria were: 2) literature did not clearly describe the dosage and the demographics of subjects, 2) the reported CQ concentration-time profiles were too vague for data extraction, 3) literature reported only serum or blood drug concentration instead of plasma concentration.
Aggregate (mean) plasma CQ PK profiles of identified publications were extracted together with the dosing information. The number of subjects that contributed data to each aggregate profile was included as a variable in the analysis dataset. An indicator variable was also created to appoint the PK profiles as either aggregate or individual PK data to allow for separately estimating their residual errors.
Population PK model development
Structural PK model
A two-compartment model with first-order oral elimination and absorption with an absorption lag was developed to describe the plasma concentration-time course of CQ (Fig. 1). The same model structure has been used in the literature to describe the PK of CQ [12,13,14]. The model parameters estimated in the structural PK model included first-order oral absorption (ka), apparent clearance (CL/F), apparent inter-compartmental clearance (Q/F), volume of distribution for the central compartment (V2/F), volume of distribution for the peripheral compartment(V3/F), and lag-time (ALAG). An exponential error model was used to characterize inter-individual variability for each parameter, where possible, assuming log-normal parameter distributions. Residual variability (σ2) for the plasma concentration data was evaluated using separate proportional error models for aggregate data from literature and individual COVID-19 patients. For aggregate profile, the residual error was weighted by the inverse of the square root of the number of individuals that contributed data to an aggregate plasma PK profile [15]. In addition to population model-based meta-analysis, the current suggested methodology for stabilizing pharmacokinetic model when analysis the sparse data is to use the $PRIOR functionality in NONMEM, which can make the model run successfully by using a priori information [16, 17]. This methodology was also conducted and compared. The population pharmacokinetic literature about chloroquine on PubMed was searched, and the information then collected and summarized. The meta-analysis of previous population pharmacokinetic studies was conducted, and the summarization of the PK parameters is provided in Table S2 in the supplementary file. The $PRIOR function of the NONMEM software was then used to rerun the model.
Covariate analysis
The main purpose of covariate analysis was to investigate the effects of covariates on CL/F and V2/F. Since many covariates were not reported in the literature, the aggregate data from literature and clinical PK data was only used to establish the base model. For covariate analysis, the model parameters were fixed to estimated values from the base model except for parameters of random effects for CL/F and V2/F. Then, this model was used to investigate the influence of covariates based on only the PK and covariates data from COVID-19 patients. The demographic data included race, age, and body weight. Baseline laboratory tests of COVID-19 patients were also analyzed, which included alanine aminotransferase (ALT), albumin (ALB), aspartate transaminase (AST), serum creatinine (SCr), direct bilirubin (DBIL), total bilirubin (TBIL), body temperature baseline (TEMB), highest body temperature in hospital (TEMP), white blood cell count (WBC), blood platelet count (PLT), hemoglobin (HGB), D-dimer, hematocrit (HCT), and creatinine clearance (CrCL). Missing covariates that were less than 5% of total covariates data were imputed by the median values, while missing covariates that were equal to or greater than 5% of total covariates data were not included in analysis. The covariates that were evaluated on PK model parameters are summarized in Table S1 in the supplementary file. The covariates were incorporated into the base model using the step-wise screening approach, which was implemented manually through forward selection and backward elimination. Power and proportional covariate models of covariate effects on PK parameters were tested for continuous variables and categorical variables respectively. Potential covariates were entered one by one into the population PK model. When the objective function value (OFV) was reduced by more than 3.84 with degrees of freedom (df) equal to 1 (p < 0.05), the covariate was kept in the model. After the development of a full multivariable model, it was checked by subtracting each covariate individually using backward elimination. Where OFV was increased by more than 6.63 (p < 0.01, df = 1), the subtracted covariate was put back into the model. Allometric scaling models using body weight normalized PK parameters to size were also evaluated [18].
Model evaluation and validation
The final population PK model was assessed using the goodness-of-fit (GOF) plots, which included the dependent variable (DV) versus individual prediction (IPRED) or population prediction (PRED), conditional weighted residuals (CWRES) versus PRED, and CWRES versus time. Prediction-corrected visual predictive check (pcVPC) [19] was also produced, which was conducted based on simulations of 1000 replicates .
Model simulation
The simulation of PK profile following various CQ phosphate dosing regimens was conducted using the individual PK parameter values from COVID-19 patients. Different dose regimens of CQ phosphate were under consideration including the standard treatment for antimalarial, the efficacious dose clinically observed [3], and recommended dose according to our previous work on the CQ physiologically based pharmacokinetic (PBPK) study. Five dosing regimens of CQ phosphate (Table 1) were proposed for the treatment of COVID-19 patients. The plasma concentration of CQ under five dosing regimens were simulated using the final population PK model. The individual PK parameters of the 50 COVID-19 patients were used to conduct simulations under each dosing scenario. The 5th, 50th, and 95th percentiles of simulated plasma CQ concentrations were plotted over time. Meanwhile, a safety margin was proposed. Chronically treated patients with serum CQ concentration below 1.3 μmol/l (416 ng/ml) demonstrated no side-effects, but 80% of patients experienced side-effects when their serum concentration was above 2.5 μmol/l (800 ng/ml) [15, 19]. Assuming plasma concentrations are equivalent to serum concentrations, a plasma concentration of 400 ng/ml was selected as a safety limit, and the warning limit was set at a maximum concentration of 800 ng/ml.
Table 1 Chloroquine phosphate dosing regimen simulated in Fig. 5 Software and platform used
Dataset arrangement and exploratory data analysis were performed using R (version 3.5.3, https://www.r-project.org/) and RStudio (version 1.1.453, https://rstudio.com/). A nonlinear mixed-effects model was implemented in NONMEM (version 7.3, Icon Development Solutions, Ellicott City, MD, USA) interfaced by Pirana (version 2.8) and Perl speaks NONMEM (PsN) (version 3.6.2) toolkit [20]. Model-based simulations were conducted using the R mrgsolve package. CQ mean concentration-time profiles were extracted using Plot Digitizer (GetData, Version 2.26).