Influence of plasma protein binding on pharmacodynamics: Estimation of in vivo receptor affinities of beta blockers using a new mechanism-based PK-PD modelling approach

Population total and unbound pharmacokinetics and pharmacodynamics of ciprofol and M4 in subjects with various renal functions

AIMS

The aim of this study was to develop a population pharmacokinetic (PK) model to simultaneously describe both total and unbound concentrations of ciprofol and its major glucuronide metabolite, M4, and to link it to the population pharmacodynamics (PD) model in subjects with various renal functions.

METHODS

A total of 401 and 459 pairs of total and unbound plasma concentrations of ciprofol and M4, respectively, as well as 2190 bispectral index (BIS) data from 24 Chinese subjects with various renal functions were available. Covariates that may potentially contribute to the PK and PD variability of ciprofol were screened using a stepwise procedure. The optimal ciprofol induction dosing regimen was determined by model-based simulations.

RESULTS

The PK of unbound ciprofol could best be described by a three-compartment model, while a two-compartment model could adequately describe unbound M4 PK. The concentrations of total and unbound ciprofol and M4 were linked using a linear protein binding model. The relationship between plasma concentrations of ciprofol and BIS data was best described by an inhibitory sigmoidal E_max model with a two-compartment biophase distribution compartment. Hemoglobin was the identified covariate determining the central compartment clearance of ciprofol; uric acid was a covariate affecting the central compartment clearance of M4 and protein binding rate, k_B . The included covariates had no effect on the PD of ciprofol. Simulation results indicated that the label-recommended dose regimen was adequate for anaesthesia induction.

CONCLUSIONS

The developed model fully characterized the population PK and PD profiles of ciprofol. No dose adjustment is required in patients with mild and moderate renal impairment.

Effect of Lactic Acid Bacteria on the Pharmacokinetics and Metabolism of Ginsenosides in Mice

This study aims to investigate the effect of lactic acid bacteria (LAB) on in vitro and in vivo metabolism and the pharmacokinetics of ginsenosides in mice. When the in vitro fermentation test of RGE with LAB was carried out, protopanaxadiol (PPD) and protopanaxadiol (PPD), which are final metabolites of ginsenosides but not contained in RGE, were greatly increased. Compound K (CK), ginsenoside Rh1 (GRh1), and GRg3 also increased by about 30%. Other ginsenosides with a sugar number of more than 2 showed a gradual decrease by fermentation with LAB for 7 days, suggesting the involvement of LAB in the deglycosylation of ginsenosides. Incubation of single ginsenoside with LAB produced GRg3, CK, and PPD with the highest formation rate and GRd, GRh2, and GF with the lower rate among PPD-type ginsenosides. Among PPT-type ginsenosides, GRh1 and PPT had the highest formation rate. The amoxicillin pretreatment (20 mg/kg/day, twice a day for 3 days) resulted in a significant decrease in the fecal recovery of CK, PPD, and PPT through the blockade of deglycosylation of ginsenosides after single oral administrations of RGE (2 g/kg) in mice. The plasma concentrations of CK, PPD, and PPT were not detectable without change in GRb1, GRb2, and GRc in this group. LAB supplementation (1 billion CFU/2 g/kg/day for 1 week) after the amoxicillin treatment in mice restored the ginsenoside metabolism and the plasma concentrations of ginsenosides to the control level. In conclusion, the alterations in the gut microbiota environment could change the ginsenoside metabolism and plasma concentrations of ginsenosides. Therefore, the supplementation of LAB with oral administrations of RGE would help increase plasma concentrations of deglycosylated ginsenosides such as CK, PPD, and PPT.

Determination of unbound fraction of dorzagliatin in human plasma by equilibrium dialysis and LC-MS/MS and its application to a clinical pharmacokinetic study

Dorzagliatin, a novel glucokinase (GK) activator targeting both pancreatic and hepatic GK, is currently in late-stage clinical development for treatment of type 2 diabetes (T2D). For the optimization of dosing regimens to ensure adequate safety and efficacy, it is critical to have a deep understanding of pharmacokinetic (PK) and pharmacodynamic (PD) profiles of the drug in various targeting patient populations, considering the fact that T2D adversely affects a vast patient population who often times also suffer from a wide range of comorbidities including severe liver and/or kidney damage. Since drug efficacy seems to be closely related to unbound drug concentrations at the site of action, therefore, the determination of plasma unbound concentrations/fractions of dorzagliatin is of crucial importance, especially when performing the PK/PD assessment in those special populations. In the current study, a method was developed and validated for determining the unbound fraction (f_u) of dorzagliatin in human plasma by using equilibrium dialysis for the separation of the bound and unbound drug, and LC-MS/MS for subsequent quantification. We have successfully addressed two widely recognized challenges for determination of the f_u, i.e., the lack of knowledge on the "true f_u" and the difficulty in assessing the accuracy and reproducibility of the measurement. Using this method, a 0.2 mL aliquot of human plasma samples were first dialyzed against 0.35 mL of phosphate buffered saline buffer at 37 °C for 5 h in the equilibrium dialysis device to separate the unbound dorzagliatin. Afterwards, post-dialysis samples were extracted by protein precipitation using acetonitrile. Separation of dorzagliatin and potential interferences were achieved using a Gemini C18 column coupled with gradient elution. Subsequent detection was carried out on tandem mass spectrometer operated by multiple reaction monitoring in positive mode using electrospray ionization. The standard curve over the concentration range of 0.125-250 ng/mL exhibits good linearity. The method was fully validated meeting the requirements in current bioanalytical guidance and was successfully applied in a clinical PK study of dorzagliatin in healthy volunteers and patients with renal function impairment. Method reproducibility was demonstrated in incurred sample reanalysis. With demonstrated accuracy, stability and reproducibility, reliable analytical results were obtained from clinical samples for PK/PD interpretation, providing valuable insight for the development of dorzagliatin.

The bioanalytical challenge of determining unbound concentration and protein binding for drugs

Knowledge regarding unbound concentrations is of vital importance when exploring the PK and PD of a drug. The accurate and reproducible determination of plasma protein binding and unbound concentrations for a compound/drug is a serious challenge for the bioanalytical laboratory. When the drug is in equilibrium with the binding protein(s), this equilibrium will shift when physiological conditions are not met. Furthermore, the true unbound fraction/concentration is unknown, and there are numerous publications in the scientific literature reporting and discussing data that have been produced without sufficient control of the parameters influencing the equilibrium. In this Review, different parameters affecting the equilibrium and analysis are discussed, together with suggestions on how to control these parameters in order to produce as trustworthy results for unbound concentrations/fractions as possible.

'Null method' determination of drug biophase concentration

PK/PD modeling is enhanced by improvements in the accuracy of its metrics. For PK/PD modeling of drugs and biologics that interact with enzymes or receptors, the equilibrium constant of the interaction can provide critical insight. Methodologies such as radioliogand binding and isolated tissue preparations can provide estimates of the equilibrium constants (as the dissociation constant, K value) for drugs and endogenous ligands that interact with specific enzymes and receptors. However, an impediment to further precision for PK/PD modeling is that it remains a problem to convert the concentration of drug in bulk solution (A) into an estimate of receptor occupation, since A is not necessarily the concentration (C) of drug in the biophase that yields fractional binding from the law of mass action, viz., C/(C + K). In most experimental studies A is much larger than K, so the use of administered instead of biophase concentration gives fractional occupancies very close to unity. We here provide a simple way to obtain an estimate of the factor that converts the total drug concentration into the biophase concentration in isolated tissue preparation. Our approach is an extension of the now classic 'null method' introduced and applied by Furchgott to determination of drug-receptor dissociation constants.

The effect of plasma protein binding on in vivo efficacy: misconceptions in drug discovery

Data from in vitro plasma protein binding experiments that determine the fraction of protein-bound drug are frequently used in drug discovery to guide structure design and to prioritize compounds for in vivo studies. However, we consider that these practices are usually misleading, because in vivo efficacy is determined by the free (unbound) drug concentration surrounding the therapeutic target, not by the free drug fraction. These practices yield no enhancement of the in vivo free drug concentration. So, decisions based on free drug fraction could result in the wrong compounds being advanced through drug discovery programmes. This Perspective provides guidance on the application of plasma protein binding information in drug discovery.

Significance of protein binding in pharmacokinetics and pharmacodynamics

The significance of plasma protein binding on drug efficacy and, subsequently, the clinical relevance of changes in protein binding has been controversially discussed for decades. The uncertainty concerning the impact of plasma protein binding on a drug's pharmacological activity is, in part, related to the approach used when investigating and interpreting protein binding effects in vitro and in vivo. Frequently, a generalized one-size-fits-all approach, such as "protein binding does matter/does not matter," may not be applicable. An appropriate analysis requires careful consideration of both pharmacokinetic and pharmacodynamic processes, as they both contribute to the safety and efficacy of drugs. Therefore, the aim of this article is to provide a concise review of the theoretical concepts of protein binding, and to discuss relevant examples where applicable.