Clearance and bioavailability study through arterio-venous drug concentrations relationship

Drug-drug interaction of ciprofol injectable emulsion with mefenamic acid capsules in healthy subjects

AIMS

To investigate the drug-drug interaction (DDI) of ciprofol injectable emulsion and mefenamic acid capsules in healthy subjects.

METHODS

Twenty healthy subjects were enrolled in this single-centre, open-label, two-period DDI study. Ciprofol (0.4 mg kg-1 ) was administered as a single dose on days 1 and 5. A 500-mg oral loading dose of mefenamic acid was given on day 4 followed by a 250-mg maintenance dose every 6 h (a total of eight doses). Blood samples for pharmacokinetic analyses were collected. Depth of anaesthesia was monitored using the Modified Observer's Assessment of Alertness and Sedation (MOAA/S) scale and Bispectral Index scores (BISs).

RESULTS

Compared with administration of ciprofol alone, administration with mefenamic acid showed no significant difference in exposure. The geometric mean ratios (GMRs) and their 90% confidence intervals (CIs) for maximum plasma concentration (Cmax ), area under the plasma concentration-time curve calculated from 0 to the last measurement point (AUC0-last ) and AUC to infinity (AUC0-inf ) were 91.6% (86.5-96.9%), 103.3% (100.3-106.4%) and 107.0% (101.2-113.2%), respectively. The MOAA/S and BIS curves for the two treatment periods essentially coincided, indicating that the anaesthesia effect of ciprofol was not affected by mefenamic acid. Seven subjects (35%) reported eight adverse events (AEs) when ciprorol was administered alone and 12 subjects (60%) reported 18 AEs when ciprofol was administered in combination with mefenamic acid. All AEs were mild.

CONCLUSIONS

Mefenamic acid, a UGT1A9 inhibitor, had no significant effect on the pharmacokinetics and pharmacodynamics of ciprofol in healthy subjects. Ciprofol was safe and well tolerated when administered with mefenamic acid.

Tissue Drug Concentration

Blood flow enables the delivery of oxygen and nutrients to the different tissues of the human body. Drugs follow the same route as oxygen and nutrients; thus, drug concentrations in tissues are highly dependent on the blood flow fraction delivered to each of these tissues. Although the free drug concentration in blood is considered to correlate with pharmacodynamics, the pharmacodynamics of a drug is actually primarily commanded by the concentrations of drug in the aqueous spaces of bodily tissues. However, the concentrations of drug are not homogeneous throughout the tissues, and they rarely reflect the free drug concentration in the blood. This heterogeneity is due to differences in the blood flow fraction delivered to the tissues and also due to membrane transporters, efflux pumps, and metabolic enzymes. The rate of drug elimination from the body (systemic elimination) depends more on the driving force of drug elimination than on the free concentration of drug at the site from which the drug is being eliminated. In fact, the actual free drug concentration in the tissues results from the balance between the input and output rates. In the present paper, we develop a theoretical concept regarding solute partition between intravascular and extravascular spaces; discuss experimental research on aqueous/non-aqueous solute partitioning and clinical research on microdialysis; and present hypotheses to predict in-vivo elimination using parameters of in-vitro metabolism.

Are Physiologically Based Pharmacokinetic Models Reporting the Right C(max)? Central Venous Versus Peripheral Sampling Site

Physiologically based pharmacokinetic (PBPK) models can over-predict maximum plasma concentrations (C_max) following intravenous administration. A proposed explanation is that invariably PBPK models report the concentration in the central venous compartment, rather than the site where the samples are drawn. The purpose of this study was to identify and validate potential corrective models based on anatomy and physiology governing the blood supply at the site of sampling and incorporate them into a PBPK platform. Four models were developed and scrutinised for their corrective potential. All assumed the peripheral sampling site concentration could be described by contributions from surrounding tissues and utilised tissue-specific concentration-time profiles reported from the full-PBPK model within the Simcyp Simulator. Predicted concentrations for the peripheral site were compared to the observed C_max. The models results were compared to clinical data for 15 studies over seven compounds (alprazolam, imipramine, metoprolol, midazolam, omeprazole, rosiglitazone and theophylline). The final model utilised tissue concentrations from adipose, skin, muscle and a contribution from artery. Predicted C_max values considering the central venous compartment can over-predict the observed values up to 10-fold whereas the new sampling site predictions were within 2-fold of observed values. The model was particularly relevant for studies where traditional PBPK models over-predict early time point concentrations. A successful corrective model for C_max prediction has been developed, subject to further validation. These models can be enrolled as built-up modules into PBPK platforms and potentially account for factors that may affect the initial mixing of the blood at the site of sampling.