Arteriovenous serum cocaine concentration difference after intravenous bolus injection and constant-rate infusions: relation to pharmacodynamic estimates in rats

Influence of Sampling Site and Fluid Flow on the Accuracy of Total Body Clearance Calculation

Studies have showed that by assuming arteriovenous drug concentrations are homogenous after intravenous injection, the determination of total body clearance based on venous drug concentrations is often inaccurate. This study considers the use of a fluidic pharmacokinetic profile generator where 28 different profile types were generated corresponding to a physiological model with varying sampling sites, administration locations, and fluid flow rates. Clearance was calculated using established equations, commercial software, and recently proposed models. The results show large differences in clearance values calculated with published equations and commercial software relative to the actual value of clearance. Alterations in sampling site, administration location, and fluid flow rates each influence the extent of calculation errors. The data show that a significant drug concentration gradient exists within the central circulatory system. The results show that the best way to address this issue would be to inject the drug at a peripheral location to allow for sufficient mixing and then sample from a large vein. Extrapolating for missing data can also lead to large errors in clearance calculation; this can be addressed by collecting more samples early after IV bolus administration or by collecting data during steady state conditions for an IV infusion.

Safety, pharmacokinetic and pharmacodynamic properties of single ascending dose and continuous infusion of remimazolam besylate in healthy Chinese volunteers

PURPOSE

The aim of the present study was to evaluate the safety, pharmacokinetic (PK) and pharmacodynamic (PD) properties of remimazolam besylate following single ascending dose (SAD) and continuous infusion in healthy Chinese volunteers.

METHODS

This was a randomized phase I study conducted in two parts. Part I was a double-blind, placebo- and midazolam-controlled, SAD study among healthy Chinese participants with a remimazolam dose of 0.025-0.4 mg/kg. Part II was an open-label, midazolam-controlled, continuous infusion study. Bispectral index (BIS) monitoring and Modified Observers Assessment of Alertness and Sedation (MOAA/S) score assessment were used to assess the PD properties.

RESULTS

The half-life range of remimazolam was from 34.1 ± 8.1 to 59.8 ± 20.5 min in the SAD study. The sedation function was initially observed at the dose of 0.05 mg/kg remimazolam. Doses of ≥ 0.075 mg/kg exerted a peak sedation effect within 1-2 min after injection, resulting in a deeper and more rapid sedation. In the 2 h continuous infusion, remimazolam showed a deeper sedation and more rapid recovery than midazolam. For general anesthesia, an induction dosage of 0.2 mg/kg/min and a maintenance dosage of 1 mg/kg/h can achieve a satisfactory efficacy effect.

CONCLUSIONS

Remimazolam was safe and well tolerated in healthy Chinese participants. Based on the phase I clinical study, we suggest that remimazolam besylate demonstrates greater sedation and quicker recovery from sedation than midazolam.

Revisiting a physiologically based pharmacokinetic model for cocaine with a forensic scope

A whole-body permeability-rate-limited physiologically based pharmacokinetic (PBPK) model for cocaine was developed and adjusted with the pharmacokinetic data from studies with animals and reparametrized scaling to humans with the aim to predict the concentration-time profiles of the drug in blood and different tissues in humans. Estimated time course concentrations could be used as an interpretation tool by forensic toxicologists. The model estimations were compared successfully with pharmacokinetic parameters and time to peak for some effects reported in the literature. Once developed, the PBPK model was employed to predict the time course tissue concentrations reported in previous distribution studies introducing individualizing data. The heart and brain concentrations estimated by the model match adequately with the time and duration of some effects such as chronotropic and psychoactive effects, respectively. This work is the first attempt for employing PBPK modeling as a tool for forensic interpretation. Future modeling of other cocaine metabolite profiles or interaction when co-administered with other substances, such as alcohol, might be developed in the future.

The pharmacokinetic determinants of the frequency and pattern of intravenous cocaine self-administration in rats by pharmacokinetic modeling

We investigated the pharmacokinetic determinants of the frequency of intravenous cocaine self-administration in 2.5-h sessions. Two groups of rats were implanted with dual catheters that permitted cocaine infusion and blood sampling via the femoral and jugular vein catheters, respectively. Half of the animals in each group self-administered one of the two cocaine unit doses (0.5 and 1 mg/kg/infusion) by pressing a lever under a continuous schedule of reinforcement. To monitor serum cocaine concentrations, the remaining animals received concurrent, response-independent infusions whenever the matched animals self-administered cocaine infusions. Multiple concentration-time data in two successive self-administrations were determined to monitor the extent of fluctuation in concentrations by pharmacokinetic modeling. Behavioral analyses revealed the higher unit dose (1 mg/kg) resulted in less frequent cocaine self-administration, and a longer interinfusion interval, whereas the total doses were similar for the two groups (24.5-27.0 mg/kg/2.5 h). Cocaine decayed biexponentially. Both the values of clearance and terminal elimination rate constant for the self-administration paradigm were significantly greater than those after the bolus cocaine dosing series (0.5 and 1 mg/kg, separated by 3 days). The regularity in cocaine self-administration produced relatively stable serum cocaine concentrations that oscillated between maximum (C(max)) and minimum (C(min)) values regardless of dose size and interinfusion interval. Although the C(max) for the 1-mg/kg unit dose (1.47 microg/ml) was significantly higher than that for the 0.5-mg/kg dose (0.82 microg/ml), the C(min) values between the groups approximated each other (0.28, and 0.34 microg/ml, respectively). Hence, the C(min) is the determinant of the initiation of the next drug-taking behavior.