The pharmacokinetics and bioavailability of prochlorperazine delivered as a thermally generated aerosol in a single breath to volunteers

Urinary Clearance of 11-Nor-9-Carboxy-Δ9 -Tetrahydrocannabinol (THCCOOH): A Detailed Pharmacokinetic Analysis

BACKGROUND

Urine is a common matrix for screening for cannabis use. Urine assays typically measure total THCCOOH concentrations after hydrolysis cleaves the glucuronide. Urine THCCOOH concentration is adjusted by urine creatinine concentration or specific gravity, to account for variable hydration states. Therefore, we performed a population pharmacokinetic analysis of the urinary THCCOOH excretion, urinary flow rate, and creatinine excretion rate data.

METHODS

Urine was obtained over 168 hours from 6 subjects who smoked low (15.8 mg) and high dose (33.8 mg) THC cigarettes on two occasions. Samples were analyzed for THCCOOH concentration by GC/MS and volume, time and creatinine concentration measured. A population pharmacokinetic model of the urinary clearance of THCCOOH was created from these data and potential covariates of urine creatinine concentration and urine creatinine excretion rate were assessed.

RESULTS

Elimination clearance of THCCOOH was estimated as 0.104 ± 0.088 L/min and its urinary clearance was 0.0022 ± 0.0015 L/min. Total urine excretion of THCCOOH was estimated a 2.3%. Urine flow rate and urine creatinine concentrations were significantly correlated, r² 0.35. Creatinine excretion rate was 129.6 ± 71.0 mL/min and the intra-subject variability was 31-52% (SD%) during the week. Urinary creatinine excretion rate was a significant covariate for the urinary clearance of THCCOOH.

CONCLUSIONS

Creatinine Clearance is a significant covariate for urinary THCCOOH clearance. Only 2-3% of bioavailable THC is excreted as THCCOOH and THCCOO-glucuronide via the urine. Correction of urine drug and/or metabolite concentration with urine creatinine concentration or specific gravity may be more problematic than previously appreciated.

Using Population Pharmacokinetic Modeling to Estimate Exposure to Δ9-Tetrahydrocannabinol in an Observational Study of Cannabis Smokers in Colorado

BACKGROUND

Self-report questionnaires, weighing products consumed, and Δ9-tetrahydrocannabinol (THC) biomarkers are established techniques for estimating cannabis exposure. Population pharmacokinetic modeling of plasma THC and metabolite concentrations by incorporating self-reported and weighed products as covariates could improve estimates of THC exposure in regular cannabis users.

METHODS

In this naturalistic study, blood samples were obtained from 36 regular smokers of cannabis for analysis of THC and its 2 metabolites at 4 time points: recruitment and during an experimental mobile laboratory assessment that included 3 time points: before, immediately after, and 1 hour after ad libitum legal market flower use. These data were analyzed using an established model of population pharmacokinetics developed from laboratory-controlled cannabis administration data. Elimination and metabolite production clearances were estimated for each subject as well as their daily THC doses and the dose consumed during the ad libitum event.

RESULTS

A statistically significant correlation existed between the daily THC dose estimated by self-report questionnaire and population pharmacokinetic modeling (correlation coefficient = 0.79, P < 0.05) between the weighed cannabis smoked ad libitum and that estimated by population pharmacokinetic modeling (correlation coefficient = 0.71, P < 0.05).

CONCLUSION

Inclusion of self-reported questionnaire data of THC consumption improved pharmacokinetic model-derived estimates based on measured THC and metabolite concentrations. In addition, the pharmacokinetic-derived dose estimates for the ad libitum smoking event underestimated the THC consumption compared with the weighed amount smoked. Thus, the subjects in this study, who smoked ad libitum and used cannabis products with high concentrations of THC, were less efficient (lower bioavailability) compared with computer-paced smokers of low potency, NIDA cannabis in a laboratory setting.

Drivers of absolute systemic bioavailability after oral pulmonary inhalation in humans

There are few studies in humans dealing with the relationship between physico-chemical properties of drugs and their systemic bioavailability after administration via oral inhalation route (Fpulm). Getting further insight in the determinants of Fpulm after oral pulmonary inhalation could be of value for drugs considered for a systemic delivery as a result of poor oral bioavailability, as well as for drugs considered for a local delivery to anticipate their undesirable systemic effects. To better delineate the parameters influencing the systemic delivery after oral pulmonary inhalation in humans, we studied the influence of physico-chemical and permeability properties obtained in silico on the rate and extent of Fpulm in a series of 77 compounds with or without marketing approval for pulmonary delivery, and intended either for local or for systemic delivery. Principal component analysis (PCA) showed mainly that Fpulm was positively correlated with Papp and negatively correlated with %TPSA, without a significant influence of solubility and ionization fraction, and no apparent link with lipophilicity and drug size parameters. As a result of the small sample set, the performance of the different models as predictive of Fpulm were quite average with random forest algorithm displaying the best performance. As a whole, the different models captured between 50 and 60% of the variability with a prediction error of less than 20%. Tmax data suggested a significant positive influence of lipophilicity on absorption rate while charge apparently had no influence. A significant linear relationship between Cmax and dose (R² = "0.79) highlighted that Cmax was primarily dependent on dose and absorption rate and could be used to estimate Cmax in humans for new inhaled drugs.

Population pharmacokinetic modeling of plasma Δ9-tetrahydrocannabinol and an active and inactive metabolite following controlled smoked cannabis administration

AIMS

Population pharmacokinetic models of Δ9-tetrahydrocannabinol (THC) have been developed for THC plasma and blood concentration data. Often, only the metabolites of THC are measurable when blood samples are obtained. Therefore, we performed a population pharmacokinetic analysis of THC, 11-OH-THC and THCCOOH plasma concentration data from a Phase I clinical trial of THC smoking.

METHODS

Frequently obtained plasma THC, 11-OH-THC and THCCOOH concentration data were obtained over 168 h from 6 subjects who smoked low (15.8 mg) and high dose (33.8 mg) THC cigarettes on 2 occasions. Bayesian estimates of the THC pharmacokinetic model from each individual for each dose were fixed prior to the sequential pharmacokinetic analysis of the metabolites.

RESULTS

A 3-compartment model of THC was developed that has a steady-state volume of distribution (Vd_SS ) of 3401 ± 788 L and a clearance of 0.72 ± 0.10 L/min. 11-OH-THC was characterized by 50 ± 6% of the THC being directly cleared to a 3-compartment model with a Vd_SS of 415.2 ± 4.3 L and clearance of 0.78 ± 0.05 L/min. The THCCOOH model shared the central compartment of the 11-OH-THC model with a Vd_SS of 29.1 ± 0.05 L and a clearance of 0.12 ± 0.02 L/min. First order kinetics were observed for THC and THCCOOH between the low and high doses, but a nonlinear pattern was observed for 11-OH-THC.

CONCLUSION

We describe the pharmacokinetics of THC, 11-OH-THC and THCCOOH including inter- and intraindividual variability of the parameter estimates of the model.

Combined Recirculatory-compartmental Population Pharmacokinetic Modeling of Arterial and Venous Plasma S(+) and R(–) Ketamine Concentrations

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

The pharmacokinetics of infused drugs have been modeled without regard for recirculatory or mixing kinetics. We used a unique ketamine dataset with simultaneous arterial and venous blood sampling, during and after separate S(+) and R(–) ketamine infusions, to develop a simplified recirculatory model of arterial and venous plasma drug concentrations.

Methods

S(+) or R(–) ketamine was infused over 30 min on two occasions to 10 healthy male volunteers. Frequent, simultaneous arterial and forearm venous blood samples were obtained for up to 11 h. A multicompartmental pharmacokinetic model with front-end arterial mixing and venous blood components was developed using nonlinear mixed effects analyses.

Results

A three-compartment base pharmacokinetic model with additional arterial mixing and arm venous compartments and with shared S(+)/R(–) distribution kinetics proved superior to standard compartmental modeling approaches. Total pharmacokinetic flow was estimated to be 7.59 ± 0.36 l/min (mean ± standard error of the estimate), and S(+) and R(–) elimination clearances were 1.23 ± 0.04 and 1.06 ± 0.03 l/min, respectively. The arm-tissue link rate constant was 0.18 ± 0.01 min–1, and the fraction of arm blood flow estimated to exchange with arm tissue was 0.04 ± 0.01.

Conclusions

Arterial drug concentrations measured during drug infusion have two kinetically distinct components: partially or lung-mixed drug and fully mixed-recirculated drug. Front-end kinetics suggest the partially mixed concentration is proportional to the ratio of infusion rate and total pharmacokinetic flow. This simplified modeling approach could lead to more generalizable models for target-controlled infusions and improved methods for analyzing pharmacokinetic-pharmacodynamic data.

Precision therapeutic targeting of human cancer cell motility

Increased cancer cell motility constitutes a root cause of end organ destruction and mortality, but its complex regulation represents a barrier to precision targeting. We use the unique characteristics of small molecules to probe and selectively modulate cell motility. By coupling efficient chemical synthesis routes to multiple upfront in parallel phenotypic screens, we identify that KBU2046 inhibits cell motility and cell invasion in vitro. Across three different murine models of human prostate and breast cancer, KBU2046 inhibits metastasis, decreases bone destruction, and prolongs survival at nanomolar blood concentrations after oral administration. Comprehensive molecular, cellular and systemic-level assays all support a high level of selectivity. KBU2046 binds chaperone heterocomplexes, selectively alters binding of client proteins that regulate motility, and lacks all the hallmarks of classical chaperone inhibitors, including toxicity. We identify a unique cell motility regulatory mechanism and synthesize a targeted therapeutic, providing a platform to pursue studies in humans.

In this study, the authors identify and validate a halogen-substituted isoflavanone able to inhibit prostate cancer cell motility, invasion and metastasis in vitro and in vivo. They demonstrate its ability to selectively inhibit activation of client proteins that stimulate cell motility.

Pharmacokinetics and Bioavailability of Inhaled Esketamine in Healthy Volunteers

BACKGROUND

Esketamine is traditionally administered via intravenous or intramuscular routes. In this study we developed a pharmacokinetic model of inhalation of nebulized esketamine with special emphasis on pulmonary absorption and bioavailability.

METHODS

Three increasing doses of inhaled esketamine (dose escalation from 25 to 100 mg) were applied followed by a single intravenous dose (20 mg) in 19 healthy volunteers using a nebulizer system and arterial concentrations of esketamine and esnorketamine were obtained. A multicompartmental pharmacokinetic model was developed using population nonlinear mixed-effects analyses.

RESULTS

The pharmacokinetic model consisted of three esketamine, two esnorketamine disposition and three metabolism compartments. The inhalation data were best described by adding two absorption pathways, an immediate and a slower pathway, with rate constant 0.05 ± 0.01 min (median ± SE of the estimate). The amount of esketamine inhaled was reduced due to dose-independent and dose-dependent reduced bioavailability. The former was 70% ± 5%, and the latter was described by a sigmoid EMAX model characterized by the plasma concentration at which absorption was impaired by 50% (406 ± 46 ng/ml). Over the concentration range tested, up to 50% of inhaled esketamine is lost due to the reduced dose-independent and dose-dependent bioavailability.

CONCLUSIONS

We successfully modeled the inhalation of nebulized esketamine in healthy volunteers. Nebulized esketamine is inhaled with a substantial reduction in bioavailability. Although the reduction in dose-independent bioavailability is best explained by retention of drug and particle exhalation, the reduction in dose-dependent bioavailability is probably due to sedation-related loss of drug into the air.

Pharmacometric Models for Characterizing the Pharmacokinetics of Orally Inhaled Drugs

During the last decades, the importance of modeling and simulation in clinical drug development, with the goal to qualitatively and quantitatively assess and understand mechanisms of pharmacokinetic processes, has strongly increased. However, this increase could not equally be observed for orally inhaled drugs. The objectives of this review are to understand the reasons for this gap and to demonstrate the opportunities that mathematical modeling of pharmacokinetics of orally inhaled drugs offers. To achieve these objectives, this review (i) discusses pulmonary physiological processes and their impact on the pharmacokinetics after drug inhalation, (ii) provides a comprehensive overview of published pharmacokinetic models, (iii) categorizes these models into physiologically based pharmacokinetic (PBPK) and (clinical data-derived) empirical models, (iv) explores both their (mechanistic) plausibility, and (v) addresses critical aspects of different pharmacometric approaches pertinent for drug inhalation. In summary, pulmonary deposition, dissolution, and absorption are highly complex processes and may represent the major challenge for modeling and simulation of PK after oral drug inhalation. Challenges in relating systemic pharmacokinetics with pulmonary efficacy may be another factor contributing to the limited number of existing pharmacokinetic models for orally inhaled drugs. Investigations comprising in vitro experiments, clinical studies, and more sophisticated mathematical approaches are considered to be necessary for elucidating these highly complex pulmonary processes. With this additional knowledge, the PBPK approach might gain additional attractiveness. Currently, (semi-)mechanistic modeling offers an alternative to generate and investigate hypotheses and to more mechanistically understand the pulmonary and systemic pharmacokinetics after oral drug inhalation including the impact of pulmonary diseases.

Inhaled vs. oral alprazolam: subjective, behavioral and cognitive effects, and modestly increased abuse potential

RATIONALE

Infrahuman and human studies suggest that a determinant of the abuse potential of a drug is rate of onset of subjective effects.

OBJECTIVES

This study sought to determine if the rate of onset of subjective effects and abuse potential of alprazolam would be increased when administered via inhalation vs. the oral route.

METHODS

Placebo, inhaled alprazolam (0.5, 1, and 2 mg), and oral alprazolam (1, 2, and 4 mg) were administered under double-blind, double-dummy conditions using a crossover design in 14 healthy participants with histories of drug abuse. Participant and observer ratings and behavioral and cognitive performance measures were assessed repeatedly during 9-h sessions.

RESULTS

Both routes of administration produced orderly dose and time-related effects, with higher doses producing greater and longer-lasting effects. Onset of subjective effects following inhaled alprazolam was very rapid (e.g., 2 vs. 49 min after 2 mg inhaled vs. oral). On measures of abuse potential (e.g., liking and good effects), inhaled alprazolam was more potent, as evidenced by a leftward shift in the dose-response curve. Despite the potency difference, at the highest doses, peak ratings of subjective effects related to abuse potential (e.g., "drug liking") were similar across the two routes. On other measures (e.g., sedation and performance), the routes were equipotent.

CONCLUSIONS

The inhaled route of administration modestly increased the abuse potential of alprazolam despite significantly increasing its rate of onset. If marketed, the reduced availability and increased cost of inhaled alprazolam may render the societal risk of increased abuse to be low.

The pharmacokinetics and pharmacodynamics of zaleplon delivered as a thermally generated aerosol in a single breath to volunteers

Pharmacokinetics, pharmacodynamics, safety, and tolerability of inhaled zaleplon were assessed in healthy volunteers. Forty participants received 0.5, 1, 2, or 4 mg zaleplon or placebo as a thermally generated aerosol in a randomized, double-blind, parallel-group, dose escalation study. Blood was collected up to 24 hours after dosing, and sedation was assessed up to 8 hours. Following inhalation, the observed median time to maximum plasma concentrations (25%, 75%) was 1.89 (1.45, 3.08) minutes and the mean (SD) elimination half-life was 1.24 (0.24) hours. The equilibration half-life for sedation (t(1/2) k(e0) ) was 1.16 (0.62, 2.17) minutes. The zaleplon AUC was dose proportional across doses, with a slope (90% confidence interval) of log-AUC versus log-dose of 0.92 (0.82, 1.02). No clinically significant changes were noted in laboratory values, vital signs, or spirometry. The most common adverse events were dizziness, somnolence, euphoria, headache, and visual disturbance. Zaleplon inhalation represents a safe, well-tolerated means of rapidly achieving effective plasma concentrations.

Inhaled fentanyl aerosol in healthy volunteers: pharmacokinetics and pharmacodynamics

BACKGROUND

Rapid delivery of potent opioid to the systemic circulation is an important feature for the effective treatment of acute and acute-on-chronic breakthrough pain. The delivery of different opioids by the pulmonary route has been inconsistent, usually resulting in low bioavailability of the drug. Staccato® Fentanyl for Inhalation is a handheld inhaler producing a single metered dose of aerosolized fentanyl during a single inspiration. The aerosol is of high purity (≥98%) at a particle size (1 to 3.5 microns) shown to be best for pulmonary absorption.

METHODS

We conducted the study in healthy volunteers in 2 stages. In the crossover stage, 10 subjects received IV fentanyl 25 µg and inhaled fentanyl 25 µg on separate occasions. The dose escalation stage was a multidose, randomized, double-blind, placebo-controlled, single-period dose escalation study of inhaled fentanyl (50 to 300 µg). Serial blood sampling was performed over an 8-hour period after drug administration to determine the pharmacokinetic profile, and serial pupillometry was performed as a measure of pharmacodynamic effect.

RESULTS

In the crossover stage the pharmacokinetic profiles of the inhaled and IV fentanyl showed similar peak arterial concentrations and areas under the curve. The time to maximum concentration was slightly shorter for the inhaled than IV fentanyl, 20.5 and 31.5 seconds, respectively. In the dose escalation stage the administration of repeated doses resulted in predictable, dose-dependent serum concentrations.

CONCLUSIONS

This study has demonstrated that the pharmacokinetic profile of single doses of inhaled fentanyl is comparable to IV administration.

Consistency of dosing with a thermal aerosol generation system: in vitro and in vivo correlation

Dosing consistency and reproducibility are presented for a novel pharmaceutical inhaler technology based on a thermal condensation process. Two different device platforms producing thermally generated aerosols have been created and used in clinical studies with a number of different drug compounds. Because this approach does not rely on energy from the user to disperse the aerosol particles, aerosol production is reliable, reproducible and virtually user independent following actuation. Pharmacokinetic data from multiple clinical studies show rapid absorption, dose proportionality, and concentration levels and variability similar to intravenous injection. In addition, products used in clinical trials show excellent subject consistency with the vast majority of devices delivering greater than 90% of the loaded dose and little drug exhaled.

Pulmonary delivery of therapeutic compounds for treating CNS disorders

Delivering therapeutic compounds via the lungs presents potential advantages relative to other routes of administration. Depending on the compound and the disease state, these advantages may include: non-invasive medication delivery, ease of administration, higher bioavailability leading to dose sparing and lower systemic toxicity, potentially greater blood–brain barrier penetration and rapid pharmacodynamic effect. The practice of inhaling drugs has been around for centuries, including both medical and recreational usage. It is only more recently that formal clinical development programs have been undertaken specifically to use medication delivery via the lung to achieve systemic blood levels for the treatment of CNS disorders. At present, there are several CNS therapies being developed for pulmonary administration, with some of those programs at or near the marketing authorization stage. While there are still regulatory hurdles before these therapies can be put into practice, the success of these programs thus far demonstrates the scientific viability of inhalation therapies for treating CNS disorders.

In vitro aerosol deposition in the oropharyngeal region for Staccato loxapine

BACKGROUND

The Staccato system employs a thermal vaporization technology to generate pure drug aerosols with a particle size optimized for alveolar deposition, leading to rapid absorption of the drug into the systemic circulation. Unlike most traditional aerosol-generation techniques, the particle size of the thermally generated aerosols is significantly affected by the airflow rate going through the device. The objective of this study was to determine the effects of flow rate and other operating conditions on predicted oropharyngeal and lung deposition when using the Staccato system.

METHODS

In vitro oropharyngeal deposition was measured at airflow rates of 15-80 L/min through the device. Oropharyngeal deposition was also measured for different inhalation profiles, different ambient temperatures and humidities, and device orientations. Deposition was measured using the Alberta geometry model, which was derived based on information available in the literature, CT scans of patients, and observations of living subjects.

RESULTS AND CONCLUSIONS

Deposition in the oropharyngeal geometry was consistently approximately 11% of the emitted dose throughout the entire range of flow rates. Such consistency in deposition was due to the fact that mass median aerodynamic diameter (MMAD) varied inversely as the square root of the flow rate, resulting in an approximately constant value for the inertial deposition parameter. Thus, an increase in flow rate, which would increase the momentum of a fixed particle size and generally lead to higher oropharyngeal deposition, was almost exactly counterbalanced by the accompanying decrease in MMAD. Results also showed that deposition in the oropharyngeal region was unaffected by other potentially relevant factors such as different airflow ramp rates, inhalation time, ambient temperature and relative humidity, and device orientations.