Pharmacokinetic Comparison Between the Long-Term Anesthetized, Short-Term Anesthetized and Conscious Rat Models in Nasal Drug Delivery

The development and validation of an HPLC-MS/MS method for the determination of eriocitrin in rat plasma and its application to a pharmacokinetic study

Eriocitrin is one of the major active constituents of lemon fruit, and it possesses strong antioxidant, lipid-lowering, anticancer and anti-inflammatory activities and has long been used in food, beverages and wine.

Physiologically Based Modeling Approach to Predict Dopamine D2 Receptor Occupancy of Antipsychotics in Brain: Translation From Rat to Human

Receptor occupancy (RO) is a translational biomarker for assessing drug efficacy and safety. We aimed to apply a physiologically based pharmacokinetic (PBPK) modeling approach to predict the brain dopamine D2 RO time profiles of antipsychotics. Clozapine and risperidone were modeled together with their active metabolites, norclozapine and paliperidone, First, in PK‐Sim a rat PBPK model was developed and optimized using literature plasma PK data. Then, blood‐brain barrier parameters including the expression and efflux transport kinetics of P‐glycoprotein were optimized using literature microdialysis data on brain extracellular fluid (brainECF), which were further adapted when translating the rat PBPK model into the human PBPK model. Based on the simulated drug and metabolite concentrations in brainECF, drug‐D2 receptor binding kinetics (association and dissociation rates) were incorporated in MoBi to predict RO. From an extensive literature search, 32 plasma PK data sets (16 from rat and 16 from human studies) and 23 striatum RO data sets (13 from rat and 10 from human studies) were prepared and compared with the model predictions. The rat PBPK‐RO model adequately predicted the plasma concentrations of the parent drugs and metabolites and the RO levels. The human PBPK‐RO model also captured the plasma PK and RO levels despite the large interindividual and interstudy variability, although it tended to underestimate the plasma concentrations and RO measured at late time points after risperidone dosing. The developed human PBPK‐RO model was successfully applied to predict the plasma PK and RO changes observed after risperidone dose reduction in a clinical trial in schizophrenic patients.

Demonstration of Direct Nose-to-Brain Transport of Unbound HIV-1 Replication Inhibitor DB213 Via Intranasal Administration by Pharmacokinetic Modeling

Intranasal administration could be an attractive alternative route of administration for the delivery of drugs to the central nervous system (CNS). However, there are always doubts about the direct transport of therapeutics from nasal cavity to the CNS since there are only limited studies on the understanding of direct nose-to-brain transport. Therefore, this study aimed to (1) investigate the existence of nose-to-brain transport of intranasally administered HIV-1 replication inhibitor DB213 and (2) assess the direct nose-to-brain transport of unbound HIV-1 replication inhibitor DB213 quantitatively by a pharmacokinetic approach. Plasma samples were collected up to 6 h post-dosing after administration via intranasal or intravenous route at three bolus doses. In the brain-uptake study, the plasma, whole brain, and cerebrospinal fluid (CSF) were sampled between 15 min and 8 h post-dosing. All samples were analyzed with LC/MS/MS. Plasma, CSF, and brain concentration versus time profiles were analyzed with nonlinear mixed-effect modeling. Structural model building was performed by NONMEM (version VII, level 2.0). Intranasal administration showed better potential to deliver HIV-1 replication inhibitor DB213 to the brain with 290-fold higher brain to plasma ratio compared with intravenous administration. Based on that, a model with two absorption compartments (nose-to-systemic circulation and nose-to-brain) was developed and demonstrated 72.4% of total absorbed unbound HIV-1 replication inhibitor DB213 after intranasal administration was transported directly into the brain through nose-to-brain pathway.

Development of a population pharmacokinetic model to predict brain distribution and dopamine D2 receptor occupancy of raclopride in non-anesthetized rat

BACKGROUND

Raclopride is a selective antagonist of the dopamine D2 receptor. It is one of the most frequently used in vivo D2 tracers (at low doses) for assessing drug-induced receptor occupancy (RO) in animals and humans. It is also commonly used as a pharmacological blocker (at high doses) to occupy the available D2 receptors and antagonize the action of dopamine or drugs on D2 in preclinical studies. The aims of this study were to comprehensively evaluate its pharmacokinetic (PK) profiles in different brain compartments and to establish a PK-RO model that could predict the brain distribution and RO of raclopride in the freely moving rat using a LC-MS based approach.

METHODS

Rats (n=24) received a 10-min IV infusion of non-radiolabeled raclopride (1.61μmol/kg, i.e. 0.56mg/kg). Plasma and the brain tissues of striatum (with high density of D2 receptors) and cerebellum (with negligible amount of D2 receptors) were collected. Additional microdialysis experiments were performed in some rats (n=7) to measure the free drug concentration in the extracellular fluid of the striatum and cerebellum. Raclopride concentrations in all samples were analyzed by LC-MS. A population PK-RO model was constructed in NONMEM to describe the concentration-time profiles in the unbound plasma, brain extracellular fluid and brain tissue compartments and to estimate the RO based on raclopride-D2 receptor binding kinetics.

RESULTS

In plasma raclopride showed a rapid distribution phase followed by a slower elimination phase. The striatum tissue concentrations were consistently higher than that of cerebellum tissue throughout the whole experimental period (10-h) due to higher non-specific tissue binding and D2 receptor binding in the striatum. Model-based simulations accurately predicted the literature data on rat plasma PK, brain tissue PK and D2 RO at different time points after intravenous or subcutaneous administration of raclopride at tracer dose (RO <10%), sub-pharmacological dose (RO 10%-30%) and pharmacological dose (RO >30%).

CONCLUSION

For the first time a predictive model that could describe the quantitative in vivo relationship between dose, PK and D2 RO of raclopride in non-anesthetized rat was established. The PK-RO model could facilitate the selection of optimal dose and dosing time when raclopride is used as tracer or as pharmacological blocker in various rat studies. The LC-MS based approach, which doses and quantifies a non-radiolabeled tracer, could be useful in evaluating the systemic disposition and brain kinetics of tracers.

Intranasal delivery of antipsychotic drugs

Antipsychotic drugs are used to treat psychotic disorders that afflict millions globally and cause tremendous emotional, economic and healthcare burdens. However, the potential of intranasal delivery to improve brain-specific targeting remains unrealized. In this article, we review the mechanisms and methods used for brain targeting via the intranasal (IN) route as well as the potential advantages of improving this type of delivery. We extensively review experimental studies relevant to intranasal delivery of therapeutic agents for the treatment of psychosis and mental illnesses. We also review clinical studies in which intranasal delivery of peptides, like oxytocin (7 studies) and desmopressin (1), were used as an adjuvant to antipsychotic treatment with promising results. Experimental animal studies (17) investigating intranasal delivery of mainstream antipsychotic drugs have revealed successful targeting to the brain as suggested by pharmacokinetic parameters and behavioral effects. To improve delivery to the brain, nanotechnology-based carriers like nanoparticles and nanoemulsions have been used in several studies. However, human studies assessing intranasal delivery of mainstream antipsychotic drugs are lacking, and the potential toxicity of nanoformulations used in animal studies has not been explored. A brief discussion of future directions anticipates that if limitations of low aqueous solubility of antipsychotic drugs can be overcome and non-toxic formulations used, IN delivery (particularly targeting specific tissues within the brain) will gain more importance moving forward given the inherent benefits of IN delivery in comparison to other methods.

The Role of Inhaled Loxapine in the Treatment of Acute Agitation in Patients with Psychiatric Disorders: A Clinical Review

Loxapine is a first generation antipsychotic, belonging to the dibenzoxazepine class. Recently, loxapine has been reformulated at a lower dose, producing an inhaled powder that can be directly administered to the lungs to treat the agitation associated with psychiatric disorders, such as schizophrenia and bipolar disorder. Thus, the aim of this narrative and clinical mini-review was to evaluate the efficacy and tolerability of inhaled loxapine in the treatment of acute agitation in patients with psychiatric disorders. The efficacy of inhaled loxapine has been evaluated in one Phase II trial on patients with schizophrenia, and in two Phase III trials in patients with schizophrenia and bipolar disorder. Moreover, there are two published case series on patients with borderline personality disorder and dual diagnosis patients. Inhaled loxapine has proven to be effective and generally well tolerated when administered to agitated patients with schizophrenia and bipolar disorder. Two case series have suggested that inhaled loxapine may also be useful to treat agitation in patients with borderline personality disorder and with dual diagnosis, but further studies are needed to clarify this point. However, the administration of inhaled loxapine requires at least some kind of patient collaboration, and is not recommended in the treatment of severe agitation in totally uncooperative patients. Moreover, the drug-related risk of bronchospasm must always be kept in mind when planning to use inhaled loxapine, leading to a careful patient assessment prior to, and after, administration. Also, the higher costs of inhaled loxapine, when compared to oral and intramuscular medications, should be taken into account when selecting it for the treatment of agitation.

Distribution of α-asarone in brain following three different routes of administration in rats

The goal of the present paper is to compare the distributions of α-asarone administered to rats through three different routes: oral, intravenous and intranasal. The concentrations of α-asarone in seven distinct brain regions, the olfactory bulb, cerebellum, hypothalamus, frontal cortex, striatum, hippocampus and medulla/pons as well as in plasma and cerebrospinal fluid (CSF), were determined by HPLC. The quantities of α-asarone accumulated in liver were measured to determine whether α-asarone could generate hepatotoxicity when administered via the three different routes. The results indicated that α-asarone could be absorbed via two different routes into the brain, after intranasal administration of dry powders. In the systemic route, α-asarone immediately entered the brain through the blood-brain barrier (BBB) after uptake into the circulatory system. In the olfactory bulb route, α-asarone traveled from the olfactory epithelium in the nasal cavity straight into brain tissue via the olfactory bulb. Furthermore, intranasal administration of α-asarone as a dry powder can ensure quick absorption and avoid excessive concentrations in the blood and liver, while achieving concentrations in the brain comparable to those attained by intravenous and oral administration routes.