Pharmacokinetics of mirtazapine and its main metabolites after single intravenous and oral administrations in rats at two dose rates

Nose to brain delivery of mirtazapine via lipid nanocapsules: Preparation, statistical optimization, radiolabeling, in vivo biodistribution and pharmacokinetic study

Mirtazapine (MZPc) is an antidepressant drug which is approved by the FDA. It has low bioavailability, which is only 50%, in spite of its rapid absorption when orally administered owing to high first-pass metabolism. This study was oriented towards delivering intranasal (IN) mirtazapine by a direct route to the brain by means of preparing lipid nanocapsules (LNCs) as a targeted drug delivery system. MZP-LNCs were constructed by solvent-free phase inversion temperature technique applying D-Optimal mixture design to study the impact of 3 formulation variables on the characterization of the formulated nanocapsules. Independent variables were percentage of Labrafac oil, percentage of Solutol and percentage of water. Dependent variables were particle size, polydispersity index (PDI), Zeta potential and solubilization capacity. Nanocapsules of the optimized formula loaded with MZP were of spherical shape as confirmed by transmission electron microscopy with particle diameter of 20.59 nm, zeta potential of - 5.71, PDI of 0.223 and solubilization capacity of 7.21 mg/g. The in vivo pharmacokinetic behavior of intranasal MZP-LNCs in brain and blood was correlated to MZP solution after intravenous (IV) and intranasal administration in mice. In vivo biodistribution of the drug in mice was assessed by a radiolabeling technique using radioiodinated mirtazapine (131I-MZP). Results showed that intranasal MZP-LNCs were able to deliver higher amount of MZP to the brain with less drug levels in blood when compared to the MZP solution after IV and IN administration. Moreover, the percentage of drug targeting efficiency (%DTE) of the optimized MZP-LNCs was 332.2 which indicated more effective brain targeting by the intranasal route. It also had a direct transport percentage (%DTP) of 90.68 that revealed a paramount contribution of the nose to brain pathway in the drug delivery to the brain.

Optimization of mirtazapine loaded into mesoporous silica nanostructures via Box-Behnken design: in-vitro characterization and in-vivo assessment

Employment of mesoporous silica nanostructures (MSNs) in the drug delivery field has shown a significant potential for improving the oral delivery of active pharmaceutical products with low solubility in water. Mirtazapine (MRT) is a tetracyclic antidepressant with poor water solubility (BCS Class II), which was recently approved as a potent drug used to treat severe depression. The principle of this research is to optimize the incorporation of Mirtazapine into MSNs to improve its aqueous solubility, loading efficiency, release performance, and subsequent bioavailability. The formulation was optimized by using of Box-Behnken Design, which allows simultaneous estimation of the impact of different types of silica (SBA-15, MCM-41, and Aluminate-MCM-41), a different drug to silica ratios (33.33%, 49.99%, and 66.66%), and different drug loading procedures (Incipient wetness, solvent evaporation, and solvent impregnation) on the MRT loading efficiency, aqueous solubility and dissolution rate. The optimized formula was achieved by loading MRT into SBA-15 at 33.33% drug ratio prepared by the incipient wetness method, which displayed a loading efficiency of 104.05%, water solubility of 0.2 mg/ml, and 100% dissolution rate after 30 min. The pharmacokinetic profile of the optimized formula was obtained by conducting the in-vivo study in rabbits which showed a marked improvement (2.14-fold) in oral bioavailability greater than plain MRT. The physicochemical parameters and morphology of the optimized formula were characterized by; gas adsorption manometry, scanning electron microscopy (SEM), polarized light microscopy (PLM), Fourier-transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRPD).

Effects of sedative psychotropic drugs combined with oxycodone on respiratory depression in the rat

Following a decision to require label warnings for concurrent use of opioids and benzodiazepines and increased risk of respiratory depression and death, the US Food and Drug Administratioin (FDA) recognized that other sedative psychotropic drugs may be substituted for benzodiazepines and be used concurrently with opioids. In some cases, data on the ability of these alternatives to depress respiration alone or in conjunction with an opioid are lacking. A nonclinical in vivo model was developed that could detect worsening respiratory depression when a benzodiazepine (diazepam) was used in combination with an opioid (oxycodone) compared to the opioid alone based on an increased arterial partial pressure of carbon dioxide (pCO2 ). The current study used that model to assess the impact on respiration of non-benzodiazepine sedative psychotropic drugs representative of different drug classes (clozapine, quetiapine, risperidone, zolpidem, trazodone, carisoprodol, cyclobenzaprine, mirtazapine, topiramate, paroxetine, duloxetine, ramelteon, and suvorexant) administered alone and with oxycodone. At clinically relevant exposures, paroxetine, trazodone, and quetiapine given with oxycodone significantly increased pCO2 above the oxycodone effect. Analyses indicated that most pCO2 interaction effects were due to pharmacokinetic interactions resulting in increased oxycodone exposure. Increased pCO2 recorded with oxycodone-paroxetine co-administration exceeded expected effects from only drug exposure suggesting another mechanism for the increased pharmacodynamic response. This study identified drug-drug interaction effects depressing respiration in an animal model when quetiapine or paroxetine were co-administered with oxycodone. Clinical pharmacodynamic drug interaction studies are being conducted with these drugs to assess translatability of these findings.

Metabolism and pharmacokinetics of pharmaceuticals in cats (Felix sylvestris catus) and implications for the risk assessment of feed additives and contaminants

In animal health risk assessment, hazard characterisation of feed additives has been often using the default uncertainty factor (UF) of 100 to translate a no-observed-adverse-effect level in test species (rat, mouse, dog, rabbit) to a 'safe' level of chronic exposure in farm and companion animal species. Historically, both 10-fold factors have been further divided to include chemical-specific data in both dimensions when available. For cats (Felis Sylvestris catus), an extra default UF of 5 is applied due to the species' deficiency in particularly glucuronidation and glycine conjugation. This paper aims to assess the scientific basis and validity of the UF for inter-species differences in kinetics (4.0) and the extra UF applied for cats through a comparison of kinetic parameters between rats and cats for 30 substrates of phase I and phase II metabolism. When the parent compound undergoes glucuronidation the default factor of 4.0 is exceeded, with exceptions for zidovudine and S-carprofen. Compounds that were mainly renally excreted did not exceed the 4.0-fold default. Mixed results were obtained for chemicals which are metabolised by CYP3A in rats. When chemicals were administered intravenously the 4.0-fold default was not exceeded with the exception of clomipramine, lidocaine and alfentanil. The differences seen after oral administration might be due to differences in first-pass metabolism and bioavailability. Further work is needed to further characterise phase I, phase II enzymes and transporters in cats to support the development of databases and in silico models to support hazard characterisation of chemicals particularly for feed additives.

Trait Sensitivity to Negative and Positive Feedback Does Not Interact With the Effects of Acute Antidepressant Treatment on Hedonic Status in Rats

Aberrant cognition plays a pivotal role in the development and maintenance of depression. One of the most important cognitive distortions associated with depression is aberrant sensitivity to performance feedback. Under clinical conditions, this sensitivity can be measured using the probabilistic reversal learning (PRL) test, which has also been recently implemented in animal studies. Although the evidence for the coexistence of depression and altered feedback sensitivity is relatively coherent, it is unclear whether this sensitivity can influence the effectiveness of antidepressant treatment. In the present research, we investigated how trait sensitivity to negative and positive feedback interacts with the effects of acute antidepressant treatment on hedonic status in rats. We tested a cohort of rats with a series of 10 PRL tests, and based on this screening, we classified each animal as sensitive or insensitive to negative and positive feedback. Subsequently, in the Latin square design, we evaluated the effects of a single administration of two antidepressant drugs (each at three different doses: agomelatine: 5, 10, and 40 mg/kg; mirtazapine 0.5, 1, and 3 mg/kg) on the hedonic status of rats in the sucrose preference tests. There was no statistically significant interaction between trait sensitivity to feedback and the effects of acute antidepressant treatment on hedonic status in rats.

The effect of mirtazapine on dopaminergic psychosis and dyskinesia in the parkinsonian marmoset

BACKGROUND

Parkinson's disease (PD) psychosis is encountered in as many as 50% of patients with advanced disease. Treatment options for PD psychosis are few. In fact, only clozapine and pimavanserin have shown efficacy in randomised controlled trials. Clinicians are often reluctant to prescribe the former, due to the risk of agranulocytosis, while the latter is not widely available yet. Because it is already clinically available and exhibits high affinity for serotonin 2A receptors, a target with which both clozapine and pimavanserin interact, we hypothesised that the anti-depressant mirtazapine might be effective to alleviate PD psychosis.

METHODS

Here, we tested the anti-psychotic potential of mirtazapine in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Five MPTP-lesioned marmosets exhibiting psychosis-like behaviours were administered L-3,4-dihydroxyphenylalanine (L-DOPA) in combination with mirtazapine (0.1, 1 and 10 mg/kg) or vehicle. We also tested the effect of mirtazapine on L-DOPA-induced dyskinesia.

RESULTS

The addition of mirtazapine 10 mg/kg to L-DOPA reduced psychosis-like behaviours by 50% (P < 0.05) and dyskinesia by 29% (P < 0.01), when compared to L-DOPA/vehicle. Importantly, the antipsychotic and antidyskinetic effects of mirtazapine were achieved without hindering L-DOPA anti-parkinsonian action.

CONCLUSIONS

Our results suggest that mirtazapine may be effective to alleviate PD psychosis and, because the drug is clinically available, clinical trials that would assess its anti-psychotic efficacy in PD could be rapidly undertaken, hopefully leading to a new treatment option for this debilitating condition.