Elucidation of Degradation Behavior of Tricyclic Antidepressant Amoxapine in Artificial Gastric Juice.

The degradation behavior of eight tricyclic antidepressants (TCAs; amitriptyline, amoxapine (AMX), imipramine, clomipramine, desipramine, doxepin, dothiepin, and nortriptyline) in artificial gastric juice was investigated to estimate their pharmacokinetics in the stomach. As a result, among the eight TCAs, only AMX was degraded in artificial gastric juice. The degradation was a pseudo first-order reaction; activation energy (Ea) was 88.70 kJ/mol and activation entropy (ΔS) was -80.73 J/K·mol. On the other hand, the recovery experiment revealed that the degradation product did not revert to AMX and accordingly, this reaction was considered to be irreversible. In the AMX degradation experiment, peaks considered to be degradation products A (I) and B (II) were detected at retention times of around 3 min and 30 min in LC/UV measurements, respectively. Structural analysis revealed that compound (I) was [2-(2-aminophenoxy)-5-chlorophenyl]-piperazin-1-yl-methanone, a new compound, and compound (II) was 2-chlorodibenzo[b,f][1,4]oxazepin-11(10H)-one. As for the degradation behavior, it was estimated that AMX was degraded into (II) via (I), i.e., (II) was the final product. The results are expected to be useful in clinical chemistry and forensic science, including the estimation of drugs to be used at the time of judicial dissection and suspected drug addiction.

Amoxapine Demonstrates Incomplete Inhibition of ß-Glucuronidase Activity from Human Gut Microbiota.

Amoxapine has been demonstrated to be a potent inhibitor of Escherichia coli ß-glucuronidase. This study aims to explore the factors causing unsatisfactory efficacy of amoxapine in alleviating CPT-11-induced gastrointestinal toxicity in mice and to predict the outcomes in humans. Amoxapine (100 µM) exhibited poor and varied inhibition on ß-glucuronidase activity in gut microbiota from 10 healthy individuals and their pool (pool, 11.9%; individuals, 3.6%-54.4%) with IC50 >100 µM and potent inhibition toward E. coli ß-glucuronidase (IC50 = 0.34 µM). p-Nitrophenol formation from p-nitrophenyl-ß-D-glucuronide by pooled and individual gut microbiota fitted classical Michaelis-Menten kinetics, showing similar affinity (Km = 113-189 µM) but varied catalytic capability (Vmax = 53-556 nmol/h/mg). Interestingly, amoxapine showed distinct inhibitory effects (8.7%-100%) toward ß-glucuronidases of 13 bacterial isolates (including four Enterococcus, three Streptococcus, two Escherichia, and two Staphylococcus strains; gus genes belonging to OTU1, 2 or 21) regardless of their genetic similarity or bacterial origin. In addition, amoxapine inhibited the growth of pooled and individual gut microbiota at a high concentration (6.3%-30.8%, 200 µM). Taken together, these findings partly explain the unsatisfactory efficacy of amoxapine in alleviating CPT-11-induced toxicity and predict a poor outcome of ß-glucuronidase inhibition in humans, highlighting the necessity of using a human gut microbiota community for drug screening.

NEW METHODOLOGY FOR DEVELOPMENT OF ORODISPERSIBLE TABLETS USING HIGH-SHEAR GRANULATION PROCESS.

Development of orodispersible delivery system of high mechanical properties and low disintegration time is a big challenge. The aim of the current work was to assess and optimize the high shear granulation process as a new methodology for development of orodispersible tablets of high quality attributes using design of experiment approach. A two factor, three levels (32), full factorial design was carried out to investigate the main and interaction effects of independent variables, water amount (XI) and granulation time (X2) on the characteristics of granules and final product, tablet. The produced granules were analyzed for their granule size, density and flowability. Furthermore, the produced tablets were tested for: weight variation, breaking force/ crushing strength, friability, disintegration time and drug dissolution. Regression analysis results of multiple linear models showed a high correlation between the adjusted R-squared and predicted R-squared for all granules and tablets characteristics, the difference is less than 0.2. All dependent responses of granules and tablets were found to be impacted significantly (p < 0.05) by the two independent variables. However, water amount demonstrated the most dominant effect for all granules and tablet characteristics as shown by higher its coefficient estimate for all selected responses. Numerical optimization using desirability function was performed to optimize the variables under study to provide orodispersible system within the USP limit with respect of mechanical properties and disintegration time. It was found that the higher desirability (0.915) could be attained at the low level pf water (180 g) and short granulation time (1.65 min). Eventually, this study provides the formulator with helpful information in selecting the proper level of water and granulation time to provide an orodispersible system of high crushing strength and very low disintegration time, when high shear granulation methodology was used as a method of manufacture.

Old drug new use--amoxapine and its metabolites as potent bacterial ß-glucuronidase inhibitors for alleviating cancer drug toxicity.

PURPOSE: Irinotecan (CPT-11) induced diarrhea occurs frequently in patients with cancer and limits its usage. Bacteria ß-glucuronidase (GUS) enzymes in intestines convert the nontoxic metabolite of CPT-11, SN-38G, to toxic SN-38, and finally lead to damage of intestinal epithelial cells and diarrhea. We previously reported amoxapine as a potent GUS inhibitor in vitro. To further understand the molecular mechanism of amoxapine and its potential for treatment of CPT-11-induced diarrhea, we studied the binding modes of amoxapine and its metabolites by docking and molecular dynamics simulation, and tested the in vivo efficacy on mice in combination with CPT-11. EXPERIMENTAL DESIGN: The binding of amoxapine, its metabolites, 7-hydroxyamoxapine and 8-hydroxyamoxapine, and a control drug loxapine with GUS was explored by computational protocols. The in vitro potencies of metabolites were measured by Escherichia coli GUS enzyme and cell-based assay. Low-dosage daily oral administration was designed to use along with CPT-11 to treat tumor-bearing mice. RESULTS: Computational modeling results indicated that amoxapine and its metabolites bound in the active site of GUS and satisfied critical pharmacophore features: aromatic features near bacterial loop residue F365' and hydrogen bond toward E413. Amoxapine and its metabolites were demonstrated as potent in vitro. Administration of low dosages of amoxapine with CPT-11 in mice achieved significant suppression of diarrhea and reduced tumor growth. CONCLUSIONS: Amoxapine has great clinical potential to be rapidly translated to human subjects for irinotecan-induced diarrhea.

Evaluation of the interaction between ß-cyclodextrin and psychotropic drugs by surface plasmon resonance assay with a Biacore ® system.

Phase-solubility studies have been used to evaluate the solubilizing effects of cyclodextrins (CDs) on lipophilic, water-insoluble drugs. However, large amounts of CDs and drugs are required to measure solubility by phase-solubility studies. Thus, more efficient approaches to evaluate the interaction of CDs with drugs are needed. Herein we introduce a method that evaluates the interaction between immobilized ß-cyclodextrin and psychotropic drugs by surface plasmon resonance assay with a Biacore(®) system. Association constants and stoichiometries observed were generally consistent with values calculated by traditional methods, such as phase-solubility and continuous variation methods. Results showed that the analytical method using Biacore(®) was suitable to evaluate CD-drug interactions.