Design, synthesis and performance evaluation of mPEG-PR: A novel non-absorbable marker

The development of a novel simultaneous in vitro dissolution - in situ perfusion system as a potential tool for studying the absorption of solid oral formulation in rat

The aim of this work is to develop a novel simultaneous in vitro dissolution - in situ perfusion system (SDPS) as a potential tool to evaluate the in vivo performance of solid oral formulation in rat. The innovative nitrendipine (NTD) tablet of Bayotensin mite® made in Germany was used as reference listed drug (RLD), and five generic products from Chinese market were compared with RLD using the in vitro dissolution test method specified by the orange book and the SDPS method developed in this study. Four self-prepared NTD tablets with different proportions of microcrystalline cellulose/starch were employed to investigate the discriminatory ability of the SDPS for formulation. In addition, the predictivity of the SDPS in relation to data from in vivo pharmaceutics studies was evaluated. The 45-min dissolution test and multiple-pH dissolution profiles of generic product 1 and 2 have no difference compared with the RLD, but their dissolution profiles from the SDPS showed statistically significant differences. A biexponential formula successfully described the concentration profiles of self-prepared formulations in SDPS experiments. The kdis (0.08 ± 0.01 ∼ 0.2 ± 0.03 min-1) and ka (about 2.30 × 10-3 min-1) values calculated by the formulas of F1-F3 suggested that the used excipients had no effect on the intestinal absorption of NTD, and it might be the property of active pharmaceutical ingredient that led to the difference among the generics. Furthermore, the in vivo rat pharmacokinetics study results of F1-F3 showed a good correlation (R2 = 0.99) with the SDPS data. In summary, the SDPS is a promising tool to detect the unexpected quality changes of pharmaceutical products in weakly regulated markets, facilitate formulation screening, and potentially reduce animal testing for estimating the in vivo absorption behavior of solid oral formulations. The absorption performance of generic drugs in vivo should be further investigated.

Effect of Pharmaceutical Excipients on Intestinal Absorption of Metformin via Organic Cation-Selective Transporters

Growing evidence has shown that some pharmaceutical excipients can act on drug transporters. The present study was aimed at investigating the effects of 13 commonly used excipients on the intestinal absorption of metformin (MTF) and the underlying mechanisms using Caco-2 cells and an ex vivo mouse non-everted gut sac model. First, the uptake of MTF in Caco-2 cells was markedly inhibited by nonionic excipients including Solutol HS 15, polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 80, and crospovidone. Second, transport profile studies showed that MTF was taken up via multiple cation-selective transporters, among which a novel pyrilamine-sensitive proton-coupled organic cation (H⁺/OC⁺) antiporter played a key role. Third, Solutol HS 15, polysorbate 40, and polysorbate 60 showed cis-inhibitory effects on the uptake of either pyrilamine (prototypical substrate of the pyrilamine-sensitive H⁺/OC⁺ antiporter) or 1-methyl-4-phenylpyridinium (substrate of traditional cation-selective transporters including OCTs, MATEs, PMAT, SERT, and THTR-2), indicating that their suppression on MTF uptake is due to the synergistic inhibition toward multiple influx transporters. Finally, the pH-dependent mouse intestinal absorption of MTF was significantly decreased by Solutol HS 15, polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 80, and pyrilamine. In conclusion, this study revealed that a novel transport process mediated by the pyrilamine-sensitive H⁺/OC⁺ antiporter contributes to the intestinal absorption of MTF in conjunction with the traditional cation-selective transporters. Mechanistic understanding of the interaction of excipients with cation-selective transporters can improve the formulation design and clinical application of cationic drugs.

Synthesis and Evaluation of PEG-PR for Water Flux Correction in an In Situ Rat Perfusion Model

Phenol red (PR) is a widely used marker for water flux correction in studies of in situ perfusion, in which intestinal absorption usually leads to the underestimation of results. In this paper, we propose a novel marker polyethylene glycol (PEG)-PR (i.e., PR modified by PEGylation) with less permeability and evaluate its application in an in situ perfusion model in rats. PEG-PR was synthesized by the chemical conjunction of polyethylene glycol-4k/5k (PEG-4k/5k) and PR. The synthesized PEG-PR was then characterized using ¹H-NMR, ¹³C-NMR, ultraviolet (UV), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analyses. The low permeability of PEG-PR was assessed using everted gut sac (EGS) methods. The apparent permeability coefficients (P_app, 3–8 × 10⁻⁷ cm/s) of PEG4k/5k-PR exhibited a nearly 15-fold reduction compared to that of PR. The different concentrations of PEG4k/5k-PR did not contribute to the P_app value or cumulative permeable percentage (about 0.02–0.06%). Furthermore, the larger molecular weight due to PEGylation (PEG5k-PR) enhanced the nonabsorbable effect. To evaluate the potential application of the novel marker, atenolol, ketoprofen, and metoprolol, which represent various biopharmaceutics classification system (BCS) classes, were selected as model drugs for the recirculation perfusion method. The water flux corrected by PEG4k/5k-PR reflected the accuracy due to the nonabsorbable effect, while the effective intestinal membrane permeability (P_eff) of atenolol corrected by PEG4k/5k-PR showed a statistically significant increase (p < 0.05) in different intestinal segments. In conclusion, PEG-PR is a promising marker for the permeability estimation when using the in situ perfusion model in rats.