Single-pass Intestinal Perfusion Technique Research Articles

Evaluation of Intestinal Drug Absorption and Interaction Using Quadruple Single-Pass Intestinal Perfusion Coupled with Mass Spectrometry Imaging.

Visualization and characterization of the intestinal membrane transporter-mediated drug absorption and interaction are challenging due to the complex physical and chemical environment. In this work, an integrated strategy was developed for in situ visualization and assessment of the drug absorption and interaction in rat intestines using quadruple single-pass intestinal perfusion (Q-SPIP) technique coupled with matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI). Compared with the traditional SPIP only available for perfusion of one single intestinal segment, the Q-SPIP model can simultaneously perfuse four individual segments of each rat intestine (duodenum, jejunum, ileum, and colon), enabling to obtain rich data from one rat. Subsequently, the drug distribution and absorption in rat intestinal tissue were accurately visualized by using an optimized MALDI MSI approach. The utility and versatility of this strategy were demonstrated via the examination of P-glycoprotein (P-gp)-mediated intestinal absorption of berberine (BBR) and its combination with natural products possessing inhibitory potency against P-gp. The change in the spatial distribution of BBR was resolved, and MALDI results showed that the signal intensity of BBR in defined regions was enhanced following coperfusion with P-gp inhibitors. However, enhanced absorption of BBR after coperfusion with the P-gp inhibitor was not observed in the ulcerative colitis rat model, which may be due to the damage to the intestinal barrier. This study exemplifies the availability and utility of Q-SPIP coupled with MALDI MSI in the examination of transporter-mediated intestinal drug absorption and interaction for fundamental inquiries into the preclinical prediction of oral absorption and drug interaction potential.

Exploring the Predictive Power of the In Situ Perfusion Technique towards Drug Absorption: Theory, Practice, and Applications.

Considering the broad applications and popularity, the in situ perfusion technique is an established and interesting approach to evaluate the absorption mechanisms of drug molecules in specific regions of the intestinal tract. Compared to perfusion studies in humans, this surrogate model shows several familiar characteristics making it interesting to apply this technique in rats in the non-clinical stage of drug product development. The differences in gastrointestinal (GI) anatomy and physiology between rats and humans are thoroughly discussed in the present review. Moreover, an in-depth overview of the Doluisio (i.e., closed-loop) versus the single-pass intestinal perfusion (i.e., open-loop) technique is shown. Finally, applications and future perspectives of the technique are presented.

Cell-penetrating peptide-surface modified liposomes to enhance the intestinal absorption of enoxaparin

Enoxaparin is low-molecular-weight heparin administered by subcutaneous/intravenous injection. The oral bioavailability of enoxaparin is restricted by its low absorption through the intestine. In this study cell-penetrating peptide-surface functionalized liposomes (CPPs-L) were prepared to improve the intestinal absorption of enoxaparin. Liposomal formulations were prepared by the ethanol injection method and the intestinal absorption of the formulation was evaluated using single-pass intestinal perfusion (SPIP) technique in rats. Meanwhile, the human fraction dose absorbed value (Fa (human)) of the formulations were predicted based on the calculated effective intestinal permeability (P effect (rat)) values obtained from the SPIP study. Liposomal enoxaparin revealed an increased intestinal absorption by ten-time compared with the free drug solution. Meanwhile, CPPs-L formulation revealed an enhanced intestinal absorption compared with the un-modified liposomal formulation. Regarding Fa (human), it is predicted that liposomal formulations could have the potential to improve the fraction dose absorbed of enoxaparin from low to intermediate level. Overall, the liposomal formulation can be considered as a mighty drug carrier for the oral delivery of enoxaparin.

Reply to "Comment on López-Yerena et al. 'Absorption and Intestinal Metabolic Profile of Oleocanthal in Rats' Pharmaceutics 2020, 12, 134".

Recently, in February 2020, we published a study exploring the intestinal absorption and metabolism of oleocanthal (OLC) in rats. A single-pass intestinal perfusion technique (SPIP) was used, involving simultaneous sampling from the luminal perfusate and mesenteric blood. Later, comments on our published paper were released, requesting clarification of specific data. In this detailed reply, we hope to have addressed and clarified all the concerns of A. Kaddoumi and K. El Sayed and that the scientific community will benefit from both the study and the comments it has generated.

Enhancement of the intestinal absorption of bortezomib by self-nanoemulsifying drug delivery system

Purpose: Intestinal drug absorption is one of the main factors that govern the fraction of oral dose absorbed (Fa) of drugs. It is reported that oral absorption of bortezomib (BTZ) can be restricted by its low intestinal permeability. In this study, we aimed to evaluate the impact of self-nanoemulsifying drug delivery systems (SNEDDS) on the intestinal absorption and Fa of BTZ.Methods: Intestinal permeability studies were conducted using in situ single-pass intestinal perfusion (SPIP) technique in rats. Human intestinal absorption (Peff (Human)) and Fa values of BTZ and BTZ-SNEDDS were predicted based on SPIP data.Results: Based on the obtained data, Peff (rat) values of (3.36 ± 0.5) × 10−5 and (8.9 ± 3) × 10−5 cm/s (mean ± SEM) were calculated for BTZ and BTZ-SNEDDS, respectively. Meanwhile, Peff (human) values of (7 × 10−5) and (68 × 10−5) cm/sec were predicted for BTZ and BTZ-SNEDDS, respectively. Besides, Fa (human) values of 72.5 and 97% were estimated for BTZ and BTZ-SNEDDS, respectively.Conclusions: According to the obtained data, it is concluded that SNEDDS can be considered as a promising drug delivery system to improve the intestinal absorption and Fa values of BTZ.

Applicability analysis and evaluation of aglycones in single-pass intestinal perfusion technique based on PBPK model

Single-pass intestinal perfusion( SPIP) is the common carrier of biopharmaceutics classification system( BCS) to study compound permeability. With the application and deepening study of BCS in the field of traditional Chinese medicine( TCM),SPIP model is becoming more and more common to study the intestinal absorption of TCM ingredients. Based on the limitations of the SPIP model in some researches on TCM permeability,it was speculated in this study that aglycone may be more suitable than the glycoside to study the intestinal absorption problem by using SPIP model. Furthermore,applicability of aglycone components was analyzed and evaluated. In this study,with quercetin,daidzein,formononetin,genistein and glycyrrhetinic acid used as research objects,the quantitative study of SPIP was used to evaluate the intestinal permeability of these aglycones and to predict the effective permeability coefficient( Peff) and absorption fraction( Fa) in human body. By combining studies comparison and analysis on multiple permeability research methods and prediction of human body absorption of aglycones in physiological-based pharmacokinetic models,this paper can further illustrate that the SPIP model is a good tool for studying the permeability of aglycones and predicting human absorption,which can provide data foundation and theoretical reference for researches on SPIP technique and BCS in intestinal absorption of TCM ingredients.

Investigating Intestinal Permeability of Bortezomib Using a Validated HPLC-UV Method.

Bortezomib (BTZ), as a proteasome inhibitor, has been used for treatment of patients with relapsed/refractory multiple myeloma and mantle cell lymphoma. BTZ is available for intravenous injection or subcutaneous administration. In this study, for evaluating the potential of BTZ oral delivery, intestinal permeability of BTZ was determined using in situ single-pass intestinal perfusion (SPIP) technique and the perfused solutions were analyzed using a validated HPLC-UV method. The chromatographic separation was performed using a C18 column via isocratic mode at a flow rate of 0.5 mL/min at 270 nm. The mobile phase was a mixture of methanol/deionized water (50:50% v/v) with 0.1% glacial acetic acid. The results indicated that calibration curves were linear (r2 ˃0.99) in a concentration range of 1.65-5 µg/mL for BTZ and 8.33-25 µg/mL for phenol red. A limit of quantitation of 1.03 and 6.67 µg/mL was obtained for BTZ and phenol red, respectively. The recovery values were in the range of 96.5-105.4% for BTZ, and 88-99.2% for phenol red. The relative standard deviations (RSD) were ≤4.9% for BTZ and ≤7% for phenol red. Stability studies indicated that the working standard solution is stable over a period of 48 h at room temperature. Finally, an effective permeability (Peff) value of (3.36±0.5)×10-5 cm/sec (mean±SEM) was achieved for BTZ. Moreover, it was predicted that BTZ belongs to the biopharmaceutical class ІІІ.

Bortezomib-loaded solid lipid nanoparticles: preparation, characterization, and intestinal permeability investigation

Bortezomib (BTZ), a proteasome inhibitor, is clinically used for the treatment of multiple myeloma and mantle cell lymphoma via intravenous or subcutaneous administration. Since BTZ has limited intestinal permeability, in this study, solid lipid nanoparticles (SLNs) were selected as lipid carrier to improve the intestinal permeability of BTZ. The nanoparticles were prepared by hot oil-in-water emulsification method and characterized for physicochemical properties. Moreover, in situ single-pass intestinal perfusion technique was used for intestinal permeability studies. Mean particle size of the BTZ-loaded solid lipid nanoparticles (BTZ-SLNs) was 94.6 ± 0.66 nm with a negative surface charge of –18 ± 11 mV. The entrapment efficiency of the BTZ-SLNs was 68.3 ± 3.7% with a drug loading value of 0.8 ± 0.05%. Cumulative drug release (%) over 48 h, indicated a slow release pattern for nanoparticles. Moreover, the SEM image showed a spherical shape and uniform size distribution for nanoparticles. Also, FTIR analysis indicated that BTZ was successfully loaded in the SLNs. The results of the intestinal perfusion studies revealed an improved effective permeability for BTZ-SLNs with a Peff value of about threefold higher than plain BTZ solution.

Further Study of Influence of Panax notoginseng on Intestinal Absorption Characteristics of Triptolide and Tripterine in Rats with Tripterygium wilfordii.

Background:Tripterygium wilfordii (TW) is widely employed to treat rheumatoid arthritis and autoimmune disorders clinically, which, however, accompany with disturbing hepatotoxicity and nephrotoxicity. The previous research showed that Panax notoginseng (PN) compatibly and significantly reduces the TW-induced hepatotoxicity.Objective:To explore the underlying mechanism, the present study was designed to reveal the influence of PN on the intestinal absorption process of TW-derived active components in rat.Materials and Methods:An in situ single-pass intestinal perfusion technique was established and preformed to obtain the perfusate samples of triptolide (TP), tripterine (TE), TW extract, and TW-PN extract. A rapid and sensitive ultra-performance liquid-chromatography tandem mass spectrometry method was subsequently developed and validated to determine the concentrations of TP and TE in the perfusate samples. Then, the absorption parameters, effective permeability, absorption rate constant, and percentage of 10 cm intestinal absorption were calculated strictly.Results:The final data indicated that both TP and TE have no special absorption site in the intestine and are primarily absorbed in a passive manner. Otherwise, the absorption of TP was decreased from compatibility of PN, but the absorption of TE was enhanced.Conclusion:The absorption reduction of TP and absorption elevation of TE from TW initiated by the combination of PN are contributed to attenuate the toxicity and reinforce the therapeutic efficacy of TW. It is practically reasonable of usage of TW compatibility with PN clinically.SUMMARY Panax notoginseng (PN) regulated the absorption process of Tripterygium wilfordii (TW) in intestineBoth triptolide (TP) and tripterine (TE), two typical components of TW, have no special absorption site in the intestine and are primarily absorbed in a passive mannerPN decreased the absorption of TP and enhanced the absorption of TE in the intestine. Abbreviations used: 10 cm% ABS: percentage of 10 cm intestinal absorption, DMARDs: Disease-modifying antirheumatic drugs, GU: Glycyrrhiza uralensis, Ka: Absorption rate constant, NSAIDs: Nonsteroidal anti-inflammatory drugs, Peff: Effective permeability, PN: Panax notoginseng, QC: Quality control, RA: Rheumatoid arthritis, RG: Rehmannia glutinosa, SPIP: Single-pass intestinal perfusion, TE: Tripterine, TP: Triptolide, TW: Tripterygium wilfordii, UPLC-MS/MS: Ultra-performance liquid-chromatography tandem mass spectrometry.

Engineered small intestinal system as an alternative to in-situ intestinal permeability model

Intestinal permeability is the most important factor that determines the bioavailability. In-vitro techniques like Caco-2 model and Ussing chamber are used for evaluating the intestinal permeability of the bioactive compound. But the lack of mucosal layer in those models makes the intestinal absorption prediction less accurate. We developed an engineered small intestinal system to evaluate intestinal permeability of bioactive compound. Following this approach, we have evaluated the intestinal permeability of fat soluble and water soluble bioactive compound and compared with in situ single-pass intestinal perfusion technique.

Overall intestinal permeability of multiple components in lotus leaf by in situ single pass intestinal perfusion models

To investigate the overall intestinal permeability of multiple components in lotus leaves and make clear the interaction in composition absorption process. Rat single-pass intestinal perfusion technique was used, and the results showed that the Peff values of nuciferine, demethylanuciferine, rutin, quercetin, kaempferol from lotus leaf were greater than 0.5×10⁻⁴ cm•s⁻¹. In the biopharmaceutics classification system (BCS) intestinal permeability property, these ingredients were high permeable components, while the hyperin was low permeable component. However, in the multi-component environment of the lotus leaf extract, component permeation was changed. Semi quantitative analysis of the unclear components showed that under the multi-component environment, four in seven components with relatively high contents had a Peff value less than 0.5×10⁻⁴ cm•s⁻¹, indicating these 4 components were of low permeability, while other 3 components were of high permeability. The results could be valuable to make clear the overall intestinal permeability of multiple components in lotus leaf, and lay a foundation for studying the mechanism of the lipid-lowering effect of lotus leaf.

Self-microemulsifying drug delivery system for improving the bioavailability of huperzine A by lymphatic uptake

Huperzine A (Hup-A) is a poorly water-soluble drug with low oral bioavailability. A self-microemulsifying drug delivery system (SMEDDS) was used to enhance the oral bioavailability and lymphatic uptake and transport of Hup-A. A single-pass intestinal perfusion (SPIP) technique and a chylomicron flow-blocking approach were used to study its intestinal absorption, mesenteric lymph node distribution and intestinal lymphatic uptake. The value of the area under the plasma concentration–time curve (AUC) of Hup-A SMEDDS was significantly higher than that of a Hup-A suspension (P<0.01). The absorption rate constant (Ka) and the apparent permeability coefficient (Papp) for Hup-A in different parts of the intestine suggested a passive transport mechanism, and the values of Ka and Papp of Hup-A SMEDDS in the ileum were much higher than those in other intestinal segments. The determination of Hup-A concentration in mesenteric lymph nodes can be used to explain the intestinal lymphatic absorption of Hup-A SMEDDS. For Hup-A SMEDDS, the values of AUC and maximum plasma concentration (Cmax) of the blocking model were significantly lower than those of the control model (P<0.05). The proportion of lymphatic transport of Hup-A SMEDDS and Hup-A suspension were about 40% and 5%, respectively, suggesting that SMEDDS can significantly improve the intestinal lymphatic uptake and transport of Hup-A.

Simultaneous Determination of Procaspase Activating Compound 1 and Permeability Markers in Intestinal Perfusion Samples and Application to a Rat Intestinal Absorption Study

A sensitive and simple HPLC method for simultaneous determination of PAC-1 (first procaspase-activating compound), phenol red, and permeability markers (carbamazepine and furosemide) in perfusion samples was developed and validated to assess intestinal absorption of PAC-1 using single-pass intestinal perfusion technique (SPIP) in rats. The chromatographic separation was carried out on a Kromasil C18 column (150 mm × 4.6 mm, 5 μm) with acetonitrile–methanol–30 mmol L−1 phosphate buffer (pH 3.0, 25:10:65, v/v/v) as mobile phase at a flow rate of 1.0 mL min−1, and the wavelength of the UV detector was set at 281 nm. The calibration curves were linear in the ranges of 2.40–48.0 μg mL−1 for PAC-1; 3.60–72.0 μg mL−1 for carbamazepine; 3.20–64.0 μg mL−1 for furosemide, and 4.80–96.0 μg mL−1 for phenol red (r > 0.999). Both the intra- and inter-day precisions (RSD%) of all analytes were less than 6.8 % at three concentration levels, while accuracy ranged from 95.4 to 104.5 %. Data obtained in all method validation studies indicated that the method was suitable for the intended purpose. The effective permeability values (Peff) considering water flux with the help of non-permeable marker phenol red was calculated to be 0.42 × 10−4, 0.62 × 10−4, 0.32 × 10−4 cm s−1 for PAC-1; 0.72 × 10−4, 0.77 × 10−4, 0.52 × 10−4 cm s−1 for carbamazepine; 0.20 × 10−4, 0.16 × 10−4, 0.12 × 10−4 cm s−1 for furosemide in duodenum, jejunum and ileum, respectively. The Peff value can be increased by co-perfusion with verapamil, indicating that absorption of PAC-1 is efficiently transported by P-glycoprotein (P-gp) in the gut wall.

Characterization of intestinal absorption of C-glycoside flavonoid vicenin-2 from Lychnophora ericoides leafs in rats by nonlinear mixed effects modeling

Vicenin-2 (apigenin-6,8-di-C-β-d-glucopyranoside) is present in hydroalcoholic extracts of the Brazilian species Lychnophora ericoides Mart., Asteraceae, leaves, and the biological effects of this compound have been demonstrated including anti-inflammatory, antioxidant and anti-tumor effects in rat models. Given the potential of this compound as a pharmacological agent, the aims of this investigation were to evaluate the extent of intestinal absorption of vicenin-2, and to determine the intestinal permeation profile using an in situ single-pass intestinal perfusion technique. A validated HPLC–UV method was applied to measure the amount of unabsorbed vicenin-2 in the gut after an oral administration of 180mgkg−1 in five rats. A nonlinear mixed effects model was used to determine the absorption pharmacokinetic parameters assuming a first order absorption and active secretion processes for this compound, wherein the active secretion was characterized by a zero-order process. The population pharmacokinetic parameters obtained were 0.274min−1 for the first-order absorption rate constant, 16.3%min−1 for the zero-order rate constant; the final percentage of the original dose that was absorbed in vivo was 40.2±2.5%. These parameters indicated that vicenin-2 was rapidly absorbed in the small intestine. In contrast to literature information indicating no absorption of vicenin-2 in Caco-2 cells, our results suggested that vicenin-2 can be absorbed in the small intestine of rats. The finding supports further investigation of vicenin-2 as a viable oral phytopharmaceutical agent for digestive diseases.

Study on biopharmaceutics classification and oral bioavailability of a novel multikinase inhibitor NCE for cancer therapy.

Specific biopharmaceutics classification investigation and study on phamacokinetic profile of a novel drug candidate (2-methylcarbamoyl-4-{4-[3- (trifluoromethyl) benzamido] phenoxy} pyridinium 4-methylbenzenesulfonate monohydrate, NCE) were carried out. Equilibrium solubility and intrinsic dissolution rate (IDR) of NCE were estimated in different phosphate buffers. Effective intestinal permeability (Peff) of NCE was determined using single-pass intestinal perfusion technique in rat duodenum, jejunum and ileum at three concentrations. Theophylline (high permeability) and ranitidine (low permeability) were also applied to access the permeability of NCE as reference compounds. The bioavailability after intragastrical and intravenous administration was measured in beagle dogs. The solubility of NCE in tested phosphate buffers was quite low with the maximum solubility of 81.73 μg/mL at pH 1.0. The intrinsic dissolution ratio of NCE was 1 × 10−4 mg·min−1·cm−2. The Peff value of NCE in all intestinal segments was more proximate to the high-permeability reference theophylline. Therefore, NCE was classified as class II drug according to Biopharmaceutics Classification System due to its low solubility and high intestinal permeability. In addition, concentration-dependent permeability was not observed in all the segments, indicating that there might be passive transportation for NCE. The absolute oral bioavailability of NCE in beagle dogs was 26.75%. Therefore, dissolution promotion will be crucial for oral formulation development and intravenous administration route will also be suggested for further NCE formulation development. All the data would provide a reference for biopharmaceutics classification research of other novel drug candidates.

A study on enhanced intestinal permeability of clarithromycin nanoparticles

The main objective of the present study was to determine the permeability of clarithromycin (CLA)-PLGA nanoparticles using single-pass intestinal perfusion technique in rats. Clarithromycin nanoparticles were prepared by nano-precipitation according to the modified quasi emulsion solvent diffusion technique and evaluated for their physicochemical characteristics. Permeability coefficients (Peff) in anaesthetized rats were determined at 3 different concentrations. Drug solution or suspensions in PBS was perfused through a cannulated jejunal segment and samples were taken from outlet tubing at different time points up to 90 min. Microbiological assay of CLA and phenol red in the samples were analyzed using an agar well diffusion procedure and HPLC method respectively. The average particle size of prepared nanoparticles was 305 ± 134 nm. The mean Peff of CLA solution in concentrations of 150, 250 and 400 µg/mL was found to be 1.20 (±0.32) ×10-3, 9.62 (±0.46) ×10-4, and 1.36 (±0.95) ×10-3 cm/sec, respectively. The corresponding values for the same concentration of nanoparticles were found to be 2.74 (±0.73) ×10-3, 2.45 (±0.88) ×10-3, and 3.68 (±0.46) ×10-3 cm/s, respectively. The two-tailed Student’s t-test showed that the intestinal permeability of CLA nanoparticle suspensions in prepared concentrations were significantly increased in comparison with its solution.

Effect of anionic macromolecules on intestinal permeability of furosemide

Context: Furosemide is an anionic molecule and has very low absorption in gastro intestinal tract.Objective: The aim of this study was to investigate the effect of anionic macromolecules on the intestinal permeability of Furosemide.Materials and methods: The intestinal permeability of Furosemide was determined using single-pass intestinal perfusion technique in rats. Briefly a jejunal segment of ∼10 cm was isolated and cannulated in both ends for inlet and outlet solution. The perfusate was collected every 10 min and samples were analyzed using the RP-HPLC method. Test samples containing furosemide and two anionic macromolecules, sodium carboxy methyl cellulose and sodium alginate, at different concentrations were used.Results: The obtained data showed that existence of Sodium carboxy methyl cellulose significantly increased the Peff values in all three investigated concentrations (p < 0.05) but sodium alginate only in concentrations <0.1% increased drug permeability.Discussion: It is concluded that the anionic macromolecules at specific concentrations could alter the permeability of anionic drugs across the biological membranes.Conclusions: Donnan phenomenon and chelating property of macromolecules could be attributed to the observed effect.

Enhanced solubility and permeability of exemestane solid dispersion powders for improved oral delivery

The aim of the present investigation was to enhance the solubility of exemestane (EXM), by solid dispersion (SD) technique using PEG 6000 as a carrier. Phase solubility studies were conducted with PEG 6000 and PEG 20000 to evaluate the effect of carriers on aqueous solubility of EXM. The aqueous solubility of EXM was favoured with PEG 6000 compared to PEG 20000. SDs of EXM using polyethylene glycol 6000 (PEG 6000) as carrier were prepared in different drug to carrier ratios. Solid-state characterization indicated decrease in crystallinity of the drug. The in vitro dissolution rate of EXM was enhanced from both SDs and tablet formulations prepared using SD compared to pure EXM. The in situ permeability studies investigated using single-pass intestinal perfusion technique in rats revealed increase in effective intestinal permeability (Peff, cm/s) by 4.45 folds with SDs. Thus, EXM-PEG 6000 SDs showed improved solubility and permeability.

Impact of Micellar Vehicles on in situ Intestinal Absorption Properties of Beta-Lapachone in Rats.

The aim of the present study was to examine the effect of micellar systems on the absorption of beta-lapachone (b-lap) through different intestinal segments using a single-pass rat intestinal perfusion technique. B-lap was solubilized in mixed micelles composed of phosphatidylcholine and sodium deoxycholate, and in sodium lauryl sulfate (SLS)-based conventional micelles. Both mixed micelles and SLS micelles improved the in situ permeability of b-lap in all intestinal segments tested although the mixed micellar formulation was more effective in increasing the intestinal absorption of b-lap. The permeability of b-lap was greatest in the large intestinal segments. Compared with SLS micelles, the effective permeability coefficient values measured with mixed micelles were 5- to 23-fold higher depending on the intestinal segment. Our data suggest that b-lap should be delivered to the large intestine using a mixed micellar system for improved absorption.

Biopharmaceutics classification and intestinal absorption study of apigenin

The aim of the study was to characterize the biopharmaceutics classification system (BCS) category of apigenin (AP) using intrinsic dissolution rate (IDR) and rat intestinal permeability, and to investigate the intestinal absorption mechanism of AP in rats. In the present investigation, equilibrium solubility and intrinsic dissolution rate (IDR) of AP were estimated in phosphate buffers. Effective intestinal permeability (P(eff)) of AP was determined using single-pass intestinal perfusion (SPIP) technique in four segments (duodenum, jejunum, ileum and colon) of rat intestine at three concentrations (10, 50 and 100 μg/ml). The aqueous solubility of AP in tested phosphate buffers was very poor with maximum solubility of 2.16 μg/ml at pH 7.5. The IDR of AP was very low with a value of 0.006 mg/min/cm(2). The minimum and maximum P(eff)s determined by SPIP were 0.198×10(-4) and 0.713×10(-4) cm/s at jejunum and duodenum site, respectively. In addition, the concentration-dependent permeability behavior was observed in the duodenum and jejunum, which suggested that AP was transported by both passive and active carrier-mediated saturable mechanism in these two intestinal segments. However, the observed concentration-independent permeability behavior in ileum and colon indicated primarily passive transport mechanism of absorption of AP in the last two intestinal segments. AP was classified as class II drug of the BCS due to its low solubility and high intestinal permeability. AP could be well absorbed in the whole intestine with the main absorption site at duodenum. The absorption of AP in four intestinal segments exhibited different transport mechanisms.