Biopharmaceutics classification and intestinal absorption of chikusetsusaponin IVa

The objective of this study was to investigate the absorption behavior of chikusetsusaponin IVa (CHS‐IVa) in the rat intestine using single‐pass intestinal perfusion (SPIP) and to classify CHS‐IVa into the biopharmaceutics classification system (BCS). The equilibrium solubility of CHS‐IVa was determined by the shaker method. The absorption mechanism of CHS‐IVa in the intestine was studied by comparing the P_eff of different concentrations of CHS‐IVa. The intestinal site dependence of CHS‐IVa absorption was studied by comparing the P_eff of the same concentration of CHS‐IVa in different intestinal segments. The relationship between CHS‐IVa and intestinal efflux protein was studied by perfusion with an efflux protein inhibitor. The permeability of CHS‐IVa was investigated by comparing the P_eff of CHS‐IVa and the reported value. The solubility of CHS‐IVa over the pH range 1.0–7.5 was 14.4 ± 0.29 to 16.9 ± 0.34 mg/ml. The P_eff of CHS‐IVa in the duodenum was 1.76 × 10^?3 to 2.00 × 10^?3 cm/min. The P_eff of CHS‐IVa in the jejunum was 1.26 × 10^?3 to 1.39 × 10^?3 cm/min. The P_eff of CHS‐IVa in the ileum was 1.25 × 10^?3 to 1.31 × 10^?3 cm/min. The P_eff of CHS‐IVa in the colon was 1.02 × 10^?3 to 1.08 × 10^?3 cm/min. There was no statistical difference of the P_eff in the four segments at different CHS‐IVa concentrations. The P_eff of CHS‐IVa (0.07, 0.7 and 7.0 mg/ml) were all notably smaller than the reported P_eff (3.00 × 10^?3 cm/min) in the jejunum. The P_eff of CHS‐IVa was not influenced by verapamil (P‐gp inhibitor), indomethacin (MRP inhibitor) and pantoprazole (BCRP inhibitor). CHS‐IVa was classified as high solubility, low permeability and BCS III. The main absorptive tracts were the upper intestinal tracts and the rank order of intestinal permeability was duodenum > jejunum ≈ ileum > colon. The transport mechanism of CHS‐IVa in all intestinal segments might be primarily passive transport. CHS‐IVa was not a substrate of P‐gp, MRP and BCRP.     

Influence of bile salts and lipids on intestinal absorption of griseofulvin in man

Summary The influence of bile salts and lipids on the intestinal absorption of griseofulvin has been studied in 11 healthy male volunteers by the intestinal perfusion technique. The drug in a nutrient solution (Realmentyl) was perfused into the second part of duodenum at 5 ml/min. Intestinal samples were taken continuously at 1 ml/min, 20 cm (at the angle of Treitz) and 45 cm distal to the perfusion point. To study the effect of lipids on griseofulvin absorption, the drug was perfused with solutions A and B, of which B contained a total lipid and caloric load three times that of A. The influence of bile salts on griseofulvin absorption was examined by perfusing the drug on Day 1 with bile salts and again on the following day after bile salt depletion. Bile salts and a varying quantity of lipid perfusate had no significant influence on the duodeno-jejunal griseofulvin absorption rate per cm of intestine. Lipids, however, may still play a role in griseofulvin absorption along the entire intestine.     

Physicochemical characteristics and gastrointestinal absorption behaviors of S-propargyl-cysteine,a potential new drug candidate for cardiovascular protection and antitumor treatment

Abstract

1. As a potential new drug candidate for cardiovascular protection and antitumor treatment, the physicochemical properties, gastrointestinal (GI) absorption behaviors and mechanisms of S-propargyl-cysteine (SPRC) were investigated in this study.

2. SPRC exhibited favorable solubility in aqueous media. The log P and log D values were low (≤1.93?±?0.08). The pK_a in the acidic and basic regions was 2.08?±?0.02 and 8.72?±?0.03, respectively. The isoelectric point was 5.40?±?0.02. SPRC was stable in the rat GI fluids, and showed no obvious adsorption and metabolism in the rat GI tract.

3. SPRC displayed poor gastric absorption and favorable intestinal absorption in the rat in situ GI perfusion model. Absorption rate constants (k_a), hourly absorption percentage (P) and apparent permeability coefficient (P_app) of SPRC in the small intestine were ≥0.77?±?0.06?h^?1, 59.25?±?4.02% and (7.99?±?0.88)?×?10^?5?cm/s, respectively. Absorption of SPRC exhibited a certain dependence on physiological pH and absorption region. Absorption of SPRC was not inhibited by l-methionine and 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid.

4. SPRC showed favorable oral absorption. It can be categorized as a BCS class I drug. The membrane pore transport appeared to be one of the predominant absorption modes for SPRC.     

Intestinal permeability of mitragynine in rats using in situ absorption model

The intestinal permeability of mitragynine was investigated in situ using a single pass intestinal perfusion (SPIP) absorption model, in small intestine of rat using mitragynine in the absence/presence of the permeability markers, P-gp and/or CYP3A4 inhibitors. Mitragynine demonstrated high intestinal permeability (P_eff of 1.11 × 10^?4 cm/s) that is in the range of highly permeable drugs such as propranolol (P_eff of 1.27 × 10^?4 cm/s) indicating that it readily crosses the intestine. The addition of azithromycin (P-glycoprotein inhibitor) and ciprofloxacin (CYP3A4 inhibitor) or combination of both has no effect on intestinal permeability of mitragynine across the rat small intestine.     

Effects of Ageing on the Oral Absorption of d-Xylose in Rats: Analysis of Gastrointestinal Disposition

The effects of ageing on the oral (gastrointestinal) absorption of d -xylose were investigated by analysing the gastrointestinal disposition after oral administration to young (9 weeks) and old (53 weeks) rats. A linear model assuming first-order gastric emptying followed by first-order intestinal absorption was fitted to remaining fraction vs time profiles for the stomach and small intestine to estimate the gastric emptying rate constant (k_g) and the intestinal absorption rate constant (k_a). In young and old rats, k_g values were 0·087 ± 0·008 and 0·070 ± 0·007 min^?1, respectively, and k_a values were 0·020 ± 0·002 and 0·018 ± 0·002 min^?1 suggesting an insignificant effect on ageing on the rate of oral absorption. The average intestinal lumen volume (V_av) was unchanged with ageing, and so was the apparent intestinal membrane permeability clearance (CL_app) as the product of k_a and V_av. However, the small intestinal transit time (T_si) was suggested to be twice that in older rats (171 min) than in young rats (78 min) by the analysis of gastrointestinal disposition of inulin, a non-absorbable marker. It was also shown that our preceding finding of an increase in the fraction absorbed of D-xylose with ageing can be solely ascribable to the delay in intestinal transit. Thus, among various determinants of oral absorption, only T_si was found to be altered with ageing. The CL_a,app and k_a of passively absorbed drugs such as D-xylose may be generally unchanged, and the fraction absorbed may increase with ageing by the delay in intestinal transit.     

Positioning of Rifampicin in the Biopharmaceutics Classification System (BCS)

The position of rifampicin with respect to the biopharmaceutics classification system (BCS) was explored on the basis of its aqueous solubility and intestinal permeability. The aqueous solubility was determined between pH 1 and 7 by the conventional shake-flask method. Permeability coefficients of rifampicin and the US FDA listed low (furosemide, ranitidine) and high permeable (caffeine, naproxen) model drugs were determined in the three segments of the rat intestine by employing the everted gut sac model. The samples were analyzed by HPLC. The maximum human single dose of rifampicin (600 mg) was insoluble in 250 ml of aqueous media between pH 3 and 7. The determined apparent permeability coefficient (Papp) values for rifampicin were 4.856×10^?6, 2.117×10^?6, and 2.149×10^?6 cm/sec in the rat duodenum, jejunum and ileum, respectively. These values were similar to those of the low permeable drugs, ranitidine and furosemide, for which Papp values were determined to be 1.767×10^?6?2.426×10^?6 and 2.469×10^?6?3.008×10^?6 cm/sec, respectively. The determined values for high permeable model drugs, viz., caffeine and naproxen, were ～10–20 folds higher than rifampicin or even ranitidine and furosemide. The study suggests that rifampicin is a drug with low solubility and even low intestinal permeability and hence qualifies to be classified in BCS Class IV, instead of Class II where it is being categorized presently. The contention is supported by the reported data on the permeability of the drug through cell monolayers, the mass balance and the absolute bioavailability values in the literature, and the data for rifampicin according to “Lipinski's rule of five”.     

Concentration- and Region-dependent Intestinal Permeability of Fluvastatin in the Rat

The purpose of this study was to investigate the mechanisms of transport of fluvastatin across the intestinal mucosa in various regions of the intestine in the rat. In-situ single-pass perfusions of the jejunum, ileum and colon were performed and the effective permeability (P_eff) of fluvastatin, antipyrine and D-glucose were assessed in each region, at three different perfusate fluvastatin concentrations (1.6, 16 and 160 μM). The effect of lovastatin acid on the bi-directional transport of fluvastatin across the ileal mucosa was also studied. The P_eff of fluvastatin was found to be dependent both on the intestinal region and on the concentration in the intestinal lumen (P < 0.001). Fluvastatin had the lowest P_eff (0.55±0.10 times 10^?4 cm s^?1) in the jejunum at 1.6 μM, and the highest P_eff (1.0±0.16 times 10^?4 cm s^?1) in the colon at 160 μM. The highest concentration of fluvastatin increased the average absorption of water from the intestine by 209% (P < 0.05), and the average P_eff of D-glucose by 29% (P < 0.05). The presence of excess lovastatin acid (100 μM, compared with fluvastatin 1.6 μM) at the luminal side increased the average absorption of water by 218% (P < 0.001), and the P_eff of fluvastatin in the ileum and the colon by 44 and 50%, respectively (P < 0.05). The presence of lovastatin acid on the luminal side in the ileum also increased the blood-to-lumen transport (exsorption) of fluvastatin by 43% (P < 0.001). The increased intestinal absorption of fluvastatin at higher concentrations does not suggest that substantial absorption occurs by any carrier-mediated process in the absorptive direction. The increased bi-directional transport when lovastatin acid was added to the lumen suggests that fluvastatin is not a P-glycoprotein substrate. Instead, the concentration-dependent increase in the absorption of fluvastatin, water and D-glucose suggests a direct effect of fluvastatin on the transcellular passive transport.     

Bioavailability Study of Glycyrrhetic Acid after Oral Administration of Glycyrrhizin in Rats; Relevance to the Intestinal Bacterial Hydrolysis

To clarify the metabolic fate of glycyrrhizin when orally ingested, we investigated the bioavailability of glycyrrhetic acid, the aglycone of glycyrrhizin, after intravenous or oral administration of glycyrrhetic acid (5.7 mg kg^?1, equimolar to glycyrrhizin) or glycyrrhizin (10 mg kg^?1) at a therapeutic dose in rat. Plasma concentration of glycyrrhetic acid rapidly decreased after its intravenous administration, with AUC of 9200 ± 1050 ng h mL^?1 and MRT of 1.1 ±0.2 h. The AUC and MRT values after oral administration were 10600± 1090 ng h mL^?1 and 9.3 ±0.6 h, respectively. After oral administration of glycyrrhizin, the parent compound was not detectable in plasma at any time, but glycyrrhetic acid was detected at a considerable concentration with AUC of 11700 ± 1580 ng h mL^?1 and MRT of 19.9 ± 1.3 h, while glycyrrhetic acid was not detected in plasma of germ-free rats at 12 h after oral administration of glycyrrhizin. The AUC value of glycyrrhetic acid after oral administration of glycyrrhizin was comparable with those after intravenous and oral administration of glycyrrhetic acid, indicating a complete biotransformation of glycyrrhizin to glycyrrhetic acid by intestinal bacteria and a complete absorption of the resulting glycyrrhetic acid from intestine. Plasma glycyrrhizin rapidly decreased and disappeared in 2 h after intravenous administration. AUC and MRT values were 2410 ± 125 μg min mL^?1 and 29.8 ± 0.5 min, respectively. Plasma concentration of glycyrrhetic acid showed two peaks, a small peak at 30 min and a large peak at 11.4 h, after intravenous administration of glycyrrhizin, with an AUC of 15400±2620 ng h L^?1 and an MRT of 18.8 ± 1.0 h. The plasma concentration profile of the latter large peak was similar to that of glycyrrhetic acid after oral administration of glycyrrhizin, which slowly appeared and declined. The difference of MRT values (19.9 and 9.3 h) for plasma glycyrrhetic acid after oral administration of glycyrrhizin and glycyrrhetic acid suggests the slow conversion of glycyrrhizin into glycyrrhetic acid in the intestine.     

Improving the dissolution and oral bioavailability of the poorly water‐soluble drug aloe‐emodin by solid dispersion with polyethylene glycol 6000

Solid dispersions (SDs) of aloe‐emodin (AE) and polyethylene glycol 6000 (PEG6000) with different drug loadings were prepared, characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) and evaluated for solubility and in vitro release. The oral bioavailability of AE from SD in rats was compared with the crystalline drug. Plasma concentrations of AE were determined by HPLC. After administration of crystalline AE (35 mg·kg^?1) in rats, the AUC_0‐600 and C_max were 393.6±77.1 mg·min·l^?1 and 1.87±0.30 mg·l^?1, respectively. For the PEG6000 SD of AE, AUC_0‐600 and C_max were boosted to 1310.5±111.9 mg·min·l^?1 and 5.86±0.47 mg·l^?1, respectively. The results indicated that the oral bioavailability of AE was increased significantly. Simultaneously, the T_max value of AE for AE crystalline was decreased from 75.6±17.3 min to 44.8±14.8 min for SD. The earlier T_max for AE from SD indicated the higher extent of absorption for SD due to their improved dissolution rate in rat intestine. This SD approach can therefore be used to enhanced dissolution and bioavailability for poorly water‐soluble drugs. Drug Dev Res, 2009. © 2009 Wiley‐Liss, Inc.     

Pharmacokinetics of intravenous and epidural ropivacaine in the rhesus monkey

Ropivacaine is a new long-acting amide local anesthetic which is possibly less cardiotoxic than bupivacaine. The absorption and disposition of ropivacaine were characterized in six rhesus monkeys in an open two-way crossover study following intravenous and epidural administration. For these studies, animals were anesthetized for placement of intravenous and intraarterial catheters. For the epidural studies, a PE-10 catheter was also inserted 3 cm into the lumbar epidural space. After recovery from anesthesia, animals received ropivacaine 1 mg kg^?1 intravenously over 1 min or 10 mg of ropivacaine epidurally (two 1 ml doses of 0.5, 5 min apart), and arterial blood samples were obtained over 5 h. Serum ropivacaine concentrations were determined by gas chromatography with NP detection. Concentration—time data following i.v. and epidural administration were fitted simultaneously. Initial parameter estimates were obtained by analyzing each route separately. Input rates and their corresponding extent of absorption were estimated using deconvolution. Mean (±SD) disposition parameters included: V_ss = 1.11±0.198 1kg^?1; CL = 0.711 ± 0.158 1 h^?1 kg^?1; t_1/2,z = 2.07 ± 0.438 h. Mean (± SD) absorption parameters included: F₁ = 0.506 ± 0.221; t = 0.060 ± 0.078 h; F₂ = 0.444 ± 0.182; t = 6.45 ± 11.09h. Ropivacaine's biphasic absorption and bioavailability are similar to those of other amide local anesthetics. The biphasic absorption may be related to partitioning into fat or regional changes in blood flow induced by the drug.     

Standardization of an ex vivo method for determination of intestinal permeability of drugs using everted rat intestine apparatus

IntroductionEverted gut sac of rat intestine is a paradigm widely employed for determination of absorption kinetics of drugs along with evaluation of effects of absorption enhancers. Since its inception in 1954, it has been optimized to enhance tissue survival and use, but it still suffers the limitation of small serosal compartment size and lack of validity of single experiment.MethodsThe aim of the present work was to standardize a new ex vivo model to study drug absorption using a specially designed glass apparatus, everted segment of rat intestine, and three absorption markers [paracellular (atenolol), transcellular (metoprolol and propranolol)]. To validate a single experiment phenol red was used as non-absorbable marker.ResultsThe mean apparent permeabilities (Papp) for the markers were found to be 0.054 ± 0.024 × 10^? 4 cm/s (atenolol), 0.84 ± 0.14 × 10^? 4 cm/s (metoprolol), and 1.64 ± 0.16 × 10^? 4 cm/s (propranolol); wherein data from only those experiment was used, which showed negligible absorption of phenol red.DiscussionThe model is simple to establish, gives excellent absorption kinetics, and most importantly provides a way to validate the experiment simultaneously. The proposed method can be used in all kinds of drug absorption studies, especially biopharmaceutical investigations studying absorption enhancement strategies.     

A Novel Method for Determining the Solubility of Small Molecules in Aqueous Media and Polymer Solvent Systems Using Solution Calorimetry

Purpose

To explore the application of solution calorimetry for measuring drug solubility in experimentally challenging situations while providing additional information on the physical properties of the solute material.

Methods

A semi-adiabatic solution calorimeter was used to measure the heat of dissolution of prednisolone and chlorpropamide in aqueous solvents and of griseofulvin and ritonavir in viscous solutions containing polyvinylpyrrolidone and N-ethylpyrrolidone.

Results

Dissolution end point was clearly ascertained when heat generation stopped. The heat of solution was a linear function of dissolved mass for all drugs (<10% RSD, except for chlorpropamide). Heats of solution of 9.8?±?0.8, 28.8?±?0.6, 45.7?±?1.6 and 159.8?±?20.1 J/g were obtained for griseofulvin, ritonavir, prednisolone and chlorpropamide, respectively. Saturation was identifiable by a plateau in the heat signal and the crossing of the two linear segments corresponds to the solubility limit. The solubilities of prednisolone and chlopropamide in water by the calorimetric method were 0.23 and 0.158 mg/mL, respectively, in agreement with the shake-flask/HPLC-UV determined values of 0.212?±?0.013 and 0.169?±?0.015 mg/mL, respectively. For the higher solubility and high viscosity systems of griseofulvin and ritonavir in NEP/PVP mixtures, respectively, solubility values of 65 and 594 mg/g, respectively, were obtained.

Conclusion

Solution calorimetry offers a reliable method for measuring drug solubility in organic and aqueous solvents. The approach is complementary to the traditional shake-flask method, providing information on the solid properties of the solute. For highly viscous solutions, the calorimetric approach is advantageous.     

Bioavailability of caffeic acid in rats and its absorption properties in the Caco-2 cell model

Context: Caffeic acid (CA) is widely distributed in edible plants, and it is beneficial to human health by exerting various biological effects. The potential pharmacological activities of CA are dependent on its absorption in the gastrointestinal tract.

Objective: To investigate the bioavailability of CA in rats and its absorption properties in the Caco-2 cell model.

Materials and methods: A sensitive LC-MS/MS method was successfully applied to determine CA in rat plasma, perfusate, and Hank's balanced salt solution (HBSS). The absolute bioavailability (F_abs) of CA was obtained after i.v. (2?mg/kg) or i.g. administration (10?mg/kg) to rats. Blood samples (approximately 250?µL) were collected from the jugular vein catheter. Pharmacokinetic parameters were calculated using the 3P97 software (version 2.0 PK software; Chinese Society of Mathematical Pharmacology, Anhui, China). The intestinal absorption of CA was explored by the in situ vascularly perfused rat intestinal preparation. CA (5?mg/kg) was administered into the duodenum. Samples (250?µL) were collected from reservoir at specific times, and the same volume fresh perfusate was replaced. The Caco-2 cell model was applied to measure the permeability of CA from the apical to basolateral side (A?→?B) and from the basolateral to apical side (B?→?A).

Results: The absolute bioavailability (F_abs) of CA was 14.7%, and its intestinal absorption was 12.4%. The P_{app A→B} values of CA were ranging from (4.87?±?1.72)?×?10^?7?cm/s to (5.05?±?0.66)?×?10^?7?cm/s as the concentration varied from 5 to 15?µg/mL.

Conclusion: CA was shown to have low oral bioavailability in rats, low intestinal absorption, and poor permeability across Caco-2 cells.     

Paracetamol absorption from different sites in the human small intestine.

Site-specificity in the small intestinal absorption of paracetamol was investigated using a segmental intestinal steady state perfusion technique (triple-lumen tubing system) combined with simultaneous measurements of serum drug concentrations. Dissolved paracetamol was perfused over 160 min into different parts of the small intestine (65-210 cm beyond the teeth). Each of the four healthy subjects was studied twice with a proximal and a more distal site of perfusion. Serum drug concentrations were similar after proximal and distal perfusions. Mean drug absorption rates calculated from intestinal aspirate concentrations were similar in both parts of the intestine--proximal: 869 micrograms 30 cm-1 min-1 (95% CI: 659-1079) vs distal: 941 micrograms 30 cm-1 min-1 (794-1088). The absorption rate was related directly to the amount of paracetamol perfused per unit time as well as to the rate of transmucosal water fluxes.     

Do antidiarrhoeal opiates accumulate in the rat intestinal lumen?

Abstract— The opiate antidiarrhoeal drugs loperamide (0·6 mg kg^?1, i.p.) or difenoxin (0·77 mg kg^?1, s.c), were administered in an anaesthetic mixture (pentobarbitone 60 mg kg^?1) to rats. A length of jejunum (approx. 30 cm) was cannulated, washed and then perfused with iso-osmotic saline for 20 min. The perfusion commenced 50 min after drug administration and continued for 20 min. The perfusates were collected for analysis of fluid transport rates and antidiarrhoeal drug content. These doses of the antidiarrhoeals caused marked inhibition of intestinal fluid secretion induced by intra-arterial infusion of vasoactive intestinal peptide. However, neither of the antidiarrhoeal drugs were detected in the intestinal perfusates (< 0·5 ng by HPLC). The results indicate that loperamide and difenoxin have a different pharmacokinetic profile compared with that previously found for morphine under the same conditions.     

Intestinal transport of bis(12)-hupyridone in Caco-2 cells and its improved permeability by the surfactant Brij-35

The objective of the present study was to elucidate the mechanisms of intestinal transport of bis(12)‐hupyridone (B12H) to predict its oral bioavailability. The effect of the B12H concentration and the contribution of the drug efflux transporters, P‐glycoprotein (P‐gp or ABCB1) and multidrug resistance‐associated proteins (MRPs or ABCC) on B12H absorption were measured and evaluated using the human intestinal epithelial Caco‐2 cell monolayer in the presence of transporter inhibitors. The results indicated that B12H was absorbed in a dose‐dependent manner at concentrations ranging from 132 to 264 µM . However, only apical efflux was observed in the directional transport studies for B12H below 88 µM (P_app(AP‐to‐BL): virtually zero; P_app(BL‐to‐AP): 1.591 ± 0.071 × 10^?5 cm s^?1). P‐gp and mixed P‐gp/MRP inhibitors significantly increased the absorptive transport (P_app(AP‐to‐BL)) to 0.619 ± 0.018 × 10^?5 and 0.608 ± 0.025 × 10^?5 cm s^?1, respectively, while decreasing secretory transport (P_app(BL‐to‐AP)) by >75%. A multiple‐MRP inhibitor, probenecid, increased the P_app(AP‐to‐BL) to 0.329 ± 0.015 × 10^?5 cm s^?1 while decreasing the P_app(BL‐to‐AP) by 50%. Another multiple‐MRP inhibitor, indomethacin, only modestly decreased the P_app(BL‐to‐AP) by ～30% and had no effect on the absorptive transport (P_app(AP‐to‐BL): virtually zero). In addition, the effect of various pharmaceutical excipients (e.g. Pluronic F‐68, Tween‐80 and Brij‐35) on B12H transport was determined and compared. Among them, Brij‐35 effectively enhanced B12H absorption at a concentration lower than its critical micelle concentration (CMC, 60 µM ). Therefore, Brij‐35 can be used as a potential enhancer to improve intestinal absorption of B12H for oral administration. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of leucine on intestinal baclofen absorption as a model compound of neutral α-aminoacids

The inhibitory effect of the essential α-aminoacid L-leucine on the intestinal absorption of the antispastic drug baclofen was examined by means of an in situ rat gut perfusion technique. When 0.5 mM baclofen solutions were perfused in the presence of increasing concentrations of the aminoacid (5–100 mM), the apparent absorption rate constant of the drug decreased as the initial leucine concentration increased. Higher leucine concentrations, however, did not completely abolish the absorption of the drug (at 100 mM of leucine, only 76% inhibition was observed). The interaction can be mathematically described as a complete competitive inhibition with a second component, K = 0.35 (±0.08)h^?1, K_i = 0.25 (±0.09)mM, AIC= ?97.02. In the light of some of the absorption features of the drug, however, the residual absorption of baclofen in the presence of high leucine concentrations should be attributed to another transport system not used by leucine. Apparent parameters characterizing absorption of leucine in the presence of baclofen (0.5mM) were V_m=61.02 (±5.46)mM h^?1; K_m=8.04 (±0.89)mM, and AIC=62.25. The results indicate that baclofen and leucine share some carriers in the intestinal absorption processes. Since leucine is an essential dietary aminoacid, and therefore a normal food component, this finding could be relevant in preventing interactions that would lead to a reduced oral bioavailability during baclofen therapy.     

The physicochemical properties of geraniin,a potential antihyperglycemic agent

Abstract

Context: Natural products play a vital role in the discovery of leads for novel pharmacologically active drugs. Geraniin (GE) was identified as the major compound in the rind of Nephelium lappaceum L. (Sapindaceae), while ellagic and gallic acids have been shown to be its main metabolites. GE and its metabolites possess a range of bioactive properties including being an anti-infective, anticarcinogenic, antihyperglycemic, and antihypertensive.

Objective: GE and its metabolites were investigated to establish its gastrointestinal absorption and physicochemical properties.

Materials and methods: GE was purified from N. lappaceum rind extract using reverse-phase C18 column chromatography. Lipophilicity (log P) was determined using the 1-octanol/water shake-flask method. Equilibrium solubility of GE and its metabolites (20?mg) was determined in water and four biorelevant media: simulated gastric, simulated intestinal, fasted state-simulated intestinal, and fed state-simulated intestinal after 72?h.

Results and discussion: The purification yield was 10.8%; where a 97–99% pure GE was obtained. Log P values for GE, ellagic, and gallic acids were established as ?0.73?±?0.17, 0.11?±?0.06, and 0.71?±?0.21, respectively, establishing them as polar compounds. All three compounds were found to exhibit poor solubility in gastric (0.61–8.10?mg/mL) but good solubility in intestinal fluids (3.59–14.32?mg/mL).

Conclusion: The above results indicate that the compounds have limited gastrointestinal absorption due to its polarities. To consider these compounds as oral drug candidates, formulation strategies are being developed.     

Pharmacokinetic and Pharmacodynamic Aspects of Artelinic Acid in Rodents

Abstract— The efficacy of artelinic acid and artemisinin, orally administered at 10 and 50 mg kg^?1 day^?1, was compared in Plasmodium berghei infected mice. Subsequently, the pharmacokinetics of artelinic acid after intravenous, intramuscular, oral and rectal administration of a 20 mg kg^?1 aqueous solution to rabbits were studied in a four-way randomized cross-over experiment. After intravenous administration, artelinic acid concentrations in blood plasma were high (C₀: 76 ± 15 mg L^?1), and the drug was rapidly eliminated from the central compartment, showing linear elimination kinetics with an elimination half-life of 15 ± 3 min. A large inter-subject variation appeared in the absorption rate and the extent of absorption (2–92%) over the 120 min interval after intramuscular administration. Also, a large inter-subject variation in individual rectal bioavailability (17–100%) was shown, which was dependent on the site of absorption in the rectum. The estimated oral bioavailability was low (4·6 ± 1·7%), probably due to a high first-pass effect and possible decomposition in the acidic gastric environment.     

The application of 1,8-cineole,a terpenoid oxide present in medicinal plants,inhibits castor oil-induced diarrhea in rats

Abstract

Context: 1,8-Cineole, a terpene, characterized as a major constituent occurring in the essential oils of several aromatic plants. It is widely used in pharmaceutical industry, as a food additive and for culinary purposes.

Objective: This study investigates the inhibitory effect of 1,8-cineole on transit time and diarrhea in animal models.

Materials and methods: Acute toxicity and lethality of 1-8-cineole was determined by Lork’s guidelines. The antidiarrheal effect of 1,8-cineole was investigated by determining the intestinal transit and enterpooling in rats. In all experiments, different doses of 1,8-cineole (20–120?mg/kg), atropine, and loperamide were administered orally.

Results: The LD₅₀ of 1,8-cineole for oral administration was estimated to be 1280?mg/kg. 1,8-Cineole (20–120?mg/kg) did not show a significant decrease in small intestine transit (p?>?0.05); however, the highest dose displayed a significant decrease in comparison with atropine (p?<?0.05). This substance decreased the peristaltic index value to 68?±?0.36% at a dose of 120?mg/kg compared with the control group (85.22?±?4.31%) in the castor oil transit test. 1,8-Cineole significantly delayed the onset of diarrhea to ?142.33?±?6.08?min at 120?mg/kg, while the time was 103.66?±?20.73?min for the control and >240?min for the loperamide. Moreover, 1,8-cineole significantly decreased intestinal fluid accumulation (p?<?0.05).

Conclusions: This study demonstrated antispasmodic and antisecretory activities of 1,8-cineole and rationalized the traditional use of the plant containing various levels of this terpene in the treatment of gastrointestinal complains such as diarrhea.