Saturable Urinary Excretion Kinetics of Famotidine in the Dog

An important elimination route of the histamine H₂ antagonist famotidine is active tubular secretion via the renal organic cation transport system. To characterize the excretion kinetics of famotidine in-vivo, the relationship between plasma concentration and urinary excretion rate was investigated in the beagle dog over a wide concentration range. The maximum transport capacity and the apparent Michaelis–Menten constant of tubular secretion were estimated. Concentration-dependent renal clearance was determined either after intravenous infusion of high doses of famotidine for a short time or during continuous infusion. From individual experiments only indications of saturation were observed; these could not be quantified. A tubular titration curve, in which the active tubular famotidine secretion was plotted against the plasma concentration, was constructed from the data from all the experiments. Active tubular secretion was calculated for each experiment separately by subtracting the famotidine filtration rate from the total excretion rate. A tubular transport maximum of 2400 ± 220 μg min^?1 and an apparent Michaelis–Menten constant for tubular secretion of 26 ± 4 μg mL^?1 (76 ± 12 μm) were estimated from the curve. To the best of our knowledge, this is the first time that saturation of famotidine renal clearance has been fully quantified in-vivo. Considering the low therapeutic plasma concentrations of famotidine (< 0.1 μg mL^?1), these results suggest that clinically the drug has a low interactive potential.     

Nasal Epithelial Permeation of Thymotrinan (TP3) Versus Thymocartin (TP4): Competitive Metabolism and Self-Enhancement

Purpose. To investigate concentration dependent permeabilities andmetabolism kinetics of thymotrinan (TP3) versus thymocartin (TP4)in nasal epithelium in vitro. Methods. Excised bovine nasal mucosa was used as an in vitro model.Permeabilities were studied in a diffusion chamber, metabolism kineticsin a reflection kinetics set-up. Studies were performed at various TP3and TP4 concentrations. The ³H-mannitol flux was measured to monitorjunctional permeability. Potential Ca²⁺-complexation was investigatedusing a Ca²⁺-selective electrode. Results. Permeability of TP3 was negligible at 0.1 and 0.2 mM andincreased drastically above 0.4 mM up to 2 × 10^–5 cm s^–1. In thepresence of 2 mM TP4 the TP3 permeabilites were significantly above(4 × 10^–5 cm s^–1) the level of TP3 without TP4, and TP3 metabolismwas totally inhibited. TP3 and TP4 showed a significant concentrationdependent effect on the permeability of ³H-mannitol. Ahyperosmolarity effect of the peptide solutions was excluded. Transepithelialelectrical resistance (TEER; 30 cm²) was unchanged by either TP3 orTP4. At 1 mM TP3 the mucosal-to-serosal permeability was four timeshigher than serosal-to-mucosal, indicating enzyme polarization. Inreflection kinetics studies, TP3 degradation was slightly higher on themucosal than on the serosal side. TP3 and TP4 followed the samenon-linear metabolism kinetics. Conclusions. Increase in permeability at high TP concentrationsinvolves competitive enzyme saturation combined with self-enhancedparacellular permeation.     

Renal Excretion and Accumulation Kinetics of 2-Methylbenzoylglycine in the Isolated Perfused Rat Kidney

The effect of protein binding on kidney function has been studied by investigating the renal accumulation and secretion of the hippurate analogue 2-methylbenzoylglycine in the isolated perfused rat kidney in the absence and presence of bovine serum albumin (BSA). Experiments were performed with either 2.5% pluronic or a combination of 2.2% pluronic and 2% BSA as oncotic agents; a wide concentration range (1–190 μg mL^?1) of 2-methylbenzoylglycine was studied. Tubular secretion appeared to be a function of the amount of unbound drug in the perfusate and was best described by a model consisting of a high and low affinity Michaelis-Menten term. Parameters obtained after the analysis of renal excretion data were maximum transport velocity for the high affinity site (T_M,H) = 3.0 ± 2.8 μg min^?1, Michaelis-Menten constant for tubular transport for the high affinity site (K_T,H) = 0.5 ± 0.8 μg mL^?1, maximum transport velocity for the low affinity site (T_M,L) = 250 ± 36 μg min^?1, and Michaelis-Menten constant for tubular transport for the low affinity site (K_T,L) = 62 ± 17 μg mL^?1. The compound accumulated extensively in kidney tissue, ratios up to 175 times the perfusate concentration were reached. Accumulation data were best analysed by a two-site model similar to the model used to describe renal excretion. Calculated parameters were theoretical maximum capacity of the high affinity site (R_M,H) = 26 ± 23 μg g^?1, affinity constant for renal accumulation at the high affinity site (K_A,H) = 0.2 ± 0.4 μg mL^?1, theoretical maximum capacity of the low affinity site (R_M,L)= 1640 ± 1100 μg g^?1 and affinity constant for renal accumulation at the low affinity site (K_A,L) = 60 ± 58 μg mL^?1. The very high accumulation in kidney tissue could be explained by active tubular uptake, mediated by the secretory mechanisms involved, and dependent on the amount of free drug in the perfusate. This study shows that anionic drugs, subject to active secretion, may reach high concentrations in tubular cells even at low plasma concentrations.     

Validation of excised bovine nasal mucosa as in vitro model to study drug transport and metabolic pathways in nasal epithelium

The present work aims at the validation of excised bovine nasal mucosa as an in vitro model to address transport and metabolism pathways relative to the nasal mucosal uptake of therapeutic peptides. Preservation of the viability of the excised tissue in the course of in vitro studies of up to 3 h was demonstrated by (i) positive viability staining, (ii) constant transepithelial electrical resistance (42 +/- 12 Omega cm(2)), (iii) constant rates of metabolic turnover, and (iv) linear permeation profiles of therapeutic peptides and (3)H-mannitol. Using 1-leucine-4-methoxy-2-naphthylamide as a model substrate, we observed no difference between bovine and human nasal aminopeptidase activity. By a series of therapeutic peptides, no direct correlation was found between their effective permeability coefficients (from 0. 1 x 10(-5) to 5 x 10(-5) cm s(-1)) and their respective molecular masses (from 417 to 3,432 Da), indicating that other factors dominate nasal permeability. For instance, the permeabilities of metabolically labile peptides were concentration dependent and saturable, as demonstrated for two short thymopoietin fragments, Arg-Lys-Asp (TP3) and Arg-Lys-Asp-Val (TP4). By permeation studies using gonadorelin and two gonadorelin derivatives, buserelin and Hoe 013, without and in the presence of the chemical enhancer bacitracin, we also verified the ability of the model to assess chemical enhancer effects and their reversibility. In conclusion, our work demonstrates the potential of the investigated in vitro model, excised bovine nasal mucosa, to explore mechanistic aspects of nasal transport and metabolism of therapeutic peptides.     

Carboxymethylcellulose-sodium Based Transdermal Drug Delivery System for Propranolol

Propranolol, a β-adrenoceptor blocker, suffers from a high degree of first-pass metabolism resulting in very low bioavailability (<10%) following administration with conventional oral formulations. To circumvent this significant therapeutic hurdle, we formulated a carboxymethylcellulose-sodium (CMC-Na) based transdermal system for propranolol and evaluated the patch for its in-vitro and in-vivo performance. In-vitro permeation studies using the excised hair-free rat skin model resulted in 66.54% permeation at the end of 24 h in a modified Franz diffusion cell. This zero-order permeation profile was characterized by a drug permeation rate of 52.87 ± 11.63 μg cm^?2 h^?1. Skin irritation studies in rats (n = 5), evaluated for flare-and-wheal with respect to a formalin control, indicated that the drug-containing patch evoked only a mild response over a 7-day period. Preliminary in-vivo studies in male albino rabbits (n = 3), indicated that plasma drug levels averaged 11.75 ± 3.40 ng mL^?1 in a 24-h study period before patch removal.     

Antipsychotic Potential and Safety Profile of TPGS-Based Mucoadhesive Aripiprazole Nanoemulsion: Development and Optimization for Nose-To-Brain Delivery

Delivering therapeutics to the brain using conventional dosage forms is always a challenge, thus the present study was aimed to formulate mucoadhesive nanoemulsion (MNE) of aripiprazole (ARP) for intranasal delivery to transport the drug directly to the brain. Therefore, a TPGS based ARP-MNE was formulated and optimized using the Box-Behnken statistical design. The improved in vitro release profile of the formulation was in agreement to enhanced ex vivo permeation through sheep mucous membranes with a maximum rate of permeation co-efficient (62.87  cm h^?1 × 10³) and flux (31.43  μg cm^?2.h^?1). The pharmacokinetic profile following single-dose administration showed the maximum concentration of drug in the brain (C_max) of 15.19 ± 2.51  μg mL^?1 and T_max of 1 h in animals with ARP-MNE as compared to 10.57 ± 1.88  μg mL^?1 and 1 h, and 2.52 ± 0.38  μg mL^?1 and 3 h upon intranasal and intravenous administration of ARP-NE, respectively. Further, higher values of % drug targeting efficiency (96.9%) and % drug targeting potential (89.73%) of ARP-MNE through intranasal administration were investigated. The studies in Wistar rats showed no existence of extrapyramidal symptoms through the catalepsy test and forelimb retraction results. No ex vivo ciliotoxicity on nasal mucosa reflects the safety of the components and delivery tool. Further, findings on locomotor activity and hind-limb retraction test in ARP-MNE treated animals established its antipsychotic efficacy. Thus, it can be inferred that the developed ARP-MNE could effectively be explored as brain delivery cargo in the effective treatment of schizophrenia without producing any toxic manifestation.     

Stability,tissue metabolism,tissue distribution and blood partition of azosemide

Stability of azosemide after incubation in various pH solutions, human plasma, human gastric juice, and rat liver homogenates, metabolism of azosemide after incubation in 9000g supernatant fraction of various rat tissue homogenates in the presence of NADPH, tissue distribution of azosemide and M1 after intravenous (IV) administration of azosemide, 20 mg kg^?1, to rats, and blood partition of azosemide between plasma and blood cells from rabbit blood were studied. Azosemide seemed to be stable for up to 48 h incubation in various pH solutions ranging from two to 13 at an azosemide concentration of 10 μg mL^?1; more than 93.4% of azosemide was recovered and a metabolite of azosemide, M1, was not detected. However, the drug was unstable in pH 1 solution: 75.8% of azosemide was recovered and 2.16 μg mL^?1 of M1 (expressed in terms of azosemide) was formed after 48 h incubation in pH 1 solution at an azosemide concentration of 10 μg mL^?1. Azosemide was stable in both human plasma and rat liver homogenates for up to 24 h incubation at an azosemide concentration of 1 μg mL^?1, and in human gastric juice for up to 4 h incubation at an azosemide concentration of 10 μg mL^?1. However,-all rat tissues stdied had metabolic activity for azosemide in the presence of NADPH, with heart having a considerable metabolic acitivity: approximately 22% of azosemide disappeared and 9.32 μg of M1 was formed per gram of heart (expressed in terms of azosemide) after 30 min incubation of 50 μg of azosemide in 9000g supernatant fraction of heart homogenates. The tissue to plasma ratios of azosemide (T/P) were greater than unity only in the liver (1.26) and kidney (1.74); however, M1 showed high affinity for all tissues studied except the brain and spleen when each tissue was collected at 30 min after IV administration of azosemide to rats. The equilibrium plasma to blood cell concentration ratios of azosemide were independent of azosemide blood concentrations: the values were 2.78–4.25 at azosemide blood concentrations of 1, 10, and 20 μg mL^?1 three rabbits. There was negligible ‘blood storage effect’ of azosemide, especially at low blood concentrations of azosemide, such as 1 and 10 μg mL^?1.     

Renal Tubular Excretion of the N4-Acetyl Metabolites of Sulphasomidine and Sulphadimethoxine in the Dog

Abstract— To investigate whether dogs are able to excrete acetylated drugs by active transport, the plasma kinetics and renal excretion of the N₄-acetyl metabolites of sulphasomidine and sulphadimethoxine were studied in the beagle dog after a rapid intravenous bolus injection. Two doses of N₄-acetylsulphasomidine (1050 and 105 mg) and one dose of N₄-acetylsulphadimethoxine (472 mg) were administered on separate occasions. The renal clearance (CL_R) was as follows: N₄-acetylsulphasomidine (1050 mg) 34 mL min^?1; N₄-acetylsulphasomidine (105 mg) 28 mL min^?1; and N₄-acetylsulphadimethoxine (472 mg) 24 mL min^?1. CL_R was higher than expected on the basis of the measured glomerular filtration rate, indicating that the N₄-acetyl metabolites may be excreted by the renal tubules by active tubular transport. Saturation of the excretion process of N₄-acetylsulphasomidine occurred with a transport maximum of 930 ± 190 μg min^?1 and a Michaelis-Menten constant of 37 ± 10 μg mL^?1. It may be concluded that the dog renal organic anion transport system is able to secrete acetylated sulphonamides.     

Absorption and secretion of monoquaternary ammonium compounds by the isolated intestinal mucosa

The transepithelial permeation and the cellular uptake of N-methylscopolamine (NMScop), N¹-methylnicotinamide (NMN), and tetraethylammonium (TEA) were studied in the isolated jejunal mucosa of the guinea pig. (1). The permeation rate, corrected for the fraction passing through the mucosa via an extracellular route (corr. permeation), was significantly higher in the direction blood-to-lumen than in the direction lumen-to-blood with concentrations below 500 μM. The corr. permeations' ratio at concentrations of 0.1 and 1 μM NMScop was 12, the corresponding values for 1 μM NMN and 50 μM TEA were 2.5 and 2, respectively. The corr. permeation blood-to-lumen decreased with increasing concentrations administered, and with the highest concentrations (1000–2000 μM) the differences in permeation in the two directions were insignificant. During anaerobiosis the corr. permeation ratios approached 1 with all concentrations, and the corr. permeations were not dependent on the concentrations administered. (2). The kinetics of cellular uptake displayed similar characteristics: the uptake from the blood side was significantly larger than that from the lumen side of the mucosa. This difference decreased with increasing concentrations or anaerobiosis without being abolished completely. (3). The three monoquaternary ammonium compounds were transported uphill, creating a concentration ratio lumen-side/blood-side greater than 1, which was highest with NMScop (1.65 within 180 min). The establishment of this gradient was prevented by anaerobiosis. (4). Rising concentrations of NMScop progressively inhibited the corr. permeation from blood to lumen and the cellular uptake of NMN from the blood side of the mucosa. The results demonstrate the existence of an active secretory system for monoquaternary ammonium compounds in the jejunal epithelium. The experimental data are consistent with a cell model, which has two transport systems in series, one in the basal and one in the luminal cell membrane and both directed towards the intestinal lumen, plus a non-saturable pathway in each of the two cell membranes.     

Cr and Hg toxicity assessed in situ using the structural and functional characteristics of algal communities

The toxicity of mercury and chromium on algal community structure have been assessed using in situ N₂ase activity, pigment diversity, autotrophic index, and ¹⁴C uptake of algae. The location was in the river Ganga and controlled ecosystem pollution experiment enclosures were used. Maximum inhibition of algal number was observed at 0.8 μg Hg mL^?1 followed by 8.0 μg Cr mL^?1. Unicellular forms, except for Anorthoneis excentrica, were very sensitive to test metals used. The decline in algal number was concentration dependent and metal specific at generic and species levels. Complete elimination of three and six species was observed respectively at 8.0 μg Cr mL^?1 and 0.8 μg Hg mL^?1 after 12 days' exposure. Likewise, a concentration-dependent and metal-specific increase in autotrophic index and pigment diversity of phytoplankton was recorded for Hg and Cr. Inhibition of ¹⁴C uptake of phytoplankton in Ganga water was almost equal (79%) at 0.8 μg Hg mL^?1 and 8.0 μg Cr mL^?1 (78%). Although complete inhibition of in situ N₂ase was observed at 0.8 μg Hg mL^?1, it was only 80% with 8.0 μg Cr mL^?1. Our study suggests that heavy metals inhibit both structural and functional variables of phytoplankton in field microcosms. Hence this technique seems to hold potential for the biomonitoring of heavy metal toxicity in the field.     

Midazolam α-Hydroxylation by Human Liver Microsomes in vitro: Inhibition by Calcium Channel Blockers,Itraconazole and Ketoconazole

Abstract: The inhibitory effects of five calcium channel blockers (diltiazem, isradipine, mibefradil, nifedipine and verapamil) and three azole antifungal agents (itraconazole, hydroxyitraconazole and ketoconazole) on the α-hydroxylation of midazolam, a probe drug for CYP3A4-mediated interactions in humans, were studied in vitro using human liver microsomes. IC₅₀ and K_i values were determined for each inhibitor. The kinetics of the formation of α-hydroxymidazolam were best described by simple Michaelis-Menten kinetics. The estimated values of V_max and K_m were 696 pmol min.^?1 mg^?1 and 7.46 μmol l^?1, respectively. All the compounds studied inhibited midazolam α-hydroxylation activity in a concentration-dependent manner, but there were marked differences in their relative inhibitory potency. Ketoconazole was the most potent inhibitor of midazolam α-hydroxylation (IC₅₀ 0.12 μmol l^?1), being 10 times more potent than itraconazole (IC₅₀ 1.2 μmol l^?1). The inhibitory effect of hydroxyitraconazole (IC₅₀ 2.3 μmol l^?1) was almost as large as that of itraconazole. Among the calcium channel blockers, mibefradil was the most potent inhibitor of the α-hydroxylation of midazolam, with an IC₅₀ value (1.6 μmol l^?1) similar to that of itraconazole. The other calcium channel blockers were much weaker inhibitors than mibefradil: verapamil exhibited a modest inhibitory effect with an IC₅₀ of 23 μmol l^?1, while isradipine, nifedipine and diltiazem, with IC₅₀ values ranging from 57 to >100 μmol l^?1, were weak inhibitors. This rank order of potency against the α-hydroxylation of midazolam was verified by the K_i values. With the exception of diltiazem, these in vitro results conform with the observed interaction potential of these agents with midazolam and many other CYP3A4 substrates in vivo in man.     

Natural Products: Anti-proliferative Effects of Lichen-derived Inhibitors of 5-Lipoxygenase on Malignant Cell-lines and Mitogen-stimulated Lymphocytes

Several lichen species have been used traditionally as medicinal plants. It has previously been shown that two low-molecular-weight lichen metabolites, lobaric acid isolated from Stereocaulon alpinum Laur. and protolichesterinic acid isolated from Cetraria islandica L. (Ach.), have in-vitro inhibitory effects on arachidonate 5-lipoxygenase. We have studied the effects of these compounds on cultured cells from man, including three malignant cell-lines (T-47D and ZR-75-1 from breast carcinomas and K-562 from erythro-leukaemia), as well as normal skin fibroblasts and peripheral blood lymphocytes. Both test substances caused a significant reduction in DNA synthesis, as measured by thymidine uptake, in all three malignant cell-lines; the dose inducing 50% of maximum inhibition (ED50) was between 1.1 and 24.6 μg mL^?1 for protolichesterinic acid and between 14.5 and 44.7 μg mL^?1 for lobaric acid. The breast-cancer cell-lines were more sensitive than K-562. The proliferative response of mitogen-stimulated lymphocytes was inhibited with a mean ED50 of 8.4 μg mL^?1 and 24.5 μg mL^?1 for protolichesterinic acid and lobaric acid, respectively. These concentrations are of the same order of magnitude as the IC50 values in the 5-lipoxygenase assay. Significant cell death (assessed by the MTS (3–4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and trypan blue exclusion) occurred in the three malignant cell-lines at protolichesterinic acid and lobaric acid concentrations above 20 and 30 μg mL^?1, respectively. In K-562 morphological changes consistent with apoptosis were detected. Up to 38% cell death was observed at 20 μg mL^?1 for protolichesterinic acid and 15 μg mL^?1 for lobaric acid in mitogen-stimulated lymphocytes but unstimulated lymphocytes were clearly less sensitive. In contrast, the DNA synthesis, proliferation and survival of normal skin fibroblasts were not affected at doses up to 20 μg mL^?1 for protolichesterinic acid and 30 μg mL^?1 for lobaric acid. We conclude that the anti-proliferative and cytotoxic effects observed might be related to the 5-lipoxygenase inhibitory activity of protolichesterinic acid and lobaric acid. These results open up the opportunity for future studies of these lichen metabolites with regard to their anti-tumour and anti-inflammatory properties.     

Effect of lignocaine on eicosanoid synthesis by pieces of human gastric mucosa

Abstract— Lignocaine can affect prostaglandin synthesis in various tissues, and it has anti-inflammatory activity. No studies have been made previously on human isolated gut tissues. When concentrations of 5, 50 and 250 μg mL^?1 lignocaine were incubated with human gastric mucosa/submucosa at 37°C for 30 min, only the highest concentration reduced the levels of prostaglandin E, thromboxane B₂ and 6-keto-PGF_1α in the incubates, and leukotriene C₄/D₄ was unaffected. Therapeutically relevant amounts of lignocaine given parenterally would therefore seem unlikely to alter gastric mucosal prostanoids, but high doses can be given orally because of extensive first-pass metabolism in the liver.     

Comparative Cardiovascular Effects of the Angiotensin II Type 1 Receptor Antagonists ZD 7155 and Losartan in the Rat

Binding experiments show that ZD 7155 is a potent angiotensin II type 1 receptor antagonist. In this study this novel substance was studied in normotensive and hypertensive rats. The relative potency and duration of the antihypertensive effects of ZD 7155 were compared with those of the reference substance, losartan. The inhibitory effects of both compounds on angiotensin II-induced pressor actions were studied in the conscious normotensive Sprague-Dawley (SD) rat and in the conscious, spontaneously hypertensive rat (SHR). Arterial blood pressure and heart rate (HR) were obtained by direct intraarterial recording. Angiotensin II infusion was administered intravenously in the dose range 53.3 ng—12.8 μg kg^?1 min^?1 to the conscious rats. ZD 7155 was administered in a bolus dose of 1.082 μmol kg^?1 (0.51 mg kg^?1) and losartan in bolus doses of 2.165 and 6.495 μmol kg^?1 (1.0 and 3.0 mg kg^?1). In conscious SD rats, ZD 7155 and losartan behaved as competitive antagonists and the pressor response curve to angiotensin II was shifted to the right. Experiments in conscious SD rats also showed that ZD 7155 was approximately ten times as potent as losartan in suppressing the angiotensin II-induced pressor response (240 ng kg^?1; 10 min infusion). In addition, experiments with conscious rats demonstrated that ZD 7155 could suppress the angiotensin II-induced pressor response for approximately 24 h when ZD 7155 was administered intravenously in a 1.082 μmol kg^?1 bolus dose and angiotensin II was given at 240 ng kg^?1 (in a 10?min infusion). Experiments in conscious SHRs using ZD 7155 (1.082 μmol kg^?1) and losartan (6.495 μmol kg^?1) as intravenous boluses indicated that both ZD 7155 and the reference compound losartan exhibited a significant antihypertensive effect. These results demonstrate that ZD 7155 is a potent angiotensin II-type 1 antagonist which is approximately ten times as potent as losartan in suppressing the angiotensin II-induced pressor response. Furthermore, ZD 7155 may suppress the angiotensin II-induced pressor response for 24 h and in the SHR ZD 7155 induces a pronounced and persistent antihypertensive effect.     

An improved primary human nasal cell culture for the simultaneous determination of transepithelial transport and ciliary beat frequency

Objectives The aim was to establish a preclinical in‐vitro system of the nasal mucosa for the simultaneous evaluation of nasal absorption and effects on ciliary activity. Methods Human nasal epithelial cells were grown in collagen‐coated transport inserts with transparent polyethylene terephthalate membranes (3 μm). Transepithelial transport and ciliary beat frequency values were measured every 15 min for 1 h. Key findings The apparent permeability coefficients (P_app) for atenolol (mainly paracellular transport) and propranolol (transcellular transport) amounted to 0.1 ± 0.1 and 23.7 ± 0.6 × 10^?6 cm/s, respectively, illustrating that the system can be used to discriminate between high permeability and low permeability compounds. Transport of talinolol (substrate for the P‐glycoprotein efflux carrier) did not reveal polarity (0.3 ± 0.2 and 0.2 ± 0.1 × 10^?6 cm/s for absorptive and secretory transport, respectively) and was not affected by verapamil (10 μm), suggesting the absence of P‐glycoprotein in the nasal cell culture. No significant effects of atenolol, propranolol and talinolol on ciliary beat frequency were observed (98 ± 20% of the control condition after 60 min). Chlorocresol significantly decreased the ciliary activity but this decrease was not accompanied by effects on the transepithelial transport of atenolol, propranolol and talinolol. Conclusions A new system was developed which offers possibilities as a fast screening tool for studying the potential of compounds for nasal drug administration, since permeability and a possible cilio‐toxic effect can be assessed simultaneously.     

The Effects of N-Benzoyl-β-alanine,a New Nephroprotective Drug,on the Distribution and Renal Excretion of Enprofylline in Rats

Abstract— The effects of the new nephroprotective drug N-benzoyl-β-alanine (BA) on the disposition and renal excretion of the bronchodilator enprofylline, which is actively secreted in urine, were investigated in rats. Enprofylline was administered intravenously at a dosage of 2·5 mg kg^?1 under three different steady-state plasma BA concentrations (100,200 and 400 μg mL^?1) which were achieved by constant infusion rates. Pharmacokinetic parameters for both total and unbound enprofylline were estimated by model-independent methods. The presence of BA (400 μg mL^?1) increased the systemic clearance by 25% and the volume of distribution at steady-state by 90%. A significant increase in the dissociation constant, which is the protein binding parameter of enprofylline was observed in the presence of BA (400 μg mL^?1), indicating that BA competitively inhibits the protein binding of enprofylline. However, BA significantly decreased the systemic clearance and volume of distribution for unbound enprofylline. These results suggest that BA, the organic anion transport inhibitor, inhibits renal excretion of enprofylline with a high affinity for renal tubular secretion, although the unbound concentration of enprofylline increases with administration of BA. We conclude that BA decreases the renal tubular secretion of enprofylline probably by reducing the affinity of the tubular transport system, and that these changes have marked effects on the pharmacokinetic behaviour of enprofylline.     

Protection by Almagate of Ethanol-induced Gastric Mucosal Damage in Rats

The study was designed to analyse the protective effects of almagate on a model of gastric injury, ethanol-induced mucosal damage, in which acid plays little, if any, role. Pretreatment with almagate dose-dependently reduced the level of gastric damage induced by oral administration of 1mL 100% ethanol. Administration of 12 μmol kg^?1 almagate 30 min before ethanol significantly reduced the area of mucosal damage by 65 ± 10%, and the maximum level of inhibition (74 ± 11%) was obtained with 150 μmol kg^?1 almagate. Administration of higher doses of almagate (200–250 μmol kg^?1) did not result in any further increase in the level of protection against ethanol-induced gastric damage. Administration of 1 mL 100% ethanol induces substantial damage to the gastric mucosa, with nearly 40% of the length of the section evaluated exhibiting deep necrotic and haemorrhagic damage. Pretreatment with almagate caused a significant diminution in all parameters of histological damage, whereas damage to the epithelial cell layer was only significantly reduced by pretreatment with the highest doses evaluated (25, 50 and 150 μmol kg^?1). Administration of aluminium hydroxide did not modify ethanol-induced mucosal damage, even at doses containing concentrations of aluminium higher than those present in gastroprotective doses of almagate. Pretreatment with sucralfate, another aluminium containing compound, at doses of 250 μmiol kg^?1 protected the mucosa, although lower doses did not. The present study has shown that almagate prevents ethanol-induced gastric mucosal damage. This protective effect seems independent of any antacid activity, related to its content in magnesium, and mediated by an increase in gastroprotective prostaglandins in the mucosa of the stomach.     

Plasma pharmacokinetics and urinary and biliary excretion of a new potent tripeptide HIV-1 protease inhibitor,KNI-272, in rats after intravenous administration

The pharmacokinetic (PK) characteristics of KNI-272, a potent and selective HIV-1 protease inhibitor, were evaluated in rats after intravenous (IV) administration. The effect of dose on KNI-272 plasma kinetics, and the urinary and biliary elimination kinetics of KNI-272, were examined. After IV administration of 10.0 mg kg^?1 KNI-272, the mean terminal elimination half-life, t_1/2λz, was 3.49 ± 0.19 (SE) h, the total plasma clearance, CL_tot, was 15.1 ± 1.2 mL min^?1 and the distribution volume at steady state, V_d,ss, was 3790±280 mL kg^?1. On the other hand, after 1.0mg kg^?1 IV administration, t_d,ss, was 3.04±0.11 h, CL_tot was 15.9±0.2mL min^?1, and V_d,ss was 6950±600 mL kg^?1. The PK parameters of KNI-272 after IV administration showed that the disposition of KNI-272 in the rat plasma is linear within the dose range from 1.0 to 10.0mg kg^?1. Using an equilibrium dialysis method, the plasma binding of KNI-272 was measured in vitro. The free fractions were 17.7 ± 0.6%, 12.1±1.5%, and 13.8 ± 1.4% at the total concentration ranges of 9.898 ± 0.097 μg mL^?1, 0.888 ± 0.008 μg mL^?1, and 0.470±0.55 μg mL^?1, respectively. The percentages of the dose excreted into the urine and bile as the unchanged form were 1.20 ± 1.06% and 1.61 ± 0.32% at 1.0mg kg^?1 dose, and 0.164 ± 0.083% and 1.42 ± 0.26% at 10.0 mg kg^?1 dose, respectively. The renal clearance (CL_R) and the biliary clearance (CL_B) were calculated to be 0.191 and 0.256mL min^?1 for 1.0mg kg^?1, and 0.0248 and 0.215 mL min^?1 for 10.0 mg kg^?1, respectively. When comparing these values with the CL_tot values, the urinary and biliary excretion of KNI-272 are minor disposition routes.     

Effect of the Hydroalcoholic Extract of Rauwolfia ligustrina on Smooth and Cardiac Muscles In-vitro

The actions of the hydroalcoholic extract (HE) of Rauwolfia ligustrina (the whole plant) on agonist-induced contractions were analysed in the rat uterus and guinea-pig ileum and trachea, and also in rat atrium contracting spontaneously in-vitro. The HE (100–400 μg mL^?1) caused concentration-dependent rightward shifts of the concentration-response curves and reduced the maximal contraction induced by oxytocin, bradykinin, angiotensin II, prostaglandin F_2α and acetylcholine in the rat uterus. The calculated mean IC50 values were: 300, 147, 158, 197 and 105 μg mL^?1, respectively. In the guinea-pig ileum the HE also caused graded displacement to the right of the concentration—response curves for bradykinin, histamine and carbachol, associated with pronounced inhibition of the agonist-induced maximal contractions. The calculated mean IC50 values were 165, 134 and 241 μg mL^?1, respectively. The HE (100–3000 μg mL^?1) caused graded relaxation (IC50 of 271 μg mL^?1) of strips of guinea-pig trachea precontracted with carbachol (0.2 μM). This effect was not infuenced by propranolol (1 μM), 3-isobutyl-1-methylxanthine (1 μM) or methylene blue (10 μM), but was significantly potentiated (1.5-to 3-fold) by indomethacin (3 μM) and forskolin (1 nM). In addition, N^G-monomethyl-L-arginine (L-NMMA, 100 nM) significantly reduced the HE-induced maximal relaxation, while indomethacin (3 μM) potentiated the HE response. Finally, the HE caused a concentration-dependent and long-lasting inotropic effect in the rat right atrium, contracting spontaneously with a mean EC50 value of 409 μg mL^?1. It is suggested that the effects of the HE of R. ligustrina on smooth and cardiac muscles ‘in-vitro’ may result from its ability to interact, at least partially, with the cAMP pathway.     

The disposition of nifurtimox in the rat isolated perfused liver: effect of dose size

Abstract— The disposition of nifurtimox was studied in the rat isolated perfused liver using a recirculating system. The drug was administered as a bolus (5·0, 15·0 or 30·0 μg mL^?1), and its disappearance was monitored by analysing perfusate samples. In all experiments perfusate disappearance was monoexponential, and no significant difference was found between the three doses for the elimination constant (0·016, 0·011 and 0·012 min^?1, respectively), half-life (46·6, 65·8 and 66·8 min, respectively), extraction rate (0·128, 0·091 and 0·099, respectively) and distribution volume (41·1, 47·3 and 30·7 mL g^?1, respectively). At 30 μg mL^?1 the hepatic clearance was lower than the other concentrations of nifurtimox (0·66, 0·51 and 0·34 mL min^?1 g^?1, respectively). Relatively little parent drug was recovered from the liver at the end of the perfusions. In summary, nifurtimox is cleared slowly from the rat isolated perfused liver, is poorly extracted by hepatocyte cells and is completely metabolized from 2 to 4 h after perfusion.