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PubMed1980

[Absorption of calcium by growing goats: effect of oxalates].

The influence of sodium oxalate and calcium oxalate upon calcium digestibility was studied in growing goats. Furthermore, and in the same animals, calcium absorption efficiency was estimated after performing duodenal fistula which allowed us to introduce calcium chloride or calcium oxalate and sodium oxalate, in order to avoid ruminal bacteria action upon the forementioned compounds. Finally, calcium absorption of an isolated intestine loop was studied in conscious goats with a Crocker Markowitz fistula, in the presence or absence of oxalate. The addition of sodium oxalate to the diet did not significantly decrease calcium absorption; but when calcium was given as oxalate, absorption was considerably lower. When calcium was introduced as calcium chloride through duodenal fistula, absorption was the same as when the substance was given in the diet. Calcium absorption drastically decreased when sodium oxalate was introduced directly into the duodenum, this fact is confirmed when calcium absorption is estimated in a jejunal loop, which shows that the differences found in relation to the effect of dietary sodium oxalate or directly introduced in duodenum are due to the substance destruction by ruminal bacteria.

Absorption↗
PubMed1998

Permeability characteristics of piperine on oral absorption--an active alkaloid from peppers and a bioavailability enhancer.

Piperine, [1-[5-[1,3-benzodioxol-5-yl]-1-oxo-2,4, pentadienyl] piperidine], is a pungent alkaloid present in Piper nigrum Linn, and P. longum Linn. It is shown to enhance the bioavailability of various structurally and therapeutically diverse drugs. A concise mechanism responsible for its bioavailability enhancing action is poorly understood. This study is an effort to understand the absorption dynamics of piperine in intestine on oral absorption. It encompasses intestinal everted sacs as an experimental model. Cycloheximide treatment and exclusion of Na+ salts from incubating medium were the variables used. Absorption half life, absorption rate, absorption clearance and apparent permeability co-efficient were computed from the data. Experiments to denote physico-chemical characteristics of this moiety exhibited that it is a weak base, highly lipophilic in nature with partial solubility in aqueous media. It exhibited passive diffusion constituting non-saturable absorption kinetics. Transport of piperine was not resisted by UWL and was proposed to be absorbed through transcellular pathway. It displayed short absorption clearance and high apparent permeability co-efficient. Data thus obtained suggested that piperine is absorbed very fast across the intestinal barrier. It may act as an apolar molecule and form apolar complex with drugs and solutes. It may modulate membrane dynamics due to its easy partitioning thus helping in efficient permeability across the barriers.

Absorption↗
PubMed1990

Absorption of 308-nm excimer laser radiation by balanced salt solution, sodium hyaluronate, and human cadaver eyes.

Absorption of the excimer laser radiations of 193-nm argon fluorine and 308-nm xenon chloride in balanced salt solution, sodium hyaluronate, and human cadaver eyes was measured. The absorption of these materials as considerably different for the two wavelengths; we found that 308-nm light experienced much less absorption than the 193-nm light. The extinction coefficient (k) for 308 nm was k = 0.19/cm for balanced salt solution and k = 0.22/cm for sodium hyaluronate. In contrast to this, the extinction coefficient for 193 nm was k = 140/cm for balanced salt solution and k = 540/cm for sodium hyaluronate. Two 1-day-old human phakic cadaver eyes showed complete absorption with both wavelengths. Using aphakic eyes, incomplete absorption was noted at the posterior pole with 308 nm and complete absorption was noted with 193 nm. The extinction in the anterior part of aphakic eyes (the first 6 mm) was 4.2/cm for 308 nm, meaning that the intensity of the light is reduced by a factor of 10 after traveling the first 5.5 mm. However, we observed that the material in the eye fluoresces, meaning the 308 nm is transformed into other (longer) wavelengths that travel through the total eye with minimal absorption. Conclusions drawn from this experiment are that the use of the 308-nm wavelength may have undesirable side effects, while the use of the 193-nm wavelength should be consistent with ophthalmic use on both the cornea and the lens.

Absorption↗
PubMed2000

Improvement of intestinal absorption of macromolecules by nitric oxide donor.

Nitric oxide (NO) is one of the most versatile mediators in mammalian biology. In the present study, we investigated the absorption-enhancing effects of an NO donor, 3-(2-hydroxy-1-methylethyl-2-nitrosohydrazino)-N-methyl-1-propa namine (NOC7), on drugs that are poorly absorbed from the gastrointestinal tract. NOC7 significantly increased the jejunal absorption of fluorescein isothiocyanate dextrans (FDs) of different average molecular weights (4000-20,000). This enhancing effect decreased as the FD molecular weight increased. Another NO donor, S-nitroso-N-acetyl-DL-penicillamine (SNAP), also increased the absorption of FD-4 from the jejunum. The absorption enhancement effect of NOC7 significantly decreased after coadministration with an NO scavenger, 2-(4-carboxyphenyl)-4,4,5, 5-tetramethylimidazole-1-oxyl-3-oxide, sodium salt. Furthermore, the enhancement effect of NOC7 was reversed shortly after cessation of the enhancer treatment. Little damage by NOC7 to the intestinal mucosa was observed in terms of release of lactose dehydrogenase and protein from the intestinal mucosa. NOC7 also increased the absorption of FD-4 by the colon and rectum. The findings suggest that an NO donor can improve the absorption of macromolecules from all regions of the rat intestine with very little mucosal damage and that an NO donor can act as a potent absorption enhancer.

Animals↗
PubMed2001

Regional-dependent intestinal absorption and meal composition effects on systemic availability of LY303366, a lipopeptide antifungal agent, in dogs.

Low oral bioavailability and a negative meal effect on drug plasma levels motivated studies on formulation and meal composition effects on the absorption of LY303366, a poorly water-soluble, semisynthetic, cyclic peptide antifungal drug. Solid drug particle size and meal composition studies were evaluated in beagle dogs. Canine regional absorption studies were also carried out utilizing surgically implanted intestinal access ports, and Caco-2 studies were performed to evaluate drug candidate intestinal permeability. Particle size and Caco-2 data indicate that drug permeability limitations to absorption are more important than dissolution rate limits. Caco-2 cell-associated LY303366 approached 10% of incubation concentration that is in the range of the oral bioavailability of the drug. Canine regional absorption studies showed that the extent of LY303366 absorption following duodenal administration was similar to that following oral administration. Significantly lower drug plasma levels were obtained following administration through a colonic access port, a result consistent with poor membrane permeation. Administration of drug with meals of mixed composition, as well as simple fat and protein meals, resulted in significant reductions in AUC(0-48h) compared with results from fasted dogs. In contrast, carbohydrate meals did not reduce drug plasma levels compared to controls. Intravenous pretreatment with devazepide, a cholecystokinin (CCK) antagonist that blocks canine biliary secretion, did not reverse the negative effect of the fat meal on LY303366. Taken together, the results from the present study suggest that membrane-permeability-limited absorption is the cause of the observed regionally dependent absorption of LY303366 in the dog and that the observed negative meal effects depend on composition but are independent of biliary secretion.

Anidulafungin↗
PubMed2001

Kinetics of finite dose absorption through skin 1. Vanillylnonanamide.

Despite the considerable success in predicting the steady-state dermal absorption rates of chemical compounds from large reservoirs applied to skin, correspondingly little progress has been made in predicting the absorption rate and extent for small doses of topically applied compounds. In the latter case, steady-state absorption rates are generally not obtained, and rapid evaporation or penetration of the dose solvent makes application of permeability coefficient models problematic. This report presents a new analysis of the finite dose problem in terms of a diffusion model with three parameters-a characteristic time for diffusion, h2/D; a skin solubility factor, S(m)h; and a capacity factor for absorption of the dose during the dry down period, M*. These parameters can be related to the molecular weight and oil and water solubilities of the permeant in a manner similar to models describing steady-state absorption from saturated solutions. Some variation of the parameter values based on the chemical nature and volume of the dose solvent is anticipated. The applicability of the model is demonstrated by analyzing the in vitro absorption rates of varying doses of vanillylnonamide (VN, synthetic capsaicin) applied to excised human skin from propylene glycol. The analysis shows that a three-parameter model that assigns all of the resistance to transport to diffusion through the stratum corneum is able to explain most of the significant features of VN absorption through skin.

Animals↗
PubMedDate not supplied

Absorption and disposition characteristics of nitrofurantoin in dogs.

This study reports the disposition kinetic properties of nitrofurantoin in dogs following single intravenous and oral administration of various formulations of nitrofurantoin. Also reported here is the effect of delaying gastric emptying by food and atropine on the absorption characteristics of nitrofurantoin. The drug absorption parameters calculated using a deconvolution computer program indicate that the rate and extent of enterohepatic recycling affects the elimination and absorption rate constants and thus confound the bioavailability calculations of nitrofurantoin, heretofore unrecognized in the literature. The plasma half-life following intravenous administration was 31 min (monoexponential equation) with little effect of enterohepatic recycling noted. Following oral administration, a biexponential equation with lag-time was used to fit the blood levels. The absorption half-lives were higher when nitrofurantoin was administered as a solid dosage form compared to a solution. The absorption half-lives following tablet administration ranged from 30 to 72 min and were not affected by food or atropine. The elimination half-lives following oral administration ranged from 19 to 87 min with significantly prolonged elimination when solid dosage forms were administered compared to solution. The extent of absorption ranged from 38 to 120 per cent. A direct correlation between the absorption and elimination half-life was established, indicating that increased biliary recycling direct affects the apparent disposition half-life. The three brands of nitrofurantoin tested for bioavailability showed that the use of blood levels without appropriate corrections for biliary recycling are not suitable for bioavailability testing of nitrofurantoin. The use of urinary excretion data in evaluating nitrofurantoin bioavailability is also questioned in the study.

Administration, Oral↗
PubMed1994

The effect of oral dose volume on the absorption of a highly and a poorly water-soluble drug in the rat.

The influence of dose volume on drug absorption following oral administration of a highly and a poorly water soluble drug was examined in male Sprague-Dawley rats. A constant mass of each 14C-labeled compound was given via gavage in dose volumes of 1, 5, 10, and 20 mL kg-1. Blood levels, as well as the quantitative excretion of radioactivity, were measured following each treatment. No significant changes in either the rate or extent of absorption of the water soluble drug were detected. In contrast, the absorption rate of the poorly water soluble drug increased with higher dose volumes, whereas no changes in the extent of absorption were observed. Drug solubility and gastric emptying appeared to be important factors affecting the rate of absorption of the poorly water soluble drug. Since changes in dose volume may affect the absorption characteristics of orally administered compounds, and the extent of such changes may be dependent upon the physicochemical properties of the drug, it is apparent that dose volume is an important experimental variable to be considered in studies comparing absorption data.

Animals↗
PubMed1995

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

The inhibitory effect of the essential alpha-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, Ki = 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 (0.5 mM) were Vm = 61.02 (+/- 5.46)mM h-1; Km = 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.

Amino Acids↗
PubMed1990

Albumin absorption and protein secretion by the gallbladder in man and in the pig.

To study albumin absorption by the gallbladder in man, an in vitro model was first established in the pig and compared with in vivo function in the same species. Water and electrolyte transport and 125I-albumin absorption and protein secretion in vivo and in vitro were compared. Then similar in vitro studies were performed on human gallbladders obtained at surgery. The in vivo study in the pig was performed without disturbing the gallbladder except to tie a cannula in the cystic duct end. The in vitro model was identical in the pig and human gallbladders. Gallbladders were excised using a technique causing minimal injury and anoxia. They were oxygenated on both mucosal and serosal surfaces in a temperature-controlled environment. Luminal and external bath test solutions consisted of modified Ringers bicarbonate with added glucose; luminal solutions also contained 125I-albumin from different species, depending on the study. Active absorption of sodium and water occurred in both types of studies in the pig but in vivo absorption rates were considerably greater than in vitro rates. Albumin absorption in vivo was substantial; although present in vitro, the absorption of albumin was diminished relatively more than electrolyte transport rates. Protein secretion rates into the gallbladder were similar in vitro and in vivo. The results of studies in the human gallbladders in vitro were similar to the pig, except albumin absorption was greater. Some human gallbladders were obtained from control patients and some from patients with cholesterol gallstones. There were no significant differences between the two groups for any of the variables studied; however, the numbers were small and some control gallbladders were not normal gallbladders.

Absorption↗
PubMed1994

Absolute bioavailability and absorption characteristics of aerosolized tobramycin in adults with cystic fibrosis.

Administration of antibiotics by the inhalational route has become part of standard protocols for treatment of and prophylaxis for Pseudomonal pneumonias in patients with cystic fibrosis. For tobramycin, however, limited data are available on the aerosol absorption patterns, and no absolute bioavailability data for tobramycin exist. The purpose of this study was to measure the absolute bioavailability and systemic absorption characteristics of tobramycin when administered in high doses by a nebulizer. Multiple serum concentrations of tobramycin were measured after administration of an intravenous dose (mean, 2.9 mg/kg every 6 hours) and after an inhalational dose (5.6 mg/kg over 1 hour). Inhalational doses were superimposed over the "tail" of a steady-state intravenous dose to improve the sensitivity of the assay procedure (Abbott-TDX). Absolute bioavailability (F) was determined from AUC ratios normalized for dose. Model-independent pharmacokinetic parameters (volume of distribution [Vss] and total clearance [CLt]) were determined for each subject. Absorption characteristics (absorption rate constant [Ka] and mean absorption time [MAT]) were assessed after calculation of the cumulative fraction of drug absorbed, amount of bioavailable drug, and percent remaining to be absorbed per unit time using the Loo-Riegelman method. Three men and three women completed the study, and all received concurrent doses of ceftazidime. Mean absolute bioavailability (+/- standard deviation) was 9.13% (+/- 3.82), and the rate of absorption into the systemic circulation was consistent with a zero-order model profile for all subjects. Mean absorption time values reflected a wide degree of subject variability and ranged from approximately 15 to 150 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1985

Dermal absorption of pesticides calculated by deconvolution.

Using published human data on skin-to-urine and blood-to-urine transfer of 12 pesticides and herbicides, the skin-to-blood transfer rates for each compound were estimated by two numerical deconvolution techniques. Regular constrained deconvolution produced an estimated upper limit on cumulative dermal absorption of the radiolabel, while minimized deconvolution produced an upper bound on cumulative dermal absorption of parent compound. Dermal absorption rate was largest within 8 h of dosing for all pesticides examined. Only carbaryl showed a lag (3.5 h) in penetration. This may indicate a prolonged transit time through skin or a chemical transformation in skin has occurred. After onset, absorption occurred rapidly with 45% of the 120 h cumulative absorption occurring in 8 h. For parathion and dieldrin, over 50% of the 120 h total absorption occurred in the first 4 h. The deconvolution technique described here permits the calculation of the temporal aspect of dermal absorption for linear systems.

Humans↗
PubMed1993

Alkali absorption and citrate excretion in calcium nephrolithiasis.

The role of net gastrointestinal (GI) alkali absorption in the development of hypocitraturia was investigated. The net GI absorption of alkali was estimated from the difference between simple urinary cations (Ca, Mg, Na, and K) and anions (Cl and P). In 131 normal subjects, the 24 h urinary citrate was positively correlated with the net GI absorption of alkali (r = 0.49, p < 0.001). In 11 patients with distal renal tubular acidosis (RTA), urinary citrate excretion was subnormal relative to net GI alkali absorption, with data from most patients residing outside the 95% confidence ellipse described for normal subjects. However, the normal relationship between urinary citrate and net absorbed alkali was maintained in 11 patients with chronic diarrheal syndrome (CDS) and in 124 stone-forming patients devoid of RTA or CDS, half of whom had "idiopathic" hypocitraturia. The 18 stone-forming patients without RTA or CDS received potassium citrate (30-60 mEq/day). Both urinary citrate and net GI alkali absorption increased, yielding a significantly positive correlation (r = 0.62, p < 0.0001), with the slope indistinguishable from that of normal subjects. Thus, urinary citrate was normally dependent on the net GI absorption of alkali. This dependence was less marked in RTA, confirming the renal origin of hypocitraturia. However, the normal dependence was maintained in CDS and in idiopathic hypocitraturia, suggesting that reduced citrate excretion was largely dietary in origin as a result of low net alkali absorption (from a probable relative deficiency of vegetables and fruits or a relative excess of animal proteins).

Acidosis, Renal Tubular↗
PubMed2004

Profile of P-glycoprotein distribution in the rat and its possible influence on the salbutamol intestinal absorption process.

The intrinsic absorption of salbutamol in different intestinal segments of the rat was measured and related with the corresponding intestinal P-glycoprotein (P-gp) expression levels. The apparent absorption rate constants (k(a), h(-1)) observed in each fraction by means of the "in situ" rat gut absorption method after perfusion of a 0.29-mM isotonic solution of salbutamol were used as absorption indexes. In a separate series of studies, a semiquantitative analysis of the mRNA expression of P-gp by means of polymerase chain reaction and Western blot with an antibody raised against the P-gp were also performed. The "in situ" k(a) values determined in the different segments (h(-1)) showed that the absorption is not homogeneous along the intestinal tract, that is, 0.499 +/- 0.054 for colon, 0.474 +/- 0.052 for the proximal segment, 0.345 +/- 0.014 for the mean, and 0.330 +/- 0.023 for the distal fraction. Addition of verapamil to the perfusion fluid did provide a better absorption of salbutamol in the distal segment. The analysis of the mRNA expression and levels of P-gp showed that the enzyme content in each section of the intestine was inversely related to salbutamol absorption.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1976

Effects of colestipol hydrochloride on drug absorption in the rat II.

The effects of colestipol hydrochloride, a hypocholesterolemic bile acid-binding anion-exchange polymer, on the GI absorption of drugs commonly used in humans were studied in the rat. Colestipol hydrochloride was given by gavage in single doses of 71.5 or 214.5 mg/kg, equivalent to 5 or 15 g, respectively, in a 70-kg human; controls received equivalent amounts of microcrystalline cellulose. Single oral doses of labeled drugs were given concurrently with colestipol hydrochloride or microcrystalline cellulose at the human therapeutic dose range on a milligrams per kilogram basis. Subsequent changes in serum drug levels were measured at several time periods, and absorption was evaluated as the total area under the time-concentration curve. Colestipol hydrochloride at either dose did not significantly alter the absorption of 6-14C-nicotinic acid, 7-3H-tetracycline, 35S-chlorpromazine, 12alpha-3H-digoxin, warfarin (alpha-14C-benzyl), or clofibrate (14C-carboxyl). In addition, the effects of 214.5 mg/kg of colestipol hydrochloride were compared with the same dose of cholestyramine with respect to the absorption of 3-14C-hydrochlorothiazide, 2-14C-phenobarbital, and 3H-digitoxin. Cholestyramine reduced absorption of hydrochlorothiazide by 42%, but colestipol hydrochloride had no significant effect. Neither resin altered phenobarbital or digitoxin absorption when compared with the the control, but a significant difference occurred between the two resins with digitoxin; areas under the time-concentration curve [in (dpm/0.1 ml serum) x hr] were: colestipol hydrochloride, 2001; cholestyramine, 16,300; and cellulose, 17, 067. These results indicate that colestipol hydrochloride and cholestyramine can differ in their effects on the absorption of certain drugs from the GI tract of the rat.

Animals↗
PubMed1981

Effects of salicylate on rectal absorption of theophylline.

The rectal absorption of theophylline in rats was facilitated by concurrent administration of salicylic acid or sodium salicylate. The absorption of theophylline depended on the simultaneous absorption of salicylate and increased with an increasing concentration of salicylate. Calcium and magnesium ions inhibited the effects of salicylate at pH 7.4 but not at pH 4.5. Sodium lauryl sulfate caused lasting changes in rectal absorption, whereas the effects of salicylate on absorption were observed only when salicylate was present Strong chelating agents, such as ethylenediaminetetraacetic acid and sodium citrate did not effect the absorption of theophylline, except at very high concentrations (30%), where membrane damage was observed. Rectal drug absorption was not enhanced by vasodilation or inflammation alone since sodium nicotinate and histamine did not facilitate the disappearance of theophylline from the perfusate.

Animals↗
PubMed1981

Optimal perfusion rate determined for in situ intestinal absorption studies in rats.

Iopanoic acid was used as a model compound to study the effect of the intestinal perfusion rate on the mean absorption clearance. Absorption of iopanoic acid followed first-order kinetics, with a first-order absorption rate constant (ka) linearly dependent on the dry intestinal weight. An absorption clearance--time plot revealed three phases. Phase I represented an equilibration phase, Phase II was a uniform phase, and Phase III was a physiological deterioration of the animal under prolonged anesthesia. The variability in the observations during Phase II of the absorptive clearance--time profiles was assessed statistically, and the minimum occurred at 9.9 microliters/sec (0.594 ml/min). The relation between the coefficient of variance (CV) and the perfusion rate is given by CV = (-5.52 X 10(-5)Q3 + (2.78 X 10(-3)Q2 - (3.87 X 10(-2)Q + 0.243, where Q is the perfusion rate through the intestinal lumen. These studies demonstrate that an optimal flow rate exists for minimizing the variability in in situ absorption studies. The dependency of the absorption clearance on the intestinal perfusion rate appears to conform to the convective diffusion model.

Animals↗
PubMed1984

Effect of systemic anaphylaxis on the absorption of salicylic acid from the rat small intestine.

Rats were immunized by intraperitoneal injection of ovalbumin (egg albumin) emulsified in Freund's incomplete adjuvant, and then the effect of an intravenous challenge with ovalbumin on salicylic acid absorption from the small intestine was examined by means of an in situ recirculation technique. The disappearance of salicylic acid from the luminal solution was significantly decreased in rats treated with ovalbumin compared with control groups treated with saline. The decreased absorption of salicylic acid in ovalbumin-immunized rats was related to the anti-ovalbumin antibody responses examined by passive cutaneous anaphylactic reactions. On the other hand, the decreased absorption of salicylic acid was not found in ovalbumin-immunized rats challenged intravenously with bovine gamma-globulin. Similar results were also noted in rats immunized via the footpads with ovalbumin. However, no significant change was observed in the intestinal absorption of salicylic acid in normal (nonimmunized) rats challenged intravenously with ovalbumin. Furthermore, intestinal absorption of sulfadimethoxine and sulfanilamide was significantly decreased during systemic anaphylaxis, whereas no change was observed in the absorption of sulfisoxazole, quinine, sulfanilic acid, and phenolsulfonphthalein. This suggests that the intestinal absorption of rapidly absorbed drugs, including salicylic acid, is more sensitive to systemic anaphylaxis than that of poorly absorbed drugs.

Anaphylaxis↗