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PubMed2006

Comparative absorption profiles of divalproex sodium delayed-release versus extended-release tablets -- clinical implications.

BACKGROUND: The distinct absorption characteristics of the conventional enteric-coated, delayed-release (DR) and the novel extended-release (ER) divalproex sodium formulations are not well recognized. OBJECTIVE: To quantitatively and qualitatively differentiate the absorption characteristics of divalproex-DR and -ER formulations. METHODS: Healthy volunteers (N = 28) received single 1000 mg doses of divalproex-DR and divalproex-ER tablets in a crossover fashion. Noncompartmental and compartmental analyses were used to estimate valproic acid (VPA) pharmacokinetics from the plasma concentration-time profiles determined from intensive blood sampling over 48 hours. RESULTS: VPA was not absorbed from divalproex-DR in the first 2 hours (absorption lag-time) after dosing. After VPA release in the intestine, approximately 63% of the dose was absorbed in less than 1 hour, that is, 2.9 hours (mean absorption time) from dosing. Maximum concentration (C(max)) was achieved approximately 4 hours after dosing. VPA absorption was complete ( approximately 93% of dose) within 3 absorption half-lives ( approximately 4.5 h) post-absorption lag-time, that is, 6-7 hours from dosing. In contrast, VPA absorption from divalproex-ER starts immediately after administration, initially at a modest rate, followed by slow and extended absorption at a constant rate for more than 20 hours; VPA concentrations at 1 and 2 hours were 28% and 40% of C(max). Approximately 53% of the dose was absorbed within 12 hours (mean absorption time); complete absorption occurred over more than 20 hours without any dose dumping. CONCLUSIONS: VPA absorption from enteric-coated divalproex-DR is rapid following a lag-time of approximately 2 hours and is complete within 6-7 hours of dosing. In contrast, VPA absorption from divalproex-ER starts immediately after administration, but occurs at a slow, approximately constant rate over more than 20 hours.

Absorption↗
PubMed2001

A comprehensive account on the role of efflux transporters in the gastrointestinal absorption of 13 commonly used substrate drugs in humans.

BACKGROUND: The potential absorption-limiting effect of intestinal efflux transporters such as P-glycoprotein (P-gp) has been well recognized, primarily based on results of numerous Caco-2 cell studies showing that flux, permeability, or transport clearance of drugs from the basolateral to the apical (B --> A) compartment is greater than that from the apical to the basolateral (A --> B) compartment. Except for very limited examples such as celiprolol, talinolol, pafenolol and paclitaxel, the potential clinical impact of these transporters on oral absorption of the vast number of commonly prescribed drug substrates in humans has not been closely examined to date. OBJECTIVE: To evaluate whether these efflux transporters may play a significant role in limiting oral absorption of 13 commonly used drugs (digoxin, etoposide, felodipine, fexofenadine, furosemide, indinavir, losartan, nadolol, propranolol, ritonavir, saquinavir, tacrolimus, and verapamil) in humans. METHODS: Drug absorption properties such as the rate (as judged by the Cmax and tmax) and extent (as judged by AUC or urinary excretion of drugs) of absorption as a function of dose, as well as the completeness of oral absorption were obtained from the literature. RESULTS: The absorption properties of these 13 drugs are not consistent with absorption-retarding expectations from in vitro studies because they all show apparent dose-independent kinetics in absorption or bioavailability and completeness of oral absorption is shown for most of the drugs evaluated. CONCLUSIONS: In spite of being substrates of intestinal efflux transporters such as P-gp, the in vivo oral absorption of 13 drugs examined apparently is not significantly impeded by efflux transporters. Thus, there may exist an apparent discrepancy between in vitro "expectations" and in vivo results; potential reasons for this are discussed. The present findings, however, do not de-emphasize potential in vivo importance of efflux transporters in affecting (increasing or decreasing) oral absorption of certain substrate drugs, especially those with low to moderate intestinal permeability and with low therapeutic index, or the importance of efflux transporters in the study of mechanisms of drug absorption and some potentially clinically significant drug-drug and drug-food interactions.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1996

The use of ethanol as a marker to detect and quantify the absorption of irrigation fluid during transurethral resection of the prostate.

During transurethral resection of the prostate (TURP), the irrigation fluid is often absorbed by the circulatory system and/or the region around prostate occasionally resulting in severe signs and symptoms. Instant detection and qualification of absorption of irrigation fluid have not been possible earlier. A method involving tagging of the irrigation fluid with ethanol for detection and quantification of absorbed irrigation fluid by measurement of ethanol in expired breath (EB) has been developed. The validity of measuring EB ethanol to detect and quantify absorption of irrigation fluid was studied in 13 patients undergoing TURP. The EB ethanol was compared with three other methods: I. Isotope tagging of the irrigation fluid and detection of absorbed fluid using a scintillation detector placed over large blood vessels. 2. Measuring changes in serum-sodium every 10 min. 3. Regular interval monitoring (RIM) of the difference between volume used for irrigation and volume recovered from patients every 10 min. The method of measuring EB ethanol was found to be highly valid. The possibility of detecting absorption and the incidence of absorption using EB ethanol in the clinical routine was studied in 192 patients undergoing TURP. Half of them absorbed irrigation fluid, 25% absorbed more than 400 ml. The proportion of patients absorbing irrigation fluid was the same for both experienced and inexperienced resectionists. Clinical assessment of absorption of irrigation fluid was performed by the resectionists and the supervising nurses in 118 patients undergoing TURP. Prerequisites for massive absorption were found by the resectionist in 8/9 patients. The resectionist falsely indicated absorption in 22 patients. The nurses correctly indicated 3/9 patients and falsely indicated 4 patients. To investigate the method measuring EB ethanol to detect absorption of irrigation fluid during general anaesthesia, 20 patients underwent TURP and EB ethanol was compared with the RIM method. There was a good correlation between the methods. Elevated pressure in the bladder and the prostatic fossa is a prerequisite for absorption of irrigation fluid. Detection and quantification of absorbed irrigation fluid by EB ethanol was used for comparing 102 patients operated on with and without a pressure warning device alarming at 1.5 kPa in the bladder. using the device reduced both the volume of absorbed irrigation fluid, and the number of patients absorbing irrigation fluid. Both ethanol per se and haemodilution by absorbed irrigation fluid may have impacts on the coagulation system. To investigate the influence of absorption of ethanol tagged mannitol on bleeding time, measurements were performed before and after TURP in 57 patients. No difference in bleeding time was found among patients who absorbed irrigation fluid as compared with those who did not. In conclusion, measurement of ethanol in EB for detection and quantification of absorbed irrigation fluid is a highly valid method when compared with three other methods. Absorption of irrigation fluid was found in 50% of the patients undergoing TURP. Clinical assessments of absorption of irrigation fluid are unreliable. EB ethanol can be used in patients during general anaesthesia. Using a pressure warning device decreases the volume of absorbed irrigation fluid, as well as the number of patients absorbing it. Absorption of ethanol tagged mannitol as irrigation fluid has no influence on bleeding time.

Absorption↗
PubMed1998

Phospholipase A2 relieves phosphatidylcholine inhibition of micellar cholesterol absorption and transport by human intestinal cell line Caco-2.

Cholesterol absorption from bile acid micelles is suppressed by phosphatidylcholine (PC) in the micelles. The effects of micellar phospholipid composition on absorption, metabolism, and secretion of lipids were examined in Caco-2 cells incubated with micelles composed of taurocholic acid, cholesterol, oleic acid, monooleoylglycerol, and phospholipid. Significant amounts of all micelle lipids were absorbed from micelles lacking phospholipid. Cholesterol absorption was accompanied by cholesterol esterification and secretion. Micellar oleic acid was also absorbed and reesterified primarily into triacylglycerol which was also secreted. Lipid absorption and secretion from micelles containing lysophosphatidylcholine (LPC) were similar to that obtained with phospholipid-free micelles. LPC was also extensively absorbed. In contrast, incubations with PC-containing micelles resulted in large reductions in the absorption, esterification, and secretion of cholesterol without significant decreases in oleic acid absorption, conversion to acylated lipids, or triacylglycerol secretion. A relatively small reduction in monoacylglycerol absorption from PC-containing micelles was detected. Retinol absorption was not affected by micellar PC. Substitution of LPC for half or more of the PC reversed the PC-dependent decrease in cholesterol absorption. Pancreatic phospholipase A2 (pPLA2) enhanced cholesterol absorption from PC-containing micelles. The pPLA2-dependent increase in cholesterol absorption was inhibited by the pPLA2 inhibitor FPL 67047XX. The results indicate micellized cholesterol absorption by enterocytes is uniquely dependent on the elimination of micellar phosphatidylcholine and thus directly dependent on the lipolytic action of pancreatic phospholipase A2 (pPLA2). Consequently, pPLA2 inhibitors may be a new and novel class of cholesterol absorption inhibitors for therapeutic use.

Benzhydryl Compounds↗
PubMed1991

Lithium absorption by the rabbit gall-bladder.

Lithium (Li+) absorption across the low-resistance epithelium of the rabbit gall-bladder was studied in order to elucidate possible routes and mechanisms of Li+ transfer. Li+ at a concentration of 0.4 mM in both mucosal and serosal media did not affect isosmotic mucosa-to-serosa fluid absorption. At this low concentration net mucosa-to-serosa Li+ absorption was insignificant when the ambient Na+ concentration was 115 mM, although the gall-bladder had a significant Li+ permeability (2.7 X 10(-5) cm s-1) and a significant mucosa-to-serosa Li+ gradient developed as a result of fluid absorption. Net Li+ absorption was induced at reduced mucosal Na+ concentrations (by lowering the Na+ concentration down to 50 mM with or without substitution with sucrose, or by adding sucrose to the mucosal medium). This Li+ absorption occurred even in the absence of a mucosa-to-serosa Li+ gradient. Na+ and Li+ absorptions occurring at 50 mM Na+ were inhibited to the same degree by mucosal 1 mM amiloride. Substitution of 5-50 mM (44%) Na+ by Li+ in the external medium dose-dependently depressed Na+ absorption by up to 76%, while substitution by 50 mM choline had no significant effect. Li+ inhibition of Na+ absorption was elicited from the mucosal side and was not accounted for by compensatory Li+ absorption; water and Na+ absorption rates decreased nearly in parallel. The effects of 0.4 mM amiloride and of substitution with 20 mM Li+ were only partly additive. It is concluded that Li+ absorption in the rabbit gall-bladder cannot be explained by passive (paracellular) transport, but must be the result of transcellular, active transport. Both at low and at high concentrations Li+ may enter the cell via an Na+/H+ exchanger in the apical cell membrane. At high concentrations Li+ may inhibit Na+ absorption by interference with the exchange mechanism and/or via effects at the cytoplasmic level. The Li+ transfer mechanism across the basolateral cell membrane remains unknown.

Amiloride↗
PubMed1998

Physiological mechanism-based analysis of dose-dependent gastrointestinal absorption of L-carnitine in rats.

We evaluated the dose-dependent (saturable) gastrointestinal absorption of L-carnitine, a lipid-lowering agent, in rats by a physiological mechanism-based approach to clarify its absorption characteristics and to examine the in vitro (in situ)-in vivo correlation in intestinal transport. The intestinal absorption rate constant (ka), which was estimated by the analysis of gastrointestinal disposition, decreased markedly from 0.1061 to 0.0042 min(-1) when the dose was increased from 0.05 micromol rat(-1) (low dose) to 100 micromol rat(-1) (high dose). The dose-dependence in ka was attributable to the saturability of intestinal transport that, in the perfused intestine, was similar to the saturability in ka. At the high dose, the apparent absorption rate constant (k'a) of 0.0021 min(-1), which was estimated by the analysis of plasma concentrations after oral administration, was an order of magnitude smaller than the gastric emptying rate constant (kg) of 0.059 min(-1) and comparable with the ka of 0.0042 min(-1), suggesting that the gastrointestinal absorption of L-carnitine is absorption-limited in the intestine. At the low dose, where intestinal L-carnitine absorption was far more efficient, the k'a of 0.0172 min(-1) was smaller than the ka of 0.1061 min(-1) and closer to the kg of 0.072 min(-1), suggesting that apparent absorption was retarded by gastric emptying which is less efficient than intestinal absorption. This shift in the rate-determining process with an increase in dose explains the less marked dose dependence in k'a compared with ka. The bioavailability decreased from 100 to 42% with an increase in dose. This could be accounted for quantitatively by a reduction in the fraction absorbed (F(a,oral)) due to a reduction in ka, assuming first-order absorption during the transit time of T(si) through the small intestine (F(a,oral) = 1 - exp(-ka x T(si))). Thus, using L-carnitine as a model, this study has successfully demonstrated that the saturability in gastrointestinal absorption can be correlated with the intestinal transport in a quantitative and mechanism-based manner. This should be of help not only for developing more efficient oral L-carnitine delivery strategies, taking advantage of in vitro (in situ) information about the intestinal transport mechanism, but also for establishing a more generally applicable in vitro (in situ)-in vivo correlation in gastrointestinal absorption.

Algorithms↗
PubMed1999

Absorption and disposition of a tripeptoid and a tetrapeptide in the rat.

The present study is concerned with the absorption and disposition of a tripeptoid (N-substituted glycine derivative) and a tetrapeptide in the rat. The two compounds have similar backbone structures but differ with respect to the presence or absence of peptide bond. [3H]tripeptoid and [3H]tetrapeptide were administered orally (30 mg kg(-1)) and intravenously (i.v.) (30 or 3 mg kg(-1)) to Sprague Dawley rats. Blood, urine and feces were collected at designated times for radioactivity and parent drug analysis. The intestinal absorptive clearances of the tripeptoid and tetrapeptide were studied using an in situ rat intestinal perfusion model. The octanol/water partition coefficient of these two compounds was also determined. The results showed that the peptoid and peptide have similar absorptive clearance and octanol/water partitioning, but different in vivo absorption and disposition characteristics. The absorptive clearances of the tripeptoid and tetrapeptide were 6.7 and 4.8 x 10(-4) mL min(-1) cm(-1), respectively, and the corresponding octanol/water partition coefficients were 0.39 and 0.30. The extent of oral absorption of the tripeptoid was only 3-8%, consistent with its low absorptive clearance. In contrast, the apparent absorption of the tetrapeptide was > 75% of the radioactive dose. The peptide was completely metabolized within 2 h after an i.v. dose, whereas the peptoid was stable in blood and was primarily eliminated in feces as intact drug. In conclusion, the difference in in vivo absorption and disposition between the peptoid and peptide was apparently due to the presence or absence of a peptide bond. The tetrapeptide was subject to rapid metabolism in the body. Its relatively high absorption appeared to represent the absorption of metabolized radioactive fragments. The peptoid appears to have advantages over the peptide in term of metabolic stability, but its low oral absorption and rapid biliary excretion present additional challenges in the selection of an optimal drug candidate.

Administration, Oral↗
PubMed1995

Neural mechanisms in basal and meal-stimulated ileal absorption.

The ingestion of a meal stimulates absorption from the jejunal lumen and is dependent on intact neural pathways. Few studies of ileal absorptive responses to a meal have been performed. This study tested two hypotheses: (1) a meal stimulates ileal glucose, water, and ion absorption, and (2) intact intestinal neurotransmission is necessary to maintain the basal and meal-stimulated absorptive states in the ileum. Absorption studies (n = 50) using 14C-labeled PEG were performed on six dogs with 25-cm ileal Thiry-Vella fistulas (TVF). Four groups were randomly studied over 4 hr. Intraluminal oxethazaine (2 mg/dl) was administered to the TVF in Groups 2 and 4 after the 1st hour to produce neural blockade. A control volume of water was administered to the TVF in Groups 1 and 3 after the 1st hour. A 480 kcal meal was ingested at the end of the 2nd hour in groups 3 and 4. Ileal water, ion, and glucose absorption were increased significantly (P < 0.05) by the ingestion of a meal. TVF oxethazaine significantly reduced (P < 0.05) basal water and ion absorption but had no effect on meal-stimulated absorption. Ileal absorption of water, ions, and glucose is significantly increased by the ingestion of a meal. Basal ileal absorption appears to be partly dependent upon intact neurotransmission. Postprandial ileal absorption appears to be independent of neural blockade, implicating circulating hormones, paracrine mediators, or neurotransmission within the myenteric plexus of the enteric nervous system as the primary modulators of meal-stimulated ileal absorption.

Absorption↗
PubMed1981

Effect of glucose on jejunal water and solute absorption in the presence of glycodeoxycholate and oleate in man.

Jejunal perfusion studies were performed in 12 healthy volunteers to study the effects of 14 and 56 mM glucose on fluid secretion induced by 5 mM glycodeoxycholate on 7 mM oleate. Glucose enhanced water absorption under control conditions and reduced water secretion induced by glycodeoxycholate or oleate (P less than 0.01). As has been observed previously, glycodeoxycholate and oleate inhibited glucose absorption (P less than 0.001) and significant linear relationships existed between net water movement and glucose absorption. Glycodeoxycholate also reduced the absorption of 14 mM arabinose (P less than 0.05) and oleate reduced the absorption of 56 mM mannitol (P less than 0.05). Reduced solute absorption in the presence of glycodeoxycholate and oleate, therefore, cannot be attributed to an effect on active transport alone. The relationships between sodium transport and water absorption varied with the glucose concentration in the perfusion solutions. Similarly, the relationships between glucose absorption and sodium absorption varied with glucose concentration. The data suggest that a significant amount of glucose can be absorbed without concomitant absorption of sodium. The data indicate that glucose absorption can stimulate water absorption directly without the mediation of sodium and that water movement follows glucose at a rate which maintains isotonicity.

Arabinose↗
PubMed1990

Effects of short chain fatty acids and K on absorption of Mg and other cations by the colon and caecum.

The influence of short chain fatty acids (SCFA) on Mg, Na, and water absorption was studied in the rat distal colon and caecum using an in vivo luminal perfusion technique. The effect of SCFA on K absorption by the distal colon and the effect of K on Mg absorption by the distal colon and caecum were also investigated. Butyrate (60 mmol/l) or a mixture of SCFA (60 mmol/l acetate, 20 mmol/l propionate, 10 mmol/l butyrate) stimulated Mg and K absorption by the distal colon, while Na and water absorption was not affected. The effect on Mg absorption was pH-dependent. In the caecum, butyrate enhanced Na and water absorption, but not Mg absorption. Acetate (60 mmol/l) did not influence electrolyte absorption by either intestinal segment. K (30 mmol/l) inhibited Mg absorption by the distal colon, but not by the caecum. It is concluded from these findings that SCFA deriving from fermentation of carbohydrates in the large intestine stimulate Mg, K, and Na absorption by delivering protons to Mg++/H+, K+/H+ and Na+/H+ exchangers located in the apical membrane of the epithelium. K seems to inhibit Mg absorption in the colon by affecting a mechanism which does not respond to SCFA.

Acetates↗
PubMed1988

Relationship between distention and absorption in rat intestine. II. Effects of volume and flow rate on transport.

Studies in intact animals have shown that intestinal solute absorption may be enhanced with increasing intraluminal volume and flow rate, perhaps because of increases in functional absorptive surface area or perturbation of unstirred layers. We used single-pass perfusions of rat ileum, performed by simultaneously infusing and withdrawing at equal rates, to determine the separate effects of volume and flow rate on solute absorption at pressures between 3.0 and 12.5 cmH2O. Distention enhanced the absorption of passive probes (3H2O, urea), had no effect on the absorption of solutes transported by carrier mechanisms (D-glucose, L-alanine), and led to decreases in the net absorption of sodium and water whenever intraluminal pressure exceeded 10 cmH2O. Increasing flow rate enhanced the absorption of both glucose and 3H2O. However, the effects of increasing flow rate and distention on 3H2O were not additive. In the presence of higher filling volume, faster flow rate led to no further increases in 3H2O absorption; vice versa, at faster flow rate, no further increases in 3H2O absorption were noted when luminal volume was increased. We conclude that increased intraluminal volume enhances the absorption of solutes transported by passive but not carrier-mediated mechanisms, perhaps via augmentation of functional absorptive surface area. Increased flow rate and volume may increase the absorption of passively absorbed probes, in part, by a similar mechanism.

Animals↗
PubMed1992

Percutaneous absorption of benzyl acetate through rat skin in vitro. 2. Effect of vehicle and occlusion.

The effect of vehicle and occlusion on the in vitro percutaneous absorption of [methylene-14C]-benzyl acetate (1.7-16.6 mg/cm2) has been studied in diffusion cells using full thickness skin from male Fischer 344 rats. Absorption of neat benzyl acetate through rat skin occluded with parafilm was 49.3 +/- 2.0% (mean +/- SD, n = 4) after 48 hr. When benzyl acetate in ethanol was applied to the skin and the skin was occluded with parafilm, the extent of absorption at 48 hr was not significantly different from that after neat application. However at 6 hr, as the ethanol content of the application mixture was increased, the absorption of benzyl acetate through occluded skin was enhanced proportionally (r = 0.999). When phenylethanol was used as a vehicle, the extent of the benzyl acetate absorption through occluded skin at 48 hr was enhanced (P less than 0.05) compared with that after application neat; with 50% (v/v) phenyl-ethanol, absorption at 48 hr was 56.3 +/- 4.9%. However, this enhanced absorption did not correlate with the proportion of phenylethanol in the application mixture. When dimethylsulphoxide was used as a vehicle, the extent of absorption of benzyl acetate through occluded skin at 48 hr was enhanced (P less than 0.05) compared with that after application neat (absorption was 59.3 +/- 3.7% of the applied dose when 50% (v/v) dimethylsulphoxide was used). As the dimethylsulphoxide content of the application mixture was increased, the absorption of benzyl acetate was enhanced proportionally. Occlusion of the skin surface with parafilm often significantly enhanced absorption (P less than 0.05), although the effect varied with time and vehicle. In general, the degree of any enhanced absorption caused by the use of a vehicle or occlusion of the skin was small, and, in most cases, would be unlikely to be toxicologically significant.

Animals↗
PubMed2005

Apparent absorption of eight micronutrients and phytic acid from vegetarian meals in ileostomized human volunteers.

OBJECTIVES: Apparent absorption of eight micronutrients and degradation of phytic acid were studied in human subjects who underwent ileostomy. The prominent factors affecting micronutrient absorption from vegetarian Indian meals (n = 11) were identified. METHODS: Levels of beta-carotene, ascorbic acid, riboflavin, and thiamine in food and ileostomy contents were estimated by spectrophotometry and spectrofluorometry. Contents of zinc, iron, copper, and manganese were estimated by atomic absorption spectrometry and that of phytic acid by gradient elution ion exchange chromatography. Statistical analyses were done with SPSS 10.0. RESULTS: Absorption of beta-carotene, ascorbic acid, riboflavin, and thiamine was 63% to 75.6%. There was a negative non-significant trend in values of beta-carotene absorption with increased intake of beta-carotene (r = - 0.51, P > 0.1) and iron (r = -0.67, P = 0.1) but a positive significant trend with riboflavin intakes (r = 0.84, P = 0.018). Percentage of absorption of ascorbic acid showed weak positive associations with intakes of riboflavin (r = 0.71) and ascorbic acid (r = 0.5). Percentage of absorption of ascorbic acid was positively correlated with percentage of absorption of beta-carotene (r = 0.80, P < 0.05), iron, and riboflavin (r = 0.64, P = 0.086), indicating some common influencing factors. Percentages of absorption for zinc (20.2), iron (9.9), and copper (17.6) was comparable with those reported for soy protein-based, high phytate diets. Pattern of phytic acid in the meals and output indicated partial degradation and absorption (34%). CONCLUSIONS: For vegetarian Indian meals, apparent absorptions of beta-carotene and ascorbic acid were 76% and 73.5% and of riboflavin and thiamine was 63%. Zinc, copper, and iron showed a lower absorption (10% to 20%).

Adult↗
PubMed1995

Absorption of lactose, glucose polymers, or combination in premature infants.

STUDY OBJECTIVE: To determine the digestion and absorption of lactose, a combination of lactose and glucose polymers, and glucose polymers alone in infants born at 28 to 42 weeks of gestation. DESIGN: Each infant received the three carbohydrate solutions (85 gm/L concentration) in random order. SETTING: Tertiary care urban children's hospital. INTERVENTIONS: A double-lumen perfusion catheter was placed in the duodenum-jejunum. Absorption was defined as the disappearance of the carbohydrate and all its components (e.g., for lactose: galactose, glucose). MEASUREMENTS AND MAIN RESULTS: Absorption of lactose was less than that of the lactose-glucose polymer combination and the glucose polymers alone. There was no relationship between lactose absorption and postnatal age, whereas absorption of the lactose-glucose polymer combination and the glucose polymers alone correlated with age. Lactose absorption was not related to the number of days that the infants received full-strength feedings or the total number of days of feeding before the study, whereas absorption of both the lactose-glucose polymer combination and the glucose polymers alone was related to both. Absorption of the three solutions was not related to gestational age or to the number of days before the initial feeding. Lactose absorption was greater in infants who received formula alone than in infants fed formula together with human milk. CONCLUSIONS: Premature infants do not digest and absorb lactose as well as glucose polymers. However, lactose does not impair the absorption of glucose polymers. Lactose assimilation is not affected by maturation, but the type of diet may affect lactose digestion and absorption. In contrast, digestion and absorption of glucose polymers are related to both postnatal age and diet.

Absorption↗
PubMed2002

Rate-limited steps of human oral absorption and QSAR studies.

PURPOSE: To classify the dissolution and diffusion rate-limited drugs and establish quantitative relationships between absorption and molecular descriptors. METHODS: Absorption consists of kinetic transit processes in which dissolution, diffusion, or perfusion processes can become the rate-limited step. The absorption data of 238 drugs have been classified into either dissolution or diffusion rate-limited based on an equilibrium method developed from solubility, dose, and percentage of absorption. A nonlinear absorption model derived from first-order kinetics has been developed to identify the relationship between percentage of drug absorption and molecular descriptors. RESULTS: Regression analysis was performed between percentage of absorption and molecular descriptors. The descriptors used were ClogP, molecular polar surface area, the number of hydrogen-bonding acceptors and donors, and Abraham descriptors. Good relationships were found between absorption and Abraham descriptors or ClogP. CONCLUSIONS: The absorption models can predict the following three BCS (Biopharmaceutics Classification Scheme) classes of compounds: class I, high solubility and high permeability; class III, high solubility and low permeability; class IV, low solubility and low permeability. The absorption models overpredict the absorption of class II, low solubility and high permeability compounds because dissolution is the rate-limited step of absorption.

Administration, Oral↗
PubMed2003

Novel experimental parameters to quantify the modulation of absorptive and secretory transport of compounds by P-glycoprotein in cell culture models of intestinal epithelium.

PURPOSE: The purpose of this work was to elucidate the asymmetric effect of P-gp on modulation of absorptive and secretory transport of compounds across polarized epithelium, to develop experimental parameters to quantify P-gp-mediated modulation of absorptive and secretory transport, and to elucidate how P-gp-mediated modulation of transport is affected by passive diffusion properties, interaction of the substrate with P-gp, and P-gp expression. METHODS: The permeability of a set of P-gp substrates was determined in absorptive and secretory directions in Madine-Darby Canine kidney (MDCK), Caco-2, and MDR-MDCK monolayers. The transport was also determined in the presence of GW918, a non-competitive P-gp inhibitor, to quantify the permeability without the influence of P-gp. From these two experimental permeability values in each direction, two new parameters, absorptive quotient (AQ) and the secretory quotient (SQ), were defined to express the functional activity of P-gp during absorptive and secretory transport, respectively. Western blot analysis was used to quantify P-gp expression in these monolayers and in normal human intestinal. RESULTS: P-gp expression in Caco-2 and MDR-MDCK monolayers was comparable to that in normal intestine, and much less in MDCK cells. For all models, the substrates encompassed a wide range of apparent permeability due to passive diffusion (PPD). The parameters AQ and SQ, calculated for all compounds, assessed the attenuation in absorptive and enhancement of secretory transport, respectively, normalized to the permeability due to passive diffusion. Analysis of these parameters showed that 1) P-gp affected absorptive and secretory transport differentially and 2) compounds could be stratified into distinct groups with respect to the modulation of their absorptive and secretory transport by P-gp. Compounds could be identified whose absorptive transport was either strongly affected or poorly affected by changes in P-gp expression. For certain compounds, AQ values showed parabolic relationship with respect to passive diffusivity, and for others AQ was unaffected by changes in passive diffusivity. CONCLUSIONS: The relationship between attenuation of absorptive transport and enhancement of secretory transport of compounds by P-gp is asymmetric, and different for different sets of compounds. The relationship between attenuation of absorption by P-gp and passive diffusivity of compounds, their interaction potential with P-gp, and levels of P-gp expression is complex; however, compounds can be classified into sets based on these relationships. A classification system that describes the functional activity of P-gp with respect to modulation of absorptive and secretory transport was developed from these results.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

How to master absorption during transurethral resection of the prostate: basic measures guided by the ethanol method.

OBJECTIVE: To evaluate the effect of basic measures to minimize the absorption of irrigating fluid during transurethral resection of the prostate (TURP) to the planned end-point, using the ethanol method to guide the surgeon. PATIENTS AND METHODS: Forty-six patients underwent TURP with intermittent irrigation using sterile water and 2% ethanol. The ethanol content in the expired breath of the patients was assessed every 5 min using a breath-alcohol monitor. In 25 patients no absorption was indicated but 21 showed some absorption according to the ethanol analyses. The operator was then immediately alerted, paused briefly to determine the route of absorption and to take advantage of blood clots to seal off leakage sites. On resuming the resection, attention was given to the pressure gradients in the operating field, based on bladder compliance and the flow in the irrigating jet. Repeated ethanol analyses were used to assess the result and to guide the surgeon's efforts. RESULTS: No operation had to be terminated prematurely; the mean absorption in the 21 patients in whom any ethanol was detected was 121 (75-230) mL. In 14 patients absorption occurred once, in six twice and in one there were three small absorption events. The group with absorption did not differ significantly from that with no absorption in operative duration (mean 48 and 47 min), resected weight (mean 32.8 and 31.6 g) or blood loss (mean 550 and 483 mL). CONCLUSION: If the surgeon is alerted at the first positive ethanol reading, effective measures to minimize absorption can be taken early. Regular use of the ethanol method as an alarm system should permit TURP with a minimum of absorption and avoid an early interruption or premature termination of surgery because of absorption.

Absorption↗
PubMed1987

The effects of fruit juices and fruits on the absorption of iron from a rice meal.

The effects of the chemical composition of fruit juices and fruit on the absorption of iron from a rice (Oryza sativa) meal were measured in 234 parous Indian women, using the erythrocyte utilization of radioactive Fe method. The corrected geometric mean Fe absorptions with different juices varied between 0.040 and 0.129, with the variation correlating closely with the ascorbic acid contents of the juices (rs 0.838, P less than 0.01). Ascorbic acid was not the only organic acid responsible for the promoting effects of citrus fruit juices on Fe absorption. Fe absorption from laboratory 'orange juice' (100 ml water, 33 mg ascorbic acid and 750 mg citric acid) was significantly better than that from 100 ml water and 33 mg ascorbic acid alone (0.097 and 0.059 respectively), while Fe absorption from 100 ml orange juice (28 mg ascorbic acid) was better than that from 100 ml water containing the same amount of ascorbic acid (0.139 and 0.098 respectively). Finally, Fe absorption from laboratory 'lemon juice' (100 ml orange juice and 4 g citric acid) was significantly better than that from 100 ml orange juice (0.226 and 0.166 respectively). The corrected geometric mean Fe absorption from the rice meal was 0.025. Several fruits had little or no effect on Fe absorption from the meal (0.013-0.024). These included grape (Vitis vinifera), peach (Prunus persica), apple (Malus sylvestris) and avocado pear (Persea americana). Fruit with a mild to moderate enhancing effect on Fe absorption (0.031-0.088) included strawberry (Fragaria sp.) (uncorrected values), plum (Prunus domestica), rhubarb (Rheum rhaponticum), banana (Musa cavendishii), mango (Mangifera indica), pear (Pyrus communis), cantaloup (Cucumis melo) and pineapple (Ananas comosus) (uncorrected values). Guava (Psidium guajava) and pawpaw (Carica papaya) markedly increased Fe absorption (0.126-0.293). There was a close correlation between Fe absorption and the ascorbic acid content of the fruits tested (rs 0.738, P less than 0.0001). There was also a weaker but significant correlation with the citric acid content (rs 0.55, P less than 0.03). Although this may have reflected a direct effect of citric acid on Fe absorption, it should be noted that fruits containing citric acid also contained ascorbic acid (rs 0.70, P less than 0.002).(ABSTRACT TRUNCATED AT 400 WORDS)

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