Lars Knutson

Characterization of fluids from the stomach and proximal jejunum in men and women

AbstractPurpose. To chemically characterize the fluids available for drug dissolution in the upper gastrointestinal tract during the fasted state in humans, and to examine variations and potential gender differences regarding the physico-chemical properties of these fluids. Methods. Twenty-four healthy volunteers, 12 females and 12 males, were intubated, and fluids from the stomach and upper jejunum were collected separately. Bulk pH, osmolality, electrolytes and total concentrations of bile acids and proteins were assessed. To study intraindividual variations, eleven of the individuals were studied on more than one occasion. Results. The stomach and upper jejunal fluids varied significantly in all the measured entities, except the total concentration of proteins. The intraindividual variability was pronounced in some of the individuals, both in the stomach and the upper jejunum. We did not, however, observe any gender differences. Conclusions. This study demonstrates the complex nature of the fluids available for drug dissolution in the stomach and the upper small intestine in humans. The results can be used when designing a more physiological in vitro dissolution media representative for the fasted state. When designing such a medium, we suggest that gender differences not be taken into account.

The Effects of Food on the Dissolution of Poorly Soluble Drugs in Human and in Model Small Intestinal Fluids

PurposeThis study was conducted to determine the effect of food on drug solubility and dissolution rate in simulated and real human intestinal fluids (HIF).MethodsDissolution rate obtained via the rotating disk method and saturation solubility studies were carried out in fed and fasted state HIF, fed dog (DIF), and simulated (FeSSIF) intestinal fluid for six aprotic low solubility drugs. The intestinal fluids were characterized with respect to physical–chemical characteristics and contents.ResultsFed HIF provided a 3.5- to 30-times higher solubility compared to fasted HIF and FeSSIF, whereas fed DIF corresponded well (difference of less than 30%) to fed HIF. The increased solubility of food could mainly be attributed to dietary lipids and bile acids. The dissolution rate was also 2 to 7 times higher in fed HIF than fasted HIF. This was well predicted by both DIF and FeSSIF (difference of less than 30%).ConclusionsIntestinal solubility is higher in fed state compared to fasted state. However, the dissolution rate does not increase to the same extent. Dog seems to be a good model for man with respect to dissolution in the small intestine after intake of a meal, whereas FeSSIF is a poorer means of determining intestinal saturation solubility in the fed state.

St John's Wort Decreases the Bioavailability of R- and S-verapamil Through Induction of the First-pass Metabolism

Our objective was to investigate the inducing effect of repeated oral administration of St Johns wort on the jejunal transport and presystemic extraction of R‐ and S‐verapamil in humans.

Jejunal absorption and metabolism of R/S-verapamil in humans.

AbstractPurpose. The purpose of this human intestinal perfusion study was to investigate the transport and metabolism of R/S-verapamil in the human jejunum (in vivo). Methods. A regional single-pass perfusion of the jejunum was performed using a Loc-I-Gut® perfusion tube in 12 healthy volunteers. Each perfusion lasted for 200 min and was divided into two periods each of 100 min. The inlet concentrations of verapamil were 4.0 and 40 mg/1 in period one and two, respectively. Results. The effective jejunal permeability (Peff) of both R- and S-verapamil increased (p < 0.05) when the inlet concentration was increased consistent with saturation of an efflux mechanism. However, both R- and S-verapamil had high intestinal Peff, consistent with complete absorption. The Peff of antipyrine also increased, but there was no difference in the Peff for D-glucose in the two periods. The appearance of R/S-norverapamil in the intestinal perfusate leaving the jejunal segment was non-linear, presumably due to saturation of the CYP3A4 metabolism. Conclusions. The increased Peff in parallel with increased entering drug concentration is most likely due to saturable efflux by P-glycoprotein(s) in the human intestine.

Multiple transport mechanisms involved in the intestinal absorption and first-pass extraction of fexofenadine.

Our objective was to investigate the main in vivo transport mechanisms of fexofenadine involved in the intestinal absorption and bioavailability of the drug in humans.

Jejunal permeability and hepatic extraction of fluvastatin in humans

The primary objective was to investigate the effective permeability and the hepatic extraction of fluvastatin, a new 3‐hydroxy‐3‐methylglutaryl‐coenzyme A (HMG‐CoA) reductase inhibitor, during a jejunal perfusion in humans. The secondary objective was to investigate the relationship between human jejunal effective permeability values and physicochemical properties for four different drugs.

Eosinophil cationic protein and histamine after intestinal challenge in patients with cow's milk intolerance

BACKGROUND Mast cells and eosinophils are key cells in the development of active symptoms in allergic diseases and other inflammatory conditions, and they mediate their action through the release of very potent granule constituents. METHODS Five patients with milk-related gastrointestinal symptoms diagnosed by double-blind placebo-controlled milk challenges, but with negative responses to skin prick tests and RASTs with milk, and eight healthy control subjects were investigated. Repeated perfusion studies were performed with a two-balloon, six-channel tube by using milk, casein, and whey as antigens. Luminal eosinophil cationic protein, histamine, and albumin were measured by radioimmunoassay. RESULTS Luminal cows milk induced a pronounced increase in intestinal secretion of histamine and eosinophil cationic protein in patients, but not control subjects, during the first 20 minutes after challenge (histamine from 123 +/- 12 to 543 +/- 175 ng/cm, hr; eosinophil cationic protein from 80 +/- 23 to 686 +/- 262 ng/cm, hr). Albumin, as a marker of plasma leakage, was also significantly increased. CONCLUSION These data indicate that mast cells and eosinophils are effector cells not only in patients with allergic disease but also in patients intolerant to foods and lacking circulating antibodies. The underlying mechanisms may be a reaction mediated by locally appearing antibodies or an immunologic activation resembling that found in intestinal disorders such as celiac disease.

FIRST-PASS EFFECTS OF VERAPAMIL ON THE INTESTINAL ABSORPTION AND LIVER DISPOSITION OF FEXOFENADINE IN THE PORCINE MODEL

The aim of this study in pigs was to investigate the local pharmacokinetics of fexofenadine in the intestine and liver by using the pig as a model for drug transport in the entero-hepatobiliary system. A parallel group design included seven pigs (10–12 weeks, 22.2–29.5 kg) in three groups (G1, G2, G3), and a jejunal single-pass perfusion combined with sampling from the bile duct and the portal, hepatic, and superior caval veins was performed. Fexofenadine was perfused through the jejunal segment alone (G1: 120 mg/l, total dose 24 mg) or with two different verapamil doses (G2: 175 mg/l, total dose 35 mg; and G3: 1000 mg/l, total dose 200 mg). The animals were fully anesthetized and monitored throughout the experiment. Fexofenadine had a low liver extraction (EH; mean ± S.E.M.), and the given doses of verapamil did not affect the EH (0.13 ± 0.04, 0.16 ± 0.03, and 0.12 ± 0.02 for G1, G2, and G3, respectively) or biliary clearance. The EH for verapamil and antipyrine agreed well with human in vivo data. Verapamil did not increase the intestinal absorption of fexofenadine, even though the jejunal permeability of fexofenadine, verapamil, and antipyrine showed a tendency to increase in G2. This combined perfusion and hepatobiliary sampling method showed that verapamil did not affect the transport of fexofenadine in the intestine or liver. In this model the EH values for both verapamil and antipyrine were similar to the corresponding values in vivo in humans.

Enterohepatic Disposition of Rosuvastatin in Pigs and the Impact of Concomitant Dosing with Cyclosporine and Gemfibrozil

The hepatobiliary transport and local disposition of rosuvastatin in pig were investigated, along with the impact of concomitant dosing with two known multiple transport inhibitors; cyclosporine and gemfibrozil. Rosuvastatin (80 mg) was administered as an intrajejunal bolus dose in treatments I, II, and III (TI, TII, and TIII, respectively; n = 6 per treatment). Cyclosporine (300 mg) and gemfibrozil (600 mg) were administered in addition to the rosuvastatin dose in TII and TIII, respectively. Cyclosporine was administered as a 2-h intravenous infusion and gemfibrozil as an intrajejunal bolus dose. In treatment IV (TIV, n = 4) 5.9 mg of rosuvastatin was administered as an intravenous bolus dose. The study was conducted using a pig model, which enabled plasma sampling from the portal (VP), hepatic (VH), and femoral veins and bile from the common hepatic duct. The biliary recoveries of the administered rosuvastatin dose were 9.0 ± 3.5 and 35.7 ± 15.6% in TI and TIV, respectively. Rosuvastatin was highly transported into bile as shown by the median AUCbile/AUCVH ratio in TI of 1770 (1640–11,300). Gemfibrozil did not have an effect on the plasma pharmacokinetics of rosuvastatin, most likely because the unbound inhibitor concentrations did not exceed the reported IC50 values. However, cyclosporine significantly reduced the hepatic extraction of rosuvastatin (TI, 0.89 ± 0.06; TII, 0.46 ± 0.13) and increased the AUCVP and AUCVH by 1.6- and 9.1-fold, respectively. In addition, the biliary exposure and fe, bile were reduced by ≈50%. The strong effect of cyclosporine was in accordance with inhibition of sinusoidal uptake transporters, such as members of the organic anion-transporting polypeptide family, rather than canalicular transporters.

Intestinal reactivity in allergic and nonallergic patients: An approach to determine the complexity of the mucosal reaction

BACKGROUND To determine whether inflammatory markers and mediators were released in response to different intestinal antigens, studies were performed in atopic patients allergic to birch, patients allergic to psyllium powder (ispaghula), and patients intolerant to milk. METHODS Allergy to birch and psyllium powder was documented by the presence of circulating IgE antibodies and positive skin tests. Patients intolerant to milk had negative outcomes of radioallergosorbent tests and skin tests but positive results of double-blind, placebo-controlled tests. Challenge of the intestine with different antigens was achieved by perfusion of a jejunal segment occluded between balloons. Basal and antigen-activated release of mast cell/basophil and eosinophil products and of substances emanating from the plasma and interstitial fluid was compared in perfusate fluid from patients (n = 8) and matched healthy controls (n = 8). RESULTS Perfusate levels of albumin and hyaluronan (previous name hyaluronic acid) were increased threefold to fivefold by antigen in all patients, but not in controls. Eosinophilic cationic protein increased in patients but also in ispaghula controls. Histamine was released in response to milk, but not in patients allergic to birch or ispaghula. Prostaglandin E2 increased in milk- and birch-sensitive patients. In response to ispaghula, however, it was released in both patients and controls. CONCLUSIONS We conclude that subclinical intestinal challenge with antigen induces an increase in the appearance rate of albumin and hyaluronan in the intestinal lumen both in atopic patients (with target organs such as the lungs or nose and eyes) and in patients with intestinal intolerance to milk. These changes in permeation are similar to those reported from other organs such as the lung. They may reflect a common response in early phase I reactions that are either IgE-mediated or occur in response to food antigens without any obvious involvement of an IgE-mediated mechanism. Subclinical provocation with intestinal antigens should prove useful for further elucidation of mechanisms underlying intestinal mucosal reactions to exogenous stimuli.