Colesevelam and colestipol: novel medication resins in the gastrointestinal tract.

We report the morphologic description of the bile acid sequestrants (BAS) colesevelam and colestipol, as well as the largest series of cholestyramine. Histologically similar medication resins from 4 institutions were prospectively collected over 1 year (26 specimens, 15 patients). Comorbidities included hyperlipidemia (4/15), hypertension (4/15), inflammatory bowel disease (4/15), coronary artery disease (3/15), diarrhea (7/15), hypothyroidism (2/15), and ischemic bowel (1/15). Sites of involvement included the esophagus (1/26), stomach (1/26), small intestine (1/26), ileocecal valve (1/26), and colorectum (22/26). Associated histologic diagnoses included normal (8/26), chronic mucosal injury (11/26), acute inflammation (9/26), erosion/ulceration (6/26), and cytomegalovirus (2/26). The BAS resins were histologically indistinguishable from each other; they were all eosinophilic on hematoxylin and eosin (H&E) and lacked internal "fish-scales." To validate these observations, respective medications were submitted for histologic processing; the processed medications were identical to those in the patient specimens. Rare, irregular "fracture" lines presented diagnostic pitfalls by mimicking the true "fish-scales" of Kayexalate and sevelamer. Clues to the correct identification of BAS include recognition that the "fracture" lines were subtle, irregular, and restricted to large fragments or thick sections, likely representing a processing artifact. Moreover, Kayexalate is violet on H&E and black on acid fast bacillus, and sevelamer characteristically displays a 2-tone color on H&E and is magenta on acid fast bacillus. An association with inflammatory injury was seen (15/26). We believe that the BAS are innocent bystanders in complicated patients, although we cannot exclude their ability to cause mucosal injury in specific settings.

The use of histological techniques for the demonstration of ion exchange resins.

AIM: To establish the staining characteristics of certain ion exchange resins in histological material, with a view to enabling confident differential identification. METHODS: Various histological staining procedures were applied to selected pathological material and prepared agar blocks containing the cation exchange resin calcium polystyrene sulphonate and the anion exchange resin cholestyramine. RESULTS: Calcium polystyrene sulphonate uniquely stained strongly by a direct Schiff's reagent procedure without any preoxidation and by the Ziehl-Neelsen method. Cholestyramine was negative by the former method but stained strongly with a standard Congo red technique. CONCLUSIONS: These staining results are consistent with the known structure and properties of polystyrene sulphonate and cholestyramine resins. Polystyrene sulphonate resins have the virtually pathognomonic feature of direct Schiff positivity, while morphology, location, and strong non-birefringent Congo red positivity facilitate the identification of cholestyramine. It is possible that the intrinsic staining characteristics of cholestyramine may be lost once it has bound to its target.

Pharmacokinetics of fluvastatin and specific drug interactions.

Fluvastatin sodium (Lescol) is the first synthetic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA)-reductase inhibitor to be studied extensively in humans. Absorption of fluvastatin is complete and unaffected by the presence of food. Systemic exposure is limited because of extensive sequestration by the liver and/or first-pass metabolism, a plasma half-life of approximately 30 min, no circulating active metabolites, and no accumulation of drug during chronic dosing. Approximately 95% of a single dose of fluvastatin is excreted via the biliary route with less than 2% as the parent compound. Studies investigating the effect of food on fluvastatin pharmacokinetics have demonstrated marked reductions in the rate of bioavailability (Cmax) of 40% to 60%. A comparison of drug administration with the evening meal or at bedtime revealed no significant differences in either the extent of bioavailability (area under the curve; AUC) or pharmacodynamic effect [reduction in low-density lipoprotein cholesterol (LDL-C)]. Relative to the general population, plasma fluvastatin concentrations do not vary as a function of either age or gender. Administration of a single 40-mg dose to a patient population with hepatic insufficiency resulted in a 2.5-fold increase in both AUC and Cmax. Drug interaction studies with fluvastatin and cholestyramine (CME) demonstrated a lower rate and extent of fluvastatin bioavailability; no impact on efficacy was demonstrated when CME was given 4 h before fluvastatin dosing in clinical trials. Interaction studies with niacin and propranolol demonstrated no effects on fluvastatin plasma levels, and fluvastatin administered to a patient population chronically receiving digoxin had no effect on the AUC of digoxin compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile salt binding properties of commonly used gastrointestinal drugs: maalox, carafate, and questran.

We have validated a method to measure bile salt binding by Maalox (aluminum hydroxide and magnesium hydroxide), Carafate (sucralfate), and Questran (cholestyramine) in vitro. The method used in this study involves a correction for adherent water volume and thus provides a correct measure of bile salt binding. With this approach, we described the binding properties of Maalox, Carafate, and Questran. The bile salt binding capacities of Carafate and Maalox are limited and do not have physiological or pharmacological significance. On the other hand, we found that Questran has substantial bile salt binding capacity. At the recommended dosage, Questran could deplete the total bile salt pool. We also found that Carafate, although not used as an antacid, has buffering capacity (maintaining a pH of solution in the range 4.2-4.8) which might contribute to its effectiveness as an ulcer treatment drug.