Effect of resin surface charge on gastric mucoadhesion and residence of cholestyramine

Previous studies performed on excised gastric tissue and in healthy volunteers revealed that the ion exchange resin, cholestyramine, exhibits mucoadherent behaviour. This study was designed to elucidate whether surface charge affected this behaviour. Gamma scintigraphy was performed on fasted normal subjects following oral administration of cholestyramine or the cationic exchanger Amberlite(R) IRP-69, either uncoated or polymer-coated to mask their charge. Subjects were fed after 4 h. The initial gastric emptying of all formulations was similar (T(50) values (mean+/-S.E.M.): cholestyramine=85.86+/-9.16 min; IRP-69=76.09+/-9.23 min; polymer-coated cholestyramine=72.0+/-12.64 min; polymer-coated IRP-69=70.25+/-10.57 min: P=0.724). However, after 3 h the emptying pattern of cholestyramine was slower than that of IRP-69. This resulted in greater retention times than IRP-69 (AUC(0-6) values (relative units)=15,200+/-1093 versus 9452+/-811; cholestyramine versus IRP-69: P=0.0004). This effect was reduced by polymer-coating the cholestyramine. Serial images showed that cholestyramine was trapped in the oropharyngeal region and subsequently displaced by the meal, resulting in higher levels of activity remaining at 6 h. Thus, cholestyramine exhibited prolonged gastric residence via mucoadhesion and was distributed throughout the stomach. The surface charge of the resin was found to have a contributory role. These materials may have potential for the delivery of drugs in the topical treatment of the gastric mucosa, for example in the eradication of Helicobacter pylori.     

In vitro assessment of the mucoadhesion of cholestyramine to porcine and human gastric mucosa.

Previous in vivo studies have suggested that the extended gastric residence and uniform intragastric distribution of cholestyramine may be due to mucoadherent properties. This series of in vitro investigations explored the possibility of the anion exchange resin exhibiting bioadhesive behaviour, and investigated the characteristics, such as particle size and surface charge, that may affect it. Tensile strength measurements were carried out to determine the mucoadhesion of cholestyramine and other test materials (resin particulates, polymers and hydrogels) with varying adhesive properties, to isolated porcine and human gastric mucosa. Optimal instrumental parameters for the system were determined initially and used; all procedures were carried out at room temperature (22 degrees C). The particle size of cholestyramine did not affect mucoadhesion to either porcine or human gastric mucosa (P=0.673, porcine; P=0.969, human), whilst anionic exchangers were found to provide better mucoadhesion than cationic exchangers (P=0.0002, porcine; P=0.0009, human). In some instances, it was found that the detachment forces recorded were lower with human gastric mucosa than with porcine gastric mucosa, although this was not consistently statistically significant. A rank order of mucoadhesion was constructed from a comparison of cholestyramine with eight other test materials. Cholestyramine produced the second highest degree of mucoadhesion, with Carbopol producing the greatest adhesion. Dextran and polyethylene glycol did not display good mucoadhesion under these conditions. From the findings presented here, we have found that cholestyramine demonstrates good mucoadhesion to both porcine and human gastric mucosa when compared to other known bioadhesives. It is suggested that particle size does not contribute to this mucoadherent behaviour but the surface charge of the resin has a significant part to play.     

DMP-504 (DuPont Pharmaceuticals Co)

DMP-504 is a novel hydrogel bile acid sequestrant being developed by DuPont for the potential treatment of primary moderate hypercholesterolemia. It is in phase III trials. Equilibrium binding studies coupled with computer simulation of human bile flow predict that DMP-504 could be 3- to 4-fold more potent than cholestyramine in a clinical setting. Preclinical pharmacology studies demonstrate DMP-504 is 6-fold more potent than cholestyramine at decreasing serum cholesterol in hamsters. Clinical studies, at doses ranging from 0.9 to 7.2 g/day, indicate that DMP-504 is well tolerated and decreases LDL-cholesterol by up to 34%. As of June 1997, DuPont was seeking to outlicense DMP-504, which will be marketed in an easy-to-swallow, non-gritty tablet.     

Adsorption of methotrexate and calcium leucovorin onto cholestyramine in vitro

Methotrexate (MTX), an antimetabolite of folic acid, is a drug widely used in the treatment of different types of cancer. When high doses are administered, it is necessary to interrupt its action by administering calcium leucovorin (CaL). The main pathway of MTX and CaL elimination in humans occurs through the kidney, but about 10% is excreted in the faeces via the bile. Drugs, foods and sorbents in intestinal lumen modify MTX and CaL reabsorption. Individual and simultaneous studies on the adsorption of MTX and CaL from aqueous phosphate buffer by cholestyramine were carried out in order to calculate the adsorption process of MTX and CaL to cholestyramine, and to characterize the influence of CaL in the adsorption of MTX to cholestyramine and vice versa. The Langmuir binding isotherms determined in buffer solutions at pH 6 indicated a greater (12.58%) adsorption capacity of cholestyramine (1.43 mmol of drug/g of resin) than at pH 7 (1.25 mmol of drug/g of cholestyramine). The affinity constant of MTX to cholestyramine was a 45.27% higher (6.67 mM(-1)) than the affinity constant of CaL to the resin (3.65 mM(-1)). Results from simultaneous assays indicate that a displacement of the MTX bound to cholestyramine by CaL is not foreseeable. The results suggest that cholestyramine may be a potentially useful adjunctive therapy in the treatment of an overdose of MTX. Consequently, cholestyramine may be of clinical value in patients who develop early renal function impairment whilst undergoing MTX therapy.     

Calorimetric Evaluation of Hydration of Cholestyramine

We have investigated the mechanism of hydration of cholestyramine, a water-insoluble resin used pharmaceutically. Two types of water of hydration (freezing and non-freezing) and the amounts of heat evolved or absorbed during the hydration of cholestyramine were determined. From differential scanning calorimetry, 0·57 g water was observed to be tightly bound per gram of resin (non-freezing water). The hydration of dry cholestyramine was found to be exothermic. The heats of hydration of cholestyramine with chloride or nitrate counter-anions were found to be ?6·05 and ?3·46 cal g^?1, respectively. Some of the partially hydrated cholestyramine samples showed absorption of heat during hydration. The data generated in the study were utilized to better understand the mechanism of hydration and swelling of cholestyramine.     

A New Approach in Gastroretentive Drug Delivery System Using Cholestyramine

We prepared cellulose acetate butyrate (CAB)-coated cholestyramine microcapsules as a intragastric floating drug delivery system endowed with floating ability due to the carbon dioxide generation when exposed to the gastric fluid. The microcapsules also have a mucoadhesive property. Ion-exchange resin particles can be loaded with bicarbonate followed by acetohydroxamic acid (AHA) and coated with CAB by emulsion solvent evaporation method. The drug concentration was monitored to maintain the floating property and minimum effective concentration. The effect of CAB: drug-resin ratio (2:1, 4:1, 6:1 w/w) on the particle size, floating time, and drug release was determined. Cholestyramine microcapsules were characterized for shape, surface characteristics, and size distribution; cholestyramine/acetohydroxamic acid interactions inside microcapsules were investigated by X-ray diffractometry. The buoyancy time of CAB-coated formulations was better than that of uncoated resin particles. Also, a longer floating time was observed with a higher polymer:drug resin complex ratio (6:1). With increasing coating thickness the particle size was increased but drug release rate was decreased. The drug release rate was higher in simulated gastric fluid (SGF) than in simulated intestinal fluid (SIF). The in vivo mucoadhesion studies were performed with rhodamine-isothiocyanate (RITC) by fluorescent probe method. The amount of CAB-coated cholestyramine microcapsules that remained in the stomach was slightly lower than that of uncoated resin particles. Cholestyramine microcapsules were distributed throughout the stomach and exhibited prolonged gastric residence via mucoadhesion. These results suggest that CAB-coated microcapsules could be a floating as well as a mucoadhesive drug delivery system. Thus, it has promise in the treatment of Helicobacter pylori.     

A new approach in gastroretentive drug delivery system using cholestyramine

We prepared cellulose acetate butyrate (CAB)-coated cholestyramine microcapsules as a intragastric floating drug delivery system endowed with floating ability due to the carbon dioxide generation when exposed to the gastric fluid. The microcapsules also have a mucoadhesive property. Ion-exchange resin particles can be loaded with bicarbonate followed by acetohydroxamic acid (AHA) and coated with CAB by emulsion solvent evaporation method. The drug concentration was monitored to maintain the floating property and minimum effective concentration. The effect of CAB: drug-resin ratio (2:1, 4:1, 6:1 w/w) on the particle size, floating time, and drug release was determined. Cholestyramine microcapsules were characterized for shape, surface characteristics, and size distribution; cholestyramine/acetohydroxamic acid interactions inside microcapsules were investigated by X-ray diffractometry. The buoyancy time of CAB-coated formulations was better than that of uncoated resin particles. Also, a longer floating time was observed with a higher polymer:drug resin complex ratio (6:1). With increasing coating thickness the particle size was increased but drug release rate was decreased. The drug release rate was higher in simulated gastric fluid (SGF) than in simulated intestinal fluid (SIF). The in vivo mucoadhesion studies were performed with rhodamine-isothiocyanate (RITC) by fluorescent probe method. The amount of CAB-coated cholestyramine microcapsules that remained in the stomach was slightly lower than that of uncoated resin particles. Cholestyramine microcapsules were distributed throughout the stomach and exhibited prolonged gastric residence via mucoadhesion. These results suggest that CAB-coated microcapsules could be a floating as well as a mucoadhesive drug delivery system. Thus, it has promise in the treatment of Helicobacter pylori .     

Interaction of tricyclic antidepressants with cholestyramine in vitro.

The adsorption of amitriptyline, desipramine, doxepin, imipramine, and nortriptyline onto cholestyramine was demonstrated in vitro with use of 1.2 mol/L HCl at 37 degrees C to simulate gastric fluid. Binding to cholestyramine was approximately 80% for each of the tricyclic antidepressants, and this was about the same degree of binding noted with a nonpharmaceutical, non-ionic resin widely used in the diagnostic toxicology laboratory (Amberlite XAD-2). In contrast, five other non-antidepressants (acetaminophen, chlordiazepoxide, procainamide, quinidine, and theophylline) showed only minimal binding to cholestyramine under these conditions. Activated charcoal completely bound all drugs studied. These findings suggest that cholestyramine should be used with caution in patients receiving tricyclic antidepressants. They also suggest that cholestyramine may be a potentially useful adjunctive therapy in treatment of overdose with the tricyclic antidepressants.     

Equilibrium and Kinetic Factors Influencing Bile Sequestrant Efficacy

In vitro bile salt binding equilibria and kinetic studies were performed with cholestyramine to determine how these factors influence bile sequestrant efficacy in vivo. Chloride ion at physiologic concentrations caused more than a twofold reduction in glycocholate (GCH) binding, compared to binding in the absence of salt, over a range of GCH concentrations and was also observed to displace bound GCH. In addition, chloride ion displaced from cholestyramine as a result of bile salt binding was measured using a chloride selective electrode, and the results show that bile salt binding is due to ion exchange. Comparison of the results of the equilibrium binding experiments to human data shows that the effect of anion binding competition alone cannot account for the lack of efficacy of cholestyramine. Consideration of other effects, such as additional binding competition or poor availability for binding, based on data from the literature, shows that adequate bile salt binding potential exists and that these interferences are not major factors influencing resin efficacy. In kinetic studies, both binding uptake of GCH and displacement of GCH from cholestyramine by chloride ion were relatively rapid, indicating that cholestyramine should equilibrate rapidly with bile salts in the GI tract. Based on these findings, it is suggested that the low efficacy of cholestyramine is a result mainly of its relatively poor ability to prevent bile salt reabsorption in the ileum.     

Fecal bile acid excretion and liver cholesterol synthesis after sucralfate and cholestyramine administration in the rat

The relative ability of the resin cholestyramine and sucralfate (disucrose octasulfate) to bind bile acids in the gastro intestinal tract and increase fecal bile acid excretion has been studied in normal rats under standard diet. Plasma and liver cholesterol concentrations and in vitro cholesterol synthesis from 14C-acetate by liver slices, have been determined before and after one and three weeks of drug administration (0.5 or 1.0 g/100 g food). Plasma and liver cholesterol levels were unchanged after one week of treatment, but a moderate decrease in liver cholesterol content was observed after 3 weeks administration of cholestyramine and, to a lesser extent of sucralfate. Both drugs increase fecal bile acid excretion with a definitely higher effect of cholestyramine at either dose or period of administration. However, the resin produced a higher bile acid excretion after one week than after three weeks, whereas sucralfate effect increases with the time of administration. In vitro cholesterogenesis was clearly increased by cholestyramine and moderately by sucralfate although 14C-acetate incorporation into cholesterol was not quantitatively correlated to the amount of bile acid excreted in feces. The potential interest of sucralfate as bile acid sequestrant and hypocholesterolemic agent in man deserves further investigations.     

Sorbent therapy of the porphyrias. IV. Adsorption of porphyrins by sorbents in vitro

The adsorption capacities (Qm's) of the ion exchange resin cholestyramine and 8 activated charcoals for uroporphyrin, protoporphyrin and coproporphyrin, porphyrins that accumulate within tissues or vasculature in certain porphyrias, have been determined. Qm's (mg porphyrin/gm dry sorbent) were derived from Langmuir isotherms, which were constructed from experiments that assessed the amount of porphyrin adsorbed after the addition of varying amounts of porphyrin in solution to a constant amount of sorbent. These experiments were carried out at pH 8.2 in 0.5% desoxycholate, to simulate conditions of the small intestine. For uroporphyrin I, the Qm for Amoco Supersorb PX-21 highly activated charcoal was greater than that for cholestyramine (mean +/- SD of 26.5 +/- 12.7 vs. 17.0 +/- 2.6; t'32 = 2.46, P less than 0.025) and highly significantly greater than those of the other charcoals. For protoporphyrin IX, cholestyramine and Amoco Supersorb PX-21 charcoal had the highest Qm's (32.4 +/- 8.6 and 30.9 +/- 9.2), but these were not significantly greater than the Qm's of 5 other charcoals. Little difference was found among sorbents in the rate of adsorption of either porphyrin. For coproporphyrin III, the Qm's of cholestyramine and Amoco Supersorb PX-21 charcoal were not significantly different (39.2 +/- 13.7 vs. 35.1 +/- 4.0) but they were greater than that of Norit USP XX (20.0). Virtually no desorption of porphyrin from either cholestyramine or Amoco Supersorb PX-21 charcoal was detected. Both cholestyramine and Amoco Supersorb PX-21 charcoal appear to be highly avid sorbents for porphyrins of varied states of carboxylation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of cholestyramine on the gastrointestinal absorption of phenprocoumon and acetylosalicylic acid in man

Summary The effect of cholestyramine on the absorption of phenprocoumon and acetylosalicylic acid has been studied in volunteers by comparing their serum concentrations after a single oral dose either of the drug alone or simultaneously with the resin in a crossover repetition arrangement. In four volunteers cholestyramine 8 g significantly reduced the absorption of a simultaneous 15 mg dose of phenprocoumon. The effect of the latter on coagulation, as measured by the thrombotest method was also diminished. The absorption of acetylosalicylic acid 500 mg was delayed by cholestyramine but there was no appreciable effect on the total amount absorbed. These results are in accordance with the stronger binding of phenprocoumon to cholestyramine inin vitro experiments.     

Effect of dose size,food and surface coating on the gastric residence and distribution of an ion exchange resin

Ion exchange resin displays prolonged gastric residence and uniform distribution over the gastric mucosa when given in a small volume of water to fasted subjects. The aim of this study was to explore factors which could influence the observed gastric retention, for example the quantity of resin administered, the fed state of the subject, and the surface charge of the resin. The study was performed as a single blind, three-way crossover in 12 healthy volunteers using gamma scintigraphy to visualize the distribution of the resin in the stomach. On the first two occasions each subject received either a 25 mg or 250 mg dose of cholestyramine (an anionic exchange resin) in 1 ml of water. On the last occasion each volunteer received 250 mg of cholestyramine coated with the inert polymer ethylcellulose, to determine if the gastric residence of the resin was influenced by the surface properties of the particles. For all formulations, half of the subjects were fed 4 h after dosing to determine the effects of inducing a fed pattern of motility on the gastric retention of the resin. Gastric retention was measured as the area under the stomach activity–time curve (AUC). Median AUC values (relative units) for the 25 mg, 250 mg and polymer coated 250 mg doses were 139.6, 199.6 and 146.0 respectively, for fasted subjects and 164.1, 256.9 and 176.1 for fed subjects. Approximately 20% of the resin persisted in the stomach for the entire 6 h of the study in every case, and this was distributed evenly throughout the fundus, body and antrum. Statistical analysis of the data showed no significant differences between the gastric emptying and distribution of any of the data sets. It can be concluded that the prolonged gastric residence and uniform distribution of ionic resins is not influenced by the dose size and that the binding of the dose to the mucosa is sufficiently strong to retain the dose during feeding 4 h after administration. The mechanism by which resin becomes mucoadherent is not clear; however, these results indicate that it is unlikely to be due to a charge-based attraction.     

Cholestyramine-induced hyperchloremic metabolic acidosis.

Cholestyramine is a nonabsorbable anion exchange resin that is used predominantly for the treatment of hypercholesterolemia in adults and the management of acute diarrhea in children. The authors report two cases of severe hyperchloremic nonanion gap metabolic acidosis associated with the use of cholestyramine therapy. The authors recommend that patients taking cholestyramine who have concomitant renal insufficiency or who are volume depleted or who are taking spironolactone be monitored carefully for the emergence of a hyperchloremic metabolic acidosis.     

Comparative scintigraphic assessment of the intragastric distribution and residence of cholestyramine, Carbopol 934P and sucralfate

It has been demonstrated that orally administered cholestyramine is distributed throughout the stomach and provides prolonged gastric residence via mucoadhesion. Gamma scintigraphy was used to compare the gastric emptying and residence of this resin with two formulations known to exhibit retentive or bioadhesive properties, Carbopol 934P and sucralfate. Fasted normal subjects received a single radiolabelled dose and gastrointestinal transit was monitored for 6 h. The subjects were fed after 4 h to determine the effects of inducing a fed pattern of motility on the retention of the formulations. Initial gastric emptying was similar (Mean T50+/-S.E.M.: cholestyramine=66.93+/-9.39 min; Carbopol=56.57+/-11.96 min; sucralfate=48.33+/-11.07 min; P=0.548: n=10), however, the emptying of cholestyramine slowed beyond 2 h. This resulted in greater residence for cholestyramine (Mean AUC0-6+/-S.E.M. (relative units)=11516+/-686 versus 7657+/-1170 versus 6170+/-998; cholestyramine versus Carbopol versus sucralfate; P=0.004: n=10), with approximately 25% remaining in the stomach at 6 h compared to 3.84 and 2.65% of Carbopol and sucralfate, respectively. Cholestyramine was also distributed widely throughout the stomach whereas Carbopol and sucralfate were concentrated in the body and antrum. Thus, as cholestyramine had a comparable emptying time to Carbopol and sucralfate but greater gastric residence and wider distribution, it could provide a potential mucoadhesive drug delivery system targeting the gastric mucosa for treatment of conditions such as Helicobacter pylori infection.     

Comparison of the combination of cholestyramine/alginates with placebo in the treatment of postgastrectomy biliary reflux gastritis

Summary Postgastrectomy biliary reflux gastritis is quite common. Several drugs have been used in its treatment, including the bile acid-binding resin cholestyramine, which seemed ineffective, possibly because of its rapid disappearance from the gastric remnant. It was suggested that by using alginates, which form a raft floating on the gastric contents, cholestyramine would be retained in the stomach for a longer period. 32 patients received either placebo or cholestyramine/alginates/bicarbonate (CAB). Gastroscopy with biopsies, laboratory studies and physical examination were performed before and after the trial. At two week intervals patients were interviewed about the effect on symptoms. A detailed Y-ray study was made of 5 patients, in which a series of pictures was taken after ingestion either of placebo or CAB together with a novel contrast medium. There was no statistical difference between treatment groups with respect to symptoms, gastroscopy or histological findings, nor did the X-ray study show any difference in retention time between placebo and CAB.     

A comparison of cholestyramine and nicotinic acid in the treatment of familial type II hyperlipoproteinaemia.

1 The effects of cholestyramine and nicotinic acid on plasma lipid concentration have been compared in patients with type IIa hyperlipoproteinaemia. 2 During a 3-month period, cholestyramine resulted in a mean decrease in cholesterol levels of 26%. Triglyceride levels rose in eight of the ten patients during treatment with this drug but in the majority of patients remained within the normal range. 3 During nicotinic acid therapy, cholesterol fell by a mean of 21% and triglyceride by a mean of 23%. 4 The slow release preparation of nicotinic acid used was acceptable to the majority of the patients studied and the results therefore suggest that this drug may be a useful alternative to the more widely used agent, cholestyramine.     

The influence of cholestyramine on the elimination of tenoxicam and piroxicam

Summary We have studied the influence of multiple oral doses of cholestyramine on the single dose pharmacokinetics of tenoxicam and piroxicam in eight healthy young volunteers.Each subject received on two occasions single intravenous injections of 20 mg tenoxicam and on another two occasions single oral doses of 20 mg piroxicam. Both medications were followed by multiple oral doses of either cholestyramine or plain water (placebo).Compared with placebo cholestyramine accelerated the elimination of both drugs. The average values of half-lives were reduced (tenoxicam: 31.9 h vs 67.4 h; piroxicam: 28.1 h vs 46.8 h) due to increases in clearance. Cholestyramine-mediated enhancement of drug elimination was most pronounced in the subjects with a comparatively low baseline drug clearance. Thus, intersubject variability in clearance was smaller when the drug administrations were followed by the anion-exchange resin.The twofold acceleration of tenoxicam elimination in the present study in man contrasts with a much larger effect (five-fold) seen in experiments with dogs. This points to a much easier access of unchanged tenoxicam to the intestinal lumen in the dogs than in man.Comparing the pharmacokinetics of tenoxicam and piroxicam in the same volunteers revealed a high degree of correlation in clearance and half-lives and similar intersubject variabilities in mean kinetic variables.     

DMP 504, a novel hydrogel bile acid sequestrant: I. equilibrium binding properties and computer simulation of human bile flow

DMP 504 is a novel bile acid sequestrant under development for the treatment of primary hypercholesterolemia. The resin is a soft-textured “hydrogel” that is synthesized from 1,10-dibromodecane and 1,6-diaminohexane. The equilibrium binding parameters for DMP 504 have been determined and compared to cholestyramine (CS) with respect to the major trihydroxy bile acid, glycocholate (GC), and the major dihydroxy bile acid, glycochenodeoxycholate (GCDC). DMP 504 had a greater maximum binding capacity (Bmax) than CS for GC (5.47 ± 0.06 vs. 2.76 ± 0.17 moles/kg) and GCDC (5.71 ± 0.14 vs. 3.26 ± 0.11 moles/kg). DMP 504 had a greater affinity, i.e., a lower Kd, than CS for GC (1.78 ± 0.04 vs. 5.24 ± 0.64 mM) and GCDC (0.19 ± 0.01 vs. 0.52 ± 0.06 mM). Similar values were obtained for the taurine conjugates of cholate and chenodeoxycholate. Since the interaction of bile acids with DMP 504 was highly cooperative, the binding isotherms were analyzed with a model that included a cooperativity parameter (W) to allow for interactions between adjacently bound bile acids. The DMP 504 binding isotherms showed greater cooperativity than CS for GC (5.10 ± 0.42 vs. 1.81 ± 0.47) and GCDC (6.28 ± 1.68 vs. 2.40 ± 0.76). A mathematical model of human bile flow, using the values for Bmax, Kd, and W determined in this study predicted that DMP 504 would be approximately threefold more potent than CS in a clinical setting. Drug Dev. Res. 41:58–64, 1997. © 1997 Wiley-Liss, Inc.     

Interaction of naproxen with cholestyramine

‘In vitro’ and ‘in vivo’ studies were used to determine the interaction of naproxen, an anti-inflammatory agent, and cholestyramine, a hypocholesterolemic substance. Cholestyramine shows a marked affinity for naproxen and the intensity of this is governed by the pH values. The maximum amount of naproxen adsorbed by the resin is close to 2·2 mMg^?1. The pharmacokinetics of naproxen was studied in eight healthy volunteers after concurrent oral administration in a single dose of 250 mg of naproxen and 4 g of cholestyramine. The resin causes an important delay in the incorporation of naproxen into the systemic circulation, though no significant modifications are seen to take place in any other pharmacokinetic parameters of the drug.