Interaction by cholestyramine on the uptake of hydrocortisone in the gastrointestinal tract

Binding interactions with sevelamer and polystyrene sulfonate in vitro

This study explored the binding of 28 drugs, which were selected based on frequency of concomitant use and chemical properties, to sevelamer and polystyrene sulfonate in vitro. The relative binding was determined by dissolving the investigated drugs alone (=control), together with 800 mg of sevelamer and 15 g of polystyrene sulfonate at different pH levels (1.5, 5.5, and 7.4), respectively. After incubation at 37℃ and shaking for 60 min, the solutions were diluted and centrifuged, and the drug concentrations were quantified with validated analytical assays. The binding assays were performed in threefold. The mean relative binding (MRB) at each pH level was calculated, with a MRB >20% for at least one pH level to be considered as relevant binding. Fourteen and 23 potentially new binding interactions were identified with sevelamer and polystyrene sulfonate, respectively. These potentially new binding interactions have to be studied in vivo to assess their clinical relevance.

Management of dyslipidemia in pediatric renal transplant recipients

Dyslipidemia after kidney transplantation is a common complication that has historically been underappreciated, especially in pediatric recipients. It is also a major modifiable risk factor for cardiovascular disease, a top cause of morbidity and mortality of transplant patients. While most knowledge about post-transplant dyslipidemia has been generated in adults, recommendations and treatment strategies also exist for children and are presented in this review. Awareness of these applicable guidelines and approaches is required, but not sufficient, for the reliable management of dyslipidemia in our patients, and additional needs and opportunities for comprehensive care in this area (e.g., quality improvement) are outlined.

Lack of effect of colesevelam HCl on the single-dose pharmacokinetics of aspirin, atenolol, enalapril, phenytoin, rosiglitazone, and sitagliptin

AIMS

Drug interactions with bile acid sequestrants are primarily due to the potential of these agents to bind to concomitant drugs. Six clinical studies were performed to determine the effects of colesevelam on the pharmacokinetics of aspirin, atenolol, enalapril, phenytoin, rosiglitazone, and sitagliptin.

METHODS

All six studies enrolled healthy subjects aged 18-45 years. The phenytoin study used a single-dose, three-period crossover design (phenytoin alone, phenytoin simultaneously with colesevelam, and phenytoin 4h before colesevelam). The other studies used a two-period crossover design (test drug alone and test drug simultaneously with colesevelam). Colesevelam (3750mg once daily) was dosed throughout the pharmacokinetic sampling period. After each single dose of the test drug, serial blood samples were collected for determination of plasma drug concentrations and calculation of pharmacokinetic parameters.

RESULTS

For all six test drugs, 90% CIs for geometric least-squares mean ratios of AUC and Cmax for the measured analytes were within specified limits, indicating no interaction between the test drug and colesevelam.

CONCLUSIONS

Aspirin, atenolol, enalapril, rosiglitazone, and sitagliptin may be taken with colesevelam. Although the phenytoin study indicated no pharmacokinetic interaction, phenytoin should continue to be taken ≥4h before colesevelam in accordance with current prescribing information.

Cholesterol and fat lowering with hydrophobic polysaccharide derivatives

Hydrophobic derivatives of highly methylated citrus pectin, chitosan and cellulose were prepared and tested as potential cholesterol lowering agents. Elemental analysis and spectroscopic methods confirmed high substitution degree for all of them. Substitution with long alkyl/acyl groups led to significant changes in physical and thermal properties of modified polysaccharides. Sorption of cholate and cholesterol by these polysaccharide-based sorbents was estimated in comparison with the synthetic drug cholestyramine. It was found that modified polysaccharides have high affinity to cholesterol. By contrast, cholestyramine was effective only in cholate sorption.

Effect of the bile acid sequestrant colesevelam on the pharmacokinetics of pioglitazone, repaglinide, estrogen estradiol, norethindrone, levothyroxine, and glyburide

The purpose of this study was to assess effects of colesevelam on the pharmacokinetics of glyburide, levothyroxine, estrogen estradiol (EE), norethindrone (NET), pioglitazone, and repaglinide in healthy volunteers. Six drugs with a potential to interact with colesevelam were studied in open-label, randomized clinical studies. The presence of a drug interaction was concluded if the 90% confidence intervals for the geometric least squares mean ratios of AUC(0-t) (AUC(0-48) for levothyroxine) and C(max) fell outside the no-effect limits of (80.0%, 125.0%). Concomitant administration of colesevelam had no effect on the AUC(0-t) or C(max) of pioglitazone but significantly decreased the AUC(0-t) and C(max) of glyburide, levothyroxine, and EE and the C(max) of repaglinide and NET. AUC(0-t) and C(max) of glyburide and EE, but not repaglinide or NET, were significantly decreased when the drug was given 1 hour before colesevelam. When glyburide, EE, or levothyroxine was given 4 hours before colesevelam, no drug interaction was observed. Although colesevelam has a cleaner drug interaction profile than other bile acid sequestrants, it does interfere with absorption of some drugs. A 4-hour window appears sufficient to eliminate these interactions.

Bile Salt Anion Sorption by Polymeric Resins: Comparison of a Functionalized Polyacrylamide Resin with Cholestyramine

Cholestyramine and a cross-linked polyacrylamide resin with lateral alkyl quaternary ammonium groups (QPDA12) were used to study their ability to bind several bile salt anions (including the cholate, glycocholate, taurocholate, and chenodeoxycholate), individually and competitively, from phosphate buffer solutions at room temperature. The latter resin showed high affinities for all the bile salt anions examined, while cholestyramine exhibited a high affinity only for the more hydrophobic chenodeoxycholate. However, for the binding with cholestyramine, cooperative effects were more pronounced, leading to the enhancement of sorption at higher concentrations. The Langmuir equation and its modified versions were used in the interpretation of both individual and competitive binding of bile salts. The data from competitive binding studies indicated that the presence of the tightly bound chenodeoxycholate did not significantly diminish the ability of QPDA12 resin to bind cholate. However, for cholestyramine, the sorption of chenodeoxycholate increased the relative binding affinity for the more hydrophilic cholate, revealing a novel "cooperative" effect involving different bile salt anions. The latter results suggest that the observed higher affinity of QPDA12 is brought about predominantly through the hydrophobic interactions with the pendant alkyl groups rather than with the resin backbone. Copyright 2000 Academic Press.

Classification of hypoglycemic disorders

The classification of symptoms of hypoglycemia, namely, reactive versus fasting, based on segregation by timing in relation to meals is no longer useful from a clinical point of view. Every patient with neuroglycopenic symptoms, regardless of relation to food ingestion, requires comprehensive evaluation. Identification of the possible cause of hypoglycemia and selection of diagnostic modalities are facilitated by considering whether the patient appears to be healthy (with or without compensated coexistent disease) or ill (with a disease known to have a proclivity to develop hypoglycemia, or is hospitalized). Medications may mediate hypoglycemia in anybody, whether they appear healthy or ill.

Hypoglycemia

The diagnosis of a hypoglycemic disorder requires a high level of suspicion, careful assessment of the patient for the presence of mediating drugs or predisposing illness, and, when indicated, methodic evaluation of the basis of well-defined diagnostic criteria. The diagnostic burden is heaviest for healthy-appearing persons with episodes of confirmed neuroglycopenia. The author's criteria for insulin mediation of hypoglycemia are plasma insulin of 6 microU/mL or higher (radioimmunoassay), C-peptide of 200 pmol/L or higher (ICMA), proinsulin of 5 pmol/L or higher (ICMA), beta OH butyrate of 2.7 mmol/L or lower, and generous (> or = 25 mg/dL) response of plasma glucose to intravenous glucagon administered when the patient is hypoglycemic. Sulfonylurea should be sought in the plasma of any hypoglycemic patient, especially by an assay which can detect the second generation of these drugs.

A comparative review of the adverse effects of treatments for hyperlipidaemia

Various lipid-lowering drugs have been shown to reduce serum cholesterol and serum triglycerides effectively. In view of trials indicating that lipid-lowering drugs may reduce cardiac morbidity and mortality but not the overall mortality in the study group, increased attention must be focused on potential harmful side effects during treatment with these agents. The adverse effects of many of the principal drugs in this category are discussed. Gastrointestinal symptoms, usually self-limited and reversible, are the most common side effects. Potential harmful adverse effects include drug interactions (cholestyramine), myopathy and hepatic injury (HMG-CoA reductase inhibitors), and increased gallstone formation and ventricular arrhythmias (clofibrate). Not all lipid-lowering drugs have been studied adequately on a long term basis, so that medications given for an indefinite period must be reevaluated frequently. However, there are several agents that lower serum lipid levels effectively and that have been used for more than 20 years without serious side effects.

Apparent reduced absorption of gemfibrozil when given with colestipol

Colestipol and gemfibrozil may be used in combination to lower serum cholesterol and triglycerides. Since colestipol is known to bind certain anionic drugs, we studied the effect of colestipol on the pharmacokinetics of gemfibrozil in 10 patients with elevated serum cholesterol and triglycerides. Each patient received 600 mg of gemfibrozil by mouth during four different studies. Gemfibrozil was given randomly either alone, with, 2 hours before, or 2 hours after 5 grams of colestipol. The serum gemfibrozil concentration time curves were similar when gemfibrozil was given alone or two hours before or after colestipol. There was also no statistical difference in peak gemfibrozil concentration (Cmax), time to Cmax (tmax), area under the curve (AUC), or serum elimination half-life (t1/2) between any of these three treatments. However, when colestipol was given with gemfibrozil, there was a decrease in AUC (43.6 +/- 21.9 mg*hr/L) compared with gemfibrozil given alone (62.6 +/- 10.3 mg*hr/L) which was statistically different by both ANOVA and paired t-test. This finding suggests a decrease in gemfibrozil bioavailability. Cmax when colestipol was given with gemfibrozil (14.7 +/- 6.6 mg/L) was not statistically different from gemfibrozil alone (20.1 +/- 4.9 mg/L). However, the mean serum concentrations when gemfibrozil was given with colestipol were significantly lower at the 0.5, 1.0 and 1.5 hour sampling times when compared to the other regimens. Gemfibrozil serum elimination half-life was not significantly altered by combination with colestipol. The data suggest a reduction of gemfibrozil bioavailability when colestipol is administered concomitantly. Separating the administration of these two drugs by at least two hours will avoid this drug interaction.

Adverse effects of hypolipidaemic drugs

Cholestyramine, colestipol, clofibrate, gemfibrozil, nicotinic acid (niacin), probucol, neomycin, and dextrothyroxine are the most commonly used drugs in the treatment of hyperlipoproteinaemic disorders. While adverse reaction data are available for all of them, definitive data regarding the frequency and severity of potential adverse effects from well-controlled trials using large numbers of patients (greater than 1000) are available only for cholestyramine, clofibrate, nicotinic acid and dextrothyroxine. In adult patients treated with cholestyramine, gastrointestinal complaints, especially constipation, abdominal pain and unpalatability are most frequently observed. Continued administration along with dietary manipulation (e.g. addition of dietary fibre) and/or stool softeners results in diminished complaints during long term therapy. Large doses of cholestyramine (greater than 32 g/day) may be associated with malabsorption of fat-soluble vitamins. Most significantly, osteomalacia and, on rare occasions, haemorrhagic diathesis are reported with cholestyramine impairment of vitamin D and vitamin K absorption, respectively. Paediatric patients have been reported to experience hyperchloraemic metabolic acidosis or gastrointestinal obstruction. Concurrent administration of acidic drugs may result in their reduced bioavailability. Serious adverse reactions to clofibrate will probably limit its role in the future. Of particular concern are ventricular arrhythmias, induction of cholelithiasis and cholecystitis, and the potential for promoting gastrointestinal malignancy which far outweigh the reported benefits in preventing new or recurrent myocardial infarction, cardiovascular death and overall death. Patients with renal disease are particularly prone to myositis, secondary to alterations in protein binding and impaired renal excretion of clofibrate. Drug interactions with coumarin anticoagulants and sulphonylurea compounds may produce bleeding episodes and hypoglycaemia, respectively. Nicotinic acid produces frequent adverse effects, but they are usually not serious, tend to decrease with time, and can be managed easily. Dermal and gastrointestinal reactions are most common. Truncal and facial flushing are reported in 90 to 100% of treated patients in large clinical trials. Significant elevations of liver enzymes, serum glucose, and serum uric acid are occasionally seen with nicotinic acid therapy. Liver enzyme elevations are more common in patients given large dosage increases over short periods of time, and in patients treated with sustained release formulations.(ABSTRACT TRUNCATED AT 400 WORDS)