Alterations in human serum alkaline phosphatase and its isoenzymes by hypolipidemic agents: colestipol and clofibrate

Safety considerations with gastrointestinally active lipid-lowering drugs

Gastrointestinally active agents such as cholesterol absorption inhibitors (CAIs) (eg, ezetimibe) and bile acid sequestrants (BAS) (the resins cholestyramine and colestipol, or colesevelam, a nonabsorbable polymer) offer important options for lipid-lowering therapy. Ezetimibe is a novel CAI that inhibits the absorption of dietary and biliary cholesterol without affecting the absorption of triglycerides or fat-soluble vitamins. In clinical trials, there has been no evidence of increased rates of myopathy or rhabdomyolysis associated with ezetimibe, whether in use as monotherapy or in a combination with statin therapy, although there exist case reports of possible ezetimibe-associated myopathy. Ezetimibe alone does not appear to increase liver transaminase levels significantly, but the coadministration of a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) with ezetimibe marginally increases this risk. However, reported increases in liver enzymes have not been associated with clinically meaningful symptoms and often return to baseline levels after the discontinuation of therapy or with continued treatment. To date, no cases of liver failure, liver transplantation, or death have been reported. BAS have been used clinically since the 1960s for lowering low-density lipoprotein cholesterol. Because they are not absorbed from the gastrointestinal tract into the blood, these agents do not contact most body organs and are therefore systemically safe. However, case reports and pharmacokinetic data disclose 3 kinds of adverse effects: (1) the decreased absorption of concomitant medications and sometimes of certain vitamins; (2) the physicochemical alteration of intestinal contents leading to constipation and, very rarely, intestinal obstruction; and (3) modest increases in plasma triglyceride levels due to the alteration of hepatic lipid metabolism. The newest BAS, colesevelam, has greater specificity for bile acids compared with the older agents cholestyramine and colestipol, eliminating most drug interactions and reducing the tendency for constipation. Overall, CAIs and BAS have excellent systemic safety profiles when used alone or in combination with other lipid-lowering drugs.

Long-term effects of sevelamer hydrochloride on the calcium x phosphate product and lipid profile of haemodialysis patients

BACKGROUND

Short-term studies have suggested that sevelamer hydrochloride, a non-aluminium- and non-calcium-containing hydrogel, is an effective phosphate binder in haemodialysis patients, and may produce favourable changes in the lipid profile.

METHODS

To determine the long-term effectiveness of sevelamer hydrochloride, we performed an open-label clinical trial in 192 adult patients with end-stage renal disease on haemodialysis. Drug-related changes in the concentrations of serum phosphorus, calcium, calcium x phosphate product, parathyroid hormone, and low- and high-density lipoprotein cholesterol concentrations were the major outcomes of interest.

RESULTS

Treatment with sevelamer was associated with a mean change in serum phosphorus of -0.71+/-0.77 mmol/l, serum calcium of 0. 08+/-0.22 mmol/l, and calcium x phosphate product of -1.46+/-1.78 mmol/l (P<0.0001 for all comparisons). There were no significant overall treatment-related changes in parathyroid hormone. Serum levels of LDL cholesterol decreased by 0.81+/-0.75 mmol/l (mean -30%, P<0.0001) and HDL cholesterol increased by a mean of 0.15+/-0.29 mmol/l (mean +18%, P<0.0001). Drug-related adverse events were infrequent and most were of mild intensity.

CONCLUSION

Sevelamer is a safe and effective phosphate binder that leads to significant improvements in the calcium x phosphate product and lipid profile of haemodialysis patients.

A comparison of the calcium-free phosphate binder sevelamer hydrochloride with calcium acetate in the treatment of hyperphosphatemia in hemodialysis patients

Current phosphate binders used in hemodialysis patients include calcium-based binders that result in frequent hypercalcemia and aluminum-based binders that result in total body aluminum accumulation over time. This investigation describes the use of a calcium- and aluminum-free phosphate-binding polymer in hemodialysis patients and compares it with a standard calcium-based phosphate binder. An open-label, randomized, crossover study was performed to evaluate the safety and effectiveness of sevelamer hydrochloride in controlling hyperphosphatemia in hemodialysis patients. After a 2-week phosphate binder washout period, stable hemodialysis patients were administered either sevelamer or calcium acetate, and the dosages were titrated upward to achieve improved phosphate control over an 8-week period. After a 2-week washout period, patients crossed over to the alternate agent for 8 weeks. Eighty-four patients from eight centers participated in the study. There was a similar decrease in serum phosphate values over the course of the study with both sevelamer (-2.0 +/- 2.3 mg/dL) and calcium acetate (-2.1 +/- 1.9 mg/dL). Twenty-two percent of patients developed a serum calcium greater than 11.0 mg/dL while receiving calcium acetate, versus 5% of patients receiving sevelamer (P < 0.01). The incidence of hypercalcemia for sevelamer was not different from the incidence of hypercalcemia during the washout period. Patients treated with sevelamer also sustained a 24% mean decrease in serum low-density lipoprotein cholesterol levels. Sevelamer was effective in controlling hyperphosphatemia without resulting in an increase in the incidence of hypercalcemia seen with calcium acetate. This agent appears quite effective in the treatment of hyperphosphatemia in hemodialysis patients, and its usage may be advantageous in the treatment of dialysis patients.

The effect of bezafibrate treatment on serum alkaline phosphatase isoenzyme activities

A reduction in serum total alkaline phosphatase (ALP) activity is a well-documented side effect of treatment with bezafibrate and other fibric acid derivatives. To evaluate the effect of bezafibrate treatment on individual ALP isoenzyme activities, 10 patients were studied on two separate occasions, first, after a 6-week period on no drug treatment, and second, after 6 weeks of bezafibrate therapy. On each occasion, serum total ALP and ALP isoenzyme activities and serum gamma-glutamyltransferase (GGT) activity were measured both after fasting and following the ingestion of a standardized high-fat meal rich in long-chain fatty acid triglycerides, as intestinal ALP activity is known to be influenced by dietary fat intake. Plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were measured on fasting samples. In the fasting state, bezafibrate treatment resulted in a 25% reduction (P < .01) in serum total ALP activity; liver ALP activity was reduced by 40% (P < .01), and biliary ALP activity was reduced in those patients in whom it was initially detectable, while bone and intestinal ALP activities were unchanged. There was also a 15% reduction (P < .05) in serum GGT activity, but no change in plasma AST or ALT activities. Serum intestinal ALP activity increased significantly (P < .01) by 1 hour following ingestion of the high-fat meal, but treatment with bezafibrate did not change the magnitude of this response. There was no change in the activity of any other ALP isoenzyme following fat ingestion. This study demonstrates that the effect of bezafibrate on serum ALP activity is confined to the liver and biliary isoenzymes.(ABSTRACT TRUNCATED AT 250 WORDS)