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At least 19 recordsLinked to original sources
PubMed1976

The effect of halofenate or halofenate free acid on human, rat and guinea pig platelet aggregation.

Halofenate free acid (HFA), the major metabolite of the hypolipemic agent halofenate, blocked the secondary phase of human platelet aggregation induced by ADP, epinephrine, or thrombin; higher concentrations of clofibrate free acid (CFA) were required to produce similar inhibitory effects on platelet aggregation. HFA and CFA inhibited collagen-induced aggregation of human, rat, or guinea pig platelets. Halofenate orally administered to rats caused inhibition of collagen-induced aggregation when plasma levels of HFA exceeded 300 mug/ml, a clinically achievable human plasma concentration. The platelet inhibitory effects of clofibrate administration were less than those observed with halofenate administration.

Animals↗
PubMed1976

Halofenate: a potent inhibitor of normal and hypersensitive platelets.

Platelet hypersensitivity has been documented in diabetes and angina pectoris and can be partially reversed in hyperbetalipoproteinemia by clofibrate. We therefore examined the effects of incubating another lipid-lowering agent, halofenate, with both normal platelets and platelets made hypersensitive in vitro by incorporation of 55 per cent excess cholesterol into their membranes. At therapeutic concentrations, halofenate caused a time- and dose-dependent inhibition of the aggregation of normal platelets by epinephrine. After 30 minutes' incubation at 37 degrees C., halofenate significantly inhibited the extent of aggregation by 88 per cent (p less than 0.01), whereas clofibrate inhibited aggregation by 44 per cent (p less than 0.01). Halofenate was a more potent inhibitor of platelets than clofibrate (p less than 0.01). The mean threshold concentration of epinephrine necessary for aggregation of normal platelets (4.2 muM) was not significatnly increased with clofibrate (10 muM) but was markedly elevated with halofenate (245 muM; p less than 0.001). Significant but less dramatic increases in threshold concentration of ADP and collagen were found with halofenate but no clofibrate. Cholesterol-rich platelets were 114-fold more sensitive to epinephrine and twofold more sensitive to ADP than normal platelets but after incubation with halofenate became even less sensitive than normal. Clofibrate inhibited the extent of aggregation of hypersensitive platelets but did not alter the threshold concentration of epinephrine necessary for aggregation. Thus, halofenate is more potent than clofibrate in reducing the sensitivity of normal platelets to aggregating agents in vitro and can completely reverse experimentally produced platelet hypersensitivity. These data suggest that halofenate might be useful in reversing increased platelet sensitivity in cardiovascular diseases.

Adenosine Diphosphate↗
PubMed1977

Studies on the mechanism of action of halofenate.

This paper reviews most of the clinical studies on the mode of action of halofenate, an established hypolipidemichypouricemic agent in man. In yeast cutlures and in isolated rat adipocytes, halofenate was found to inhibit the conversion of pyruvate to acetyl CoA. While pyruvate dehydrogenase was inhibited in vitro, halofenate also inhibited the activety of various other isolated enzymes. In rats maintained on halofenate in the diet (0.02-0.10%) for 2-14 days, there were 20-40% decreases in plasma cholesterol, trigly cerides, phospholipids, and free fatty acids. Inhibition of liver HMG-CoTA reductase does not appear to account for the hypocholesterolemic effect, and activation of mitochondrial alpha-glycerophosphate dehydrogenase does not explain the hypotriglyceridemic action. Kinetic measurements of the serum appearance and disappearance of triglycerides in drug-treated rats suggest that the hypotriglyceridemic activity is due to a net inhibition of hepatic triglyceride synthesis. Reduction of very low density lipoprotein (VLDL) and high density lipoprotein (HDL) levels in rats with sucrose-induced hyperlipidemia and normalization of the altered apolipoprotein profiles are in accord with the effects of halofenate on plasma triglyceride and cholesterol levels. The reduced insulin-to-glucagon ratio observed in Zucker obese hyperlipemic rats is also consistent with halofenat's hypotriglyceridemic activity. Preliminary experiments in rats on the mechanism of its hypoglycemic activity, observed in some diabetic hyperlipidemic patients, indicate that halofenate acts differently than conventional oral hypoglycemic agents. Some, but not all, of the effects of halofenate were observed with clofibrate at two to ten times higher levels.

Adipose Tissue↗
PubMed1976

Effect of halofenate on serum thyroid hormone determinations in vitro.

Halofenate has been shown to decrease thyroxine (T4) binding to thyroxine-binding globulin (TBG) in vitro. Several indirect serum thyroid hormone assays are dependent on thyroid hormone binding and the results might be altered by halofenate in the serum. Halofenate free acid (50-500 mug/ml) was added to serum samples in vitro, and the samples were assayed for total serum T4 by competitive protein-binding assay (CPB) and radioimmunoassay (RIA), the per cent of dialyzable T4 (%FT4), total serum triiodothyronine (T3) by RIA, and resin T3 uptake (RT3U). Halofenate increased the measured T4 (CPB), %FT4, T3 (RIA), AND RT3U, but did not alter the T4 (RIA) determination. Thus, halofenate appears to diminish T4 binding to TBG in vitro, and artifactually alters the serum determinations of T4 (CPB), %FT4, T3 (RIA), AND RT3U. Calculated values derived from these measurements for the free thyroxine index and "free" T4 will also be affected halofenate. Only the T4 (RIA) determination was unchanged by the presence of halofenate in vitro.

Antigens↗
PubMed1976

Changes in serum thyrotropin (TSH) in man during halofenate administration.

Halofenate, a serum lipid-lowering agent which inhibits binding of thyroid hormone to thyroxine-binding globulin (TBG), was administered daily for 14 days to 8 hypothyroid subjects with elevated TSH concentrations as a result of incomplete thyroxine (T4) therapy. Drug administration resulted in mean increases in serum dialyzable fraction T4 (DFT4) of 52% over pretreatment levels (P less than 0.01) and in dialyzable fraction triiodothyronine (DFT3) of 26% in 7 subjects, (P less than 0.01). During halofenate treatment in these 7 subjects, serum TSH concentrations decreased significantly (mean = 39%, P less than 0.01) when DFT4 and DFT3 were increased by halofenate. In only two subjects was there a convincing temporal relationship between increased serum absolute free T4 (AFT4) and decreased serum TSH concentrations. Contrary to what would be predicted from the "free hormone hypothesis", changes in serum TSH concentration in these hypothyroid patients appeared to relate primarily to changes in the free fraction of circulating T4 and T3 (DFT4, DFT3), rather than to alterations in AFT4 or AFT3. Halofenate did not alter serum TBG binding capacity. An eighth subject did not show increased DFT4 and DFT3 during halofenate treatment despite achievement of therapeutic serum levels of the agent; in this patient, serum TSH levels rose progressively throughout the period of inadequate T4 replacement and halofenate administration. In hypothyroid patients, short-term halofenate use suggests that the pituitary-thyroid hormone feedback circuit can respond to increases in serum DFT4 and DFT3 in the absence of detactable increases in absolute free hormone concentrations.

Adult↗
PubMed1975

Alterations in the effects of warfarin in dogs by halofenate: an influence upon the kinetics of prothrombin.

The interaction between warfarin and the new lipid lowering agent halofenate (MK 185) [2- acetamidoethyl (p-chlorophenyl) (m-trifluoromethylphenoxy) acetate] was studied in dogs in both short- and long-term experiments. Our data suggest that halofenate potentiates the anticoagulant effect of warfarin by increasing the degradation of prothrombin (factor II) (Kdeg on placebo = 211 +/- 32 X 10(-4) X Hr-1 mean +/- SEM; on halofenate = 268 +/- 39 X 10(-4) X Hr-1 mean +/- SEM; P less than 0.01). However, a concomitant increase in factor II synthesis of 34% results in resistance to warfarin's effect if halofenate is administered prior to warfarin. The mean prothrombin time of 4 dogs on 2 mg of warfarin following halofenate pretreatment for 8 weeks was 74.8% +/- 17.3 (SE) of the anticoagulated control dog. On 2 mg of warfarin alone, it was 133.7% +/- 42.0 (P less than 0.001). Cessation of halofenate from combined therapy resulted in a delayed augmentation of warfarin effect. These data suggest that the nature of the interaction between warfarin and drugs such as halofenate which alter the kinetics of prothrombin may depend on the sequence of administration.

Animals↗
PubMed1976

One-year trials with halofenate, clofibrate, and placebo.

The hypolipidemic as well as other laboratory and clinical effects of halofenate, clofibrate, and placebo were compared in 29 patients with type IV hyperlipoproteinemia in a double-blind, controlled, therapeutic trial of 1 yr duration. Plasma drug levels were obtained to monitor compliance. Clofibrate and halofenate lowered serum triglycerides to a similar extent. The hypotriglyceridemic effect of halofenate was significant only when data from noncompliant patients were discarded. Only clofibrate lowered baseline levels of plasma cholesterol. Very low density lipoproteins were decreased and low density lipoproteins were increased by clofibrate but not by halofenate. Halofenate had a marked hypouricemic effect that was greater than that of clofibrate. The hypouricemic effect of halofenate and clofibrate was paralleled by a concomitant decrease in serum bilirubin. Abnormal increases in serum creatine phosphokinase were observed with both drugs primarily in patients who had abnormal initial levels.

Adult↗
PubMed1975

Potentiation of hypoglycemic effect of sulfonylureas by halofenate.

We investigated the possibility of a drug interaction between the antilipemic agent halofenate and sulfonylureas. Twelve young, healthy men were given 1 g of tolbutamide by mouth before and after 12 days of double-blind treatment with 1 g per day of halofenate, or placebo. There was a significant increase in serum tolbutamide at eight, 10 and 12 hours (P less than 0.01) and a significant (P less than 0.01) decrease in serum glucose at one, four and six hours after halofenate treatment, but not after placebo. In a long-term, double-blind study of halofenate or clofibrate treatment of patients with Type IV hyperlipoproteinemia, diabetic patients receiving a sulfonylurea and halofenate either required a reduction in the dose of the sulfonylurea or demonstrated significantly improved control of hyperglycemia (P less than 0.05) or both. No appreciable decrease in serum glucose levels was noted in diabetic patients receiving sulfonylurea and clofibrate. This interaction between halofenate and sulfonylureas is clinically important, especially in view of the association of hyperlipemia and diabetes.

Adult↗
PubMed1977

Potentiation of hypoglycemic effect of chlorpropamide and phenfromin by halofenate.

The potentiation of oral hypoglycemic drugs by the antilipemic agent halofenate is reported. Forty-seven diabetic patients were treated for 48 weeks with halofenate, clofibrate, or placebo. Five patients in the halofenate group were taking phenformin plus either chlorpropamide or tolbutamide. Their average initial fasting plasma glucose was 160 mg./dl. All five patients experienced a slow but but substantial fall in fasting plasma glucose. The mean fasting plasma glucose for the five patients after 80 days of halofenate treatment was 63 mg./dl. As oral treatment for diabetes was reduced, the fasting plasma glucose returned to prehalofenate levels. In this study, we did ont detect an effect of halofenate on the fasting plasma glucose of diabetic patients treated with insulin or on the fasting plasma glucose levels of patients treated with diet alone.

Blood Glucose↗
PubMed1977

Comparison of clofibrate with halofenate in diabetics with hyperlipidaemia.

In a double-blind, randomized study which lasted 48 weeks the effects of clofibrate and halofenate were compared in maturity-onset diabetics with hyperlipidaemia. With the use of both clofibrate and halofenate serum cholesterol values were lowered only slightly. Both agents significantly reduced triglyceride values, but the decreases were modest and transient. Both drugs significantly lowered serum urate values, although the effect of halofenate was distinctly greater. Halofenate, but not clofibrate, had a considerable hypoglycaemic effect on the patients, most of whom were also receiving oral antidiabetic medicines. The drugs produced a number of clinical and biochemical adverse reactions, and in about 20% of all patients the trial had to be discontinued prematurely. The management of hyperlipidaemia in maturity-onset diabetics is briefly discussed, and it is concluded that neither clofibrate nor halofenate is to be recommended.

Aged↗
PubMed1976

Halofenate in the treatment of type II hyperlipoproteinemia. Double blind comparison with clofibrate.

A double-blind study comparing halofenate, a new lipid-lowering investigation drug, with an established drug, clofibrate, was conducted on 33 clinic patients with Type II hyperlipoproteinemia for a period of 48-96 weeks. All but 10 patients had some type of symptomatic major vascular disease. With respect to serum cholesterol levels, a comparable proportion (56-59%) of patients in each group responded to the respective treatment but the magnitude of lowering was substantially less for the halofenate responders (12% mean decrease versus 25%). Type IIa patients in both groups were more likely than Type IIb patients to have a favorable cholesterol-lowering response. Weight gain of 5% or greater was prejudicial to cholesterol lowering. In the case of serum triglycerides, the proportion of patients responding to clofibrate treatment was somewhat greater (87% versus 57% for halofenate) but the mean magnitude of lowering (27-34%) was comparable for responders in the two groups. Weight gain did not influence appreciably the triglyceride-lowering effect. Elevated concentrations of triglyceride (Type IIb) in the control period favored a triglyceride lowering response by clofibrate but was only a moderate influence on the response to halofenate.

Adult↗
PubMed1975

The metabolic spectrum of halofenate.

Halofenate is a new antilipemic drug which is an ester of carboxylic acid. In dosages ranging from 10 to 15 mg/kg, halofenate produces prominent decreases in serum triglycerides and uric acid, with only a slight reduction in serum cholesterol. The decrease in serum uric acid is due to augumented uricosuria. Halofenate is less antilipemic, but more antiuricemic than clofibrate. It apparently interferes with the protein binding of some hormones (thyroid) and drugs (tolbutamide), which can produce changes in the laboratory or clinical findings. In general, halofenate was well tolerated, except for occasional gastrointestinal symptoms.

Blood Glucose↗
PubMedDate not supplied

Effects of halofenate on glucose tolerance in patients with hyperlipoproteinemia.

Halofenate, a triglyceride- and uric acid-lowering drug, potentiated the effect of oral hypoglycemics. Its effect on serial glucose tolerance was evaluated in ten patients with hypertriglyceridemia without overt diabetes. Six-hour oral glucose tolerance tests were done during a control period and every 24 weeks over two years of halofenate treatment. Abnormal glucose tolerance (chemical diabetes) was observed during the control period in six of ten patients. The number of abnormal tests gradually decreased to none by 48 weeks. Plasma glucose, insulin, and free fatty acid values during the glucose tolerance tests were reduced significantly. Halofenate induced significant serum uric acid reduction. No significant regressions were observed among levels of lipids, hormones, glucose, and uric acid. The mechanisms by which lipid-lowering drugs improve glucose tolerance are as yet unexplained.

Adult↗
PubMed1975

Effect of halofenate and clofibrate on lipid synthesis in rat adipocytes.

The free acids of the plasma lipid-lowering agents, halofenate and clofibrate inhibited the incorporation of radioactive glucose and pyruvate into fatty acids of isolated adipocytes prepared from rat epididymal fat pads. The concentration which inhibited fatty acid synthesis was dependent on the bovine serum albumin concentration in the incubation. The 50 per cent inhibitory concentration of the free acid of halofenate in 1 per cent, 2 percent and 4 per cent albumin was 0.9 mM, 2.3 MM and 4.4 mM, respectively. The potency of clofibrate was also lowered by increasing the albumin concentration. These compounds inhibited the uptake of both [14C]glucose and [14C]pyruvate to the same degree as the incorporation of these substrates into fatty acids. However, the drugs either had no effect on , or stimulated the uptake of palmitate by the cells. Leucine accumulation by the adipocytes was unaffected by halofenate (free acid) and inhibited by clofibrate (free acid). A comparison of these agents with (minus)-hydroxycitrate, kynurenate and cerulenin (inhibitors of ATP-citrate lyase, acetyl CoA carboxylase and fatty acid synthetase, respectively) on the oxidation of pyruvate suggested that they inhibited pyruvate metabolism at or near the enzyme, pyruvate dehydrogenase.

Adipose Tissue↗
PubMedDate not supplied

Comparison of the effects of halofenate (MK-185) and clofibrate on plasma lipid and uric acid concentration in hyperlipoproteinemic patients.

The plasma lipid and serum uric acid lowering effect of halofenate (MK-185, 1 g/day) was compared with the action of clofibrate (2 g/day) in a double-blind 1-yr study in 23 patients with Type 2, 3, 4, and 5 hyperlipoproteinemia. It could be demonstrated that clofibrate decreased the plasma cholesterol concentration significantly to 75% and the triglyceride concentration to 49% of the placebo period level. Halofenate produced no consistent effect on plasma cholesterol but ther was an average reduction of the plasma triglyceride concentration to 84%, which was, however, not significant. If only the Type 4 patients were taken into account, a mean significant decrease to 47% of the triglyceride concentration was observed during the second 24-week period of treatment. In contrast, halofenate lowered the serum uric acid concentration significatnly to 77% of the placebo period level, whereas the decreasing action of clofibrate was weaker (88%) and of lesser significance.

Adult↗
PubMedDate not supplied

A two-year crossover therapeutic trial with halofenate and clofibrate.

Twelve patients with Type IV hyperlipoproteinemia were treated with clofibrate and halofenate in a double blind, crossover trial for two years. Drug intake was monitored by determination of the level of the drugs in serum. Halofenate and clofibrate were equally effective in lowering plasma triglycerides and cholesterol levels. Patients who were secretors of ABO blood group antigens in saliva had a greater hypocholesterolemic response to both drugs than those who were nonsecretors. Clofibrate treatment resulted in a significant rise of low density lipoprotein cholesterol. Both drugs lowered serum bilirubin levels and this effect had a significant positive correlation with that on uric acid levels. Halofenate had a greater hypouricemic effect than clofibrate and may be a useful drug for treatment of patients with Type IV hyperlipoproteinemia who have concomitant hyperuricemia.

ABO Blood-Group System↗
PubMed1976

Halofenate and clofibrate: mechanism of hypotriglyceridemic action in the rat.

Rats fed a fat-free diet containing no drug, 0.02% or 0.10% halofenate, or 0.25% clofibrate for 14 days were injected intravenously with equivalent amounts of either [2-3H]glycerol or [1(3)-3H]glycerol. Blood samples were collected at times up to 150 min after injection and serum triglycerides were isolated and assayed for radioactivity. Kinetic analysis of the serum appearance and clearance curves of 3H-labeled triglyceride permits estimation of serum total 3H-labeled triglyceride formation and triglyceride fractional turnover rates. The total amounts of 3H-labeled triglyceride formed from [2-3H] or from [1(3)-3H] glycerol in control-fed animals were very similar. Over 95% of the serum 3H-labeled triglyceride formed from either substrate circulated in a rapidly turning-over triglyceride pool (t1/2 = 8 min). Treatment with 0.10% halofenate or 0.25% clofibrate decreased labeling of serum triglycerides by 75-80% without increasing serum 3H-labeled triglyceride fractional turnover rates. Furthermore, both drugs decreased incorporation in vivo of 14C from [U-14C]glycerol into hepatic but not intestinal triglycerides without significantly decreasing incorporation of 14C into total phospholipids of either tissue. From these observations we suggest that, in the intact normal rat, sustained reduction of serum triglyceride levels produced by treatment with halofenate or clofibrate is due to inhibition of hepatic triglyceride formation.

Animals↗
PubMedDate not supplied

Halofenate. Its selection and trial as a primary uricosuric agent.

In vitro binding studies on antiinflammatory and uricosuric acidic anions performed under "physiologic" conditions have demonstrated that these substances displace urate from its protein bond. The property of urate displacement appears to be a useful marker for potential uricosuric activity in vivo, and thereby a means to detect novel uricosuric drugs. One such drug, halofenate, was indeed a safe and effective uricosuric (comparable to probenecid) when used to treat hyperuricemia/gout over the long term; it did result in a modest and variable fall in serum lipid concentrations. However, used as a single fixed dose, halofenate did not produce a marked and consistent effect on the elevated serum triglyceride concentrations so commonly present in gouty patients.

Adult↗