Dushan Dvornik

The Metabolic Disposition of Etodolac in Rats, Dogs, and Man

The metabolic disposition of etodolac (etodolic acid) was studied after oral and intravenous administration of the 14C-labeled or unlabeled drug to rats and dogs, and after oral administration of the drug to man. In all species, peak serum drug levels were attained within 2 hr after dosing. In rats and dogs, virtually all of the oral dose was absorbed; etodolac represented 95% of the serum radioactivity in rats and 75% in dogs. Serum levels in all species were generally dose-related. The elimination portion of the serum drug concentration/time curves was characterized by several peaks, which in rats were shown to be due to enterohepatic circulation. Tissue distribution studies in rats showed that radioactivity localized primarily in blood vessels, connective tissue, and highly vascularized organs (liver, heart, lung, and kidney) and that the rate of elimination of radioactivity from tissues was similar to that found in the serum. The apparent elimination half-life of etodolac averaged 17 hr in rats, 10 hr in dogs, and 7 hr in man. Etodolac was extensively bound to serum proteins. Liver microsomal cytochrome P-450 levels were unaltered in rats given etodolac daily for 1 week. The primary route of excretion in rats and dogs was via the bile into the feces. Preliminary biotransformation studies in dogs showed the presence of the glucuronide conjugate of etodolac in bile, but not in the urine. Glucuronide conjugates were not seen in the rat. Four hydroxylated metabolites in rat bile were tentatively identified. It was concluded that, in rats and dogs, etodolac is well absorbed, is subject to extensive enterohepatic circulation, undergoes partial biotransformation, and is excreted primarily into the feces.U

The effects of a new aldose reductase inhibitor (tolrestat) in galactosemic and diabetic rats

Tolrestat(N-[[5-(trifluoromethyl)-6-methoxy-1-naphthalenyl] thioxomethyl]-N-methylglycine; AY-27,773; Alredase) is a potent, structurally novel inhibitor of aldose reductase (AR). In vitro, tolrestat inhibited in dose-dependent fashion the AR from bovine lenses (IC50, 3.5 X 10(-8) mol/L) and the formation of sorbitol in human RBC incubated with glucose (IC50, 3 X 10(-8) mol/L). Upon administration with the diet to rats made galactosemic or diabetic, tolrestat decreased, in a dose-related fashion, the accumulation of galactitol or sorbitol in the sciatic nerve and lens. The effectiveness of tolrestat depended upon the experimental conditions and tended to be higher in less severe galactosemia and after suitable pretreatment, particularly in galactosemic rats, resulting in ID50 of 5 mg/kg/d in the sciatic nerve and 12-15 mg/kg/d in the lens. Tolrestat also decreased, in dose-related manner, the RBC sorbitol levels in normal and in streptozotocin diabetic rats; in the latter, at less than 2 mg/kg/d, the RBC sorbitol was reduced to control levels.

Prevention of urinary albumin excretion in 6 month streptozocin-diabetic rats with the aldose reductase inhibitor tolrestat

Recent clinical data strongly suggest that elevated urinary albumin excretion (UAE) identifies diabetic subjects at risk of developing nephropathy. Elevated UAE is attributed to increased transglomerular pressure, which is associated with poor metabolic control in rats. Because excess glucose in diabetes is metabolized via the polyol pathway, we were interested in whether the diabetes-induced elevation in UAE in rats could be prevented by inhibiting aldose reductase (AR), the first enzyme in the polyol pathway, with the AR inhibitor tolrestat. In fact, in rats made diabetic with streptozocin (35 mg/kg IV), treatment for 6 months with tolrestat (25 mg/kg/day in the diet) prevented both sorbitol accumulation in the kidney and the increase in UAE. Sorbitol accumulation and the increased UAE were not associated with statistically significant mesangial expansion, and the thickening of glomerular basement membranes was not affected by tolrestat treatment. The authors conclude that the 4.7-fold elevation in UAE in chronically diabetic rats is linked to the increased flux of glucose through the polyol pathway since it was prevented by inhibiting aldose reductase with tolrestat.

Propranolol dosage, plasma concentration, and beta blockade

One hundred sixty‐nine normal men received varying propranolol dosage regimens and placebo. Dose level and frequency were compared with plasma propranolol levels and beta blockade, as assessed by reduction of exercise tachycardia. Propranolol levels above 20 ng/ml induced significant beta blockade. An average daily propranolol dose slightly in excess of 160 mg led to a minimum plasma level above 20 ng/ml. Approximately 50% of subjects achieved 20 bpm or greater decrease in exercise tachycardia with 160 mg per day. The degree of beta blockade at the daily minimum propranolol level was related to dose and not dose frequency. The relation of propranolol dose and plasma levels to beta blockade in normal subjects appears to reflect observations in large clinical trials.

Studies on the disposition of diosgenin in rats, dogs, monkeys and man

Rats, dogs and squirrel monkeys were given a single oral dose of [4-(14)C]diosgenin. Virtually all of the radioactivity was excreted in the feces. All of the absorbed radioactivity was eliminated via the bile. The percent of dose absorbed decreased with increasing dose. The amount of radioactivity in livers of rats given [4-(14)C]diosgenin was less than that after [4-(14)C]cholesterol, but more than after [4-(14)C]beta-sitosterol. Absorbed radioactivity in rats distributed into tissues, most notably the liver, adrenals, and walls of the gastrointestinal tract. No serum diosgenin was detected after a single large dose to rats and dogs. After multiple doses (100 mg/kg/day for 4 weeks) of diosgenin to dogs, up to 15 micrograms/ml of unchanged diosgenin was found in serum. Serum from human subjects receiving 3 g/day of diosgenin for 4 weeks contained less than 1 microgram/ml of unchanged drug. After a single dose of [14C]diosgenin, several metabolites were detected in the bile of rats and dogs; the pattern of metabolites was dissimilar in the two species. No diosgenin or 7-hydroxydiosgenin was found. One of the major biliary metabolites was diosgenin monohydroxylated in the F ring, but the location of the hydroxyl group was different in the two species. Although rat caecal contents were capable of reducing diosgenin to smilagenin in vitro, no smilagenin was present in the feces of rats given chow supplemented with diosgenin. It was concluded that diosgenin is poorly absorbed in the species tested, and that the amount which is absorbed undergoes extensive biotransformation.

Prevention of Cataract Development in Severely Galactosemic Rats by the Aldose Reductase Inhibitor, Tolrestat

Abstract With a fixed time period of galactose feeding, the rate of appearance of lenticular opacities depended on the severity of galactosemia, while with a fixed amount of galactose fed, the rate was time dependent. The capacity of tolrestat, a structurally novel inhibitor of aldose reductase (AR), to control cataract development was assessed in rats fed 30-50% galactose with the diet for 7 to 277 days. In rats fed 30% galactose for 31 days, the controlling effect of tolrestat was dose dependent, and no cataracts were detected at a dose of 35 mg/kg/day. In rats given tolrestat with the diet for 14 days, then rendered severely galactosemic with a diet containing 50% galactose, and subjected to continued treatment with tolrestat at a dose of 43 mg/kg/day, no changes were detected by slit-lamp microscopy after 207 days. The preventive effect was also dose dependent. In view of the established similarity in the pathogenesis of galactosemic and diabetic cataracts, the results obtained with tolrestat support its potential for controlling cataract development in diabetics.

Disposition and biotransformation of 14C-etodolac in man

Four human subjects were given a capsule containing 200 mg of 14C-etodolac. At the peak (two hours after dosing), most of the radioactivity in serum was due to etodolac; subsequently, metabolites gradually appeared. The elimination half-life of etodolac from serum averaged six hours. Etodolac was greater than 99% bound to human serum proteins. An average of 73% of the dose was excreted in the urine and 14% in faeces within seven days, with 61% appearing in the urine during the first 24 h. Microbial transformation of etodolac was employed to biosynthesize sufficient amounts of two urinary metabolites to facilitate structure elucidation. Five metabolites, representing 65% of the radioactivity in urine collected 0-24 h after dosing (61% of the dose was excreted in urine within 24 h), were isolated and characterized by t.l.c., g.c., h.p.l.c., n.m.r (1H and 13C) and m.s. Most of the identified urinary components were conjugates of etodolac and three hydroxylated metabolites (6-hydroxyetodolac, 7-hydroxyetodolac and 8-(1-hydroxyethyl)etodolac). Two metabolites were identified as glucuronyl ester conjugates of etodolac and 7-hydroxyetodolac; the former represented about 20% of the urinary radioactivity. False positive tests for bilirubin in urine of patients treated with etodolac were found to be due to the two phenolic metabolites.

Effect of tolrestat on red blood cell sorbitol levels in patients with diabetes

The effect of the aldose reductase inhibitor, tolrestat, on red blood cell (RBC) sorbitol levels was studied in 23 patients with diabetes after oral dosing with tolrestat, 25 or 100 mg b.i.d. The mean (± SE) RBC sorbitol levels (measured 12 hours after the preceding dose) after 3, 7, and 13 days of dosing decreased after both dose levels. After 25 mg tolrestat the RBC sorbitol levels fell from 25.1 ± 4.0 to 20.0 ± 5.7 nmol/gm hemoglobin (21%) and after 100 mg tolrestat the level fell from 26.7 ± 3.7 to 11.4 ± 1.7 nmol/gm hemoglobin (57%; P < 0.001). This latter RBC sorbitol concentration is similar to levels in individuals without diabetes. At both dosage levels the maximum decrease in RBC sorbitol levels occurred after only 3 days of dosing. Tolrestat had no effect on plasma glucose or hemoglobin A1 concentrations. The overall mean plasma unbound drug concentration measured 12 hours after 100 mg tolrestat (11.7 ± 3.0 ng/ml; 3.3 × 10−8 mol/L) was similar to the median inhibitory level (3 × 10−8 mol/L) of tolrestat for sorbitol accumulation in human RBCs incubated in a high‐glucose medium. Our results demonstrate the systemic bioavailability of tolrestat and its aldose reductase inhibitory activity in erythrocytes of patients with diabetes.

Pharmacokinetics and hypolipidemic activity of clofibrate-nicotinic acid combinations in rats.

Abstract Male albino rats were given various oral doses of clofibrate and nicotinic acid. both alone and in combination, daily for 1 week. In normal animals, the combination of drugs produced greater decreases in serum lipids, notably triglycerides, than equimolar doses of either drug alone. Synergistic decreases in serum triglycerides were observed in rats rendered hypertriglyceridemic with fructose and treated simultaneously with both drugs. The peak level of serum nicotinic acid was higher and the area under the serum nicotinic acid concentration-time curve (AUC) was 59 per cent greater when nicotinic acid was given with clofibric acid (CPIB) than when given alone. Pretreatment for 1 week with nicotinic acid slightly increased the apparent volume of distribution and the elimination half-life of intravenously injected CPIB. The presence of nicotinic acid in rat serum did not affect the protein binding of CPIB. The results show that the combined hypolipidemic effect of clofibrate and nicotinic acid in rats is accompanied by changes in the pharmacokinetics of the drugs, the most pronounced being a decrease in the rate of elimination of nicotinic acid.

Evaluation of the lipid-lowering activity of AY-25,712 in rats

The effect of AY-25,712 (2-methyl-2-phenyl-3(2H)-furanone-5-carboxylic acid) on serum lipids, hepatic lipogenesis and biliary cholesterol was investigated in male rats. Based on one-week treatment, the minimal effective dose of AY-25,712 which lowered serum triglycerides was 1 mg/kg/day, and LDL-cholesterol, 5 mg/kg/day. Nicotinic acid produced a similar lipid-lowering profile albeit at 5 times higher doses. AY-25,712 at doses of 2 mg/kg/day and higher significantly increased the ratio of HDL to total cholesterol. Unlike clofibrate, AY-25,712 did not increase liver weight or liver mitochondrial alpha-glycerophosphate dehydrogenase, nor increase biliary cholesterol levels in rats fed a diet containing 2% cholesterol and 0.5% cholic acid. AY-25,712 lowered serum cholesterol, triglycerides and phospholipids in rats rendered hyperlipidemic with Triton WR-1339 and decreased the elevated serum triglycerides in streptozotocin-diabetic rats. [14C]Acetate incorporation into cholesterol by liver homogenate was suppressed in rats given AY-25,712 p.o. for 1 week. The results show that AY-25,712 is a potent LDL-cholesterol- and triglyceride-lowering agent in rats, and that its lipid-lowering profile differs from that of clofibrate but resembles that of nicotinic acid.