The bioavailability and nonlinear pharmacokinetics of MK-679 in humans.

MK-679 (R(-)-3-((3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl)(3- (dimethylamino)-3-oxo-propyl)thio)methyl)thio)propanoic acid) is a potent and specific LTD4-receptor antagonist. The disposition of MK-679 was investigated in a three-way crossover study in 12 healthy males receiving single intravenous doses of 75, 250, and 500 mg of MK-679. A greater than proportional increase in the area under the plasma concentration-time curve of MK-679 was observed with increase in dose. The plasma concentration data for each subject fitted well to the differential equations for a two-compartment model with linear tissue distribution and Michaelis-Menten elimination from the central compartment, indicating that the elimination of MK-679 in humans is saturable. In a previous study, the disposition of MK-679 in humans was also dose-dependent when given together with its S(+)-isomer, L-668,018. Thus, the disposition of MK-679 in humans is dose-dependent regardless of the presence of its stereoisomer. Also, the bioavailability of MK-679 was determined in six healthy males receiving simultaneously an oral dose of 250 mg of MK-679 and intravenous infusion of 1 mg 14C-MK-679. Results of this study indicate that the oral bioavailability of MK-679 is nearly quantitative.

Physiological disposition of aerosolized MK-679 in rats.

[14C]MK-679, a potent antagonist of leukotriene D4, was suspended in freon under pressure and sprayed into rat lungs through a tracheal cannula. The particle size of the drug was 1 to 5 microns, and the mean dose was 98.8 +/- 4.46 micrograms/rat. Time course studies indicate that MK-679 was slowly but efficiently absorbed from the lung, with only 6% of the dose remaining in the lung at 6 hr. Biliary excretion, the major route of elimination of aerosolized MK-679, accounted for 48% of the dose in 6 hr. Concentrations of the parent drug plateaued in plasma at 1 to 4 hr, and drug was not detectable in plasma at 6 hr. The parent drug accounted for 94% of the radioactivity in the lung, indicating no significant metabolism by lung tissue. The concentration of MK-679 after aerosol administration was higher in the lung and lower in plasma than after iv administration of the drug at 28 times the aerosol dose. The results of this study suggest that inhalation of MK-679 should be a considered route of administration for the treatment of asthma.

Interspecies differences in stereoselective protein binding and clearance of MK-571.

(+)-3-(((3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl)((3-(dimethylamino)- 3-oxopropyl)thio)methyl)thio)propanoic acid (MK-571), is a potent and specific antagonist of leukotriene D4 action in vitro and in vivo. The compound, which is being developed for the treatment of asthma, contains a chiral center at the methine carbon of the dithio side chain and exists in two forms. The binding of MK-571 enantiomers to plasma protein was extensive (greater than 99.5%), stereoselective, and species dependent. The R-(-)-enantiomer was bound to rat plasma to a greater extent than the S-(+)-enantiomer, while in dog and monkey plasma the reverse was the case. The elimination clearance of the enantiomers was inversely related to the stereoselective plasma protein binding, that with the greater unbound fraction being cleared more rapidly. Thus, the pharmacologically more active S-(+)-enantiomer was cleared 3.7 times more rapidly than its antipode in rats following iv administration of the racemate (10 mg/kg), whereas in dogs and monkeys the R-(-)-enantiomer was cleared more rapidly. Kinetic analysis of the data revealed that the intrinsic clearances of the unbound enantiomers were similar within species, suggesting that stereoselectivity in elimination is not attributable to differences in metabolism and biliary excretion. Bioavailabilities of the S-(+)- and R-(-)-enantiomers in the rat were similar (75% and 71%, respectively) suggesting that MK-571 was not stereoselectively absorbed in that species.

Species-dependent enantioselective plasma protein binding of MK-571, a potent leukotriene D4 antagonist.

The plasma protein binding of the enantiomers of MK-571 was stereoselective and the stereoselectivity was species dependent. The 12 mammalian species studied could be classified into three groups: those that bind the S-(+)-enantiomer to a greater extent than the R-(-)-enantiomer (human, baboon, monkey, cow, dog, and cat); those that bind the R-(-)-enantiomer more extensively (rat, guinea pig, and sheep); and those that show no stereoselectivity (rabbit, hamster, and mouse). The stereoselective binding appears to have no phylogenetic relationship. Using serum albumin instead of plasma, a similar degree of stereoselective binding was observed for human, dog, sheep, and rat, suggesting that albumin is the major binding component for MK-571 enantiomers, and that species differences in stereoselective binding are likely due to structural differences in the albumin molecule. Displacement studies with [14C] diazepam, [14C]warfarin, and [3H]digitoxin indicated that the enantioselective differences in protein binding are most likely due to the differences in binding affinity rather than to different binding sites.

Effect of experimental diabetes on elimination kinetics of diflunisal in rats.

The effects of insulin-deficient diabetes on the elimination of diflunisal were investigated in streptozotocin-treated rats. Diflunisal, a fluorinated salicylate with nonsteroidal antiinflammatory properties, is eliminated primarily as the ester and ether glucuronides. After an iv injection of a 10 mg/kg dose, diabetic rats cleared diflunisal more rapidly than control rats; time-averaged total body clearances were 1.96 +/- 0.29 and 1.10 +/- 0.12 ml/min/kg, respectively. For a low clearance drug such as diflunisal, changes in the total body clearance can result from changes in the extent of plasma protein binding and/or drug metabolic rate. To determine whether the pronounced changes in elimination clearance in diabetic rats were due to the changes in plasma protein binding or enzyme activity, diflunisal was infused to obtain steady state kinetics. At steady state, the unbound intrinsic clearance increased from 43.4 +/- 16.4 ml/min/kg in the control rats to 82.5 +/- 21.1 ml/min/kg in diabetic rats at a high infusion rate (72 micrograms/min). When the infusion rate was lowered to 4.5 micrograms/min, the respective values for the unbound intrinsic clearance were 353 +/- 101 ml/min/kg and 561 +/- 112 ml/min/kg. Diabetic rats, however, showed no changes in plasma protein binding of diflunisal. The data suggest that the elimination of diflunisal was increased as a result of increased enzyme activity. Insulin treatment appeared to reverse the diabetic effect, suggesting that the effect on drug metabolism was the result of insulin deficiency and not a secondary or nonspecific effect of streptozotocin.(ABSTRACT TRUNCATED AT 250 WORDS)

The physiological disposition of aerosolized 4-[(3-(4-acetyl-3-hydroxy-2-propylphenoxy)propyl)sulfonyl]-gamma -oxobenzenebutanoate (L-648,051) in rats.

14C-labeled 4-[(3-(4-acetyl-3-hydroxy-2-propylphenoxy)propyl)-sulfonyl]-gamma- oxobenzenebutanoate (L-648,051) was suspended in Freon under pressure and injected into rat lungs via a tracheal cannula. The particle size of the drug was 1 to 5 microns and the mean dose was approximately 0.2 mg/kg. Levels of radioactivity in the lung/trachea declined in a monoexponential manner. Absorption, estimated from radioactivity remaining in the lung and trachea, was 73% in 1 hr and 95% in 4 hr. L-648,051 and its pharmacologically active metabolite L-657,098 (formed by ketoreduction of the butanoic acid moiety of L-648,051) accounted for 96% of the radioactivity in the lung at 10 min after the dose and 91% after 60 min. The lung:plasma concentration ratio of active drug (L-648,051 plus L-657,098) was at least 176:1 at 10 min and 17:1 at 60 min (compared with 1:1 after 2 mg/kg iv) suggesting that aerosol administration of L-648,051 in humans may result in an ideal therapeutic ratio, with high levels of pharmacologically active ingredient in the lung and low levels in the plasma.

Disposition and metabolism of sodium 4-[(3-(4-acetyl-3-hydroxy-2-propylphenoxy)propyl)sulfonyl]-gamma -oxobenzenebutanoate in rats and dogs.

The disposition of sodium 4-[(3-(4-acetyl-3-hydroxy-2-propylphenoxy)propyl)sulfonyl]-gamma-o xo benzenebutanoate (L-648,051) was determined in rats and dogs. L-648,051 is a potent receptor antagonist for leukotriene D4 and is potentially useful in the treatment of asthma and other allergic disorders. After a dosage of 10 mg/kg iv, L-648,051 declined rapidly with a half-life of approximately 2 min in rat and dog plasma. Although the compound was well absorbed, it exhibited poor bioavailability due to efficient first-pass metabolism. In rats receiving 25, 50, and 150 mg/kg po, bioavailabilities were 0.5, 4.8, and 38.7%, respectively. In dogs, bioavailability of 10 and 50 mg/kg po was 0 and 23%, respectively. Two metabolites were identified, 4-[(3-(4-acetyl-3-hydroxy-2-propylphenoxy)propyl)sulfonyl-gamma- hydroxybenzenebutanoic acid (metabolite I), formed by ketoreduction, and 4-[(3-(4-acetyl-3-hydroxy-2-propylphenoxy)propyl)sulfonyl] benzeneacetic acid (metabolite II) formed by catabolic oxidation of the butanoic acid moiety of L-648,051. Ketoreduction resulted in the production of a chiral center and two enantiomers of metabolite I. In vitro studies suggest that rat erythrocytes formed the (+)-enantiomer exclusively. When L-648,051 was administered orally or iv to rats, both the (+)- and (-)-enantiomers were observed in the plasma. The data suggest that either two L-648,051 ketoreductases were present or that inversion of the hydroxyl stereocenter of metabolite I occurred.

A sensitive analytical method for the determination of a novel lipoxygenase inhibitor, 4-bromo-2,7-dimethoxy-3H-phenothiazin-3-one, in plasma using reductive electrochemical detection.

A reversed-phase high-performance liquid chromatographic assay using electrochemical detection in the reductive mode has been developed for the analysis of 4-bromo-2,7-dimethoxy-3H-phenothiazin-3-one (1) in plasma to determine drug absorption. Free drug in plasma in concentrations as little as 0.25 ng/mL can be estimated with a mean coefficient of variation (CV) of 6.3 +/- 2.6%. Metabolites which can be converted to the parent drug by acid hydrolysis can be quantified in concentrations of 10 ng/mL or more, with a mean CV of 4.3 +/- 1.9%. To test the procedure, plasma was obtained from dogs receiving 14C-labeled 1. After acid hydrolysis of plasma, the electrochemical assay for parent drug showed good agreement with the radioactive equivalents in plasma, suggesting that parent drug and metabolites can be satisfactorily analyzed by this procedure.

Assay methodology for quantification of the ester and ether glucuronide conjugates of diflunisal in human urine.

Diflunisal is a salicylate derivative with analgesic and anti-inflammatory properties. It is excreted in the urine as an ether glucuronide, a 1-O-acyl glucuronide and as unchanged drug. The 1-O-acyl glucuronide rearranges to isomeric esters of glucuronic acid under neutral to alkaline pH conditions. The development of a urine assay for the conjugates enables the elucidation of diflunisal non-linear pharmacokinetics. The assay quantitates the ether and ester glucuronides and free diflunisal in urine at 0.5-1.0 micrograms/ml. Analysis of the glucuronides does not require authentic standards.

Diflunisal-induced maternal anemia as a cause of teratogenicity in rabbits.

Diflunisal [5-(2,4-difluorophenyl)-salicylic acid] is a new analgesic antiinflammatory drug that, when administered orally to rabbits at 40 and 60 mg/kg/day, caused terata, most commonly axial skeletal defects. These same dosage levels also caused a severe maternal hemolytic anemia following a dramatic decrease in erythrocyte ATP levels. The teratogenicity, anemia, and depletion of ATP were unique to the rabbit among species examined. To test the possible causality between the teratogenic effects and anemia induced by diflunisal, a single dose of 180 mg/kg diflunisal was administered to rabbits on gestation day 5. This treatment produced an anemia that persisted through gestation day 15 in addition to causing the characteristic axial skeletal defects. Since diflunisal was cleared from maternal blood before gestation day 9, the critical day for induction of similar axial skeletal defects by hypoxia, the skeletal malformations probably resulted from maternal hypoxia secondary to anemia and not from a direct and specific effect of the drug on the embryo. In addition, we observed that the diflunisal level in the embryo was less than 5% of the peak maternal blood level probably as a result of high plasma protein binding of diflunisal in the maternal blood (greater than 98%). This relatively low placental transfer may explain the lack of diflunisal teratogenicity in rats and mice compared to aspirin which crosses the placenta more readily. These studies demonstrate that a species that exhibits unusually severe drug-specific maternotoxicity is probably an unsuitable model for the prediction of the teratogenic potential of that drug in humans.

The physiological disposition and metabolism of enalapril maleate in laboratory animals.

N-[1-(S)-carboxy-3-phenylpropyl]-L-alanyl-L-proline (MK-422), is a potent angiotensin I-converting enzyme (ACE) inhibitor, but as a diacid is poorly absorbed in laboratory animals. Enalapril maleate, the monoethyl ester of MK-422, proved to be significantly better absorbed in both rats and dogs. Peak levels of radioactivity in plasma occurred in 30 min in rats and 2 hr in dogs after a single dose of 14C-enalapril maleate (1 mg/kg, po). Rats excreted 26% of the dose in the urine and 72% in the feces in 72 hr; dogs excreted 40% of the dose in the urine and 36% in the feces. After the intravenous dose, the presence of radioactivity in the feces of both species suggested that some biliary excretion had occurred. Absorption was estimated to be 34% in the rat and 61% in the dog. The major metabolite of enalapril maleate in dogs, accounting for 86% of the urine radioactivity, was identified as MK-422 by GC/MS. A procedure was developed for the quantitation of MK-422 and enalapril in plasma and urine by their inhibition of purified ACE. The assays showed that enalapril was absorbed intact in dogs and converted to MK-422 after absorption.

Urinary metabolites of timolol from humans and laboratory animals. Syntheses and beta-adrenergic blocking activities.

Syntheses are reported for three metabolites (2-4) of timolol (1) formed by oxidative metabolism of the morpholine ring. GLC-MS comparisons are presented which establish that the two metabolites whose structures were previously in question are identical with their synthetic counterparts 2 and 3. In 2, metabolic oxidation of the 4-morpholinyl group of 1 had occurred at the carbon next to oxygen to give the 2-hydroxy-4-morpholinyl moiety, whereas in 3, the morpholine of 1 has been oxidized one step further and then ring opened to produce the N-(2-hydroxyethyl)glycine substituent. Biological testing of synthetic samples of the three major metabolites from human urine (3, 4, and 6) indicated that only 4, in which the morpholine moiety has been degraded to a 2-hydroxyethylamino group, had significant beta-adrenergic blocking activity (one-seventh that of timolol in anesthetized dogs).

Timolol metabolism in man and laboratory anamals.

The two major urinary metabolites of 14C-timolol in man, involving oxidation and hydrolytic cleavage of the morpholine ring, are also observed in both Sprague-Dawley rats and CRCD-1 mice. These are the N-T(4-[3-(1,1-dimethylethyl)amino]-2-hydroxypropoxy)-1,2,5-thiadiazol-3-ylT-N-(2-hydroxyethyl)glycine and 1-(1,1-dimethylethylamino-3-([4-(2-hydroxyethylamino)-1,2,5-thiadiazol-3-yl]oxy)-2-propanol. The former was previously identified erroneously as the isomeric compound 1-(1,1-dimethylethylamino)-3-([4-(N-2-hydroxyethylglycolamido)-1,2,5-thiadiazol-3-yl]oxy)-2-propanol. Rats and mice had two additional metabolites in common, 1-[(1,1-dimethylethyl)amino]-3-([4-(2-hydroxy-4-morpholinyl)-1,2,5-thiadiazol-3-yl]oxy)-2-propanol and a compound now proposed to be the corresponding morpholino lactone 1-[1,1-dimethylethyl)-amino]-3-([4-(2-oxo-4-morpholinyl)-1,2,5-thiadiazol-3-yl]oxy)-2-propanol but for which the corresponding isomeric morpholino lactam structure 1-[(1,1-dimethylenthyl)-amino]-3-([4-(3-oxo-4-morpholinyl)-1,2,5-thiadiazol-3-yl]oxy))-2-propanol was tentatively proposed in an earlier publication. A metabolite observed in the rat, but not in the other species studied, was 4-(4-morpholinyl)-1,2,5-thiadiazol-3-ol-1-oxide. The metabolic pattern in these rodents does not change significantly after repeated doses. A scheme summarizing the metabolic fate of timolol in man and laboratory animals is presented.

Analgesic activity of diflunisal [MK-647; 5-(2,4-difluorophenyl)salicylic acid] in rats with hyperalgesia induced by Freund's adjuvant.

A method is described for testing analgesia for narcotic or nonnarcotic drugs in rats injected with Freund's adjuvant in the tail, by manipulation of the tail the day after injection, or of the feet after the development of adjuvant arthritis. The method is responsive to a behavioral depressant or an anti-inflammatory steroid. Diflunisal (MK-647; 5-(2,4-difluorophenyl)salicylic acid] exhibited activity in this assay after oral administration with potency about 25 times greater than that of aspirin, about 3 times that of glafenine and twice that of zomepirac. The onset of activity was within a 1/2 hour for narcotic analgesics but required about an hour for non-narcotic compounds. With the latter, the peak of activity was not attained until 2 to 4 hr, depending on the compound. The peak for diflunisal was delayed until the 3rd or 4th hour, but the onset of action was more prompt and the duration greater as the dose was increased. [14C]Diflunisal was concentrated to some extent in the inflamed tissue after adjuvant injection. Peak levels both in plasma and tissue appeared about 2 hr before peak analgesic effect. Repeated administration of large doses produced neither tolerance nor sensitization to the analgesic action of diflunisal. Naloxone and naltrexone did not antagonize the action of the compound, but when morphine and diflunisal were given together, the overall effect was enhanced.

Physiological disposition and metabolism of 2-aminomethyl-4-(1,1-dimethylethyl)-6-iodophenol hydrochloride.

MK-447-(14)C [2-aminomethyl-4-(1,1-dimethylethyl)-6-iodophenol hydrochloride] was well absorbed and metabolized in man, rats, and dogs. Peak plasma levels of radioactivity were observed in these species 1-2 hr after oral administration of 2 mg/kg to rats and dogs and 25 mg to man. At the peak, parent drug represented about 15% of the radioactivity in human plasma and only approximately 5% in rat and dog plasma. The half-life of the parent drug in human plasma was approximately 4 h. Human subjects excreted 96% of the dose, with 76% in the urine and 20% in the feces, in 3 days. Rats excreted 80% of an oral and 82% of an intravenous 2-mg/kg dose in 72 hr, with 66% in the urine and 12-16% in the feces. In dogs given a 2-mg/kg dose intravenously, the recovery of radioactivity in 72 hr was approximately 99%, with 85% in the urine and 14% in the feces. The major metabolite in rat and dog urine, constituting approximately 90% of the urine radioactivity, was the O-sulfate conjugate of MK-447. In man, this metabolite accounted for 17% of the radioactivity in the urine. The major metabolite in human urine, constituting approximately 73% of the urine radioactivity, was tentatively identified as the N-glucuronide of MK-447. Less than 1% of the radioactivity in the urine of the three species was in intact MK-447.

Stereospecific binding of timolol, a beta-adrenergic blocking agent.

The beta-adrenergic blocking agent, timolol, appears to be bound to stereospecific as well as nonspecific sites in the particulate fraction (8500g pellet) of the heart, lungs, and brain, whereas the d-isomer of timolol was bound to nonspecific sites only. Timolol disappeared from the particulate fraction at a slower rate than did its optical isomer. At 1 hr after a 0.1-mg/kg dose, the concentration of the l-form in the lung was 1.8 times that of the d-isomer and at 3 and 4 hr the difference was at least 33-fold. The concentration of 14C-timolol in the particulate fraction of rat tissues was inhibited by iv administered timolol and by the l-isomer of propanolol, but not by their corresponding d-forms. Competition for binding sites was dose dependent. Pretreatment with timolol at 0.1 and 5.0 mg/kg reduced the binding of 14C-timolol (dose, 0.1 mg/kg) to lung tissue by 41% and 86%, respectively. In the heart and lung tissue of rats, racemic timolol, propranolol, bunolol, and bunitrolol were approximately equally effective in competing for the binding sites of 14C-timolol. Practolol and sotalol and the beta 2-selective agent butoxamine did not significantly inhibit the binding of 14C-timolol. Similar competition was also observed in the whole brain of rats. This report suggests that the stereospecific binding of timolol may be related to the beta-adrenoreceptor process.

Electron-capture GLC determination of timolol in human plasma and urine.

A GLC procedure was developed for measuring nanogram quantities of timolol in plasma and urine. The unchanged drug was extracted into heptane-4% isoamyl alcohol from alkalinized plasma or urine, together with a homolog of timolol which served as the internal standard. The compounds were subsequently back-extracted into 0.1 N HC1 and then into chloroform following adjustment of the acid phase to an alkaline pH. The compounds in the chloroform extract were derivatized with heptafluorobutyrylimidazole to form the diheptafluorobutyryl derivatives; these were quantitated by electron-capture GLC. Recovery of timolol added to normal plasma and urine was quantitative and reproducible, and no interfering substances were observed in normal biological samples. The method is capable of measuring concentrations as low as 2 ng/ml in plasma or 20 ng/ml in urine. After a 10-mg oral dose of 14C-timolol, peak plasma levels of approximately 30 ng/ml were ovserved in 1-2 hr.

Physiological disposition and metabolism of 5-(2',4'-difluorophenyl)salicyclic acid, a new salicylate.

5-(2'4'-Difluorophenyl) [carboxy-14C]salicyclic acid (MK-647) was quickly and completely absorbed in rats, dogs, and man. Peak levels of plasma radioactivity occurred in 1-2 hr after oral administration. The dose was 10 mg/kg in rats and dogs, and 50 or 500 mg in man. Most of the drug in plasma was intact MK-647 which was extensively bound to plasma protein. In man the peak concentration following the 500-mg dose was approximately 10 times that after the lower dose, which suggests that absorption rates of both doses were similar. Elimination of drug from plasma was dose-dependent. The area under the curve for MK-647-14C in plasma was 18 times higher following the 500-mg dose than the 50-mg dose. Dogs given 10 mg/kg orally or intravenously excreted 44% of the dose in the urine and 42% in the feces in 72 hr. Rats given the same dose level by either route of administration excreted 80% in the urine and 11% in the feces. In man approximately 95% of a 50- or 500-mg oral dose was excreted in the urine and 3% in the feces, in 96 hr. MK-647 and two metabolites were present in the urine of three species. The ether and ester glucuronides were identified in human urine. The latter metabolite was also identified in rat and dog urine. The glycine conjugate of MK-647 was not observed in the urine of the three species. No interaction was observed between MK-647 and bishydroxycoumarin in the prothrombin time test nor with tolbutamide in the glucose tolerance test. A significant lowering of hexobarbital sleeping time was observed in female, but not male rats after four consecutive daily doses of MK-647. After repeated daily administration of MK-647 (12.5-100 mg/kg), the diurnal plasma level in dogs was not significantly altered, indicating that no saturation, induction, or inhibition of its own metabolism took place.