Usefulness of Optimized Human Fecal Material in Simulating the Bacterial Degradation of Sulindac and Sulfinpyrazone in the Lower Intestine.

The first aim of this study was to evaluate the usefulness of optimized human fecal material in simulating sulforeductase activity in the lower intestine by assessing bacterial degradation of sulindac and sulfinpyrazone, two sulforeductase substrates. The second aim was to evaluate the usefulness of drug degradation half-life generated in simulated colonic bacteria (SCoB) in informing PBPK models. Degradation experiments of sulfinpyrazone and of sulindac in SCoB were performed under anaerobic conditions using recently described methods. For sulfinpyrazone, the abundance of clinical data allowed for construction of a physiologically based pharmacokinetic (PBPK) model and evaluation of luminal degradation clearance determined from SCoB data. For sulindac, the availability of sulindac sulfide and sulindac sulfone standards allowed for evaluating the formation of the main metabolite, sulindac sulfide, during the experiments in SCoB. Both model compounds degraded substantially in SCoB. The PBPK model was able to adequately capture exposure of sulfinpyrazone and its sulfide metabolite in healthy subjects, in ileostomy and/or colectomy subjects, and in healthy subjects pretreated with metoclopramide by implementing degradation half-lives in SCoB to calculate intrinsic colon clearance. Degradation rates of sulindac and formation rates of sulindac sulfide in SCoB were almost identical, in line with in vivo data suggesting the sulindac sulfide is the primary metabolite in the lower intestine. Experiments in SCoB were useful in simulating sulforeductase related bacterial degradation activity in the lower intestine. Degradation half-life calculated from experiments in SCoB is proven useful for informing a predictive PBPK model for sulfinpyrazone.

Characterization of the comparative drug binding to intra- (liver fatty acid binding protein) and extra- (human serum albumin) cellular proteins.

1. This study compared the extent, affinity, and kinetics of drug binding to human serum albumin (HSA) and liver fatty acid binding protein (LFABP) using ultrafiltration and surface plasmon resonance (SPR). 2. Binding of basic and neutral drugs to both HSA and LFABP was typically negligible. Binding of acidic drugs ranged from minor (fu > 0.8) to extensive (fu < 0.1). Of the compounds screened, the highest binding to both HSA and LFABP was observed for the acidic drugs torsemide and sulfinpyrazone, and for ß-estradiol (a polar, neutral compound). 3. The extent of binding of acidic drugs to HSA was up to 40% greater than binding to LFABP. SPR experiments demonstrated comparable kinetics and affinity for the binding of representative acidic drugs (naproxen, sulfinpyrazone, and torsemide) to HSA and LFABP. 4. Simulations based on in vitro kinetic constants derived from SPR experiments and a rapid equilibrium model were undertaken to examine the impact of binding characteristics on compartmental drug distribution. Simulations provided mechanistic confirmation that equilibration of intracellular unbound drug with the extracellular unbound drug is attained rapidly in the absence of active transport mechanisms for drugs bound moderately or extensively to HSA and LFABP.

The induction and inhibition of UDP-glycosyltransferases in Haemonchus contortus and their role in the metabolism of albendazole.

Albendazole (ABZ) is an anthelmintic frequently used to treat haemonchosis, a common parasitosis of ruminants caused by the gastrointestinal nematode Haemonchus contortus. This parasite is able to protect itself against ABZ via the formation of inactive ABZ-glycosides. The present study was designed to deepen the knowledge about the role of UDP-glycosyltransferases (UGTs) in ABZ glycosylation in H. contortus. The induction effect of phenobarbital, a classical inducer of UGTs, as well as ABZ and ABZ-sulphoxide (ABZSO, the main active metabolite of ABZ) on UGTs expression and UGT activity toward ABZ was studied ex vivo in isolated adult nematodes. The effect of three potential UGT inhibitors (5-nitrouracil, 4,6-dihydroxy-5-nitropyrimidine and sulfinpyrazone) on ABZ glycosylation was tested. Pre-incubation of nematodes with ABZ and ABZSO led to increased expression of several UGTs as well as ABZ-glycosides formation in subsequent treatment. Phenobarbital also induced UGTs expression, but did not affect ABZ biotransformation. In the nematode's subcellular fraction, sulfinpyrazone inhibited UGT activity toward ABZ, although no effect of other inhibitors was observed. The inhibitory potential of sulfinpyrazone on the formation of ABZ-glycosides was also proved ex vivo in living nematodes. The obtained results confirmed the role of UGTs in ABZ biotransformation in H. contortus adults and revealed sulfinpyrazone as a potent inhibitor of ABZ glycosylation in this parasite. The possible use of sulfinpyrazone with ABZ in combination therapy merits further research.

Use of cryopreserved transiently transfected cells in high-throughput pregnane X receptor transactivation assay.

Cryopreserved, transiently transfected HepG2 cells were compared to freshly transfected HepG2 cells for use in a pregnane X receptor (PXR) transactivation assay. Assay performance was similar for both cell preparations; however, cryopreserved cells demonstrated less interassay variation. Validation with drugs of different PXR activation potencies and efficacies demonstrated an excellent correlation (r(2) > 0.95) between cryopreserved and fresh cells. Cryopreservation did not change the effect of known CYP3A4 inducers that have poor cell permeability, indicating that cryopreservation had little effect on membrane permeability. In addition, cryopreserved HepG2 cells did not exhibit enhanced susceptibility to cytotoxic compounds compared to transiently transfected control cells. The use of cryopreserved cells enables this assay to run with enhanced efficiency.

Therapeutic implications of drug interactions with acetaminophen and aspirin.

Only drug-drug interactions that are believed clinically important and that are primarily pharmacokinetic in nature are discussed in this article. Drugs reported to interact with aspirin are oral anticoagulants, methotrexate, probenecid, and sulfinpyrazone; those that are believed to interact with acetaminophen are propantheline bromide, narcotics, and metoclopramide hydrochloride, as well as food (carbohydrates). Ethyl alcohol, ammonium chloride, antacids, oral antidiabetic agents, corticosteroids, and heparin sodium probably interact with aspirin. Fenoprofen calcium, gold sodium thiomalate, indomethacin, naproxen, penicillin, phenylbutazone, phenytoin sodium, and spironolactone may also cause such interactions. Ethyl alcohol, beta-adrenergic blockers, oral anticoagulants, chlorpromazine hydrochloride, and miscellaneous mutual toxicities may cause interactions with acetaminophen. The concomitant use of drugs that are believed to interact importantly with either aspirin or acetaminophen should be avoided when designing a treatment regimen. The remaining agents discussed here (of doubtful importance in man) demand careful monitoring in difficult clinical situations and must be submitted to further controlled studies.

Sulfinpyrazone kinetics after intravenous and oral administration.

Sulfinpyrazone kinetics has been investigated after intravenous and oral doses. They may be described by a 3-compartment open model. In the body about half the drug is in the plasma or in interstitial fluids, which equilibrated with plasma. Most of the rest is in an extravascular compartment, from which it easily diffuses back to the plasma. About 3% of the dose is still in the body after 24 hr and is located mainly in a deep compartment. After oral administration, sulfinpyrazone is quickly absorbed, largely from the stomach.

Kinetics and metabolism of sulfinpyrazone.

Six normal subjects (three men and three women) took 200 mg sulfinpyrazone in two oral preparations, a capsule and a suspension. Plasma and urine levels of sulfinpyrazone and the sulfide, p-hydroxy, and sulfone metabolites were measured over three days. The plasma sulfinpyrazone/time concentration profiles indicated a postabsorptive biexponential decline with a mean terminal half life (t1/2) of 299 +/- 107 min. There was intersubject variation in the formation of the metabolites, the greatest being with the sulfide metabolite. Mean t1/2 of the sulfide metabolite was 659 +/- 192 min. The apparent fraction of sulfinpyrazone absorbed was 0.93 +/- 0.24 and the free fraction in plasma was 1.26 +/- 0.04%. Since the sulfide metabolite has a more potent antiplatelet effect and its formation in normal subjects is variable, direct administration of the sulfide may provide a more predictable antithrombotic effect in patients.

Dose-related cardiac electrophysiologic effects of sulfinpyrazone.

To test the hypothesis that sulfinpyrazone exerts cardiac electrophysiologic effects, the drug was intravenously injected into 20 subjects during invasive electrophysiologic testing. Sulfinpyrazone was given intravenously as a bolus and by infusion to achieve two different and stable serum levels. The 20 subjects who were treated with drug were assigned to either a low- (N = 10) or high- (N = 10) dose regimen. The resultant four serum levels of sulfinpyrazone were 102 +/- 45, 199 +/- 75, 278 +/- 57, and 352 +/- 77 X 10(-3) mumol (means +/- SD). Electrophysiologic measurements were made during a baseline electrophysiologic study and at each of the sulfinpyrazone levels and at equivalent times in an untreated control group (N = 11). Two electrophysiologic measurements differed when measured at the highest level of sulfinpyrazone and in control subjects: increased HV interval in sinus rhythm and shortened atrial functional refractory period in sinus rhythm (only for those values below the median). Serum levels of sulfinpyrazone correlated with increased sinoatrial conduction time (only for those values above the median; r = 0.64) and with shortened atrial functional refractory periods (r = 0.37). The latter was stronger (r = 0.67) when only values below the median were included in analysis. Shortening of atrial functional refractory period correlated with serum sulfinpyrazone levels during atrial pacing at fixed cycle lengths of 600 and 500 msec. Serum levels of sulfinpyrazone did not correlate with changes in HV interval. HV intervals did not increase in subjects receiving sulfinpyrazone during atrial pacing and, therefore, the effect on HV interval in sinus rhythm is felt to be spurious.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ischaemic heart disease, Crohn's disease and antimicrobial therapy on the pharmacokinetics of sulphinpyrazone.

The renewed interest in sulphinpyrazone in recent years has arisen from its potential to inhibit platelet aggregation. In vivo much of the activity is probably due to the thioether or sulphide metabolite which has a greater potency and a longer half-life than the parent compound. The sulphide metabolite is formed exclusively by the gut microflora in man. The pharmacokinetics of sulphinpyrazone (200 mg orally) have been studied, with particular attention to the formation of the sulphide metabolite, in groups of patients who might be expected to show abnormal formation of this active metabolite due to altered delivery of the drug to the lower gut or altered gut flora. Five patients studied 1 month after a myocardial infarction did not differ markedly from young, normal volunteers with respect to either sulphinpyrazone or its metabolite. Crohn's disease in the quiescent phase did not significantly alter the pharmacokinetics or metabolism of the drug, but 1 patient who had undergone a hemicolectomy formed negligible concentrations of the active metabolite. Antimicrobial therapy produced highly variable results with almost complete suppression of sulphide formation in some subjects but no apparent effect in others.

Sulfinpyrazone: a review of its pharmacological properties and therapeutic use.

Sulfinpyrazone1 has long been recognised as a potent uricosuric agent, but has more recently been studied extensively as a platelet inhibitor and antithrombotic agent. It is active in man following oral administration and has been reported to be effective in reducing the incidence of transient ischaemic attacks, thromboembolism associated with vascular and cardiac prostheses, recurrent venous thrombosis, arteriovenous shunt thrombosis and sudden cardiac death following myocardial infarcton. Sulfinpyrazone has not been demonstrated to be effective in preventing or reducing the risk of stroke or death in patients with cerebrovascular disease with a recent history of cerebral or retinal ischaemioc attacks. The normal total dose of sulfinpyrazone as an antithrombotic agent is 800mg daily. The drug has been used continuously for up to 4 years with no serious adverse reactions or laboratory abnormalities. There has been no apparent diminution of effect with time. Sulfinpyrazone is not a substitute for conventional anticoagulant agents (e.g. the coumarin derivatives) in the treatment of venous thrombosis, but is an important drug for the treatment of conditions associated with arterial thrombosis and possibly for the prophylaxis of recurrent venous thrombosis.

The role of the gut flora in the reduction of sulphinpyrazone in the rat.

Sulphinpyrazone underwent both reduction to a sulphide and oxidation to a sulphone after parenteral administration to normal Wistar rats. Oral administration was associated with a bioavailability of about 75% and with a 3-fold greater formation of the sulphide. However, no sulphide was detected in the plasma after oral administration of sulphinpyrazone to germ-free (BD/X) rats or normal rats treated with oral antibiotics. In vitro studies showed that the major site of reduction of sulphinpyrazone was the contents of the hind gut with little activity detected in the liver or other tissues. The sulphide was oxidised in vivo to sulphinpyrazone and small amounts of sulphone, while the latter underwent only slight reduction to sulphinpyrazone, but did not give detectable levels of the sulphide. These data suggest that the gut microflora are the main site of reduction of sulphinpyrazone in the rat in vivo.

Sulphoxide reduction by rat and rabbit tissues in vitro.

The reduction of sulindac, sulphinpyrazone and diphenyl sulphoxide to their thioether analogues has been studied in vitro using rat and rabbit tissues. Sulindac reduction was about 10-fold higher in homogenates of rat kidney and liver than in other tissues although the tissue differences decreased when dithiothreitol was used as a co-factor. The greatest sulindac reducing activity in rat liver was in the cytosolic fraction whereas reoxidation of the thioether back to the sulphoxide was largely in the microsomal fraction. Studies using NADPH/NADH, acetaldehyde and dithiothreitol as cofactors showed that aldehyde oxidase was the main sulindac reducing system in rat and rabbit liver cytosols but not in renal cytosols where reduction was probably linked to the thioredoxin system, as reported previously. Menadione and hydralazine caused essentially complete inhibition of sulindac reduction by hepatic but not renal cytosol and the inhibition was dependent on preincubation of the enzyme with the inhibitor, which is indicative of aldehyde oxidase activity. Little reduction of sulphinpyrazone or diphenyl sulphoxide was detected with rat or rabbit kidney or renal cytosols, although increased reduction was detected when acetaldehyde was added as a cofactor to rabbit and rat liver cytosols. The data indicate that different enzyme systems are responsible for sulphoxide reduction in the liver and kidney.

Sulphoxide reduction by rat intestinal flora and by Escherichia coli in vitro.

The caecal microflora from female rats show a greater ability to reduce the sulphoxide group of sulindac than either the liver or kidneys. Studies on sulphoxide reduction by Escherichia coli showed that NADH, NADPH and dithiothreitol (DTT), but not acetaldehyde could act as cofactors. The cytosolic fraction was responsible for about 90%, 80% and 60% of the total reducing activity with sulindac, diphenyl sulphoxide and sulphinpyrazone, respectively. The main NADPH linked activity in the E. coli cytosol was dependent on thioredoxin, since the activity was essentially abolished by passing through a G50 column or by the addition of anti-thioredoxin anti-serum. Partial purification and separation of sulphoxide reducing activity by DEAE-cellulose chromatography separated two main protein bands, each of which possessed sulindac reducing activity. The importance of thioredoxin for much of the NADPH dependent activity was confirmed but the eluate fractions also showed the presence of other activities with NADH, NADPH and DTT that were independent of thioredoxin. Incubation of the DEAE-cellulose eluate fractions with flosequinan and sulphinpyrazone showed that the reducing activity in the two main protein peaks showed different substrate specificities and that there were multiple sulphoxide reductase systems present in E. coli cytosol.

Inhibition of human platelet cyclo-oxygenase activity by sulfinpyrazone and three of its metabolites.

Sulfinpyrazone and three of its major metabolites were compared in vitro for their inhibitory effect on human platelet cyclo-oxygenase activity. Sulfinpyrazone appeared to be about 15-20 times less potent than its sulfide metabolite (G25671) and 6-7 times less potent than the other two compounds, the sulfone metabolite (G31442) and p-hydroxysulfide (G33378). All four compounds were apparently competitive inhibitors of platelet cyclo-oxygenase activity. Comparison of the potency of sulfinpyrazone and its metabolites, as determined in the present study and the plasma levels previously measured in man, indicates that sulfinpyrazone and G33378 were not potent enough to be effective in man. G31442 showed inhibitory potency slightly lower than its corresponding plasma levels, whereas G25671 was effective at concentrations well below those found in human plasma. This study supports the hypothesis that sulfinpyrazone metabolites (in particular the sulfide) rather than the drug itself affect platelet function when administered therapeutically.

A pharmacokinetic and platelet function study of the combined administration of metoprolol and sulfinpyrazone to healthy volunteers.

In a double-blind study on healthy subjects who underwent three 3-week periods of treatment with metoprolol (M) + sulfinpyrazone (S), M + placebo, and S + placebo, pharmacokinetics and plasma levels of M were not affected by concurrent administration of S. Analysis of variance change-over demonstrated a significant difference between treatments only for serum uric acid levels. Analysis of post-treatment and baseline data within each treatment showed: decreased platelet count by M, lowered serum 6-keto PGF1 alpha by all three treatments, decreased serum TXB2 generation and arachidonic acid-induced platelet aggregation by S + M. No negative interaction between S + M was found.

Two metabolites of sulphinpyrazone and their identification and determination by mass spectrometry.

Sulphinpyrazone is an antiplatelet in vivo and in vitro. Two active metabolites, a sulphide (S) and a hydroxylated sulphide (S-OH) have been identified in rabbit and human plasma and a selective and sensitive g.c.-m.s.-method for quantitative determination of the sulphide and hydroxylated sulphide in plasma and urine has been evolved which allows concentrations down to 5 ng ml-1 for the sulphide and 30 ng ml-1 for the hydroxylated sulphide to be detected. The time course of the metabolite concentrations in plasma corresponds to the biological findings, suggesting that the metabolites contribute significantly to the in vivo effects of the drug.

[Pharmacology of anti-platelet agents]. / Pharmacologie des agents antiplaquettaires.

A new class of drugs has appeared alongside classical anti-thrombotic agents such as heparin and oral anticoagulants, characterised by their ability to modify the behaviour of platelets: "anti-platelet" agents. This article reviews the platelet actions, pharmacokinetics, conditions of use and side effects of the four chief agents available: acetylsalicylic acid (ASA), sulfinpyrazone, dipyridamole and ticlopidine. The mode of action of the first of them is that best studied. ASA opposes the conversion of arachidonic acid to prostaglandins and thromboxane, by the irreversible acetylation of cyclo-oxygenase. Nevertheless, major therapeutic trials involving ASA have yielded only poor results. There are at least two possible explanations for this state of affairs: --aggregation may occur even when thromboxane is blocked, in particular in response to thrombin; --ASA has been used at doses also capable of inhibiting the formation by the vascular wall of an anti-aggregant prostaglandin, PGI2. Current efforts by pharmacologists which should result in better adapted and hence more effective anti-thrombotic methods, are essentially concerned with the following points: --to understand why sulfinpyrazone, which in principle has the same mode of action as ASA, seems sometimes more active and sometimes less active than the latter according to whether coronary or cerebrovascular accidents are involved; --to propose a rational prescription programme for ASA, in such a way that it inhibits only little, and for as short a time as possible, the production of PGI2 (e.g. 200 mg every three days): --to perfect more active combinations; --synthesis of new substances, e.g. thromboxane synthetase inhibitors, or stable analogues of PGI2. The reasons which suggest that such substances could be used more beneficially in man are expanded.