Nonsteroidal anti-inflammatory drug sensitizes Mycobacterium tuberculosis to endogenous and exogenous antimicrobials.

Existing drugs are slow to eradicate Mycobacterium tuberculosis (Mtb) in patients and have failed to control tuberculosis globally. One reason may be that host conditions impair Mtb's replication, reducing its sensitivity to most antiinfectives. We devised a high-throughput screen for compounds that kill Mtb when its replication has been halted by reactive nitrogen intermediates (RNIs), acid, hypoxia, and a fatty acid carbon source. At concentrations routinely achieved in human blood, oxyphenbutazone (OPB), an inexpensive anti-inflammatory drug, was selectively mycobactericidal to nonreplicating (NR) Mtb. Its cidal activity depended on mild acid and was augmented by RNIs and fatty acid. Acid and RNIs fostered OPB's 4-hydroxylation. The resultant 4-butyl-4-hydroxy-1-(4-hydroxyphenyl)-2-phenylpyrazolidine-3,5-dione (4-OH-OPB) killed both replicating and NR Mtb, including Mtb resistant to standard drugs. 4-OH-OPB depleted flavins and formed covalent adducts with N-acetyl-cysteine and mycothiol. 4-OH-OPB killed Mtb synergistically with oxidants and several antituberculosis drugs. Thus, conditions that block Mtb's replication modify OPB and enhance its cidal action. Modified OPB kills both replicating and NR Mtb and sensitizes both to host-derived and medicinal antimycobacterial agents.

Structural and ligand-binding properties of serum albumin species interacting with a biomembrane interface.

In the process of drug development, preclinical testing using experimental animals is an important aspect, for verification of the efficacy and safety of a drug. Serum albumin is a major binding protein for endogenous and exogenous ligands and regulates their distribution in various tissues. In this study, the structural and drug-binding properties of albumins on a biomembrane surface were investigated using reverse micelles as a model membrane. In reverse micelles, the secondary structures of all albumins were found, to varying degrees, to be intermediate between the native and denatured states. The tertiary structures of human and bovine albumin were similar to those of the native and intermediate states, respectively, whereas those of the dog, rabbit, and rat were in a denatured state. Thus, bovine albumin is an appropriate model for studying structural changes in human albumin in a membrane-water phase. Binding studies also showed the presence of species difference in the change in binding capacity of albumins during their interaction with reverse micelles. Among the albumins, rat albumin appears to be a good model for the protein-mediated drug uptake of human albumin in a biomembrane environment. These findings are significant in terms of the appropriate extrapolation of pharmacokinetics and pharmacodynamics data in various animals to humans.

Analysis of phenylbutazone residues in horse tissues with and without enzyme-hydrolysis by LC-MS/MS.

Phenylbutazone (PBZ) is permitted to be used for the treatment of musculoskeletal pain and inflammation in race horses but it is not approved for use in horses destined for human consumption. In a recent study initiated in our laboratory to study the disposition of PBZ and its oxyphenbutazone (OXPBZ) metabolite in equine tissues, we compared the effect of an additional enzymatic hydrolysis step with ß-glucuronidase on the results of the analysis for PBZ without enzymatic hydrolysis. Incurred tissue samples obtained from a female horse dosed with PBZ at 8.8 mg/kg for 3 days and sacrificed 6 days following the last administration were used for this study. Liver, kidney, and muscle tissues were collected, extracted, cleaned up on a silica-based solid-phase extraction (SPE) preceded by a weak-anion exchange SPE and analyzed with our in-house validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for PBZ and OXPBZ. Addition of the hydrolysis step resulted in a significant increase in recovery of both PBZ and OXPBZ residues. © 2016 Her Majesty the Queen in Right of Canada. Drug Testing and Analysis © 2016 John Wiley & Sons, Ltd.

A study on the allosteric interaction between the major binding sites of human serum albumin using microcalorimetry.

The binding of warfarin and oxyphenbutazone to albumin has been studied at pH 6.8 and pH 9.2 by measuring the heat of binding of these ligands to their high-affinity binding sites on albumin (delta Ho'1). The -delta Ho'1 values for the binding of warfarin at pH 6.8 and 9.2 and oxyphenbutazone at pH 6.8 and 9.2 were found to be 16.9(+/- 0.6), 28.8(+/- 0.6), 10.5(+/- 0.4) and 17.4(+/- 0.6) kJmol-1, respectively. The Gibbs energies (delta Go'1) corresponding to these delta Ho'1 values cover a much smaller range. The pH dependences of delta Go'1 and delta Ho'1 are explained in terms of pK shifts in the albumin upon binding warfarin or oxyphenbutazone. Diazepam, which binds to a site on albumin which is different from the warfarin-oxyphenbutazone binding site, increases - delta Ho'1 for the binding of warfarin and oxyphenbutazone to albumin at pH 6.8, but it does not influence the -delta Ho'1 at pH 9.2. This phenomenon may be attributed to an allosteric interaction between the diazepam binding site and the warfarin binding site. This allosteric interaction must have its origin in a phenomenon other than the N-B transition.

Inhibition of drug metabolism by hydroxylated metabolites: cross-inhibition and specificity.

Inhibition of drug metabolism was studied in adult male Sprague-Dawley rats. A hydroxylated metabolite of phenylbutazone (oxyphenbutazone) inhibited the elimination of phenytoin, which is metabolized by oxidative pathways. The biotransformation of a relatively polar and only slightly plasma protein-bound drug, antipyrine, was subject to product inhibition by a hydroxylated metabolite, 4-hydroxyantipyrine. Neither oxyphenbutazone nor 4-hydroxyantipyrine measurably affected the elimination kinetics or metabolic fate of a drug (sulfanilamide) that is not metabolized by oxidative pathways.

Determination of binding conformations of drugs to human serum albumin by transferred nuclear overhauser effect measurements and conformational analyses using high-temperature molecular dynamics calculations.

The binding conformations of oxyphenbutazone (OXY), Nepsilon-dansyl-L-lysine (DNS-LYS), and furosemide (FU) to human serum albumin (HSA) have been investigated by molecular dynamics (MD) calculations and transferred nuclear Overhauser effect (TRNOE) measurements. We have combined distance information obtained from the Conformational Analyzer with Molecular Dynamics And Sampling (CAMDAS) calculation and experimental NOE spectroscopy measurements to determine a "binding conformation" for each drug which binds to site I of HSA. For OXY, only one conformer (conf9) among the conformer set generated by MD calculation satisfied the distance restraint conditions obtained from TRNOE measurements. For DNS-LYS and FU, 17 and 5 conformers satisfied distance restraint conditions, respectively. The structure of conf9 of OXY was taken as a "template" to choose binding conformers for DNS-LYS and FU. By fitting the "template" to the 17 conformers of DNS-LYS and 5 conformers of FU, we could efficiently obtain one binding conformer for DNS-LYS (conf144) and FU (conf26). It is suggested from the feature of the binding conformation that the three-dimensional location of a hydrophobic aromatic ring, alkyl chain, and electronegative functional group is important for binding to site I of HSA. This method, which combines MD calculations and NOE information, is thought to be effective for determining the binding conformation of drugs to HSA.

Pharmacokinetics, metabolism and excretion of phenylbutazone in cattle following intravenous, intramuscular and oral administration.

The absorption, metabolism and urinary excretion of phenylbutazone were investigated in six adult cattle in a cross-over study involving administration intravenously, intramuscularly and orally at a dose rate of 4.4 mg kg-1. Following intravenous injection plasma disposition was described by a three compartment open model with mean elimination half-life (t1/2 beta) and clearance (ClB) values of 35.9 hours and 2.77 ml kg-1 h-1, respectively. Somewhat longer t1/2 beta values were obtained after oral and intramuscular dosing and these may have resulted from sequestration within and slow absorption from the gastrointestinal tract and continual uptake from intramuscular sites following precipitation as a depot. Absorption was more complete after intramuscular than after oral dosing; area under curve values were almost twice as high for the intramuscular route. Double peaks in the plasma concentration time curves after oral dosing were recorded in some cows. These may have resulted from drug adsorption on to and subsequent desorption from hay or as a consequence of enterohepatic shunting. There was no evidence for opening of the oesophageal groove and direct passage of the drug into the abomasum. Two hydroxylated metabolites of phenylbutazone, oxyphenbutazone and gamma-hydroxyphenylbutazone were detected in trace amounts in plasma for 72 hours and in much higher concentrations in urine for 168 hours. Approximate urine:plasma (U/P) concentration ratios for the metabolites approached and occasionally exceeded the U/P ratio for endogenous creatinine, indicating poor reabsorption and, possibly, tubular secretion. Cumulative urinary excretion data indicated that the hydroxylated derivatives of phenylbutazone are probably formed more slowly in cattle than in horses.

Absorption of phenylbutazone from a paste formulation administered orally to the horse.

The absorption pattern of phenylbutazone was studied in five horses during administration of the drug in a paste formulation on days 1, 5, 8 and 12 of a 12-day dosing schedule. Since two or more plasma concentration peaks were usually obtained following each oral dose, it was concluded that phasic absorption was a particular feature of the oil:water formulation of the product. Possible causes of this unusual absorption pattern are discussed and the therapeutic implications of both phasic absorption and the recorded values of Cmax, tmax and AUC024 for phenylbutazone and its active metabolite oxyphenbutazone are considered.

Pharmacokinetics of phenylbutazone and its metabolites in the horse.

Phenylbutazone was given orally to 2 groups of horses and the plasma levels of the drug and its 2 principal metabolites oxyphenbutazone and gamma-hydroxyphenylbutazone measured by high performance liquid chromatography. Animals in Group 1 received single oral doses in a range from 1.1 to 13.2 mg/kg and were sampled over the succeeding 24 h. Considerable individual variation was observed both in timing and magnitude of the plasma drug responses between horses, but 24 h after dosing a clear dose response relation was recorded. Group 2 horses were given the recommended therapeutic dosage regimen and sampled over 24 h periods twice weekly. After 4 days at 8.8 mg/kg in 2 divided doses mean peak plasma levels of phenylbutazone reached 24 micrograms/ml and showed evidence of cumulation. After 4 days at 4.4 micrograms/kg, peak plasma concentrations had fallen to 10 micrograms/ml and mean peak levels just failed to reach 4 micrograms/ml 3 days after reducing dosage to 2.2 mg/kg once daily. Plasma concentrations of oxyphenbutazone did not exceed 25 per cent of the parent drug and the gamma-hydroxy metabolite was only just detectable and never exceeded 1 microgram/ml.

A review of drug "clearance times" in racehorses.

A review is presented of published and some unpublished work dealing with aspects of drug clearance from horses. This work includes plasma half-lives and urinary clearance times for specified drugs, as well as a consideration of more general factors likely to influence these values. The review is presented primarily as a guide to the veterinary surgeon in practice, to assist in the drug therapy of horses without contravening the Rules of Racing relating to doping.

Pharmacokinetics of phenylbutazone in camels.

OBJECTIVE: To document disposition variables of phenylbutazone and its metabolite, oxyphenbutazone, in camels (Camelus dromedarius) after single i.v. bolus administration of phenylbutazone, with a view to making recommendation on avoiding violative residues in racing camels. ANIMALS: 6 healthy camels (4 males, 2 females), 5 to 7 years old, and weighing from 350 to 450 kg. PROCEDURE: Blood samples were collected to 0, 5, 10, 15, 45, and 60 minutes and at 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 12, 24, 26, 28, 30, 40, 48, 50, 53, and 60 hours after i.v. administration of 4.5 mg of phenylbutazone per kg of body weight. Urine was obtained in fractions during the entire blood sample collection period. Serum and urine phenylbutazone concentrations were measured by high-performance liquid chromatography; assay sensitivity was 100 ng/ml. Serum oxyphenbutazone concentration was measured by gas chromatography/mass spectrometry; assay sensitivity was 10 ng/ml. RESULTS: Disposition of phenylbutazone was best described by a two-compartment open model. Mean +/- SEM elimination half-life was 13.44 +/- 0.44 hours. Total body clearance was 12.63 +/- 1.64 mg/kg/h. Renal clearance was between 0.3 and 0.4% of total body clearance. The elimination half-life of oxyphenbutazone was 23.9 +/- 2.09 hours. CONCLUSIONS: The elimination half-life and total body clearance of phenylbutazone in camels are intermediate between reported values in horses and cattle. Extrapolation of a dosage regimen from either species to camels is, therefore, not appropriate. Elimination of phenylbutazone in camels is mainly via metabolism. Owing to the long half-life of phenylbutazone and of oxyphenbutazone, and to the zero drug concentration regulation adopted by the racing commissioner in the United Arab Emirates, practicing veterinarians would be advised not to use phenylbutazone in camels for at least 7 days prior to racing.

Availability of oxyphenbutazone from different suppository formulations.

The in vitro release of oxyphenbutazone as well as its rectal absorption in rabbits from different suppository formulations were investigated. It was proved that polyethylene glycol base gave higher medicament release than adeps solidus base. Incorporation of nonionic surfactants in Witepsol H 15 increased or decreased oxyphenbutazone release while incorporation of hydrophilic aerosil caused a reduction in the released amount of the medicament. A mixture of Witepsol H 15 or H 12 and Brij 58 (85:5) gave the highest in vitro release and the highest rectal absorption of the medicament. A correlation was found to exist between the in vitro release of oxyphenbutazone and its rectal absorption in rabbits.

Phenylbutazone in racing greyhounds: plasma and urinary residues 24 and 48 hours after a single intravenous administration.

The concentrations of phenylbutazone (PBZ), oxyphenbutazone (OPBZ) and gammahydroxyphenylbutazone (OHPBZ) in plasma and urine from 50 Greyhounds 24 and 48 h after the intravenous administration of a single dose of PBZ (30 mg/kg) were measured. The 24 h plasma concentrations of OPBZ and OHPBZ, the 48 h plasma concentration of OHPBZ and the 24 h urinary concentration of PBZ were normally distributed, while log transformations were required before the 24 h plasma concentration of PBZ and the 24 and 48 h urinary concentrations of OPBZ and OHPBZ became normally distributed. The 95%, 99%, 99.9% and 99.99% upper predicted confidence intervals for both 24 h and 48 h plasma and urinary concentrations demonstrated wide potential variation in the concentration of the analytes should PBZ be administered to Greyhounds. The 24 h plasma and urinary concentrations of PBZ were weakly correlated, but no similar relationship existed for OPBZ or OHPBZ. The urinary concentrations of each analyte were not affected by the trainer or sex of the Greyhound or the urinary pH. We conclude that it would be impossible to predict the timing of the PBZ administration or the plasma concentration of PBZ from the measurement of the concentration of PBZ in a single sample of urine.

[Trans-placental transfer of four anti-inflammatory agents. A study carried out by in vitro perfusion (author's transl)]. / Passage trans-placentaire de quatre anti-inflammatoires. Son étude par perfusion in vitro.

Phenylbutazone, oxyphenylbutazone, ketoprofene and indocid transfer through the placenta (TFp) were studied by perfusing a placental cotyledon at term in vitro. These drugs were used in the therapeutic doses that are employed in human clinical practice. Antipyrine was used as a control material to check the validity of the perfusion in each experiment. TFp of phenylbutazone was 25.83 per cent +/- 0.46, of oxyphenylbutazone 22.48 per cent +/- 1.38, of ketoprofene 35.574 per cent +/- 0.95 and of indomethacin 36.19 per cent +/- 0.26. The authors point out the advantages and the possible dangers of non-steroid anti-inflammatory agents used in pregnant women. They prefer the use of ketoprofene of indomethacin because the anti-prostaglandin properties of ketoprofene are greater although the TFp is significantly less.