Dipyrone elicits substantial inhibition of peripheral cyclooxygenases in humans: new insights into the pharmacology of an old analgesic

Dipyrone (INN, metamizol) is a common analgesic used worldwide. Its widespread prescription or over-the-counter use in many countries (e.g., Brazil, Israel, Mexico, Russia, Spain) requires insight into its mode of action. This study therefore addressed the impact of its metabolites 4-methyl-amino-antipyrine (MAA) and 4-amino-antipyrine (AA) on peripheral cyclooxygenases (COX). Pharmacokinetics of metabolites and ex vivo COX inhibition were assessed in five volunteers receiving dipyrone at single oral doses of 500 or 1000 mg. Coagulation-induced thromboxane B2 formation and lipopolysaccharide-induced prostaglandin E2 synthesis were measured in vitro and ex vivo in human whole blood as indices of COX-1 and COX-2 activity. In vitro, metabolites elicited no substantial COX-1/COX-2 selectivity with MAA (IC50=2.55 micromol/L for COX-1; IC50=4.65 micromol/L for COX-2), being approximately 8.2- or 9-fold more potent than AA. After administration of dipyrone, MAA plasma concentrations remained above the IC50 values for each isoform for at least 8 h (500 mg) and 12 h (1000 mg) postdose. COX inhibition correlated with MAA plasma levels (ex vivo IC50 values of 1.03 micromol/L [COX-1] and 0.87 micromol/L [COX-2]). By contrast, plasma peak concentrations of AA after the 1000 mg dose were 2.8- and 6.5-fold below its IC50 values for COX-1 and COX-2, respectively. Maximal inhibitions of COX-1 and COX-2 were 94% and 87% (500 mg), 97% and 94% (1000 mg). Taken together, dipyrone elicits a substantial and virtually equipotent inhibition of COX isoforms via MAA. Given the profound COX-2 suppression by dipyrone, which was considerably above COX-2 inhibition by single analgesic doses of celecoxib and rofecoxib, a significant portion of its analgesic action may be ascribed to peripheral mechanisms. In view of the observed COX-1 suppression, physicochemical factors (lack of acidity) rather than differential COX-1 inhibition may be responsible for dipyrone's favorable gastrointestinal tolerability compared with acidic COX inhibitors.

Bioavailability of two metamizole (dipyrone) solutions as single doses of 2 g versus metamizole capsules

OBJECTIVE

The aim of this study was to investigate the extent and the rate of absorption of metamizole, appearing in blood as methylaminoantipyrine (MAA), from a new oral solution and a parenteral solution administered by the oral route relative to capsules.

METHODS

An open, randomized, 3 single-dose (2 g metamizole), crossover study with intervals of 7 days between periods was performed in 19 male and female healthy volunteers (age 22 - 45 years, body weight 49 - 88 kg, body height 156 - 189 cm). Metamizole metabolites were measured with an HPLC technique. The test formulations were considered bioequivalent with the reference formulation if the 90% confidence limits of the AUC0-->infinity and Cmax ratios and the tmax differences were within the range of 80 - 125%.

RESULTS

The 90% confidence limits of the comparisons between capsules (reference) and oral solution, capsules (reference) and ampoules, and ampoules (reference) and oral solution were 98.5 - 117.8, 99.5 - 132.6 and 81.3 - 105.8 for AUC0-->infinity 98.7 - 119, 101.7 to 129.2, and 82.1 - 104.8 for Cmax, and 84.4 to 115.6, 100 - 105.6 and 70.3 - 100 for tmax, respectively.

CONCLUSION

The oral solution was bioequivalent to capsules with regard both to the extent and the rate of MAA absorption. Metamizole as oral solution was bioequivalent to reference ampoules in the extent of MAA absorption, but absorption rate was faster. Ampoules showed a higher MAA bioavailability than capsules.

Death due to baclofen and dipyrone ingestion

A fatal suicidal intoxication with unusual drugs is reported. A 56-year-old man was found dead in his house; near by the corpse several empty drugs boxes were found. An autopsy was performed and the biological fluids were submitted to a full toxicological work-up. The analytical results supported the hypothesis of a death due to the acute baclofen (4-amino-3-(p-chlorophenyl)butyric acid) and dipyrone (sodium [N-(1,5-dimethyl-3-oxo-2-phenylpyrazolin-4-yl)-N-methylamino] methanesulfonate) intoxication.

Limited-sampling strategy models for estimating the pharmacokinetic parameters of 4-methylaminoantipyrine, an active metabolite of dipyrone

Bioanalytical data from a bioequivalence study were used to develop limited-sampling strategy (LSS) models for estimating the area under the plasma concentration versus time curve (AUC) and the peak plasma concentration (Cmax) of 4-methylaminoantipyrine (MAA), an active metabolite of dipyrone. Twelve healthy adult male volunteers received single 600 mg oral doses of dipyrone in two formulations at a 7-day interval in a randomized, crossover protocol. Plasma concentrations of MAA (N = 336), measured by HPLC, were used to develop LSS models. Linear regression analysis and a "jack-knife" validation procedure revealed that the AUC(0-infinity) and the Cmax of MAA can be accurately predicted (R2>0.95, bias <1.5%, precision between 3.1 and 8.3%) by LSS models based on two sampling times. Validation tests indicate that the most informative 2-point LSS models developed for one formulation provide good estimates (R2>0.85) of the AUC(0-infinity) or Cmax for the other formulation. LSS models based on three sampling points (1.5, 4 and 24 h), but using different coefficients for AUC(0-infinity) and Cmax, predicted the individual values of both parameters for the enrolled volunteers (R2>0.88, bias = -0.65 and -0.37%, precision = 4.3 and 7.4%) as well as for plasma concentration data sets generated by simulation (R2>0.88, bias = -1.9 and 8.5%, precision = 5.2 and 8.7%). Bioequivalence assessment of the dipyrone formulations based on the 90% confidence interval of log-transformed AUC(0-infinity) and Cmax provided similar results when either the best-estimated or the LSS-derived metrics were used.

Impairment of the metabolism of dipyrone in asymptomatic carriers of the hepatitis-B virus does not occur in rapid acetylators

OBJECTIVE

We previously found that, compared with healthy subjects. asymptomatic hepatitis-B virus (HBV) carriers displaying slow acetylator phenotype demonstrate a significant prolongation of the elimination half-life of 4-methylaminoantipyrine (MAA) and a decrease in the clearance of formation of 4-aminoantipyrine (AA) and 4-formylaminoantipyrine (FAA). However, the formation of 4-acetylaminoantipyrine (AAA) was unchanged. The present study was designed to examine the effect of the asymptomatic HBV carrier state on the metabolism of dipyrone. as a model drug, in rapid acetylators.

METHODS

The plasma and urine concentrations of the metabolites of dipyrone were measured in eight asymptomatic HBV carriers and eight healthy subjects who had normal liver function tests, all displaying the rapid acetylation phenotype and genotype, after the administration of a 1.0-g oral dose of dipyrone.

RESULTS

The following pharmacokinetic parameters were evaluated: peak plasma concentration, time to peak plasma concentration, elimination rate constant, area under the plasma concentration-time curve (0-->infinity), amount excreted (0-->infinity), renal and non-renal clearances for MAA and the clearances of formation for AA, FAA and AAA. No significant differences were found between the two subject groups.

CONCLUSION

The effect of hepatic viral carrier state on drug metabolism may vary according to metabolic pathways and genetic polymorphism.

[Studies on HPLC method for determination of 4-methylaminoantipyrine and relative bioavailabilities of analgin nasal drops in human volunteers]

A new HPLC method for the determination of a metabolite of analgin, MAA (4-methylaminoantipyrine), in plasma and its application to determine the bioavailabilities of analgin nasal drops in human volunteers is reported in this paper. A Waters Model 481 instrument was used throughout the experiment. IAA (isopropylaminoantipyrine) was shown to be the most suitable internal standard at absorption wavelength of 254 nm. A mixture of phosphate buffer (pH 5.5) and methanol (68:32) was used as the mobile phase with a flow rate of 2 ml.min-1, and YWG-C18H37 as stationary phase. Calibration curve was linear (gamma = 0.9998) in the concentration range of 0.1-5 micrograms.ml-1. The within day and day-to-day precision (RSD) of this method were 2.35% and 2.61%, respectively, with average recoveries of 99.3%-103.9%. No interference was found in the body fluid. The plasma samples of healthy volunteers were treated with acid and extracted with ether. The system of mobile phase and the process of blood sample treatment were simpler than those reported in literature. So, the method is suitable for the study of pharmacokinetics and clinical determination of blood level of analgin. The studies on bioavailabilities of analgin nasal drops were carried out in 8 men relative to intramuscular injection and 6 men relative to oral tablets, respectively, at the dose of 250 mg analgin in different preparations administered by cross-over method. The main pharmacokinetic parameters were shown in Table 3. The results indicate that analgin nasal drops exhibited a higher bioavailability (relative to injection) and faster absorption (relative to tablet). So, analgin is suitable to be developed as a nasal preparation.

Chemiluminescence analysis of menadione sodium bisulfite and analgin in pharmaceutical preparations and biological fluids

A novel chemiluminescence (CL) flow system for two sulfite-containing drugs, namely, menadione sodium bisulfite (MSB) and analgin is described. It is based on the weak chemiluminescence induced by the oxidation of sulfite group in drugs with dissolved oxygen in the presence of acidic Rh6G. Tween 80 surfactant micelles showed a strong enhancement effect on this weak chemiluminescence. For MSB analysis, online conversion of MSB in alkaline medium into sodium bisulfite was necessary, whereas analgin could be determined directly. The proposed method allowed the measurement of 0.05-50 microg/ml(-1) MSB and 0.05-10 microg/ml(-1) analgin. The limits of detection (3sigma) were 0.01 microg/ml(-1) MSB and 0.003 microg/ml(-1) analgin. The method was applied satisfactorily to pharmaceutical preparations as well as biological fluids.

Cerebrospinal fluid and plasma concentrations of dipyrone metabolites after a single oral dose of dipyrone

OBJECTIVE

Dipyrone is a veteran analgesic and antipyretic drug. After oral administration it is rapidly converted by hydrolysis to 4-methylaminoantipyrine (MAA), which is further metabolized to 4-formylaminoantipyrine (FAA), 4-aminoantipyrine (AA) and 4-acetylaminoantipyrine (AAA). It is still debated whether the site of dipyrone action is in the central nervous system or in the periphery. The purpose of this study was to assess whether dipyrone metabolites cross the blood-brain barrier (BBB) when administered systemically.

METHODS

Twenty-eight patients undergoing diagnostic lumbar puncture (LP) were randomly assigned to receive two 0.5-g dipyrone tablets either 30 min, 1, 1.5, 2, 4, 6, 8 h or 12 h before the lumbar tap. A 5-ml blood sample was drawn concomitantly.

RESULTS

All four metabolites were found in the cerebrospinal fluid (CSF). Their appearance in the CSF lagged but followed that found in the plasma. Mean CSF/plasma ratios were 0.40 (for samples taken between 0.5-2 h) and 0.83 (for samples taken between 4-12 h) for MAA, 0.62 for AA, 0.55 for FAA and 0.40 for AAA (for all samples). Significant correlation was found between plasma and CSF concentrations for MAA, AA, FAA and AAA.

CONCLUSION

The concentration-time course of dipyrone metabolite CSF concentrations are in agreement with that of their plasma concentrations and the analgesic effect of dipyrone.

Pharmacokinetic study of dipyrone metabolite 4-MAA in the horse and possible implications for doping control

The pharmacokinetic behaviour of dipyrone metabolite 4-MAA in serum was determined in seven horses of different breeds after a single intravenous dose administration. A biexponential formula was fitted to the serum concentration vs. time data. The median half-life of the elimination phase (t1/2 beta) was 4.85 h (range 5.04 h), the median volume of distribution (Vd(area)) was 1.85 L/kg (range 3.2 L/kg) and median of total clearance was 4.0 mL/min/kg (range 2.3 mL/min/kg).

Bilirubin and metamizol do not interfere with the randox enzymatic creatinine test. An evaluation of a new enzymatic creatinine determination method

We evaluated the new commercially available enzymatic test kit for creatinine (Randox Laboratories Ltd. Ardmore, Crumlin, UK). The test correlated well with the reference HPLC method (yenz = 0.98x + 1.4; r = 1.00; n = 72). The correlations with the Jaffe method (yenz = 1.00x + 14.1; r = 0.99; n = 72) and the dry slide technique (yenz = 1.07x + 4.1; r = 1.00; n = 72) were also good, but these techniques gave slightly higher creatinine results than the HPLC or the Randox enzymatic method. This new test is insensitive to bilirubin interference. It has been reported that patients receiving metamizol showed unusually low values of creatinine, when determined enzymatically, but this drug does not interfere with the Randox method. The test evaluated is more specific than enzymatic methods published earlier and it provides an attractive alternative to the traditional picrate test.

Determination of antipyrine metabolites in human plasma by solid-phase extraction and micellar liquid chromatography

A rapid solid-phase extraction (SPE) procedure was developed for the quantitative isolation of three important antipyrine (dipyrone) metabolites from human plasma: 4-formylaminoantipyrine (FAA), 4-aminoantipyrine (AA) and 4-methylaminoantipyrine (MAA). Separation and quantitation were performed using micellar liquid chromatography (MLC) with a 0.1 mol l-1 sodium dodecyl sulfate (SDS)-2.5% pentanol mobile phase and UV detection at 262 nm. The metabolites were well resolved in less than 5 min using an octadecyl silica-bonded stationary phase. The extraction procedure involved passing 0.3 ml of plasma sample through a disposable SPE cartridge packed with C18 bonded porous silica. The adsorbed metabolites were removed from the cartridge with methanol. The eluent was evaporated to dryness and the residue was reconstituted with mobile phase and injected into the chromatographic system. The cartridge blank interferent peaks, the effects on reproducibility of sample loading in the cartridge and volume needed for desorption of metabolites were evaluated. The concentration of metabolites ranged between 2.4 and 4 micrograms ml-1. The present procedure yields recoveries for the three metabolites ranging from 93 to 100%. The relative standard deviation (Sr) ranged between 1.2 and 13.6%. Limits of detection (LODs) were 10.5, 11.5 and 17.0 ng ml-1 for FAA, AA and MAA, respectively.

Interference of metamizol (dipyrone) on the determination of creatinine with the Kodak dry chemistry slide comparison with the enzymatic method from Boehringer

In order to eliminate positive interferences that take place with the Jaffé technique, the Kodak Ektachem and Boehringer Mannheim Companies have chosen an enzymatic method for the determination of creatinine in serum and urine. Pathological and clinical samples often contain metabolites in elevated concentrations or exogenous compounds such as drugs or toxic compounds. We noticed that patients receiving metamizol-containing drugs showed unusually low values of creatinine when determined with an Ektachem analyser. We investigated the effect of the main metabolites of this prodrug on the creatinine enzymatic methods of Kodak and Boehringer. We concluded that methyl-amino-antipyrine, the active substance after administration of metamizol (prop. INN) was responsible for the interference, and that no reliable determination of creatinine could be performed with these methods in the serum of patients receiving this drug.

Dipyrone interference on several common biochemical tests

We studied the effect in vitro and in vivo of dipyrone on the determination of several biochemical tests in two analyzers, a Hitachi 747 and a Kodak Ektachem 700. From studies in vitro, we found significant interference by dipyrone (P < 0.05) in the determination of creatine kinase (CK), lactate dehydrogenase (LD), uric acid, triglycerides, cholesterol, aspartate aminotransferase, alanine aminotransferase, and urea nitrogen with both instruments, and in the determination of creatinine in the Ektachem analyzer. We also studied the effect of intravenously administered dipyrone in 14 patients. Dipyrone interfered significantly (P < 0.05) in the determination of CK, LD, uric acid, triglycerides, and cholesterol with both instruments, and creatinine only with the Ektachem analyzer. Using high-performance liquid chromatography (HPLC), we measured concentrations of dipyrone in the serum of patients who had received the drug and observed a negative correlation between the concentrations of dipyrone in the blood and the percentage of each analyte concentration.

Formation and excretion of dipyrone metabolites in man

The formation and urinary excretion of the dipyrone metabolites, methylaminoantipyrine (MAA), aminoantipyrine (AA), formylaminoantipyrine (FAA) and acetylaminoantipyrine (AAA) were determined following administration of a single oral 1.0 g dose of dipyrone to 12 healthy volunteers. The AAA/AA plasma ratio showed that 3 subjects were slow and 9 were rapid acetylators. Pharmacokinetic parameters were determined separately for each group. A good correlation was found between the plasma and urine AAA/AA ratios. The renal clearance of the four metabolites was similar for both phenotypes. A significant difference in the rate of formation of dipyrone metabolites was found for AA, 0.25 (slow) vs 0.1 ml.min-1.kg-1 (rapid), and for AAA 0.75 (slow) vs 7.53 ml.min-1.kg-1 (rapid). There were comparable differences between slow and rapid acetylators in the AUC and the urinary excretion extrapolated to infinity for AA and AAA. The present results show that the kinetics of dipyrone metabolites in plasma and urine can provide a useful measure of the activity of the enzymes involved in their production.

Simultaneous determination of the main metabolites of dipyrone by high-pressure liquid chromatography

A simple, rapid, and sensitive procedure is described for the determination of the main metabolites of dipyrone in plasma and urine. After adding isopropyl aminoantipyrine as internal standard and a deproteinizer the plasma of urine samples are alkalized and extracted with chloroform. The residue of the evaporated organic phase is dissolved in mobile phase and separated by HPLC. The compounds are detected by ultraviolet light at 265 nm. The following metabolites can be determined selectively by this method: 4-methylamino-antipyrine, 4-aminoantipyrine, 4-formylaminoantipyrine and 4-acetylaminoantipyrine. The detection limit for all four metabolites is 0.1 microgram/ml in plasma and 2 micrograms/ml in urine. The results of a human pharmacokinetic study are also presented.

Effect of age on the pharmacokinetics of dipyrone

The pharmacokinetics of the dipyrone metabolite, 4-methylaminoantipyrine (MAA) was evaluated, following the administration of a single oral dose of dipyrone 1.0 g to 12 young (21-30 years) and 9 elderly (73-90 years) healthy volunteers. Maximal concentration, time to peak and absorption rate of MAA were similar for both groups. The elimination half-life was 2.6 (0.2) h for the young and 4.5 (0.5) h for the elderly subjects. Total clearance of MAA, corrected for lean body mass (LBM), was lower in the elderly than in the young 2.65 vs 3.97 ml.min-1.kg-1 LBM. There was no differences between the groups in the apparent volume of distribution. A good correlation was found between the total body clearance of MAA and the creatinine clearance, which was also reduced in the elderly (r = 0.61).

Influence of food on the pharmacokinetics of dipyrone

Twelve healthy volunteers were given a single oral dose of dipyrone 1 g, once while fasting and once after a standard breakfast. Plasma levels of the active dipyrone metabolite-Methylaminoantipyrine (MAA) were measured and the calculated pharmacokinetic parameters were compared. Taking dipyrone with food resulted in a small delay in the mean time to peak from 1.5 h to 1.9 h (p less than 0.01). However, there was no significant difference in AUC, Cmax or K(elim) between fasting and nonfasting conditions. The rate of absorption, expressed as the mean K(abs), was somewhat slower in the nonfasting state, but not significantly so. It is suggested that dipyrone may be taken regardless of the times of eating.

Kinetics of hexobarbital and dipyrone in critical care patients receiving high-dose pentobarbital

The effect of pentobarbital treatment in a mean dose of 30 mg/kg/day on the clearance of hexobarbital (Evipan) and dipyrone (Novalgin) has been evaluated in critical care patients receiving a large number of drugs as comedication. Eleven patients treated with pentobarbital showed a hexobarbital half-life of 2.79 h and a total plasma clearance of 9.80 ml X min-1 X kg-1 as compared to 10 patients without pentobarbital administration in whom there was a significantly longer half life (6.92 h) and lower clearance (2.97 ml X min-1 X kg-1). The kinetics of hexobarbital were correlated with the urinary excretion of D-glucaric acid, a non-invasive parameter of drug metabolising activity. In 10 patients on pentobarbital, the total plasma clearance of N-4-methyl-aminoantipyrine, the active form of dipyrone, did not differ from that in 8 patients not receiving pentobarbital. As drug kinetics show great variability in these patients, it is difficult to discriminate enzyme induction from other mechanisms, for example competitive inhibition or changes in volume of distribution. In the presence of pentobarbital, however, induction of drug metabolising enzymes should be considered as a possible reason for the higher clearance of hexobarbital.

Excretion of dipyrone metabolites in human breast milk

Breast milk and plasma levels of dipyrone metabolites in 8 mothers given a single oral dose of the drug were determined by HPLC. Four metabolites were demonstrated by the analytical method: 4-methylaminoantipyrine (MAA), 4-aminoantipyrine (AA), 4-formylaminoantipyrine (FAA) and 4-acetylaminoantipyrine (AAA). A good correlation was found between the plasma and milk concentrations of the metabolites. The mean (+/- SD) milk to plasma concentration ratios were: MAA = 1.37 +/- 0.28, AA = 1.15 +/- 0.40, FAA = 1.03 +/- 0.09, AAA = 0.97 +/- 0.24. The disposition pattern of the dipyrone metabolites in milk was studied in two mothers. None of the metabolites was detectable 48 h after drug administration.

Plasma kinetics of dipyrone metabolites in rapid and slow acetylators

The pharmacokinetics of the dipyrone metabolites 4-methylaminoantipyrine (MAA), 4-aminoantipyrine (AA), 4-formylaminoantipyrine (FAA) and 4-acetylaminoantipyrine (AAA) were evaluated following the administration of a single oral 1.0 g dose of dipyrone to 23 healthy volunteers. Twelve were slow and 11 were rapid acetylators as previously determined by dapsone phenotyping. For MAA and FAA the mean peak plasma concentrations were 10.5 +/- 2.8 micrograms/ml and 2.1 +/- 0.8 micrograms/ml and the half-lives were 3.3 +/- 1.0 and 10.1 +/- 1.8 h, respectively. No significant difference was found between rapid and slow acetylators in MAA and FAA kinetics. For AA, the mean peak plasma concentrations were 2.7 +/- 0.6 and 1.6 +/- 0.7 micrograms/ml (p less than 0.01), the peak times 6.7 +/- 2.1 and 3.1 +/- 1.1 h (p less than 0.01) and the half-lives were 5.5 +/- 1.0 and 3.8 +/- 1.2 h in slow and rapid acetylators, respectively. For AAA, the mean peak plasma concentrations were 1.6 +/- 0.4 and 4.4 +/- 1.1 micrograms/ml (p less than 0.01) and the peak time 16.1 +/- 5.1 and 10.0 +/- 2.6 h (p less than 0.01) in slow and rapid acetylators, respectively. There was no difference in the elimination half-life between the two groups (10.6 +/- 2.2 h). Thus, it has been demonstrated that the AAA/AA ratio is an indicator of the acetylation phenotype, as it is closely correlated with that determined by dapsone (r = 0.895, p less than 0.0005).

High-performance liquid chromatography of dipyrone and its active metabolite in biological fluids

New high-performance liquid chromatography methods were developed to measure dipyrone and its active metabolite 4-monomethylaminoantipyrine (MAA) in biological fluids. While no detectable level of the unchanged dipyrone was found in plasma of four subjects taking 1000-mg oral doses of the drug, values ranging from 1.25 to 14.99 micrograms/ml of MAA were observed. Twenty-four hour urinary excretion of MAA varied from 9.56 to 21.21 mg. Concentrations as low as 0.25 micrograms/ml of MAA can be measured with acceptable coefficients of variation. The method, therefore, is suitable for microquantification of MAA in biological fluid which enables convenient and rapid assessment of the drug disposition in body.

[Blood level kinetics of sodium noramidopyrine methanesulfonate (Analgin) in late pregnancy]

The pharmacokinetic parameters were investigated after a single application of 1,0 g of Analgin to women in labour in comparison with a nonpregnant control group. During the late stage of pregnancy the distribution volume is only slightly increasing. For Analgin a fundamental influence on the level of serum concentration could not be shown. The biological half-life of Analgin shows remarkable individual differences and does not differ significantly between the two investigated groups. Therefore, during pregnancy a change of the applied dose is not indicated.

[Quantitative thin-layer chromatographic estimation of aminophenazone (I.N.N.), 4-methylaminophenazone and 4-aminophenazone in plasma (author's transl)]

A TLC method for measurement of aminophenazone (1) and of its degradation products 4-methylaminophenazone (2) and 4-aminophenazone (3) in plasma was described. After chloroform extraction amd separation on Silufol plates the substances were stained by ferric chloride/potassium hexacyanotoferrate(III) and the area of the spots was measured. Concentrations from 1 to 25 micrograms 1, 2 and 3 per ml plasma could be estimated.

Further production and characterization of antibodies reactive with pyrazolone derivatives

A sensitive radioimmunoassay for pyrazolone derivatives has been developed. Anti-antipyrine antisera were produced in rabbits by repeated immunization with 4-succinamidoantipyrine coupled to bovine serum albumin. Less than 1 ng of antipyrine could be detected by this procedure. Various substituents on the carbon-4 position of the pyrazolone ring decreased the affinity for the antibody. The concentrations in ng of various pyrazolone derivatives required to inhibit [3H]antipyrine binding by 50% were: antipyrine, 6.8; aminopropylon, 8.5; sulpyrine, 35.5; isopropylantipyrine, 1320; and aminopyrine, 2820. The antibody showed no cross-reactivity with any other antipyretics such as pyrazolidine or aniline derivatives. The determination of antipyrine and sulpyrine concentrations in rat serum after i.p administration was also carried out.

Colorimetric assay of noramidopyrine methanesulfonate sodium in formulations and in blood and urine samples

A simple, rapid, specific and sensitive colorimetric method is proposed for the quantitative estimation of noramido-pyrine methanesulfonate sodium in different dosage forms as well as in blood and urine samples. The method is based on the reaction of 3-sulfonic-5-amino-alpha-naphthol with formaldehyde liberated from noramidopyrine methanesulfonate sodium after treatment with conc. sulfuric acid where a yellow colour appeared immediately which turned to blue on dilution with water. The blue colour obeyed Beer's law (10--400 microgram) and remained stable for more than 1 h. The effect of other drugs, tablet excipients, parentral vehicles and suppository bases was studied.

The reliability of a mechanized procedure (Perkin-Elmer C4) for the Enzymatic determination of uric acid according to Kageyama

The enzymatic determination of the uric acie concentration in urine and serum according to Kageyama ((1971), Clin. Chim. Acta 31, 421--426), which excludes the deproteinization of samples, was adapted to the C4 automatic analyzer (Perkin-Elmer). The reliability of this procedure and its correlation with an UV-method were investigated. The interaction from-sample-to-sample was considerable, but this could be reduced by the addition of Brij-35. The recovery of uric acid added to protein-containing samples (about 96%) was better than with the UV-method. Novaminsulfone was the only substance tested which interfered significantly.