Paramagnetism and Fluorescence of Zinc(II) Tripyrrindione: A Luminescent Radical Based on a Redox-Active Biopyrrin.

The ability of bilins and other biopyrrins to form fluorescent zinc complexes has been known for more than a century; however, the exact identity of the emissive species remains uncertain in many cases. Herein, we characterize the hitherto elusive zinc complex of tripyrrin-1,14-dione, an analogue of several orange urinary pigments. As previously observed for its Pd(II), Cu(II), and Ni(II) complexes, tripyrrindione binds Zn(II) as a dianionic radical and forms a paramagnetic complex carrying an unpaired electron on the ligand π-system. This species is stable at room temperature and undergoes quasi-reversible ligand-based redox chemistry. Although the complex is isolated as a coordination dimer in the solid state, optical absorption and electron paramagnetic resonance spectroscopic studies indicate that the monomer is prevalent in a tetrahydrofuran solution. The paramagnetic Zn(II) tripyrrindione complex is brightly fluorescent (λabs = 599 nm, λem = 644 nm, ΦF = 0.23 in THF), and its study provides a molecular basis for the observation, made over several decades since the 1930s, of fluorescent behavior of tripyrrindione pigments in the presence of zinc salts. The zinc-bound tripyrrindione radical is thus a new addition to the limited number of stable radicals that are fluorescent at room temperature.

Pharmacokinetic profiles of the active metamizole metabolites after four different routes of administration in healthy dogs.

Metamizole (MT), an analgesic and antipyretic drug, is rapidly hydrolyzed to the active primary metabolite 4-methylaminoantipyrine (MAA) and relatively active secondary metabolite 4-aminoantipyrine (AA). The aim of this study was to assess the pharmacokinetic profiles of MAA and AA after dose of 25 mg/kg MT by intravenous (i.v.), intramuscular (i.m.), oral (p.o.), and rectal (RC) routes in dogs. Six dogs were randomly allocated to an open, single-dose, four-treatment, four-phase, unpaired, crossover study design. Blood was collected at predetermined times within 24 hr, and plasma was analyzed by a validated HPLC-UV method. Plasma concentrations of MAA and AA after i.v., i.m., p.o., and RC administrations of MT were detectable from 5 (i.v. and i.m.) or 30 (p.o. and RC) min to 24 hr in all dogs. The highest concentrations of MAA were found in the i.v., then i.m., p.o., and RC groups. Plasma concentrations of AA were similar for i.v., i.m., and RC, and the concentrations were approximately double those in the PO groups. The AUCEV/IV ratio for MAA was 0.75 ± 0.11, 0.59 ± 0.08, and 0.32 ± 0.05, for i.m., p.o., and RC, respectively. The AUCEV/IV ratio for AA was 1.21 ± 0.33, 2.17 ± 0.62, and 1.08 ± 0.19, for i.m., p.o., and RC, respectively. Although further studies are needed, rectal administration seems to be the least suitable route of administration for MT in the dog.

Pharmacokinetic profiles of the active metamizole metabolites in healthy horses.

Metamizole (MT) is an analgesic and antipyretic drug labelled for use in humans, horses, cattle, swine and dogs. MT is rapidly hydrolysed to the active primary metabolite 4-methylaminoantipyrine (MAA). MAA is formed in much larger amounts compared with other minor metabolites. Among the other secondary metabolites, 4-aminoantipyrine (AA) is also relatively active. The aim of this research was to evaluate the pharmacokinetic profiles of MAA and AA after dose of 25 mg/kg MT by intravenous (i.v.) and intramuscular (i.m.) routes in healthy horses. Six horses were randomly allocated to two equally sized treatment groups according to a 2 × 2 crossover study design. Blood was collected at predetermined times within 24 h, and plasma was analysed by a validated HPLC-UV method. No behavioural changes or alterations in health parameters were observed in the i.v. or i.m. groups of animals during or after (up to 7 days) drug administration. Plasma concentrations of MAA after i.v. and i.m. administrations of MT were detectable from 5 min to 10 h in all the horses. Plasma concentrations of AA were detectable in the same range of time, but in smaller amounts. Maximum concentration (Cmax ), time to maximum concentration (Tmax ) and AUMC0-last of MAA were statistically different between the i.v. and i.m. groups. The AUCIM /AUCIV ratio of MAA was 1.06. In contrast, AUC0-last of AA was statistically different between the groups (P < 0.05) with an AUCIM /AUCIV ratio of 0.54. This study suggested that the differences in the MAA and AA plasma concentrations found after i.m. and i.v. administrations of MT might have minor consequences on the pharmacodynamics of the drug.

Pharmacokinetic investigations of the marker active metabolites 4-methylamino-antipyrine and 4-amino-antipyrine after intramuscular injection of metamizole in healthy piglets.

Metamizole (MT) is a pyrazolone nonsteroidal anti-inflammatory drug labelled for humans and animals. The aim of this study was to assess the pharmacokinetics of its active metabolites 4-methylamino-antipyrine (MAA) and 4-amino-antipyrine (AA) in male piglets after a single intramuscular injection of MT. Eight healthy male piglets were administered MT (100 mg/kg) intramuscularly. Blood was sampled at scheduled time intervals, and drug plasma concentrations evaluated by a validated HPLC method. MAA and AA plasma concentrations were quantitatively detectable from 0.25 to 48 h and 0.50 to 72 h, respectively, in 6 of 8 and 7 of 8 animals. The average maximum concentrations of MAA and AA were of 47.59 and 4.94 mg/mL, respectively. The average half-lives were 8.57 and 13.3 h for MAA and AA, respectively. This study showed that the amount of MAA and AA produced in piglets is different to that in the animal species previously investigated. Further studies are necessary to understand whether these differences in MAA and AA plasma concentrations between animal species necessitate diverse therapeutic drug dosing.

Magnetic microspheres based on pectin coated by chitosan towards smart drug release.

This study reports the preparation of microspheres of pectin and magnetite nanoparticles coated by chitosan to encapsulate and deliver drugs. Magnetic-pectin microspheres were obtained by ionotropic gelation followed by polyelectrolyte complexation with chitosan. Characterization data show that magnetite changes the physicochemical and morphological properties of the microspheres compared to the non-magnetic samples. Using metamizole (Mtz) as a drug model, the magnetic microspheres showed appreciable encapsulation efficiency (85 %). Release experiments performed in simulated gastric (pH 1.2) and intestinal (pH 6.8) fluids suggested that the release process is pH-dependent. At pH 6.8, the Mtz release is favored achieving 75 % after 12 h. The application of an external magnetic field increased the release to 91 % at pH 6.8, indicating that the release also is magnetic-dependent. The results suggest that the magnetic microspheres based on pectin/chitosan biopolymers show the potential to be used as a multi-responsive drug delivery system.

Understanding the dipyrone oxidation allying electrochemical and computational approaches.

Electroanalytical methodology by boron-doped diamond electrode (BDDE) associated to the square-wave voltammetry (SWV) for the determination of hydrolyzed dipyrone (DIP) in commercial formulations, raw natural waters and in human urine was developed. Through cyclic voltammetry (CV), it was shown that the oxidation of the DIP on the BDDE was irreversible with diffusional control. Computational studies suggested that the oxidation mechanism of DIP occurred with participation of two electrons and one proton. The analytical curves were obtained for concentrations of DIP ranging from 1.0 × 10-6 to 6.5 × 10-5 mol L-1 (r = 0.9994). The values of detection limit (LOD) and quantification limit (LOQ) of DIP were calculated from SWV and found to be 2.6 × 10-7 mol L-1 and 8.8 × 10-7 mol L-1. The methodology was effectively applied to real samples with the values of calculated recoveries varying between 91.0% and 117.3% and validated by iodometric titration experiments whose values were between 93.3% and 106.9%. The proposed methodology with BDDE represents an alternative tool and it has advantageous, such as very easy handling, low cost, no need for modification, low detection limit. Furthermore, it can be used for the routine analysis of DIP in different real samples.

Non-immunological toxicological mechanisms of metamizole-associated neutropenia in HL60 cells.

Metamizole is an analgesic and antipyretic, but can cause neutropenia and agranulocytosis. We investigated the toxicity of the metabolites N-methyl-4-aminoantipyrine (MAA), 4-aminoantipyrine (AA), N-formyl-4-aminoantipyrine (FAA) and N-acetyl-4-aminoantipyrine (AAA) on neutrophil granulocytes and on HL60 cells (granulocyte precursor cell line). MAA, FAA, AA, and AAA (up to 100 µM) alone were not toxic for HL60 cells or granulocytes. In the presence of the myeloperoxidase substrate H2O2, MAA reduced cytotoxicity for HL60 cells at low concentrations (<50 µM), but increased cytotoxicity at 100 µM H2O2. Neutrophil granulocytes were resistant to H2O2 and MAA. Fe2+ and Fe3+ were not toxic to HL60 cells, irrespective of the presence of H2O2 and MAA. Similarly, MAA did not increase the toxicity of lactoferrin, hemoglobin or methemoglobin for HL60 cells. Hemin (hemoglobin degradation product containing a porphyrin ring and Fe3+) was toxic on HL60 cells and cytotoxicity was increased by MAA. EDTA, N-acetylcystein and glutathione prevented the toxicity of hemin and hemin/MAA. The absorption spectrum of hemin changed concentration-dependently after addition of MAA, suggesting an interaction between Fe3+ and MAA. NMR revealed the formation of a stable MAA reaction product with a reaction pathway involving the formation of an electrophilic intermediate. In conclusion, MAA, the principle metabolite of metamizole, increased cytotoxicity of hemin by a reaction involving the formation of an electrophilic metabolite. Accordingly, cytotoxicity of MAA/hemin could be prevented by the iron chelator EDTA and by the electron donors NAC and glutathione. Situations with increased production of hemin may represent a risk factor for metamizole-associated granulocytopenia.

Photodegradation study of three dipyrone metabolites in various water systems: identification and toxicity of their photodegradation products.

The photochemical behaviour of three relevant metabolites of the analgesic and antipyretic drug dipyrone, 4-methylaminoantipyrine (4-MAA), 4-formylaminoantipyrine (4-FAA) and 4-acetylaminoantipyrine (4-AAA), was evaluated under simulated solar irradiation (Suntest system). For 4-MAA, different aqueous solutions (synthetic seawater, freshwater and Milli-Q water) as well as different operational conditions were compared. According to the experimental results, 4-MAA resulted as being an easily degraded molecule by direct photolysis, with half-life times (t1/2) ranging from 0.12 to 0.58 h, depending on the irradiation conditions. Faster degradation was observed in synthetic waters, suggesting that the photolysis was influenced by the salt composition of the waters. However, no effect on the degradation rate was observed by the presence of natural photosensitizers (dissolved organic matter, nitrate ions). 4-FAA and 4-AAA showed slower photodegradation kinetics, with t1/2 of 24 and 28 h, respectively. A study of photoproduct identification was carried out by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) (ESI positive mode), which allowed us to propose a tentative photodegradation pathway for 4-MAA and the identification of persistent by-products in all the cases. Finally, the application of an acute toxicity test (Daphnia magna) showed an increase in toxicity during the photolytic process, a consequence of the formation of toxic photoproducts.

Ag-doping on ZnO support mediated by bio-analytes rich in ascorbic acid for photocatalytic degradation of dipyrone drug.

The analytes such as ascorbic acid (AA) present in Sechium edule were extracted (294 mg AA kg-1 fruit) in an aqueous media for its potential application for Ag-doping onto wurtzite ZnO. The bandgap of ZnO was decreased to 2.85 eV at the optimal Ag-loading of 1.18% (w/w) against 3.13 eV for the control catalyst without using the analytes and, the commercial AA only could reduce the bandgap to 2.91 eV. The saturation photo-electrochemical current density (46.68 mA cm-2) at Eanode ≥ 0.31 V vs. Ag/AgCl was almost double than pristine ZnO under visible light illumination (λmean = 525 nm, 18 K lux) and, the current density was insignificant in the dark. The doped catalyst exhibited the maximum 79.5% degradation (71% COD removal) of an anti-analgesic drug, dipyrone (100 µg L-1 dipyrone, catalyst 100 mg L-1) resulted from the formation of O2•- radical (g-factor of 2.002-2.008) and paramagnetic oxygen vacancies (g-factor of 2.020) and, no effect of dye-sensitization was noted. The highest quantum yield was found to be 34.7%. The catalyst loss was 6% after the fourth cycle and the dipyrone degradation was reduced to 70.8%.

Dissolution studies of metamizole sodium and pseudoephedrine sulphate dosage forms - comparison and correlation of electronic tongue results with reference studies.

This work reports a critical evaluation of the results of the release of active substances (APIs) from novel pharmaceutical formulations provided by an electronic tongue system (ET). Detailed dissolution studies of modified-release granules used in pharmacotherapy containing metamizole sodium and pseudoephedrine sulphate were carried out. The impact of the dissolution-modifying excipients (carmellose sodium and hypromellose) on the dissolution process as well as on the outcomes of the sensor array of ion-selective electrodes was investigated. The obtained dissolution profiles were compared and correlated with those registered during the reference studies performed according to the pharmacopoeial method. It was pointed out that the proper evaluation of the efficiency of the release modification requires the examination of dosage forms as well as physical mixtures of API and excipient. Moreover, the results obtained using potentiometric ET were complementary to the classical methodology. Their partial inconsistency, remarked during several experiments, should be interpreted with caution owing to simultaneous sensing of APIs and excipients by the sensors and their various performances (i.e. selectivity and sensitivity) towards these components.

Chitosan/waste coffee-grounds composite: An efficient and eco-friendly adsorbent for removal of pharmaceutical contaminants from water.

Waste coffee-grounds (WCG), a poorly explored source of biocompounds, were combined with chitosan (Cs) and poly(vinyl alcohol) (PVA) in order to obtain composites. Overall, WCG showed a good interaction with the polymeric matrix and good dispersibility up to 10 wt-%. At 5 wt-% WCG, the composite exhibited a noticeable enhancement (from 10 to 44%) of the adsorption of pharmaceuticals (metamizol (MET), acetylsalicylic acid (ASA), acetaminophen (ACE), and caffeine (CAF)) as compared to the pristine sample. The highest removal efficiency was registered at pH 6 and the removal followed the order ASA > CAF > ACE > MET. For all pharmaceuticals, the adsorption kinetics was found to follow the pseudo-second order model, while the adsorption mechanism was explained by the Freundlich isotherm. Reuse experiments indicated that the WCG-containing composite has an attractive cost-effectiveness since it presented a remarkable reusability in at least five consecutive adsorption/desorption cycles.

Influence of dissolution-modifying excipients in various pharmaceutical formulations on electronic tongue results.

The overall performance of a potentiometric electronic tongue (ET) as well as the sensitivity and selectivity pattern of particular ion-selective electrodes forming the array towards exemplary APIs (metamizole sodium, pseudoephedrine sulphate) and excipients (hypromellose, carmellose, Eudragit E) was determined. Simultaneous sensing of both API and the encapsulating excipient in their physical mixture was noticed using potentiometric sensors. Usually, such altering of chemical image is treated as an evidence of taste masking/modified release effect (linked with chemical entrapment of API in polymer matrix), while the observed "mixture effect" can also take place which may complicate the interpretation of ET results. Moreover, the influence of the same excipients on chemical images of various APIs was compared and related to sensor array performance. The presented considerations should be taken into account in the case of ET assessment of drug dissolution profiles and detection of modified release effect, especially when novel drug delivery systems are considered.

Considerations about the theoretically expected crushing strength of tablets from binary powder mixtures: double layer tablets versus arithmetic additivity rule.

The theoretically expected breaking strength of tablets from powder mixtures is often calculated by the weighted arithmetic mean from the breaking strength of the single components, which corresponds to a linear interpolation. The validity of this additivity of fracture strength shall be evaluated by the underlying model of parallel couplings. It assumes the components linked in parallel with respect to the direction of loading during diametrical strength testing. Parallel couplings were experimentally realised by the preparation of double layer tablets from crystalline and spray-dried lactose on the one hand and from maltitol and metamizol-sodium on the other. Constant total true volumes of the single substances and of layered powders in varying ratios of true volume were compressed on an eccentric tabletting machine to constant geometric mean punch force. Simulated crushing profiles of parallel couplings were derived from force-displacement profiles measured during diametrical compression of the one-component tablets. At given finely graded deformation levels, the forces exerted by the components during loading were added in the proportion of the true volume fractions of the components in the coupling. The results from the experiments and from the simulations are in good accordance. They demonstrate that a linear change of the crushing strength in dependence on the true volume fraction of the components can only be assumed if the single components deform to the same extent up to the point of fracture. This behaviour was approximately found with the parallel lactose system. In all other cases it must be expected that the crushing strength of parallel systems will be lowered beneath the weighted arithmetic mean values or even below the crushing strength of the single components. The latter was observed with the maltitol-metamizol combinations. Thus, if tablets from binary powder mixtures exhibit a crushing strength depression, this is not necessarily an indication of weak bonding between the components or of structural defects.

Prediction of tablet hardness based on near infrared spectra of raw mixed powders by chemometrics.

The purpose of this research is to elucidate the effect of lubricant mixing on tablet hardness by near-infrared (NIR) chemometrics as a basic study of process analytical technology. Formulation cellulose (F-C) consisted of sulpyrine (SP), microcrystalline cellulose (MC), and magnesium stearate (MgSt). Formulation lactose/starch (F-L) consisted of SP bulk drug powder, spray-dried lactose (SL), corn starch (CS), and MgSt. First, F-L and F-C without MgSt were mixed in a twin-shell mixer for 60 min. MgSt was added to the mixed powder, and was mixed for various mixing times, after which the mixed powders were compressed by 8-mm diameter punch and die. NIR spectra of raw mixed powders of F-L and F-C were taken using a reflection type of Fourier transform NIR spectra spectrometer, and chemometric analysis was performed using principal component regression (PCR). The tablet hardnesses of F-L and F-C decreased with increasing mixing time. All NIR spectra of the mixed powders of F-L and F-C fluctuated depending on mixing time. In order to predict tablet hardness before tablet compression, NIR spectra of F-L and F-C mixed powders were analyzed and evaluated for hardness by PCR. The minimum standard error of cross-validation values could be realized by using five- and six-principal component models, respectively. In the cases of F-L and F-C, the relationships between the actual and predicted tablet hardnesses showed straight lines, respectively. In the regression vectors of F-L and FC, the peaks related to hydrogen groups of SP, CS, and MC appeared as positive peaks. In contrast, the peaks related to hydrocarbon due to MgSt appeared as negative peaks in the regression vectors. The calibration models to evaluate the tablet hardness were obtained based on NIR spectra of raw mixed powders by PCR. This approach to predicting tablet hardness prior to compression could be used as a routine test to indicate the quality of the final product without spending time and energy to produce samples of questionable quality.

Do pediatric medicines induce topographic changes in dental enamel?

The purpose of the present study was to evaluate the effect of common pediatric liquid medicines on surface roughness and tooth structure loss and to evaluate the pH values of these medicines at room and cold temperatures in vitro. Eighty-four bovine enamel blocks were divided into seven groups (n = 12): G1-Alivium®, G2-Novalgina®, G3-Betamox®, G4-Clavulin®, G5-Claritin®, G6-Polaramine® and G7-Milli-Q water (negative control). The pH was determined and the samples were immersed in each treatment 3x/day for 5 min. 3D non-contact profilometry was used to determine surface roughness (linear Ra, volumetric Sa) and the Gap formed between treated and control areas in each block. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were also performed. The majority of liquid medicines had pH ≤ 5.50. G1, G4, and G5 showed alterations in Ra when compared with G7 (p < 0.05). According to Sa and Gap results, only G5 was different from G7 (p < 0.05). Alteration in surface was more evident in G5 SEM images. EDS revealed high concentrations of carbon, oxygen, phosphorus, and calcium in all tested groups. Despite the low pH values of all evaluated medicines, only Alivium®, Clavulin®, and Claritin® increased linear surface roughness, and only Claritin® demonstrated the in vitro capacity to produce significant tooth structure loss.

In vitro interference by acetaminophen, aspirin, and metamizole in serum measurements of glucose, urea, and creatinine.

OBJECTIVE: Here we aimed to investigate the in vitro effects of three analgesic-antipyretic drugs frequently used in clinical practice in Mexico - acetaminophen (AAP), aspirin (ASA) and metamizole (MMZ) - on serum measurements of glucose, urea, and creatinine. DESIGN AND METHODS: Each analyte was measured in a base-serum pool spiked with the drugs at subtherapeutic, therapeutic, and toxic doses. Serum glucose and urea were measured using the hexokinase/G-6PDH and urease/GLDH kinetic assays, respectively. Serum creatinine (SCr) was measured with a Jaffe procedure based on the alkaline-picrate reaction and with an enzymatic dry-chemistry system. Measurements were carried out in IL-Monarch and Vitros DT60-II analyzers, respectively. Data were analyzed by the difference-paired interference test and by ANOVA. RESULTS: By the kinetic Jaffe/Monarch procedure, we found positive interference by the drugs on the SCr measurements and by only ASA for urea measurement. For creatinine measurements, the total errors (TEs) were 22-51%, 18-105%, and 15-26% for AAP, ASA, and MMZ respectively, while for urea measurement the TE was 16-21% for ASA. A negative interference by MMZ on SCr (TE=-47%), but no-interference for AAP or ASA, were found via the enzymatic/DT60-II system. CONCLUSIONS: In vitro positive interference induced by AAP, ASA, and MMZ (via the alkaline-picrate reaction), or negative interference by MMZ (via a dry-chemistry system), on the SCr measurements highlights the importance of investigating all possible sources of variation that may alter the accuracy of the laboratory tests, in order to provide useful results for making medical decisions for optimal patient care.

Hypothermic and antipyretic effects of 3-methyl- and 3-phenyl-5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole-1-carboxyamides in mice.

The effect of novel pyrazolines, 3-methyl-5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole-1-carboxyamide (MPCA) and 3-phenyl-5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole-1-carboxyamide (PPCA) on body temperature and endotoxin-induced fever was investigated in mice. The subcutaneous (s.c.) administration of 1.5 mmol/kg dipyrone, MPCA or PPCA and the intracerebroventricular (i.c.v.) administration of 225 nmol dipyrone reduced basal rectal temperature. Intracerebroventricular administration of 225 nmol MPCA or PPCA did not alter basal rectal temperature. The administration of 0.15 mmol/kg (s.c.) or 25 nmol (5 microl) dipyrone (i.c.v.), MPCA or PPCA had no effect on basal rectal temperature, but reversed lipopolysaccharide-induced fever. These results suggest that MPCA and PPCA cause antipyresis, which is similar to that caused by dipyrone, and may be useful antipyretic agents.

Tune compounds for electrospray ionisation/in-source collision-induced dissociation with mass spectral library searching.

Haloperidol, paracetamol, metronidazole and metamizole have been tested as tune compounds for electrospray ionisation in-source collision-induced dissociation MS (ESI-CID-MS) with two different mass spectrometers (Sciex API 365 and Agilent 1100 MSD SL). The different electrospray sources of API 365 and MSD 1100 SL consist of an orifice with nitrogen curtain gas and a capillary interface, respectively. In-source CID occurs in both interfaces in front of the skimmers, which separate a region with a vacuum of approximately 300 Pa and the high vacuum (<10(-3) Pa). Comparison of the breakdown curves of selected tune compounds, depending on collision energy (orifice or fragmentor voltage), showed, that very similar fragmentation can be obtained with both instruments, when adjusting the fragmentor voltage of the MSD 1100 SL to higher values than the orifice voltage of the API 365. For three energy levels--low, medium and high--the corresponding voltages were 20, 50 and 80 V for the API 365 and 110, 190, 230 V for the MSD 1100 SL. These voltages resulted in the most similar spectra for haloperidol and paracetamol with both instruments. The comparison of ESI-CID-MS of all tune compounds at three energy levels showed, that - despite variations in relative ion abundances - all significant ions were present in one of the three CID spectra. Therefore, mass spectral library searching of an ESI-CID-MS library set-up with one of the two instruments should be possible with the other instrument after adjusting the CID energies by means of at least two tune compounds such as haloperidol and paracetamol, metronidazole or metamizole.

Amperometric determination of dipyrone in pharmaceutical formulations with a flow cell containing gold electrodes from recordable compact discs.

A simple, rapid, and precise amperometric method for quantification of dipyrone in pharmaceutical formulations is presented. The proposed method permits determinations in the 10(-7) mol L(-1) of the analyte and enables 90 determinations h(-1), employing only 100 microL of sample per determination. This method is based on the direct quantification of dipyrone in many pharmaceutical products, avoiding cumbersome processes such as previous separations, solvent extraction, or sample filtration. This new procedure was applied to commercial pharmaceutical tablets, and the results obtained were in excellent agreement with the ones obtained by the classical iodometric method.

Characterization of the role of physicochemical factors on the hydrolysis of dipyrone.

Dipyrone is a prodrug which is used mainly for its analgesic and antipyretic effects. After oral intake, dipyrone is rapidly hydrolyzed to its main metabolite, 4-methylaminoantipyrine (4-MAA), from which many other metabolites are produced by enzymatic reactions. Even though it is well known that dipyrone is a prodrug and hydrolyzed non-enzymatically, in most of the studies of dipyrone the prodrug form is tested using in vitro methodologies, which do not represent or predict the actual in vivo activity of dipyrone. In this study, we characterize the hydrolysis kinetics of dipyrone as functions of concentration, temperature, and pH using a HPLC assay. Concentration is an important factor in the hydrolysis of dipyrone. Low concentrations of dipyrone are hydrolyzed more rapidly than are solutions of higher concentrations. At a concentration of 0.1M, which is 140 times, the concentration of the marketed pharmaceutical form, dipyrone is only minimally (10%) hydrolyzed to 4-MAA at 5h. Temperature, as expected, affects the hydrolysis reaction dramatically. We tested three temperatures (4, 21, and 37 degrees C) and found that at body temperature the hydrolysis is significantly faster than at room or at refrigerator temperatures. Compared with more alkaline solutions, the hydrolysis rate of dipyrone increases dramatically in acidic solutions. At low pH (2.5) and at a 0.01 mM concentration, the hydrolysis of dipyrone is completed within almost 30 min, which is the highest rate we observed. Experiments which involve in vitro and/or local application of dipyrone should consider these physicochemical factors and interpret the results accordingly.