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Development of a multicommuted flow-through optosensor for the determination of a ternary pharmaceutical mixture.

The combination of multicommutation and flow-through multioptosensing is presented in this work as a powerful strategy for the routine analysis of active principles in pharmaceuticals. By coupling methodologies, the selectivity and sensitivity of optosensors is maintained, while the use of the multicommutation approach provides additional advantages, such as low reagent consumption, low waste generation and reduced human supervision. The potential of this integration is enhanced when implemented with multiwavelength detection mode. An UV sensor is here developed for the simultaneous determination of three widely used active principles: salicylamide, caffeine and propyphenazone. The measuring wavelengths were 276 nm for caffeine and propyphenazone, and 302 nm for salicylamide. The five three-way solenoid valves used in the system are controlled by Java-written home-made software. The sensor is based on the on-line selective retention of two of the three analytes on a precolumn placed just before the sensing zone and filled with the same solid support than the flow-through cell (C(18) silica gel). This approach allows the sequential arrival of the analytes to the sensing zone, so allowing their determination with only one sample injection. So, the use of C(18) placed, in both the precolumn and the flow-cell combines the advantages of the increase of sensitivity and selectivity in the detection solid zone with the additional increase of the selectivity in the precolumn. The sensor was applied to the determination of the analytes in several pharmaceutical preparation of the Spanish Pharmacopoeia, obtaining satisfactory results.

Antipyrine↗

Potential neuroleptic agents. 4. Chemistry, behavioral pharmacology, and inhibition of [3H]spiperone binding of 3,5-disubstituted N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-methoxysalicylamides.

A series of 3,5-disubstituted N-[(1-ethyl-2-pyrrolidinyl) methyl]-6-methoxysalicylamides was synthesized, starting from the 2,6-dimethoxybenzoic acids, by boron tribromide demethylation of the corresponding 3,5-disubstituted 2,6-dimethoxybenzamides and separation of the two positional isomers. The correct structure assignments were based on selective decoupling studies on their 13C NMR spectra. The salicylamide derivatives were tested for antidopamine activity in vivo by their ability to inhibit the apomorphine syndrome in the rat and in vitro by their ability to displace [3H]spiperone from striatal preparations of the rat brain. The activity seems to reside exclusively in the S enantiomer. Several compounds were considerably more potent than haloperidol, particularly those having an ethyl group in the 3-position and a halogen atom in the 5-position of the aromatic ring. The corresponding 5-alkyl-3-halogen-substituted compounds were much less active. A low acute toxicity was found for the most potent compounds. Some of the salicylamides displayed a 10-20-fold separation between the dose which blocks apomorphine-induced hyperactivity and that which blocks apomorphine-induced stereotypy. One compound, S-(-)-3,5-dichloro-N-[(1-ethyl-2-pyrrolidinyl) methyl]-6-methoxysalicylamide (raclopride, FLA 870) (13) had a stereotypy--hyperactivity separation more than twice that of sulpiride while being 100 times more potent in blocking the apomorphine effects. On this basis, 13 was selected for clinical trials against schizophrenia.

Animals↗

N-fluoroalkylated and N-alkylated analogues of the dopaminergic D-2 receptor antagonist raclopride.

A series of raclopride [(S)-2-[(3,5-dichloro-6-methoxy-2- hydroxybenzamido)methyl]-1-ethylpyrrolidine] derivatives bearing pyrrolidino N-fluoroalkyl or -alkyl substituents were synthesized and evaluated as potential dopaminergic receptor-based positron tomography radiopharmaceuticals. Radiosynthetic procedures for producing the corresponding N-[18F]fluoroalkylated analogues of raclopride from 18F- (beta+, t1/2 = 110 min) in high specific activity were also developed. In vitro binding assays using competitive displacement of [3H]spiperone from primate caudate tissue indicated that the N-alkylated analogues of raclopride had Ki values of 5-40 nM, whereas the corresponding values for analogous N-fluoroalkylated derivatives ranged from 90-160 nM. The relatively low D-2 binding affinity of these fluorinated salicylamides was corroborated by in vivo tissue biodistribution results in rodents. On the basis of structure-binding correlations, the impact of intramolecular hydrogen bonding, ligand basicity, and steric bulk on the affinity of the benzamides for D-2 receptor binding are discussed. Strategies are presented for the development of alternative fluorinated salicylamides that are both receptor active and metabolically stable.

Animals↗

Effects of various in vitro--inhibitors of benzo(a)pyrene metabolism in isolated rat lung perfusion.

Various in vitro-inhibitors were added with 3H-benzo(a)pyrene (BP) into the perfusion fluids in isolated rat lung perfusions to see whether their effects are dependent on the integrity of tissue. 3H-BP and its metabolites were measured by thin-layer chromatography and radiometry from both samples of perfusion medium and homogenates of lung tissue. The total covalent binding to lung tissue was used as a measure of the formation of reactive metabolites. In methylcholanthrene-induced rat lung, the metabolism of BP was inhibited by alpha-naphthoflavone, an inhibitor of monooxygenase, and less with diethylmaleate, a depletor of glutathione, with salicylamide, an inhibitor of conjugases, and, astonishingly, with D-saccharo-1,4-lactone, an inhibitor of beta-glucuronidase. With trichloropropene oxide, which inhibits epoxide hydratase, the metabolism was either decreased or unchanged. Nicotine had no effect on BP-metabolism. Nicotine and diethylmaleate increased statistically significantly and alpha-naphthoflavone and salicylamide decreased the covalent binding of radioactivity to lung tissue. In most cases, the changes in BP metabolism observed during perfusion can be explained on the basis of effects of modifiers on the enzyme systems.

Animals↗

Black lipid membranes as a model for intestinal absorption of drugs.

Black lipid membranes were generated in isotonic buffer (pH 4-5 and pH 6-5) from egg phosphatidylcholine and intestinal lipid, and the permeability to salicylamide, salicylic acid, p-aminobenzoic acid and tryptophan of these membranes was studied. Electrical resistance of intestinal lipid membranes was higher than that of phosphatidylcholine membranes. The presence of cholesterol produced an increase in the electrical resistance of black lipid membranes and a small decrease in the permeability of membranes to drugs. The permeability coefficient of salicylamide, an uncharged drug, was much larger than the coefficients of the charged drugs examined. The values for salicylic acid and p-aminobenzoic acid were much larger than comparable values predicted from their partition coefficients. Intestinal lipid membranes were more permeable to acidic drugs than phosphatidylcholine membranes. It is suggested that phospholipids and other lipid components of the small intestine may play an important role in the membrane permeability to acidic drugs. This method may be of interest in studying the complex processes of drug absorption from intestine.

4-Aminobenzoic Acid↗

Effects of aspirin-like drugs on mitogen-stimulated DNA synthesis of lymphocytes from pregnant rats and offspring.

Previous studies have shown that salicylates and protein-calorie malnutrition compromise immunological responses in humans and experimental animals. The present study compared the effects of prenatal normal and low protein diets, with and without aspirin-like drug treatments, on lymphocyte blastogenesis measured by tritiated thymidine uptake for DNA synthesis in splenic lymphocytes from pregnant rats and their offspring following stimulation with the mitogens concanavalin A, phytohemagglutinin, and pokeweed mitogen. Aspirin treatment was associated with increased lymphocyte thymidine uptake for blastogenesis in pregnant rats fed the normal protein control diet and their offspring. The phytohemagglutinin-stimulated increase detected in offspring lymphocytes could not be statistically guaranteed. A low protein diet alone and a normal protein diet combined with salicylamide treatment was associated with decreased blastogenesis in pregnant rats but not in their offspring. Salicylamide or aspirin combined with a low-protein diet decreased blastogenesis in both dams and their offspring. Aspirin combined with a normal protein diet did not adversely affect blastogenesis in either pregnant rats or their offspring. This study suggests that low dietary protein and aspirin-like drugs may independently decrease lymphocyte blastogenesis of pregnant rats and in combination they may also reduce lymphocyte blastogenesis in offspring. The significance of increased lymphocyte blastogenesis in both mothers and offspring following aspirin treatment of pregnant rats fed a normal protein diet is unclear.

Animals↗

Effect of taurine on the gastrointestinal absorption of drugs--ionic requirement for the action.

In order to resolve the mechanism of taurine-induced enhancement of drug absorption, the effect of ionic components of the luminal solutions on drug absorption was examined by using the loop of rat stomach in situ. K+ has its remarkable influence on the control values of aspirin absorption. The control values, at and above 25 mM already reached to a nearly corresponding degree as that of taurine-induced enhancement, resulting in apparent disappearance of enhancement effect. On the other hand, the action of taurine on salicylamide absorption is revealed to be K+ concentration-dependent, whereas all the control values remain fairly constant. Moreover, at the higher concentration of 10 mM, aspirin absorption turned out to be significantly inhibited in the presence of taurine, and this finding is supposed to be attributed to the protection of taurine against aspirin-induced gastric mucosal damage. On the contrary, salicylamide absorption was greatly enhanced. All these results clearly support that the mechanism of action of taurine toward both drugs should be separately considered.

Animals↗

Vascularly perfused rat small intestine: a research model for drug absorption.

Rat isolated small intestine was perfused at a fixed flow rate through the superior mesenteric artery with whole rat blood recycled from a devised oxygenator-reservoir. As indicated by perfusion pressure, tissue glucose and oxygen consumption, and histological studies, the perfused intestine remained in a viable state over the perfusion period of 2 hr. Rapid absorption of glucose from the intestinal tract was observed after the intraduodenal injection. When single doses of acetaminophen were injected into the duodenal lumen or poured over the perfused intestine, the absorption was rapid and dose-dependent. Shortly after single intraduodenal injections of salicylamide, salicylamide in free and conjugated forms (sulfate and glucuronide) appeared in the circulating blood. These results indicate that the vascularly perfused intestinal preparation has wide applications in biochemical experimental fields.

Acetaminophen↗

Enhanced bioavailability and decreased clearance of analgesics in patients with cirrhosis.

The effect of moderate cirrhosis on the bioavailability and systemic clearance of three model analgesic compounds (pethidine, pentazocine, and salicylamide) with substantial first-pass metabolism was examined in 8 cirrhotic subjects and 4 agematched healthy controls. There was a 46% decrease in the clearance of pentazocine and a 278% increase in bioavailability. The corresponding figures for pethidine were 36% and 81%. The area under the plasma curve after oral salicylamide was increased by 551% in cirrhotic subjects compared with controls. This study demonstrated that drugs with the highest hepatic clearance will have the largest relative increases in bioavailability in cirrhotic patients due to portosystemic shunting. The decrease in clearance and increase in bioavailability will have multiplicative, rather than simply additive, effects on total area under the curve and, if related, pharmacologic response.

Adult↗

The construction and uses of factorial designs in the preparation of solid dosage forms. Part 3. Effect of temperature and time on the mechanical properties of sintered tablets.

The present and forecoming series of experiments illustrate the application of factorial design to the study of the sintering phenomena of pharmaceutical tablets. This part was concerned with the effect of temperature (X1) and time (X2) on the mechanical properties of sintered tablets. A 2 X 2 design was developed for salicylamide tablets with the two factors at two levels, and a 3 X 3 design for phenobarbital tablets with the two factors at three levels. Analysis of variance was used to determine the significant effects. Empirical regression equations were obtained which indicated that the hardness of sintered tablets was markedly improved by using the high level of X1 at the low level of X2 in phenobarbital tablets, and the high levels of both X1 and X2 in salicylamide tablets. The tablets tensile strength was a linear function of X1 and X2, but the interaction effect X1X2 was insignificant. Significant quadratic effects of X2/2 and/or X2/1 were also detected for the mechanical properties of phenobarbital tablets.

Drug Compounding↗

The construction and uses of factorial designs in the preparation of solid dosage forms.

The present experiments were factorially designed to study the effect of particle size (X3), at different levels of both temperature (X1) and time (X2), on the hardness and mechanical strength of sintered tablets. A 2 X 2 X 3 design was constructed for salicylamide tablets with X1, X2 and X3 at 2,2 and 3 levels respectively. For phenobarbital tablets, a 3 X 3 X 3 factorial experiment was run. On the basis of analysis of variance, empirical regression equations have been developed. Within the limits of the factors, it was found that the quadratic effect of X 2/3, on the average, was the most significant. The significance of the linear effects was in the following order: X3 greater than X1 greater than X2 in salicylamide tablets and X1 greater than X3 greater than X2 in phenobarbital tablets. A change of X3 from the high to the low or intermediate levels caused an increase in the mechanical properties of tablets. The only linear interaction was that of X1X3 for the hardness data of phenobarbital tablets, but it was of least significance among the other effects. Other quadratic main effects of X 2/1, X 2/2 and quadratic interaction effects of X 2/3X1 and X 2/1X2 were also found to be significant. The optimum values of the factors studied, that would maximize any given mechanical property, were located.

Drug Compounding↗

The oriented development of antituberculotics: salicylanilides.

On the basis of our previous results 22 salicylanilides were synthesized. The compounds were tested for in vitro antimycobacterial activity against Mycobacterium tuberculosis, Mycobacterium kansasii, and Mycobacterium avium. The Free-Wilson method was used to evaluate structure-antimycobacterial activity relationships. 4-Chloro-N-(4-propylphenyl)salicylamide and 5-chloro-N-(4-propylphenyl)salicylamide were selected for preclinical studies.

Antitubercular Agents↗

High-pressure liquid chromatographic determination of salicylic acid in aspirin powder and pharmaceutical dosage forms.

A sensitive, simple, and rapid method for the quantitation of salicylic acid in aspirin powders and its dosage forms was developed. The method is based on reversed-phase high-pressure liquid chromatography using a mobile phase containing 20% methanol in aqueous phosphate buffer of pH 2.3. Other common ingredients present with aspirin such as acetaminophen, caffeine, codeine phosphate, phenacetin, and salicylamide do not interfere. Salicylic acid quantities as low as 0.1 microgram can be assayed with a relative standard deviation of +/- 2.3%. Sensitivity can be increased by using lower sensitivity settings. The method was tried on numerous commercial products and an old aspirin powder. The results generally were excellent, except that all of the aspirin and salicylic acid could not be extracted from suppositories. The old aspirin powder failed the USP limit test for salicylic acid. The powder apparently absorbed moisture and contained salicylamide as an impurity.

Aspirin↗

Molecular interaction between riboflavin and salicylic acid derivatives in nonpolar solvents.

The interaction of riboflavin-2',3',4',5'-tetrabutyrate (I) with salicylic acid (II), aspirin (acetylsalicylic acid, III), and salicylamide (IV) has been spectroscopically investigated to determine the binding mechanism. NMR and absorption spectra were measured in nonpolar solvents. The association constant K of the formation of complex was calculated from the absorption spectra. Compounds I and II form a 1:1 cyclic hydrogen-bonded dimer through the N-3 proton and the C-2 carbonyl oxygen of the isoalloxazine ring, and the carboxylic hydroxyl proton and carbonyl oxygen of II. Compounds I and III form a 1:1 cyclic hydrogen-bonded dimer by the same mode. Compound IV forms a 1:1 cyclic hydrogen-bonded dimer with I through the N-3 proton and the C-2 carbonyl oxygen of the isoalloxazine ring, and the amino proton and the carbonyl oxygen of IV. Salicylates produce marked changes in the absorption spectra of I. These spectral changes are attributed to the formation of the hydrogen-bonded dimer. It appeared that the strongest complex was formed with salicylic acid, a weaker one with aspirin, and an even weaker one with salicylamide.

Chemical Phenomena↗

Influence of various drugs on the glass transition temperature of poly(vinylpyrrolidone): a thermodynamic and spectroscopic investigation.

PURPOSE: To determine the influence of hydrogen bonding and solubility parameter on the glass transition temperature (T(g)) of various drug-poly(vinylpyrrolidone) blends. METHODS: The T(g) of PVP films containing either acetaminophen, naproxen, salicylamide, carbamazepine, griseofulvin or propranolol hydrochloride were measured using differential scanning calorimetry. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction was used to characterize the specific interactions between the drug-PVP blends and the physical state of the films, respectively. The total solubility parameter and its individual components were calculated using the method of Van Krevelen. RESULTS: Salicylamide displayed the greatest plasticizing effect, depressing the T(g) to the minimum. This was consistent with the FTIR data, which indicated the presence of hydrogen bonding with PVP. Griseofulvin showed the least plasticizing effect due to lack of interaction with PVP. All the drugs except griseofulvin were amorphous within the film up to 30% (w/w) drug composition. The correlation between the various components of the solubility parameters and the plasticizing effect of drugs was very poor. CONCLUSIONS: Spectroscopic investigation for the presence of interaction between the drugs and PVP proved to be extremely predictive of the plasticizing effect of various drugs. In contrast, solubility parameters appeared to be far less sensitive indicators of drug-PVP miscibility.

Chemistry, Pharmaceutical↗

Physicochemical properties of amorphous precipitates of cimetidine-indomethacin binary system.

We have found that the binary system, consisting of a precipitate of cimetidine and naproxen, became amorphous due to intermolecular interaction. In order to clarify the interaction between cimetidine and other drugs, the physicochemical properties of binary systems consisting of cimetidine and drugs, phenacetin, salicylamide or indomethacin, were investigated. X-ray powder diffraction patterns and thermal analysis findings for the precipitates indicated that the cimetidine-indomethacin system has an amorphous structure, whereas the cimetidine-phenacetin and cimetidine-salicylamide systems do not. Fourier-transform infra-red (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy findings suggested that there is an intermolecular interaction between a proton in the imidazole ring of cimetidine and the C=O in the COOH of indomethacin. Since an interaction by the hydrogen bond between cimetidine and indomethacin would prevent three-dimensional arrangements of the molecules, the precipitate would be amorphous. In the cimetidine-indomethacin system, decarboxylation of indomethacin occurred below the melting temperature, indicating that the chemical stability decreased upon precipitation. Cimetidine was found to interact with drugs with a carboxyl group. The interaction would be applicable to make the amorphous system of the drugs and increase the solubility of the drugs.

Anti-Inflammatory Agents, Non-Steroidal↗

Syntheses and relaxation properties of mixed gadolinium hydroxypyridinonate MRI contrast agents.

The tripodal ligand tris[(3-hydroxy-1-methyl-2-oxo-1,2- didehydropyridine-4-carboxamido)ethyl]amine (TREN-Me-3,2-HOPO) forms a stable Gd3+ complex that is a promising candidate as a magnetic resonance imaging (MRI) contrast agent. However, its low water solubility prevents detailed magnetic characterization and practical applicability. Presented here are a series of novel mixed ligand systems that are based on the TREN-Me-3,2-HOPO platform. These new ligands possess two hydroxypyridinone (HOPO) chelators and one other chelator, the latter of which can be easily functionalized. The ligands described use salicylamide, 2-hydroxyisophthalamide, 2,3-dihydroxyterephthalamide, and bis(acetate) as the derivatizable chelators. The solution thermodynamics and relaxivity properties of these new systems are presented. Three of the four complexes (salicylamide-, 2-hydroxyisophthalamide-, and 2,3-dihydroxyterephthalamide-based ligands) possess sufficient thermodynamic stability for in vivo applications. The relaxivities of the three corresponding Gd3+ complexes range from 7.2 to 8.8 mM-1 s-1 at 20 MHz, 25 degrees C, and pH 8.5, significantly higher than the values for the clinically employed polyaminocarboxylate complexes (3.5-4.8 mM-1 s-1). The high relaxivities of these complexes are consistent with their faster rates of water exchange (< 100 ns), higher molecular weights (> 700), and greater numbers of inner-sphere coordinated water molecules (q = 2) relative to those of polyaminocarboxylate complexes. A mechanism for the rapid rates of water exchange is proposed involving a low energy barrier between the 8- and 9-coordinate geometries for lanthanide complexes of HOPO-based ligands. The pathway is supported by the crystal structure of La[TREN-Me-3,2-HOPO] (triclinic P1: Z = 4, a = 15.6963(2) A, b = 16.9978(1) A, c = 17.1578(2) A, alpha = 61.981(1) degrees, beta = 75.680(1) degrees, gamma = 71.600(1) degrees), which shows both 8- and 9-coordinate metal centers in the asymmetric unit, demonstrating that these structures are very close in energy. These properties make heteropodate Gd3+ complexes promising candidates for use in macromolecular contrast media, particularly at higher magnetic field strengths.

Contrast Media↗