OBJECTIVES The objectives of this study were to assess the bioavailability of an optimized mephenamic acid (MFA) microspheres (test) against a Ponstan® capsule (reference) in healthy volunteers, and to establish a correlation with in vitro parameters. SUBJECTS AND METHODS Four subjects received the test and reference (250 mg MFA each) in a randomized crossover design, separated by a 1-week washout period. The drug was analyzed in plasma by a specific high-performance liquid chromatographic method. The relevant pharmacokinetic parameters [maximum plasma concentration (C(max)), time of peak concentration (T(max)), area under plasma concentration-time curves from 0 to 12 h (AUC(0-12)) and area under plasma concentration-time curves from zero to ∞ (AUC(0-)∞)] were calculated from the plasma drug concentration-time data. RESULTS The test product exhibited faster absorption (T(max) of 1.87 ± 0.482 vs. 2.14 ± 0.20 h; C(max) of 5.91 ± 0.604 vs. 3.58 ± 0.671 μg/ml) when compared to the reference. The relative bioavailability of the test compared to the reference capsule was 172%. Good correlations were established between the in vitro 90% dissolution (T90) and each of the AUC(0-12) and T(max), as well as between the percentage of drug released and plasma concentrations. CONCLUSION The formulation of MFA microsphere with polyethylene glycol improved the dissolution rate and bioavailability of MFA, as evidenced by a higher C(max), AUC(0-12) and AUC(0-)∞, and shorter T(max) values. Good correlations between T90 and both AUC(0-12) and T(max) as well as between the percentage of drug released and plasma concentrations were achieved.

Mefenamic acid is a nonsteroidal anti-inflammatory drug commonly used in analgesia. The use of this drug has been implicated in several cases of nephrotoxicity including acute renal failure and tubulointerstitial nephritis. One theory of drug-induced tubulointerstitial nephritis is that the drug or a derivative of the drug becomes irreversibly bound to certain sites in renal tissue and an immune response is directed against the hapten-host conjugate. Previous studies have shown that in humans the nonsteroidal anti-inflammatory drug mefenamic acid is metabolized by both phase I enzymes and the phase II enzyme family UDP-glucuronosyltransferase. Indeed, three glucuronides were identified and isolated from human urine by semipreparative HPLC after oral administration of mefenamic acid. This study focuses on mefenamic acid glucuronide and further characterizes this acyl glucuronide in terms of stability and its ability to bind irreversibly to proteins. Stability studies of mefenamic acid glucuronide in aqueous buffer highlighted the relative stability of this acyl glucuronide at physiological pH. The half-life at 37 degrees C, pH 7.4, was 16.5 +/- 3.1 hr, which is considerably longer than those reported for many acyl glucuronides. The degradation of mefenamic acid glucuronide was accelerated under alkaline conditions, decreasing the half-life to 5 +/- 1.6 hr at pH 8.0. Mefenamic acid glucuronide, although extremely stable in buffer at physiological pH, was found to bind irreversibly to human serum albumin in vitro. Irreversible binding to cellular proteins in culture was also evident with the addition of mefenamic acid to the heterologous Chinese hamster lung fibroblast cell line V79 expressing the human UDP-glucuronosyltransferase isoenzyme UGT1*02. This binding was directly related to glucuronide formation, because irreversible binding was not evident in the untransfected cell line V79.

The effect of various antacids on the absorption of tolfenamic and mefenamic acids has been investigated in three separate crossover studies, each consisting of four phases. Single doses of magnesium hydroxide (85 mg, 425 mg and 1700 mg) or of water (150 ml) were given by mouth to 6 healthy volunteers immediately after tolfenamic acid 400 mg (Study 1), and, using an identical study design, after mefenamic acid 500 mg (Study 3). In Study 2 sodium bicarbonate 1 g, aluminium hydroxide 1 g, an antacid preparation containing both aluminium and magnesium hydroxides, or water alone were ingested with tolfenamic acid 400 mg. Plasma concentrations of tolfenamic and mefenamic acids and their cumulative excretion in urine were determined up to 24 h. Magnesium hydroxide greatly accelerated, in a dose-dependent manner the absorption of both tolfenamic and mefenamic acids. The peak times in plasma were shortened by about 1 h by 425 mg and 1700 mg magnesium hydroxide, and the peak plasma concentrations of both fenamates were elevated up to 3-fold. The area under the plasma concentration-time curve between 0 and 1 h of tolfenamic acid was increased up to 7-fold and that of mefenamic acid up to 3-fold. The total bioavailability of tolfenamic and mefenamic acids was only slightly increased. Aluminium hydroxide alone and in combination with magnesium hydroxide significantly retarded the absorption and lowered the peak plasma concentration of tolfenamic acid. Sodium bicarbonate had no significant effect on its absorption. The interaction with magnesium hydroxide leads to higher and earlier peak plasma concentrations of the fenamates.(ABSTRACT TRUNCATED AT 250 WORDS)

Mefenamic acid is a problematic drug in granulation, tableting, and dissolution due to its poor solubility, hydrophobicity, and tendency to stick to surfaces. In most cases, the specifications of a drug by the pharmacopoeia include identification and purity, but they do not describe the physicochemical drug properties precisely. To characterize the mefenamic acid particle size, surface area measurements, X-ray pattern, differential scanning calorimetry (DSC), wettability, crystal habit, and compression behavior of different batches from two manufacturers were investigated. Due to larger particle size and better wettability, mefenamic acid of Il Yang type was easier to handle in a granulation process. The compression behavior of both types was nearly the same, although particle size, crystal habit, and wettability were very different.

A quantitative method for the analysis of flunixin, 2-(2-methyl-3-trifluoromethylanilino) nicotinic acid, in equine urine by gas chromatography with nitrogen-phosphorus detection has been developed. Flunixin and the internal standard, mefenamic acid, N-(2,3-xylyl) anthranilic acid, were analysed after extractive methylation of the carboxylic acid group using methyl iodide. The extraction and alkylation conditions of flunixin and mefenamic acid have been studied. The detection limit of the method was 0.25 mumol/l flunixin in urine (74 ng/ml). Flunixin was found to be conjugated to 96.5% in equine urine, and the conjugate was spontaneously hydrolysed to free flunixin. This approach can also be used to confirm the presence of flunixin or mefenamic acid in horse urine in the doping control of racehorses.

PURPOSE Prodrug of non-steroidal anti-inflammatory drugs (NSAIDs) or NSAIDs linked with guaiacol have been reported to suppress gastrointestinal (GI) toxicity or induce GI protective effect. In this study. mefenamic-guaiacol ester was synthesized and its physicochemical properties. stability, and transport across Caco-2 monolayers were investigated. METHODS Synthesis of the ester was carried out using mefenamic acid, guaiacol. N. N'-dimethylaminopyridine, and N,N'dicyclohexylcarbodiimide. The hydrolysis of the ester was investigated in aqueous buffer solutions pH 1-12 as well as in Caco-2 homogenate, human plasma, and porcine liver esterase. Caco-2 cell monolayers were utilized for transport studies. Due to the high lipophilicity of the ester with a calculated logP of 6.15, bovine serum albumin (BSA, 4%) was included in the receiver compartment to obtain a good in vitro-in vivo correlation. Permeation of the ester was assessed with or without the exposure of cells to PMSF, an inhibitor of esterase. RESULTS The ester was stable at a wide pH range from 1-10. However, it was hydrolyzed by enzymes from porcine liver esterase and Caco-2 homogenate. With the PMSF exposure on the apical (AP) side and in the presence of 4% BSA on the basolateral (BL) side, the transported amount of the ester from AP-to-BL direction was 14.63% after 3 hr with a lag time of 23 min. The Papp for the ester was 4.72 x 10(-6) cm s(-1). CONCLUSION The results from hydrolysis studies indicate that this ester is a prodrug. The Papp value suggests the moderate absorption characteristic of the compound. The accumulation of this highly lipophilic ester in Caco-2 cells is reduced in the presence of BSA.

The objectives of these studies were, first, to determine the effect of elevated luminal viscosity on the gastrointestinal absorption of four model drugs and, second, to identify the key processes influencing drug absorption under elevated viscosity conditions. Studies were conducted in vitro and in healthy female mongrel dogs under fasting conditions. In the canine model, both the rate and extent of paracetamol and hydrochlorothiazide absorption were significantly decreased by the coadministration of 15 g guar gum dissolved in 500 ml normal saline. In the case of cimetidine, the rate but not extent of absorption was decreased. Owing to the high variability in the data, no statistically based conclusion could be drawn about the effects of coadministered guar gum on the oral absorption of the poorly soluble mefenamic acid. Based on the in vitro data, it appears that substantial reductions in the dissolution rate of paracetamol, hydrochlorothiazide and cimetidine account for the effects observed in vivo. It is concluded that the effect of an elevation in the intraluminal viscosity on drug absorption is greatest for highly soluble drugs, and results from a combination of a decrease in dissolution rate and gastric emptying rate.

The preparation of mefenamic acid (MH)-alkanolamine [monoethanolamine, diethanolamine, triethanolamine and propanolamine] complexes was attempted to increase the transdermal flux of MH. A lipophilic enhancer system consisting of isopropyl myristate (IPM) and ethanol (9:1; EI system) produced a marked enhancement of MH flux from the alkanolamine complexes through hairless rat skin membrane. Among the alkanolamines examined, the propanolamine complex had the greatest enhancing effect on the permeation of MH. The observed permeation enhancement of MH-alkanolamine complexes by the EI system was explained by an analysis based on a two-layer diffusion model. The stratum corneum immersed in IPM forms a continuous phase of vehicle and stratum corneum and, from the phase, ethanol transport the MH-alkanolamine complexes to the epidermis and dermis, and the complexes, which are more water soluble than MH, exhibit increased partition into the epidermis and dermis, as the flux increases.

Optimum conditions for the preparation of non-magnetic and magnetic microspheres of albumin-globulin mix (alglomix) containing mefenamic acid have been standardized. The effect of various parameters has been investigated with regard to the appearance, yield, drug content and encapsulation efficiency. The physicochemical parameters of the microspheres such as density, particle size distribution, surface topography and wall thickness, as well as the magnetite contained within the magnetic microspheres, have been determined. The infrared spectroscopic analysis confirmed the encapsulation of the drug and absence of free drug on the surface of the microspheres. The X-ray diffraction analysis confirmed that the crystallinity of the drug remained unchanged indicating thereby that no complex formation had taken place between core and coat materials. The in vitro release profiles of the microspheres have been studied. An attempt has also been made to check the in vivo efficacy in rats.

Three major metabolites of mefenamic acid were isolated from the urine of a normal adult man receiving mefenamic acid orally. The structures of those metabolites were determined as glucuronides of mefenamic acid, its hydroxymethyl derivative, and its carboxylic acid derivative on the basis of spectral data.

Encapsulation of mefenamic acid (MFA), a potent non-steroidal anti-inflammatory drug with cationic acrylic resin, Eudragit E, was carried out using a fluidized-bed granulator (Glatt AG). Three drug:polymer ratios were prepared using 50 ml of 1, 2.5 and 5 per cent w/v aqueous suspension of Eudragit to coat 100 mg powdered drug. The bioavailability of the coated and uncoated drug was studied using four groups of animals, each consisting of six male rabbits (2-2.5 kg). Investigations were performed using the rabbits to examine the effects of prolonged administration of the coated and the uncoated MFA with Eudragit E(1 and 5 per cent) in a dose of 100 mg filled in hard gelatin capsules. One capsule was given daily for 30 days. Plasma levels of MFA with Eudragit E were significantly higher than those of drug only. Meanwhile, 5 per cent w/v polymer coating afforded higher drug availability than 2.5 per cent w/v which induced a higher level than 1 per cent w/v. Chronic gastric ulcers with different severities were found in the internal mucosa of all animals. In addition, there were multiple erosions in the glandular mucosa of stomachs of rabbits receiving MFA within the treatment period. IN the control group the gastric photograph was normal in every instance. Despite the extensive morphological damage at the end of treatment, the observed changes in the stomach of rabbits given coated drug is less deleterious than that treated with uncoated drug. The results of this study indicate that the coating of MFA with cationic Eudragit E increases its bioavailability and decreases the probability of ulceration.(ABSTRACT TRUNCATED AT 250 WORDS)