2-氨基-5-甲基噻唑的合成及应用研究

以1，2，3－三氯丙烷为原料，与氢氧化钠反应生成2，3－二氯－1－丙烯（2），接着与硫氰酸钾反应并异构化生成2－氯－2丙烯基异硫氰酸酯（3），再与氨水反应得N－（2－氯－2－丙烯基）硫脲（4），然后再在80％的硫酸作用下环合得2－氨基－5－甲基噻唑（1），总收率由文献报道的24．3％提高到41．3％。利用（1）和吡罗昔康的中间体（5）缩合制得美洛昔康（6）。     

Powdered self-emulsified lipid formulations of meloxicam as solid dosage forms for oral administration

The objectives of this study were to prepare a powdered self-emulsified (SEDDS) formulation of meloxicam and to compare its oral bioavailability against commercial Mobic^® tablets. The SEDDS formulation was prepared by in situ salt formation of meloxicam in a blend of lipid excipients and aqueous tris (hydroxymethyl) aminomethane solution. The liquid SEDDS was subsequently adsorbed on silica powder and was tested for size, flow, and crystal growth. The flowability index of the powdered SEDDS was borderline acceptable. Absence of crystal growth with storage was confirmed by DSC and PXRD studies. Dissolution of meloxicam from the powdered SEDDS was >90% vs. <12% for powdered meloxicam and <80% for the commercial tablets. Stability of the powdered formulations after storage in gelatin and HPMC capsules was also evaluated to study the effect of water migration from the fill into capsule shells. Capsules softened to a different extent as a function of fill material with HPMC capsules showing greater resistance to water migration. Finally, oral bioavailability of the formulations was evaluated in beagle dogs. Powdered meloxicam SEDDS formulation showed a 1.3-fold increase in AUC vs. commercial Mobic^® tablets. Overall, this study described a novel SEDDS formulation of meloxicam and outlined a systematic approach to adsorbing and testing the flow and stability behavior of powdered SEDDS formulations.     

The binding of orally dosed hydrophobic active pharmaceutical ingredients to casein micelles in milk

Casein proteins (α_S1-, α_S2-, β- and κ-casein) account for 80% of the total protein content in bovine milk and form casein micelles (average diameter = 130 nm, approximately 10¹⁵ micelles/mL). The affinity of native casein micelles with the 3 hydrophobic active pharmaceutical ingredients (API), meloxicam [351.4 g/mol; log P = 3.43; acid dissociation constant (pK_a) = 4.08], flunixin (296.2 g/mol; log P = 4.1; pK_a = 5.82), and thiabendazole (201.2 g/mol; log P = 2.92; pK_a = 4.64), was evaluated in bovine milk collected from dosed Holstein cows. Native casein micelles were separated from raw bovine milk by mild techniques such as ultracentrifugation, diafiltration, isoelectric point precipitation (pH 4.6), and size exclusion chromatography. Acetonitrile extraction of hydrophobic API was then done, followed by quantification using HPLC-UV. For the API or metabolites meloxicam, 5-hyroxy flunixin and 5-hydroxy thiabendazole, 31 ± 3.90, 31 ± 1.3, and 28 ± 0.5% of the content in milk was associated with casein micelles, respectively. Less than ～5.0% of the recovered hydrophobic API were found in the milk fat fraction, and the remaining ～65% were associated with the whey/serum fraction. A separate in vitro study showed that 66 ± 6.4% of meloxicam, 29 ± 0.58% of flunixin, 34 ± 0.21% of the metabolite 5-hyroxy flunixin, 50 ± 4.5% of thiabendazole, and 33 ± 3.8% of metabolite 5-hydroxy thiabendazole was found partitioned into casein micelles. Our study supports the hypothesis that casein micelles are native carriers for hydrophobic compounds in bovine milk.     

The Effect of Mixed-Solvent and Terpenes on Percutaneous Absorption of Meloxicam Gel

The purpose of the present study was to develop the meloxicam transdermal dosage form. The response surface methodology was used to obtain an appropriate mixed-solvent system of pH-7.4 buffer and ethanol for preparing meloxicam hydrogel. The enhancement effects of terpenes on drug precautious absorption were evaluated via in vitro and in vivo study. The result showed that the solubility of meloxicam was dependent on the pH value of buffer solution. The mixed-solvent system of pH-7.4 buffer and ethanol had a synergistic effect on the increase of drug solubility. The highest solubility was obtained in the ratio of 50/50 pH 7.4 buffer/ethanol. A series of terpenes were used as enhancer for improving the penetration rate of meloxicam. The penetration rates were significantly increased by about 70–593 fold and the lag times were shortened from 7.92 to 0.17 hr by enhancer incorporation. Among these terpenes, menthol showed the greatest effect. In vivo penetration study, the AUC_48h was increased by about 1.7 fold by the addition of 5% menthol as enhancer.     

Preparation of a Solid Dispersion by a Dropping Methodto Improve the Rate of Dissolution of Meloxicam

Application of a solid dispersion system is one of the methods used to increase the bioavailability of poorly water-soluble drugs. Adaptation of the dropping method from the chemical industry as a formulation procedure may help the scaling-up process and simplify the formulation of poorly water-soluble compounds. Meloxicam (ME), a nonsteroidal anti-inflammatory drug that is poorly soluble in water, and polyethylene glycol (PEG) 4000, a water-soluble carrier, were formulated by using a dropping method in an attempt to improve the dissolution of ME. Pure ME and physical mixtures and tablets of ME–PEG 4000 (1:3 ratio) were compared as regards their dissolution with samples formulated by the dropping method. The results revealed that the round particles (solid drops) exhibited a higher dissolution rate than those of the physical mixtures, tablets, and pure ME. Self-modeling curve resolution (SMCR) as a chemometric method was used to evaluate X-ray powder diffractometry (XRPD) data. The results demonstrated the presence of a new crystalline phase in the solid dispersion, which can help the fast and quantitative dissolution from the solid drops. The round particles can be adapted to individual therapy by using a distributor.     

Nanostructured lipid carriers based nanogel for meloxicam delivery: mechanistic,in-vivo and stability evaluation

Aim: Our investigation was aimed to investigate the potential suitability of meloxicam-loaded nanostructured lipid carriers (MLX-NLC) gel for topical application.

Main methods: MLX-NLC gel was prepared and in vivo skin penetration ability of the NLC gel was evaluated using confocal laser scanning microscopy. We studied the effect of MLX-NLC gel on the changes in lipid profile of skin to get an insight into its skin penetration enhancement mechanism. Acetic acid induced writhing test was performed to evaluate the analgesic effect. Drug concentration-time profile of MLX in rat plasma and skin after topical and oral treatment with MLX-NLC gel and oral MLX-solution, respectively, was observed. MLX-NLC gel was subjected to primary skin irritation test, sub-acute dermal toxicity study. Storage stability of MLX-NLC gel was also assessed for 90 days.

Key findings: NLC gel was effective in permeating Rhodamine 123 to deeper layers of rat skin. Changes in skin lipid prolife were observed in the rat skin on treatment with MLX-NLC gel and the results supported skin lipid extraction as a possible penetration enhancement mechanism. MLX-NLC gel demonstrated sustained pain inhibitory effect. Pharmacokinetics study established that topical application of MLX-NLC gel had the potential to avoid systemic uptake and hence the risk of systemic adverse effects. MLX-NLC gel demonstrated good skin tolerability and biosafety. Excellent physical stability of nanogel was observed at 4?±?2?°C.

Significance: The study revealed that NLC gel is a promising carrier system for the topical application of MLX without side effects.     

Short communication: A comparison of 2 nonsteroidal antiinflammatory drugs following the first stage of a 2-stage fistulation surgery in dry dairy cows

Postoperative pain and its management following fistulation surgery in cattle are poorly understood. The purpose of this study was to compare 2 nonsteroidal antiinflammatory drugs (NSAID) as potential postoperative pain management treatments following the first stage of a 2-stage fistulation surgery. A randomized complete block design trial was conducted in dry Holstein cows (n = 10) following fistulation surgery. Ketoprofen (3 mg/kg of body weight i.m.) was administered on the day of surgery and 24 h later, whereas meloxicam (0.5 mg/kg of body weight s.c.) was administered once only on the day of surgery. Outcomes evaluated at 0, 2, 9, 24, 26, and 33 h postsurgery were heart rate, respiration rate, rectal temperature, and infrared temperature around the surgical site. Outcomes evaluated on the day of surgery and d 1 following surgery and compared with the average for the 4 d before surgery were lying activity (total lying time, total time spent lying on the left side, and percentage of time lying on the left side) and feed intake. A difference was observed in dry matter intake on d 1 but this effect was not different on d 0 compared with presurgical averages. A difference was observed in time spent lying on the left side and a difference was observed in heart rate following the first stage of fistulation surgery compared with presurgical averages. The infrared temperature readings around the surgical site were significantly greater in the hours following surgery compared with presurgical averages. The respiration rate increased over time after 24 h postsurgery compared with presurgical values. Although it was clear that the surgery is painful, the drug effects were more difficult to explain. On d 0 and 1, the meloxicam-treated cows ate 3 kg more but spent 101 min/d less time lying on their left side compared with ketoprofen-treated cows. The first stage of a 2-stage fistulation surgery was considered painful based on changes in heart rate, respiration rate, infrared temperature readings, dry matter intake, and time spent lying on the left side. It is clear that left flank surgery is painful and that NSAID can improve outcomes associated with that pain, but we cannot make recommendations as to which NSAID to choose based on these results.     

Meloxicam affects the inflammatory responses of bovine mammary epithelial cells

Nonsteroidal anti-inflammatory drugs are used as supportive therapy with antimicrobial treatments for mastitis in cows to alleviate pain of the inflamed mammary gland. They act mainly by inhibition of cyclooxygenases. Meloxicam (MEL) is a drug designed for cyclooxygenase-2 selectivity, which is upregulated upon inflammation, acting as a key enzyme for the conversion of arachidonic acid to prostaglandins. Although some studies in dairy cows showed positive results in recovery from mastitis when MEL was added to the treatments, direct effects of MEL on the immune system of mastitic cows are unknown. The aim of this study was to investigate effects of MEL on the immune response of bovine mammary epithelial cells (MEC) with or without simultaneous immune stimulation by pathogen-associated molecular patterns of common mastitis pathogens. Mammary epithelial cells from 4 cows were isolated and cultured. To evaluate dose effects of MEL, MEC were challenged with or without 0.2 µg/mL lipopolysaccharide (LPS; serotype O26:B6 from Escherichia coli) with addition of increasing concentrations of MEL (0, 0.25, 0.5, 1.0, 1.5, or 2.0 mg/mL). The addition of MEL prevented the increase of mRNA expression of key inflammatory factors in LPS-challenged MEC in a dose-dependent manner. To investigate the effects of MEL on pathogen-specific immune responses of MEC, treatments included challenges with LPS from E. coli and lipoteichoic acid from Staphylococcus aureus with or without 1.5 mg/mL MEL for 3, 6, and 24 h. Meloxicam prevented the increase of mRNA abundance of key inflammatory mediators in response to LPS and lipoteichoic acid, such as tumor necrosis factor, serum amyloid A, inducible nitric oxide synthase, and the chemokines IL-8 and CXC chemokine ligands 3 and 5. The prostaglandin E₂ synthesis in challenged and nonchallenged cells was reduced by MEL within 24 h. Furthermore, MEL reduced the viability and consequently the total RNA yield of the cells. However, mRNA abundance of apoptosis-related enzymes was not affected by any treatment. Meloxicam had clear dose-dependent effects on the immune response of MEC to pathogen-associated molecular patterns of common mastitis pathogens by preventing increased expression of important factors involved in inflammation. This nonsteroidal anti-inflammatory drug also has detrimental effects on cell viability. How these effects would influence the elimination of pathogens from an infected mammary gland during mastitis therapy with meloxicam needs to be further investigated.     

Defining the design space for freeze-dried orodispersible tablets with meloxicam

Objective: This work focused on simultaneously investigating formulation variables and freeze-drying parameters when preparing orodispersible tablets with meloxicam (Mel), by a Quality by Design (QbD) approach.

Materials and methods: Methylcellulose (MC) was selected as a matrix forming agent and mannitol (Man) as cryoprotectant, both at two concentration levels. The freezing regime was also varied between fast and shelf-ramped, to find out how it affects the final products. The tablet formulations were characterized for their disintegration time, wetting properties, mechanical properties, morphology and in vitro dissolution. Response Surface Modeling completed the statistical analysis that assessed the effects of independent variables on the responses.

Results: All the responses showed good fitting to the chosen model. The increase in MC content determined a positive effect on disintegration time, wetting time, mechanical strength and a negative effect on Mel dissolution. High levels of Man-determined brittle products with low-absorption capacity and fast Mel dissolution. The freezing rate had an important effect on the structure of tablets: fast freezing determined slightly thicker pore walls with smooth surfaces, while shelf-ramped freezing led to a multiple-layer structure with increased hardness. Still, shelf-ramped freezing yielded higher Mel release, due to physical changes of the active substance during the freeze-drying process.

Conclusion: From the generated design space, an optimal formulation was obtained and the results validated the experimental design. The QbD approach was an efficient manner of understanding formulation and process parameters at the freeze-dried orodispersible tablets preparation.     

Development and validation of NIR-chemometric methods for chemical and pharmaceutical characterization of meloxicam tablets

Context: Near-Infrared (NIR) spectroscopy is an important component of a Process Analytical Technology (PAT) toolbox and is a key technology for enabling the rapid analysis of pharmaceutical tablets.

Objective: The aim of this research work was to develop and validate NIR-chemometric methods not only for the determination of active pharmaceutical ingredients content but also pharmaceutical properties (crushing strength, disintegration time) of meloxicam tablets.

Materials and methods: The development of the method for active content assay was performed on samples corresponding to 80%, 90%, 100%, 110% and 120% of meloxicam content and the development of the methods for pharmaceutical characterization was performed on samples prepared at seven different compression forces (ranging from 7 to 45?kN) using NIR transmission spectra of intact tablets and PLS as a regression method.

Results: The results show that the developed methods have good trueness, precision and accuracy and are appropriate for direct active content assay in tablets (ranging from 12 to 18 mg/tablet) and also for predicting crushing strength and disintegration time of intact meloxicam tablets.

Discussion: The comparative data show that the proposed methods are in good agreement with the reference methods currently used for the characterization of meloxicam tablets (HPLC-UV methods for the assay and European Pharmacopeia methods for determining the crushing strength and disintegration time).

Conclusion: The results show the possibility to predict both chemical properties (active content) and physical/pharmaceutical properties (crushing strength and disintegration time) directly, without any sample preparation, from the same NIR transmission spectrum of meloxicam tablets.