Study of stability of methotrexate in acidic solution Spectrofluorimetric determination of methotrexate in pharmaceutical preparations through acid-catalyzed degradation reaction

Facile Integration of Hanztsch's Switch-Off/On Modeled Fluorogenic Probe for Feasible Tagging and Tracking of the Midodrine Drug in Different Matrices; First Evaluation of the Method's Greenness, Whiteness, Blueness, Quantum Yield, and Tablets' Content Homogeneity

The proposed investigation follows a certain methodology to guarantee that the procedure employed is sustainable and green. It is noteworthy to mention that various tools have been implemented as potential indicators of environmental sustainability (greenness and whiteness). From a novelty viewpoint, a new tool, BAGI, for the method's blueness evaluation was applied to the planned method and showed a high applicability score. Fortunately, the WAC concept, which combines ecological and functional variables using the Green/Red/Blue design (RBG 12 tool), identifies the established analytical approach as white. In the planned study, a new, green, simple, nano-trace-sensitive, original fluorimetric methodology was established to analyze and assess midodrine hydrochloride content in different matrices. Midodrine's primary amine moiety reacts with Diacetylmethane/Oxymethylene reagent in an acetate buffer, which leads to generating a fluorescent dihydrolutidine derivative (Hantzsch-named reaction). Consequently, the signal strength of this compound was quantified at 487 nm, with an excitation wavelength of 426 nm. This analysis indicated that the technique exhibited linearity within the range of 0.05 to 1.1 µg mL-1 concentrations, accompanied by remarkably good sensitivity values (LOD and LOQ). The methodology employed in this examination was subjected to validation following the rules recognized by ICH. From the perspective of pharmacy and chemistry, the method presented in this study was successfully employed to analyze commercially available tablets, oral drops, and human fluids. The outcomes obtained demonstrated satisfactory recovery rates without any interference from excipients. Following the USP recommendations, the intended technique was finally implemented to explore the content homogeneity evaluation.

Facile decoration of one-pot fluorescence probe-patterned reaction for sensing and ultrasensitive determination of tradjenta, a new type 2 diabetes oral therapy

Type 2 diabetes can be cured by using tradjenta (also known as Linagliptin), a new therapeutic drug that is an inhibitor of the dipeptidyl peptidase-4 enzyme. Tradjenta is administered orally alone or in combination with metiguanide or empagliflozin. An easy and specific fluorimetric analysis of Tradjenta was developed and demonstrated in the present investigation. The Hantzsch reaction method, which generates a fluorescent dihydropyridine derivative, is the basis of this assay. In a Toerell-Stenhagen buffered solution, the unsubstituted amine group of Tradjenta interacted with 2,4-Pentadione/Oxomethane. Spectrofluorimetry was utilized for this investigation at an excitation/emission wavelength of 421/480 nm. When comparing the Tradjenta concentration to the tracked fluorimetric signal, the method revealed linearity over the concentration range of 0.05 to 1.2 µg/mL. By strictly altering system parameters and analyzing the validation factors following International Council for Harmonisation (ICH) requirements, the outcomes were achieved. Finally, the proposed approach was successfully applied to assay the drug not only in its raw form and prescribed formulations but also to evaluate the tablet's uniformity of content.

Photodegradation of methotrexate in aqueous solution: degradation kinetics and identification of transformation products

Methotrexate is an antineoplastic folate analog of high environmental concern, due to its low biodegradability and toxicological properties. This study focused on its photodegradation under two irradiation conditions, aiming to be representative of environment (300-450 nm) and drinking water treatment (254 nm). The photodegradation experiments were conducted at two pH, to vary the methotrexate ionization state and to produce a large variety of transformation products (TPs). The degradation kinetics determined through LC-UV monitoring were contrasted according to pH and irradiation wavelength. However, the quantum yields were independent of ionization state at 254 nm and the changes in kinetics at higher wavelengths were attributed to a change in the degradation mechanism. The TPs formed during the reactions were identified by UHPLC-MS/MS, using both the positive and negative modes. Among the eleven proposed structures, five were described as methotrexate TPs for the first time. The TPs result from N-demethylation, glutamic acid oxidation, and C-N cleavage, all of them leading to further degraded photoproducts presenting modified or lost glutamic acid part. This was made possible thanks to the negative mode, which allowed the exploration of the glutamic acid moiety modifications. Cytotoxicity assessment on A549 cancer cells demonstrated that all photoproducts formed at pH 7 were less toxic than the parent compound.

An innovational validated spectrofluorimetric technique for determination of 6-Aminocaproic acid in pure form and its tablet: Application to spiked human plasma and urine

An innovative and sensitive spectrofluorimetric method has been developed for determination of 6-aminocaproic acid (ACA) in its pure form and its laboratory prepared tablets. The aim of this method is the reaction of ethyl acetoacetate and formaldehyde with the primary amino group presented in ACA as aimed in the Hantzsch reaction, this reaction resulted in formation of a yellow fluorescent dihydropyridine derivative that can be easily detected spectrofluorimetrically at 438 nm (excitation at 358 nm). At the optimum conditions of the reaction, the linear range was found to be (0.7-3.5 µg\mL) with limit of detection is 0.231 µg\mL and limit of quantitation is 0.700 µg\mL. The proposed method used for detection of ACA laboratory prepared tablets with average percentage 100.721 ± 0.701% without any interference from any excipients. This method used for in vitro determination of ACA in spiked human plasma with a percent mean recovery 99.874 ± 1.416%. In addition, the developed method used for determination of ACA in spiked human urine with percent mean recovery 100.314 ± 1.793%.

Ultrasensitive fluorescence detection of antitumor drug methotrexate based on a terbium-doped silica dendritic probe

A novel strategy was developed for the detection of methotrexate (MTX) via the quenching effect of MTX on the fluorescence intensity of terbium-doped dendritic silica particles (Tb@KCC-1). The fluorescence intensity of Tb@KCC-1 can be effectively quenched by MTX at 546 nm under an excitation wavelength of 233 nm. The quenched fluorescence is proportional to the amount of MTX in both plasma and exhaled breath condensate (EBC) samples. Under the optimal conditions, the linear dynamic ranges of the developed method were 44 nM to 2.2 μM for EBC, 44 nM to 0.22 μM and 0.22-2.2 μM for plasma samples. The limit of detection (LOD) and limit of quantification (LOQ) in both plasma and EBC media are 35 and 116 nM, respectively. The developed method has the benefits of fast analysis time, simple approach, high specificity, and sensitivity for the detection of MTX in both media. This nanoprobe has been successfully utilized for the quantification of MTX in patients' plasma and spiked EBC samples, proving the applicability of the nanoprobe for MTX detection in real samples.

Derivatization of γ-Amino Butyric Acid Analogues for Their Determination in the Biological Samples and Pharmaceutical Preparations: A Comprehensive Review

γ-Aminobutyric acid (GABA) plays an important role in regulating neuronal excitability. Four structurally related drugs to GABA including pregabalin (PGB), gabapentin (GBP), vigabatrin (VGB), and baclofen are used for the treatment of central nervous system disorders. These drugs are small aliphatic molecules having neither fluorescent nor strong absorbance in the ultraviolet/visible region; therefore, direct determination of these analytes by optical methods is difficult. Additionally, their high boiling point makes gas chromatography impossible. Accordingly, the amine or acid moiety in these drugs is derivatized in order to improve their selectivity and sensitivity during determination in the biological samples. This review focuses on derivatization based methods and their different reactions for determination of PGB, GBP, VGB, and baclofen in the biological samples and pharmaceutical preparations reported between 1980 and 2020. High-performance liquid chromatography methods coupled with different detectors are a commonly used methods for determination of GABA analogs after derivatization. These methods cover 38.89% of all developed methods for determination of GABA analogs.

Effect of methotrexate and its photodegradation products on the temperature induced denaturation of human serum albumin

Effect of the photodegradation of chemotherapeutic agent methotrexate on the denaturation of human serum albumin has been studied by differential scanning calorimetry and fluorimetric measurements. Photoluminescence studies highlighted entropy driven binding of both methotrexate molecules and its degradation products to the albumin molecules. The calorimetric measurements evaluated by the Kissinger method show elevated activation energy in the presence of methotrexate. Similar but moderated enhancement of the activation energy was obtained in the presence of the photodegradation products of methotrexate. These results highlight stabilization of the human serum albumin by the methotrexate drug which finding may contribute to fine tuning of methotrexate applications in therapy.

Patient-ready syringes containing 25 mg/mL methotrexate can be kept at temperature ranging from 4 °C to 37 °C for up to 12 weeks for use in psoriatic and rheumatologic conditions

BACKGROUND

Methotrexate (MTX) is a mainstay drug in the treatment of psoriatic and rheumatologic conditions. Subcutaneous MTX has become a feasible treatment alternative with the development of prefilled syringes or autoinjectors containing MTX solution that can be self-administered by the patient at home. However, MTX prefilled auto-injector pens are still not available in some countries.

OBJECTIVE

This study aimed to investigate the stability and sterility of 25 mg/mL MTX solution in a disposable plastic syringe over a 12-week period under light protection at temperatures of 4 °C, 25 °C, and 37 °C.

METHODS

This study was conducted during November 2019 to February 2020 at the Faculty of Medicine Siriraj Hospital, Mahidol University. Stability was evaluated using ultra-high-performance liquid chromatography technique, and sterility was assessed by cultures for bacterial and fungal contamination.

RESULTS

Our results revealed that patient-ready syringes containing 25 mg/mL MTX solution can be prepared in advance and kept for up to 12 weeks under light protection, and they can be kept at temperatures ranging from 4 to 37 °C.

CONCLUSION

This system for delivering MTX to patients that are refractory to or intolerant of oral MTX via a self-administered pre-filled syringe is both efficient and easy to implement in care settings where commercially alternatives are not yet available.

Factorial approach for the optimization and development of stability indicating study of the contraceptive suspension for injection(Depo-Provera®)

The study involves use of factorial design for optimization of forced degradation conditions and development of stability indicating method for medroxyprogestrone acetate (MPA) or depo-provera as known in the market. MPA is an important contraceptive and anticancer drug especially for treatment of breast cancer and it is the first time to study the different conditions affecting its stability. MPA was subjected to different variables such as solvent type, pH and the time subjected to UV light. Factorial design has been used during forced degradation to determine significant factors responsible for degradation and to optimize degradation conditions reaching maximum degradation. Factors responsible for forced degradation were statistically evaluated using Bubble and Surface plots. Variables proved to be significant (p < 0.05) and the suggested model represented a perfect example for indicating the efficiency of factorial designs in optimizing the degradation conditions that give maximum percent of degradation. We investigated also the solubility and stability profiles of MPA in aqueous solutions. Stability study results showed a very low stability profile of MPA in all the aqueous solutions with rapid degradation rate more than other solvents. The current research may contribute to enrich the knowledge of the physicochemical properties of this drug for exploring its full anticancer potential in the future.

Sensitive inexpensive spectrophotometric and spectrofluorimetric analysis of ezogabine, levetiracetam and topiramate in tablet formulations using Hantzsch condensation reaction

Two highly sensitive, simple and selective spectrophotometric and spectrofluorimetric assays have been investigated for the analysis of ezogabine, levetiracetam and topiramate in their pure and in pharmaceutical dosage forms. The suggested methods depend on the condensation of the primary amino-groups in the three drugs with acetylacetone and formaldehyde according to Hantzsch reaction yielding highly fluorescent yellow colored dihydropyridine derivatives. The reaction products of ezogabine, levetiracetam and topiramate were measured spectrophotometrically at 418, 390 and 380nm or spectrofluorimetrically at λ_em/ex of 495/425nm, 490/415nm and 488/410nm, respectively. Various experimental conditions have been carefully studied to maximize the reaction yield. At the optimum reaction conditions, the calibration curves were rectilinear over the concentration ranges of 8-25, 60-180 and 80-200μg/mL spectrophotometrically and 0.02-0.2, 0.2-1.2 and 0.2-1.5μg/mL spectrofluorimetrically for ezogabine, levetiracetam and topiramate, respectively with good correlation coefficients. The suggested methods were applied successfully for the analysis of ezogabine, levetiracetam and topiramate in their commercial tablets with high percentage recoveries and negligible interference from various excipients in pharmaceutical dosage forms. The results were statistically analyzed and showed the absence of any significant difference between both developed and published methods. The procedures were validated and evaluated by the ICH guidelines revealing good reproducibility and accuracy. Therefore, the two proposed methods may be considered of high interest for practical and reliable analysis of ezogabine, levetiracetam and topiramate in pharmaceutical dosage forms.

Stability study of methotrexate in 0.9% sodium chloride injection and 5% dextrose injection with limit tests for impurities

PURPOSE

Results of an evaluation of the stability of methotrexate in 0.9% sodium chloride injection and 5% dextrose injection are presented.

METHODS

Methotrexate concentrated solution (100 mg/mL) was diluted to nominal concentrations of 0.2 and 20 mg/mL in infusion bags containing 0.9% sodium chloride injection or 5% dextrose injection. The filled bags were stored for 28 days at 25 °C and 60% relative humidity and protected from light. Samples were withdrawn for analysis on the day of preparation and after 3, 7, 14, 21, and 28 days. The test program included visual inspections, measurements of pH and infusion bag weight loss, and high-performance liquid chromatography assays to determine methotrexate content and characterize degradation products.

RESULTS

At both evaluated concentrations, methotrexate in 0.9% sodium chloride injection was stable for 28 days; only minor (<0.05%) increases in amounts of known and unknown degradation products were detected. In 5% dextrose injection, methotrexate at the higher concentration was stable for 28 days, with minor formation of degradation products; in the 0.2-mg/mL solution, however, methotrexate was stable for only 3 days. At later time points, an unknown impurity present at a concentration higher than 0.1% was observed.

CONCLUSION

At concentrations of 0.2 and 20 mg/mL, methotrexate in 0.9% sodium chloride injection was found to be stable for 28 days when stored at 25 °C and protected from light. Under the same storage conditions, methotrexate in a 20-mg/mL solution prepared with 5% dextrose injection was stable for 28 days, whereas a 0.2-mg/mL solution in the same diluent was stable for only 3 days.

Micelle-enhanced direct spectrofluorimetric method for the determination of linifanib: Application to stability studies

A new simple stability-indicating spectrofluorimetric method has been developed and validated for the determination of the tyrosine kinase inhibitor, linifanib (LNF). The proposed method makes use of the native fluorescence characteristics of LNF in a micellar system. Compared with aqueous solutions, the fluorescence intensity of LNF was greatly enhanced upon the addition of Tween-80. The relative fluorescence intensity of LNF was measured in a diluting solvent composed of 2% Tween-80: phosphate buffer pH 8.0 (20: 80, v/v) using excitation and emission wavelengths of 290 and 450 nm, respectively. The proposed method was fully validated as per the ICH guidelines. The recorded fluorescence intensity of LNF was rectilinear over a concentration range of 0.3-2 μg/ml with a high correlation coefficient (r = 0.9990) and low limits of detection (0.091 μg/ml) and quantitation (0.275 μg/ml). The applicability of the method was extended to study the inherent stability of LNF under different stress degradation conditions including, alkaline, acidic, oxidative, photolytic and thermal degradation. Moreover, the method was utilized to study the kinetics of the alkaline and oxidative degradation of LNF. The pseudo-first order rate constants and half-lives were calculated.

An eco-friendly direct spectrofluorimetric method for the determination of irreversible tyrosine kinase inhibitors, neratinib and pelitinib: application to stability studies

A new rapid and simple stability-indicating spectrofluorimetric method has been developed for the determination of two irreversible tyrosine kinase inhibitors (TKIs), neratinib (NER) and pelitinib (PEL). The method is based upon measurement of the native fluorescence intensity of both drugs at λ_ex 270 nm in aqueous borate buffer solutions (pH 10.5). The fluorescence intensity recorded at 545 nm (NER) and 465 nm (PEL) were rectilinear over the concentration range of 0.1-10 μg/mL for both drugs with a high correlation coefficient (r > 0.999). The proposed method provided low limits of detection and of quantitation of 0.07, 0.11 μg/mL (NER) and 0.02, 0.05 μg/mL (PEL), respectively. The method was successfully applied for the determination of NER and PEL in bulk powder. The proposed methods were fully validated as per the International Conference on Harmonisation (ICH) guidelines. The application of the method was extended to stability studies of both NER and PEL under different forced-degradation conditions (acidic-induced, base-induced, oxidative, wet heat, and photolytic degradation). Moreover, the kinetics of the base-induced and oxidative degradation of both drugs was investigated and the pseudo-first-order rate constants and half-lives were estimated at different temperatures. Also, an Arrhenius plot was applied to predict the stability behaviour of the two drugs at room temperature. Copyright © 2016 John Wiley & Sons, Ltd.

Two different spectrophotometric determinations of potential anticancer drug and its toxic metabolite

Flutamide is a hormone therapy used for men with advanced prostate cancer. Flutamide is highly susceptible to hydrolysis with the production of 3-(trifluoromethyl)aniline, which is reported to be one of its toxic metabolites, impurities and related substances according to BP and USP. Flutamide was found to be stable when exposed to oxidation by 30% hydrogen peroxide and direct sunlight for up to 4h. Two accurate and sensitive spectrophotometric methods were used for determination of flutamide in bulk and in pharmaceutical formulations. Method (I) is the area under curve (AUC) spectrophotometric method that depends on measuring the AUC in the wavelength ranges of 275-305 nm and 350-380nm and using Cramer's rule. The linearity range was found to be 1-35 μg/mL and 0.5-16 μg/mL for the drug and the degradate, respectively. In method (II), combination of the isoabsorptive and dual wavelength spectrophotometric methods was used for resolving the binary mixture. The absorbance at 249.2 nm (λiso) was used for determination of total mixture concentration, while the difference in absorbance between 232 nm and 341.2 nm was used for measuring the drug concentration. By subtraction, the degradate concentration was obtained. Beer's law was obeyed in the range of 2-35 μg/mL and 0.5-20 μg/mL for the drug and its degradate, respectively. The two methods were validated according to USP guidelines and were applied for determination of the drug in its pharmaceutical dosage form. Moreover AUC method was used for the kinetic study of the hydrolytic degradation of flutamide. The kinetic degradation of flutamide was found to follow pseudo-first order kinetics and is pH and temperature dependent. Activation energy, kinetic rate constants and t1/2 at different temperatures and pH values were calculated.

Validated spectrofluorimetric method for determination of selected aminoglycosides

New, sensitive, and selective spectrofluorimetric method was developed for determination of three aminoglycoside drugs in different dosage forms, namely; neomycin sulfate (NEO), tobramycin (TOB) and kanamycin sulfate (KAN). The method is based on Hantzsch condensation reaction between the primary amino group of aminoglycosides with acetylacetone and formaldehyde in pH 2.7 yielding highly yellow fluorescent derivatives measured emission (471 nm) and excitation (410 nm) wavelengths. The fluorescence intensity was directly proportional to the concentration over the range 10-60, 40-100 and 5-50 ng/mL for NEO, TOB and KAN respectively. The proposed method was applied successfully for determination of these drugs in their pharmaceutical dosage forms.

Experimental design and machine learning strategies for parameters screening and optimization of Hantzsch condensation reaction for the assay of sodium alendronate in oral solution

An experimental design was adopted to attain the optimum reaction parameters of chemical derivatization of anhydrous sodium alendronate in an oral solution formulaviaHantzsch condensation reaction.

Development and validation of a stability-indicating spectrofluorimetric method for the determination of H1N1 antiviral drug (oseltamivir phosphate) in human plasma through the Hantzsch reaction

A simple and sensitive spectrofluorimetric method has been described and validated for the determination of oseltamivir phosphate (OSP) in its pure form and pharmaceutical dosage forms.

Kinetic study and mechanism of Niclosamide degradation

A spectrophotometric kinetic study of Niclosamide alkaline degradation as a function of drug concentration, alkaline concentration and temperature has been established utilizing double divisor-ratio spectra spectrophotometric method. The developed method allowed determination of Niclosamide in presence of its alkaline degradation products; namely; 2-chloro-4-nitro aniline (DEG I) and 5-chloro salicylic acid (DEG II) with characterization of its degradation mechanism. It was found that degradation kinetic of Niclosamide followed pseudo-first order under the established experimental conditions with a degradation rate constant (k) of 0.0829 mol/h and half life (t1/2) of 8.35 h. The overall degradation rate constant as a function of the temperature under the given conditions obeyed Arrhenius equation where the activation energy was calculated to be 3.41 kcal/mol.

Two validated spectrofluorometric methods for determination of gemifloxacin mesylate in tablets and human plasma

Two new, sensitive, and selective spectrofluorometric methods were developed for the determination of gemifloxacin mesylate (GFX) in tablets and spiked human plasma. Method A was based on measurement of the enhanced fluorescence spectral behaviour of GFX in a sodium dodecyl sulphate (SDS) micellar system. In aqueous solution of acetate buffer pH 5.5, the fluorescence intensity of GFX was greatly enhanced about tenfold in the presence of SDS. The fluorescence intensity was measured at 402 nm after excitation at 274 nm. Method B was based on Hantzsch condensation reaction between the primary amino group of GFX with acetylacetone and formaldehyde in acetate buffer of pH 3.5 yielding a highly yellow fluorescent derivative. The reaction of GFX with acetylacetone-formaldehyde system solution resulted in bathochromic shift of both emission (476 nm) and excitation (420 nm) wavelengths. The fluorescence intensity was directly proportional to the concentration over the range 10–1000 ng/ml and 100–2000 ng/ml for method A and B, respectively. The proposed methods were applied successfully for determination of GFX in its tablets and spiked plasma. Therefore, these methods can be considered of real interest for reliable and practical quality control analysis of GFX.

On-line coupling of derivatization with pre-concentration to determine trace levels of methotrexate

A new simple, sensitive and precise green analytical procedure using an automated packed-reactor derivatization technique coupled with on-line solid-phase enrichment (SPEn) has been developed and evaluated to determine trace levels of methotrexate (MTX). The method was based on injection of MTX into a flowing stream of phosphate buffer (0.04 M, pH 3.4), carried through the packed oxidant reactor of Cerium (IV) trihydroxyhydroperoxide for oxidative cleavage of the drug into highly fluorescent product, 2,4-diaminopteridine-6-carboxylic acid, followed by SPEn on a head of short ODS column (10 mm×4.6 mm i.d., 5 μm particle size). The flow rate was 0.25 mL/min and packed reactor temperature was 40 °C. The trapped product was back-flush eluted from the ODS column to the detector by column-switching with an environmentally friendly mobile phase consisting of ethanol and phosphate buffer (0.04 M, pH 3.4) in the ratio of 5:95 (v/v). The eluent was monitored at emission and excitation wavelengths of 460 and 360 nm, respectively. The calibration curve was linear over the concentration range of 1.25–50 ng/mL with a detection limit of 0.08 ng/mL. The method was successfully applied to determine MTX in pharmaceutical formulations with mean percentage recovery ranging from 99.48 to 99.60.

Simple and sensitive spectrofluorimetric method for the determination of pregabalin in capsules through derivatization with fluorescamine

A new, simple and sensitive spectrofluorimetric method has been developed for the determination of pregabalin (PG) in capsules. The method is based on the reaction between pregabalin and fluorescamine in borate buffer solution of pH 10 to give a highly fluorescent derivative that is measured at 487 nm after excitation at 390 nm. The different experimental parameters affecting the development and stability of the reaction product were carefully studied and optimized. The fluorescence intensity concentration plot was rectilinear over the range of 0.01-0.3 µg mL⁻¹ with a lower detection limit of 0.0017 µg mL⁻¹ and limit of quantitation of 0.005 µg mL⁻¹. The developed method was successfully applied to the analysis of the drug in its commercial capsules. The mean percentage recovery of PG in its capsule was 99.93±1.24 (n = 3). Statistical comparison of the results with those of the comparison method revealed good agreement and proved that there was no significant difference in the accuracy and precision of the two methods. A proposed reaction pathway was postulated.

Determination of dissociation constants of folic acid, methotrexate, and other photolabile pteridines by pressure-assisted capillary electrophoresis

Pressure-assisted CE (PACE) was applied to determine the previously inaccessible complete set of pK values for folic acid and eight related multiprotic compounds. PACE allowed the determination of all acidity macroconstants at low (<or=0.1 mM) concentration without interferences of selfassociation or photodegradation throughout the pH range. The accuracy of the constants was verified by NMR-pH, UV-pH, and potentiometric titrations and the data could be converted into physiological ionic strength. It was shown that even three overlapping pK values can be determined by CE with good precision (<0.06) and accuracy if an appropriately low sample throughput is used. Experimental aspects of PACE for the quantitation of acid-base properties are analyzed. The site-specific basicity data obtained for folic acid and methotrexate (MTX) reveal that apparently slight constitutional differences between folic acid and MTX carry highly different proton-binding propensities at analogous moieties, especially at the pteridine N(1) locus, providing straightforward explanation for the distinctive binding to dihydrofolate reductase at the molecular level.

Application of 2-acetylbutyrolactone to spectrofluorimetry: Fluorescence properties of Schiff bases derived from 2-acetylbutyrolactone and spectrofluorimetric determination of primary amine-containing compounds

2-Acetylbutyrolactone (ABL) has been characterized for use as a fluorogenic reagent for the spectrofluorimetric determination of primary amines. The reagent forms strongly fluorescent Schiff bases upon the reaction with primary amines in acid-catalized aqueous solutions or in dimethylformamide (DMF). Sulfamethoxazole (SMX) and ampicillin sodium (AMP Na) were used as model amines of type ArNH(2) and RNH(2), respectively. The reaction conditions, fluorescence spectral properties and the stability of the derivatives have been investigated. The chemistry and the pathway of the reaction have been discussed. Calibration data, accuracy, precision, limits of detection, limits of quantification and other aspects of analytical merit were presented in the text. The utility of ABL for the analysis of the model drugs in pharmaceutical preparations was demonstrated. The results indicated that the proposed methods are equally accurate and precise as the official or other reported methods.

Determination of methotrexate in pharmaceutical formulations by flow injection analysis exploiting the reaction with potassium permanganate

A highly sensitive, precise and accurate flow injection procedure for the determination of methotrexate (MTX) was described. The method was based on oxidation of MTX into highly fluorescence product (2,4-diaminopteridine-6-carboxylic acid) by acidic potassium permanganate. A three-line manifold was used with potassium permanganate as an oxidant (3 mmol l(-1)) and sulfuric acid (6 mmol l(-1)) as carrier streams. The oxidation process was conducted at 65 degrees C through a reaction coil of 3 m (0.5 mm, i.d.). It was essential to eliminate the excess of potassium permanganate before passing to the detector using 8 mmol l(-1) sodium sulfite as a decolorizing stream. The fluorescence intensity was measured at excitation and emission wavelengths of 369 and 465 nm, respectively. The calibration graph was linear over the range 40-400 ng ml(-1) MTX. The developed method was successfully applied to the determination of MTX in pharmaceutical formulations, at a sampling rate of 90 sample h(-1) and showed a % recovery ranging from 99.96 to 100.07 and SD% ranging from 0.51 to 0.65%.