Determination of Aminophylline in Human Serum Using Hydrogel Microspheres for Coupled Surface-Enhanced Raman Spectroscopy (SERS) and Solid-Phase Extraction.

Aminophylline (AMP) is a bronchodilator. The therapeutic and toxic doses are very close. Therefore, therapeutic drug monitoring (TDM) of AMP is essential in clinical practice. Microgels were synthesized by free radical precipitation polymerization. Silver@poly(N-isopropyl acrylamide) (Ag@PNIPAM) hybrid microgels were obtained by loading silver (Ag) nanoparticles into the three-dimensional network of the microgels by in situ reduction. The microgel is a three-dimensional reticular structure with tunable pore size, large specific surface area, and good biocompatibility, which can be used as a sorbent for solid-phase extraction (SPE) of target molecules in complex matrices and as a surface-enhanced Raman spectroscopy (SERS) substrate. We optimized the conditions affecting SERS enhancement, such as silver nitrate (AgNO3) concentration and SPE time, according to the SERS strategy of Ag@PNIPAM hybrid microgels to achieve label-free TDM for trace AMP in human serum. The results showed good linearity between the logarithmic concentration of AMP and its SERS intensity in the range of 1-1.1 × 102 µg/mL, with a correlation coefficient (R2) of 0.9947 and a low detection limit of 0.61 µg/mL. The assay accuracy was demonstrated by spiking experiments, with recoveries ranging from 93.0 to 101.8%. The method is rapid, sensitive, reproducible, requires simple sample pretreatment, and has good potential for use in clinical treatment drug monitoring.

Photocatalytic interaction of aminophylline-riboflavin leads to ROS-mediated DNA damage and cell death: A novel phototherapeutic mechanism for cancer.

The accompanied tissue devastation and systemic toxicity of chemotherapy has shifted the quest for having an effective and palliative cancer therapy towards photodynamic therapy (PDT). Riboflavin (Rf), an essential micronutrient is emerging as a potent tool of PDT, due to its excellent photosensitizing properties. It can be used as an efficient adjuvant for various anticancer drugs. The hemolytic and proteolytic effect of photoilluminated aminophylline (Am), a xanthine derivative, and Rf is well documented in literature. In this study, using human peripheral lymphocytes we have demonstrated the strong pro-oxidant effects of photocatalytic interaction between Am and Rf. The photo degradation kinetics of Am in the presence of Rf was monitored using UV spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy. The resultant pro-oxidant action of Am was monitored through various assays like lipid peroxidation, protein carbonylation, and reactive oxygen species (ROS) generation. Furthermore, the cytotoxic potential of this system was studied using comet and MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay. Treated lymphocytes were visualized using fluorescence and scanning electron microscopy to further validate apoptosis. ROS scavengers ameliorated the oxidative damage caused by this system suggesting pivotal role of ROS in causing apoptotic cell death. As cancer cells exhibit increased absorption of Rf as well as are very sensitive in any further ROS level increment, this putative pathway can serve as an effective anodyne phototherapeutic strategy for cancer treatment. © 2017 IUBMB Life, 69(8):611-622, 2017.

Comparative study of the binding of pepsin to four alkaloids by spectrofluorimetry.

The interactions between pepsin and four alkaloids, including caffeine (Caf), aminophylline (Ami), acefylline (Ace), diprophylline (Dip), were investigated by fluorescence, UV-visible absorption, resonance light scattering, synchronous fluorescence spectroscopy and 3D spectroscopy under mimic physiological conditions. The results revealed that Caf (Ami/Ace/Dip) caused the fluorescence quenching of pepsin by the formation of Caf (Ami/Ace/Dip)-pepsin complex. The binding constants and thermodynamic parameters at three different temperatures, the binding locality and the binding power were obtained. The hydrophobic and electrostatic interactions were the predominant intermolecular forces to stabilize the complex. Results showed that aminophylline was the stronger quencher and bound to pepsin with higher affinity than other three alkaloids.

Preliminary evaluation of the in vitro release and in vivo absorption in rabbits of the modified-release dosage forms.

OBJECTIVE: The suitability of the rabbit as an animal model for the primary screening and selection of the pilot scale batches during the early stages of the formulation development was studied. MATERIALS AND METHODS: Three modified-release formulations of aminophylline consisted of Carbopol® 971P/HPMC K4M (F-I), and HPMC K100M (F-II) or HPMC K4M (F-III) were used. Commercial products were Aminofilin retard 350 mg tablets, Srbolek, Serbia (R-I) and Phyllocontin(®) 350, tablets Purdue Frederic, Canada (R-II). RESULTS: Calculated release rate constants and the ƒ2 values between R-I/F-I (84.1) and R-II/F-III (83.4) indicated similar in vitro release while the coefficient n showed presence of different mechanisms of release from Anomalous transport, Fickian diffusion to Case-II transport. Higher Tmax, was found in the rabbits, dosed with F-II (12.00 h), F-III (10.50 h), and R-II (15.00 h) formulation. The highest Cmax (9.22 mg/L) was obtained with F-II, similar lower values was seen for F-I and F-III, while commercial products showed the lowest values R-I (5.58 mg/L) and R-II (4.18 mg/L). Higher AUC values were detected for all three formulations (from 115.90 to 204.06 mgh/L) in relation to commercial products (105.33 and 113.25 mgh/L). DISCUSSION AND CONCLUSION: The results demonstrated a good correlation of Level A (r(2) = 0.97) for the two formulations (F-I, F-III) and commercial product (R-I) indicates that there is a reasonable assumption that the rabbit might be use as a model for the preliminary comparison of scale up formulations in the early stages of the product development.

pH- and Temperature-Responsive P(DMAEMA-GMA)-Alginate Semi-IPN Hydrogels Formed by Radical and Ring-Opening Polymerization for Aminophylline Release.

A novel poly((2-dimethylamino) ethyl methacrylate-glycidyl methacrylate)-alginate (P(DMAEMA-GMA)alginate) semi-IPN hydrogel was synthesized via radical polymerization of the double bonds and ring-opening of the epoxy groups without using catalyst and cross-linker. (1)H-NMR, FT-IR and DSC data were consistent with the expected structures for the hydrogels. The interior morphology of the hydrogels was also investigated by SEM. The swelling ratio and compressive strength of the hydrogels were measured. The semi-IPN hydrogel had pH and temperature sensitivity, and pH-sensitive points of all hydrogels were found to be at pH 5.0. The release behavior of the model drug, aminophylline, was found to be dependent on the hydrogel composition and environment pH, which manifests that these materials have potential applications as intelligent drug carriers.

Study on the ternary mixed ligand complex of palladium(II)-aminophylline-fluorescein sodium by resonance Rayleigh scattering, second-order scattering and frequency doubling scattering spectrum and its analytical application.

The interaction between palladium(II)-aminophylline and fluorescein sodium was investigated by resonance Rayleigh scattering, second-order scattering and frequency doubling scattering spectrum. In pH 4.4 Britton-Robinson (BR) buffer medium, aminophylline (Ami) reacted with palladium(II) to form chelate cation([Pd(Ami)]2+), which further reacted with fluorescein sodium (FS) to form ternary mixed ligand complex [Pd(Ami)(FS)2]. As a result, resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency doubling scattering spectrum (FDS) were enhanced. The maximum scattering wavelengths of [Pd(Ami)(FS)2] were located at 300 nm (RRS), 650 nm (SOS) and 304 nm (FDS). The scattering intensities were proportional to the Ami concentration in a certain range and the detection limits were 7.3 ng mL(-1) (RRS), 32.9 ng mL(-1) (SOS) and 79.1 ng mL(-1) (FDS), respectively. Based on it, the new simple, rapid, and sensitive scattering methods have been proposed to determine Ami in urine and serum samples. Moreover, the formation mechanism of [Pd(Ami)(FS)2] and the reasons for enhancement of RRS were fully discussed.

An investigation into effects of in vitro test condition on the release properties of theophylline from HPMC matrices using factorial design.

The purpose of this study was to investigate the effect of various in vitro test conditions, on the release properties of theophylline (TP) from aminophylline (AP) matrices based on different hydroxypropylmethylcellulose (HPMC) ratio and viscosity grades. The general full factorial experimental design 3 x 3 x 3 was used, based on three independent variables: applied in vitro test (X1), HPMC/drug ratio (X2) and polymer viscosity grade (X3). The drug release percent at 2h (Y(2h)), 4h (Y(4h)) and 8 h (Y(8h)) and time for 50% of TP release from matrices (Y(T50%)) were response variables. Three in vitro tests were used: test 1 and test 4 (theophylline extended-release capsules, USP 30) and half-change method. According to factorial design analyses, in vitro test was the most significant factor influencing mechanism and amount of drug release. For half change method erosion was the predominant mechanism indicating case - II transport, while for test 1 the release mechanism were followed by both diffusion and erosion. The lowest release exponent n values, obtained from Ritger-Pepass equation, for test 4 indicate diffusion process inclining from Fickian diffusion to anomalous transport. Therefore, it is in the stage of development, useful to consider the influence of various in vitro test conditions on the formulation, in order to choose an optimal test for the purpose of future drug release examination.

A novel spectrophotometric method for the determination of aminophylline with boric acid in pharmaceutical and mixed serum samples.

This paper firstly describes a novel method to determine aminophylline (Ami) with boric acid (BA) by spectrophotometry. The study indicates that at pH 12.00 the absorbance of Ami decreases when BA is added. A simple, rapid, sensitive and reliable novel method based on the product of Ami and BA is obtained. Beer's law is obeyed in the range of Ami concentrations of 0.20-200 microg ml(-1). The equation of linear regression is A=-2.57309x10(-4)-0.00355C (microg ml(-1)), with a linear correlation coefficient of 0.9969 and RSD 0.28%. The method is successfully applied to the determination of Ami in pharmaceutical samples and mixed serum samples, and average recoveries were in the range of 97.1-105.9%.

Synthesis, pharmacological activity and nitric oxide generation by nitrate derivatives of theophylline.

Nitrates of theophylline derivatives - potential nitric oxide (NO) donors - were synthesized by esterification of 7-hydroxyalkyl theophylline derivatives with fuming nitric acid. The nitrates obtained were tested in-vitro in reactions with sulfydryl compounds at appropriately adjusted pH and temperature. Under the applied conditions, the synthesized compounds underwent decomposition to release NO, quantified using a polarographic method using a selective isolated (ISO-NO) sensor. The effects of dyphylline and proxyphylline and their new synthesized nitrates on arterial blood pressure (BP) were measured in spontaneously hypertensive (SH) rats. BP was measured in conscious SH rats using the tail-cuff method. Both short- and long-term administration of the xanthines tested significantly decreased systolic, diastolic and mean BP. The hypotensive effect of a single dose of nitrate dyphylline on mean BP was greater than that of the parent compound (P = 0.000012; P=0.000472 at 30 and 60 min post-dose, respectively), whereas proxyphylline and its nitrate derivative had similar activity. In rats treated with the tested compounds for 9 days twice daily, the decrease in BP persisted for at least 16 h after the last dose. Proxyphylline produced the most marked decrease in diastolic and mean BP. Among the xanthines examined, proxyphylline nitrate had the strongest hypotensive effect when administered in a single dose to animals pretreated with the same compound for 9 days. These results indicate that insertion of a nitrate group weakly modifies the hypotensive action of the studied xanthines in SH rats.

Modifying the release of proxyphylline from PVA hydrogels using surface crosslinking.

Drug release profiles were altered to prevent the initial burst effect or introduce a lag phase by creating surface crosslinked layers in poly(vinyl alcohol) (PVA) hydrogels. Confocal laser scanning microscopy (CLSM) confirmed the successful introduction of these surface crosslinked layers. The thickness and crosslinking density of the surface crosslinked layer were highly dependent on the surface crosslinking conditions (i.e., exposure time and glutaraldehyde (GTA) concentration used). By judicious selection of these parameters, the initial burst release could be eliminated and a reproducible delayed release could be achieved. Highly surface crosslinked layers had a tendency to rupture during the swelling process of PVA hydrogels; these raptures were found to coincide with delayed release of proxyphylline from surface crosslinked PVA hydrogels.

A novel spectrophotometric method for the determination of aminophylline in pharmaceutical samples in the presence of methanol.

A rapid, simple and sensitive method for the determination of aminophylline (Ami) using sodium 1, 2-naphthoquine-4-sulfonate (NQS) and methanol is established in this paper. It is based on the fact that a russety product can be formed by the reaction between aminophylline (Ami) and sodium 1, 2-naphthoquine-4-sulfonate (NQS) in pH 13.00 buffer solution. When methanol is added to the solution, the sensitivity of the color development reaction between Ami and NQS is improved, and the color of the system of NQS-Ami becomes a salmon pink. Beer's law is obeyed in a range of 4.97-69.5 microg ml(-1) of Ami at the maximum absorption of 453 nm (epsilon=4.87 x 10(3) l mol(-1) cm(-1)). The linear regression equation of the calibration curve is A=0.14458+0.00832C (microg ml(-1)), with a linear regression correlation coefficient of 0.9944. The detection limit is 0.7 microg ml(-1) (3sigma/k), R.S.D. is 1.1% and the recovery rate is in range of 92.5-105%. Furthermore, this method has been successfully applied to the determination of Ami in pharmaceutical samples.

Surface crosslinking for delayed release of proxyphylline from PHEMA hydrogels.

Delayed release systems find applications in chronotherapeutics and colon-specific delivery. They have also been considered suitable carriers for the oral delivery of peptides and proteins. In prior work, our research group has reported surface crosslinking as an effective technique to modify drug release profiles for poly(vinyl alcohol) (PVA) hydrogels, reducing the early burst effect in particular. Here, we demonstrate the feasibility of delayed release of proxyphylline from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels via surface crosslinking. Studies on in vitro drug release and the morphology changes of PHEMA hydrogels during swelling and drug release showed that the highly surface crosslinked layers and the ruptures occurring in these layers during swelling were likely responsible for the delayed release. In addition, the initial burst was significantly reduced or even eliminated from the drug release profile for PHEMA to achieve near zero-order release by judicious selection of two surface crosslinking parameters: crosslinking reagent concentration and exposure time used for the surface crosslinking treatment.

Vehicle and enhancer effects on human skin penetration of aminophylline from cream formulations: evaluation in vivo.

The effects of four essential oils (rosemary, ylang, lilacin, and peppermint oils), and three plant oils (jojoba oil, corn germ oil, and olive oil) on the permeation of aminophylline were studied using human skin. The permeation effects of these oils were compared with those of three chemical penetration enhancers. Although all oils enhanced the permeation of aminophylline, their effects were less than that of ethanol. Jojoba oil was found to be the most active, causing about a 32% peak height decrease of N-H bending absorbances in comparison with the control, while peppermint, lilacin, rosemary, and ylang oils caused 28%, 24%, 18%, and 12% peak height decreases, respectively. Microemulsions containing 10% jojoba oil and 30% corn germ oil were found to be superior vehicles for the percutaneous absorption of aminophylline. Comparision with results obtained from high-performance liquid chromatography shows good agreement.

[Studies on drug release from aminophylline konjac glucomannan matrix tablet].

OBJECTIVE: In vitro aminophylline release from matrix tablets with konjac glucomannan (KGM) were studied to elevate the feasibility of KGM used as carrier materials to prepare matrix tablets. METHOD: KGM hydrophilic matrix tablets were prepared by direct compression method with aminophylline as the model drug. The effects of test methods, pH values, ionic strength of dissolution media and rotation speeds on drug release were studied by in vitro dissolution experiment. RESULT: The MDT value tested by Paddle method was less than that tested by Basket method (P < 0.05). Among the rate of drug release in different dissolution media, distillded water is the fastest, pH 6. 8 PBS is the second, 0.1 mol x L(-1) HCL is the slowest. MDT increased with increasing the ionic strength of dissolution media (P < 0.05). MDT decreased with increasing the rotation speed, but the rate of drug release did not increase when the rotation speed was more than 100 r x min(-1) (P > 0.1). The mechanism of drug release were diffusion and erosion. CONCLUSION: KGM can be used in sustained delivery systems as a good candidate of hydrophilic polymer.

Dog colonoscopy model for predicting human colon absorption.

PURPOSE: This study was conducted to develop and validate a dog colon model that predicts colon permeability in humans. METHODS: The following compounds were studied: Class 1 highly soluble (HS)/highly permeable (HP): aminophylline, propranolol, CP-409092; Class 2 LS/HP: nifedipine; trovafloxacin, sertraline; Class 3 HS/LP: azithromycin, atenolol, CP-331684, CP-424391; Class 4 LS/LP: CJ-13610. Administration to dogs was made 30 cm cranial to the anal sphincter with a lubricated Schott Model VFS-5 flexible endoscope. The bioavailability of the compound following the colon administration in dogs, relative to the same formulation administered orally (relative bioavailability), was determined. RESULTS: Except for atenolol, a small hydrophillic molecule, the relative bioavailability from administration to the colon of the dog correlated well with the following compound properties: high solubility and high, passive permeability > high solubility, low permeability > low solubility, high, passive permeability approximately low solubility, low permeability. CONCLUSION: The dog colon model is proposed as a surrogate for human intubation studies when the controlled release candidate falls in BCS Classes 2 (LS/HP), 3 (HS/LP), and 4 (LS/LP). However, no human intubation or dog colon studies are required for Class 1 (HS/HP), as these compounds are likely to be well absorbed from the colon.

Investigation of solid-state reactions using variable temperature X-ray powder diffractometry. II. Aminophylline monohydrate.

PURPOSE: The object of this investigation was to demonstrate the utility of X-ray powder diffractometry (XRD) to study the kinetics of a complex pharmaceutical solid-state reaction wherein the reactant, product and intermediate phases were all simultaneously quantified. METHODS: Aminophylline monohydrate (I) decomposed to anhydrous theophylline (III) either directly or through an intermediate (anhydrous aminophylline, II). The reaction kinetics were studied isothermally at several temperatures ranging from 65 to 100 degrees C. By measuring the intensities of the XRD peaks unique to I, II and III, it was possible to simultaneously quantify the 3 phases during the entire reaction. RESULTS: Assuming that all the reaction steps follow first-order kinetics. the three equations describing the concentrations of I, II and III as a function of time, were derived. By fitting the experimental data to these equations, it was possible to obtain the rate constants for the three reaction steps. The rate constants were obtained at different temperatures and were used to draw Arrhenius type plots from which the activation energies were determined. At lower temperatures (< 80 degrees C). the concentration of the intermediate phase, i.e., II, was low throughout the reaction while at higher temperatures (> 90 degrees C), there was rapid formation and accumulation of II during the early stages of the reaction. These differences could be attributed to the fact that k1 (I --> II) had a more pronounced temperature dependence than k2 (I --> III) and k3 (II --> II). The XRD results were confirmed with isothermal thermogravimetry. CONCLUSIONS: Variable temperature XRD is a powerful tool to probe reaction kinetics in crystalline pharmaceuticals since it permits simultaneous quantification of multiple solid phases.

Biopharmaceutical characterization of oral theophylline and aminophylline tablets. Quantitative correlation between dissolution and bioavailability studies.

Considering the narrow therapeutic index of theophylline and the low range between the safe and toxic serum concentrations of this drug, the study of its pharmacokinetic properties is necessary. However, considering the time consuming and expensive in vivo tests, quantitative correlation between in vivo bioavailability and in vitro dissolution tests can be used routinely in quality control tests of these drug products to predict the in vivo pharmacokinetic parameters. For this reason healthy human volunteers were used for in vivo studies and serum samples were analyzed by a fluorescence polarization immunoassay analysis (FPIA) method. The results showed that an open one compartmental model could best describe the pharmacokinetic properties of orally administered theophylline and aminophylline tablets. Linear regression analysis by least-square method showed a good correlation between some in vivo and in vitro parameters obtained from dissolution studies by rotating basket and paddle methods. D(30)% (percentage of drug dissolved in vitro after 30 min) and F(0.5)% (drug absorbed in vivo after half an hour calculated by Wagner-Nelson equation) showed best correlation (r=0. 99036). C(max) (maximum serum concentration) of this drug also correlates well with t(25%) (time required to dissolve 25% of the drug). The calculated correlation coefficients could best predict the actual values of some pharmacokinetic parameters; AUC(0-->infinity), AUC(0-->1), F(0.5)% and C(max).

Rheological behavior of drug suspensions in Gelucire mixtures and proxyphylline release from matrix hard gelatin capsules.

Mixtures of Gelucires 50/02 and 50/13 showing different hydrophilic-lipophilic balances (HLB) and of proxyphylline were used to prepare suspensions at a concentration of 25% and to manufacture extended release hard gelatin capsules by cooling. The rheological behaviors of Gelucire mixtures with and without drug were determined by adjustment of the rheograms to the Ostwald power-law and by statistical assessment of the flow index. Pure Gelucire mixtures were very slightly shear thickening whereas proxyphylline suspensions had a thixotropic shear thinning behavior. These rheological behaviors can be explained by the chemical composition and by the ratio of the two Gelucires used. Extended release of proxyphylline was obtained with all these mixtures. Drug release increased with Gelucire mixture HLB owing to higher erosion. A viscosity-release relationship was found and allowed, with these two Gelucires of extreme HLB and viscosities, to define the formulations which will give an optimal drug release, by the determination of their suspension viscosity. Modeling of dissolution kinetics has generally shown the predominance of surface erosion of the plugs relative to drug diffusion inside the matrix. This was confirmed by the better linearization of percentage released, according to Hixson-Crowell as compared with Higuchi.