Solid-state acetylation of codeine phosphate by aspirin

Degradation of vitamin D3 in a stressed formulation: The identification of esters of vitamin D3 formed by a transesterification with triglycerides

Four unknown degradants in the LC-UV profile of a stressed experimental tablet formulation that contains vitamin D3 have been identified by a combination of Ag+-cationization electrospray ionization (ESI) LC/MS and atmospheric pressure chemical ionization (APCI) LC/MS/MS. The peaks elute in the method chromatography in two pairs of two peaks. The first pair of peaks has m/z 511 while the second pair has m/z 539. The major, first peak of each set of peaks corresponds to the octanoate and decanoate ester of vitamin D3, respectively. These are formed by a transesterification with the two major fatty acid components (octanoate and decanoate) of the triglycerides present in the formulation. The formation of two degradation products with each fatty acid is due to the presence of both vitamin D3 (major component) and the isomeric pre-vitamin D3 (minor component) in the stressed formulation.

Preparation and evaluation of combination tablet containing incompatible active ingredients

Combination preparation plays an important role in clinical treatment because of its better and wider curative synergism and weaker side effects. However, the existence of incompatibility between active ingredients or between active ingredients and excipients presents a serious obstacle in the preparation of such combination solid dosage forms. In this study, aspirin and ranitidine hydrochloride, between which there existed a chemical interaction, were selected as model drugs. Aspirin powders without any additives were granulated with hydroxypropyl methyl cellulose (HPMC) water solution as a binder using a Wurster coating apparatus and the operation conditions were optimized by Artificial Neural Network (ANN) analysis. Under these conditions, the aspirin granules prepared showed good flowability and compressibility. On the other hand, ranitidine hydrochloride was coated with Aquacoat (ethyl cellulose aqueous dispersion) after preliminary granulation with the Wurster coating apparatus. The aspirin granules and coated ranitidine hydrochloride particles were compressed into tablets with suitable excipients. The combination tablets showed good dissolution, content uniformity and improved stability of active ingredients.

A novel X-ray powder diffractometric method for studying the reaction between pseudoephedrine enantiomers

The opposite enantiomers of pseudoephedrine were observed to react in the solid state to form the racemic compound. A novel powder X-ray diffractometric method was developed for studying the kinetics and mechanism of this reaction. The powder X-ray diffraction patterns of the enantiomers were identical, but the racemic compound exhibited a different pattern because of its different crystal structure. The powder patterns of the enantiomers and the racemic compound revealed that the 4.62 and 4.25 A lines were unique to the enantiomers and the racemic compound, respectively. Teflon holders were filled with equimolar mixtures of the two enantiomers, and the integrated intensities of the 4.62 and 4.25 A lines were measured at 30-min intervals over a period of 8 h. Thus, the disappearance of the crystalline enantiomers and the appearance of the crystalline racemic compound were quantified simultaneously. The rate of disappearance of the crystalline enantiomers followed a diffusion-controlled reaction model originally proposed by Jander in 1927. During the kinetic experiment, the sum of the weight fractions of the enantiomers and the racemic compound progressively decreased from an initial value of unity suggesting the existence of an intermediate noncrystalline phase. The presence of the noncrystalline phase was confirmed by a steady increase in the background of the X-ray patterns. Thus, the unique ability of the X-ray method to quantify only the crystalline phases has demonstrated the existence of a non-crystalline amorphous intermediate in this solid-solid reaction.

Comparison of three new spectrophotometric methods for simultaneous determination of aspirin and salicylic acid in tablets without separation of pharmaceutical excipients

Simultaneous analysis of aspirin (ASA) and salicylic acid (SA) in pharmaceutical tablet preparations was performed by two multicomponent UV-spectrophotometric methods utilizing principal component regression and classical least square algorithm. Additionally, an assay procedure based on second-derivative spectroscopy was developed. The analysis was performed in turbid solutions without separation of interfering excipients. The range, as determined by the second-derivative methods, was 0.2 to 103.2 micrograms/mL for ASA and 0.07 to 44.5 micrograms/mL for SA. Sensitivity for determination of SA was 0.004% of ASA content for the second-derivative method and 0.2% of ASA content for both multicomponent methods. The methods were applied to laboratory mixtures and commercial tablet formulations containing ASA and SA. The advantage of the second-derivative method in determining small amounts of SA in commercial tablet preparations is shown in comparison with a conventional HPLC method. All UV-spectrophotometric methods are rapid, accurate, and reproducible.

Formation of the racemic compound of ephedrine base from a physical mixture of its enantiomers in the solid, liquid, solution, or vapor state

Physical mixtures (conglomerates) of the two enantiomers of ephedrine base, each containing 0.5% (w/w) of water, were observed to be converted to the 1:1 racemic compound in the solid, liquid, solution, or vapor state. From a geometrically mixed racemic conglomerate of particle size 250-300 microns (50-60 mesh), the formation of the racemic compound follows second-order kinetics (first order with respect to each enantiomer), with a rate constant of 392 mol-1 hr-1 at 22 degrees C. The reaction appears to proceed via the vapor phase as indicated by the growth of the crystals of the racemic compound between diametrically separated crystals of the two enantiomers in a glass petri dish. The observed kinetics of conversion in the solid state are explained by a homogeneous reaction model via the vapor and/or liquid states. Formation of the racemic compound from the crystals of ephedrine enantiomers in the solution state may explain why Schmidt et al. (Pharm. Res. 5:391-395, 1988) observed a consistently lower aqueous solubility of the mixture than of the pure enantiomers. The solid phase in equilibrium with the solution at the end of the experiment was found to be the racemic compound, whose melting point and heat of fusion are higher than those of the enantiomers. An association reaction, of measurable rate, between the opposite enantiomers in a binary mixture in the solid, liquid, solution, or vapor state to form the racemic compound may be more common than is generally realized.

Solid-state esterification of codeine phosphate by the acid constituent of effervescent tablets

Codeine phosphate in a paracetamol:codeine effervescent tablet was found to react at room temperature and 37 degrees C with the citric acid constituent to form citrate esters of codeine. The esterification was confirmed in a solid-state reaction at elevated temperature. The structures of the three possible monosubstituted esters (1-3) were elucidated from spectroscopic data (nuclear magnetic resonance and mass spectrometry) and by selective hydrolysis of the dimethyl esters to give symmetrical and asymmetrical dimethyl citrates. In the degradation reaction, formation of the symmetrically substituted citrate ester of codeine, 1, was found to predominate. Tartaric acid, which can be used in effervescent tablet formulations, was also found to give an ester with codeine phosphate in a similar nonsolvolytic reaction. A liquid chromatographic method was developed for the separation of the citrate esters of codeine.

Analysis of a complex analgesic formulation by high-performance liquid chromatography with column-switching

An isocratic method is described which allows the complete separation of acetylsalicylic acid, paracetamol, caffeine, carbromal, bromisoval and codeine as well as the potential impurities salicylic acid, diacetyl-p-aminophenol and acetylcodeine. A column-switching technique was developed employing two columns (10 cm and 25 cm) containing 7-microm Zorbax C(8) material. The separation is better and faster than that obtained with a gradient elution method.

Stability of aspirin in solid mixtures

It has been shown that the degradation of aspirin in mixtures may be monitored by thermal analytical techniques. The methodology employed differential scanning calorimetry and thermal gravimetric analysis by standard techniques providing simple and rapid analysis for screening the stability of aspirin in mixtures. The degradation was found to depend on the nature of the additive but, in particular, the presence of acidic or basic groups within its structure.

Analysis of tablets containing acetylsalicylic acid and phenylephrine by high-performance liquid chromatography

A high-performance liquid chromatographic method permitted the quantitation of acetylsalicylic acid, phenylephrine, caffeine and phenacetin in tablets, and of the main impurities, salicylic acid and mono- and diacetyl derivatives of phenylephrine. A C8 reversed-phase column was used with a mobile phase containing methanol-1 M phosphoric acid-water 34:5:61 v/v/v.

Simultaneous GLC analysis of aspirin and nonaspirin salicylates in pharmaceutical tablet formulations

The analysis of aspirin and nonaspirin salicylates in buffered and plain tablet formulations employing nearly nonaqueous extraction is described. The results obtained compare favorably with those obtained from USP procedures. A simultaneous assay for aspirin and nonaspirin salicylates in buffered tablets involves the use of an acidified chromatographic siliceous earth column for the separation of the aspirin and nonaspirin salicylates from various buffers or antacids. The methods described here have definite advantages over USP XX procedures, and the buffered aspirin tablet procedures also is adaptable to aspirin formulations containing codeine, acetaminophen, propoxyphene, caffeine, and many antihistamines.