Free radicals in irradiated drugs: an EPR study

Exposure of dry powder forms of the drugs nitrendipine, nifedipine, felodipine, and nimodipine to gamma-radiation results in the formation of free radicals detected by electron paramagnetic resonance (EPR) spectroscopy. The four structurally related drugs show qualitatively identical EPR spectral features in terms of g-values, the qualitative descriptive parameter. These radicals are very stable, surviving long periods of time in excess of 9 months and possibly beyond conventional shelf-life of the drugs. The residual radical population is high enough to be detectable after long storage. Administration of such radiation-treated drugs may present patients with quantities of free radicals and possibilities of secondary cell damage.

Evaluation of nifedipine preparations by chromatographic-spectrophotometric methods

The content of nifedipine in 10 currently available preparations (tablets, capsules, dragees and drops) was analyzed. In the qualitative analysis, a TLC method was employed, whereas in the quantitative analysis, a chromatographic-spectrophotometric method developed in our laboratory (TLC-UV), a TLC-UV method according to USP XXI, and the method of gas chromatography coupled with mass spectrometry (GC-MS) were employed. For all the preparations under study, the presence of at least one decomposition product as well as a decrease in the content of active component, in most cases proportional to the storage time, were observed. However, in none of the preparations pyridine nitro derivative decomposition products were found, but in each the presence of nitroso derivative was reported. As a result, it was stated that about a half of the preparations studied do not meet the requirements of USP XXI as for as the content of the active substance is concerned, which suggests that the expiration date is shorter by 6 to 12 months.

Photochemical decomposition of phenazone derivatives. Part 7: Mechanism of decomposition in aqueous solutions

Kinetic studies, supplemented by the isolation and identification of the products of decomposition, have proved the process of photochemical decomposition of phenazone derivatives to be a complex reaction, involving several successive parallel reactions, one of which is predominant depending on the concentration of the solution and the atmosphere above it. In an oxygen-free atmosphere and at low concentrations (10(-4) mol/dm3) decomposition is almost wholly the result of second photolysis of zero order to aziridine derivative----aniline----isonitrile. At higher concentrations (10(-3)-10(-2) mol/dm3), the contribution from the reaction of water photoaddition to the double bond C3-C4 increases. Whereas at concentrations of order greater than or equal to 10(-2) mol/dm3, photoisomerization to imidazole derivatives is predominant. In air, one onserves additionally a second reaction of photooxidation to 4-hydroxy-phenazone----1-acetylo-1-methyl-2-phenyl-hydrazine, a reaction of photodemethylation at N2 with simultaneous oxidation to the 4-ketoderivative, and reactions of hydrolysis characteristic for the individual derivatives. The principal primary photolytic reaction for the group of compounds studied consists in cleavage of the N1-N2 bond of the pyrazoline ring.

Photochemical decomposition of phenazone derivatives. Part 6: Effect of substituents on mass fragmentation and photochemical stability

Mass spectra (EI) of phenazone, aminophenazone, 4-aminophenazone, noramidopyrine, isopropyl-aminophenazone, niphenazone, propylphenazone and morazone are obtained. The fragmentation pathways are discussed and the mechanisms of spectrometric fragmentation, as well as their similarities and differences within the group under investigation, are determined. A Hammett relationship is found to hold between the intensity of certain ions and the type of substituent on the C-4 positions. Certain similarities are established between photochemical decomposition and spectroscopic fragmentation, and it is suggested that MS may prove useful when making predictions concerning the photochemical stability of phenazone derivatives.

Photochemical decomposition of phenazone derivatives. Part 5(1): Isolation and identification of decomposition products in aqueous solution

From aqueous solutions of phenazone, aminophenazone, propyphenazone, nifenazone, morazone, noramidopyrine, 4-aminophenazone and isopropylaminophenazone, UV irradiated at lambda = 254 nm in oxygen free atmosphere as well as in the presence of air, 24 decomposition products were isolated and identified as derivatives of pyrazoline, pyrazolidinone, imidazoline, hydantoin, aziridine, phenylhydrazine and aniline.

Kinetics of drug decomposition. Part 73. Kinetics and mechanism of vitamin K3 soluble form thermal decomposition in solid phase

Kinetics of thermal decomposition of trihydrate of sodium salt of 1,2,3,4-tetrahydro-2-methyl-1,4-dioxo-2-naphthalenesulfonic acid (MDS, vitamin K3 soluble form) in solid state by accelerated aging method at elevated temperature has been studied. It was found that the process occurs according to Prout-Tompkins model and its rate depends on temperature, humidity and particle size of the substance. Thermodynamic parameters of the reaction (Q10(0), EA, delta H not equal to, delta S not equal to, delta G) were determined and theoretically predicted stability of MDS at room temperature is given. The reaction mechanism assumes a preliminary dehydration occurring via the successive elimination of one and a half, two and a half and finally three molecules of water. The obtained anhydrous form decomposes thermally forming free radical intermediates and yielding finally 2-methyl-1,4-naphthoquinone (vitamin K3), SO2 and NaOH.

Kinetics of drug decomposition. Part 69: Effect of excipients on the thermal decomposition of the mixture of aminophenazone allobarbital and adiphenine hydrochloride in the solid

By the method of accelerated testing at elevated temperature, the thermal decomposition rate of the mixture of aminophenazone (AP), allobarbital (AB) and adiphenine hydrochloride (AD) and its individual components in the presence of the excipients starch (potato), agar, talcum, kaolin and magnesium stearate is studied. The individual and joint effect of the excipients on the components of the mixture AP + AB + AD as well as on the mixture as a whole is determined and compared. The theoretically predicted stability of the components is discussed and compared with the results of "self-life" tests in the presence and absence of the excipients.

Kinetics of drug decomposition. Part 60. Thermal decomposition of the mixture of aminophenazone, allobarbital and adiphenine hydrochloride in the solid state

Kinetics of decomposition of a mixture of aminophenazone, allobarbital and adiphenine hydrochloride has been examined using accelerated testing at elevated temperatures (333-353 K). The reaction order, rate constants and activation parameters (Q10 degrees, EA, delta H#, delta S#, delta G) have been determined and compared for each component, in the presence of each component of the mixture and in the presence of two components of the mixture. The effect of individual components of the mixture on the rate of decomposition of the other components has been observed, the value of this effect has been determined using the rate constants obtained. The rate constants and times t10% for room temperature were calculated. The "shelf-life time" (t10%) was calculated from accelerated testing data at elevated temperature and compared with that obtained for Vegantalgin ragées in the mixture studied at 293 K.

Chemical characterization of decomposition products of drugs. Part 6. Mass spectrometry of some perazine derivatives

Mass spectra of perazine, prochlorperazine, tiethylperazine, trifluperazine, butaperazine and thioproperazine were obtained. All possible fragmentation routes were discussed. The mechanism of fragmentations, their similarities and differences within the investigated group of compounds were established. The Hammett type relationship was found between the intensities of some ions and the kind of substituents at the C2 position. The utility of mass spectra for the prediction of drug stability was demonstrated.

Kinetics of drug decomposition. Part 46. Photooxidation and photolysis of some perazine derivatives

The rate and type of the photochemical degradation of perazine derivatives in acidic aqueous solutions depends upon the nature of the substituent at C2 atom. Free perazine degrades by two parallel reactions, namely a fast reversible first-order photooxidation and a slow zero-order photolysis. An introduction of the substituent in the C2 position results frequently in the elimination of one of these reactions.

Kinetics of drug decomposition. Part 47. Effect of substituents on photochemical stability of perazine derivatives

A quantum yield phi of photooxidation of perazine derivatives estimated actinometrically and the pKa, values were used for the correlation with the substituent volumes. The Hammett type plots of phi= f(sigma) and phi= f(pKa10--pKa1) are discussed.