A Systematic Degradation Kinetics Study of Dalbavancin Hydrochloride Injection Solutions

The degradation kinetics of the glycopeptide antibiotic dalbavancin in solution are systematically evaluated over the pH range 1–12 at 70°C. The decomposition rate of dalbavancin was measured as a function of pH, buffer composition, temperature, ionic strength, and drug concentration. A pH-rate profile was constructed using pseudo first-order kinetics at 70°C after correcting for buffer effects; the observed pH-rate profile could be fitted with standard pseudo first order rate laws. The degradation reactions of dalbavancin were found to be strongly dependent on pH and were catalyzed by protons or hydroxyl groups at extreme pH values. Dalbavancin shows maximum stability in the pH region 4–5. Based on the Arrhenius equation, dalbavancin solution at pH 4.5 is predicted to have a maximum stability of thirteen years under refrigerated conditions, eight months at room temperature and one month at 40°C. Mannosyl Aglycone (MAG), the major thermal and acid degradation product, and DB-R6, an additional acid degradation product, were formed in dalbavancin solutions at 70°C due to hydrolytic cleavage at the anomeric carbons of the sugars. Through deamination and hydrolytic cleavage of dalbavancin, a small amount of DB-Iso-DP2 (RRT-1.22) degradation product was also formed under thermal stress at 70°C. A greater amount of the base degradation product DB-R2 forms under basic conditions at 70°C due to epimerization of the alpha carbon of phenylglycine residue 3.     

Isoxazoles. VII: Hydrolysis of 4-methyl-5-isoxazolylnaphthoquinone derivatives in aqueous solutions

The kinetics for the degradation of 2-(4-methyl-5-isoxazolylamine)-N-(4-methyl-5-isoxazolyl)-1,4 -naphthoquinone-4- imine (1) in solution were investigated at 70 degrees C and at a constant ionic strength of 0.5 over a pH range of 1.75 to 12.85. The degradation rates were determined by absorption and second-derivative UV spectrometry. Two degradation products were identified in acidic and neutral pHs; they are 4-N-(4-methyl-5-isoxazolyl)-1,2-naphthoquinone (2) and 2-methyl-cyanoacetamide (5), respectively. In alkaline pH, two degradation products, 2-hydroxy-N-(4-methyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (3) and 5-amino-4-methylisoxazole (4), were isolated. The pathway for degradation of 1 in acidic and neutral pH followed consecutive first-order kinetics since 2 undergoes hydrolysis giving 2-hydroxy-1,4-napthoquinone (6) and 2-methylcyanoacetamide (5). No appreciable buffer effect on the degradation of 1 and 2 was observed for any of the buffer species in this study. The pH-rate profiles exhibited specific acid and specific basic catalysis for 1 and specific acid catalysis for 2. The maximum stability for 1 and 2 occurred in the neutral pH region.     

Degradation kinetics of phentolamine hydrochloride in solution

The degradation kinetics of phentolamine hydrochloride in aqueous solution over a pH range of 1.2 to 7.2 and its stability in propylene glycol- or polyethylene glycol 400-based solutions were investigated. The observed rate constants were shown to follow apparent first-order kinetics in all cases. The pKa determination for phentolamine hydrochloride was found to be 9.55 +/- 0.10 (n = 5) at 25 +/- 0.2 degrees C. This indicated the protonated form of phentolamine occurs in the pH range of this study. The pH-rate profile indicated a pH-independent region (pH 3.1-4.9) exists with a minimum rate around pH 2.1. The catalytic effect of acetate and phosphate buffer species is ordinary. The catalytic rate constants imposed by acetic acid, acetate ion, dihydrogen phosphate ion, and monohydrogen phosphate ion were determined to be 0.018, 0.362, 0.036, and 1.470 L mol-1 h-1, respectively. The salt effect in acetate and phosphate buffers followed the modified Debye-Huckel equation quite well. The ZAZB value obtained from the experiment closely predicts the charges of the reacting species. The apparent energy of activation was determined to be 19.72 kcal/mol for degradation of phentolamine hydrochloride in pH 3.1, 0.1 M acetate buffer solution at constant ionic strength (mu = 0.5). Irradiation with 254 nm UV light at 25 +/- 0.2 degrees C showed a ninefold increase in the degradation rate compared with the light-protected control. Propylene glycol had little or no effect on the degradation of phentolamine hydrochloride at 90 +/- 0.2 degrees C; however, polyethylene glycol 400 had a definite effect.     

Degradation kinetics of a new cephalosporin derivative in aqueous solution.

The degradation kinetics of a new cephalosporin derivative (1) in aqueous solution were investigated at 60 degrees, mu = 0.05, at pH 2.0-10.0. The observed degradation rates followed pseudo-first-order kinetics and were influenced significantly by H2O and OH- catalysis. No primary salt effect was observed in the acid region, but a positive salt effect was observed at pH 9.4. A general base catalytic effect by a phosphate buffer species was observed at pH 7-8. The pH-rate profile for I exhibited a degradation minimum at pH 6.05. The Arrhenius activation energies determined at pH 4.0 and 9.4 were 27.2 and 24.5 kcal/mole, respectively. Excellent agreement between the theoretical pH-rate profile and the experimental data supported the hypothesized degradation process. A comparison of I and cefazolin revealed close structural and stability analogies.     

Kinetics and mechanisms of degradation of the antileukemic agent 5-azacytidine in aqueous solutions.

The hydrolytic degradation of 5-azacytidine was studied spectrophotometrically as a function of pH, temperature, and buffer concentration. Loss of drug followed apparent first-order kinetics in the pH region below 3. At pH less than 1,5-azacytosine and 5-azauracil were detected; at higher pH values, drug was lost to products which were essentially nonchromophoric if examined in acidic solutions. The apparent first-order rate constants associated with formation of 5-azacytosine and 5-azauracil from 5-azacytidine are reported. Above pH 2.6, first-order plots for drug degradation are biphasic. Apparent first-order rate constants and coefficients for the biexponential equation are given as a function of pH and buffer concentration. A reaction mechanism consistent with the data is discussed together with problems associated with defining the stability of the drug in aqueous solutions. At 50 degrees, the drug exhibited maximum stability at pH 6.5 in dilute phosphate buffer. Similar solutions were stored at 30 degrees to estimate their useful shelflife. Within 80 min, 6 times 10(-4) M solutions of 5-azacytidine decreased to 90% of original potency based on assumptions related to the proposed mechanisms.     

Kinetics and mechanism of degradation of cefotaxime sodium in aqueous solution

The degradation kinetics and mechanism of a potent new cephalosporin, cefotaxime sodium, in aqueous solution were investigated at pH 0-10 at 25 degrees and an ionic strength of 0.5. The degradation rates were determined by high-pressure liquid chromatography and were observed to follow pseudo first-order kinetics with respect to cefotaxime sodium concentration. The data suggested that the rate of degradation was influenced significantly by solvolytic, hydrogen ion, and hydroxide ion catalysis. No primary salt effects were observed in the acid or neutral regions; however, a positive salt effect was observed at pH 8.94. Buffer catalysis due to the buffer species employed was not seen during the kinetic studies. The pH-rate profile at 25 degrees indicated that the maximum stability of cefotaxime sodium occurred in the pH 4.5-6.5 region. In aqueous solution, cefotaxime was shown to degrade by two parallel reactions: de-esterification at the C-3 position and beta-lactam cleavage. Good agreement between the theoretical pH-rate profile and the experimental data support the proposed degradation process.     

Stability of batanopride hydrochloride in aqueous solutions.

The degradation of batanopride hydrochloride, an investigational antiemetic drug, was studied in aqueous buffer solutions (pH 2-10; ionic strength, 0.5; 56 degrees C) in an attempt to improve drug stability for parenteral administration. Degradation occurs by two different mechanisms depending on the pH of the solution. In acidic media (pH 2-6), the predominant reaction was intramolecular cyclization followed by dehydration to form a 2,3-dimethylbenzofuran. There was no kinetic or analytical (high-performance liquid chromatography) evidence for the formation of an intermediate; therefore, the rate of dehydration must have been very rapid compared with the rate of cyclization. In alkaline media (pH 8-10), the primary route of degradation was cleavage of the C-O alkyl ether bond. In the intermediate pH range (pH 6-8), both reactions contributed to the overall degradation. Both degradation reactions followed apparent first-order kinetics. The pH-rate profile suggests that batanopride hydrochloride attains its optimal stability at pH 4.5-5.5. Citrate buffer was catalytic at pH 3 and 5, and phosphate buffer was catalytic at pH 8. No catalytic effect was observed for the borate buffer at pH 9-10.     

A kinetic study of the chemical stability of the antimetastatic ruthenium complex NAMI-A

NAMI-A is a novel ruthenium complex with selective activity against cancer metastases currently in Phase I clinical trials in The Netherlands. The chemical stability of this new agent was investigated utilizing a stability-indicating reversed-phase high performance liquid chromatographic assay with ultraviolet detection and ultraviolet/visible light spectrophotometry. The degradation kinetics of NAMI-A were studied as a function of pH, buffer composition, and temperature. Degradation of NAMI-A follows first-order kinetics at pH<6 and zero-order kinetics at pH > or =6. A pH-rate profile, employing rate constants extrapolated to zero buffer concentration, was constructed, demonstrating that NAMI-A is most stable in pH region 3-4. The degradation rate is not significantly affected by specific buffer components. Storage temperature strongly influences the degradation rate.     

Triazolines. XXI: Preformulation degradation kinetics and chemical stability of a novel triazoline anticonvulsant.

The effect of pH, temperature, and two buffer species (citric acid-phosphate and bicarbonate-carbonate) on the stability of 1-(4-chlorophenyl)-5-(4-pyridyl)-delta 2-1,2,3-triazoline (ADD17014; 1), a novel triazoline anticonvulsant, was determined by HPLC. One of the main degradation products of 1 at pH 7.0 was isolated by TLC and identified as the aziridine derivative by MS. Investigations were carried out over a range of pH (2.2-10.7) and buffer concentration [ionic strength (mu), 0.25-4.18] at 23 degrees C. The degradation followed buffer-catalyzed, pseudo-first-order kinetics and was accelerated by a decrease in pH and an increase in temperature. The activation energy for the degradation in citric acid-phosphate buffer (pH 7.0 and constant ionic strength mu at 0.54) was 12.5 kcal/mol. General acid catalysis was observed at pH 7.0 in citric acid-phosphate buffer. The salt effect on the degradation obeyed the modified Debye-Hückel equation well; however, the observed charge product (ZAZB) value (2.69) deviated highly from the theoretical value (1.0), perhaps because of the high mu values (0.25-4.18) of the solutions used. The stability data will be useful in preformulation studies in the development of a stable, oral dosage form of 1.     

Effects of alkali and simulated gastric and intestinal fluids on danazol stability

The degradation kinetics of methanolic solution of danazol (0.020% w/v) in aqueous buffers and sodium hydroxide was investigated using stability-indicating HPLC method. The drug degrades in alkaline medium through a base-catalysed proton abstraction rather than via an oxidative mechanism involving oxygen species. The degradation followed pseudo-first-order kinetics. The rates pH-profile exhibited specific base catalysis. The stability of the drug was found to be dependent on pH, buffer concentration, buffer species (acetate, borate, phosphate) and temperature. The ionic strength did not affect the stability of the drug. The energy of activation according to Arrhenius plot was estimated to be 22.62 kcal mol(-1) at pH 12 and temperatures between 30 and 60 degrees C. The effect of simulated gastric and intestinal fluids on the drug stability was also investigated. Two major hydrolytic degradation products were separated and identified by IR, NMR and mass spectrometry and the degradative pathway suggested.     

Nefopam hydrochloride degradation kinetics in solution

A stability-indicating reversed-phase high performance liquid chromatographic method was developed for the detection of nefopam hydrochloride and its degradation products under accelerated degradation conditions. The degradation kinetics of nefopam hydrochloride in aqueous solutions over a pH range of 1.18 to 9.94 at 90 +/- 0.2 degrees C was studied. The degradation of nefopam hydrochloride was found to follow apparent first-order kinetics. The pH-rate profile shows that maximum stability of nefopam hydrochloride was obtained at pH 5.2-5.4. No general acid or base catalysis from acetate, phosphate, or borate buffer species was observed. The catalytic rate constants on the protonated nefopam imposed by hydrogen ion and water was determined to be 7.16 X 10(-6) M-1 sec-1, and 4.54 X 10(-9) sec-1, respectively. The pKa of nefopam hydrochloride in aqueous solution was determined to be 8.98 +/- 0.33 (n = 3) at 25 +/- 0.2 degrees C by the spectrophotometric method. The catalytic rate constant of hydroxyl ion on the degradation of nefopam in either protonated or nonprotonated form was determined to be 6.63 X 10(-6) M-1 sec-1 and 4.06 X 10(-6) M-1 sec-1, respectively. A smaller effect of hydroxyl ion on the degradation of nonprotonated than on the degradation of protonated nefopam was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Degradation kinetics and mechanism of N6-[(dimethylamino)methylene]mitomycin C in aqueous solutions

The degradation of N6-[(dimethylamino)methylene]mitomycin C, a semisynthetic analogue of mitomycin C, was studied in aqueous solution. The compound degraded rapidly and followed pseudo-first-order kinetics in both acidic (pH less than 5) and basic pH greater than or equal to 9) media. In the near-neutral pH region, however, biphasic kinetics were observed. At the pH of maximum stability (6.5), 10% activity was lost after approximately 6 h at 22 degrees C. Citrate and phosphate species were catalytic at pH 6.5. Spectrophotometric and HPLC methods were used to elucidate the degradation mechanism at pH 7-9. Under these conditions, equilibrium addition of one water molecule into the amidine side chain occurred, followed by parallel formation of mitomycin C and N6-(formyl)mitomycin C. The latter compound subsequently hydrolyzed to mitomycin C.     

Solution stability of ciclosidomine

The stability of N-cyclohexanecarbonyl-3-(4-morpholino)-sydnone imine hydrochloride (ciclosidomine) in solution was studied as a function of pH, temperature, ionic strength, and buffer species. The rate of hydrolysis in the absence of light was found to be apparent first order in drug and general acid- and base-catalyzed reactions. The pH rate profile at an ionic strength of 0.1 M at 60 degrees C had a minimum value near pH 6. Change in ionic strength in the range of 0.05 to 0.2 M did not affect the rate of degradation at pH 7 (carbonate buffer) or pH 2 (phosphate buffer) at 60 degrees C. Similar degradation rates were noticed in air or nitrogen in the dark at pH 3, 5, and 6. However, degradation in light was very rapid in either case at pH 3, 5, and 6, and, therefore, the protection of solutions from light was required during all studies. The time for 10% loss of drug in solution at pH 6 in dilute phosphate or citrate buffer at an ionic strength of 0.154 M was projected to be 9 months at 20 degrees C and 2.6 months at 30 degrees C.     

Kinetics of degradation of cefazolin and cephalexin in aqueous solution.

The kinetics of degradation of cefazolin and cephalexin in aqueous solution were investigated at 60 degrees C and constant ionic strength over the entire pH range. The observed degradation rates were obtained by measuring the residual cephalosporin and were shown to follow pseudo-first-order-kinetics. They were influenced significantly by solvolytic and hydroxide ion catalysis. No primary salt effect was observed in the acid or basic pH region. Of the buffer systems employed in the kinetics studies only the phosphate buffer system showed a catalytic effect. The pH-rate profile for cefazolin showed a degradation minimum between pH 5.5 and 6.5. Cephalexin did not show a pH minimum in that region. The apparent energies of activation were determined for cefazolin and cephalexin at pH 5.5 and were calculated to be 24.3 Kcal/mole and 26.2 Kcal/mole, respectively. The agreement between the calculated theoretical pH-rate profiles and the experimental points for both compounds support the hypothesis presented concerning the reactions involved in their respective degradation pathways.     

Stability of the new antileukemic 4-pyranone derivative, BTMP, using HPLC and LC-MS analyses

The stability of the new antileukemic kojic acid derivative, 5-benzyloxy-2-thiocyanatomethyl-4-pyranone (BTMP) was investigated. The degradation of BTMP was studied using specific and reproducible HPLC and LC-MS methods. Accelerated stability studies of BTMP were conducted in 0.1 M hydrochloric acid solution, physiological phosphate buffer solution (pH 7.5) and basic phosphate buffer solution (pH 9.0) at 30, 40 and 60 degrees C, respectively. The degradation of BTMP was found to follow pseudo-first order kinetics. In basic solution (pH 9.0) BTMP underwent rapid hydrolysis at a degradation rate constant (0.183-0.638 h-1) and degradation half-life (3.67-1.06 h) depending on the temperature setting. On the other hand, BTMP was significantly stable in 0.1 M hydrochloric acid solution (kdeg: 0.0017-0.0052 h-1; degradation half-life t1/2: 408.6-135.7 h), whereas in physiological phosphate buffer solution (pH 7.5), BTMP was only moderately stable (kdeg: 0.006-0.231 h-1; degradation half-life: 117.7-3.0 h). Arrhenius plots were constructed to predict the degradation kinetic parameters of BTMP at 25 degrees C and 4 degrees C. LC-MS analyses confirmed the degradation of BTMP in basic solutions and indicated at least two degradation products; namely 5-benzyloxypyran-2-ol-4-one (m/z 217.8) and 2-thiocyanatomethylpyran-5-ol-4-one (m/z 181.6).     

Synthesis and chemical stability of a disulfide bond in a model cyclic pentapeptide: cyclo(1,4)-Cys-Gly-Phe-Cys-Gly-OH

Many cyclic peptides are formed using a disulfide bond to increase their conformational rigidity; this provides receptor selectivity and increased potency. However, degradation of the disulfide bond in formulation can lead to a loss of structural stability and biological activity of the peptide. Therefore, the objective of this study was to study the stability of peptide 1 (cyclo(1,4)-Cys-Gly-Phe-Cys-Gly-OH). This cyclic peptide was synthesized using Boc strategy via solution-phase peptide synthesis and purified using semi-preparative HPLC. The accelerated stability studies of the cyclic peptide were conducted in buffer solutions at pH 1.0-11.0 with controlled ionic strengths at 70 degrees C. The pH-rate profile shows that the peptide has an optimal stability around pH 3.0 with a V-shape between pH 1.0 and 5.0. Two small plateaus are observed at pH 5.0-7.0 and pH 8.0-10.0, indicating hydrolysis on different ionized forms of the cyclic peptide. One product was observed at acidic pH due to peptide bond hydrolysis at Gly2-Phe3. The number of degradation products increases as the pH increases from neutral to basic, and most of the degradation products at neutral and basic pH are derived from the degradation at the disulfide bond.     

Preformulation study of atenolol-containing solutions.. I. The pH dependence of thermostability

The stability of atenolol solutions was evaluated under accelerated isothermal degradation conditions at 90 degrees C. A specific and sensitive HPLC method was adapted to study the pH dependence of the stability. The maximum stability of atenolol was achieved at pH 4 with a k value of 1.1 x 10(-3) h-1. The degradation of atenolol followed first-order kinetics at above mentioned conditions.     

Stability experiments in human urine with EO9 (apaziquone): a novel anticancer agent for the intravesical treatment of bladder cancer

EO9 (apaziquone) is a novel, promising anticancer agent, which is currently being investigated for the intravesical treatment of bladder cancer. EO9 contains a highly reactive aziridine ring in its structure that limits its chemical stability in acidic aqueous solutions. The stability of the pharmaceutically formulated EO9 in human urine, including the effects of several parameters such as temperature, buffer strength and pH have been investigated. Urine extracts were analyzed by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (HPLC-MS/MS) using a TurboIonspray interface and positive-ion multiple reaction monitoring. EO9 was unstable in urine at 43 degrees C during the instillation for longer than 1 h. However, the drug was stable in human urine for 3 h at 37 degrees C. EO9 is stable in urine stabilized with TRIS buffer (pH 9.0; 5 mM) for up to three freeze/thaw cycles at -20 and -70 degrees C and 3 months of storage at -70 degrees C. The results also illustrated that with the lower pH in urine, EO9 became more unstable. Furthermore, a new degradation product of EO9 was discovered and successfully identified as EO9-Cl. The outcomes of these stability experiments will be implemented to insure proper sample handling at the clinical sites, transport, storage, and sample handling during analysis in the forthcoming preclinical studies of EO9 in superficial bladder cancer, supported by bioanalysis and pharmacokinetic monitoring.     

Analysis of the stability and degradation products of triptolide

Triptolide is the major active ingredient of the Chinese herbal remedy Tripterygium wilfordii Hook F. (TwHF). As triptolide content is used to estimate the potency of preparations of TwHF, assessment of its stability is warranted. The accelerated stability of triptolide was investigated in 5% ethanol solution in a light-protected environment at pH 6.9, within a temperature range of 60-90 degrees C. The observed degradation rate followed first-order kinetics. The degradation rate constant (K25 degrees C) obtained by trending line analysis of Arrhenius plots of triptolide was 1.4125 x 10(-4) h(-1). The times to degrade 10% (t1/10) and 50% (t1/2) at 25 degrees C were 31 and 204 days, respectively. Stability tests of triptolide in different solvents and different pH conditions (pH4-10) in a light-protected environment at room temperature demonstrated that basic medium and a hydrophilic solvent were the major factors that accelerated the degradation of triptolide. Triptolide exhibited the fastest degradation rate at pH 10 and the slowest rate at pH 6. In a solvent comparison, triptolide was found to be very stable in chloroform. The stability of triptolide in organic polar solvents tested at both 100% and 90% concentration was greater in ethanol than in methanol than in dimethylsulphoxide. Stability was also greater in a mixture of solvent:pH6 buffer (9:1) than in 100% solvent alone. An exception was ethyl acetate, which is less polar than the other solvents tested, but permitted more rapid degradation of triptolide. Two of the degradation products of triptolide were isolated and identified by HPLC and mass spectroscopy as triptriolide and triptonide. This suggested that the decomposition of triptolide occurred at the C12 and C13 epoxy group and the C14 hydroxyl. The opening of the C12 and C13 epoxy is an irreversible reaction, but the reaction occurring on the C14 hydroxyl is reversible. These results show that the major degradation pathway of triptolide involves decomposition of the C12 and C13 epoxy group. Since this reaction is very slow at 4 degrees C at pH 6, stability is enhanced under these conditions.     

Stability of aqueous solutions of mibolerone.

The kinetics and mechanism of degradation of mibolerone were studied in aqueous buffered solutions in the pH range of 1-8 at 67.5 degrees. Mibolerone showed maximum stability between pH 5.5 and 6.4. At pH 1-2, the major degradative pathway was dehydration followed by migration of the 18-methyl group to form 7alpha,17,17-trimethylgona-4,13-dien-3-one. While there was only one degradation product at pH 1-2, the degradation at pH 7-8 was complex. As many as 12 degradation products were detected by GLC. Mass spectral data indicated that the majority of these products were either oxidation products or isomers. At pH 7.6, the apparent first-order rate constants exhibited marked dependency on buffer concentration. Incorporation of a sequestering agent into the solutions eliminated this dependency, suggesting that trace metal impurities from the buffer reagents were catalyzing the degradation. This was confirmed by degradation studies of solutions in water for injection containing 5 ppm of trace metal ions. Sn+2, Cu"2, and Fe+2 accelerated the degradation, with Fe+2 having the most catalytic effect. The temperature dependence of the rate of degradation was studied in 0.05 M phosphate buffer at pH 6.4. The activation energy was 19.6 +/- 1.63 kcal/mole.