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Saranjit Singh

Publications and source records attributed to Saranjit Singh.

At least 19 recordsLinked to original sources
PubMed2006

LC and LC-MS study of stress decomposition behaviour of isoniazid and establishment of validated stability-indicating assay method.

Isoniazid was subjected to different ICH prescribed stress conditions of thermal stress, hydrolysis, oxidation and photolysis. The drug was stable to dry heat (50 and 60 degrees C). It showed extensive decomposition under hydrolytic conditions, while it was only moderately sensitive to oxidation stress. The solid drug turned intense yellow on exposure to light under accelerated conditions of temperature (40 degrees C) and humidity (75% RH). In total, three major degradation products were detected by LC. For establishment of stability-indicating assay, the reaction solutions in which different degradation products were formed were mixed, and the separation was optimized by varying the LC conditions. An acceptable separation was achieved using a C-18 column and a mobile phase comprising of water:acetonitrile (96:4, v/v), with flow rate and detection wavelength being 0.5 ml min(-1) and 254 nm, respectively. The degradation products appeared at relative retention times (RR(T)) of 0.71, 1.34 and 4.22. The validation studies established a linear response of the drug at concentrations between 50 and 1000 microg ml(-1). The mean values (+/-R.S.D.) of slope, intercept and correlation coefficient were 35,199 (+/-0.88), 114,310 (+/-4.70) and 0.9998 (+/-0.01), respectively. The mean R.S.D. values for intra- and inter-day precision were 0.24 and 0.90, respectively. The recovery of the drug ranged between 99.42 and 100.58%, when it was spiked to a mixture of solutions in which sufficient degradation was observed. The specificity was established through peak purity testing using a photodiode array detector. The method worked well on application to marketed formulation of isoniazid, and a fixed-dose combination containing isoniazid and ethambutol HCl. It was even extendable to LC-MS studies, which were carried out to identify the three degradation products. The m/z values of the peaks at RR(T) 0.71 and RR(T) 1.34 matched with isonicotinic acid and isonicotinamide, respectively. The product appearing at RR(T) 4.22 was isolated using preparative LC-MS, and turned out to be a yellow compound that was identified as isonicotinic acid N'-(pyridyl-4-carbonyl)-hydrazide based on mass, FTIR and (1)H/(13)C NMR spectral data. The same was indicated to be responsible for discolouration of isoniazid bulk drug substance and formulations, which is a familiar problem. The mechanism of formation of the said compound is outlined.

Biological Assay↗
PubMed2006

ICH guidance in practice: validated stability-indicating HPLC method for simultaneous determination of ampicillin and cloxacillin in combination drug products.

Ampicillin and cloxacillin were degraded together under different stress test conditions prescribed by International Conference on Harmonization. The samples so generated were used to develop a stability-indicating high performance liquid chromatographic (HPLC) method for the two drugs. The drugs were well separated from degradation products using a reversed-phase (C-18) column and a mobile phase comprising of acetonitrile:phosphate buffer (pH 5.0), which was delivered initially in the ratio of 15:85 (v/v) for 1 min, then changed to 30:70 (v/v) for next 14 min, and finally equilibrated back to 15:85 (v/v) from 15 to 20 min. Other HPLC parameters were: flow rate, 1 ml/min; detection wavelength, 225 nm; and injection volume, 5 microl. The method was validated for linearity, precision, accuracy, specificity and selectivity. It was also compared with the assay procedures given in British Pharmacopoeia for individual drugs. Similar results were obtained, indicating that the proposed single method allowed selective analysis of both ampicillin and cloxacillin, in the presence of their degradation products formed under a variety of stress conditions. The developed procedure was also applicable to the determination of instability of the drugs in commercial products.

Acetonitriles↗
PubMed2006

Study of the interaction between rifapentine and isoniazid under acid conditions.

A well-known problem of anti-tuberculosis fixed-dose combination (FDC) products containing rifampicin (R) and isoniazid (H) is the fall in bioavailability, in particular of R, when two or more drugs are present together. The same has been ascribed to hydrolysis of R to 3-formylrifamycin (3-RIF) under stomach acid conditions and reaction of the latter with H to form isonicotinyl hydrazone (HYD). The objective of present study was to explore whether the same reaction occurred when H was present along with rifapentine (Rp), a newer long acting rifamycin, which is structurally similar to R. Clinical trials are currently undergoing for co-administration of Rp with H in patients who had completed 2 months of standard chemotherapy. For the purpose, first a validated HPLC method was developed for the separation of Rp and H, and the same was used for the study of interaction between the two drugs. Like R, Rp was also found to convert to 3-RIF in acid conditions, which reacted further with H to form HYD. The pH-rate profile was also similar in shape to that established with the combination of R and H; maximum decomposition occurred at pH 2, where Rp loss was to an extent of approximately 30%, while corresponding decomposition of H was approximately 9%. These values were similar to those reported for the combination of R (approximately 33%) and H (approximately 10%). Hence, the study suggests that co-administration of Rp and H should be avoided, like in case of R and H, and the two drugs should not be formulated directly into a single dosage form.

Antitubercular Agents↗
PubMed2006

Stress degradation studies on ezetimibe and development of a validated stability-indicating HPLC assay.

Ezetimibe was subjected to different ICH prescribed stress conditions. Degradation was found to occur in hydrolytic and to some extent in photolytic conditions, while the drug was stable to oxidative and thermal stress. The drug was particularly labile under neutral and alkaline hydrolytic conditions. A stability-indicating HPLC method was developed for analysis of the drug in the presence of the degradation products. It involved a C-8 column and a mobile phase composed of ammonium acetate buffer (0.02 M, pH adjusted to 7.0 with ammonium hydroxide) and acetonitrile, which was pushed through the column in a gradient mode. The detection was carried out at 250 nm. The method was validated for linearity, range, precision, accuracy, specificity, selectivity and intermediate precision.

Azetidines↗
PubMed2005

Mechanistic explanation to the catalysis by pyrazinamide and ethambutol of reaction between rifampicin and isoniazid in anti-TB FDCs.

Rifampicin and isoniazid are known to interact with each other in solid formulation environment to yield isonicotinyl hydrazone (HYD). In earlier studies, this reaction was indicated to be catalyzed by pyrazinamide and ethambutol hydrochloride, the two other co-drugs present in oral anti-tuberculosis fixed-dose combination (FDC) formulations. Accordingly, the present study was carried out to understand the catalytic role of pyrazinamide and ethambutol hydrochloride on the reaction between rifampicin and isoniazid. For the purpose, organic bases and amides similar in structure to pyrazinamide and ethambutol hydrochloride were combined individually with rifampicin and isoniazid. The compounds employed were pyrazine, piperdine, pyrollidine, pyridine, triethylamine, diisopropylethylamine, picolinamide, benzamide, ethylenediamine, ethanolamine, diethanolamine, and triethanolamine. An additional study was also carried out in the presence of free base of ethambutol. The mixtures were exposed to accelerated stability test condition of 40 degrees C/75% RH for 15 d. The nature of the products formed and the changes in relative concentrations of the drugs and products were followed by HPLC. The drugs showed different extent of degradation, yielding HYD, and in some cases degradation products of rifampicin. The results confirmed the catalytic role of pyrazinamide and ethambutol hydrochloride. The catalysis is postulated to involve intra-molecular proton transfer during transhydrazone formation process, entailing a tetrahedral mechanism.

Amides↗
PubMed2005

Validated specific HPLC method for determination of zidovudine during stability studies.

The objective of the current study was to develop a validated stability-indicating assay method (SIAM) for zidovudine (3'-azido-3'-deoxythymidine) after subjecting it to forced decomposition under hydrolysis, oxidation, photolysis and thermal stress conditions. The drug decomposed under hydrolytic stress upon refluxing, and also on exposure to light. It was stable to oxidation and thermal stress. The same major decomposition product could be seen in all the decomposed solutions, which was identified as thymine through comparison with the standard. Separation of drug from major and minor degradation products was successfully achieved on a C-18 column utilising water-methanol in the ratio of 77:23. The detection wavelength was 265 nm. The method was validated and response was found to be linear in the drug concentration range of 25-500 microg ml(-1). The mean values (+/-R.S.D.) of slope and correlation coefficient were 21,859 (+/-0.213) and 0.9995 (+/-0.00578), respectively. The R.S.D. values for intra- and inter-day precision were <0.9 and <1.6%, respectively. The method was established to have sufficient intermediate precision as similar separation was achieved on another instrument handled by a different operator. The recovery of the drug from a mixture of degraded samples ranged between 100.6 and 100.9%. PDA peak purity test confirmed the specificity of the method. The method was also successful in analysis of drug in marketed tablets subjected to stability testing under accelerated conditions of temperature, humidity, and to thermal and photolytic stress.

Chromatography, High Pressure Liquid↗
PubMed2005

Establishment of inherent stability of stavudine and development of a validated stability-indicating HPLC assay method.

The present study describes degradation of stavudine under different stress conditions (hydrolysis, oxidation, photolysis and thermal stress), and establishment of a stability-indicating reversed-phase HPLC assay method. The drug was found to hydrolyse in acidic, neutral and alkaline conditions and also under oxidative stress. The major degradation product formed under various conditions was thymine, as evidenced through comparison with the standard and spectral studies (NMR, IR and MS) on the isolated product. Separation of drug, thymine and another minor degradation product was successfully achieved on a C-18 column utilising water-methanol in the ratio of 90:10. The detection wavelength was 265 nm. The method was validated with respect to linearity, precision (including intermediate precision), accuracy and specificity. The response was linear in the drug concentration range of 25-500 microg ml(-1). The mean values (+/-R.S.D.) of slope and correlation coefficient were 24256 (+/-0.679) and 0.9994 (+/-0.0265), respectively. The R.S.D. values for intra- and inter-day precision studies were <0.210 and <1%, respectively. The recovery of the drug ranged between 99.7 and 101.5% from a mixture of degraded samples. The method even proved to be affective on application to a stressed marketed capsule formulation.

Chromatography, High Pressure Liquid↗
PubMed2005

Behavior of moisture gain and equilibrium moisture contents (EMC) of various drug substances and correlation with compendial information on hygroscopicity and loss on drying.

The behavior of moisture gain and equilibrium moisture content (EMC) was determined for 30 drug substances at relative humidities (RH) ranging from 11% to 93%. Based on the results, the drugs were categorized into different classes, following the classification system proposed by Callahan et al. About 23 fell under Class-I (nonhygroscopic), four under Class-II (slightly hygroscopic), and three under Class-III (moderately hygroscopic). Most of the Class-III drugs converted from solid to liquid state at > 75% RH, and the moisture increase was more than 40% above 90% RH. However, the moisture increase was comparatively much smaller at humidities < 40%-50%. Hence, no drug could be categorized in Class-IV (very hygroscopic), where gain of moisture is generally higher even at lower humidities. The results were correlated to the statements given in the compendia on hygroscopicity, and also the values of loss on drying (LOD). The study suggests that there is a need to rationalize the pharmacopoeial information.

Absorption↗
PubMed2005

Drug-drug interaction studies on first-line anti-tuberculosis drugs.

The purpose of this study was to carry out drug-drug compatibility studies on pure first line anti-tuberculosis drugs, viz., rifampicin (R), isoniazid (H), pyrazinamide (Z), and ethambutol hydrochloride (E). Various possible binary, ternary, and quaternary combinations of the four drugs were subjected to accelerated stability test conditions of 40 degrees C and 75% relative humidity (RH) for 3 months. For comparison, parallel studies were also conducted on single drugs. Changes were looked for in the samples drawn after 15, 30, 60, and 90 days of storage. Analyses for R, H, and Z were carried out using a validated HPLC method. The E was analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), as it does not absorb in ultraviolet (UV). All single pure drugs were relatively stable and showed only 3%-5% degradation under accelerated conditions for 3 months. However, significant interactions were observed in case of the drug mixtures. In particular, ternary and quaternary drug combinations containing R and H along with Z and/or E were very unstable, showing 90%-95% and 70%-75% loss of R and H, respectively. In all these cases, isonicotinyl hydrazone (HYD) of 3-formylrifamycin and H was found to be the major degradation product. In case of RE and RZE mixtures, where H was absent, 3-formylrifamycin was instead the key degradation product. Another unidentified peak was observed in the mixture containing RZE. Apart from these chemical changes, considerable physical changes were also observed in pure E and the mixtures containing E, viz., RE, ZE, RHE, RZE, and RHZE. In addition, significant physical changes associated with noteworthy loss of H and E were also observed in mixtures containing HE and HZE. The present study thus amply shows that the four primary anti-tuberculosis drugs, when present together, interact with each other in a multiple and complex manner.

Antitubercular Agents↗
PubMed2004

Overestimation of rifampicin during colorimetric analysis of anti-tuberculosis products containing isoniazid due to formation of isonicotinyl hydrazone.

When present together in fixed-dose combinations (FDC) of anti-tuberculosis drugs, rifampicin (R) and isoniazid (H) interact with each other to form isonicotinyl hydrazone (HYD). In a preliminary study, this product was found to possess similar colorimetric spectrum to that of rifampicin. Therefore, an investigation was undertaken to determine interference of HYD during analysis of rifampicin in FDC products by colorimetry. For the purpose, standard plots were constructed for rifampicin and HYD at 475 nm, the wavelength maximum for both the compounds. The plots were linear in the range of 10-100 microg/ml. Molar absorptivity values for rifampicin and HYD were 15279 and 5034, respectively. It indicated that HYD possessed one-third absorptivity to that of rifampicin. The analysis of combinations of rifampicin and HYD revealed that rifampicin could be overestimated to a maximum extent of 33%, while interference varied at other relative ratios of the two compounds. This was also confirmed by colorimetric and HPLC analysis of a degraded marketed product and samples from a dissolution study. Thus this investigation suggests that any method devoid of interference of HYD should be preferred for analysis of rifampicin, whenever it is present along with isoniazid.

Antitubercular Agents↗
PubMed2004

ICH guidance in practice: establishment of inherent stability of secnidazole and development of a validated stability-indicating high-performance liquid chromatographic assay method.

The degradation behaviour of secnidazole was investigated under different stress degradation (hydrolytic, oxidative, photolytic and thermal) conditions recommended by International Conference on Harmonisation (ICH) using HPLC and LC-MS. A stability-indicating HPLC method was developed that could separate drug from degradation products formed under various conditions. Secnidazole was found to degrade significantly in alkaline conditions, oxidative stress, and also in the presence of light. Mild degradation of the drug occurred in acidic and neutral conditions. The drug was stable to dry heat. Resolution of drug and the degradation products formed under different stress studies were successfully achieved on a C-18 column utilizing water-methanol in the ratio of 85:15 and at the detection wavelength of 310 nm. The method was validated with respect to linearity, precision (including intermediate precision), accuracy, selectivity and specificity.

Chromatography, High Pressure Liquid↗
PubMed2004

Interference of isonicotinyl hydrazone in the microbiological analysis of rifampicin from anti-tuberculosis FDC products containing isoniazid.

Microbiological assay is a sensitive method for the estimation of rifampicin (R). In the present study, interference due to isonicotinyl hydrazone (HYD), an interaction product of R and isoniazid (H), was checked during microbiological analysis of R, employing Bacillus subtilis and Sarcina lutea. The assays were done by disc diffusion method. Both R and HYD showed linear log response curves in the range of 0.01-10microg. In the presence of HYD, R was overestimated when tested against S. lutea and underestimated in case of B. subtilis. The same extent and type of interference was observed on assay of a marketed anti-tuberculosis fixed-dose combination product, subjected to accelerated stability testing (40 degrees C/75% RH) for 1 month. This means that response of organisms used in microbiological assay of R might vary in the presence of HYD, with possibility of incorrect conclusions. Therefore, the study suggests that before a microbiological method involving a particular organism is extended to the determination of R in FDC formulations containing H, it should be tested for the influence of HYD and used only if non-interfering.

Antitubercular Agents↗
PubMed2004

Mechanistic explanation to the variable degradation behaviour of stavudine and zidovudine under hydrolytic, oxidative and photolytic conditions.

The kinetics of decomposition of zidovudine and stavudine was studied under ICH recommended stress conditions of hydrolysis, oxidation and photolysis. The two drugs, which are closely related in structure, showed the same order of sensitivity under hydrolytic conditions, viz. acid > water > alkali. But stavudine was found to hydrolyse overall much faster than zidovudine. Both drugs were almost stable under basic conditions. Stavudine showed decomposition on exposure to peroxide while zidovudine was stable. On the contrary, zidovudine showed more sensitivity to light than stavudine, which was almost photostable. Thymine was formed as a major decomposition product of both the drugs under all the three stress conditions. The observed behaviour is explained mechanistically.

Hydrolysis↗
PubMed2004

HPLC and LC-MS studies on stress degradation behaviour of tinidazole and development of a validated specific stability-indicating HPLC assay method.

The objective of the current investigation was to study the degradation behaviour of tinidazole under different ICH recommended stress conditions by HPLC and LC-MS, and to establish a validated stability-indicating HPLC method. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal decomposition. Extensive degradation was found to occur in alkaline medium, under oxidative stress and in the photolytic conditions. Mild degradation was observed in acidic and neutral conditions. The drug was stable to thermal stress. Successful separation of drug from degradation products formed under stress conditions was achieved on a C-18 column using water-acetonitrile (88:12) as the mobile phase. The flow rate was 0.8 ml x min(-1) and the detection wavelength was 310 nm. The method was validated with respect to linearity, precision, accuracy, specificity and robustness. The utility of the procedure was verified by its application to marketed formulations that were subjected to accelerated stability studies. The method well separated the drug and degradation products even in actual samples. The products formed in marketed liquid infusions were similar to those formed during stress studies.

Chromatography, High Pressure Liquid↗
PubMed2004

Validated specific HPLC methods for determination of prazosin, terazosin and doxazosin in the presence of degradation products formed under ICH-recommended stress conditions.

The present paper describes development of stability-indicating high-performance liquid chromatographic (HPLC) assay methods for three alpha-adrenergic-blocker drug substances, namely, prazosin, terazosin and doxazosin, in the presence of degradation products generated from forced decomposition studies. Resolution of drugs from degradation products was obtained using a reversed-phase C-18 column using water/acetonitrile/methanol/glacial acetic acid/diethylamine (25:35:40:1:0.017) as mobile phase for prazosin and terazosin and acetonitrile/water/glacial acetic acid/diethylamine (65:35:1:0.02) for doxazosin. The detection was done at 254 nm. The methods were validated with respect to linearity, precision, accuracy, specificity and robustness.

Chromatography, High Pressure Liquid↗
PubMed2004

An explanation for the physical instability of a marketed fixed dose combination (FDC) formulation containing isoniazid and ethambutol and proposed solutions.

An investigation was carried out to explore the possible reason for the physical instability of a marketed strip packaged anti-TB fixed dose combination (FDC) tablet containing 300 mg of isoniazid (H) and 800 mg of ethambutol hydrochloride (E). The instability was in the form of distribution of white powder inside the strip pockets. High-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS-MS) studies confirmed that both H and E were present in the powder. The same was also confirmed through Fourier-transform infrared (FTIR) spectroscopy, which also indicated absence of interaction between the two drugs. No sublimation of the drugs was observed up to 110 degrees C, indicating that the observed instability was not due to this reason. Subsequently, attention was paid to the possibility of moisture gain by the tablets through defective packaging (which was established) due to hygroscopicity of E. To understand the phenomenon further, pure drugs and their mixtures were stored under accelerated conditions of temperature and humidity [40 degrees C/75% relative humidity (RH)] and both increase in weight and physical changes were recorded periodically. The mixtures gained moisture at a higher rate than pure E and those with higher content of E became liquid, which on withdrawal from the chambers, became crystallized. The drug mixture containing H:E at a ratio of 30:70 w/w, which was similar to the ratio of the drugs in the tablets (27:73 w/w), crystallized fastest, indicating formation of a rapid crystallizing saturated system at this ratio of the drugs. It is postulated that the problem of instability arises because of the formation of a saturated layer of drugs upon moisture gain through the defective packaging material and drying of this layer with time. The study suggests that barrier packaging free from defects and alternatively (or in combination) film coating of the tablets with water-resistant polymers are essential for this formulation.

Antitubercular Agents↗