Abu M. Rustum

The use of differential scanning calorimetry for the purity verification of pharmaceutical reference standards

Reference standards are routinely used in pharmaceutical industry to determine strength, content, and the quality of drug products, active pharmaceutical ingredients (API), preservatives, antioxidants and excipients. Traditionally, chromatographic techniques such as High Performance Liquid Chromatography (HPLC) and Gas Chromatography (GC) in conjunction with other analytical techniques have been used to determine the purity and strength of a specific lot of a compound for the purpose of qualifying the lot to use as a reference standard. The assigned purity of the reference standard for a wide variety of compounds can be verified using an absolute method such as Differential Scanning Calorimetry (DSC). In this paper, purity of 16 reference standards was determined by DSC and the results were then compared to the purity values that were obtained using HPLC and other analytical techniques. The results indicate that the purity obtained from DSC analysis is comparable to the chromatographic purity for organic compounds that are at least 98% pure. Use of DSC for purity determination is not appropriate if a compound lacks sharp melting point, decomposes in the defined temperature range or exhibits other thermal event(s) which interfere with the melting point of the compound. The use of DSC as an alternative and or complementary method to verify the purity of a compound as part of the pharmaceutical reference standard certification process is discussed.

Development and validation of a stability-indicating RP-HPLC method to separate low levels of dexamethasone and other related compounds from betamethasone.

Betamethasone (BM) is an active pharmaceutical ingredient (API) or an intermediate which is used to manufacture various finished pharmaceutical products. Betamethasone is also used as a starting material to manufacture other APIs that are related to this steroid family. It is quite a challenging task to separate dexamethasone (DM) peak (the alpha epimer) and other structurally related compounds from BM. A stability-indicating reversed-phase high performance liquid chromatography (RP-HPLC) method has been developed which can separate and accurately quantitate low levels of DM and other related compounds from BM and also from each other. This method was successfully validated for the purpose of conducting stability studies of betamethsone in quality control (QC) laboratories. The stability-indicating capability of this method was demonstrated by adequate separation of DM and all the degradation product peaks from BM peak and also from each other in aged stability samples of betamethasone. A gradient mobile phase system consisting of (A) water:acetonitrile (90:10, v/v) and (B) acetonitrile:isopropanol (80:20, v/v) was used with an ACE Phenyl column (10 cm x 4.6 mm, 3 microm particles, 100 A pore size) and an ultraviolet (UV) detection at 240 nm.

Comparison study of porous, fused-core, and monolithic silica-based C18 HPLC columns for Celestoderm-V Ointment® analysis

In this paper, three C18 columns with different substrates (i.e., porous ACE-3 C18, 3 microm, fused-core Halo C18, 2.7 microm, and monolithic Chromolith C18 were compared for the analysis of a pharmaceutical product, Celestoderm-V Ointment, that contains one active pharmaceutical ingredient, betamethasone-17-valerate and one critical pair of low level impurities, betamethasone-E-enolaldehyde and betamethasone-Z-enolaldehyde. Key column performance for the analysis of pharmaceutical products including selectivity, efficiency, separation impedance, resolution factor, sample loading capacity, linearity and lifetime from the three columns were determined. The potential applications of these three C18 columns for different methods for Celestoderm-V Ointment analysis are also recommended.

Development and validation of a stability-indicating HPLC method for simultaneous determination of salicylic acid, betamethasone dipropionate and their related compounds in Diprosalic Lotion®

Diprosalic Lotion is an anti-inflammatory drug product that contains salicylic acid and betamethasone dipropionate as active pharmaceutical ingredients (APIs). A reversed-phase high performance liquid chromatography (RP-HPLC) method was developed for simultaneous determination of salicylic acid, betamethasone dipropionate, and their related compounds in Diprosalic Lotion. A 150 mm x 4.6 mm I.D. YMC Jsphere ODS-H80 column at 35 degrees C and UV detection at 240 nm was used. A gradient elution was employed using 0.05% (v/v) methanesulfonic acid solution and acetonitrile as mobile phases. A total of thirty three compounds from Diprosalic Lotion samples were separated in 38 min. The stability-indicating capability of this method has been demonstrated by the adequate separation of all the impurities and degradation products in expired stability samples of Diprosalic Lotion. The method was validated as per the current ICH guidelines.

Development of a high performance size exclusion chromatography method to determine the stability of Human Serum Albumin in a lyophilized formulation of Interferon alfa-2b.

Intron Powder for Injection is a lyophilized formulation of Interferon alfa-2b marketed for treatment of Hepatitis C and some cancer indications. Human Serum Albumin (HSA) is used as a lyoprotectant and cryoprotectant at 1.0 mg/mL in the product formulation. No stability-indicating method, which can quantitate HSA and its dimer or oligomer aggregates in the formulated product, has been published to date. This paper describes the development and validation of a stability-indicating high performance size exclusion chromatography (HPSEC) method for the assay of HSA and estimation of HSA related compounds in lyophilized Intron Powder for Injection. The method employs a YMC-Pack Diol-200 column (7.8 mm x 30 cm, 5 microm porous particles with 250 A pore size), UV detection at 214 nm, and a mobile phase of 0.1 M phosphate buffer at pH 7.0 with 0.1 M sodium sulfate. The mobiles phase runs in an isocratic mode at 1.0 mL/min and the total chromatographic run time is 30 min. The method was validated for specific, linearity, accuracy, sensitivity, and robustness. It was shown to be specific for HSA and HSA aggregates (dimer and oligomers) with a limit of quantitation of 0.0005 mg/mL or 0.05% of HSA label claim in the presence of active therapeutic protein, Interferon alfa-2b, and the other pharmaceutical excipients, glycine, sodium phosphate dibasic, sodium phosphate monobasic. The method is stability indicating and is suitable for assay of HSA from 0.0005 mg/mL to 1.5mg/mL. (0.05-150% of HSA label claim) and for estimation of HSA related aggregates (dimer, and oligomer) from 0.0005 mg/mL to 0.15 mg/mL (0.05-15% of HSA label claim). The method is robust for routine use in product quality control. The method was applied to the analysis of batches of lyophilized Intron Powder for Injection of low, middle and high strength from the beginning, middle and end of shelf-life. The results indicated that HSA is stable in the product through out its shelf-life.

Rapid separation of desloratadine and related compounds in solid pharmaceutical formulation using gradient ion-pair chromatography.

We reported the development of an ion-pair chromatographic method to separate desloratadine and all known related compounds in Clarinex Tablets, which use desloratadine as active pharmaceutical ingredient (API). For the first time, baseline separation for desloratadine and all known related compounds was achieved by utilizing a YMC-Pack Pro C(18) column (150 mm x 4.6 mm I.D., 3 microm particle size, 120A pore size) and a gradient elution method. The mobile phase A contains 3 mM sodium dodecylsulfate (SDS), 15 mM sodium citrate buffer at pH 6.2, and 40 mM sodium sulfate, while the mobile phase B is acetonitrile. Chromsword, an artificial intelligence method development tool, was used to optimize several key chromatographic parameters simultaneously including buffer pH/solvent strength, and temperature/gradient profile. The resolution of desloratadine and desloratadine 3,4-dehydropiperidine derivative, one of the critical pairs was improved by adding 40 mM sodium sulfate. Ultraviolet detection at 267 nm was used to achieve the detection for desloratadine and all compounds. This method has been successfully validated according to ICH guidelines in terms of linearity, accuracy, quantitation limit/detection limit, precision, specificity and robustness. It could be used as a stability indicating method for desloratadine drug substances or drug products that use desloratadine as active pharmaceutical ingredient.

Application of LC–MSn in conjunction with mechanism-based stress studies in the elucidation of drug impurity structure: Rapid identification of a process impurity in betamethasone 17-valerate drug substance

Through a case study, the use of LC-MS(n) technique in conjunction with a mechanism-based stress study is shown to be a very effective way in the rapid elucidation of unknown drug impurities. In this case, the drug substance sample was first analyzed using LC-MS(n) through which the unknown species was found to be a valeryl-containing, isomeric impurity of the active pharmaceutical ingredient (API), betamethasone 17-valerate, based on its molecular ion and major fragments. Since a substantial knowledge regarding a large number of isomeric impurities of betamethasone has been accumulated in the literature as well as in our laboratory, a hydrolytic stress study (forced degradation) of the isolated unknown species was then designed and carried out accordingly in order to remove the valeryl group from the unknown species. During the stress study, a betamethasone isomer was generated as expected. However, a new unknown species isomeric to betamethasone 17-valerate was also formed unexpectedly. By comparing the UV spectra and more importantly MS(n) fragmentation patterns of the two newly formed species with those of betamethasone, dexamethasone, betamethasone 17-valerate, and betamethasone 21-valerate, these two unknown species generated in the stress study were identified as dexamethasone and dexamethasone 21-valerate, respectively. Based on the plausible reaction mechanism of the forced degradation, the original impurity present in betamethasone 17-valerate drug substance was then identified as dexamethasone 17-valerate; the structure assignment was later confirmed by various 1D and 2D NMR experiments. The efficient conversion from dexamethasone 17-valerate to dexamethasone 21-valerate was also observed during a 2D NMR acquisition of the isolated dexamethasone 17-valerate sample.

Development and validation of a stability-indicating RP-HPLC method for assay of betamethasone and estimation of its related compounds

Betamethasone (9alpha-fluoro-16beta-methylprednisolone) is one of the members of the corticosteriod family of active pharmaceutical ingredient (API), which is widely used as an anti-inflammatory agent and also as a starting material to manufacture various esters of betamethasone. A stability-indicating reverse-phase high performance liquid chromatography (RP-HPLC) method has been developed and validated which can separate and accurately quantitate low levels of 26 betamethasone related compounds. The stability-indicating capability of the method was demonstrated through adequate separation of all potential betamethasone related compounds from betamethasone and also from each other that are present in aged and stress degraded betamethasone stability samples. Chromatographic separation of betamethasone and its related compounds was achieved by using a gradient elution at a flow rate of 1.0mL/min on a ACE 3 C18 column (150mmx4.6mm, 3microm particle size, 100A pore size) at 40 degrees C. Mobile phase A of the gradient was 0.1% methanesulfonic acid in aqueous solution and mobile phase B was a mixture of tert-butanol and 1,4-dioxane (7:93, v/v). UV detection at 254nm was employed to monitor the analytes. For betamethasone 21-aldehyde, the QL and DL were 0.02% and 0.01% respectively. For betamethasone and the rest of the betamethasone related compounds, the QL and DL were 0.05% and 0.02%. The precision of betamethasone assay is 0.6% and the accuracy of betamethasone assay ranged from 98.1% to 99.9%.

A comparative study of enol aldehyde formation from betamethasone, dexamethasone, beclomethasone and related compounds under acidic and alkaline conditions

Enol aldehydes are one type of key degradation and metabolic intermediates from a group of corticosteroids containing the 1,3-dihydroxyacetone side chain on their D-rings, such as betamethasone, dexamethasone, beclomethasone, and related compounds. The formation of enol aldehydes from these corticosteroids is via acid-catalyzed beta-elimination of water from the side chain, a process known as Mattox rearrangement. It was recently reported by our group that enol aldehydes could also be formed directly from the corresponding 17,21-diesters of these corticosteroids but only under alkaline condition, which was proposed to follow a variation pathway of the original Mattox rearrangement. In this paper, we report the results of a comparative study of enol aldehyde formation from these structurally similar corticosteroids (under the original acidic Mattox condition) and their 17,21-diesters (under the alkaline Mattox variation condition), respectively. In general, enol aldehydes were found to be formed under both conditions; however, the ratios of the E- and Z-isomers of the enol aldehyde were different in each case. The only exception was beclomethasone 17,21-diester under the alkaline condition, where a competing elimination of HCl from the 9,11-positions became predominant. These results can be explained by their structural differences with regard to the Mattox mechanism and its variation pathway. Lastly, solvent effect under acidic condition was studied between an aprotic and a protic solvent and the result suggests that enol aldehyde formation is greatly favored in an aprotic environment.

Rapid structure elucidation of drug degradation products using mechanism-based stress studies in conjunction with LC–MSn and NMR spectroscopy: identification of a photodegradation product of betamethasone dipropionate

Betamethasone dipropionate is an active pharmaceutical ingredient (API) that is used in various dosage forms of finished products for the treatment of inflammatory disorders. An unknown degradant was observed during a solution stability study of betamethasone dipropionate. An approach that combines LC-MS(n), mechanism-based stress studies, semi-preparative HPLC purification and structure elucidation by NMR spectroscopy was used to identify the unknown species. The key step of this approach is the design of relevant stress studies based on the plausible degradation mechanism that is revealed by the informative LC-MS(n) analysis. The appropriately designed mechanism-based stress studies not only verify the degradation mechanism but also produce enough quantities of the unknown species for further structure elucidation/confirmation by NMR spectroscopy. With this strategy, the unknown degradant was rapidly identified as lumibetametasone dipropionate, a photodegradation product of betamethasone dipropionate.