Pharmaceutical scientists 2007

Chirality plays a major role in biological processes, and the enantiomers of a bioactive molecule often possess different biological effects. For example, all pharmacological activity may reside in one enantiomer of a molecule, or enantiomers may have identical qualitative and quantitative pharmacological activity. In some cases, enantiomers may have qualitatively similar pharmacological activity, but different quantitative potencies.

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Directly from its beginning—now 100 years ago, when Michail Tswett developed the principles [1, 2] with the isolation of chlorophyll—chromatography has always been a preparative technology, and its value in producing compounds of high purity cannot be overemphasized. It was Paul Karrer [3] who stated very early “. . . it would be a mistake to believe that a preparation purified by crystallization should be purer than one obtained from chromatographic analysis. In all recent investigations chromatographic purification widely surpassed that of crystallization.

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The most widely used analytical separation technique for the qualitative and quantitative determination of chemical mixtures in solution in the pharmaceutical industry is high-performance liquid chromatography (HPLC). However, conventional detectors used to monitor the separation, such as UV, refractive index, fluorescence, and radioactive detectors, provide limited information on the molecular structure of the components of the mixture. Mass spectrometry (MS) and nuclear magnetic resonance (NMR) are the primary analytical techniques that provide structural information on the analytes.

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The modern drug discovery process, in general, involves the identification of a biochemical target (usually protein target), screening of synthetic compounds or compound libraries from combinatorial chemistry/natural sources for a lead compound, and optimization of the lead compound (activity, selectivity, pharmacokinetics, etc.) for recommending a potential clinical candidate.

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For much of the early development of liquid chromatography, separations were carried out at ambient temperature and many laboratories did not attempt to regulate or control the temperature of the column. Frequently, the column would be mounted on the side of the pump or detector and thus would be subjected to changes in the room temperature or changes due to external factors, such as sunlight. However, the influence of temperature on the retention times of analytes was well known and had been studied by a number of groups—in particular, Melander et al. [1].

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Developing fast high-performance liquid chromatography (HPLC) methods can improve work efficiency during research, development, or production of a drug substance or a drug product. HPLC is a key technique in all of these areas. Until recently, analysis times of greater than 30 minutes were common. Modern pharmaceutical R&D, with its high-throughput screening, demands high-throughput methods to deal with the large number of samples. To reduce production cycle time, fast HPLC methods are essential for on-line or at-line process control and for rapid release testing.

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Analytical technology transfer and manufacturing is the mechanism by which knowledge acquired about a process for making a pharmaceutical active ingredient or dosage form during the clinical development phase is transferred from research and development to commercial scale-up operation or shared between internal groups or with third parties. Analytical technology transfer guarantees that laboratories can routinely execute tests, obtain acceptable results, and be able to accurately and independently judge the quality of commercial batches.

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What is the definition of a formulation? Why is it needed? What is the importance of a formulation? These are some important questions that need to be addressed during the development of a potential drug product. The strict definition of the word is to specify a formula or to express a formula in systematic terms or concepts. The formula, in the current case, is a pharmaceutical dosage form. A formulation is needed to deliver the drug or the active pharmaceutical ingredient (API) to its targeted site. In order to overcome some of the physiochemical limitations of an API,...

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In the drug discovery area, a compound with desired therapeutic properties is identified, and its structure may be modified by synthetic alterations to enhance potency and specificity or to decrease toxicity and undesired side effects. The lead drug candidate is then transitioned into the drug development area. Only small amounts of drug (typically less than a gram) are required to support the required studies in the Drug Discovery area. However larger amounts are required to support the studies conducted in the Drug Development area.

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Recent advances in mass spectrometry have rendered it an attractive and versatile tool in industrial and academic research laboratories. As a part of this rapid growth, a considerable body of literature has been devoted to the application of mass spectrometry in clinical studies. In concert with separation techniques such as liquid chromatography, mass spectrometry allows the rapid characterization and quantitative determination of a large array of molecules in complex mixtures.

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Preformulation is a bridge between discovery and development where development scientists participate in selection and optimization of lead compounds. It is very critical at this stage to evaluate the developability of potential drug candidates in order to select new chemical entities and decrease the number of failures during future drug development. On average, only one out of ten new chemical entities (NCE) entering firstin-human testing reaches registration, approval, and marketing stage.

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Great efficiencies have been achieved in the drug discovery process as a result of technological advances in target identification, high-throughput screening, high-throughput organic synthesis, just-in-time in vitro ADME (absorption, distribution, metabolism, and excretion), and early pharmacokinetic screening of drug leads. These advances, spanning target selection all the way through to clinical candidate selection, have placed greater and greater demands on the analytical community to develop robust high-throughput methods.

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In modern high-performance liquid chromatography (HPLC), computers in a broad sense are used in every instrumental module and at every stage of analysis. Computers control the flow rate, eluent composition, temperature, injection volume, and injection process. Detector output signal is converted from analog form into the digital representation to recognize the presence of peaks, and then at higher level of computer analysis a chromatogram is obtained. All these computer-based functions are performed in the background, and the chromatographer usually does not think about them.

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The method validation process is to confirm that the method is suited for its intended purpose. Although the requirements of validation have been clearly documented by regulatory authorities [ICH, USP, and FDA], the approach to validation is varied and open to interpretation. Validation requirements differ during the development process of pharmaceuticals. The method validation methodologies in this chapter will focus on the method requirements for preliminary and full validation for both drug substance and drug product.

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Size-exclusion chromatography (SEC) separates polymer molecules and biomolecules based on differences in their molecular size. The separation process in simplified form is based on the ability of sample molecules to penetrate inside the pores of packing material and is dependent on the relative size of analyte molecules and the respective pore size of the absorbent. The process also relies on the absence of any interactions with the packing material surface. Two types of SEC are usually distinguished: 1. Gel permeation chromatography (GPC)—separation of synthetic (organic-soluble) polymers.

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High-performance liquid chromatography (HPLC) is a separation tool par excellence for the analysis of compounds of wide polarity. Since its inception approximately four decades ago, HPLC has revolutionized numerous disciplines of science and technology. Among the various modes of HPLC, reversed-phase and normal-phase chromatography (NPC) are employed most commonly in separation. Normal-phase chromatography was the first liquid chromatography mode, discovered by M. S.

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Figure 4-43. Adsorption isotherms of alkylsulfates on Hypersil-ODS from methanol/water (20/80) with 0.02 M phosphate buffer at pH 6.0. (Reprinted from reference 119, with permission.) Figure 4-44. Capacity factor of tyrosinamide versus concentrations of dodecyl sulfate (upper curve), decyl sulfate (middle curve), and octyl sulfate (lower curve). (Reprinted from reference 119, with permission.)

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An empirical formula representing the variation of the . quantity with mole fraction of acetonitrile (/) from the values in Table 4-4 could be determined using equation (4-20). The dependence of . versus the mole fraction of ace- tonitrile is shown in Figure 4-25.

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Over 25 years ago, Horvath and Melander, in their fundamental work [1], discussed the reason behind the explosive popularity of reversed-phase liquid chromatography (RPLC) for analytical separations. It was estimated that about 80–90% of all analytical separations were performed in RPLC mode, and the authors noted that “the variation of eluent composition alone extends both retention and selectivity in HPLC [high-performance liquid chromatography] over an extremely broad range.

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The column is the only device in the high-performance liquid chromatography (HPLC) system which actually separates an injected mixture. Column packing materials are the “media” producing the separation, and properties of this media are of primary importance for successful separations.

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