Drug molecule and its

There are a number of problems associated with the use of peptides as drug molecules. Peptides are rapidly degraded by proteases and, therefore, their biological half lives are normally too short to be useful In a therapeutic sense. Most peptides exhibit more than one type of biological effect making lack of specificity a problem to be overcome. The size of even "small" peptides Is larger than most common drug molecules, and it is usually desirable, if for no other reason than ease of synthesis, to simplify the structures as much as possible. Finally, for the small number of peptides which have been studied by the oral route, poor bloavallablllty has been a problem. 

The strength of the interaction between a drug molecule and its receptor can be determined directly from the equilibrium constant for the interaction ... 

Identify the potential of a drug molecule (and its metabolites) to delay ventricular repolarization. 

Relate the extent of the delayed repolarization to the concentration of the drug molecule and its metabolites. 

Surface area has a prominent effect on the interactions which occur between a drug molecule and its surroundings. When the surface area is introduced as a de.scriptor in chemo-metric analyses, it has been found to contribute. stati.stically significant information in correlations developed for water solubility, octanol-water partition coefficients, activity coefficients and boiling points. " ... 

Another variable that influences the saturation solubility of a drug molecule is its degree of solvation. Since the anhydrous, hydrated, and alcoholated forms of a drug have slightly different solubilities, they may well have different dissolution rates and, therefore, different rates of absorption. However, these differences may not be clinically significant [35],... 

Avdeef et al. [556] measured the PAMPA permeabilities of a series of drug molecules and natural products using both dodecane- and (dodecane + 2%DOPC)-coated filters. It was proposed that a new H-bonding scale could be explored, based not on partition coefficients but on permeabilities. 

D. E. Leahy, J. Lynch, D. C. Taylor. Mechanisms of absorption of small molecules. In eds. L. F. Prescott and W. S. Nimmo, Novel Drug Delivery and its Therapeutic Application. Wiley, New York 1989, 33-44. 

During phase I the analytical laboratory continues characterization of the drug molecule and optimization and refinement of the methodology. Production is also refining the process to increase purity and yield and make it amenable to scaling up. Formulation studies usually consist of excipient screening during this phase. 

Because living cells are complex, it is necessary to establish their history and assure that they are free of components and viruses that may have deleterious effects on the drug molecules and humans when these cells are administered with such drug molecules. 

This technique is primarily used for the high-resolution analysis of smaller molecules and it often provides excellent fragment spectra. For this reason, it is used for preliminary structural elucidation of synthetic compounds, including potential neuropharmaceuticals, or for structural confirmation of drugs destined for biological experiments. 

The chiral separation of drug molecules and of their precursors, in the case of the synthesis of enantiomerically pure drugs, is one of the important application areas of HPLC in pharmaceutical analysis. Besides HPLC, capillary electrophoresis is another technique of choice for chiral separations. In this chapter we give an overview of the different modes (e.g., direct and indirect ones) by which it is possible to obtain a chiral separation in HPLC and CE. The direct approaches, i.e., those where the compound of interest is not derivatized prior to separation, are discussed in more detail since they are the most frequently used... 

Though in competition with other analytical techniques, CE has proven its potential and necessity to be used for the characterization of small-molecule pharmaceuticals. Due to the versatility of the system, CE can be applied for the determination of physicochemical properties, identification, purity and stability analysis, and cleaning verification of the drug substance, its precursors, process chemicals, the drug product, and its excipients. 

Many drugs are racemates, including 13-blockers, nonsteroidal anti-inflammatory agents, and anticholinergics (e.g benzetimide A). A racemate consists of a molecule and its corresponding mirror image which, like the left and right hand, cannot be superimposed. Such chiral ( handed ) pairs of molecules are referred to as enantiomers. Usually, chirality is due to a carbon atom (C) linked to four different substituents ( asymmetric center ). Enantiomerism is a special case of stereoisomerism. Non-chiral stereoisomers are called diaster-eomers (e.g., quinidine/quinine). 

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