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Drug Zafirlukast/bioavailability - Essay Example

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This paper discusses how drug degradation, diffusion, partitioning (transport) and permeability influence the bioavailability of drugs in vivo and it will focus particularly on two derivatives (derivative 1 and derivative 2) in comparison to the parent drug Zafirlukast…
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Drug Zafirlukast/bioavailability
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"Drug Zafirlukast/bioavailability"

Download file to see previous pages Permeability measures the ability of the drug to cross the plasma membrane as a function of distance over time (Verbeeck, Blackburn & Lowen, 2003). Drug absorption is in turn determined by molecular properties of the drug. The study focused on the analysis of Total polar surface area (TPSA), molecular weight and Log P to investigate possible correlation between these properties and bioavailability. TPSA refers to the sum of all polar atoms on a drug molecule (Martin et al., 2003). Log P is a measure of the hydrophobicity of a molecule. Zafirlukast is an oral leukotrine (LTRA) antagonist, used for the maintenance treatment of asthma (Surhone, Timpledon and Marseken, 2010).
Drug absorption and bioavailability are vital drug factors that determine how much of the dosage is able to reach the patient’s systemic circulation. In an attempt to investigate how these factors influence bioavailability, the study focused on the three molecular properties that are TPSA, Log P and molecular weight. Drug molecules with a higher TPSA have the capability of forming the H- bond with water leading to higher solubility and hydrophilicity. However, hydrophilicity is a barrier against the process of drug molecule crossing the intestinal lining during absorption as it increases the permeability of the drug molecule. In contrast, to TPSA, Log P is a measure of hydrophobicity (Martin et al., 2003). Hydrophobicity enhances permeability by increasing the rate of the drug molecule crossing the intestinal lining resulting in a higher bioavailability. In addition, high molecular weight of a drug molecule slows the rate of drug permeability leading to low bioavailability.
From case 1 of the case study, we used GASTRO PLUS and determined that parent Zafirlukast had a calculated permeability of 0.453 times 10 -4 cm/s. A high molecular weight would show a decrease in bioavailability as deduced from experimental values. However, this does not correlate with the parent drug and the two ...Download file to see next pagesRead More
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