Rates, Rate Constants, and Order
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Rates, Rate Constants, and Order book
The concept of order and its application to rate processes originated in chemical kinetics. There are three commonly encountered zero-order rate processes: constant-rate intravenous infusions, sustained-release drug delivery systems, metabolism or enzyme transport rates under saturated conditions. Since the rate processes are competing for reactant, the product yields are related to the relative values of the competing rate constants. The rate of loss of penicillin through ß-lactam hydrolysis has been observed to be first order in dilute solutions of penicillin in acid. The rates of hydrolysis in aqueous solutions are often first order with respect to the concentration of drug. Hydrolysis represents a common drug instability problem during the storage of aqueous solutions and during passage through the gastrointestinal tract. A drug in solution in the gastrointestinal tract is known to undergo hydrolysis at a first-order rate with a hydrolysis constant value of 0.130 hr–1.