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An anticancer chemotherapeutic agent that acts by first-order kinetics would be expected to kill a
A. constant number of cancer cells
B. constant proportion of cancer cells
C. variable number of cells depending on the half-life of the drug
D. variable number of cells depending on the proportion of cells in S phase
E. variable proportion of cells depending on the number of cells in the G0 phase
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i got this one wrong...can anybody pls exaplain B.Thx
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The correct answer is B. First-order kinetics, when applied to the concept of cytotoxicity, means that the drug will kill a constant proportion of tumor cells (rather than a constant number, choice A). The log kill hypothesis refines this by stating that the magnitude of killing by a cytotoxic agent is a logarithmic function. Therefore, a drug producing a 3-log kill will reduce 1012 cells to 109, or will reduce 106 cells to 103 (three orders of magnitude in either case). This hypothesis accounts for the far better results observed with chemotherapy when the total tumor burden is low.
The half-life of the drug (choice C) does not determine the number of cells killed, assuming an adequate dose is given.
Choices D and E are both reflections of cell cycle specificity, the ability of a drug to specifically kill cells in a particular phase of the cell cycle (eg, S phase or G0 phase), and are unrelated to first-order kinetics.
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Remember that Zero-order elimination refers to a constant AMOUNT of drug eliminated per unit time and first order elimination refers to a constant FRACTION of drug eliminated per unit time. I wish it'll help you.
