What is true regarding the concentrations of most drugs at therapeutic plasma le

Question

What is true regarding the concentrations of most drugs at therapeutic plasma levels? Select one: a. Plasma levels are much higher than the Michaelis-Menten constant. b. The Michaelis-Menten constant is not important for the therapeutic action of drugs. c. Plasma levels are equal to the Michaelis-Menten constant. d. Plasma levels are much lower than the Michaelis-Menten constant. The hepatic enzymes responsible for oxidation and reduction of drugs and certain natural metabolites are located in Select one: a. Hepatocyte endoplasmic reticulum b. Hepatocyte nuclei c. Hepatocyte RNA d. Hepatocyte mitochondria For a drug that is both renally excreted unchanged and metabolized, what is true if renal excretion becomes impaired due to a disease? Select one: a. Less drug will be excreted and hepatic metabolism may become the primary elimination route. b. Less drug will be excreted and less drug will be metabolized. c. The processes of drug elimination will continue unchanged. d. More drug will be excreted because reabsorption will decrease and metabolism will decrease as well. The Michaelis-Menten Km is equal to Select one: a. 2 x Vmax b. Michaelis-Menten affinity constant + Vmax c. Vmax d. 0.5 Vmax The rate constant of elimination is the sum of what? Select one: a. The first-order rate constant for metabolism and the first-order rate constant for excretion b. The zero-order rate constant for metabolism and the first-order rate constant for excretion c. The zero-order rate constant for metabolism and the zero-order rate constant for excretion d. The first-order rate constant for metabolism and the zero-order rate constant for excretion The reciprocal of the Michaelis-Menten equation is called the Select one: a. Double-Lineweaver equation b. Triple-reciprocal equation c. Lineweaver-Haltom equation d. Lineweaver-Burk equation In Michaelis-Menten kinetics, maximum velocity (Vmax) corresponds to what? Select one: a. The rate when all substrate has been consumed b. The rate when all available enzymes have produced the product of the reaction c. The rate when all available enzymes are in the form of the drug-enzyme intermediate [ED] d. The rate of reaction when all enzymes have been regenerated Genetic Polymorphism in Drug Transport Genetic variants of P-glycoprotein drug transporters (MDR1 [ABCB1], for example) are found in approximately 5% of Caucasians and can cause cytotoxic drugs that are usually effective against cancer to become ineffective by Select one: a. Causing transport of drugs out of cells with resulting low levels of drugs in targeted cells b. Blocking the membrane pores through which the drugs normally penetrate into cells c. Degrading drugs before they are able to distribute across membrane barriers or into cells d. Conjugating with drugs resulting in a complex that is much less lipophillic The hepatic enzymes resonsible for oxidation and reduction of drugs and certain natural metabolites are know as what? Select one: a. Mixed-function oxidases b. Mixed-function hepatases c. Mixed-function proteases d. Mixed-function reductases Whether a change in drug elimination is more likely to be affected by renal disease, hepatic clearance, or a drug-drug interaction may be predicted by what? Select one: a. Determining renal absorption fraction for a drug b. Measuring the fraction of drug that is eliminated by metabolism or excretion. c. Determining the Michaelis-Menten constant for a drug d. Establishing the percentage of protein binding for a drug Phase I biotransformation reactions are also know as Select one: a. Conjugation reactions b. Acetylation reactions c. Synthetic reactions d. Asynthetic reactions Genetic Polymorphism in Drug Metabolism Genetic variants in CYP and other metabolic enzymes can affect the pharmacodynamics of drugs by Select one: a. Altering the target cells causing the pharmacodynamics of drugs to be highly variable in a patient b. Increasing the absorption and distribution pharmacokinetics of drugs in a given patient c. Speeding the transport of drugs across membrane barriers, thereby causing a super-therapeutic or toxic effect in a patient d. Altering the clearance of a drug and, therefore, the overall pharmacokinetics for a given patient The rate constant of metabolism is difficult to measure for most drugs and is usually found as what? Select one: a. The difference between k elimination and k absorption b. The difference between k elimination and k excretion c. The sum of k absorption and k elimination d. The sum of extraction fraction and percent of protein binding The elimination of most drugs from the body involves what processes? Select one: a. Biotransformation and conversion b. Metabolism and renal excretion c. Metabolism and extraction d. Metabolism and biotransformation Hepatic clearance of a drug may be defined how? Select one: a. The amount of drug that is removed from the body by the liver per unit time. b. The volume of blood that perfuses the liver that is cleared of drug per unit time. c. Renal clearance plus total body clearance. d. Extraction fraction plus absorption factor.

Explanation / Answer

b. The Michaelis-Menten constant is not important for the therapeutic action of drugs

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