2
Drugs and the body
Learning objectives
Upon completion of this chapter, you should be able to:
1.
Describe how body cells respond to the presence of drugs that are capable of altering their function.
2.
Outline the process of dynamic equilibrium that determines the actual concentration of a drug in the body.
3.
Explain the meaning of half-life of a drug and calculate the half-life of given drugs.
4.
List at least six factors that can influence the actual effectiveness of drugs in the body.
5.
Define drug–drug, drug–alternative therapy, drug–food and drug–laboratory test interactions.
Glossary of key terms
absorption:
what happens to a drug from the time it enters the body until it enters the circulating fluid; intravenous administration
causes the drug to directly enter the circulating blood, bypassing the many complications of absorption from other routes
active transport:
the movement of substances across a cell membrane against the concentration gradient; this process requires the
use of energy biotransformation
agonist:
drug that interacts directly with a receptor site to cause an effect
antagonist:
drug that interacts with a receptor but does not cause an effect, instead blocks it
biotransformation:
the process by which drugs are changed into new, less active chemicals
chemotherapeutic agents:
synthetic chemicals used to interfere with the functioning of foreign cell populations; this term is
frequently used to refer to the drug therapy of neoplasms, but it also refers to drug therapy affecting any foreign cell
competitive antagonist:
drug that interacts with a receptor, blocking the ability of another drug to combine with it
distribution:
movement of a drug to body tissues; the places where a drug may be distributed depend on the drug’s solubility,
perfusion of the area, cardiac output and binding of the drug to plasma proteins
effective concentration:
the concentration a drug must reach in the tissues that respond to the particular drug to cause the desired
effect
endocytosis:
the process through which cells absorb molecules by engulfing them
endogenous substances:
naturally occurring chemicals that are vital to the normal functioning of the body, e.g. neurotransmitters,
hormones and paracrines
enzyme induction:
process by which the presence of a chemical that is biotransformed by a particular enzyme system in the liver
causes increased activity of that enzyme system
excretion:
removal of a drug from the body; primarily occurs in the kidneys, but can also occur through the skin, lungs, bile or faeces
first-pass effect:
a phenomenon in which drugs given orally are carried directly to the liver after absorption, where they may be largely
inactivated by liver enzymes before they can enter the general circulation; oral drugs are frequently given in higher doses than drugs
given by other routes because of this early breakdown
glomerular filtration:
the passage of water and water-soluble components from the plasma into the renal tubule
half-life:
the time it takes for the amount of drug in the body to decrease to half of the peak level it previously achieved
hepatic microsomal system:
liver enzymes tightly packed together in the hepatic intracellular structure, responsible for the
biotransformation of chemicals, including drugs
loading dose:
use of a higher dose than that which is usually used for treatment to allow the drug to reach the effective concentration
sooner
Test your current knowledge of drugs and the body with a PrepU Practice Quiz!
