Chapter 15 - Drug Action, Metabolism,Elimination, Administration, Absorption and Penetration of CNS Flashcards
drug metabolism
eliminates a drug’s ability to pass through lipid membranes of cells so that it can no longer penetrate the blood–brain barrier. In addition, small amounts of some psychoactive drugs are passed from the body in urine, sweat, feces, breath, and mother’s milk.
The actions of most drugs are terminated by
enzymes synthesized by the liver.
Once a drug enters the bloodstream,
it is carried to the blood vessels of the central nervous system. Fortunately, a protective filter, the blood–brain barrier, makes it difficult for many potentially dangerous blood-borne chemicals to pass from the blood vessels of the CNS into the extracellular space around CNS neurons and glia.
Some drugs can be administered through
he mucous membranes of the nose, mouth, and rectum. Cocaine, for example, is commonly self-administered through the nasal membranes (snorted)—but not without damaging them.
Some drugs can be absorbed into
the bloodstream through the rich network of capillaries in the lungs. Many anesthetics are typically administered by inhalation, as are tobacco and marijuana. The two main shortcomings of this route are that it is difficult to precisely regulate the dose of inhaled drugs, and many substances damage the lungs if they are inhaled chronically.
after an intravenous injection,
there is little or no opportunity to counteract the effects of an overdose, an impurity, or an allergic reaction.
subcutaneously (SC)
drug injection into the fatty tissue just beneath the skin;
intramuscularly (IM)
drug injection into the large muscles;
intravenously (IV)
drug injection directly into veins at points where they run just beneath the skin.
Advantages of oral administration
its ease and relative safety
Disadvantage of oral administration
ts unpredictability: Absorption from the digestive tract into the bloodstream can be greatly influenced by such difficult-to-gauge factors as the amount and type of food in the stomach.
Oral Route of administration
Preferred route. Once they are swallowed, drugs dissolve in the fluids of the stomach and are carried to the intestine, where they are absorbed into the bloodstream. However, some drugs readily pass through the stomach wall (e.g., alcohol), and these take effect sooner because they do not have to reach the intestine to be absorbed. Drugs that are not readily absorbed from the digestive tract or that are broken down into inactive metabolites (breakdown products of the body’s chemical reactions) before they can be absorbed must be taken by some other route.
Drugs are usually administered in one of four ways:
oral ingestion, injection, inhalation, or absorption through the mucous membranes of the nose, mouth, or rectum.
