# Pharm test 1

PHARMACODYNAMIC
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Terms in this set (334)
The mechanisms by which drugs interact, on a molecular level, with constituents of cells or cellular environments to produce biochemical and/or physiological changes in cells, tissues, organs, and ultimately patients.

A study of the mechanisms by which drug molecules influence target cells, or cellular environments, that result in physiological or biochemical alterations recognized as the pharmacologic action of the drug.
Drugs which work by non-specific physiochemical actions produce pharmacodynamic effects by influencing the environment of cells, and thus altering extracellular body compartments. They do not produce any direct effect on cells but can alter the functioning of cells by indirectly affecting the cell's environment. Their actions do not require any interaction between the drug and any component of the cell.
Drugs can be used to alter gastric or extracellular pH, extracellular osmotic pressure, or composition of extracellular electrolytes.

Examples:

1. Antacids are used to alter gastric pH.
2. Mannitol alters osmotic pressure of extracellular fluids
3. Electrolyte solutions alter the composition of serum electrolytes
Drugs can be used to form an irreversible chemical bond between themselves and some other molecular substance in the intestinal tract. By binding to these substances, their absorption is prevented because the drugs to which they are bound cannot be absorbed.

Examples:

1. Kaopectate adsorbs orally ingested microbial enteric toxins
2. Cholestyramine (Questran) adsorbs bile salts, thereby preventing absorption of dietary fat. It can also bind to other orally ingested medications, preventing their absorption
3. Activated Charcoal binds to (adsorbs) other orally ingested drugs and toxins, preventing their absorption
These drugs, by interposing themselves between cells and some other injurious environmental substance, can block injury to cells from their exterior.

Examples:

1. Sunscreens coat the skin cells blocking ultraviolet radiation injury from the sun
2. Sulcralfate (Carafate) forms an insoluble paste with hydrochloric acid, coating the base of a peptic ulcer blocking additional injury to the gastric wall from the acid
These drugs coat the surface of cells (or tissues) decreasing the abrasive forces (friction) that cells are subjected to from their external environment. By decreasing mechanical injury to the cells, the lubricant drugs perform a protective function.

Examples:

1. Mineral Oil (ingested orally or taken rectally) decreases friction between colonic wall and stool, allowing easier defecation
2. Talcum Powder, applied to the inframammary surfaces, decreases close apposition of skin surfaces and friction between these surfaces
These drugs alter the physical forces that exist between two different states of matter (i.e., solids and liquids). In general, they decrease the natural resistance of the two states of matter to mix allowing the liquid phase of matter to "enter" the solid phase.

Examples:

1. Stool softeners alter the surface of hard stool allowing water from the colonic lumen to enter the stool, making it softer
(1) A drug may bind to the same physical location on the enzyme that is normally occupied by the substrate of that enzyme. In doing so, the drug competes with the substrate for the active site on the enzyme, preventing the enzyme from functioning normally.

(2) A drug may interact with an enzyme target changing the physical structure of the enzyme and disrupting its integrity.

Examples:

1. Digoxin binds to and blocks the action of the enzyme Na/K ATPase which inhibits the movement of sodium ions from within the cardiac muscle cells to the extracellular fluid. This, in turn, enhances the entry of calcium ions into the cells, making the cardiac muscle contract more forcefully and, thereby, improving cardiac output.
2. ACE inhibitor drugs bind to and block the action of angiotensin-converting enzyme which inhibits the formation of angiotensin II. This enzyme-blocking action thereby results in an inhibition of peripheral vasoconstriction that would normally occur with angiotensin II. The ultimate result is a lowering of blood pressure.
3. Sildenifil (Viagra) binds to and blocks the action of phosphodiesterase V which prevents the degradation of a naturally occuring compound called cGMP. The "build-up" of cGMP results in vasodilatation of the penile arteries and increased blood flow into the penis.