1、Administration and Absorption of Drugs,Factors that effect the action of a drug,1. Rate of accumulation at its site of action2. Concentration of the drug at the site of action3. The duration of the drugs contact at those sites,Pharmocokinetics,Refers to the movement of chemicals in a biological syst
2、emThis includes: Administration and absorption Distribution Binding properties Metabolic mechanisms Elimination from the system,Administration of drugs,To be effective a drug must enter the body and get to its site of actionBest method of administration of a drug depends on the drug Most drugs disso
3、lved in a fluid (saline) or contained in a mixture as in pills or capsules type of substance is importantInjections tend to be fast acting, oral administration is usually slow acting and of a longer duration,Routes of administration Enteral routes,Administered through the alimentary canal oral or an
4、al Common problem is that absorption rate can be highly variable Absorption of orally administered drugs is greatly influenced by stomach contents Hostile acid environment can interfere with absorption Other problems: Some people cannot take pills Uncooperative patients may refuse or “cheek” them,Ro
5、utes of administration Parenteral routes,Injection Intravenous drug injected into vein Advantages fastest way administer drug and dosage most accurate Disadvantages chance of infection if conditions not sterile and no way to retrieve the drug in case of allergic or toxic reaction Intramuscular drug
6、injected into muscle mass slower but safer Subcutaneous injection under the skin or implanted under the skin Direct injection in the nervous system,Routes of administration Parenteral routes,Pulmonary routes inhalation into the lungsTopical routes placing drug on the surface usually a surface with a
7、 mucous membrane Sublingual placed under the tongue Intranasal powder or liquid absorbed through mucous membrane in the nose Skin skin patches or topical anesthesia,Absorption of Drugs,With the exception of drugs directly injected into the nervous system and topical anesthesia, drugs have to cross a
8、t least 2 membranes to reach its site of action At a minimum, it has to cross into the blood stream, out of the blood stream, and into the cell Walls of blood vessels and cell membranes are semi-permeable,The bloodstream and drug movement,How fast a drug gets into the bloodstream depends on route of
9、 administration Once in the blood, a drug has access to all types of tissue, muscle, fat skin, lungs, etc.,Structure of capillaries,Capillaries in most of the body are made up of cells with gaps in between the cells These gaps allow some substances, but not blood cells of large proteins, to move in
10、and out of the capillaries Some drug molecules will bind to these large proteins reducing the amount of “free” molecules in the blood When these free molecules leave the blood stream, bound molecules become unbound to maintain a stable concentration,Blood brain barrier,In the brain, the cells are mo
11、re tightly packed so molecules have to move through the cells themselves this makes up part of the blood-brain barrier Astrocytes make up the rest of the blood-brain barrier by sending out “feet” that help seal the capillary walls,Blood-brain barrier,Very few substances can cross this barrier Membra
12、nes of the capillary cells and astrocytes are made up of lipids Only lipid soluble substances can be absorbed into the cells and pass through them This barrier important because the brain has no immune system,Movement across semi-permeable membranes,Three types of fluid Fluid in the bloodstream Flui
13、d outside the cells extra cellular fluid Fluid inside the cells intracellular fluid These fluids can move back and forth across membranes Example thirst Lack of fluid in blood Extra cellular fluid moves into bloodstream Intracellular fluid moves out of the cells Loss of fluid detected; signal sent t
14、o drink,Movement across semi-permeable membranes,Filtration as fluid moves into a cell the membrane filters out large molecules which include many drug moleculesMovement through diffusion follows chemical gradient chemicals flow from areas of high concentration to areas of low concentration If a che
15、mical is highly concentrated outside a cell, and openings exist, it will move into the cell,Placental Barrier,A weak barrier between mother and fetus Large amounts of materials are exchanged between mother and fetus Most drugs easily cross the placental barrier almost every drug a mother takes the fetus takes,Solubility,Lipid soluble drugs drugs that can be dissolved in lipids fatty substances that make up cell membranes including the blood-brain barrierWater soluble drugs drugs that can dissolve in water they will not passively move through a cell membrane so they require active transport,
