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What are the 4 phases of Pharmacokinetics
A drug moves from the site of administration to the venous or lymphatic circulations
What are the 3 most important ways that drugs cross cell membranes?
- 1. passage through channels or pores
- 2. passage with aid of transport system
- 3. direct penetration of membrane itself
Delivery of the drug into any and all body compartments it can penetrate
What are some factors that effect distribution
- Regional blood flow
- Capillary permiability
- ability of drug to exit the vascular system
- ability of drug to enter cells
- degree of plasma protien binding
- physiological barriers
Areas with high blood flow absorb drugs fast or slow?
Which is more easily absorbed, topical or sublingual
What kind of pts will have capillary absorption problems?
- Peripheral vascular disease
List 2 physiologic barriers that can affect distribution
- Abscesses (pocket of purulent drainage)
- Solid Tumors
What are some factors affecting absorption
- Surface area
- Rate of dissolution (how long it takes to dissolve)
- Blood Flow
- Lipid solubility (the higher the faster)
- pH partioning
- aka Biotransformation
- enzymatically mediated alteration of drug structure. The alteration or changing of a drug to more ionized or water soluble and lipid soluble forms (called metabolites.)
Fun fact: women tend to have more problems with anesthesia due to the high amt of fat cells.
movement of drugs and metabolites out of the body
Elimination usually begins with ______ followed by ______.
- hepatic metabolism
- renal excretion
Why are ionized drugs poorly absorbed?
they cannot easily diffuse across lipid membranes
Are non ionized drugs lipid soluble?
Yes and easily pass through lipid membranes.
a drug accumulates on the side of a membrane where the pH most favors its ionization
How do hypotensive pts and dehydrated pts absorptions differ?
they are delayed due to the blood flow.
What are the advantages of parenteral routes
- rapid onset
- avoid barriers because it goes straight to site of administration
- use of large fluid volumes
- use of irritant medications
What are some disadvantages of parenteral routes
- rapid onset and irreversable
- volume overload(especially in elderly, risk of CHF)
which parenteral route has a bigger risk of infection?
central (going in superior vena cava or inferior vena cava)
What are some factors that affect absorption through the enteral route?
- gastric and intestinal pH
- solubility and stability of a drug
- gastric emptying
- coadministration of drugs
List 3 topical routes
- sublingual or buccal
- skin or mucous membranes
the fraction of the administered dose that reaches the systemic circulation and produces effects
Drugs must be ______ or have ______ to cross the blood brain barrier
lipid soluble or have a transport system. This is why it is hard to treat infections and diseases of the CNS
Fun Fact: The membranes of the placenta separate the maternal circulation from the fetal circulation. The membranes of the placenta do NOT constitute an absolute barrier to the passage of drug
What plasma protein do drugs usually bind to?
Drug molecules that are bound to a protein are what?
Bound drug molecules are pharmacologically inactive and they remain that way until released from the protein.
In addition to plasma protien binding, where else can drugs be stored
bones, fat, other plasma protiens
What is a hepatic metabolizing enzymes system?
Cytochrome P450 system = causes changes in rate of metabolism of certain drugs requiring changes in dosage
What is the First-pass Phenomenon
Orally administered drugs are first absorbed through the walls of the small intestine and initially travel through the portal vein to the liver, where they undergo metabolism before reaching the systemic circulation. This is known as the first-pass phenomenon.
Polar compounds are readily excreted
Drugs and their metabolites can exit the body in urine, bile, sweat, saliva, breast milk, and expired air. The most important organ for drug excretion is the
what is glomerular filtration?
As blood flows through the glomerular capillaries, fluids and small molecules—including drugs—are forced through the pores of the capillary wall. This process, called glomerular filtration
- Minimum Effective concentration
- the plasma drug level below which therapeutic effects will not occur.
The plasma level at which toxic effects begin
- Steady State
- evenly distributed concentration of a drug, occurs when the administration rate equals the rate of drug elimination.
is the time needed for the plasma concentration of a drug to be reduced by 50%.
to achieve plateau more quickly, an initial large dose may be given. Used for drugs with long half –lives
plateau maintained via smaller doses given after a loading dose
How long does it usually take for a drug to be eliminated out of the body?
4 half lives