Flashcards in Lecture 2: Pharmacokinetics & Dynamics Deck (28):
4 Processes of Pharmacokinetics
Diffusion or Passive Transport
-Usually small, nonionized, or lipid-soluble molecules
-People in a crowded room, "passively" spilling into the hallways
-Usually large, ionized, or water-soluble molecules
-People "pushing" their way into our crowded pharmacology classroom
-Movement from site of administration to circulating fluids
-Primary factor determining length of time for effect of drug to occur
Factors Affecting Drug Absorption
-Route of administration
-Digestive motility (if givenPO)
-Digestive tract enzymes (if given PO)
-Blood flow at admin site (IM or Subcut)
-Degree of ionization of drug
-pH of surrounding environment (PO)
Medications are distributed by Blood
-Greater blood flow to area, higher concentration of drug is delivered
-IV vs. IM vs. Subcut
-Drugs excreted in bile
-Bile recirculates to liver
-Prolongs activity of drug
Primary site of excretion of drugs is kidneys.
-Secretion mechanism is less active in infants and older adults
-Drugs retained for extended times
-Dosages must be reduced
-Must avoid any nephrotoxic drug, but all drugs should be monitored and doses lowered.
Serum Peaks and Troughs
-A serum trough level is drawn about 30 minutes prior to your next dose of the medication. This will show the amount of the drug at its lowest level in your system
-The peak level is usually drawn 30 minutes after med admin if in IV form or about an hour or two if orally. The peak shows the medication at its highest level in your system .
This allows the doctor to maintain a safe level of medication in the system
Median Effective Dose (ED50)
Dose that produces therapeutic response in 50% of a group
Many clients require more or less
food increases the pH of the stomach
food can SLOW absorption
Drug-drug interactions can compete for absorption
Herbs can make a difference in absorption
Barriers affecting drug distribution
& Capillary beds
Drug-protein complexes make the drug to large to pass through capillary beds or cells
These complexes are too large to cross capillary membranes; thus the drug is not available for distribution to body tissues.
Only unbound (free) drugs can reach their target cells or be excreted by the kidneys.
Considerations for Pt's w/ Low Albumin
-Total protein 3
If a pt has low albumin levels and overall protein levels drugs will not bind with protein complexes.
The drugs should be given in lower doses
Pts should be monitored for adverse signs
The liver is the primary site of drug metabolism
Hepatic microsomal enzyme system
Most metabolism in the liver is accomplished by the hepatic microsomal enzyme system. This enzyme complex is sometimes called the P-450 system.
Drugs taken orally can cross directly into the hepatic portal circulation, which carries blood to the liver before it is distributed to other body tissues.
Some drugs can be completely metabolized to inactive forms before they reach circulation.
Some drugs are secreted in the bile, a process known as biliary excretion. Most bile is circulated back to the liver by enterohepatic recirculation
This can increase the half-life of the drug significantly.
Blood Flow and Excretion **TEST ?**
If there is low blood flow to the kidneys, excretion will be adversely effected and drugs can create toxicity in ALL DRUGS.
People that might develop toxicity more easily w/ excretion??
Low protein in blood stream
pH and Urine ***TEST***
Kidneys will excrete medication faster if it is the OPPOSITE pH of the urine.
A drug that is basic in acidic urine will lead to faster excretion
Oral medication and Constipation?
Diarrhea and oral medication
decreased absorption because it won't spend enough time in the GI
High Protein Levels and Meds
Increase dose of medication due to drug protein complex.
If there is low protein...
decrease dose of medication
Empty Stomach and Med
Makes the stomach more Acidic
Acidic drugs will be absorbed more readily
Length of time required for the plasma concentration of a med to decease by half after admin.