Pharmacokinetics, Pharmacodynamics, and Drug Interactions Flashcards
What is pharmacokinetics?
the study of drug movement throughout the body
What is drug absorption?
the drugs movement from its site of administration into the blood
What is drug distribution?
the drugs movement from the blood to its interstitial space and into the cells
What is drug metabolism?
enzymatically mediated alteration of drug structure (happens in liver/kidneys)
What is drug excretion?
the movement of the drug and their metabolites out of the body
metabolism+excretion=
elimination
What are the three ways to cross a cell membrane?
1) Channels and pores: very few cross channels or pores- only small compounds like potassium/sodium…
2) Transport system: carriers that move drugs from one side of cell membrane to another. They are selective. Example: certain oral drugs can’t be absorbed unless there is a transport system to move them across the intestine > blood stream.
3) Direct penetration of a membrane: movement throughout the body is dependent on the ability to penetrate membranes directly because MOST drugs are too large to pass through channels/pores and MOST drugs lack transport systems to help them cross all the membranes *remember “like dissolves like: which means membranes are made up of lipids so to directly penetrate a membrane, a drug much be lipid soluble
Are ions able to cross membranes?
No. They must become non-ionized to cross from one side to the other
Many drugs are weak organic acids or weak organic bases. What significance does this play?
This means they can be “charged or uncharged” and the electrical charge is determine by the pH of the surrounding medium
What are polar molecules?
They have an uneven distribution of electrical charge. polar molecules dissolve in polar solvents
Rate of absorption determines what? Amount of absorption determines what?
RATE determines how soon effects will begin.
AMOUT determines how intense it’s effects will be.
What is the rate of dissolution?
Before a drug can be absorbed it must dissolve. Drugs with slower dissolution have slower onset.
How does surface area affect absorption?
The surface area available for absorption is a major determinant of the rate of absorption. For THIS reason, orally administered drugs are greater in the small intestine than the stomach due to the large surface area of the microvilli
How does blood flow affect absorption?
drugs are absorbed most rapidly from sites where blood flow is high. the greater the concentration gradient the more rapid absorption
How does lipid solubility affect absorption?
lipid soluble drugs are absorbed more rapidly than those who lipid solubility is low
How does pH partitioning affect absorption?
Absorption is enhanced when the difference between the pH of plasma and pH at the site of admin is such that drug molecules have a greater chance to be ionized in plasma
How can abscesses and tumors affect distribution?
Abscesses lack blood supply so abx cannot reach bacteria within. Solid tumors also have limited blood supply so they are often resistant to any type of drug therapy
How do drugs exit the vascular system?
They leave the blood BETWEEN not through capillary beds
How can drugs pass the BBB?
There are tight junctions between the cells of the capillaries in the CNS which prevent drug passage. Only lipid soluble drugs can cross the BBB. This is not fully developed in a newborn so that’s part of why they re more sensitive to drugs.
How does placental drug transfer work?
membranes of the placenta separate the maternal circulation from fetal but it is not an absolute barrier for passage of drugs. Most drugs cross the placenta via simple diffusion… lipid soluble and nonionized compounds readily pass from maternal bloodstream > fetus
How does protein binding affect drug distribution?
drugs can form reversible bonds with various proteins in the body. Plasma albumin is most important because it is too large to leave the blood steam. Important consequence is restriction of drug is restriction of drug distribution bc albumin is too large to leave the bloodstream so drug molecules that are bound to albumin cannot leave either.
What is biotransformation?
the enzymatic alternation of drug structure
