Pharmacokinetics Flashcards
define pharmacokinetics
what the body does with the drug
ie. what happens to it after administration, what actions it has in the body
(the disposition of a compound within an organism)
the study of drug metabolism
what is the acronym for the different mechanisms of pharmacokinetics ?
AD-ME
Absorption -> drug taken into circulation. how readily is it absorbed?
Distribution -> drug going around body, where is it taken? what is the rate of this movement
Metabolism -> drug chemically changed and used by body. how is it broken down?
Excretion -> drug leaves body, how?
define ABSORPTION
the process of transfer from the site of administration into the general or systemic circulation
how does drug ionisation affect ABSORPTION?
Ionization is a basic property of most drugs that are either weak acids or weak bases
Ionizable groups are essential for the mechanism of action of most drugs as ionic forces are part of the ligand receptor interaction
Ionized form regarded as most water soluble and un-ionised as lipid soluble
Unionised drugs can get through more barriers therefore often high concentration of this part
oral absorption - where in the body does this happen?
ie. where are drugs that have been administered orally been absorbed into in the body?
- absorbed in the gut before it reaches the systemic circulation
(large SA and high blood flow on the small intestine makes it rapid)
factors that affect the rate of absorption for oral drugs
DRUG STRUCTURE
ie. what structural features do oral drugs need to be absorbed in the gut?
need to be lipid soluble to be absorbed from gut
need to be able to withstand acidic pH and presence of digestive enzymes (if cannot, need alternate pathway)
factors that affect the rate of absorption for oral drugs
DRUG FORMULATION
ie. how are oral drugs formulated to be able to be absorbed in the gut?
The capsule/ tablet must disintegrate and dissolve to be absorbed
Some formulated to dissolve slowly or have a coating that is resistant to the acidity of the stomach
factors that affect the rate of absorption for oral drugs
GASTRIC EMPTYING and gut motility
ie. how does gastric emptying affect absorption?
rate of gastric emptying determines how soon a drug taken orally is delivered to small intestine
eg. rate is slow after eating food therefore can slow down drug absorption
factors that affect the rate of absorption for oral drugs
FIRT PASS METABOLISM
ie. what metabolic barriers do oral drugs encounter on their way to reaching the systemic circulation
Drugs taken orally have to pass 4 major metabolic barriers to reach circulation;
- Intestinal lumen
- Intestinal wall
- Liver
- Lungs
is the rate of absorption fast or slow for drugs administered:
Intradermally and subcutaneously
slow
only small volume can be given
however does avoid barrier of the stratum corneum
used for local effect or to deliberately limit rate of absorption
is the rate of absorption fast or slow for drugs administered:
intramuscularly
Depends on blood flow and water solubility
Increase in either enhances removal of drug from injection site
Can make a depot injection by incorporating drug into lipophilic formulation which releases drug over days or weeks
is the rate of absorption fast or slow for drugs administered:
inhalation
large SA and blood flow but limited by risks of toxicity to alveoli and delivery of non-volatile drugs
Largely restricted to volatiles such as general anesthetics and locally acting drugs such as bronchodilators in asthma
Asthma drugs non-volatile so given as aerosol or dry powder
what is the effect of protein binding in drug DISTRIBUTION
Many drugs can bind to plasma or tissue proteins eg. albumin
Binding lowers the free concentration of drug
if you give 2 highly protein bound drugs, they will make each other strong and increase their effect
- > so you always need to make sure you know what drugs the patient has taken before giving them new drugs
in drug DISTRIBUTION where can drugs go?
into the proteins, other tissues or the effect site
what quality makes drugs able to pass through he blood brain barrier and placenta easily?
small lipid soluble drugs
