Pharmacokinetics - The process in which medications move through the body
What are the 4 phases of pharmacokinetics? - absorption, distribution,
... [Show More] metabolism,
excretion
Absorption - happens with drug movement from the GI tract into the bloodstream.
Most meds are taken by mouth.
Oral absorption - Takes awhile to get absorbed because it has to go through the GI
system
Usually takes 2-4 hours
•Enteric coated
aspirin - hard on stomach
can not crush pill
•Extended release
absorbed in the small intestine
IM absorption - Absorbed 1-2 hours
IV absorption - Absorbed 30-60 minutes
dissolution - Dissolution happens when a po medication breaks down into
particles, disintegrates, and dissolves to combine with liquid so absorption from the
GI tract into the bloodstream occurs.
Liquid medications are absorbed faster than solids. Food can interfere with the
absorption of drugs.
Drugs that resist dissolution - Parenteral medications (SL, eyedrops, inhalants,
transdermal) do not pass through the GI tract.
Enteric coated medications are designed to resist disintegration until the pill
reaches the small intestine. EC and sustained release meds should not be crushed.
Factors that affect absorption - •Lack of muscle and increased fat changes
medicine absorption
•Food consumption - will change medicine potency (delayed)
•Stress - Exercise, medicine goes to muscle
•pH - Medicine is made for acidic environments•Antacid changes absorption
•Taken alone so it doesn't change the action
Excipients - Fillers and other substances that make up tablets as a pill is not 100%
drug.
Sometimes an excipient enhances the absorption of a drug such as with PCN,
which is not well absorbed from the GI tract.
Adding Na to PCN, which makes it penicillin sodium, will increase the absorption
of PCN
first pass effect - •the oral drugs go to liver via portal vein where some of the drug
becomes inactive
•Only happens with oral medications
delayed gastric emptying - Food doesn't move like it should
Distribution - refers to the movement of the drug from the circulation to body
tissues
Factors affecting distribution - -blood flow to tissues
-protein binding
-blood brain barrier
-drug's affinity to the tissue
protein binding - Drugs bind with proteins in blood
Some drugs are highly protein bound and other are weakly protein bound
free drugs - drugs not bound to protein
Drug Toxicity - -Two highly protein bound drugs compete and one might
accumulate and cause a toxicity
-it is important to know if you are administering highly protein bound medications
and monitor albumin levels in patients with liver or kidney disease.
-Some drugs that are highly protein bound include: Warfarin
Furosemide
Diazepam
Drug distribution and albumin - -A decrease in albumin levels decrease the
protein-binding sites, which means more of the free drug is circulated.
-This can be fatal with some meds.-Free drugs are those not bound to protein, which means they are active in the body
and cause a pharmacologic response.
-Older adults, malnourished individuals, and those with liver or kidney disease
have low albumin levels. [Show Less]