Pharmacokinetics Flashcards
(43 cards)
Define drug.
Is a single chemical entity that may be
one of the constituents of a medicine.
Define medicine.
May contain one or more active constituents (drugs) together with additives to facilitate administration
Define therapeutic index.
Relationship between a drug’s therapeutic effect and adverse effects, a ‘margin of safety’
What are the processes involved in pharmokinetics?
Absorption Distribution Metabolism Excretion Toxicity
What are gastrointestinal factors that influence absorption?
Oesophageal phase
pH of GI tract
Gastric motility
Presence of food and drink
Name administration routes for medication.
Enteral
- oral
- rectal
Parenteral (Avoid gut)
- buccal
- sublingual
- topical
- transdermal
- lung etc
How many mls should be drunk to adsorb medication correctly!
200ml
Factors that affect drug distribution.
Blood flow in the tissue- sympathetic system which could activated in hypoxia, hypotension, hypo/hyperthermia, exercise
Binding to plasma protein
Cellular binding
Adipose store in the tissue
Define drug distribution.
Movement of a drug between the blood plasma and tissues continues until drug equilibrates
Consequences of drugs with a narrow therapeutic index with polyparmacy.
Competition in drug- protein binding means that increased amount of free lipid soluble drug as more than one molecule is attempting to bind to the protein.
This danger is increased with kidney issues
Define plasma binding.
Drug binding varies widely, for example warfarin is 98-99% bound to plasma albumin leaving only 1 - 2% free. Only the drug that is unbound or free is able to distribute to target tissues.
What occurs in phase one metabolism?
Takes a fat soluble substance and breaks it down to become a more water soluble molecules
Generally associated with small molecules
Drug metabolism.
Is the process by which the body breaks down and converts medication into active chemical substances.
What occurs in phase two metabolism?
Adds/conjugated on a water soluble molecule to make the whole complex more water soluble
Why are drugs metabolised?
Is crucial to drug exertion by making these molecules more water soluble.
What is cytochrome P450?
It is a phase 1 metabolic enzyme.
Responsible for metabolising >60% of all therapeutic drugs
What are ways of eliminating drugs?
Redistribution Liver metabolism Renal excretion Bile from liver Lungs, faeces, saliva, sweat, breast milk, hair
What are the effects of metabolism?
- renders the drug metabolites water soluble
- produced metabolites are active in their own right
- activates the active ingredient of the drug from a pro-drug molecules
E.g. Enalapril (ACE inhibitors)
Define pharmacokinetics.
Study of a drug’s alterations as it is absorbed
into, distributed through, metabolised in and
excreted from an organism
What are the effects of protein binding?
- Highly bound drugs require larger loading doses
- Highly bound drugs have limited tissue distribution
- Changes in available plasma protein, may have a profound effect on free drug availability
Define first-past effect.
Process by which orally administered drugs
progress from the intestinal lumen to the
hepatic system before entering the general
circulation
Define Bioavailability.
Degree to which a drug is
absorbed and reaches the
general circulation
Define half-life
Time required to reduce the total amount
of a drug in a person’s body by 50%
Where in the body is the main location for drug absorption?
The small intestine due to its large surface area
