Pharmacokinetics Flashcards
Define Pharmacokinetics
The effect of the body on the drug
Study of the drug’s alterations as it is absorbed into, distributed through, metablised in and excreted from an organism
Define a drug
A single chemical entity that may be one of the constituents of a medicine
Defina medicine
either one or more active chemical entities (drugs) plus additives to facilitate administration
What is the therapeutic index?
relationship between a deug’s therapeutic effect and adverse effects.
give a an example of a drug in the ward which has a narrow therapeutic index?
heparin
gentomyicin
vancomyicin
Why might it be undesirable to administer medication via an enteral oral route?
medication may be destroyed in the gut either via stomach acid or digestive enzymes etc.
distribution of drug may be very poor by blood stream therefore meds must be given directly into area i.e epidermal
drugs affecting the brain.
in terms of pharmacokinetics what is the aim in the design of the drug?
that it is fat soluble at the time of it’s absorption
What is usually prefererred rout of absorbtion for a drug?
diffusion
Where is largest area of absorbtion via enteral route?
small intestine
How much water should a patient frink to get medication from the mouth to the stomach?
250 mls of water
If a patient does not drink a sufficient amount of water, and drug does not reach it’s area of expected area of absorption what will happen?
drug is not absorbed very well therefore you lose the drug effect.
May cause ulcerations and perforations
What gastrointestinal factors which influence absorption?
oesophageal passage
the pH of the GI tract
Gastric motility
What could happen to the medication if you take it before food?
Pylorus of stomach becomes closed off due to digestion in stomach.
Medication may become stuck in the stomach
Therefore medication cannot get into small intestine
What is drug efflux?
a mechanism which involves drug efflux proteins which use energy to push drugs back into the intestine. limiting the absorption of fat soluble drugs via the intestinal walls
where are drug efflex proteins found?
on the surface of epithelial and endothelial cells
Where do drugs usually accumulate in the body?
in fatty areas - subcutaneous fat
What is the most fat soluble type of medication?
anaesthetics
List factors which could affect drug distribution in the body?
Blood flow in the tissue
Binding to plasma proteins
cellular binding
adipose store in the tissue
What system carries blood from the digestive tract to the liver?
hepatic portal vein
What organ is the least circulated?
skin
What is plasma protein binding?
degree to which medications attach to proteins within the blood
Give an example of a protein in the systemic circulation which may bind medication
albumin
what is polypharmacy?
The simultaneous of multiple medications by a patient
Last the disadvantages of protein plasma binding in terms of drug distribution
The efficiency of the drug
In the case of polypharmacy, there is risk of accumulation of drugs in the body.
What is drug metabolism?
the breaking down of a drug in the body
How many phases of drug metabolism are there?
2
Describe Phase 1 metabolism
causes the breakdown of a molecuyl;e into more water soluble parts
Describe Phase 2 metabolism
Adds on water conjugate molecules to make the whole complex water soluble.
How much paracetamal can individual taken before getting a overdose?
4g
What is cytochrome P450?
a phase 1 metabolic enzyme
what is the main phase 1 metabolic enzyme you should remember for the exam?
cytochronme P450
Why is cytochrome p450 such a significant phase 1 metabolic enzyme in the body?
responsible for metabolising >60% of all therapeutic drugs in the body.
Why should patients on polypharmacy not drink grapefruit juice?
CYP450 is inhibited by a number of substances found in grapefruit juice
What are the three ways in which drugs are eliminated from the plasma?
redistribution
liver metabolism
renal excretion
What effect does overdoseing have on phase 2 metabolism>
Less phase 2 metablic enzymes are made to further change the metabolites of phase 1
Whatis the main aim of kidney elimination of drugs?
To remove the non-metabolised drugs in the bloodstream
What problem can intestinal flora cause on metabolising drugs?
May de-conjugate metabolised drug to liberate parent drug
What is First-past effect?
process by which orally administered drugs progress from the intestinal lumen to the hepatic system before the general circulation
What is bioavailability
Degree to which a drug is absorbed and reaches the general circulation.
What is drug half life?
Time required to reduce the total amount of a drug in a person’s body by 50%
