Session 1 - Pharmacokinetics Flashcards
(30 cards)
Describe some patient-related problems that cause prescription errors:
- More rapid throughput of patients
- New drug developments
- Increasing complexity of medical care
- Increased specialisation
- Sicker and older patients
- More elderly patients with co-morbidities
Describe some pharmaceutical problems that cause prescription errors:
- There are a vast number of new drugs
- Clinical evidence is produced in patients who are young, relatively healthier and only on one drug at a time.
- Some side effects only unveiled in post-market research
- Blind adherence to guidelines leads to prescription errors where interactions or contraindications exist.
Describe some doctor-related problems that cause prescription errors:
- What knowledge is available - is their training in medical school/postgrad level?
- Sleep deprived
- Limited support
Describe some Medical problems that cause prescription errors:
- Reduced hours and shift work leads to less exposure to teaching.
- Less ward teaching and feedback
- Poorer morale
- Lack of continuity of care
- Lack of pharmacology training
- too many students
Describe some problems that cause prescription errors when prescribing on call:
- Rarely know the patient
- Routine boring jobs - rewrite drug chart/prescribe fluids/prescribe new unfamiliar drugs/prescribe old drugs in absence of result.
What key facts should be confirmed before writing a prescription?
Name of drug - approved drug name - no abbreviations Dose Strength Units in full Frequency Duration of Treatment Allergies/adverse effects Indication Adherence
What are black triangle drugs?
One being intensively monitored, this may be because it is newly released, changed indication, change formulation or a combination product.
What drug reactions should be reported?
Black triangle drugs - all suspected reactions
Unlicensed herbal preparations - all suspected reactions
Established products and vaccines - report all suspected serious reactions even if already know and recognised.
All Paediatric reactions
Define Pharmacokinetics:
Study of the movement of the drug into and out of the body - what the body does to the drug
Define Pharmacodynamics:
Study of the drug effect and mechanism of action - what the drug does to the body.
Define Pharmacogenetics
The effect of genetic variability on the pharmacokinetics or dynamics of a dug on an individual
Define First order reactions:
A constant fraction of the drug is eliminated at a time - this gives a more predictable reaction - can calculate half life - if plotted on a logarithmic scale it will give a straight line.
Define Zero order reactions:
Rate of elimination is constant no matter the concentration of the drug. When active sites of enzymes become saturated at high doses drug which originally followed first order kinetics will switch to zero order.
Which types of drugs are more likely to result in toxicity and why?
Zero Order kinetics - small increases in doses may result in the dose saturating metabolising enzymes/binding proteins so will result in a proportionally larger concentration of drug unbound free to react.
What is first pass metabolism?
Any metabolism that occurs before the drug has entered the metabolism. This can occur in the gut lumen, gut wall and the liver.
What is bioavailability?
The fraction of the dose which finds its way into a body compartment - usually the circulation. (IV bolus = 100%)
What factors affect bioavailability?
Drug formulation Age Food Lipid soluble? - more easily absorbed Vomiting Malabsorption
Describe clearance:
The ability of the drug to excrete a drug - normally equates to GFR - half like is inversely proportional to clearance - e.g. if there is a reduction in clearance then half life is increased.
What is distribution?
The ability of the drug to dissolve in the body - key factors include protein binding - e.g to albumin and globulins and volume of distribution. Half life is proportional to the volume of distribution.
How can the volume of distribution be larger than the volume of the body?
Because drugs are capable of binding to proteins and cell surface receptors which increase the apparent volume of the body even though they are not fluids.
What is metabolism (drugs)?
The extent to which the liver breaks down drugs and converts them by conjugating them with other molecules to make them water soluble to that they can be eliminated by the kidney . Metabolism can also convert inactive drugs to ones which are pharmacologically active. Similarly the by products of metabolism may also be pharmacologically active.
What is elimination?
Mainly via the kidney although can be via the lungs, breast milk, sweat, tears, genital secretions, bile and saliva.
What three processes determine renal excretion of drugs?
Glomerular filtration
Tubular reabsorption
Tubular active secretion
What value is represented by the area under the curve?
Total drug exposure
