2.2 Pharmacodynamics Flashcards
What is pharmacodynamics?
The study of the effect of drugs and their mechanisms of action on the body
Where do drugs work?
- cell surface receptors
- nuclear receptors
- enzyme inhibitors
- ion channel blockers
- transport inhibitors
What is the importance of drug selectivity?
The more selective a drug is for its target, the less chance that it will interact with different targets and have less undesirable side effects.
Target them against a specific receptor subtype to be targeted against specific organ
E.g heart b1
Lungs b2
How can high doses of salbutamol effect vasoculture?
Tachycardia
B2 receptors in lungs, also in blood vessels causes vasodilation = fall in TPR = tachycardia
What is affinity?
Defines the tendency of a drug to bind to a specific receptor type
What is efficacy?
The ability of a drug to produce a response as a result of the receptor or receptors being occupied
Described the max effect of a drug
What is potency?
Dose required to produce the desired biological response. Describes the different doses of two drugs required to the exact the same effect.
What is the therapeutic index?
The relationship between concentrations causing adverse effects and concentrations causing desirable effects.
Ideally want a wide index
Index = EC50 (adverse effect)/ EC50 (desired effect)
What is the therapeutic window?
The range of dosages that can effectively treat a condition while still remaining safe. It is the range between the lowest dose that has a positive effect and the highest dose before the negative effects outweigh the positive effects.
What agonist and antagonists work at the same receptor?
Opiated
Naloxone
Beta blockers
B2 agonists
What agonist and antagonists work at different receptors?
Warfarin and aspirin are examples
What are examples of non selective drugs?
Anti depressants work on manny receptor subtypes e.g adrenergic and noradrenergic
Name drugs that are cleared renally?
Digoxin, aminoglycoside antibiotics
What happens in hepatic disease?
Reduced clearance of hepatic metabolised drugs Reduced CYP 450 activity Much longer half lives Toxicity Classic = opiates in cirrhosis
What does falling cardiac output lead to?
Excessive response to hypotension agents
Reduced organ perfusion
- reduced hepatic blood flow and clearance
- reduced renal blood flow and clearance
What is an adverse drug reaction?
An unwanted or harmful reaction which occurs after administration of a drug or drugs and is suspected or known to be due to the drugs
What puts people at high risk for adverse reactions?
- polypharmacy
- patient at extremes of age = altered pharmacokinetics profiles (renal/hepatic) or co morbidities
- reckless prescribing
- multiple medical problems
- use of drugs with narrow therapeutic indexes = high risk of toxicity
- drugs are being used near their minimum effective concentration = increased risk of treatment failure if metabolism increased
Why are there variabilities in drug responses with people?
Body weight and size Age and sex Genetics Condition of health Placebo effect
Also due to conditions of administration
- dose and route
- drug resistance
- drug interactions e.g chemical or physical, GI absorption, metabolism, excretion, etc.
What is a loading dose?
A loading dose is an initial higher dose of a drug that may be given at the beginning of a course of treatment before dropping down to a lower maintenance dose.
A loading dose is most useful for drugs that are eliminated from the body relatively slowly, i.e. have a long systemic half-life
