Pharmacodynamics Flashcards
Name the mechanisms of drug action
Agonist/Antagonist
Disruption of structural protein
Drug is an enzyme
Drug covalently links to macromolecules
Drug reacts chemically with small molecules
Drug binds free molecules or atoms
Describe drug selectivity and drug specificity
Drug selectivity - more selective a drug is for its target, the less chance it will interact with different targets and have less undesirable side effects
Drug specificity - targeting drugs against specific receptor subtypes often allows drugs to be targeted against specific organs
What is affinity, what is efficacy and what is potentcy
Affinity - tendency of a drug to bind to a specific receptor type. Kd is the affinity constant. Lower Kd = higher affinity
Efficacy - ability of a drug to produce a response as a result of the receptor or receptors being occupied. Describes max effect of a drug - Emax used
Potency - dose required to produce the desired response. EC50 used
What is the therapeutic index and what is the therapeutic window
Therapeutic index - relationship between concentrations causing adverse effects and concentrations causing desirable effects. Is the EC50(adverse)/EC50(desired)
Therapeutic window - range of dosages that can effectively treat a condition while still remaining safe. Is the range between the lowest dose that has a +ve effect and highest dose before the -ve effects outweigh the +ves
What is CYP450 induction and name some drugs that cause induction
CYP450 induction is where there is increased amount of enzyme present for a specific action
Inducers include:
- Phenytoin
- Carbamazepine
- Barbiturates
- Alcohol (chronic)
- Sulphonylureas and St John’s Wort
What are CYP450 inhibitors and name some substances that cause inhibition
CYP450 inhibitors are molecules that cause inhibition of CYP450s
CYP450 inhibitors include:
- Omeprazole
- Disulfiram
- Erythromycin
- Valproate
- Isoniazid
- Cimetidine and Ciprofloxacin
- Ethanol (acute)
- Sulphonamides
What pharmacodynamic interactions can occur at receptors
Agonism/antagonism at the same receptor
Agonism/antagonism at different receptors
Non-selective nature of drug can mean the drug can act at many receptors within a system
Enhanced effect by other means
Which drugs usually cause drug-drug interactions
Anticonvulsants
Antibiotics
Anticoagulants
Antidepressants/Antipyschotics
Antiarrhythmics - can prolong the QT interval and cause torsade des pointes
When are drug-disease interactions more common, give some examples
More common at extremes of age and in chronic medical conditions
In renal disease there is a decreased GFR -> decreased excretion of drugs
Hepatic disease causes a reduced hepatocyte function and a decreased clearance of hepatic metabolised drugs -> have longer half-life and toxicity
Cardiac disease results in decreased CO leading to excessive response to hypotensive agents and reduced organ perfusion (can affect kidney and liver)
Name two drug-food interactions and describe them
Grapefruit juice - inhibits several CYP450 isoenzymes: simvastatin, amiodarone (long QT), terfenadine (long QT)
Cranberry juice - inhibits CYP2C9 isoform and so decreases clearance of warfarin -> enhances anticoagulant effect -> increased risk of haemorrhage
What are ADRs and name the groups
ADR - adverse drug reactions. Cause unwanted or harmful reactions after administration of a drug(s) and is suspected or known to be due to the drug. Classes:
- Augment pharmacologic effect
- Bizarre effects
- Chronic effects
- Delayed effects
- End of treatement effects
- Failure of treatment effects
What makes patients at risk of ADRs
Ignorant, inappropriate or reckless prescribing
Polypharmacy
Patients at extremes of age
Multiple medical problems
Use of drugs with narrow therapeutic index
Drugs being used near to their minimum effective concentration
Name some causes of variability in how a patient responds to a drug
Body weight and size
Age and sex
Genetics
Conditions of health
Placebo effect
Dose, formulation and route of administration
Repeated administration of drug leading to drug resistance, tolerance and/or allergy
Drug interactions with the body
