Lec 19-Drug interactions Flashcards
1
Q
What is a drug interaction
A
- An interactions occur when
- The effects of one drug are altered by the co-administration of another drug; herbal medicine; food drink or other environment chemical agent
2
Q
What is a drug interaction
A
Effects of one drug are changed
- Presence/effects of another drug
- Herbal medicine
- Food or drink
- Environmental chemical agents
3
Q
What might happen
A
- Additive or enhanced effect of one or more drugs
- Antagonism of the effect of one or more drugs
- Any other alteration in the effect of one or more drugs
- NB drug interactions vs ADR
- NB effect vs Clinical effect
4
Q
More at risk patients
A
- Risk increases with number of drugs used
- ADR patients taking 6-10 drugs:7%
- ADR patients taking 16-20 drugs: 40% (rise largely attributed to drug infraction’s)
5
Q
Risk groups of Polypharmacy
A
- Hepatic disease
- Renal disease
- Long term therapy for chronic disease
- Patients in intensive care
- Transplants patients
- Patients undergoing complicated surgery
- Those with more than 1 prescriber
6
Q
Risk factor for drug interactions
A
- Number of drugs
- Extremes of age
- Chronic medical conditions
- Transplantation
- Critical illness
- Complex surgical procedures
7
Q
Problem drugs
A
- Narrow therapeutic index (safety ratio): warfarin; phenytoin; Li; digoxin; theophylline
- Hepatic enzyme inducers: rifampicin; carbamazepine; phenytoin; phenobarbitone
- Hepatic enzyme Inhibitors: fluconazole; erythomycin; fluoxetine; cimetidine; ciprofloxacin; diltazem; verapamil
8
Q
Inhibition
A
- Normal drug metabolism: normal levels of enzymes convert drugs into metabolites. Depending on the drug, these metabolites may be therapeutic, harmful or inactive
- Inhibitors and drug metabolism : inhibiting compounds block drug metabolism enzymes. Depending on the drug, inhibition can lead to reduced therapeutic effects or toxic buildup of unmetabolized compounds
9
Q
Clinical consequences
A
- Therapeutic failure
- Toxicity
- Enhanced therapeutic effect
10
Q
Pharmacodynamic interactions
A
- How a drug acts on the body
- Pharmacodynamic interactions include
- Agonists and antagonists same receptors
- Additive effects on a physiological systems
- Opposing effects on a physiological system
- Alterations in fluid/electrolyte balance
- Interference with transport mechanisms
11
Q
Pharmacodynamic interaction examples
A
- Synergism (multiplication of effects more than additive) : progesterone and oestrogen; Alcohol and anti-depressants
- Additives: Multiple anti-HTN: ACEI’s and thiazide diuretics
- Antagonism: B-agonists and B-blocker; Anti-coagulants and vit K
12
Q
Pharmacokinetics (kinesis is moving about)
A
-What the body does to a drug Interactions can affect: -Absorption-how drugs get to site -Distribution- how drugs get to site -Metabolism- how there removed -Excretion- how there removed
13
Q
Pharmacokinetic stages
A
- Drug –> GI tract -(absorption) –> intravascular compartment (circulation) Extravascular compartment (tissue) —> effect
- Drug removed by metabolism/excretion at intravascular compartment
14
Q
Absorption
A
- Rate of absorption will be affected by route of administration
- Intravenous= fast
- Oral; intramuscular; percutaneous= slower
15
Q
Oral administration
A
- Drug absorbed from small intestine
- Cell membranes are lipid barriers between aqueous compartments of the body
- Rate of drug absorption determined by: lipid solubility; ionisation
