Drug interactions Flashcards
Define a drug interaction
When effect of one drug are changed by presence of another drug, food, drink or other environmental chemical agent
What are the consequences of interactions?
- Prevent correct treatment
- Cause harm
- Require expensive tests
- Prolong hospital stay
Give an example of a useful interaction
Ace + diuretics
- Synergistic for hypertension
- Careful dose adjustments + blood monitoring
Give examples of a predisposing factor
- Age (polypharmacy)
- Co-existing disease
- Race/genetic polymorphism
Pharmacokinetics
- Absorption
- Drug displacement
- Metabolism
- Excretion
Pharmacodynamics
- Additive/synergistic interactions
- Antagonistic interactions
- Changes in drug transport
- Changes in electrolyte balance
How long do enzyme inducers usually take for maximal effect?
1-3 weeks
How long do enzyme inhibitors usually take for maximal effect?
24 hrs
What are the gradings of severity listed in the BNF?
- Severe: life threatening/permanent detrimental effect
- Moderate: considerable distress/partially incapacitate, longterm effects
- Mild: unlikely to cause concern/incapacitate majority of patients
- Unknown: interactions predicted - insufficient evidence
What are the different levels of evidence listed in the BNF?
- Study: based on formal study
- Anecdotal: based on single case report
- Theoretical: derived from in vitro studies
What are action messages?
- Interaction will describe effect + action to be taken
- Included where combination is avoided, dose adjustment required or specific administration requirements
Give examples of drugs w/ a narrow therapeutic window
- Warfarin
- Digoxin
- Anti-epileptics
- Theophylline
- Ciclosporins
- Lithium
Give examples of drugs which require careful dosage control
- Antihypertensive
- Antidiabetic
Give examples of enzyme inducers
- Rifampicin
- Phenytoin
- Carbamazepine
- Barbiturates
Give examples of enzyme inhibitors
- Cimetidine
- Ketoconazole
- Ciprofloxacin
- Erythromycin
