11 - Drug interactions Flashcards
Different types of drug interactions
Desirable effects - Potentiation (combination antibiotics) , Antagonsim (drug overdose)
Undesirable effects - Toxicity, loss of effect
Pharmacokinetic and pharmacodynamic drug interactions
PK - drug altering concentration via absorption, metabolism, elimination (harder to anticipate)
PD - interacting drug alters the effect - receptor mediated, non-receptor mediated - (easier to anticipate)
Drugs altering absorption
- Change in pH (H2 blockers)
- Some molecules binding drug to reduce absorption
- gastric emptying rate (can get some drugs that increase this rate and some that slow release)
- gut motility
- malabsorption
- hepatic metabolism (blood flow and amount of enzymes- changes amount in systemic circulation)
Inhibitors vs Inducers
INDUCES TAKE LONGER BECAUSE MUST SYNTHESIZE ENZYME
Inhibitors -time to maximal drug interaction determined by - half life and time to steady state of the inhibitor drug and time required for substrate to reach a new steady state
CYP3A4
50% of medicines
- Substrate - simvasatin (lipid lowering medication) HMG-CoA reductase inhibitor
- loinavir - Anti HIV
Inhibitors - grapefruit juice
Inducers - St johns wart
CYP2C9
Warfarin
inhibitors - Fluxetine
Inducers - St johns wort
CYP2C19
Clopidogrel (anti-platelet agent)
inhibitors - omeprazole
inducers - rifampicin
CYP1A2
Theophylline
inducers - tobacco
inhibitor - cimetidine
Renal elimination
- Changes in renal blood flow
- Competition for same transporter - cimetidine competes with metformin
- changes in urine pH
P glycoprotein
Digoxin
Inhibitor - grapefruit juice
Inducers - st johns wart
Shared receptors and Shared effects
Shared receptor - can reduce effectiveness of some drugs
Shared effect - can increase the effect of something e.g aspirin and warfarin - inhibit blood clotting - bleeding
ACE inhibitors, diuretics - reduce renal blood flow - renal failure
Sildenafil and nitrate - lower blood pressure
