Pharmacokinetics III: Drug Interactions & Individual Variation to Drug Responses Flashcards
What are Drug Interactions?
A change in the magnitude or duration of response of one drug due to presence of a second drug
Are drug interactions chemical or physiological interactions?
Physiological
What is a rare example of a chemical interaction between two drugs?
Thiopental + Suxamethonium = Precipitate
What are the TWO potentially dangerous effects of drug interactions?
- Additive - Drug B BOOSTS Drug A effects
- Negating Effect - Drug B DECREASES Drug A effect
What is the equation for the Therapeutic Index for a drug?
What are the some pharmacodynamic considerations for drugs with NARROW therapeutic ranges?
- Small REDUCTION in drug plasma -> Loss of efficacy
- Small INCREASE in drug plasma -> Toxicity
What is a pharmacokinetic consideration if the concentration-response for a drug is STEEP?
Small change in drug plasma -> Big change in effect
Where do Pharmacodynamic Drug Interactions occur?
At the receptor
How is gastrointestinal absorption affected by drugs that inhibit gastric emptying?
Slowed absorption
How is gastrointestinal absorption affected by drugs that speed up gastric emptying?
Accelerated absorption
Which drug do Ca2+ and Fe2+ form insoluble complexes with in the GI tract?
Tetracycline
Which TWO drugs does Colestyramine (bile acid-binding resin) bind in the GI tract?
Warfarin and Digoxin
What effect does complex formation in the GI tract cause?
- DECREASED drug absorbance
- DECREASED drug plasma concentrations
What happens to the levels of free drugs in the plasma with concurrent administration of two drugs with high binding to plasma proteins?
INCREASED free drug levels for both drugs
What is Enzyme Induction?
Increase in enzyme activity caused by a foreign compound (inducer)