drug interactions Flashcards
(31 cards)
when does a drug interaction occur?
occurs when a substance alters the expected performance of a drug
what are the two types of drug interactions?
- Pharmacodynamic
- Pharmacokinetic
when do pharmodynamic interactions occur?
Occur when drugs have an effect on the same target or physiological system
when do pharm-kinetic reactions occur?
Occur when a drug affects the pharmacokinetics (absorption, distribution, metabolism or excretion) of another drug
describe pharmacodynamic interactions
Pharmacodynamic interactions are either synergistic or antagonistic
Due to drugs acting on the same drug receptor(s) or physiological system
Generally predictable (related to pharmacology of drug)
Highly selective drugs are less likely to be problematic
Pharmacodynamic interactions (drug receptors)
Synergistic interaction
Pharmacodynamic interactions (drug receptors)
Antagonistic interaction
Pharmacodynamic drug reactions (physiological system)
Synergistic interaction
Pharmacodynamic drug reactions (physiological system)
Synergistic interaction
Pharmacodynamic drug reactions (physiological system)
Synergistic interaction
define synergy
interaction of drugs such that the total effect is greater than the sum of the individual effects (1+1>2)
define antagonism
an antagonist is a substance that acts against and blocks an action (2 drugs opposed to each other) (1+1=0)
define summation
different drugs used together to have the same effect as a single drug would (1+1=1)
define potentiation
enhancement of one drug by another so that the combined effect is greater than the sum of each one alone (1+1=1+1.5)
define pharmacodynamics
the effect the drug has on the human body
define pharmacokinetics
what the body does with the drug (the disposition of a compound within an organism)
risk factors f
Narrow therapeutic index
Steep dose/response curve
Saturable metabolism
what are the pharmacokinetics mechanisms?
Absorption, Distribution, Metabolism, Excretion
describe Absorption in ADME
Motility – if the gut has slowed digestion, the drugs won’t work as well (oral contraceptive pill and antibiotics is the most common interaction)
Acidity – pH and pKa interactions.
Solubility
Complex formation
Describe distribution in ADME
Drugs can go into the proteins, other tissues or the effect site
Protein binding
How is protein binding helpful in drug distribution?
If you give 2 highly protein bound drugs, they will make each other strong and increase their effect so you always make sure you know what drugs the patient has taken before giving them new drugs
describe metabolism in ADME
CYP450
INHIBITION
INDUCTION
EXCRETION
describe CYP450 in metabolism
Haemoproteins
Metabolise many substrates – endogenous and exogenous
describe inhibition in metabolism
Drug A blocks metabolism of drug B, leaving more free drug B in the plasma so it has an increased effect
