Drug Interactions Flashcards
1
Q
Definition
A
- An interaction is said to occur when the effects of one drug are changed by the presence of another drug, herbal medicine, food, drink or by some environment chemical agent
2
Q
Outcomes
A
- Harmful by increased toxicity of a drug
- Harmful by decreased efficacy of a drug
- Beneficial
- No clinical difference
3
Q
Types of drug interactions
A
- Pharmacodynamic
- effects of one drug are changed by the presence of another drug as it’s a site of action
- Pharmacokinetic
- Effects of a drug on the process of ADME of another drug
4
Q
Pharmacodynamic
Additive or synergistic
A
- Additive or Synergistic
- E.g. sedative drugs have additive CNS depressant effects with alcohol
- SSRI AND SJW
- ACEI and K+- sparing diuretic
- Insulin and sulphonylurea
- ACEI and thiazide
5
Q
Pharmcodynamic
Antagonistic or opposing
A
- NSAIDs and Loop diuretics
- Hypoglycaemic and glucocorticoids
- Levodopa and typical antipsychotics
- Beta-agonists (Salbutamol) and beta-antagonists (propranolol)
6
Q
PK- Absorption
A
- Change in GI pH
- Adsorption, chelation and other complexing mechanisms
- Change in Gastric motility
- Induction or inhibition of drug transport proteins
- Malabsorption caused by drugs
7
Q
PK- distribution
A
- Protein binding- usually only result in transient increase in free drug
- Induction or inhibition of drug transport proteins
8
Q
PK- metabolism
A
- Changes in first pass metabolism- grapefruit juice and calcium channel blockers
- Enzyme induction- phenytoin, rifampicin, smoking
- Enzyme inhibition- erythromycin, acute alcohol
9
Q
PK- Elimination
A
- Change in urinary pH- MTX and sodium bicarbonate
- Change in active renal tubular transport- MTX and NSAIDs
- Change in renal blood flow- NSAID and Li
10
Q
Factors affecting susceptibility
A
- Age
- Elderly- decreased renal and hepatic function
- Elderly- Polypharmacy
- Genetic
- Clinical status
11
Q
Time course of interactions
A
- Starting
- Stopping
- Change of dose
- Route of administration
- Half life of drugs
- Mechanism of interaction e.g. enzyme inducers vs enzyme inhibitors
12
Q
Managing drug interactions
A
- Avoid the combination
- adjust doses
- Monitor
- If not clinically significant, do nothing
13
Q
Where to find information
A
- BNF
- Stockleys
- SPC
- MI centre