Pharmacokinetics- Drug Interactions Flashcards
1
Q
What does ‘drug interactions’ mean?
A
- When one drug interferes with response to another
2
Q
What are pharmacodynamic interactions?
A
- Often deliberate to enhance wanted pharmacological/physiological effect
- Or unwanted
3
Q
What are pharmacokinetic interactions?
A
- Usually unwanted consequence of polypharmacy
- Patients with more than one condition
- Interference by one drug with ADME of another drug
- Alters conc. hence activity of affected drug
4
Q
What are the 4 types of pharmacokinetic interactions?
A
- Affecting absorption
- Affecting distribution
- Affecting metabolism
- Affecting excretion
5
Q
Describe PK interactions affecting absorption
A
- Antacids that neutralise stomach pH, may alter absorption
- Drugs that alter gut motility may alter gut transit time of drugs
6
Q
Describe PK interactions affecting distribution
A
- Plasma protein binding
- Drugs may compete for binding
- Increases free conch. of one/both drugs
- Not usually clinically important
7
Q
What PK interactions affect metabolism
A
- CYP450 induction and inhibition
8
Q
Describe PK interactions affecting metabolism (induction)
A
- Some CYP450 substrates induce their own metabolism and that of other drugs metabolised by same enzyme
- Induction is slow as more enzyme is expressed by transcription, persists after treatment as additional enzyme slowly degrades
9
Q
Describe PK interactions affecting metabolism (inhibition)
A
- Occurs when a particular metabolic pathway, cannot metabolise 2 or more drugs at same rate as when either drug is alone
- 1 or both drugs may be metabolised slower
- Depends on existing isozyme, so inhibition can occur rapidly
- H2 antihistamine cimetidine inhibits isozymes, reducing warfarin metabolism
10
Q
Give examples of inducers
A
Alcohol, phenobarbitone and phenytoin
11
Q
Give examples of inhibitors
A
Cimetidine, nicotine, omeprazole and grapefruit juice
12
Q
Give examples of substrates (victim)
A
Theophylline, warfarin and others
