Drug-drug Interactions (DDIs)

Question 1

Aspirin & warfarin DDI leads to..

Answer 1

Increased risk of bleeding
- aspirin: anti-platelet
- warfarin: anti-coagulant

Question 2

Sulfonamides & warfarin DDIs leads to:

Answer 2

Increased risk of bleeding (haemorrhage)
- sulfonamides displace warfarin from binding site => free drug conc of warfarin

Question 3

Fluconazole(antifungal) & Lignocaine DDI leads to

Answer 3

Fluconazole inhibits CYP450 enzyme => inhibits metabolism of lignocaine

• toxic accumulation, systemic & CNS toxicity
• LA toxicity (prolonged effect of LA) leads to type A ADRs of LA

Question 4

What are some CYP450 enzyme inducers?

Answer 4

1. Anti-epileptic (Phenytoin, Carbamazepine, Phenobarbitone)
2. Anti-TB (Rifampicin)

Question 5

What are some CYP450 enzyme inhibitors?

Answer 5

1. Valproate
2. Fluroquinolones
3. Erythromycin, Clarithryomycin
4. Triazoles
5. Terbinafine
6. Metronidazole
7. Antidepressants (selective serotonin uptake inhibitors)
8. Grapefruit, pomelo

(Antifungals & ABs & antidepressant are very good enzyme inhibitors)

Question 6

Name an example of DDI due to distribution.

Answer 6

Btn 1. Valproate & 2. Diazepam
- drug competition for binding sites on plasma protein
- valproate displaces diazepam from binding sites
- increases free drug conc of diazepam

Question 7

What drugs enhance warfarin effect? (Increase risk of bleeding)

Answer 7

1. Penicillins
2. Cephalosporins

Question 8

PD interactions can be:

Answer 8

Aka drug changed by presence of another drug at target site
1. Agonist-antagonist
2. Synergism/potentiation

Question 9

What is an example of agonist-antagonist PD interaction?

Answer 9

Salbutamol(β2 agonist) & Propranolol (β antagonist)
- cuz agonist and antagonist

Question 10

What happens if gentamycin & vancomycin is taken tgt?

Answer 10

Synergism/potentiation PD interactions
- gentamycin is aminoglycoside
- both lead to ototoxicity & nephrotoxicity

Question 11

What happens if benzodiazepines + opioids given tgt?

Answer 11

Worsens sedation
- synergism/potentiation PD interaction

Question 12

What happens when aminoglycosides & loop diuretics given tgt?

Answer 12

Nephrotoxicity due to synergism/potentiation PD interactions

Question 13

What are 3 examples of synergism/potentiation PD interactions

Answer 13

1. Gentamicin + Vancomycin
2. Benzodiazepine + opioids
3. Aminoglycoside + loop diuretics