Drug Interactions

Question 1

2 classes of drug interactions

Answer 1

pharmacodynamic - ability of drug to interact w receptor altered by co-administration of another substance → synergistic/additive or antagonistic

pharmacokinetic - when one drug alters ADME (absorption, distribution, metabolism excretion) of another drug → altering the concentration at site of action

Question 2

synergistic vs additive

Answer 2

synergistic - 2 drugs clinical response greater than expected by sum of individual effects

additive - response equal to sum of effect by each agent alone

Question 3

Interaction between (alcohol + CNS depressant) or (2 CNS depressants)

Answer 3

additive/synergistic

Question 4

Internation between tramadol/pethidine/fentanyl + antidepressants

Answer 4

can also interact w St John’s wort

ADDITIVE/SYNERGISTIC

risk of serotonin toxicity - hyperreflexia, clonus, tremor, confusion, agitation, shivering, sweating, fever, diarrhoea

Question 5

Interaction between NSAIDs + ACE inhibitor (‘pril’s)

Answer 5

increased risk of renal impairment and hyperkalaemia (abnormal heart rhythm)

ADDITIVE/SYNERGISTIC

ACEI inhibits conversion of angiotensin I to angiotensin II

and

NSAIDS inhibit PG production

both reduce pressure in glomerulus

Question 6

Interaction between salbutamol and atenolol (for high bp and angina)

Answer 6

antagonistic

reduced efficacy of salbutamol

(salbutamol is B-adrenergic receptor agonist and atenolol is B-AR antagonist)

Question 7

Interaction between corticosteroid + oral hypoglycaemic

Answer 7

hypo’s reduce BGL, CCS’s increase BGL

Question 8

Why should tetracycline and fluoroquinoline abx be taken away from some metals (Ca, Mg), dairy products and resins (1hr before or 2-3hr after)

Answer 8

potential chelators (form insoluble complex that renders the abx ineffective)