ch. 6 Drug Interactions

Question 1

drug-drug interactions

Answer 1

• occurs when pt takes two or more drugs
• includes interactions with OTC drugs
• outcomes:
  • intensify: allowing drug
    to act longer or stronger;
    can also cause increase
    in unwanted effects (taking 2 anticoags= iincrease risk of bleeding)
  • reduce effects: decrease effectiveness or decrease AE (tetracyclines and antacids)
  • New effect: unexpected effect that each drug does not normally cause - ex. alcohol with disulfiram causes vomiting

Question 2

4 basic mechanisms of drug-drug interaction

1. Direct

Answer 2

1. Direct chemical/physical interaction

• most common when mixed in IV solution- precipitate forms= what happens in you inject a solid into the blood stream

Question 3

4 basic mechanisms of drug-drug interaction

2. Pharmacokinetic

Answer 3

Absorption: ex. drugs that change gastric pH, laxatives increase motility=decreased time in gut

Distribution: protein-binding or alteration in extracellular pH which affects ionization of drug (allowing it to become lipophilic to cross cell membrane)

Metabolism: activation or depression or CYP450 system (**IMPORTANT)

P-Glycoprotein: alteration much like the CYP450 system

Question 4

4 basic mechanisms of drug-drug interaction

3. Pharmacodynamic

Answer 4

Same receptor: almost always inhibitory (drug blocks access to another drug)

Different receptor: two drugs acting on 2 different sites but with same effects= increased effects or can reverse effects if actions contradict one another
ex: valium and morphine= increased risk of resp. depression

Question 5

4 basic mechanisms of drug-drug interaction

4. combined toxicity

Answer 5

if both drugs are toxic to same organ= increased chance of injury to organ

Question 6

Cytochrome P450 system

Answer 6

Question 7

Drug-food interactions

Answer 7

Decreased absorption
- food most often causes decreases in absorption
- Ex: tetracyclines bind to Ca++- avoid milk products)

Question 8

Drug-food interactions
Increased absorption

Answer 8

Increased absorption
- ex. saquinavir (invirase) for HIV- double absorption

Question 9

Drug food interactions

altered metabolism (increaesd):

Answer 9

can persist for 3 days after last grapefruit juice

Question 10

Drug food interactions

Drug toxicity

Answer 10

much like drug-drug interactions-chemicals interact

• ex. MAOI with food containing tyramine (aged cheeses, yeast extracts, chianti wine)
• ex. K+ sparing diuretics and salt substitutes=dangerously high levels of K+

Question 11

Drug food interactions

Drug Action:

Answer 11

ex. high levels of ingested Vit K (broccoli, greens) counteracts warfarin (Coumadin)

Question 12

Drug food interactions

Answer 12

Timing of dosing
- if drug food interaction expected, will be instructed to “administer on empty stomach”- 1 hr before or 2 hrs after meals
- if interaction not expected but side effect of nausea d/t administration, may see “take with food”- give with food or shortly after a meal