26 - Drug interactions

Question 1

Erythromycin

Answer 1

INHIBITOR

Question 2

Ketoconazole

Answer 2

INHIBITOR

Question 3

Phenytoin

Answer 3

Enzyme INDUCER

Question 4

Carbamezepine

Answer 4

Enzyme INDUCER

Question 5

Grapefruit Juice

Answer 5

INHIBITOR

of cyp3a4

Question 7

Ciprofloxacin

Answer 7

INHIBITOR

Question 8

Amiodarone

Answer 8

Enzyme INHIBITOR

Question 9

Fluoxetine

Norfluoxetine

Answer 9

INHIBITOR

Question 10

Cimetidine

Answer 10

INHIBITOR

Question 11

Rifampin

Answer 11

Enzyme INDUCER

Question 12

St. John’s Wort

Answer 12

Enzyme INDUCER

Question 13

Object Drug

Answer 13

Drug that is AFFECTED by the interaction

Question 14

Precipitant Drug

Answer 14

Drug that is CAUSING the interaction

Question 15

Narrow Therapeutic Index

NTI

Answer 15

Effective Dose - Toxic dose = SMALL

small gap between ED & LD

• Anticoags
• Anti diabetics
• Digoxin / benzo
• Immunosuppresant / cytotoxic drugs

Question 16

3 Different Mechanisms of Drug Interactions

Answer 16

pharmaCEUTICAL

pharmaCOKINETIC

pharmaCODYNAMIC

Question 17

PharmaCEUTICAL Interactions

Answer 17

AKA Incompatability

Occurs BEFORE drug is administered to patient

• Drugs given by IV
  
  • haziness / color change / particulates
• Phenytoin + Dextrose = crystalization
• Ampacillin / chlorpromazine / barbs
  
  • –> interact w/ dextran solution

Question 18

PharmacoKINETIC interactions

Answer 18

ADME Interactions

Altered PLASMA CONCENTRATION of drug

• ADME interactions

Question 19

Absorption

PharmacoKINETIC Interactions

Answer 19

Faster / Slower Absorption

More / Less complete interaction

• Complexation
• Alter of pH
• Gut motility
• Inhibition of GI enzymes
• Gi microflora
• MALABSORPTION Syndrome

Question 20

Metabolism

PharmacoKINETIC Interactions

Answer 20

Metabolism of Object Drug is Aletered

• Enzyme INDUCTION
  
  • ​–> Increased metabolism
• ​Enzyme INHIBITION
  
  • ​–> decreased metabolism
    
    • –> MOST SIGNIFICANT INTERACTIONS
      
      • ​–> TOXICITY CAN BE FATAL

Question 21

Prodrugs

PharmacoKINETIC Interactions

Answer 21

Produce the OPPOSITE

Drug needs metabolism –> to be ACTIVE

codeine / clopidogrel

Question 22

Excretion

PharmacoKINETIC Interactions

Answer 22

Excretion pattern of object drug is altered

• Alteration in RENAL BLOOD FLOW
  
  • ​AntiHypertensives / NSAIDS
• urine pH
• Competition for active secretion
• Forced diuresis

Question 23

Antihypertensives & NSAIDS

Answer 23

NSAIDS can reduce effectiveness of Antihypertensives

Reverse effects of hypotensive drugs

both block COX-1 cox2

– which impairs prostaglandin synth

Question 24

pharmacoDYNAMIC Interactions

Answer 24

Mechanism of Action of Drugs

Acting or blocking the SAME RECEPTOR

SAME PHYSIOLOGICAL AFFECT

• Beta-2 receptors
  
  • ​Propranolol can block effects of Salbutamol for asthma treatment
• Muscarinic Receptors
  
  • Antihistamines / Antidepressants / Phenothiazines
    
    • ​–> Confusion / memory loss
  • ​MANY DRUGS HAVE AntiCHOLINERGIC EFFECTS

Question 25

Additive Adverse Interactions

Answer 25

• Weak sedatives:
  
  • Diphenhydramine / quetiapine / mirtazapine / pregablin / gabapentin
• _​_May not cause sedation on their own but..
  
  • PROFOUND SEDATION WHEN COMBINED

Question 26

How to Reduce Patient Harm

from Drug Interactions

Answer 26

• Recognize drugs with NTI
• recognize drugs that are major perpratrators
  
  • Inducers / Inhibitors
• ​Applying pharmacological clinical principles
• Elderly / Chronically ill patients
  
  • ​are at higher risk of DI’s