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Drug Interactions
Dr. Williams Block 4
8
Pharmacology
Graduate
01/27/2012

Additional Pharmacology Flashcards

 


 

Cards

Term

Decreased Delivery to site of Action

Decreased GI absorption

Definition
  • Binding
    • Cholestyramine + levothyroxine → ↓ levothyroxine absorption
    • Antacids (Ca, Al, Mg) + tetracycline → chelate formation with ↓ tetracycline absorption
    • ferrous sulfate + tetracycline → ↓ tetracycline absorption
  • Altered gut motility-no example given
  • Altered pH gastrointestinal fluid
    • cimetidine (or ranitidine) + ketoconazole → ↓ ketoconazole abs
    • May be due to decreased ketoconazole dissolution at ↑ pH
    • cimetidine should be given 2 hrs after ketaconazole
    • fluconazole + cimetidine (oral) → ↓ fluconazole abs
    • fluconazole + cimetidine (IV) → fluconazole abs does not change
Term

Decreased delivery to site of action

Decreased transport to cellular site of action

Definition
  • tricyclic antidepressents + guanethidine →                 ↓ guanethidine uptake by sympathetic nerve endings → ↓ anti-hypertensive effects
  • ephedrine, amphetamines, phenothiazines have similar effect
Term

Decreased delivery to site of action

Enhanced Elimination

Definition
  • Enzyme Stimulation
    • Examples of INDUCERS of CYP inculde phenobarbital, carbamazepine, phenytoin, rifampin, St, Johns Wart
    • Phenobarbital + warfarin → ↓ anticoagulant effect (↓ plasma levels of warfarin)
  • Interactions with St. Johns Wart
    • Induction of CYP enzymes; can also induce P-glycoprotein transporter
    • St. Johns wart + (indinavir or cyclosporine via CYP or digoxin via p-glycoprotein) → ↓ plasma drug concentration
  • Increased renal elimination
    • alkalinization of urine + phenobarbital → ↑ excretion of drug
    • acidification of urine + amphetamines → ↑ excretion of drug  
Term

Increased Delivery to Site of Action

 

Definition
  • Increased Absorption-no example given
  • Decreased plasma protein binding-no example given
  • Decreased Elination
  • Inhibition of p-glycoprotein
Term

Increased Delivery to Site of Action

Decreased Elimation

Definition
  • Inhibition of Xanthine Oxidase
    • allopurinol + azathioprine (6-MP) → ↑ toxicity due to increased levels of MP
    • This occurs in both IV and oral forms according to package insert
  • Inhibition of CYP enzymes
    • Examples of inhibitors of CYP include amiodarone, erythromycin, ketoconazole, grapefruit juice
    • amiodarone + warfarin → ↓ warfarin elimination → ↑ warfarin plasma levels
    • Ketoconazole + terfenadine (Seldane) → ↓ terfenadine elimination → ventricular arrhythmia
      • Ketoconazole blocks the conversion of terfenadine → fexofenadine (not active)
    • Grapefruit juice + felodipine → ↑ plasma felodipine concentration
  • Inhibition of monoamine oxidase
    • MAO inhibitor + tyramine → hypertension
    • MAO inhibitor + selective serotonin reuptake inhbitor → serotonin syndrome
Term

Increased Delivery to Site of Action

Decreased Renal Excretion

Definition
  • Prodenecid + penicillin → ↓ penicillin excretion
  • Thiazide diuretic + lithium → ↓ lithium excretion

 

Term

Increased Delivery to Site of Action

Inhibition of P-glycoprotein

Definition
  • quinidine + digoxin → ↓ digoxin clearance
  • Quinidine reduces the clearance of digoxin; inhibition of P-glycoprotein-mediated digoxin transport has been implicated
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