Drug Interactions Flashcards

1
Q

Definition

A
  • An interaction is said to occur when the effects of one drug are changed by the presence of another drug, herbal medicine, food, drink or by some environment chemical agent
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2
Q

Outcomes

A
  • Harmful by increased toxicity of a drug
  • Harmful by decreased efficacy of a drug
  • Beneficial
  • No clinical difference
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3
Q

Types of drug interactions

A
  • Pharmacodynamic
    • effects of one drug are changed by the presence of another drug as it’s a site of action
  • Pharmacokinetic
    • Effects of a drug on the process of ADME of another drug
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4
Q

Pharmacodynamic

Additive or synergistic

A
  • Additive or Synergistic
    • E.g. sedative drugs have additive CNS depressant effects with alcohol
    • SSRI AND SJW
    • ACEI and K+- sparing diuretic
    • Insulin and sulphonylurea
    • ACEI and thiazide
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5
Q

Pharmcodynamic

Antagonistic or opposing

A
  • NSAIDs and Loop diuretics
  • Hypoglycaemic and glucocorticoids
  • Levodopa and typical antipsychotics
  • Beta-agonists (Salbutamol) and beta-antagonists (propranolol)
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6
Q

PK- Absorption

A
  • Change in GI pH
  • Adsorption, chelation and other complexing mechanisms
  • Change in Gastric motility
  • Induction or inhibition of drug transport proteins
  • Malabsorption caused by drugs
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7
Q

PK- distribution

A
  • Protein binding- usually only result in transient increase in free drug
  • Induction or inhibition of drug transport proteins
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8
Q

PK- metabolism

A
  • Changes in first pass metabolism- grapefruit juice and calcium channel blockers
  • Enzyme induction- phenytoin, rifampicin, smoking
  • Enzyme inhibition- erythromycin, acute alcohol
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9
Q

PK- Elimination

A
  • Change in urinary pH- MTX and sodium bicarbonate
  • Change in active renal tubular transport- MTX and NSAIDs
  • Change in renal blood flow- NSAID and Li
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10
Q

Factors affecting susceptibility

A
  • Age
    • Elderly- decreased renal and hepatic function
    • Elderly- Polypharmacy
  • Genetic
  • Clinical status
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11
Q

Time course of interactions

A
  • Starting
  • Stopping
  • Change of dose
  • Route of administration
  • Half life of drugs
  • Mechanism of interaction e.g. enzyme inducers vs enzyme inhibitors
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12
Q

Managing drug interactions

A
  • Avoid the combination
  • adjust doses
  • Monitor
  • If not clinically significant, do nothing
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13
Q

Where to find information

A
  • BNF
  • Stockleys
  • SPC
  • MI centre
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