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Pharm > Lecture 31: Drug Interactions > Flashcards

Lecture 31: Drug Interactions Flashcards

1
Q

Where are drug interactions usually listed?

A

In product monographs

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2
Q

What does information about the product monograph do?

A

Informs physicians about contraindicated conditions or potential drug interactions

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3
Q

What kind of drugs are most susceptible to issues with drug interactions?

A

Drugs with a narrow therapeutic window

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4
Q

What is a consequence of small change in a therapeutic window?

A

Small changes in our responsiveness can lead to toxic outcomes

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5
Q

What are the types of Pharmacodynamic Interactions?

A
  • Antagonistic Interactions
  • Synergism or Additive interactions
  • Indirect interactions
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6
Q

How does Antagonistic Interaction work?

A

Drug A may act as an antagonist at a receptor for Drug B reducing the effectiveness of drug B

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7
Q

what is an example of Antagonistic Interaction?

A

Vitamine K rich foods and Warfarin

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8
Q

What is Warfarin?

A

An anticoagulant in patients with blood clots

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9
Q

How does Warfarin work?

A

It inhibits Vitamin K epoxide reductase which recycles oxidized vitamin K to reduced vitamin K which is used in clotting factors

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10
Q

What is Clotting closely monitored using?

A

The Prothrombin time

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11
Q

What is Prothrombin Time?

A

A measure of time required for blood to clot under a set of standard lab conditions

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12
Q

How is PT usually reported?

A

As INR

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13
Q

What does a high INR mean?

A

The sample required a long time to form a clot like in the case of an individual taking warfarin

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14
Q

How do foods rich in Vitamin K affect Warfarin?

A

They weaken the effectiveness of warfarin because they compete for occupancy of K epoxide reductase

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15
Q

What is Synergism or Additive interactions?

A

When multiple agonists/modulators act on the same receptor leading to excessive activation

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16
Q

What does Synergism refer to?

A

Effects that are greater than the individual effects of two drugs

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17
Q

What does Additive refer to?

A

Effects that are roughly the sum of the individual effects of two drugs

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18
Q

What is an example of Synergism or additive interactions?

A

Drugs like benzos, alcohol, barbiturates acting on GABAA receptors

19
Q

What kind of channel is the GABAA channel?

A

A chloride channel

20
Q

What are examples of Benzos?

A
  • Xanax

* Valium

21
Q

How do Benzos affect GABAa?

A

They are positive allosteric modulators of GABAa

22
Q

What are Barbiturates to GABAA receptors?

A

They are positive allosteric modulators or agonists of GABAA

23
Q

What is Alcohol to GABAA receptors?

A

They are PAM of GABAa

24
Q

What are Zolpidem to GABAA receptors?

A

Positive allosteric modulators of GABAA

25
Q

What kind of interactions are Benzos, Barbiturates, Alcohol and Zolpidem at the same time?

A

Synergism or additive interactions

26
Q

What are Indirect reactions?

A

The effects of multiple drugs influence the same signalling pathways but not the same receptor

27
Q

What is an example of Indirect interactions?

A

Serotonin Syndrome

28
Q

What does Serotonin syndrome arise from?

A

Combinations of drugs that lead to overabundance of 5-HT/serotonin in the CNS and overstimulation of 5-HT receptors

29
Q

What is Serotonin Syndrome characterized by?

A

High body temperature, agitation, sweating, dilated pupils, muscle twitching, elevated BP

30
Q

What are the 6 key drugs involved in Serotonin Syndrome?

A
  • Monoamine oxidase inhibitors
  • Tricyclic antidepressants, SSRIs and SNRIs
  • Opioids
  • St. John’s wort
  • Recreational drugs (MDMA, methamphetamine)
  • Precursors of Serotonin
31
Q

How are MAOs involved in serotonin syndrome?

A

They prevent the breakdown of 5-HT. serotonin by MAO-A and lead to increased cellular levels of 5-HT

32
Q

How are Tricyclic antidepressants, SSRIs, and SNRIs involved in serotonin syndrome?

A

The prevent the reuptake of 5-HT from the synaptic cleft prolonging the lifetime of 5-HT in the synapse

33
Q

How are various opioids involved in serotonin syndrome?

A

Their metabolites may have direct serotonergic effects or interfere with serotonin reuptake

34
Q

How is St. John’s wort involved in serotonin syndrome?

A

It acts as a serotonin reuptake inhibitor

35
Q

How are recreational drugs involved in involved in serotonin syndrome?

A

MDMA and Meth promote serotonin release by causing uptake pumps to act in reverse

36
Q

How Precursors of Serotonin involved in serotonin syndrome?

A

5-HTP and L-tryptophan are used as antidepressants

37
Q

What do Pharmacokinetic interactions do?

A

They alter drug availability

38
Q

What are the mechanisms that affect absorption and distribution (pharmacokinetic interactions)?

A
  • Drugs that alter gut motility, pH, can alter the absorption of a drug
  • Drugs that alter local blood flow can alter absorption of a drug
39
Q

How can drugs./food affect CYP enzymes?

A
  • they can induce the expression of specific CYP enzymes that will reduce the lifetime and abundance of their substrates
  • They inhibit CYP enzyme activity which will prolong the lifetime and activity of their substrates
40
Q

What is the most common enzyme for the biotransformation of drugs?

A

CYP3A4

41
Q

How does CYP3A4 affect warfarin?

A

It breaks down warfarin

42
Q

How does an increase in CYP3A4 affect warfarin?

A

People taking something that increase CYP3A4 will be resistant to warfarin because it breaks down warfarin

43
Q

What can inhibit CYP3A4?

A

Grapefruit juice

Pharm (31 decks)

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