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Pharmacology and Drugs / Poisons 9.14 > Drug interactions & metabolism > Flashcards

Drug interactions & metabolism Flashcards

1
Q

Name 5 main types of drug interactions

A
  1. Absorption reactions
  2. Distribution reactions
  3. Metabolism reactions
  4. Excretion reactions
  5. Pharmacodynamic reactions
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2
Q

Give 2 examples of drugs that react with metal ions eg Ca, Mg, Fe

A

Ciprofloxacin

Tetracyclines (eg Doxycycline)

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3
Q

Cholestyramine does what with other drugs in the GIT

A

Absorbs them so dropping their effectiveness

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4
Q

How can you minimised the problem of absorption reactions between diff substances

A

Give at diff times to avoid interaction

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5
Q

How does metclopramide influence the uptake of paracetamol in the drug Paramax

A

It incr gut motility so incr absorption of paracetamol

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6
Q

How do PPIs influence the uptake of acid drugs e.g. Ketoconazole (anti fungal)

A

By reducing stomach acidity - reduces absorption of weak acids

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7
Q

How does rifampicin interact with the transporter P-glycoprotein and what affect does this have on Digoxin absorption

A

P-glycoprotein reduces Digoxin absorption in gut.

Rifampicin INDUCES P-glycoprotein so will reduce level of Digoxin absorbed even more.

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8
Q

What effect does clarithromycin have on CYP450 enzymes. How might this influence the metabolism of statins and what might be the consequence

A

It is an INHIBITOR - will prevent CYP450 from metabolizing free drug.
Will increase free statin in blood - lead to neuropathy.

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9
Q

What effect does rifampicin have on CYP450 enzymes. How might this influence the metabolism of statins and what might be the consequence

A

It is an INDUCER - will speed up metabolism of free drug.

Will have less statin free in blood (but not clinically shown to be an issue)

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10
Q

What drugs reduce kidney perfusion.

How does this affect the levels of renally excreted drugs e.g. methotrexate.

A

NSAIDs e.g. aspirin, ibuprofen reduce kidney perfusion.

This reduces renal excretion so will get incr in methotrexate = toxicity

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11
Q

How do antidiuretics influence the excretion of lithium

A

Antidiuretics retain Na - Lithium v similar molecule so is also retained. = Lithium toxicity

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12
Q

How does urine alkilinisation help in OD of aspirin

A

Increases the excretion of weak acids e.g. aspirin, methotrexate.

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13
Q

Additive pharmacodynamic effects:

What is the possible consequence of adding Beta2 agonist (eg ventolin) and diuretics.

A

Hypokalaemia

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14
Q

Additive pharmacodynamic effects:

What is the possible consequence of adding Alcohol and anti-histamines

A

Drowsiness

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15
Q

Additive pharmacodynamic effects:

What is the possible consequence of adding aminoglycosides & ciclosporin

A

Renal toxicity

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16
Q

Opposing effects:

Why should patients on antihypertensives (eg ACE inhibitors) avoid NSAIDs

A

NSAIDs cause increased BP

17
Q

Why should patients on warfarin avoid too much green veg

A

Green veg = vit K, which acts as warfarin antagonist

18
Q

Why should patients taking anti-diabetic drugs be cautious of using corticosteroids

A

Corticosteroids increase blood glucose

19
Q

Name 7 drugs with a narrow therapeutic window and so are at high risk of drug interactions

A
  1. Warfarin (anti coag)
  2. Gentamicin (aminoglycoside antibiotic)
  3. Tacrolimus (immuno suppressant - transplants)
  4. Lithium - (psych sedation)
  5. Digoxin - (slow HR - used in congestive hrt fail)
  6. Phenytoin (anti-epileptic)
  7. Carbamazepine (anti-epileptic)
20
Q

What does a black dot in the BNF indicate

A

A significant interaction

21
Q

Name 7 common CYP450 INDUCERS

A
  1. Rifampicin
  2. Green veg / broccoli etc. (Vit K)
  3. Alchohol
  4. Smoking
  5. St John’s wort
  6. Phenytoin
  7. Carbamazepine
22
Q

Name7 common CYP450 inhibitors

A
  1. Grapefruit juice
  2. Clarithromycin / erythromycin
  3. Metronidazole
  4. Cimetidine
  5. Miconazole
  6. Verapamil
  7. Amiodarone
23
Q

What are the main 2 aims of drug metabolism

A
  1. Make drug more hydrophillic - easier to excrete in urine

2. Inactivate drug - reduce free amount in system

24
Q

Main 2 sites & enzymes of drug metabolism

A
  1. Liver - CYP450

2. Gut - Monoamine Oxidase (MAO)

25
Q

Principle of first pass metabolism

A

Orally consumed drugs enter bloodstream at intestine - enter portal system and liver - metabolised before reach any part of body.

26
Q

3 examples of drugs which will be increased in effect by liver damage due to reduced first pass metabolism

A

Morphine
Propanolol
Diazepam

27
Q

2 main PHASES of drug metabolism

A
  1. Modification - make lipophilic drugs more water soluble

2. Conjugation - add large molecules to drug to make more water soluble

28
Q

3 types of modification and egs

A
  1. Oxidation - Dopamine to adrenaline by MAO
    - Hypoxanthine - xanthine - uric acid by Xanthine oxidase
  2. Reduction - Warfarin by CYP450
  3. Hydrolysis - in plasma e.g. Aspirin to Salicylic acid.
29
Q

Example of conjugation with a large molecule to make more water soluble

A

Aspirin added to GLUCORONIC acid - Glucoronide.

30
Q

What is the basic meaning of First order kinetics

A

There are still sufficient enzymes avail to metabol drug, so rate of drug metabolism is prop. to rate of drug dose increase.

31
Q

What is basic meaning of Zero order kinetics,(non linear / saturation kinetics) why is it important.

A

All available enzymes have been saturated so as you increase amount of drug the level of metabolism does not increase any further. - Drugs build up in body this way causing toxicity

32
Q

What is a pro-drug - give an example

A

An inactive form of a drug which is then metabolized to the active form.
e.g. L-DOPA - Dopamine

33
Q

What reduction in GFR might you expect in 50yr old and 70 yr old respectively

A

25% and 50% reduction in GFR

Pharmacology and Drugs / Poisons 9.14 (7 decks)

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