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Introduction to Metabolism and Pharmacology > Basic Principles of Pharmacology > Flashcards

Basic Principles of Pharmacology Flashcards

1
Q

What is meant by Pharmacodynamic interactions ?

A

Occur when one drug alters the action of another drug

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2
Q

What are the different Pharmacodynamic interactions ?

A 
Direct:
- Additive/Synergistic/Potentiating 
- Inhibitory/antagonistic 
Indirect:
- Physiological interactions
- Pathological interactions
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3
Q

Explain Direct synergistic (potentiating) interactions?

A

When 2 drugs act in the same way at the same site of action

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4
Q

Give some examples of Direct synergistic (potentiating) interactions?

A
  • Alcohol increases (potentiates) the effects of all drugs that on the brain (e.g. antipsychotics and anxiolytics)
  • Monoamine oxidase inhibitors (e.g. Phenelzine, isocarboxacid) used as antidepressant increased the amount of noradrenaline stored in nerve terminals and interact dangerously with drugs such as ephedrines (present in cough and decongestant preparations) or tyramine (present in food such as matured cheese, marmite, etc…) that release stored N. These interactions may cause a fatal rise in blood pressure (hypertensive crisis)
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5
Q

Explain Direct inhibitory interactions?

A

Occur when 2 drugs act in opposing ways at the same site of action

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6
Q

Example of harmful interactions ?

A

β-adrenoreceptor antagonists (‘beta blockers’, such as atenolol, propanolol) diminish the effectiveness of β-adrenoreceptor agonists such as salbutamol (avoid the use of beta-blockers in asthmatics)

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7
Q

Examples of beneficial interactions ?

A
  • naloxone reverses opiate (e.g. morphine) toxicity

- Vitamin K reverses warfarin toxicity

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8
Q

Explain Indirect physiological interactions?

A

Occur when one drug produces a physiological change that alters the action of another drug

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9
Q

Give an example of Indirect physiological interactions ?

A

Diuretics (e.g. thiazides and furosemide) lower the plasma K+ concentration, thereby potentiating the action of digoxin and hence increasing its toxicity

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10
Q

Explain Indirect pathological interactions?

A

Occur when one drug produces pathological change that alters the action of another drug

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11
Q

Give an example of Indirect pathological interactions ?

A

Increased risk of stomach bleeding when patients taking warfarin and aspirin or other NSAIDs

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12
Q

What is meant by Pharmacokinetic interactions?

A

Occur when the ADME (Absorption, Distribution, Metabolism and Excretion) of a drug is altered by another drug

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13
Q

In Absorption interactions what mechanisms include?

A
  • Change in pH of GI fluids
  • Effects on gastric emptying and GI motility
  • Binding or chelation of drugs
  • Competition for active absorption mechanisms
  • Toxic effects on the GIT
  • Changes in gut bacterial flora
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14
Q

Explain Distribution interactions ?

A
  • Many drugs (and metabolites) are highly bound to plasma proteins (e.g. albumin)
  • Displacement of one drug by another from plasma proteins will cause an increase in the concentration of the unbound, active drug leading to a potential increase in its effects
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15
Q

Such interactions are only likely to be of importance if 2 criteria are met ?

A
  1. The drug is highly protein bound (<90%)

2. The drug has low Vd

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16
Q

Explain Metabolism interactions ?

A

Occurs when the metabolism of Drug A is either increased or inhibited by Drug B through:

  • CYP enzyme induction OR
  • CYP enzyme inhibition
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17
Q

Give examples of Metabolism interactions ?

A
  • Induction of CYP enzymes by alcohol increases metabolism of paracetamol to its toxic metabolite NAPBQI
  • St John’s Wort and anti-TB drug rifampicin induces the enzymes that metabolise many different drugs including oral contraceptive pills, warfarin and digoxin
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18
Q

Explain Excretion interactions and how it’s affected ?

A

The main mechanism by which one drug can affect the renal excretion of another are:

  • Altering protein binding and hence filtration
  • Inhibiting tubular secretion
  • Altering urine pH and/or urine flow
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19
Q

Many acidic drugs and metabolites share the same?

A

Proximal tubular active transport system and can complete for secretion from the blood into the kidney tubules

20
Q

One drug may therefore interfere with ?

A

The renal excretion of another and can cause accumulation and toxicity

21
Q

Give an example of this inhibition of tubular secretion ?

A
  • Probenecid competes with penicillin for OATs, reduces extraction ratio and prolongs action of penicillin
  • Aspirin (or NSAIDs) competes with methotrexate causes reduced tubular secretion of methotrexate leading to increased risk of methotrexate toxicity
22
Q

What is P-glycoprotein (P-gp) and what does it do ?

A

P-glycoprotein is an ABC transporter. It pumps a wide range of substrates out of cells, including drugs

23
Q

Where was it first discovered ? and where is it found ?

A
  • First discovered in tumour cells, where it contributes to multidrug-resistance (MDR)
  • P-gp is found throughout the intestinal tract, it affects the absorption of all oral drugs that are substrates
  • P-gp is also found in the liver and kidney, where it acts to increase the excretion of drugs by transporting the molecules into the bile and urine respectively
24
Q

Chinese patients are more sensitive to ? whilst Afro-Caribbean people are ?

A

Chinese patients are more sensitive to propranolol, a beta blocker, than white Europeans, whilst Caribbean people are less sensitive

25
Q

What do patients of African or Caribbean origin respond poorly to ?

A

ACE inhibitors (e.g. captopril) as antihypertensive - reason unclear but may be related to ethnic differences in the expression of angiotensin receptors or the converting enzymes

26
Q

Japanese patients are 3 times more likely to respond to ?

A

Cancer treatment with gefitinib than caucasian patients

27
Q

How do analgesics may prevent/reduce pain by:

A
  1. Block endogenous pain-producing substances
  2. Mimic endogenous pain-relieving substances
  3. Prevent nerve transmission (local anaesthetics)
28
Q

What are the different types of pain and explain them ?

A
  1. Somatic
    - Localised in the skin, soft tissue, muscles and bones
    - Caused by activation of pain receptors in either the body surface or musculoskeletal tissues
  2. Visceral
    - Viscera refers to the internal areas of the body that are enclosed in a cavity (i.e. lungs, liver, stomach)
    - Visceral pain results from inflammation, distension or stretching of the internal organs
  3. Neuropathic pain
    - Results from damage to the peripheral nervous system or the central nervous system (CNS) or both
29
Q

What are the different categories of pain and explain them ?

A
  1. Acute
    - Relatively brief sensation, usually less than 6 months duration
    - Usually a response to a specific trauma (e.g. surgery)
    - Forms the basics for danger warnings and subsequent learning
  2. Chronic
    - Lasts more than 6 months
    - Exists beyond the time for normal organic healing
    - The pain begins to impair other functions
    - Few objective medal findings
30
Q

Explain Nociceptive afferent fibres (first order neurons) ?

A

Carries signal from brain to spinal cord

31
Q

Explain Spinal nociceptice affferent fibres (second order neurons) ?

A

Carries signal from spinal cord to brain

32
Q

What do noxious stimuli initiate and transmit ? and what can this be called ?

A

Noxious stimuli initiate action potentials in nociceptive afferent neurons, which transmit pain signals from peripheral nociceptors to spinal cord. They sometimes known as first order neurons or primary afferent fibres

33
Q

Explain Aδ fibres ?

A
  • Myelinated
  • Transmit sharp localised pain
  • Fast, conduct impulses at the rate of 20m/s
34
Q

Explain C fibres ?

A
  • Unmyelinated
  • Transmit dull diffuse pain
  • Slow, conduct impulses at he rate of 1m/s
35
Q

What do both release ?

A

Glutamate, acting on AMPA and NMDA receptors

36
Q

What do synapse with ?

A

They synapse with second order neurons in the dorsal horn of the spinal cord

37
Q

Substance P and CGRP released from primary afferent neurons also act in? and promotes ?

A

The periphery, promoting inflammation by their effects on blood vessels and immune cells

38
Q

What does Substance P (acting on NK1 receptors) and glutamate (acting on NMDA receptors) facilitate?

A

The transmission of pain impulses at dorsal horn neurons in the spine

39
Q

Explain Prostaglandins ?

A

Released during inflammation

  • Prostaglandins do not cause pain by itself but facilitate the actions of other substances, e.g. bradykinin or 5-HT
  • It does this partly by inhibiting K+ channels
40
Q

What drugs are used in pain management ?

A
  1. Paracetamol (acetaminophen) - ‘non-opioid’ analgesic
  2. Non-steroid anti-inflammatory drugs drugs (NSAIDs)
    - Non-selective (inhibits both COX-1 and COX-2)
    - Selective COX-2 inhibitors
  3. Opioids
    - ‘Weak’ opioids
    Codeine, dihydrocodeine
    Tramadol
    - ‘Strong’ opioids
    Morphine
    Oxycodone
    Fentanyl
    Methadone
41
Q

Explain the mechanism of action of Paracetamol ?

A
  • Paracetamol is an analgesic without anti-inflammatory activity and therefore NOT an NSAID
  • It has very little inhibitory effect on COX-1 or 2 in the peripheral tissues
  • In the CNS, it inhibits COX-2 by reducing the availability of an essential co-substrate
  • There is also a weak inhibition of COX-3 in the CNS, may not be clinically important
42
Q

What does NSAIDs inhibits?

A

Cycloxygenase (COX), prevent prostaglandins production

43
Q

Where is Opium extracted from ?

A

Poppy plant

44
Q

Differences between opiates and opioids ?

A

Classically, natural substances extracted from opium is called opiates, e.g. morphine and codeine; while synthetic or semi-synthetic opiates are referred as opioids

45
Q

Opioids causes ? by binding to ?

A

Opioids cause analgesia by binding to GPCRs and:

  • Stimulating descending inhibitory pathways
  • Inhibiting transmission of pain signals at dorsal horn
  • Inhibiting action potentials in nerve terminals in periphery
46
Q

What are some actions of morphine ?

A
  1. Analgesia
  2. Sedation
  3. Cough suppressant
    - used to treat cough
  4. Decreased respiration
    - cause of death in overdose
  5. Euphoria
  6. Pupil constriction (pinpoint pupils)
  7. Reduced gastrointestinal motility, constipation
    - can be used to treat diarrhoea
  8. Nausea and vomitting
    - stimulation of chemoreceptor trigger zone (CTZ)
  9. Histamine release
    - can cause itching, bronchoconstriction

Introduction to Metabolism and Pharmacology (16 decks)

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