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GIL: Pharmacology > Nausea, vomiting + electrolyte imbalance > Flashcards

Nausea, vomiting + electrolyte imbalance Flashcards

1
Q

What stimulates N+V?

A

Toxins

Smells

Motion sickness

Migraine

Pregnancy

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2
Q

What drugs stimulate N+V?

A

Chemotherapy

SSRIs

Digoxin / theophylline

Iron salts

Erythromycin

Levodopa

Opioids e.g. morphine

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3
Q

What happens physiologically to the body when someone is about to vomit?

A
  1. Discomfort, dry mouth, salivary inhibition
  2. Yawning
  3. Reappearance of saliva
  4. Pyloric sphincter closes
  5. Tone of stomach decreases
  6. deep breath
  7. Contraction of abdominal muscles to force food out
  8. Forced expiration to prevent inhalation
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4
Q

How do we centrally regulate vomiting in the body?

A

Central regulation of vomiting occurs in the vomiting centre + chemoreceptor trigger zone (CTZ)

CTZ is sensitive to chemical stimuli - main site of anti-emetic drugs

Output from the CTZ stimulate the vomiting centre leading to vomiting

Neuronal signals from GIT feed in to CTZ + vomiting centre

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5
Q

What hormones/neurotransmitters are involved in N+V?

A

Histamine

Acetylcholine

Dopamine

5-HT

(Blocking these receptors in the brain prevents N+V)

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6
Q

How does chemotherapy induce N+V?

A

Chemotherapy agents stimulate release of 5-HT from enterochromaffin cells in GI Tract

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7
Q

Types of anti-emetic drugs

A

H1-Histamine receptor antagonists

  • e.g. promethazine
  • effective in motion sickness
  • produce drowsiness

Anti-muscarinic agents

  • e.g. hyoscine
  • effective in motion sickness
  • reduce gastric motility
  • anti-muscarinic side effects (dry mouth)
  • produce drowsiness

Dopamine antagonist

  • e.g. domperidone + metoclopramide
  • act in CTZ, has unwanted CNS effects
  • stimulates gastric emptying = reduce nausea

5-hydroxytryptamine antagonist

  • e.g. ondansetron
  • blocks 5-HT at 5-HT3-receptors in gut + CNS
  • effective against anti-cancer drugs
  • not effective for motion sickness

Cannabinoid receptor agonist

  • action unknown

Neurokinin receptor antagonist

  • NK1 receptors activated by substance P
  • NK1 receptor antagonists suppress nausea + vomiting
  • e.g. aprepitant
  • used in cancer chemotherapy

Steroids

  • e.g. dexamethasone
  • used in chemotherapy
  • action unknown
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8
Q

What is the standard prescription for cancer chemotherapy nausea + vomiting?

A

5-HT3 receptor antagonist

Steroid

NK1 receptor antagonist

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9
Q

Vomiting causes electrolyte imbalance.

What are the consequences of this?

A

Vomiting = loss in H+, K+ + H2O

Consequences

  • acid/base imbalance
  • electrolyte imbalance
  • nerve/muscle function
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10
Q

How does diarrhoea affect electrolyte imbalance? And what are the consequences?

A

Losses in Na+ + H20

Dehydration leads to:

  • low blood pressure
  • muscle weakness/cramps
  • reduced level of consciousness
  • heart failure
  • convulsions
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11
Q

How does urine affect electrolyte imbalance?

A

Variable fluid loss

High K+, low Na+

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12
Q

What is the most abundant extracellular cation?

What regulates H20 + its excretion in kidneys?

A

Sodium

Osmotic activity of extracellular fluid depends on relative proportion of Na+ + H20

Na+ + H20 excretion in kidney regulated by vasopressin + aldosterone

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13
Q

What is Hyponatraemia?

A

Sodium depletion

Caused by fluid retention e.g. renal failure, heart failure

Extracellular fluid should have 145mmol/l of sodium

Hyponatraemia = < 135mmol/l of sodium

Hypernatraemia = > 145 mmol/l

Leads to:

  • water into cells
  • cerebral oedema (brain swelling)
  • nausea/vomiting
  • coma
  • death
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14
Q

How does MDMA affect electrolyte imbalance?

A

MDMA = ecstasy

Makes you drink more water

Stimulates vasopressin secretion (water retention)

Causes hyponatraemia

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15
Q

What is the treatment of Hyponatraemia?

A

Water restriction

Increase salt intake

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16
Q

What causes Hypernatraemia?

How does Hypernatraemia lead to death?

A

Due to decrease in water

Rare as thirst stimulates drinking

Diabetes = increase urination leading to increase in water loss

H20 leaves cells

Decrease in cell volume

Decrease brain size

Coma

Death

17
Q

Condition for when there is a depletion of potassium

A

Hypokalaemia

  • <2.5mmol/l
  • Muscle weakness
  • ECG changes
  • Decrease intake
  • alkaloosis
  • increase losses = vomiting
  • increased urinary losses - diuretics
  • Impaired renal function
18
Q

Condition for when there is an excess of potassium

A

Hyperkalaemia

  • extracellular > 5.5mmol/l
  • muscle weaknes
  • ECG changes = arrhythmias
  • Decreased excretion - renal failure

Acidosis

  • ACEi with K+ supplements
19
Q

How does pH affect electrolyte balance?

A

Decrease in pH (acidosis)

  • H+ enter cells
  • K+ move out of cells
  • Causes hyperkalaemia (+ decreased loss in urine)

Increase in pH (alkalosis)

  • Increase entry of K+ into cells
  • Causes hypokalaemia (+ increased loss in urine)

GIL: Pharmacology (10 decks)

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