Nausea and vomiting

What neurotransmitters have a role in nausea/ emesis?

Histamine - H1

Serotonin 5HT3

Dopamine D2

Where in the body are serotonin receptors found?

• 89% found in gut

• 1% found in brain

• 10% found in plasma platelets

  • Hence SSRIs deplete platelet stores of serotonin, increasing bleeding risk as they cannot aggregate as well - affects clotting

What is the neurotransmitter serotonin responsible for?

neuronal excitation and emesis

Explain the different causes of emesis

Different causes of emesis include:

• Gastric irritation - foods which irritate the mucosal lining and cause emesis

• Cytotoxic medications such as chemotherapeutics can cause emesis

• Emesis in response to psychological thoughts, emotions, trauma etc

• Emesis due to the delivery of medication such as cytotoxic medications

• innear ear dysfunction/ motion sickness

What is the chemo-receptor trigger zone?

The chemo-receptor trigger zone is an area which sits outside of the blood-brain barrier and is able to detect changes in the blood such as cytotoxic drugs, irritants, and inner ear dysfunction. The chemo-receptor trigger zone is fundamental for the bodys ability to detect a noxious stimulus

What is the emetic centre?

The emetic centre is a region of the brain which controls emesis. It contains sensory neurons and there is a point at which once a stimulus takes place then emesis has to occur and no longer any voluntary control

What is motion sickness, and how is it treated?

Motion sickness is caused by inner ear dysfunction which causes too many stimuli too be sent to the brain. It is treated by anti-muscarinics or anti-histamine tablets. Note that promethazine is most sedating but should caution due to drowsiness in all anti-sickness medications and explain to the patient if this occurs, they should avoid driving - always check the nature of the journey.

• Hyoscine - anti-muscarinic

• Cinnarazine - anti-histamine

• Promethazine - anti-histamine

What is ‘morning sickness’ and how do we treat it?

Morning sickness occurs in pregnancy, typically worst in the first trimester and can occur at any time of the day and not just in the morning. We try to avoid the use of anti-emetics in pregnancy and instead give non-pharmacological advice. Eat dry toast and biscuit before getting up, eating small frequent meals instead of one big meal, drinking plenty of water but not in large volumes at once and avoiding trigger foods and spicy foods.

When would we treat morning sickness with medication?

We would treat motion sickness if it impairs the womens health e.g. canot keep fluids and foods down so a risk of dehydration and nutritional deficiencies - in this case give antiemetic and IV fluids for rehydration. Thiamine also given IV

What is the only licensed medication for sickness in pregnancy?

Doxylamine - the only licensed anti-sickness medication in pregnant women - the rest are unlicensed - anti-histamine

What are the available anti-emetics and their MOA

Anti-histamine - Doxylamine - only LICENSED

Antihistamine/ H1 receptor antagonist - Promethazine, cyclizine

D2 antagonist - Domperidone/ Prochlorperazine, levomepromazine (1st generation antipsychotic/anti-emetic)

D2/5-HT3 antagonist -Metoclopramide

5-HT3 antagonist -Ondansterone

Steroid - prednisolone

What is often used in combination with anti-emetic?

Steroid - dexamethasone

Why do cytotoxic medications cause emesis?

Cytotoxic medications target rapidly dividing cells, including the gut epithelium cells. When they are broken down they release serotonin and sertonin neurotransmitters, triggering the emesis centre to cause vomiting and nausea (remember 89% of serotonin stores are found in the gut)

What is anticipatory nausea and vomiting and how is it treated?

Anticipatory N&V occurs in anticipation of chemotherapy and is typically due to past chemotherapy-induced nausea and vomiting. Not treated with anti-emetics and CBT is most effective option.