Antiemetics Flashcards
What happens in vomiting?
1) A deep breath is taken, the glottis closes and the larynx rises to open the upper esophageal sphincter. The soft palate rises to close off posterior nares.
2) The diaphragm contracts sharply down, which decreases intrathoracic pressure, which opens the oesophagus and the lower oesophgeal sphincter.
3) The abdominal muscles contract, which increases the intragstric pressure. The pylorus is closed, the oesophgus is open…..
WHat can vomiting do to the blood?
Causes a hypochloraemic metabolic alkalosis with a hypokalemia.
Describe receptor distrubution in the mechanism of vomitng.
The vomiting centre is part of the nucleus solitraius. It has receptors for 5HT2, Ach and H1.
Inputs: 1) The chemotactic trigger zone. It has receptors for D2, NK and 5HT3. 2) The vestibular system- recpetors for Ach and H1. 3) The cardiac and GIT system- receptors for 5HT3 and varois machano/chemoreceptors. There is also input from the cortex e.g. anxiety, inreased ICP can cause vomiting.
What is promethazine and what does it mainly inhibit?
It is a phenothiazine derivative and it primairy inhibits H1 recptors. It acts at the central voming centre, the CTZ and the vestibular system.
What is promethazine used to treat? Describe side effects.
MOTION SICKNESS (can be taken during, 4 hours peak), HYPEREMESIS GRAVIDARUM, LABYRINTH disorders and PRE AND POST. Side effects: dizziness, tinnitus, fatigue, sedation. Can be anti-muscarinic in excess (H1>M>D2)
What are metoclopramide and demperidone? What can they be used to treat?
They are D2 receptor anatgonists, so mainly inhibit vomiting at the CTZ. Have prokinetic effects in the GIT. They are NOT effective against motion sickness. They’re used to treat N+V associated with CANCER THERAPY, RADIATION sickness, URAEMIA and ANTI-PARKINSONS drugs.
Name 3 pharmacokinetic points and 2 concerns with meteclopramide and domperidone?
Pharmacokinetics: can be administered orally but extensive first pass metabolism so IV may be preferable. Meteclopramide can cross the BBB and both cross placenta. 2 concerns: increase kinetics of the gut so affect the absorption of other drugs and may cause malnutrition.
Name unwanted effects of meteclopramide and domperidone
Meteclopramide can cross the BBB- can cause dizziness, depression and anxiety and possibly a Parkinsonian syndrome in children. Both have endocrine effects- hyperprolactinaemia with galactorhea and menstrual disorders.
What is hyoscine? What is it used for? (2)
A muscarinic receptor antagonist, which inhibts N+V mainly at the vestibular nucleus and the CTZ. Used for MOTION SICKNESS (only pre, depsite peak effect 1-2 hours) and PRE op.
What is odensetron? What is it used for?
A 5HT3 receptor blocker, so acts as an antiemtic via inhibiton at the CTZ and visceral afferents. Use for CANCER THERAPY vomiting, RADIATION sickness and POST-op. Used with corticosteroids for high emetogenic chemotherapy.
Name 3 side effects of odensatron.
Odensatron is a 5HT3 receptor antagonist. Causes headache, flushing and constipation.
How do cannabinoids work as anti-emetics?
CB1 recptors are presynaptic- decrease NT release and also inhibit PG synthesis.
