Antiemetics

• Antiemetics overview


  Antiemetic drugs are used to decrease nausea/vomiting
• Antiemetic examples


  antihistamines: diphenhydramine, dimenhydramine, hydroxyzine, meclizine

  phenothiazines: prochlorperazine, perphenazine, promethazine,

  sedative hypnotics:

  cannabinoids: dronabinol

  5-HT3RA: palonosetron, ondansetron

  anticholinergics: scopolamine

  P/NK1RA: aprepitant
• Pharmacodynamics of antihistamines


  blocks histamine1 which results in decreased salivary secretion. Some also bind to cholinergic receptors
• pharmacodynamics of phenothiazines


  block dopamine receptors in the chemoreceptor trigger zone

  they also block cholinergic, alpha, and histamine receptors
• pharmacodynamics of cannabinoids


  works in the CNS to prevent nausea and vomiting by binding to cannabinoid receptors
• pharmacodynamics of 5-HT3 receptor anatagonists

  block serotonin both peripherally and centrally
• pharmacodynamics of anticholinergic antiemetics

  acts as a competitive inhibitor of muscarinic receptors

  decrease GI motility and saliva
• pharmacodynamics of P/NK1RA


  occupies NK1 receptors and augments activity of 5-HT3 receptors
• Precautions and contraindications of antihistamines

  caution in patients on anticholinergics

  caution in glaucoma, seizure, hyperthyroidism, cardiovascular disease

  contraindicated in liver impairment
• precaution and contraindication of phenothiazines

  produce extrapyramidal reactions so contraindicated in children and infants
• precaution and contraindication of dronabinol


  contraindication in allergy to sesame or cannabinoid oil

  caution in seizures, cardiac disease, history of drug abuse
• precaution and contraindication of 5-HT3R Antagonists

  may mask progressive ileus

  caution with PKU
• precaution and contraindication of anticholinergics

  caution in glaucoma, GI or GU obstruction, older adult
• adverse reaction of phenothiazines

  drowsiness

  extrapyramidal symptoms, dystonia, akathisia, tardive dyskinesia, agranulocytosis
• adverse reaction of phenothiazine

  promethazine can cause fatal respiratory depression in children younger than 2

  anticholinergic effects

  discolor urine
• adverse effects of cannabinoid

  euphoria, depression, paranoia, palpitations, tachycardia, seizures
• 5-HT3R antagonists


  constipation, headache, fatigue, dizziness, diarrhea
• adverse reaction of anticholinergic antiemetics

  dry mouth, drowsiness, blurred vision
• antihistamines block histamine 1 receptors which results in decreased salivary secretions which assists in nausea. 1st generation antihistamines an also bind to cholinergic receptors and produce antiemetic effects
• Phenothiazines block dopamine in the CTZ, they also bind to cholinergic, alpha 1 adrenergic and histamine 1 receptors
• Antihistamines include diphenhydramine, hydroxyzine, and meclizine
• phenothiazines include: prochlorperazine, promethazine
• cannabinoids activate cannabinoid receptors which prevent nausea and vomiting
• 5HT3RA block serotonin on vagal nerve terminalsa nd in the CTZ
• 5HT2RA examples include ondansetron and other -etron drugs