Antiemetics and Antinausea Drugs Overview

Antiemetics and Antinausea Drugs

Antiemetic drugs help prevent nausea and vomiting, they play a crucial role in various medical settings.
Nausea: An unpleasant sensation that's often a precursor to vomiting
Vomiting: The forceful expulsion of gastric contents, occasionally intestinal contents
Vomiting Center (VC): Located in the medulla oblongata, receives signals from various sources and initiates the vomiting reflex when stimulated.
Chemoreceptor Trigger Zone (CTZ): Located near the VC but outside the blood-brain barrier, detects toxins in the blood and stimulates the vomiting reflex.
Multiple pathways trigger vomiting, antiemetics work by blocking these pathways and preventing vomiting signals.
Neurotransmitter blockade: Many drugs block neurotransmitters to prevent vomiting; blocking the transmission of nausea-inducing stimuli.
Receptor Interactions: Drugs bind to receptors to stop the vomiting signals.
Antiemetics are used to prevent and reduce the severity of nausea and vomiting symptoms
Antiemetics are used to treat various conditions such as surgery, chemotherapy, and motion sickness.

Anticholinergic Drugs

Block acetylcholine (ACh) receptors to prevent transmission of nausea-inducing stimuli.
Scopolamine: A common anticholinergic drug, available as a 72-hour transdermal patch that releases 1 mg of scopolamine, effective for motion sickness and post-operative nausea.

Antihistamine Drugs

Inhibits acetylcholine (ACh) by binding to H1 receptors, preventing cholinergic stimulation reducing nausea
Effective for motion sickness, nonproductive coughs, and allergy symptoms. Some also provide sedation.
Common antihistamines: dimenhydrinate (Dramamine), diphenhydramine (Benadryl), meclizine (Antivert), and hydroxyzine (Vistaril).

Antidopaminergic Drugs

- Block dopamine receptors in the chemoreceptor trigger zone (CTZ) reducing nausea
- Used to treat psychotic disorders and intractable hiccups.
- Examples: Prochlorperazine (Compazine), promethazine (Phenergan), Amisulpride (Barhemsys), Droperidol
- Oral and IM routes are preferred for promethazine; IV route is common for Droperidol but not preferred and never intraarterial.

Neurokinin Receptor Antagonists

- Inhibit substance P/neurokinin 1 receptors.
- Effective in preventing chemotherapy-induced nausea.
- Aprepitant: Inhibits neurokinin 1 receptors, reducing chemotherapy-induced nausea.
- Fosaprepitant: Water-soluble prodrug of aprepitant, rapidly absorbed for convenient IV administration.
- Rolapitant: Another neurokinin-1 receptor antagonist, effective for preventing CINV (chemotherapy-induced nausea and vomiting).

Prokinetic Drugs

- Block dopamine receptors in the chemoreceptor trigger zone (CTZ).
- Stimulate GI tract peristalsis and enhance the emptying of stomach contents, reducing delayed gastric emptying and gastroesophageal reflux disease.
- Metoclopramide (Reglan) is a common example, but long-term use may cause tardive dyskinesia.

Serotonin Blockers

- Block serotonin receptors in the GI tract, chemoreceptor trigger zone (CTZ), and vomiting center (VC).
- Used for nausea and vomiting in chemotherapy and post-operative patients.
- Examples: Dolasetron (Anzemet), Granisetron (Kytril), Ondansetron (Zofran), Palonosetron (Aloxi).

Tetrahydrocannabinoids

- Tetrahydrocannabinoids (THC) are the primary psychoactive components in marijuana, exerting inhibitory effects on the brain.
- THC alters mood and perception, impacting brain pathways related to nausea and vomiting.
- Clinically used to manage chemotherapy-induced nausea and vomiting, as well as anorexia in HIV/AIDS patients.
- Dronabinol (Marinol) binds to cannabinoid receptors, reducing nausea and vomiting.

Miscellaneous Antinausea Drugs

- Phosphorated Carbohydrate Solution (Emetrol): A mint-flavored oral solution used off-label for motion sickness, considered relatively safe.

Adverse Effects

- Drowsiness:  A common side effect of many antiemetics due to anticholinergic effects.
- Dry Mouth:  A common anticholinergic effect.
- Blurred Vision:  Can be caused by antihistamines.
- Constipation:  Can be caused by some antiemetics.

Ginger

- A natural remedy used to treat nausea and vomiting.
- Conditions treated: chemotherapy-induced nausea, morning sickness, and motion sickness.
- Potential side effects: Mild gastrointestinal upset and skin reactions.
- Interactions: Can increase the absorption of some oral medications and increase bleeding risk with anticoagulants.

Nursing Implications

- Assessment:  Thoroughly assess the patient's history of nausea and vomiting, including any precipitating factors, allergies, and current medications.
- Medications:  Carefully review current medications and identify potential drug interactions.
- Contraindications: Check for contraindications and warn patients about potential drowsiness and advise against operating machinery after taking antiemetics.
- Patient Education:  Educate patients on potential drug interactions, such as with alcohol, and emphasize slow position changes to prevent hypotension. 
- Monitoring: Closely monitor patients for both therapeutic and adverse effects, observing for nausea, vomiting, and other symptoms.
- Medication Timing: Administer antiemetics 30-60 minutes before chemotherapy for optimal effectiveness.