Antiemetics and Their Functions

Antiemetic and Antinausea Drugs

• Antiemetics are medications used to relieve nausea and vomiting (emesis).
• Several categories of antiemetic drugs exist, each with different mechanisms of action, though many work by blocking pathways that induce vomiting.
• The chemoreceptor trigger zone (CTZ) in the brain is a key area involved in nausea and vomiting.

Metoclopramide (Reglan)

• Class: Prokinetic Drug
• Routes include oral (PO), parenteral, and requires a prescription.
• Indications: Gastroesophageal reflux disease (GERD), delayed gastric emptying, nausea, and vomiting.
• Mechanism: Blocks dopamine receptors in the CTZ, desensitizing it to signals from the GI tract. It stimulates GI peristalsis, enhancing stomach emptying.
• Contraindications: Seizure disorders, pheochromocytoma, breast cancer, GI obstruction, and allergy to the medication or related compounds (procaine, procainamide).
• Adverse Effects: Long-term use can cause irreversible tardive dyskinesia.

Ondansetron (Zofran)

• Classification: Serotonin Blocker
• Routes include oral (PO) and injectable (IV) forms.
• Indications: Nausea and vomiting associated with chemotherapy and post-operative procedures.
• Mechanism: Blocks serotonin receptors in the GI tract, CTZ, and vomiting center (VC).
• Contraindications: Known allergy and concerns for the development of cleft palate in the first trimester of pregnancy.
• Adverse Effects: Known drug allergy and other potential side effects.

Meclizine (Antivert)

• Classification: Antihistamine (H1 receptor blocker)
• Route: Oral (PO)
• Indications: Motion sickness, non-productive cough, allergy symptoms, sedation, and vertigo.
• Mechanism: Inhibits acetylcholine (ACh) by binding to H1 receptors, preventing cholinergic stimulation in the vestibular and reticular areas, thereby preventing nausea and vomiting.
• Contraindications: Shock and lactation.
• Adverse Effects: Drowsiness.

Promethazine (Phenergan)

• Classification: Antidopaminergic
• Routes: Oral (PO), intramuscular (IM) (preferred), and intravenous (IV) (common).
• Indications: Psychotic disorders, intractable hiccups, hay fever symptoms, and allergic conjunctivitis.
• Mechanism: Blocks dopamine receptors in the CTZ (CTV).
• Contraindications: Children under 2 years old due to risks of fatal respiratory depression.
• Adverse Effects: Most common is sedation, but may also result in drowsiness, dry mouth, and lightheadedness.
• Nursing Implications: Dilute in at least 10 mL of fluid for administration and administer through a large-bore intravenous (IV) line, avoiding the patient's veins.

Scopolamine (Transderm-Scop, Scopace)

• Classification: Anticholinergic (ACh) blocker
• Route: 72-hour transdermal patch that releases 1 mg of the medication.
• Indications: Nausea and vomiting related to motion sickness and post-operative situations.
• Mechanism: Reduces secretions before surgery by binding to and blocking ACh receptors in the inner ear labyrinth and blocks nauseating stimuli to the CTZ and stimuli from the reticular formation to the VC.
• Contraindications: Glaucoma, pyloric obstruction, urinary bladder neck obstruction.

Additional Adverse Effects and Nursing Implications

• Several medications for nausea and vomiting have potential adverse effects like dizziness, blurred vision, confusion, hallucinations, and urinary retention.
• Nursing implications include assessing patient history, current medications, monitoring for contraindications, and educating patients on potential side effects, especially regarding driving or hazardous activities.