Antiemetic and Antinausea Drugs Overview

Antiemetic and Antinausea Drugs

• Antiemetics are medications used to treat nausea and vomiting.
• Seven categories exist, with varying mechanisms of action, primarily via blocking pathways that initiate vomiting.
• Chemoreceptor Trigger Zone (CTZ) is the brain area involved in nausea and vomiting sensations.

Metoclopramide (Reglan)

• Class: Prokinetic Drug
• Routes: Oral, Parenteral (injection), prescription-only
• Indications include Gastroesophageal Reflux Disease (GERD), delayed gastric emptying, and nausea/vomiting (N/V).
• Mechanism of Action: blocks dopamine receptors in the CTZ, desensitizing it to GI tract impulses; stimulates GI tract peristalsis to enhance stomach emptying.
• Contraindications: seizure disorders, pheochromocytoma (adrenal gland tumor), breast cancer, and GI obstruction.
• Allergies to metoclopramide or related drugs (procaine, procainamide) are also contraindications.
• Adverse effects include long-term tardive dyskinesia (movement disorder) and extrapyramidal effects (tremors, muscle contractions, eye spasms, lip smacking, tongue protrusion).

Ondansetron (Zofran)

• Class: Serotonin Blocker
• Routes: Oral, injectable (IV push over 2 minutes)
• Indications include nausea/vomiting associated with chemotherapy and post-surgical procedures; also used for hyperemesis gravidarum (severe nausea and vomiting during pregnancy).
• Mechanism of Action: blocks serotonin receptors in the GI tract, CTZ, and vomiting center, preventing nausea and vomiting.
• Contraindications: known drug allergies, some concerns about use during the first trimester of pregnancy related to potential effects on fetal development (cat B medication).

Meclizine (Antivert)

• Class: Antihistamine (H1 receptor blocker)
• Route: Oral
• Indications include motion sickness, non-productive cough, allergy symptoms, and vertigo.
• Mechanism of Action: Inhibits acetylcholine (ACh) action in the vestibular and reticular areas, which prevents nausea and vomiting.
• Contraindications include shock and breastfeeding (lactation).

Promethazine (Phenergan)

• Class: Antidopaminergic
• Routes: Oral, Intramuscular (IM, preferred), Intravenous (IV).
• Indications include psychotic disorders, intractable hiccups, hay fever, and allergic conjunctivitis.
• Mechanism of action: Blocks dopamine receptors in the chemoreceptor trigger zone (CTZ).
• Contraindications: Children under 2 years old due to risk of fatal respiratory depression.

Scopolamine (Transderm-Scop, Scopace)

• Class: Anticholinergic (acetylcholine blocker)
• Route: Transdermal patch (72-hour release)
• Indications include nausea/vomiting associated with motion sickness, post-surgical procedures, and pre-operative use to reduce secretions.
• Mechanism of Action: blocks acetylcholine receptors in the inner ear labyrinth, CTZ, and the reticular formation to prevent nausea and vomiting.
• Contraindications for use include glaucoma, pyloric obstruction, urinary bladder neck obstruction.

Adrenergic Agonists (Sympathomimetics)

• Catecholamines (epinephrine, norepinephrine, and dopamine) play a role as endogenous adrenergic agonists.
• Alpha 1 receptors are located on postsynaptic cells (effector cells).
• Alpha 2 receptors are on presynaptic cells.
• Beta 1 receptors are mainly in the heart; Beta 2 receptors are primarily in the lungs and some arteries.
• Dopamine receptors dilate blood vessels in renal, mesenteric, coronary, and cerebral regions.
• Indications: include cardiovascular conditions (heart failure, shock); respiratory conditions (bronchodilation, nasal congestion); some urinary conditions.

Epinephrine (Epi-Pen)

• Class: Alpha and Beta adrenergic agonist
• Indications for use include anaphylaxis, bronchospasm, cardiac arrest, and asthma.
• Mechanism of Action: binds to alpha receptors causing vasoconstriction
• Contraindications: hypertension, hypersensitivity, CAD, tachyarrhythmias.
• Adverse effects include palpations, leading to dysrhythmias; seizures and stroke (extreme BP).
• Antidotes include sympatholytic medications, frequently clonidine

Dopamine (Inotropen)

• Class: Beta 1 adrenergic agonist.
• Route: Intravenous (IV)
• Indications: Low to moderate doses dilate blood vessels in the brain, increasing blood flow; higher doses improve cardiac contractility and output; highest dose indicated for vasoconstriction.

Mirabegron (Myrbetriq)

• Class: GU Adrenergic Agonist (Beta 3 adrenergic)
• Route: Oral (PO)
• Indications: overactive bladder
• Mechanism of Action: relaxes detrusor muscles to increase bladder capacity

Tamsulosin (Flomax)

• Class: Alpha adrenergic blocker
• Route: Oral (PO)
• Indications include benign prostatic hyperplasia (BPH) in males; kidney stones or urinary retention in females.
• Mechanism of Action: blocks alpha adrenergic receptors in the prostate and bladder to improve urinary flow

Sotalol (Betapace)

• Class: Nonselective beta blocker
• Route: Oral (PO)
• Indications: difficult to treat dysrhythmias
• Mechanism of Action: Class III antiarrhythmic properties

Metoprolol (Lopressor)

• Class: Beta-1 blocker
• Routes: IV and PO
• Indications: hypertension; Angina, heart failure
• Mechanism of Action: acts on beta-1 receptors in the heart to reduce the effects of catecholamines on cardiac function

Memantine (Namenda)

• Class: NMDA receptor antagonist
• Route: Oral (PO)
• Indications: Alzheimer's dementia
• Mechanism of Action: blocks the stimulation of NMDA receptors, reducing the development or progression of dementia symptoms

Pyridostigmine (Mestinon)

• Class: Indirect-Acting Cholinergic Drugs
• Route: Oral (PO)
• Indications: Myasthenia gravis, to reverse the effects of nondepolarizing neuromuscular drugs after surgery
• Mechanism of Action: increases acetylcholine by inhibiting acetylcholinesterase

Oxybutynin (Ditropan)

• Class: Anticholinergic
• Route: Oral (PO), Transdermal patch
• Indications: overactive bladder (OAB), neurogenic bladder associated with spinal cord injuries and congenital conditions
• Mechanism of Action: blocks muscarinic action of acetylcholine on smooth muscle cells in the bladder to inhibit involuntary contractions and increase bladder capacity

Dicyclomine (Bentyl)

• Class: Synthetic Antispasmodic Cholinergic Blocker
• Route: Oral (PO)
• Indications: irritable bowel syndrome, functional disturbances of the GI tract
• Mechanism of Action: blocks the muscarinic action of acetylcholine on smooth muscle cells in the GI tract

Cultural and Ethical Considerations

• Veracity: truthfulness and honesty.
• Nonmaleficence: avoiding harm to patients.
• Autonomy: patients' right to make medical decisions.
• Beneficence: doing good and promoting wellbeing for patients.
• Confidentiality: protecting patient information.
• Justice: fairness and equal treatment.
• Breach of Duty: deviating from the expected standard of care.
• Causation: establishing a direct link between the breach and harm.
• Damage: the harm or injury suffered by the patient.
• Cultural Assessment: systematic process to understand patient's background, beliefs, values, and preferences, including language, family, diet, traditional healing, views of health, illness, suffering, spirituality, and death.

Explore the classifications, mechanisms, and indications of antiemetic and antinausea drugs. This quiz covers various drug categories, with a focus on Metoclopramide (Reglan), its uses, contraindications, and adverse effects. Test your understanding of how these medications work to alleviate nausea and vomiting.