Usage
Hyoscyamine is prescribed for various gastrointestinal and genitourinary conditions involving smooth muscle spasms. This includes irritable bowel syndrome (IBS), peptic ulcer disease, diverticulitis, pancreatitis, biliary and renal colic, cystitis, and neurogenic bladder. It’s also used as an adjunctive therapy in Parkinson’s disease to manage tremors and drooling, as a pre-operative medication to reduce secretions, during surgery to manage bradycardia, and to reverse the effects of neuromuscular blockade. Its pharmacological classifications include anticholinergic, antimuscarinic, and antispasmodic.
Hyoscyamine’s mechanism of action involves competitively antagonizing acetylcholine at muscarinic receptors, primarily in the parasympathetic nervous system. This leads to decreased smooth muscle tone and reduced secretions in various organs.
Alternate Names
Hyoscyamine is also known as Daturine. Brand names include Anaspaz, Cystospaz, Levbid, Levsin, HyoMax, and Symax.
How It Works
Pharmacodynamics: Hyoscyamine exerts its effects by blocking the action of acetylcholine at muscarinic receptors. This results in decreased smooth muscle contractions, reduced glandular secretions (saliva, sweat, gastric acid), and increased heart rate.
Pharmacokinetics: Hyoscyamine is well-absorbed following oral administration, including sublingual and buccal routes. It is metabolized in the liver, primarily by CYP3A4 enzymes, and eliminated mainly through renal excretion. The half-life is relatively short, about 2-3 hours.
Mode of Action: Hyoscyamine competes with acetylcholine for binding at muscarinic receptor subtypes (M1-M5), with a slight preference for M1 and M3 receptors. This competitive antagonism prevents acetylcholine from activating these receptors, thereby inhibiting the downstream effects of parasympathetic stimulation.
Elimination Pathways: Primarily renal excretion, with some hepatic metabolism via CYP3A4.
Dosage
Standard Dosage
Adults:
- Oral (immediate-release): 0.125-0.25 mg every 4 hours as needed, not exceeding 1.5 mg/24 hours.
- Oral (extended-release): 0.375-0.75 mg every 12 hours, not exceeding 1.5 mg/24 hours.
- Sublingual: 0.125-0.25 mg every 4 hours as needed, not exceeding 1.5 mg/24 hours.
- Parenteral (IM, IV, SubQ): 0.25-0.5 mg every 4 hours as needed, not exceeding 4 doses/24 hours.
Children:
Dosing varies based on age, weight, and formulation. Consult pediatric dosing guidelines or specific product information. Oral drops and elixir formulations are available for younger children. For children 2 to under 12 years of age: Consult a healthcare professional. For children 12 years and older, please consult a physician. Sublingual, IM, or SC/IV injections are used as a preanesthetic. As with adults, the hyoscyamine dose is 0.005 mg/kg.
Special Cases:
- Elderly Patients: Start with lower doses and titrate cautiously due to increased sensitivity to anticholinergic effects.
- Patients with Renal Impairment: Dose adjustments may be necessary.
- Patients with Hepatic Dysfunction: Use with caution and consider dose reduction.
- Patients with Comorbid Conditions: Exercise caution in patients with cardiovascular disease, glaucoma, urinary retention, and gastrointestinal obstruction.
Clinical Use Cases
- Intubation: Pre-anesthetic: 0.005 mg/kg IM, IV, or SubQ 30-60 minutes before intubation.
- Surgical Procedures: During surgery: 0.125 mg IV, repeated in increments of 0.125 mg as needed for bradycardia.
- Mechanical Ventilation: Not specifically indicated for routine use.
- Intensive Care Unit (ICU) Use: Primarily for managing secretions or specific gastrointestinal/genitourinary issues.
- Emergency Situations: Organophosphate poisoning: 1-2 mg IV initially, followed by additional doses as needed.
Dosage Adjustments
Adjustments may be needed for renal or hepatic impairment, elderly patients, or those with certain comorbid conditions.
Side Effects
Common Side Effects:
Dry mouth, blurred vision, constipation, urinary retention, drowsiness, dizziness, headache.
Rare but Serious Side Effects:
Confusion, hallucinations, tachycardia, palpitations, acute angle-closure glaucoma, paralytic ileus, heat stroke.
Long-Term Effects:
Chronic use can lead to cognitive impairment, especially in the elderly.
Adverse Drug Reactions (ADR):
Anaphylaxis, Stevens-Johnson syndrome (rare).
Contraindications
Glaucoma (especially angle-closure), urinary retention, severe gastrointestinal obstruction, myasthenia gravis, hypersensitivity to hyoscyamine or other anticholinergics.
Drug Interactions
Other anticholinergic drugs (additive effects), antacids (decreased hyoscyamine absorption), potassium chloride (increased gastrointestinal irritation), drugs metabolized by CYP3A4 (potential for altered metabolism).
Pregnancy and Breastfeeding
Pregnancy Safety Category: C. Use with caution during pregnancy, weighing the risks and benefits. It’s excreted in breast milk, so use cautiously during breastfeeding.
Drug Profile Summary
- Mechanism of Action: Muscarinic receptor antagonist.
- Side Effects: Dry mouth, blurred vision, constipation, urinary retention, drowsiness, dizziness.
- Contraindications: Glaucoma, urinary retention, bowel obstruction, myasthenia gravis.
- Drug Interactions: Other anticholinergics, antacids, potassium chloride.
- Pregnancy & Breastfeeding: Use with caution.
- Dosage: Varies based on indication and route. See detailed dosage section.
- Monitoring Parameters: Heart rate, blood pressure, intraocular pressure (if at risk for glaucoma), symptoms of anticholinergic toxicity.
Popular Combinations
Hyoscyamine is often combined with other antispasmodics (dicyclomine, methscopolamine), analgesics (acetaminophen, ibuprofen) or sedatives (phenobarbital).
Precautions
Caution in elderly patients, patients with cardiovascular disease, hepatic or renal impairment, and those with pre-existing gastrointestinal or urinary tract conditions. Avoid alcohol.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Hyoscyamine?
A: The dosage varies depending on the condition, age, and formulation. Refer to the detailed dosage section above.
Q2: How should Hyoscyamine be administered?
A: Hyoscyamine can be administered orally (tablets, capsules, liquid), sublingually, or parenterally (IM, IV, SubQ).
Q3: What are the common side effects of Hyoscyamine?
A: Common side effects include dry mouth, blurred vision, constipation, urinary retention, drowsiness, and dizziness.
Q4: What are the contraindications for using Hyoscyamine?
A: Contraindications include glaucoma, urinary retention, bowel obstruction, and myasthenia gravis.
Q5: Does Hyoscyamine interact with any other medications?
A: Yes, it can interact with other anticholinergic drugs, antacids, potassium chloride, and medications metabolized by CYP3A4.
Q6: Can Hyoscyamine be used during pregnancy and breastfeeding?
A: Use with caution during pregnancy and breastfeeding. Consult a healthcare professional for personalized advice.
Q7: What are the signs of Hyoscyamine overdose?
A: Overdose symptoms can include confusion, hallucinations, rapid heart rate, dilated pupils, difficulty breathing, and seizures.
Q8: What should patients do if they miss a dose of Hyoscyamine?
A: Take the missed dose as soon as you remember. If it’s almost time for the next dose, skip the missed dose and resume your regular schedule. Don’t double the dose.
Q9: How should Hyoscyamine be stored?
A: Store at room temperature away from moisture, heat, and light. Keep out of reach of children.
