Drug Guide
Carbachol
Classification
Therapeutic: Eye drops for ophthalmic procedures or glaucoma management
Pharmacological: Cholinergic agonist; parasympathomimetic
FDA Approved Indications
- Induction of miosis during ophthalmic surgery (e.g., cataract surgery)
Mechanism of Action
Carbachol is a non-selective cholinergic agonist that stimulates both muscarinic and nicotinic receptors, leading to contraction of the iris sphincter muscle, ciliary muscle, and increased aqueous humor outflow to cause miosis and reduce intraocular pressure.
Dosage and Administration
Adult: Typically, 0.75% to 4% solution instilled into the conjunctival sac as needed during surgery.
Pediatric: Use is generally restricted; consult ophthalmic guidelines.
Geriatric: Adjust as per clinical response; no specific age-related dose modifications established.
Renal Impairment: No specific recommendations; use caution and monitor for adverse effects.
Hepatic Impairment: No specific recommendations; use caution. Immature hepatic function in pediatric patients may alter metabolism.
Pharmacokinetics
Absorption: Topically absorbed through ocular tissues, minimal systemic absorption.
Distribution: Limited systemic distribution due to topical application.
Metabolism: Metabolized locally within ocular tissues.
Excretion: Primarily local; systemic metabolites excreted via renal route.
Half Life: Not well established; effects are localized and transient.
Contraindications
- Active inflammation or infection in the eye.
- Corneal ulcerations.
- Hypersensitivity to carbachol or other cholinergic agents.
Precautions
- Use with caution in patients with bronchial asthma, cardiac disease, peptic ulcer, or hyperthyroidism. Monitor for systemic cholinergic effects. Avoid in patients with narrow-angle glaucoma unless directed by ophthalmologist.
Adverse Reactions - Common
- Transient decrease in visual acuity (Common)
- Corneal irritation or cysts (Uncommon)
Adverse Reactions - Serious
- Eye pain, eye inflammation, or allergic reactions (Rare)
- Systemic cholinergic effects (e.g., salivation, nausea, bronchospasm) if absorbed systemically (Rare)
Drug-Drug Interactions
- Other parasympathomimetic agents; may enhance effects. Caution with anticholinergic agents which may oppose effects.
Drug-Food Interactions
N/ADrug-Herb Interactions
N/ANursing Implications
Assessment: Monitor patient’s ocular response, intraocular pressure, and for signs of systemic cholinergic effects.
Diagnoses:
- Risk for ocular irritation or injury.
- Risk for systemic cholinergic effects.
Implementation: Administer as prescribed; instill drops into conjunctival sac without touching eye with bottle tip.
Evaluation: Assess for effective miosis, lowered intraocular pressure, and absence of adverse reactions.
Patient/Family Teaching
- Use as directed and do not exceed prescribed dosage.
- Report eye pain, vision changes, or signs of allergic reaction.
- Follow pre- and post-operative instructions from the ophthalmologist.
Special Considerations
Black Box Warnings:
- None specific, but systemic absorption can occur, leading to cholinergic effects.
Genetic Factors: No specific genetic considerations.
Lab Test Interference: No known interference with lab tests.
Overdose Management
Signs/Symptoms: Excessive muscarinic stimulation: salivation, nausea, vomiting, diarrhea, bronchospasm, bradycardia.
Treatment: Discontinue use; administer atropine as an antidote for severe systemic effects; symptomatic and supportive care.
Storage and Handling
Storage: Store in a cool, dry place, protected from light.
Stability: Stable up to the expiration date on the package under recommended conditions.