carbachol
Carbastat, Carboptic, Isopto Carbachol, Miostat

Available forms
Available by prescription only
Intraocular injection: 0.01%
Ophthalmic solution: 0.75%, 1.5%, 2.25%, 3%

Indications and dosages
 Ocular surgery (to produce pupillary miosis). Adults: 0.5 ml of 0.01% (intraocular form) instilled gently into the anterior chamber for production of satisfactory miosis. May be instilled before or after securing sutures.
 Open-angle or angle-closure glaucoma. Adults: 2 drops of 0.75% to 3% solution up to t.i.d.

Pharmacodynamics
Miotic action: Cholinergic activity causes contraction of the sphincter muscles of the iris, producing miosis, and contraction of the ciliary muscle, resulting in accommodation. Acts to deepen the anterior chamber and dilate conjunctival vessels of the outflow tract.

Pharmacokinetics
Absorption: Penetrates intact corneal epithelium very poorly.
Distribution: No information available.
Metabolism: No information available.
Excretion: No information available.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug and in those in whom cholinergic effects, such as constriction, are undesirable (such as in those with acute iritis, some forms of secondary glaucoma, pupillary block glaucoma, or acute inflammatory disease of the anterior ocular chamber).
  Use cautiously in patients with acute heart failure, bronchial asthma, peptic ulcer, hyperthyroidism, GI spasm, Parkinson’s disease, and urinary tract obstruction.

Interactions
Drug-drug. Cyclopentolate, ophthalmic belladonna alkaloids (atropine, homatropine): May interfere with antiglaucoma actions of carbachol. Use together cautiously.

Adverse reactions
CNS: headache, syncope.
CV: arrhythmias, hypotension, flushing.
EENT: spasm of eye accommodation, conjunctival vasodilation, eye and brow pain, transient stinging and burning, corneal clouding, bullous keratopathy.
GI: abdominal cramps, diarrhea, salivation.
GU: urinary urgency.
Respiratory: asthma.
Skin: diaphoresis.

Effects on lab test results
None reported.

Overdose and treatment
Signs and symptoms of overdose include miosis, flushing, vomiting, bradycardia, bronchospasm, increased bronchial secretion, sweating, tearing, involuntary urination, hypotension, and seizures.
 With accidental oral ingestion, vomiting is usually spontaneous; if not, induce emesis and follow with activated charcoal or a cathartic. Treat dermal exposure by washing the area twice with water. Treat CV or blood pressure responses with epinephrine. Atropine has been suggested as a direct antagonist for toxicity.

Special considerations
• Drug is especially useful in glaucoma patients resistant or allergic to pilocarpine hydrochloride or nitrate.
• Premixed drugs should be used only for single-dose intraocular use.
• Discard unused portions of injectable drug.
• Obtain periodic tonometric readings.
Pregnant patients
• Safe use during pregnancy hasn’t been established. Use during pregnancy only when the benefits justify possible risk to the fetus.
Breast-feeding patients
• It isn’t known whether carbachol appears in breast milk. Use cautiously in breast-feeding women.
Pediatric patients
• Safety and efficacy haven’t been established.

Patient education
• Tell patient with glaucoma that long-term use may be needed. Stress compliance, and explain importance of medical supervision for tonometric readings before and during therapy.
• Instruct patient to apply finger pressure on the lacrimal sac for 1 to 2 minutes after topical instillation of drug.
• Reassure patient that blurred vision usually diminishes with continued use.
• Teach patient how to instill eyedrops correctly, and warn patient not to touch eye or surrounding area with dropper.
• Warn patient not to drive for 1 or 2 hours after administration until effect on vision is determined.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use