CARBACHOL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CARBACHOL (CARBACHOL).
Direct-acting cholinergic agonist that mimics the effects of acetylcholine at muscarinic and nicotinic receptors, causing miosis, increased aqueous humor outflow, and smooth muscle contraction.
| Metabolism | Hydrolyzed by plasma pseudocholinesterase and acetylcholinesterase. |
| Excretion | Primarily renal excretion; approximately 80-90% of the dose is excreted unchanged in urine within 24 hours via glomerular filtration and active tubular secretion. Minor biliary/fecal excretion (<10%). |
| Half-life | Terminal elimination half-life is approximately 0.5–1 hour in patients with normal renal function. Clinically, due to rapid metabolism and excretion, effects dissipate quickly; accumulation may occur in renal impairment. |
| Protein binding | Approximately 10% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | Vd approximately 0.3–0.5 L/kg, indicating distribution primarily in extracellular fluid. |
| Bioavailability | Topical: Low systemic bioavailability (<1%) due to local application and rapid uptake into ocular tissues. Oral: Not available (clinically not used orally). Intravenous: 100% for systemic administration. |
| Onset of Action | Intraocular (topical): 10–20 minutes for miosis and intraocular pressure reduction. Intravenous: 2–5 minutes for systemic cholinergic effects. |
| Duration of Action | Intraocular (topical): Miosis lasts 4–8 hours; intraocular pressure reduction lasts 6–8 hours. Intravenous: Duration of systemic effects is 15–30 minutes due to rapid hydrolysis. |
For ophthalmic use: 0.01% to 3% solution, 1-2 drops up to 3 times daily. For intraocular use: 0.01% solution, 0.5 mL intracamerally. Not used systemically.
| Dosage form | SOLUTION |
| Renal impairment | No specific guidelines; systemic absorption limited with ophthalmic use. For systemic use (not standard), caution with GFR <30 mL/min; dose reduction unspecified. |
| Liver impairment | No specific guidelines; hepatic impairment unlikely to affect ophthalmic use. Systemic use not recommended. |
| Pediatric use | Not established; safety and efficacy not determined. Use only under specialist guidance. |
| Geriatric use | No specific adjustments; standard dosing may be used. Monitor for increased intraocular pressure and systemic effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for CARBACHOL (CARBACHOL).
| Breastfeeding | It is unknown if carbachol is excreted in human milk. Due to potential for serious adverse reactions in nursing infants, breastfeeding is not recommended during therapy. M/P ratio: not available. |
| Teratogenic Risk | Carbachol is not recommended during pregnancy. Human data are insufficient to assess risk; animal studies have shown teratogenic effects at high doses. First trimester exposure carries unknown risk. Second and third trimester use may cause uterine hyperstimulation, leading to fetal distress. Avoid use during pregnancy unless clearly needed. |
■ FDA Black Box Warning
Intraocular administration may cause severe corneal edema and bullous keratopathy. Use only with extreme caution in patients with compromised corneas.
| Serious Effects |
["Hypersensitivity to carbachol","Acute iritis or uveitis","Conditions where cholinergic effects are undesirable (e.g., asthma, bradycardia, peptic ulcer)"]
| Precautions | ["Risk of retinal detachment, especially in patients with pre-existing retinal disease","May cause transient lenticular opacities","Systemic absorption may cause bradycardia, hypotension, and bronchospasm"] |
| Food/Dietary | No significant food interactions have been reported with ophthalmic carbachol. Systemic absorption is minimal, so dietary restrictions are not required. |
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| Fetal Monitoring |
| Monitor for signs of uterine hyperstimulation, fetal heart rate patterns, and maternal cholinergic effects (e.g., bradycardia, hypotension, bronchospasm). In pregnancy, fetal monitoring is advised if used for ophthalmic purposes, though systemic absorption is low. |
| Fertility Effects | Carbachol may cause uterine contractions and could theoretically affect implantation or fertility based on its pharmacodynamic action. No specific reproductive studies in humans are available. |
| Clinical Pearls | Carbachol is a direct-acting cholinergic agonist used primarily for ophthalmic purposes to induce miosis and lower intraocular pressure. It is not systemically absorbed significantly when applied topically. Onset of miosis occurs within 10-20 minutes and lasts 4-8 hours. Use with caution in patients with iritis, as it may increase inflammation. Systemic side effects (e.g., bradycardia, hypotension) are rare but possible with excessive dosing or in sensitive individuals. |
| Patient Advice | Use exactly as prescribed; do not touch the dropper tip to any surface to avoid contamination. · Temporary blurred vision or eye discomfort may occur; avoid driving or operating machinery until vision clears. · Report any eye pain, redness, or changes in vision to your doctor immediately. · If you wear contact lenses, remove them before instilling the drops and wait at least 15 minutes before reinserting. · Do not use more often than directed, as overuse may lead to eye irritation or systemic side effects. |