Miostat (Carbachol)

Carbachol acts on the ocular muscarinic pathway to manage pressure‑related and surgical eye conditions.

• Glaucoma: reduces intraocular pressure by increasing aqueous humor outflow.
• Intraocular surgery: induces miosis to improve surgical visualization and control.
• Ocular hypertension: helps lower elevated eye pressure in patients at risk of glaucoma.

• Carbachol directly stimulates muscarinic receptors on the sphincter pupillae and ciliary body. Activation of these receptors causes contraction of the pupillary sphincter, producing miosis, and enhances trabecular meshwork outflow, facilitating increased aqueous humor drainage and lowering intraocular pressure.

Carbachol may cause ocular and systemic reactions that vary in frequency.

Common Side Effects

• Blurred vision: transient loss of visual clarity after administration.
• Eye pain or discomfort: mild irritation at the instillation site.
• Conjunctival redness: mild hyperemia of the eye.
• Increased lacrimation: excess tearing.
• Headache: mild to moderate headache following dosing.
• Transient visual disturbances: temporary halos or glare.

Serious or Rare Side Effects

• Severe allergic reaction: swelling, rash, or anaphylaxis.
• Persistent miosis: prolonged pupil constriction affecting vision.
• Corneal edema: swelling of the cornea leading to visual impairment.
• Systemic cholinergic effects: bradycardia, bronchospasm, or hypotension.
• Hypotony: abnormally low intraocular pressure.
• Endophthalmitis: intraocular infection (rare).

Before using Carbachol, consider the following safety measures.

• Pregnancy: safety not established; avoid unless benefit outweighs risk.
• Breastfeeding: unknown excretion; use with caution.
• Narrow‑angle glaucoma: contraindicated due to risk of angle closure.
• Respiratory disease: use cautiously in asthma or COPD as cholinergic effects may exacerbate bronchospasm.
• Cardiovascular disease: monitor patients with bradycardia or heart block for systemic effects.
• Store at room temperature: keep in original container, protect from light and moisture.

Carbachol can interact with other medications affecting cholinergic pathways or ocular physiology.

Major Interactions (Avoid)

• Systemic anticholinergics: may diminish Carbachol's ocular effect.
• Cholinesterase inhibitors: can potentiate ocular cholinergic activity, increasing risk of miosis.
• Other miotics (e.g., pilocarpine): additive pupil constriction may lead to excessive miosis.
• Systemic cholinergic agents: heightened systemic side effects such as bradycardia.

Moderate Interactions (Monitor Closely)

• Topical NSAIDs: may increase ocular irritation when used together.
• Corticosteroid eye drops: could mask inflammatory signs while Carbachol is administered.
• Systemic beta‑agonists: may counteract intraocular pressure‑lowering effect.