ATC Class:S01EB02

VA Class:OP102

AHFS Class:

• Miotics 52:40.20

Generic Name(s):

• Carbachol

Carbachol, a direct-acting parasympathomimetic agent, is a miotic.

Administration

In the treatment of glaucoma, carbachol is applied topically to the conjunctiva as an ophthalmic solution. Finger pressure should be applied on the lacrimal sac for 1-2 minutes following topical instillation of miotic ophthalmic solutions to minimize drainage into the nose and throat and reduce the risk of absorption and systemic reactions. Excess solution around the eye should be removed with a tissue, and any medication on the hands should be rinsed off immediately.

To produce miosis during surgery, carbachol injection is instilled into the anterior chamber of the eye. For intraocular instillation, the appropriate dose of carbachol injection should be prepared according to the manufacturer's directions. The manufacturer of Miostat^® states that the appropriate dose of carbachol injection for intraocular use should be withdrawn into a sterile disposable syringe through a 0.45-µm filter provided by the manufacturer using a 21-gauge needle. Prior to administration, the attached needle and filter should be removed from the syringe and replaced with a suitable atraumatic cannula for intraocular irrigation. Instillation should be gentle and parallel to the iris face and tangential to the pupil border. Unused portions of the injection should be discarded.

Dosage

For the treatment of glaucoma, the concentration and frequency of instillation of carbachol ophthalmic solutions must be adjusted to the requirements and responses of individual patients as determined by tonometric readings before and during therapy. The usual dosage is 1-2 drops of a 0.75-3% ophthalmic solution every 4-8 hours.

The usual intraocular dose of carbachol to produce miosis during surgery is 0.5 mL of a 0.01% injection instilled into the anterior chamber before or after securing sutures.

Topical carbachol shares the toxic potentials of the direct-acting miotics, and the usual precautions of miotic therapy should be observed. The manufacturer states that intraocular carbachol does not produce the adverse effects of topically applied carbachol; corneal clouding, persistent bullous keratopathy, retinal detachment, and postoperative iritis following cataract extraction have been reported in some patients.

Carbachol preparations are contraindicated in patients with known hypersensitivity to carbachol or to any ingredient in the formulation.

Pharmacokinetics

Following topical application of a solution of carbachol with benzalkonium chloride to the conjunctival sac, miosis occurs within 10-20 minutes and persists 4-8 hours. Maximal reduction in intraocular pressure (IOP) occurs within 4 hours after topical application and reduced IOP persists approximately 8 hours. A 3% carbachol solution has a slightly longer duration of action than do lower concentrations. Following instillation of a 0.01% solution of carbachol into the anterior chamber of the eye, miosis is maximal within 2-5 minutes and persists about 24 hours.

Chemistry and Stability

Chemistry

Carbachol, a direct-acting parasympathomimetic agent, is a choline ester that is structurally related to acetylcholine. Carbachol occurs as white or faintly yellow, hygroscopic crystals or crystalline powder and is freely soluble in water and sparingly soluble in alcohol. The drug is odorless or has a slight amine-like odor. Commercially available ophthalmic solutions contain benzalkonium chloride as a preservative and wetting agent. The commercially available ophthalmic solution of carbachol has a pH of 5-7; the commercially available intraocular injection has a pH of 5-7.5.

Stability

Carbachol intraocular injection should be stored at 15-30°C and protected from freezing and excessive heat. The commercially available carbachol intraocular injection is stable for 18 months after the date of manufacture.

Additional Information

For further information on pharmacology, pharmacokinetics, uses, cautions, drug interactions, and dosage and administration of carbachol, see the Miotics General Statement 52:40.20.