Acetylcysteine Eye Drops

Acetylcysteine, also known as N-Acetylcysteine or NAC, is a medication derived from the amino acid cysteine. It is most commonly known for treating acetaminophen (Tylenol) poisoning and as a mucolytic agent that breaks down mucus.

When compounded into ophthalmic drops, acetylcysteine acts as artificial tears that help soothe and lubricate chronically dry eyes.

Acetylcysteine eye drops are used to treat chronic dry eyes, particularly a condition known as keratoconjunctivitis sicca.

Dry eye symptoms are often caused by chronic inflammation of the lacrimal (tear-producing) functional unit, leading to loss of tear film integrity and an inability of the eye surface to respond to environmental challenges.

A key mechanism in chronic dry eye is tear hyperosmolarity, which leads to ocular surface inflammation, damage, and compensatory mucus accumulation in the conjunctival sac.

Acetylcysteine is a mucolytic agent — it thins and breaks down mucus. When applied to the eye, it reduces mucus accumulation and controls mucus secretion.

The free sulphydryl group in the acetylcysteine molecule reduces the disulphide bonds of mucoproteins present in mucus, reducing the viscosity (stickiness) of tears. This allows tears to flow more freely over the eye surface, improving lubrication and hydration.

There is no commercially manufactured acetylcysteine eye drop in Canada, so these are prepared as a sterile compounded preparation. Prescriptions are commonly written at 5% or 10%, typically preservative-free, in an ophthalmic vehicle.

Sterile ophthalmic compounding is done under controlled aseptic conditions, which is why these drops take longer to prepare than a cream or capsule and carry a short beyond-use date. Conditions sometimes referenced on prescriptions include keratoconjunctivitis sicca and filamentary keratitis — the prescriber chooses the strength and schedule for the condition being treated.

Possible side effects include:

• A burning sensation when instilling the drops
• A noticeable odor (a sulphur-like smell is normal for NAC and not a sign the drops have spoiled)
• Rarely, increased discomfort

Precautions:

• Do not use if pregnant or breastfeeding without discussing risks with your doctor
• Do not use if allergic to any component of the drops
• Do not use with soft contact lenses

These drops are usually applied to the affected eyes four times daily, or as directed by your physician.

1. Wash your hands thoroughly
2. Tilt your head back and pull down the lower eyelid
3. Instill the prescribed number of drops
4. Close your eye gently for 1–2 minutes
5. Do not touch the dropper tip to any surface

• Store in the refrigerator
• The label carries a short beyond-use date — sterile preservative-free preparations are dated conservatively for safety. Discard after that date even if drops remain, and time refill requests accordingly
• Do not use if the solution appears cloudy or discolored
• Never touch the dropper tip to the eye or any surface — contamination shortens the safe life of a preservative-free bottle

Sterile ophthalmic compounding is more involved than non-sterile preparations, and price depends on the strength and quantity prescribed — the pharmacy can quote a specific prescription before it is filled. Many private drug plans cover compounded prescriptions when the formula meets the plan's rules, and eligible costs can count toward the Manitoba Pharmacare deductible.

Prescriptions are commonly written as acetylcysteine 5% or 10% ophthalmic solution, preservative-free, with the schedule for the condition being treated. Fax the prescription or call the compounding lab to confirm current preparation timing and beyond-use dating — sterile preparations are made to order.