N-acetyl-cysteine (NAC) is a derivative of a natural amino acid. It is used for it ability to break down mucous in respiratory disorders. It also has anti-inflammatory properties and this is important for dry eye disease as inflammation plays a big role.
Traditionally steroids have been used to suppress inflammation in dry eye. They are best used for short periods as they can lead to raised eye pressure, cataracts and an increased risk of infection. A 5% solution of N-acetyl-cysteine (NAC) has been shown to be well tolerated and have similar anti-inflammatory properties to Tobradex which is a steroid-antibiotic combination.
Traditionally, in the eye N-acetyl-cysteine has been used for its ability to break down mucous in a condition called filamentary keratitis which is a form of severe dry eye. More evidence is emerging that its anti-inflammatory properties are useful in less severe dry eye.
There is a medication available to treat moderate dry eye in the UK. It is produced by Moorfields Eye Hospital and is called Ilube which is a combination of artificial tears (hypromellose) and 5% N-acetyl-cysteine. It is be used 3-4 times pre day but unfortunately contains preservatives.
Compounding pharmacies can manufacture a 5% solution which is unpreserved but it needs to be stored in a fridge and discarded after 30 days. It has a slight rotten eggs smell and can sting a little on insertion.
Another possibility is oral N-acetyl-cysteine (NAC). It is contraindicated in those patients who have had organ transplants or those with stomach ulcers. It can interact with other medications and it is best taken with the support of your G.P.
There are a few small studies that have shown the benefits of N-acetyl-cysteine using a dose of 100mg 3 times a day for 12 weeks but the evidence at this stage is limited.