Lecrolyn: Uses, Dosage & Side Effects

What Is Lecrolyn and What Is It Used For?

Lecrolyn is the trade name for ophthalmic preparations of sodium cromoglicate (known as cromolyn sodium in the United States), a medication belonging to the class of drugs called mast cell stabilizers. Unlike antihistamines, which block histamine after it has already been released, sodium cromoglicate works at an earlier stage in the allergic cascade by preventing mast cells from degranulating and releasing their inflammatory contents in the first place. This unique mechanism of action makes Lecrolyn a primarily prophylactic (preventive) treatment that is most effective when used regularly before and during periods of allergen exposure.

Sodium cromoglicate was first synthesized in 1965 by Dr Roger Altounyan, a physician and pharmacologist who himself suffered from severe asthma and allergies. The drug was originally developed for inhaled use in asthma before its ophthalmic applications were recognised. Over the decades since its introduction, sodium cromoglicate has established itself as one of the safest anti-allergic medications available, owing to its purely local mechanism of action, negligible systemic absorption when applied to the eyes, and an exceptional safety record spanning more than 50 years of clinical use. It is listed on the World Health Organization (WHO) Model List of Essential Medicines for its role in managing allergic conditions.

The primary indication for Lecrolyn eye drops is seasonal allergic conjunctivitis, commonly associated with hay fever (pollen allergy). During pollen season, individuals with sensitised immune systems experience an allergic reaction when pollen grains land on the conjunctival surface of the eye. This triggers mast cells in the conjunctival tissue to release histamine, leukotrienes, prostaglandins and other pro-inflammatory mediators, leading to the characteristic symptoms of allergic conjunctivitis: intense itching (pruritus), redness (conjunctival hyperaemia), excessive tear production (epiphora), swelling of the eyelids (periorbital oedema), and a sensation of grittiness or foreign body in the eye.

Beyond seasonal pollen allergy, Lecrolyn is also effective in managing perennial allergic conjunctivitis caused by year-round allergens such as house dust mites, animal dander and mould spores. Some ophthalmologists also use sodium cromoglicate as an adjunctive treatment for vernal keratoconjunctivitis (VKC) and atopic keratoconjunctivitis (AKC), although these more severe forms of allergic eye disease often require additional therapies such as topical corticosteroids or calcineurin inhibitors for adequate symptom control.

Sodium cromoglicate is also available in oral formulations under the brand name Lomudal (or Nalcrom in some markets) for the management of food allergy symptoms and certain gastrointestinal conditions. The oral solution works by stabilising mast cells in the gastrointestinal mucosa and is used to prevent symptoms such as abdominal cramps, diarrhoea and nausea triggered by food allergens. This article, however, focuses primarily on the ophthalmic use of Lecrolyn, while noting the oral formulations where relevant.

How Lecrolyn Works

The therapeutic mechanism of sodium cromoglicate centres on the stabilisation of mast cell membranes. Mast cells are immune cells found abundantly in the conjunctival tissue and other mucosal surfaces throughout the body. In individuals with allergic sensitisation, these mast cells carry immunoglobulin E (IgE) antibodies on their surface, bound to high-affinity IgE receptors (FcεRI). When a specific allergen — such as grass pollen — bridges two adjacent IgE molecules on the mast cell surface, it initiates a signalling cascade that leads to degranulation: the rapid release of preformed mediators (particularly histamine) from intracellular granules, along with the de novo synthesis of lipid mediators (leukotrienes and prostaglandins) and cytokines.

Sodium cromoglicate prevents this degranulation process by stabilising the mast cell membrane, though the precise molecular mechanism has been the subject of ongoing research since the drug's introduction. Current evidence suggests that sodium cromoglicate acts on chloride channels in the mast cell membrane, inhibiting the calcium influx that is essential for the degranulation process. By blocking this critical step, sodium cromoglicate prevents the release of histamine, slow-reacting substance of anaphylaxis (SRS-A, now known to be a mixture of leukotrienes), prostaglandin D2, platelet-activating factor, and various cytokines and chemokines. It is important to note that sodium cromoglicate does not directly block histamine receptors and has no direct antihistamine, anti-inflammatory, or vasoconstrictor activity — its benefit derives entirely from preventing mediator release at the source.

Because sodium cromoglicate acts by preventing the initiation of the allergic response rather than counteracting its effects after they have occurred, the drug is most effective as a prophylactic (preventive) treatment. For optimal results in seasonal allergic conjunctivitis, treatment should ideally be started a few days to two weeks before the anticipated onset of the pollen season, allowing the drug to establish its stabilising effect on the local mast cell population. When used reactively to treat symptoms that have already developed, the onset of clinical benefit may be slower, typically requiring several days of regular use before a noticeable improvement is achieved.

Pharmacokinetics

When applied as eye drops, sodium cromoglicate is absorbed locally into the conjunctival tissue, where it exerts its mast cell stabilizing effect. Systemic absorption from the ophthalmic route is extremely low — studies have shown that less than 0.03% of the applied dose reaches the systemic circulation. This negligible systemic bioavailability is one of the key factors contributing to the drug's outstanding safety profile, particularly in vulnerable populations such as pregnant women and young children. Any small amount that is absorbed systemically is rapidly excreted unchanged in the urine and bile, with no significant hepatic metabolism. The elimination half-life of systemically absorbed sodium cromoglicate is approximately 80–90 minutes.

On the ocular surface, sodium cromoglicate remains at therapeutic concentrations in the conjunctival tissue for several hours after application. The standard formulation of Lecrolyn contains 40 mg/ml (4%) sodium cromoglicate in an aqueous solution. The lower concentration formulation (20 mg/ml, or 2%) is available in some markets. Both concentrations have demonstrated clinical efficacy, though the 4% solution is the most widely used and studied. The drug does not penetrate significantly into the anterior chamber of the eye or deeper ocular structures, which means it has no therapeutic effect on intraocular tissues and no risk of the intraocular side effects associated with some other ophthalmic medications (such as elevated intraocular pressure from corticosteroid eye drops).

What Should You Know Before Using Lecrolyn?

Contraindications

Lecrolyn is contraindicated in individuals with a known hypersensitivity to sodium cromoglicate or to any of the excipients contained in the formulation. True allergy to sodium cromoglicate is exceedingly rare, consistent with the drug's excellent safety profile over more than five decades of clinical use. However, some individuals may develop sensitivity to the preservative benzalkonium chloride, which is present in the standard multi-dose Lecrolyn formulation. Patients who experience worsening eye irritation, increased redness, or swelling after using Lecrolyn should discontinue use and consult their healthcare provider, as these symptoms may indicate a reaction to the preservative rather than to the active ingredient itself.

There are no absolute contraindications based on age, and sodium cromoglicate eye drops are suitable for use in both adults and children. Unlike corticosteroid eye drops, sodium cromoglicate does not raise intraocular pressure and is not contraindicated in patients with glaucoma. Similarly, unlike some decongestant eye drops, it does not cause rebound congestion with prolonged use and can safely be used throughout an entire allergy season without risk of tachyphylaxis (tolerance development).

Warnings and Precautions

If your eye symptoms do not improve within a few days of starting Lecrolyn, or if symptoms affect only one eye, you should consult a healthcare provider. Unilateral (one-sided) eye symptoms may indicate a condition other than allergic conjunctivitis — such as viral conjunctivitis, bacterial infection, foreign body, corneal abrasion, or acute angle-closure glaucoma — that requires different treatment. Similarly, symptoms accompanied by significant pain, vision changes, light sensitivity, or purulent discharge should be evaluated by an eye care professional promptly.

After instilling the eye drops, vision may be temporarily blurred. You should not drive a vehicle or operate dangerous machinery until your vision has fully returned to normal. This temporary blurring is a common effect of any eye drop and is caused by the fluid film disrupting the tear layer on the corneal surface; it typically resolves within a few seconds to minutes after blinking.

Pregnancy and Breastfeeding

Sodium cromoglicate has an excellent reproductive safety profile. No adverse effects on the foetus have been demonstrated in animal reproductive studies or in the extensive post-marketing experience with this drug over more than 50 years of clinical use. Lecrolyn eye drops can be used during pregnancy, and the negligible systemic absorption from the ophthalmic route provides an additional margin of safety. International guidelines, including those from the British National Formulary (BNF) and the European Medicines Agency (EMA), support the use of sodium cromoglicate eye drops during pregnancy when clinically needed.

Similarly, Lecrolyn can be used during breastfeeding. Given the extremely low systemic absorption of sodium cromoglicate from eye drops (less than 0.03% of the applied dose), the amount that could potentially reach breast milk is clinically insignificant. Even if a small quantity were to be ingested by the nursing infant, sodium cromoglicate is poorly absorbed from the gastrointestinal tract (less than 1% oral bioavailability), further minimising any potential exposure. Many allergy and obstetric guidelines consider sodium cromoglicate one of the preferred options for managing allergic conditions during pregnancy and lactation precisely because of this favourable safety profile.

Driving and Operating Machinery

As with any eye drop, instillation of Lecrolyn may cause temporary blurring of vision that typically resolves within seconds to a few minutes. You should not drive or operate dangerous machinery until your vision has returned to normal after applying the drops. This precaution applies to the physical act of instilling the drops rather than to any pharmacological effect of sodium cromoglicate on alertness or cognitive function — the drug has no sedating properties and no effects on the central nervous system.

You are personally responsible for assessing whether you are fit to drive or perform activities requiring sharp vision and concentration. If you need to use eye drops before driving, apply them well in advance and ensure that your vision is completely clear before getting behind the wheel. Using the drops during a brief stop rather than immediately before driving is a practical approach that avoids any temporary visual disturbance while on the road.

How Does Lecrolyn Interact with Other Drugs?

One of the notable advantages of sodium cromoglicate is its lack of clinically significant drug interactions. Because the drug acts purely locally on the conjunctival mucosa and is absorbed into the systemic circulation in negligible quantities (less than 0.03% of the ophthalmic dose), pharmacokinetic interactions with other medications — whether oral, injectable, or topical — are not expected. Sodium cromoglicate is not metabolised by hepatic cytochrome P450 enzymes and does not inhibit or induce any known drug-metabolising enzymes, eliminating the potential for the metabolic drug interactions that complicate the use of many other medications.

Sodium cromoglicate also has no known pharmacodynamic interactions. It does not potentiate or antagonise the effects of antihistamines, corticosteroids, decongestants, non-steroidal anti-inflammatory drugs (NSAIDs), or any other class of medication commonly used in the management of allergic conditions. In fact, sodium cromoglicate eye drops are frequently used in combination with oral antihistamines for patients whose allergic conjunctivitis is part of a broader allergic rhinoconjunctivitis syndrome, with each medication contributing complementary mechanisms of action for optimal symptom control.

The only practical consideration regarding concurrent medication use relates to the administration of multiple ophthalmic preparations. When using Lecrolyn alongside other eye drops — whether other anti-allergy drops, lubricating (artificial tear) drops, or medications for other eye conditions such as glaucoma — a minimum interval of 15 minutes should be observed between instillation of the different products. This spacing ensures that the first preparation has been adequately absorbed into the conjunctival tissue before the second product is applied, preventing dilution and washout of either medication. As a general rule, if one of the products is a viscous gel or ointment, it should be applied last to avoid creating a physical barrier that impedes absorption of the other drops.

Using Multiple Eye Drops

Many patients with allergic eye conditions, particularly those with concurrent dry eye disease or glaucoma, may need to use multiple eye drop preparations throughout the day. Proper spacing of instillations is important to ensure each medication is effectively absorbed. The following practical approach is recommended: apply the most important or time-critical drops first (such as prescribed glaucoma medication), wait 15 minutes, then apply the next preparation. Lecrolyn can be fitted into any point in the schedule as long as the 15-minute rule is observed. If using a viscous artificial tear gel or any eye ointment, apply it last as it will temporarily blur vision and may interfere with absorption of subsequently applied drops.

For patients using the preservative-free Lecrolyn sine formulation in single-dose units, each unit should be used immediately after opening and any remaining solution discarded, as preservative-free solutions do not remain sterile once the container is opened. This is in contrast to the multi-dose preserved formulation, which can be stored and used for up to 28 days after opening.

What Is the Correct Dosage of Lecrolyn?

Lecrolyn should always be used exactly as described in the patient information leaflet or as directed by your healthcare provider, pharmacist, or nurse. The medication is designed for regular, preventive use rather than as-needed symptom relief. For the best results in seasonal allergic conjunctivitis, treatment should ideally begin before the expected onset of symptoms — for example, a week or two before pollen season typically begins in your area — and continue throughout the entire season. If you start treatment after symptoms have already developed, allow several days of consistent use before expecting full therapeutic benefit, as the mast cell stabilising effect builds up gradually with regular application.

How to Apply Eye Drops Correctly

Correct application of eye drops is essential for ensuring the medication reaches the intended site of action and for minimising contamination of the bottle. The following step-by-step technique is recommended by ophthalmologists and pharmacists internationally:

1. Wash your hands thoroughly with soap and water before handling the eye drop bottle or touching your eyes.
2. Sit down in front of a mirror so that you can see what you are doing clearly.
3. Unscrew the cap from the bottle. Do not touch the tip of the bottle with your fingers or allow it to come into contact with your eye, eyelid, or any other surface, as this can introduce bacteria into the solution.
4. Hold the bottle upside down between your thumb and middle finger in one hand.
5. Tilt your head back and look upward.
6. Gently pull down the lower eyelid with the index finger of your free hand to create a small pocket between the eyelid and the eye.
7. Squeeze the bottle gently to release one drop into the pocket formed by the lower eyelid. Avoid squeezing too hard, as this may release multiple drops unnecessarily.
8. Close your eye gently (do not squeeze it shut) and press lightly with one finger on the inner corner of the eye (near the nose) for 1–2 minutes. This technique, known as nasolacrimal occlusion, reduces drainage of the eye drop through the tear duct into the nasal cavity and systemic circulation, keeping more of the medication on the eye surface.
9. Repeat the procedure for the other eye if both eyes require treatment.
10. Replace the cap and screw it on tightly immediately after use.

The eye drop bottle is personal and should not be shared with other individuals, even family members, to prevent cross-contamination and the potential spread of eye infections.

Missed Dose

If you forget to apply Lecrolyn at the scheduled time, use the drops as soon as you remember. However, if it is nearly time for your next scheduled dose, skip the missed dose entirely and continue with your regular dosing schedule. Do not apply a double dose to compensate for a missed application. Since sodium cromoglicate works as a preventive treatment with a cumulative protective effect, the occasional missed dose is unlikely to cause a significant recurrence of symptoms, though consistent regular use provides the best overall protection.

Overdose

No adverse effects attributable to overdose of sodium cromoglicate eye drops have been reported. Given the extremely low systemic absorption of the drug from ophthalmic application, clinically significant systemic toxicity from topical ocular use is not expected, even with substantially higher doses than recommended. If the drops are accidentally swallowed (for example, by a child), the oral bioavailability of sodium cromoglicate is less than 1%, so significant systemic effects are highly unlikely. Nevertheless, if a large quantity of the medication is accidentally ingested, or if you have any concerns, contact a healthcare provider or your local poison control centre for advice.

What Are the Side Effects of Lecrolyn?

Like all medicines, Lecrolyn can cause side effects, although not everybody experiences them. Sodium cromoglicate has one of the best tolerated safety profiles of any ophthalmic medication, consistent with its purely local mechanism of action and negligible systemic absorption. The vast majority of patients use Lecrolyn without experiencing any adverse effects beyond the brief, mild stinging that is common to many eye drop preparations.

It is important to distinguish between side effects caused by the active ingredient (sodium cromoglicate) and those attributable to the preservative (benzalkonium chloride) in the standard multi-dose formulation. The preservative-free formulation (Lecrolyn sine) eliminates the preservative-related effects and may be preferred by patients who experience irritation with the standard product.

Understanding the Stinging Sensation

The most commonly reported side effect of Lecrolyn is a mild, transient stinging or burning sensation upon instillation. This occurs in a minority of users and typically lasts only a few seconds. The stinging is caused by the interaction between the eye drop solution and the highly sensitive corneal nerve endings, and is a feature shared by many ophthalmic preparations regardless of their active ingredient. The sensation is usually tolerable and diminishes with regular use as the eye becomes accustomed to the drops. If the stinging is persistent, severe, or accompanied by significant redness, swelling, or pain, this may indicate sensitivity to the preservative benzalkonium chloride, and switching to the preservative-free formulation (Lecrolyn sine) should be considered.

Preservative-Related Effects

Benzalkonium chloride (BAK) is a quaternary ammonium compound used as a preservative in many multi-dose ophthalmic preparations to prevent microbial contamination. While effective as a preservative, BAK has well-documented cytotoxic effects on the corneal and conjunctival epithelium, particularly with long-term or frequent use. Patients with pre-existing dry eye disease, meibomian gland dysfunction, or other ocular surface disorders may be more susceptible to BAK-induced irritation. The concentration of BAK in Lecrolyn (0.07 mg/ml) is relatively low but may still contribute to ocular surface discomfort in sensitive individuals.

For patients who require long-term treatment with sodium cromoglicate (for example, throughout a prolonged pollen season or for perennial allergic conjunctivitis), the preservative-free Lecrolyn sine formulation offers a well-tolerated alternative that eliminates BAK-related ocular surface toxicity. This is also the preferred formulation for contact lens wearers, as BAK can accumulate in soft contact lens materials and cause lens discolouration and reduced wearing comfort over time.

Reporting Side Effects

It is important to report suspected side effects after a medicine has been authorised. This allows ongoing monitoring of the medicine's benefit-risk balance. Healthcare professionals are particularly encouraged to report any suspected adverse reactions. Patients can also report side effects directly to their national medicines regulatory authority — such as the Medicines and Healthcare products Regulatory Agency (MHRA) in the United Kingdom via the Yellow Card Scheme, the European Medicines Agency (EMA), or the Food and Drug Administration (FDA) MedWatch programme in the United States.

How Should You Store Lecrolyn?

Proper storage of eye drops is essential for maintaining the sterility, stability and efficacy of the medication throughout its shelf life. Lecrolyn should be stored at room temperature (typically below 25°C / 77°F), protected from direct sunlight and excessive heat. Do not freeze the eye drops. Keep the bottle tightly closed when not in use to prevent contamination and evaporation of the solution.

Store this medicine out of the sight and reach of children. Eye drop bottles can pose a choking hazard for young children, and accidental ingestion should be prevented. While sodium cromoglicate has very low oral toxicity, the preservative and other excipients may cause gastrointestinal discomfort if ingested in quantity.

Do not use Lecrolyn after the expiry date (marked as EXP on the bottle and carton). The expiry date refers to the last day of the indicated month. Once opened, the multi-dose bottle should be used within 28 days. It is helpful to write the date of opening on the bottle label as a reminder. After 28 days, discard any remaining solution even if the bottle is not yet empty, as the preservative system may no longer adequately prevent microbial contamination. Do not use the drops if the solution has become cloudy or visibly discoloured, as this may indicate microbial contamination or chemical degradation.

Medicines should not be disposed of via the wastewater system or household waste. Return unused or expired eye drops to your pharmacy for proper disposal. This protects the environment by preventing pharmaceutical waste from entering water systems and soil.

What Does Lecrolyn Contain?

Active Ingredient

The active substance in Lecrolyn is sodium cromoglicate (also known internationally as cromolyn sodium or cromoglicic acid disodium salt). Each millilitre of the standard Lecrolyn eye drop solution contains 40 mg of sodium cromoglicate, corresponding to a 4% (w/v) concentration. This is the most widely used concentration for ophthalmic sodium cromoglicate preparations and has been the standard formulation since the drug's initial development for eye drop use. Some formulations, including certain generic preparations and the oral solution (Lomudal), may use a lower concentration of 20 mg/ml (2%).

Sodium cromoglicate is a disodium salt of chromone-2-carboxylic acid. It is a white, hydroscopic, crystalline powder that is freely soluble in water, making it well suited for formulation as an aqueous eye drop solution. The molecular formula is C₂₃H₁₄Na₂O₁₁, and its molecular weight is approximately 512.3 daltons. The drug has a pKa of approximately 2.0, meaning it is fully ionised at physiological pH, which contributes to its poor lipophilicity and consequently its minimal penetration across biological membranes and into the systemic circulation.

Inactive Ingredients (Excipients)

The inactive ingredients in Lecrolyn eye drops serve specific pharmaceutical functions:

• Benzalkonium chloride: A quaternary ammonium compound used as an antimicrobial preservative to maintain sterility of the multi-dose bottle after opening. Concentration: approximately 0.07 mg/ml. Absent in the preservative-free Lecrolyn sine formulation.
• Glycerol: A tonicity-adjusting agent (osmotic agent) that helps ensure the eye drop solution is isotonic with the tear film, reducing stinging upon instillation and minimising osmotic stress on the corneal epithelium.
• Disodium edetate dihydrate (EDTA): A chelating agent that enhances the effectiveness of the benzalkonium chloride preservative by binding divalent cations (calcium and magnesium ions) that can otherwise interfere with the preservative's antimicrobial activity. EDTA also contributes to the chemical stability of the formulation.
• Polyvinyl alcohol (PVA): A water-soluble synthetic polymer that acts as a viscosity-enhancing agent and mucoadhesive, increasing the residence time of the eye drop on the ocular surface and thereby improving the duration of contact between sodium cromoglicate and the conjunctival tissue.
• Water for injections: The pharmaceutical-grade vehicle (solvent) in which all other components are dissolved to form the final eye drop solution.

Appearance and Packaging

Lecrolyn eye drops are a clear, colourless to slightly yellowish aqueous solution. The solution is packaged in a white plastic (low-density polyethylene) bottle with a white plastic screw cap and integral dropper nozzle. The standard pack size is 5 ml, which provides approximately 150–200 drops depending on drop size. The packaging is designed to deliver one drop at a time when the bottle is held inverted and gently squeezed.

The manufacturer and marketing authorisation holder for Lecrolyn is Santen Oy, a Finland-based pharmaceutical company specialising in ophthalmic products. Santen has a strong presence in the eye care pharmaceutical market globally and is recognised for its expertise in developing and manufacturing high-quality ophthalmic formulations.