Monoprost: Uses, Dosage & Side Effects

What Is Monoprost and What Is It Used For?

Monoprost contains the active substance latanoprost at a concentration of 50 micrograms per milliliter (0.005%). Latanoprost is a synthetic prostaglandin F2-alpha analog, specifically an isopropyl ester prodrug that is converted to its biologically active acid form by esterases in the cornea after topical administration. Monoprost is supplied in single-dose containers (unidoses), and unlike most other commercially available latanoprost products, it contains no preservative. This is a significant advantage because the most commonly used preservative in ophthalmic preparations, benzalkonium chloride (BAK), is a known ocular surface irritant that can cause or exacerbate dry eye disease, meibomian gland dysfunction, and conjunctival inflammation with long-term use.

Glaucoma is the leading cause of irreversible blindness worldwide, affecting an estimated 80 million people globally according to World Health Organization data. The most common form, primary open-angle glaucoma (POAG), is a chronic, progressive optic neuropathy characterized by structural damage to the optic nerve head and corresponding visual field loss. Elevated intraocular pressure (IOP) is the primary modifiable risk factor for glaucoma, and all current treatment strategies are directed at lowering IOP to slow or halt disease progression. Ocular hypertension (OHT), defined as IOP consistently above 21 mmHg without evidence of optic nerve damage or visual field loss, is a major risk factor for developing glaucoma and often warrants treatment.

Latanoprost reduces IOP primarily by increasing the uveoscleral (non-conventional) outflow of aqueous humor. After corneal penetration and enzymatic hydrolysis to its active acid form, latanoprost binds to prostaglandin FP receptors located in the ciliary muscle and trabecular meshwork. This receptor activation triggers a cascade of intracellular signaling events that lead to remodeling of the extracellular matrix within the ciliary muscle interstitial spaces. The resulting structural changes — including increased expression of matrix metalloproteinases (MMPs) and degradation of collagen fibers — create wider channels between the muscle bundles, facilitating enhanced aqueous humor drainage through the uveoscleral pathway. Additionally, there is evidence that latanoprost may modestly increase trabecular (conventional) outflow through its effects on the trabecular meshwork extracellular matrix.

Clinical studies have consistently demonstrated that latanoprost reduces IOP by approximately 30–35% from baseline, making it one of the most effective single-agent IOP-lowering medications available. The onset of IOP reduction occurs within 3 to 4 hours after topical administration, with the maximum effect reached at approximately 8 to 12 hours. The IOP-lowering effect is sustained for at least 24 hours, which supports the once-daily dosing regimen. The evening (bedtime) dosing is preferred because peak drug effect coincides with the early morning hours, when IOP is typically at its highest (the physiological diurnal IOP curve).

Prostaglandin analogs, including latanoprost, are recommended as first-line monotherapy for POAG and OHT by all major international ophthalmology organizations, including the American Academy of Ophthalmology (AAO), the European Glaucoma Society (EGS), the National Institute for Health and Care Excellence (NICE), and the World Glaucoma Association (WGA). This recommendation is based on their superior IOP-lowering efficacy, excellent once-daily dosing convenience, minimal systemic side effects, and well-characterized long-term safety profile. Latanoprost was the first prostaglandin analog approved for glaucoma treatment (1996) and has since accumulated over two decades of clinical experience, with an extensive evidence base supporting its efficacy and safety across diverse patient populations.

What Should You Know Before Taking Monoprost?

Contraindications

The primary contraindication for Monoprost is known hypersensitivity to latanoprost or to any of the excipients in the formulation. Although serious allergic reactions to latanoprost are rare, contact allergy and allergic conjunctivitis have been reported. If you experience signs of hypersensitivity such as severe itching, swelling, rash, or difficulty breathing after using the eye drops, discontinue use immediately and seek medical attention.

Monoprost should also be used with caution (and is considered relatively contraindicated by some clinicians) in the following situations:

• Active intraocular inflammation (uveitis or iritis): Latanoprost may exacerbate or reactivate intraocular inflammation. If you have a current episode of uveitis, your doctor may choose an alternative IOP-lowering medication until the inflammation is controlled.
• Herpes simplex keratitis: Prostaglandin analogs may trigger reactivation of herpes simplex virus (HSV) infection in the eye. If you have a history of recurrent HSV keratitis, inform your ophthalmologist before starting treatment.
• Neovascular, inflammatory, or angle-closure glaucoma: There is limited experience with latanoprost in these specific types of glaucoma. Monoprost is specifically indicated for open-angle glaucoma and ocular hypertension.

Warnings and Precautions

Before starting Monoprost, discuss the following with your ophthalmologist or healthcare provider:

• Aphakia or pseudophakia with torn posterior lens capsule: Patients without a natural lens (aphakic) or with an artificial lens and a torn posterior lens capsule may be at increased risk of developing cystoid macular edema (CME) during latanoprost therapy. CME involves swelling of the central retina and can cause blurred or decreased vision. If you have had previous cataract surgery with complications, inform your doctor.
• Risk factors for macular edema: Patients with known risk factors for macular edema (such as diabetic retinopathy, retinal vein occlusion, or prior intraocular surgery) should be monitored closely during treatment with latanoprost.
• Eyelash and periorbital changes: Latanoprost may cause gradual changes to eyelashes and fine hairs around the eye, including increased length, thickness, pigmentation (darkening), and number of lashes. It may also cause darkening of the eyelid skin. These changes are usually reversible upon discontinuation of treatment but may take several months to resolve.
• Contact lens use: Although Monoprost is preservative-free, it is recommended to remove contact lenses before instillation and wait at least 15 minutes before reinserting them to ensure proper drug absorption.
• Multiple eye drops: If you are using other topical eye medications, wait at least 5 minutes between each drop to avoid dilution and washout effects. Apply Monoprost last if possible.

Pregnancy and Breastfeeding

The safety of latanoprost during pregnancy has not been established in adequate and well-controlled clinical studies in humans. Animal reproductive studies have shown embryo-fetal toxicity at high doses, including increased incidence of skeletal variations. Although systemic absorption after topical ocular administration of latanoprost is very low, it should not be used during pregnancy unless the potential benefit to the mother clearly outweighs the potential risk to the fetus. Women of childbearing potential should use effective contraception during treatment, and if you become pregnant while using Monoprost, inform your doctor immediately.

Latanoprost and its metabolites may be excreted in human breast milk. Due to the potential for adverse reactions in nursing infants, a decision should be made whether to discontinue breastfeeding or to discontinue Monoprost, taking into account the importance of the medication for the mother. Given the minimal systemic absorption from topical ophthalmic use, the actual risk to a breastfed infant is likely very low, but the data are insufficient to completely rule out an effect. Discuss with your doctor to weigh the benefits and risks for your specific situation.

Driving and Operating Machinery

Monoprost eye drops may cause temporary blurred vision immediately after instillation. This effect is usually brief, lasting only a few minutes. If you experience blurred vision after applying the eye drops, do not drive or operate hazardous machinery until your vision has returned to normal. Applying the drops in the evening (at bedtime) as recommended minimizes any impact on daytime activities.

How Does Monoprost Interact with Other Drugs?

One of the practical advantages of topical ophthalmic medications like Monoprost is that systemic drug interactions are generally minimal due to the very low systemic absorption following topical ocular administration. However, there are important local (ocular) interactions to be aware of when Monoprost is used alongside other eye medications.

The most clinically relevant interaction is with other prostaglandin analogs. Although it might seem logical that combining two prostaglandin analogs would produce additive IOP-lowering effects, clinical evidence has shown that simultaneous use of two prostaglandin analogs (for example, latanoprost and travoprost, or latanoprost and bimatoprost) can result in a paradoxical increase in IOP or a reduced IOP-lowering effect compared to either agent used alone. This is thought to occur due to competitive binding at the FP receptor or receptor desensitization. Therefore, do not use Monoprost in combination with another prostaglandin analog.

Another notable interaction involves eye drops preserved with thiomersal (also known as thimerosal). When latanoprost comes into contact with thiomersal, a chemical precipitation reaction can occur, potentially reducing the efficacy of both medications and causing ocular irritation. If you are using any eye drops that contain thiomersal, apply them at least 5 minutes apart from Monoprost.

In clinical practice, latanoprost is frequently combined with other classes of IOP-lowering medications when monotherapy does not achieve the target pressure. The most common combinations include latanoprost with a topical beta-blocker (such as timolol), a carbonic anhydrase inhibitor (such as dorzolamide or brinzolamide), or an alpha-adrenergic agonist (such as brimonidine). These combinations produce additive IOP-lowering effects through complementary mechanisms of action. When using multiple eye drops, always wait at least 5 minutes between each medication to prevent washout and ensure adequate ocular absorption of each drug.

Regarding systemic drug interactions, no clinically significant interactions have been identified with latanoprost when used at the recommended ophthalmic dose. The systemic absorption of latanoprost after topical ocular administration is very low — plasma concentrations of the active acid metabolite are barely detectable (peak levels of approximately 50–100 pg/mL) and the systemic half-life is only about 17 minutes. Therefore, latanoprost is not expected to interact with systemic medications through hepatic enzyme pathways or protein binding. Patients taking systemic medications for other conditions can generally use Monoprost without concern for drug-drug interactions.

What Is the Correct Dosage of Monoprost?

Monoprost should always be used exactly as prescribed by your ophthalmologist. The medication is supplied in single-dose containers (unidoses), each containing a sufficient volume of solution for treating both eyes. The standardized dosing regimen is straightforward: one drop per eye, once daily, in the evening.

Adults (Including Elderly)

No dose adjustment is necessary for elderly patients. Clinical pharmacokinetic studies have not identified significant differences in latanoprost absorption, distribution, or clearance between younger and older adults. The once-daily evening dosing regimen applies equally to all adult age groups.

It is critically important not to administer Monoprost more than once daily. Clinical pharmacology studies have demonstrated that more frequent administration (for example, twice daily) can actually result in a reduced IOP-lowering effect compared to once-daily dosing. This counterintuitive phenomenon is believed to be related to prostaglandin FP receptor desensitization that occurs with excessive stimulation. If you accidentally miss a dose, simply apply the next dose at the usual time the following evening; do not double the dose.

How to Apply Monoprost Eye Drops

Proper application technique is essential for optimal drug delivery and to minimize side effects. Follow these steps each time you use Monoprost:

1. Wash your hands thoroughly with soap and water before handling the single-dose container.
2. Separate one single-dose container from the strip by twisting it off at the perforation.
3. Open the container by twisting off the tab. Do not touch the dropper tip to avoid contamination.
4. Tilt your head back slightly and look upward. Gently pull down the lower eyelid to form a small pocket.
5. Squeeze one drop into the pocket formed between the lower eyelid and the eye. Avoid touching the eye or eyelid with the tip of the container.
6. Close your eye gently and press a finger against the inner corner of the eye (nasolacrimal occlusion) for 1–2 minutes. This technique reduces systemic absorption through the nasolacrimal duct and helps keep the drug on the ocular surface longer, improving efficacy and reducing the risk of systemic side effects.
7. Wipe away any excess solution from the skin around the eye. This is important because latanoprost contact with periorbital skin may cause localized eyelash growth, skin pigmentation, or eyelid changes.
8. Discard the single-dose container immediately after use, even if solution remains. Do not save leftover solution for later use, as the preservative-free formulation provides no antimicrobial protection against contamination.

Children and Adolescents

The safety and efficacy of Monoprost in children and adolescents under 18 years of age have not been fully established. While latanoprost has been used in some pediatric glaucoma cases (particularly congenital glaucoma) in clinical practice, the data are limited. Pediatric use should only be considered when prescribed by a pediatric ophthalmologist who can carefully weigh the benefits against the potential risks, including the unknown long-term effects of iris pigmentation changes in growing children.

Missed Dose

If you miss your evening dose of Monoprost, simply apply the next dose at the regular time the following evening. Do not apply two drops to make up for a missed dose, as this will not improve the IOP-lowering effect and may increase the risk of side effects. If you frequently forget doses, consider setting a daily reminder on your phone or pairing the eye drop application with another daily routine, such as preparing for bed.

Overdose

Ocular overdose (applying too many drops) may cause transient eye irritation, conjunctival hyperemia (redness), and blurred vision. If you have accidentally instilled too many drops, rinse the eye with clean water or saline. If Monoprost is accidentally swallowed, note that a single-dose container of Monoprost contains approximately 1.5 micrograms of latanoprost. Even ingestion of the entire contents of multiple containers would result in a very small dose of latanoprost. However, if large quantities are ingested, contact your local poison control center or seek medical attention. Symptoms of systemic overdose may theoretically include nausea, abdominal discomfort, dizziness, fatigue, and flushing, though significant systemic toxicity from ophthalmic latanoprost would be extremely unlikely.

What Are the Side Effects of Monoprost?

Like all medicines, Monoprost can cause side effects, although not everybody gets them. The following overview lists the most commonly reported adverse effects organized by frequency category. The preservative-free formulation of Monoprost is generally better tolerated on the ocular surface than preserved formulations, with lower rates of conjunctival hyperemia, stinging, burning, and dry eye symptoms. However, the side effects related to the active ingredient latanoprost itself (such as iris pigmentation changes and eyelash alterations) occur at similar rates regardless of whether the formulation contains a preservative.

It is important to distinguish between the expected pharmacological effects of latanoprost (such as increased pigmentation and eyelash growth) and adverse effects that may require medical attention. While most side effects of Monoprost are mild and localized to the eye, you should report any unusual or persistent symptoms to your ophthalmologist.

The iris pigmentation change deserves special attention. It is caused by an increase in melanin content within the stromal melanocytes of the iris, not by an increase in the number of melanocytes. This distinction is clinically important because it means the change is not associated with malignant melanocytic proliferation. In clinical trials lasting up to 5 years, the incidence of noticeable iris color change was approximately 33% in patients with mixed-color irises, 10–15% in those with hazel eyes, and less than 1% in patients with uniformly blue or brown eyes. The pigmentation change typically progresses very slowly (over months to years) and may be permanent even after discontinuation of treatment.

Prostaglandin-associated periorbitopathy (PAP) is a recognized class effect of all prostaglandin analogs, including latanoprost. It refers to a constellation of periorbital changes including deepening of the upper eyelid sulcus, enophthalmos (sunken appearance of the eye), dermatochalasis (loosening of eyelid skin), and loss of periorbital fat. These changes may be more noticeable in patients treated unilaterally (one eye only) due to asymmetry. The changes are generally mild and partially reversible upon discontinuation of treatment, though full reversal may take months.

How Should You Store Monoprost?

Proper storage of Monoprost is essential to maintain the stability and efficacy of the medication. Because Monoprost is preservative-free and supplied in single-dose containers, the storage requirements differ from multi-dose eye drop bottles.

Unopened pouches: The single-dose containers are supplied in sealed aluminium foil pouches. Store unopened pouches in a refrigerator at 2–8°C (36–46°F). Protect from light. Do not freeze. Latanoprost is sensitive to heat, and prolonged exposure to elevated temperatures may degrade the active ingredient and reduce efficacy.

After opening the foil pouch: Once you open the aluminium foil pouch, the individual single-dose containers inside can be kept at room temperature (below 25°C / 77°F) for a maximum of 7 days. After 7 days, any remaining unopened single-dose containers from that pouch should be discarded, even if they appear intact. This is because the foil pouch provides an additional barrier against moisture and light that is lost once opened.

After opening a single-dose container: Each single-dose container should be used immediately after opening for a single application. Discard the container and any remaining solution after use. Because there is no preservative to prevent microbial contamination, an opened container should never be stored for later use.

Keep this medication out of the sight and reach of children. Do not use Monoprost after the expiry date printed on the single-dose container and the outer packaging. The expiry date refers to the last day of that month. Do not throw away any medicines via wastewater or household waste; ask your pharmacist about proper disposal methods.

What Does Monoprost Contain?

The active ingredient in Monoprost is latanoprost at a concentration of 50 micrograms per milliliter (0.005% w/v). Latanoprost is the isopropyl ester of a prostaglandin F2-alpha analog. Its chemical name is isopropyl-(Z)-7-[(1R,2R,3R,5S)-3,5-dihydroxy-2-[(3R)-3-hydroxy-5-phenylpentyl]cyclopentyl]-5-heptenoate. It has a molecular weight of 432.58 g/mol and is a colorless to slightly yellow oil that is practically insoluble in water but freely soluble in acetonitrile.

The excipients (inactive ingredients) serve important pharmaceutical functions:

• Macrogolglycerol hydroxystearate 40 (Cremophor RH 40): A non-ionic solubilizer and emulsifier that replaces the traditional preservative benzalkonium chloride (BAK) used in preserved latanoprost formulations. It helps to solubilize latanoprost in the aqueous solution and also has mild surfactant properties that aid corneal penetration of the active ingredient. This excipient is a key component that enables the preservative-free formulation.
• Sorbitol: A tonicity-adjusting agent that helps to make the solution isotonic (similar in osmolality to tears), reducing stinging and discomfort upon instillation.
• Carbomer 974P: A viscosity-enhancing polymer that slightly increases the residence time of the solution on the ocular surface, improving drug contact time and absorption.
• Disodium edetate (EDTA): A chelating agent that enhances the stability of the formulation and also has mild antimicrobial properties that contribute to the overall stability of the preservative-free product during its limited use period.
• Sodium hydroxide: Used for pH adjustment to bring the solution to a physiologically compatible pH (approximately 6.0–7.0).
• Water for injections: The vehicle (solvent) for the formulation.

Each single-dose container holds 0.2 mL of eye drop solution. The containers are made of low-density polyethylene (LDPE) and are supplied in strips of 5 or 10 containers, which are then packaged in sealed aluminium foil pouches. The clear, colorless to slightly yellow solution should be free of visible particles. Do not use if the solution appears cloudy, discolored, or contains particles.