Bimatoprost

Description

Bimatoprost was first introduced in the US and Brazil as Lumigan?, an ophthalmic solution (0.03%) for the reduction of elevated intraocular pressure (IOP) in patients with open-angle glaucoma or ocular hypertension, a proven risk of glaucomatous visual field loss. Bitamoprost is a new agent belonging to the PGF_2α analog class of prostamides launched in this indication after latanoprost, the most efficaceous topical medication currently available. This synthetic fatty acid amide can be prepared by esterification of 17- phenyl-18,19,20-trinorprostaglandin F_2α followed by ethylamidation. Bimatoprost, as related prostamides, is devoid of typical activities associated with PGF2,, analogs; it exhibits a unique pharmacological profile in contracting the feline iris sphincter with an EC₅₀ of 34 nM without interacting with any known prostanoid receptors. Thus it mimics the action of endogenous prostamides on specific receptors that lower IOP by increasing aqueous humor outflow through both pressure-insensitive and pressure-sensitive pathways without reducing humor formation. In a 3-month controlled clinical trial of efficacy and safety in patients with elevated IOP, bimatoprost demonstrated lower mean intraocular pressures at every time point throughout the study, as well as a good tolerance and systemic safety profile compared to latanoprost.

The Uses of Bimatoprost

Bimatoprost is a prostaglandin analog used topically (as eye drops) to control the progression of glaucoma and in the management of ocular hypertension. It reduces intraocular pressure (IOP) by increasing the outflow of aqueous fluid from the eyes. 

Indications

Bimatoprost is used for the reduction of elevated intraocular pressure in patients with open-angle glaucoma or ocular hypertension. These patients must be intolerant to other intraocular pressure lowering medications or inadequately responsive to other treatments.
Bimatoprost is also indicated to treat eyelash hypotrichosis.

Background

Bimatoprost, also known as Latisse or Lumigan, belongs to a group of drugs called prostamides, which are synthetic structural analogs of prostaglandin. Bimatoprost, marketed by Allergan, is administered in both the ophthalmic solution and implant form. It has the ability to reduce ocular hypotension, proving effective in conditions such as ocular hypertension and glaucoma. Bimatoprost is also used to treat eyelash hypotrichosis, or sparse eyelash growth. It was initially approved by the FDA in 2001 for ocular hypertension and later approved for hypothrichosis in 2008, as eyelash growth became a desirable adverse effect for patients using this drug.

Pharmacokinetics

High intraocular pressure is a major risk factor for glaucoma-related visual field loss. A linear relationship exists between intraocular pressure and the risk of damaging the optic nerve, which can lead to considerable visual impairment. Therefore, conditions such as ocular hypertension and glaucoma can cause dangerous elevations of intraocular pressure. Bimatoprost rapidly decreases intraocular pressure and reduces the risk for visual field loss from ocular hypertension due to various causes.
Other effects of this drug may include gradual changes in eyelid pigmentation, changes in iris pigmentation, changes in eyelash pigmentation, growth and thickness. Patients should be informed of these possible effects, especially if this drug is only administered to one eye, which may noticeably change in appearance with bimatoprost treatment.

Absorption

This drug is absorbed systemically when administered to the eye. A study was performed on 15 healthy volunteers and bimatoprost ophthalmic solution 0.03% was administered once daily for 14 days. The mean Cmax was approximately 0.08 ng/mL and AUC0-24hr was approximately 0.09 on days 7 and 14 of the study. By 10 minutes, peak blood concentration was achieved. Bimatoprost was not detectable at 1.5 hours after administration in most subjects. The maximum blood concentration in a study of 6 healthy volunteers was determined to be 12.2 ng/mL. Steady state was reached in the first week of dosing.
One drug label mentions that onset of decreased intraocular pressure occurs approximately 4 hours after the first administration and the peak effect occurs in the range of 8-12 hours. Bimatoprost effects may last up to 24 hours.

Metabolism

Bimatoprost is hydrolyzed to its active form, bimatoprost acid, in the eye. Bimatoprost undergoes oxidation, N-deethylation, and glucuronidation after it is systemically absorbed, and this leads to the production of various metabolites. In vitro studies show that CYP3A4 is an enzyme that participates in the metabolism of bimatoprost. Despite this, many enzymes and pathways metabolize bimatoprost, therefore, no significant drug-drug interactions are likely to occur. Glucuronidated metabolites comprise most of the excreted drug product in the blood, urine, and feces in rats.

Side Effects

Bimatoprost has several adverse side effects. The most frequent one is conjunctivitis, which occurs in more than 10% of patients. Others include blurred vision, redness, burning, and darkening of the iris. Eyelid infection and darkening can occur when the drug is used on eyelashes.