Bimatoprost

Indications

Bimatoprost is primarily indicated for lowering elevated intraocular pressure in patients who suffer from open-angle glaucoma or ocular hypertension. This treatment is specifically recommended for patients who either cannot tolerate other intraocular pressure-lowering medications or do not achieve adequate results from alternative therapies. Additionally, Bimatoprost is approved for the treatment of eyelash hypotrichosis, aiding in the improvement of eyelash growth.

Pharmacodynamics

The reduction of intraocular pressure is critical, as high levels are a substantial risk factor for progressive glaucoma-related visual field loss. There exists a linear correlation between increased intraocular pressure and damage to the optic nerve, which can severely impair vision. Bimatoprost is effective in swiftly diminishing intraocular pressure, thereby minimizing the risk of visual field loss due to ocular hypertension from different causes. Notably, Bimatoprost may lead to gradual changes in pigmentation of the eyelids, iris, and eyelashes and affect eyelash growth and thickness. Patients should be aware of these potential effects, particularly if only one eye is treated, as it could alter the eye's appearance noticeably.

Absorption

When administered as an ophthalmic solution, Bimatoprost is systemically absorbed. In a study involving healthy volunteers where the 0.03% solution was applied daily over 14 days, the mean maximum concentration (Cmax) reached was approximately 0.08 ng/mL, with an AUC from 0 to 24 hours around 0.09 on study days 7 and 14. Peak blood concentration is typically reached within 10 minutes post-administration, but the drug is mostly undetectable after 1.5 hours in many subjects. The drug's maximum blood concentration in a particular set of volunteers was determined to be 12.2 ng/mL, with steady-state parameters being achieved within the first week of treatment. The reduction in intraocular pressure commences around 4 hours following the initial dose, with the peak effect reached between 8 to 12 hours. The drug's effects can last up to 24 hours following administration.

Metabolism

Once in the eye, Bimatoprost is hydrolyzed into its active form, bimatoprost acid. Upon systemic absorption, it undergoes further metabolic processes including oxidation, N-deethylation, and glucuronidation, resulting in various metabolites. According to in vitro studies, the cytochrome CYP3A4 enzyme plays a role in its metabolism; however, several enzymes and pathways are involved, reducing the likelihood of significant drug-drug interactions. In rats, bimatoprost is predominantly excreted through glucuronidated metabolites in blood, urine, and feces.

Mechanism of Action

Bimatoprost functions by emulating the actions of prostamides, particularly prostaglandin F2α. This mechanism results in a mild stimulation of aqueous humor outflow, which alleviates elevated intraocular pressure and reduces the risk of optic nerve damage. Bimatoprost effectively lowers intraocular pressure in humans by enhancing the outflow of aqueous humor through both the trabecular meshwork and uveoscleral pathways. This is accomplished by reducing the tonographic resistance to aqueous humor outflow. Importantly, bimatoprost does not influence the production of aqueous humor.