Ocular Pharmacology & Pharmacokinetics

Instructor: Justine Fritzel

Justine has been a Registered Nurse for 10 years and has a Bachelor's of Science in Nursing degree.

The human eye is a complex structure and requires complex medications to treat conditions. In this lesson, we will learn about ocular medications and the pharmacology of them.

Eye Infection

You may have experienced it. You wake up and your eye is crusted shut covered in dry goop. You pry your eye open and go wash your eye. You look in the bathroom mirror and your eye is blood shot and oozing yellow tinged fluid. You make an appointment with your doctor and he prescribes an antibiotic eye drop.

The eye has many different layers and structures that work to protect the eye from things that could damage it. Due to this very unique structure, it has been a challenge for medicine to develop drugs that are effective in treating different eye conditions. The different administration routes that are used to treat the eye include topical, systemic, and periocular. Let's take a closer look at each.

Types of Ocular Medications

Topical ocular administration is typically through the use of eye drops. It is effective in treating conditions affecting the front layers of the eye, such as pink eye. It is easy to self-administer and is a simple procedure for treatment.

Systemic ocular administration is medication taken orally to treat eye conditions. There are two barriers in the eye that make systemic administration very difficult, but it can be an effective treatment for certain eye conditions.

Periocular administration is an injectable medication. Different medications can be injected into different parts of the eye depending on the eye condition. This is a very invasive procedure, unlike the topical and systemic routes, but it is very effective in treating eye conditions that are otherwise difficult to treat based on the anatomy of the eye.

Let's look at how each of these routes of medications work within the body.

Pharmacology and Pharmacokinetics

Pharmacology is the study of how drugs work and pharmacokinetics is a part of pharmacology that specifically looks at how the body processes a drug to elicit it's effects. Pharmacokinetics includes how a drug is absorbed in the body, how it is metabolized or changed and how it is excreted or leaves the body.

Topical ocular medications, such as eye drops, are not absorbed very efficiently in the eye and are very minimally absorbed systemically. However, there are very few side effects with topical administration.

In our example of having pink eye, the doctor will likely prescribe Ciprofloxacin eye drops. These eye drops are administered to the conjunctiva but are very poorly absorbed. Therefore, high doses and frequent administration are required for effective results. Less than 10% of the medication is actually absorbed. Much of the medication is lost through tears.

Ciprofloxacin is a bactericidal medication, meaning it treats bacterial infection. It is metabolized in the liver and has a half-life of four hours. Half-life is a term meaning how long it takes for the body to eliminate half of the medication. The absorbed medication is excreted through urine and feces.

Systemic ocular medications are in pill form taken by mouth. The eye has a blood-aqueous barrier and blood-retinal barrier that medications have to cross in order to enter the eye. This is not easy to do! Therefore, high doses of medications that are highly available in the blood are usually required to cross the barriers. That can also mean high likelihood of adverse effects from the medications. With systemic administration, only 1-5% of the medication is absorbed into the vitreous chamber of the eye.

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