pharmacokinetics Flashcards
(24 cards)
pharmacokinetics??
studies the movement of drugs within teh body, specifically how drugs are absorbed, distributed, metabolised and excreted
2 main catergories of drug activity in optometry?
Extraocular activity: Affects the surface of the eye (e.g., antibacterials, topical anaesthetics, anti-inflammatory agents, anti-histamines).
Extraocular activity: Affects the surface of the eye (e.g., antibacterials, topical anaesthetics, anti-inflammatory agents, anti-histamines).
How much volume do typical eye drops contain?
Typical eye drops contain about 50 µL, whereas the palpebral capacity (space inside the eyelid) is only 30 µL.
What is the tear film volume, and how much of the eye drop is retained on the eye?
The tear film holds about 7-10 µL, so only a portion of the drop remains on the surface before it starts draining.
What is the importance of the tear turnover rate in drug absorption?
The tear turnover rate is crucial for drug absorption, as it affects how long the drug stays in contact with the eye. Proper lid closure and canalicular occlusion (blocking the tear ducts) can help improve absorption.
What are the main layers the drug must pass through during corneal transmission?
The drug must pass through:
Corneal epithelium (fat-soluble)
Corneal stroma (water-soluble)
Corneal endothelium (water-soluble)
How does the drug solubility affect corneal transmission?
Non-ionized (fat-soluble) drugs pass through the corneal epithelium more easily, while ionized (water-soluble) drugs pass through the corneal stroma.
What systemic effect can occur from conjunctival vascular absorption?
Systemic effects can occur if the drug is absorbed through the conjunctival vasculature, leading to unintended side effects beyond the eye.
What is the role of the canal of Schlemm in drug excretion?
Drugs can be excreted by diffusion into the canal of Schlemm, which drains the aqueous humor from the eye into the bloodstream.
How does vascular absorption of a drug occur?
Vascular absorption may occur through drainage via the nasal puncta route or diffusion via the lid,
conjunctiva, limbal and episcleral vessels
which corneal layer contains the most water?
stroma
which organs are primarily responsible for drug metabolism and excretion??
liver and kidneys are primarily responsible for the metabolism and excretion of drugs
What factors influence drug metabolism and excretion?
Age: Reduced efficiency of the liver and kidneys with age.
Body weight: Low body weight in children requires smaller doses, while high BMI in adults may lead to longer drug retention.
Gender: Differences in liver function between men and women.
Pathology: Liver and kidney diseases can impair metabolism and excretion.
How does age affect pharmacokinetics?
As a person ages, liver and kidney functions decrease, which can affect how drugs are metabolised and excreted, requiring dose adjustments.
Why does body weight affect pharmacokinetics?
People with low body weight (such as children) require smaller drug doses, while those with high BMI may store drugs longer, potentially enhancing the risk of toxic effects.
How do genetic factors affect pharmacokinetics?
Certain individuals have genetic traits that make them more likely to react adversely or idiosyncratically to certain drugs, such as corticosteroids.
What is the impact of tolerance on drug use over time?
With prolonged use, the body can develop tolerance to drugs, requiring higher doses for the same effect, which may increase the risk of side effects.
how do drug interactions influence pharacokinetics??
Drug interactions can alter the way drugs are metabolised, making them more or less effective or causing harmful side effects. For example, phenylephrine can interact with some antidepressant drugs.
How does the time of day affect drug absorption?
Time of day can influence drug absorption, especially when combined with the amount of food ingested. Many drugs are most effective when taken after meals.
What is biphasic solubility, and how does it relate to drug absorption?
Biphasic solubility refers to the drug’s ability to exist in both ionised (water-soluble) and non-ionised (fat-soluble) forms. The solubility of the drug in different layers of the cornea affects its ability to pass through.
what are some common factors that modify drug absorption in ophthalmic pharmacology?
age
body weight
gender
time of day
tolerance
genetic factors
pathology affecting the liver and kidneys
What is the role of lipid-soluble (non-ionised) and water-soluble (ionised) particles in drug absorption?
non-ionised (lipid soluble) drugs pass more easily thru the fatty corneal epithelium, while ionised (water-soluble) drugs are better absorbed thry the water-based layers like the corneal stroma
significance of the tear film in drug absorption?
The tear film helps in drug distribution across the eye surface. The quality of tears, the lid closure, and canalicular occlusion can improve absorption and minimise drainage.
What is the mechanism of intraocular drug excretion?
Intraocular drugs are excreted by diffusion into the circulating blood via intraocular vessels and the aqueous humor into the canal of Schlemm.
