Which of the following factors can increase the bioavailability of an ophthalmic topical drug?

Bioavailability refers to the proportion of a drug that enters the systemic circulation when it is introduced into the body and is available for therapeutic effect. In the context of ophthalmic topical medications, several factors influence bioavailability, including drug formulation and physicochemical properties.

The choice that states "lipid solubility, small molecule size, uncharged, weak base" highlights key characteristics that enhance the absorption and ultimately the bioavailability of ophthalmic drugs.

1. Lipid Solubility: Lipid-soluble compounds can easily penetrate cell membranes, which are largely composed of lipid bilayers. This property enables the drug to pass through the cornea, leading to greater availability in the systemic circulation.

2. Small Molecule Size: Smaller molecules generally diffuse more easily through biological barriers. Larger molecules can have restrictions due to physical dimensions, limiting their ability to permeate tissues effectively.

3. Uncharged: The ionization state of a drug can significantly impact its absorption. Uncharged molecules tend to be more lipophilic, which facilitates their ability to cross cell membranes. Weak bases, when in a slightly alkaline environment, are more likely to remain uncharged and thus can enhance their absorption.

4. Weak Base: