Question

When a drug or chemical is applied in water to cure fish disease, what will be bioavailability of that drug

• A. 100%
• B. $<$ 100%
• C. $>$ 100%
• D. 0%

Hint:

Pharmacology Rule: Bioavailability is always 100% for the Intravenous (IV) route. For all other routes—including bath treatments in fish—it is always less than 100%.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question explores the concept of "bioavailability" in the context of bath treatments or water-applied medications in aquaculture.
Detailed Explanation:

• Bioavailability: This is defined as the fraction of an administered dose of unchanged drug that reaches the systemic circulation (blood).

• Bath Treatment Challenges: When a drug is added to water (immersion treatment), it must cross biological barriers (primarily the gills or skin) to enter the fish's body.

• Factors Reducing Bioavailability:
• Dilution: Much of the drug remains in the surrounding water.

• Adsorption: Some drug binds to organic matter or suspended solids in the pond.

• Photodegradation: Breaking down of the chemical by sunlight.

• Incomplete Absorption: The gills/skin are not 100% efficient at absorbing all chemicals.

• Conclusion: Only intravenous (IV) injection is considered to have 100% bioavailability by definition. All other routes (oral, bath, IM) will result in a bioavailability of less than 100% ($<$ 100%).

Step 3: Final Answer:
The bioavailability of a drug applied in water is less than 100%.