A Level Chemistry OCR Practice Exam

Why is it important to consider water of crystallisation in pharmaceutical compounds?

1. It affects the color of the drug.

2. It can alter the bioavailability of the drug.

3. It determines the pH of the compound.

4. It increases the toxicity of the drug.

The correct answer is: It can alter the bioavailability of the drug.

In the context of pharmaceutical compounds, water of crystallisation plays a crucial role in determining the bioavailability of a drug. Bioavailability refers to the extent and rate at which the active ingredient or active moiety is absorbed and becomes available at the site of action in the body. When a drug crystallizes, the incorporation of water molecules can influence the physical properties of that crystal, such as solubility and stability. For instance, a drug that is a hydrate (contains water of crystallisation) may dissolve more readily in biological fluids compared to its anhydrous counterpart. This improved solubility can enhance the absorption of the drug in the gastrointestinal tract, leading to an increase in bioavailability. Conversely, if the drug has a form that is less soluble due to its crystallization state, this can impede absorption and reduce its efficacy. The other aspects, such as color, pH, and toxicity, may not have a direct correlation with water of crystallisation or are secondary to the critical factor of how a drug is absorbed and utilized by the body. Thus, the influence on bioavailability is a key reason to consider water of crystallisation when developing and formulating pharmaceutical compounds.