The most commonly used diluent in powders for capsules

• A. Sucrose
• B. Mannitol
• C. Xylitol
• D. Lactose

Answer: (D)

In capsule powders, the diluent serves as a bulk filler that is inert, flows well, and is compatible with a wide range of drugs. Lactose fits these needs exceptionally well: it provides reliable bulk, mixes uniformly with active ingredients, and has favorable flow properties for filling hard capsules. It’s available in several forms (like spray-dried or anhydrous lactose) to tailor moisture control, porosity, and dissolution behavior, making it versatile for many formulations. Because of these advantages, lactose has become the standard diluent used in most capsule fillings.

Other options exist, but they’re less universally suitable. Sucrose can be too hygroscopic and may cause stability or handling issues; sugar alcohols like mannitol or xylitol are useful in specific, sugar-free formulations or where particular mouthfeel or solubility needs apply, but they don’t match lactose’s broad applicability and cost-effectiveness for general capsule use.