Question

State the order of decomposition of drug in suspension dosage form (if the drug decomposes in solution)

• A. \( \text{Zero order kinetics} \)
• B. \( \text{Apparent zero order kinetics} \)
• C. \( \text{First-order kinetics} \)
• D. \( \text{Apparent first order kinetics} \)

Hint:

Think of a saturated solution – the concentration of the dissolved substance remains constant as long as there is undissolved substance present. If the dissolved part degrades at a constant rate, the overall process appears zero-order.

Answer 1

The Correct Option is B

In a suspension, the drug is present as solid particles dispersed in a liquid vehicle. If the drug undergoes decomposition in the solution phase (i.e., the dissolved portion), the concentration of the drug in solution is governed by its solubility. As the dissolved drug decomposes, more drug dissolves from the solid particles to maintain the solubility limit (assuming the solid drug is in excess and solubility is the rate-limiting step for the amount in solution). This process maintains a relatively constant concentration of the drug in solution over time, leading to an apparent zero-order decomposition rate. The rate of decomposition becomes independent of the total concentration of the drug in the suspension but depends on the saturated solubility and the rate constant of decomposition in solution.