What can be used as a substitute for methyl cellulose as a vehicle in prescriptions?

• A. Sodium carboxymethylcellulose (CMC)
• B. Gelatin
• C. Povidone
• D. Hydroxypropyl methylcellulose

Answer: (A)

When choosing a vehicle for a prescription suspension, the key is to have a substance that thickens the liquid and helps keep insoluble drug particles evenly dispersed and stable over time.

Sodium carboxymethylcellulose is a water-soluble cellulose derivative that acts as an effective suspending and thickening agent. It creates viscosity at relatively low concentrations and, due to its anionic nature, helps stabilize suspensions by promoting electrostatic repulsion between particles, reducing aggregation. This makes it a reliable substitute for methyl cellulose in many liquid dosage forms, with good compatibility, broad pH stability, and broad use in oral suspensions.

Gelatin and povidone serve different primary roles (gel formation and binding/solubilizing, respectively) and aren’t ideal substitutes for a suspending vehicle in the same way. Hydroxypropyl methylcellulose is another cellulose ether and can function as a thickener, but sodium carboxymethylcellulose is the classic alternative for providing reliable suspension stability in aqueous systems.