How are absorption bases used?

• A. to incorporate limited volumes of aqueous solutions into hydrocarbon base
• B. to emulsify large volumes of water
• C. to dissolve salts in water
• D. to harden waxy substances

Answer: (A)

Absorption bases are special ointment bases that can take up water. They are not purely oil-loving bases; they can absorb a limited amount of aqueous solution and form a water-in-oil emulsion within the hydrocarbon base. This lets you mix in small volumes of an aqueous drug solution into a petrolatum-like base, creating a semi-solid preparation that contains some water without becoming fully aqueous. The key is the limited water absorption: enough to incorporate the aqueous phase, but not large volumes. They won’t dissolve salts in water, and their primary role isn’t to harden waxy substances—that effect comes from the wax content in other bases.