Sodium bisulfite is used as a preservative in local anesthetic solutions only when what is added to the solution?

Sodium bisulfite is used as a preservative in local anesthetic solutions only when what is added to the solution?

• A. A vasoconstrictor
• B. A buffering agent
• C. A coloring agent
• D. A sugar

Answer: (A)

The main idea is that sodium bisulfite acts as an antioxidant preservative to protect the stability of vasoconstrictors in local anesthetic solutions. Vasoconstrictors like epinephrine are prone to oxidation, which can reduce their potency. Sodium bisulfite is added to prevent that oxidation, keeping the vasoconstrictor effective and the solution stable. If no vasoconstrictor is present, there’s no oxidation risk to guard against, so the preservative isn’t needed. That’s why sodium bisulfite is used only when a vasoconstrictor is included. The other options don’t serve this protective role: buffering agents adjust pH, which affects absorption and efficacy but isn’t about preserving the vasoconstrictor; coloring agents are for identification; sugars are not a typical component of these injections.

The main idea is that sodium bisulfite acts as an antioxidant preservative to protect the stability of vasoconstrictors in local anesthetic solutions. Vasoconstrictors like epinephrine are prone to oxidation, which can reduce their potency. Sodium bisulfite is added to prevent that oxidation, keeping the vasoconstrictor effective and the solution stable. If no vasoconstrictor is present, there’s no oxidation risk to guard against, so the preservative isn’t needed. That’s why sodium bisulfite is used only when a vasoconstrictor is included.

The other options don’t serve this protective role: buffering agents adjust pH, which affects absorption and efficacy but isn’t about preserving the vasoconstrictor; coloring agents are for identification; sugars are not a typical component of these injections.