Step 1: Understanding the Concept:
Parenterals are injections. Small volume parenterals (SVPs) are under 100 mL, while LVPs are typically 500 mL or more (like Saline or Dextrose infusions).
Step 2: Detailed Explanation:
1. Preservatives: Substances like phenol or benzalkonium chloride are toxic if given in high amounts.
2. Concentration vs. Volume: In a 5 mL injection (SVP), the total amount of preservative is very tiny and safe. However, in a 1000 mL infusion (LVP), the patient would receive a massive cumulative dose of the preservative.
3. Pharmacopoeial Rule: Therefore, the Indian and British Pharmacopoeias strictly forbid adding antimicrobial preservatives to any injection intended for administration in volumes greater than 15 mL at one time.
Step 3: Final Answer:
The large volume administered in LVPs makes the inclusion of preservatives dangerous due to the cumulative systemic toxicity they would cause.