Which statement correctly describes intraperitoneal injections in mice?

• A. Delivered intravenously
• B. Delivered into the peritoneal cavity
• C. Delivered subcutaneously
• D. Delivered into the muscle

Answer: (B)

Intraperitoneal injections involve delivering a substance into the peritoneal cavity—the space inside the abdomen that surrounds the organs. In mice, this route places the material inside the abdominal cavity rather than into a blood vessel, under the skin, or into muscle. The peritoneal lining is well vascularized, so compounds can be absorbed into the systemic circulation, and this method can accommodate somewhat larger volumes than subcutaneous or intramuscular routes. It’s chosen when a rapid systemic effect is needed or when intravenous access is difficult. Delivering into a vein would be intravenous, under the skin is subcutaneous, and into muscle is intramuscular.