Certified Medical Assistant (CMA AAMA)PharmacologyMedium
A medical assistant is preparing to administer an intramuscular injection to an adult patient. The medication is oil-based and requires a slow absorption rate. Which of the following needle gauges is most appropriate for this administration?
- A21-gauge
- B27-gauge
- C18-gauge
- D25-gauge
Show answer & explanationAnswer & explanation
Correct answer: A. 21-gauge
For viscous, oil-based intramuscular injections, a larger needle gauge (smaller number) is typically preferred to facilitate easier passage of the medication. A 21-gauge needle offers a good balance between patient comfort and effective delivery for such medications.
Why the other options are wrong
- B. A 27-gauge needle is typically used for intradermal or subcutaneous injections, not intramuscular.
- C. An 18-gauge needle is generally too large for routine IM injections and can cause unnecessary tissue trauma.
- D. A 25-gauge needle is too small for viscous, oil-based intramuscular medications and would make administration difficult.
Needle Gauge for Viscous IM
Needle gauge refers to the diameter of the needle lumen; a lower gauge number indicates a larger needle diameter. For viscous intramuscular injections, a larger diameter needle (smaller gauge number, typically 21-22 gauge) is preferred to ensure smooth administration.
- Gauge is inversely proportional to needle diameter.
- Viscous medications require larger diameter needles.
- Common IM gauges are 20-25; 21-22 are often used for thicker solutions.
Memory trick: Gauge Goes Bigger, Hole Gets Smaller