Chan et al used CT scanning to determine if an intramuscular (IM) injection into the buttocks of an adult actually reached muscle or was deposited in adipose tissue. The authors are from Adelaide and Meath Hospital in Dublin, Ireland.
The risk of an injection being into fat rather than muscle using a standard 24 gauge needle was highest in an obese woman with low muscle mass.
Consequences of injection into fat:
(1) failure to absorb drug, with subtherapeutic levels
(2) damage to adipose tissue
Factors affecting final location of an IM injection:
(1) gender
(2) thickness of fat layer (associated with the person's obesity)
(3) thickness of muscle layer
|
Parameter
|
Finding
|
Points
|
|
gender
|
male
|
1
|
|
|
female
|
0
|
|
thickness of fat layer
|
< 2 cm
|
1
|
|
|
>= 2 cm
|
0
|
|
thickness of muscle layer
|
< 3 cm
|
0
|
|
|
>= 3 cm
|
1
|
total score =
= SUM(points for all 3 factors)
Interpretation:
• minimum number of factors: 0
• maximum number of factors: 3
• The higher the score the more likely the IM injection will actually be deposited into muscle.
• The lower the score the more likely the injection will be deposited into fat.
If the person is determined to be at risk, then options are:
(1) to use a longer needle
(2) select an alternative site for the injection
(3) select an alternative route (oral, intravenous, subcutaneous, per rectum) for drug administration
