What is the acceptable volume for a single dose of immune globulin (IG) to inject into the deltoid muscle or the vastus lateralis (thigh) of a normal-weight adult?

There are no precise volume limits published by CDC or professional organizations. Professional judgment is required. Here are CDC’s suggested volumes:
Deltoid:

• Average 0.5 mL
• Range 0.5–2 mL

Vastus Lateralis:

• Average 1–4 mL
• Range 1–5 mL

Infants and toddlers would fall at the lower end of the range, whereas adolescents and adults would generally fall on the higher end of the range.

The same injection volume ranges above also apply when considering administration of multiple vaccinations or a combination of an antibody product and vaccination (e.g., nirsevimab and vaccine) in the same muscle.