Intramuscular injection is the type of injection which is given directly into the muscle. The site of injection depends on the kind of drug and the purpose. The injected drug may be absorbed fairly quickly or gradually depending on the chemical nature of it but is faster than subcutaneous injection. Many drugs - antibiotics, vaccines, steroids etc. are administered via this route.
Usually the upper dosage limit for adults is 5 ml and that for infants is 0.5 ml. But 3 ml is the fair average upper limit for adults too.
The maximum volume of IM administration varies on the site of injection. For eg., when given in the muscles, Rectus femoris and Vastus lateralis, maximum dosage can be upto 5 ml. But it should be less than 2 ml when given in the deltoid.
If the maximum dosage volume is exceeded, this results in a very high concentration of the drug in the muscle. This can be harmful as well as cause painful muscle cramps.