the three most commonly used sites for intramuscular injections are
The deltoid muscle of the upper arm, the gluteal muscle of the buttock, in infants, the vastus lateralis muscle of the thigh
Introduction
Common sites for intramuscular injections include the deltoid muscle of the upper arm and the gluteal muscle of the buttock. In infants, the vastus lateralis muscle of the thigh is commonly used. 
The deltoid muscle, the ventrogluteal site and the vastus lateralis site. The deltoid muscle, ventrogluteal, vastus lateralis muscle. The deltoid muscle, the ventrogluteal site and the vastus lateralis site.
Intramuscular injection Intramuscular injection Intramuscular injection
Injection sites Injection sites Injection sites
The deltoid muscle (upper arm) is used for injections of small volume, usually equal or less than 2 ml. This includes most intramuscular vaccinations. It is not recommended to use the deltoid for repeated injections due to its small area, which makes it difficult to space out injections from each other. The deltoid site is located by locating the lower edge of the acromion process, and injecting in the area which forms an upside down triangle with its base at the acromion process and its midpoint in line with the armpit. An injection into the deltoid muscle commonly uses a 1-inch long needle, but may use a -inch long needle for younger people or very frail elderly people.

The ventrogluteal (hip) site is used for injections which require a larger volume to be administered, greater than 1 ml, and for medications which are known to be irritating, viscous, or oily. It is also used to administer narcotic medications, antibiotics, sedatives and anti-emetics. The ventrogluteal site is locate The deltoid muscle (upper arm) is used for injections of small volume, usually equal or less than 2 ml. This includes most intramuscular vaccinations. It is not recommended to use the deltoid for repeated injections due to its small area, which makes it difficult to space out injections from each other. The deltoid site is located by locating the lower edge of the acromion process, and injecting in the area which forms an upside down triangle with its base at the acromion process and its midpoint in line with the armpit. An injection into the deltoid muscle commonly uses a 1-inch long needle, but may use a -inch long needle for younger people or very frail elderly people.

The ventrogluteal (hip) site is used for injections which require a larger volume to be administered, greater than 1 ml, and for medications which are known to be irritating, viscous, or oily. It is also used to administer narcotic medications, antibiotics, sedatives and anti-emetics. The ventrogluteal site is locate The deltoid muscle (upper arm) is used for injections of small volume, usually equal or less than 2 ml. This includes most intramuscular vaccinations. It is not recommended to use the deltoid for repeated injections due to its small area, which makes it difficult to space out injections from each other. The deltoid site is located by locating the lower edge of the acromion process, and injecting in the area which forms an upside down triangle with its base at the acromion process and its midpoint in line with the armpit. An injection into the deltoid muscle commonly uses a 1-inch long needle, but may use a -inch long needle for younger people or very frail elderly people.

The ventrogluteal (hip) site is used for injections which require a larger volume to be administered, greater than 1 ml, and for medications which are known to be irritating, viscous, or oily. It is also used to administer narcotic medications, antibiotics, sedatives and anti-emetics. The ventrogluteal site is locate
wiki:4781791
Intramuscular injection [SEP] Introduction
Rarely, nerves or blood vessels around the injection site can be damaged, resulting in severe pain or paralysis. If proper technique is not followed, intramuscular injections can result in localized infections such as abscesses and gangrene. While historically aspiration was recommended to prevent inadvertent administration into a vein, it is no longer recommended for most injection sites.