Optimal needle insertion length for intramuscular injection of risperidone long-acting injectable (RLAI)

Risperidone long-acting injectable (RLAI) is approved for the treatment of schizophrenia in many countries. The suggested site is the gluteal muscle with a needle length of two inches (50 mm) in Japan, which is longer than the ordinarily used needle for intramuscular injections. The aim of this study was to determine the optimal needle insertion length for accurate delivery of RLAI procedure among subjects who have normal body mass index (BMI: 18 to 25) and high BMI (>25). Thirty-seven patients with schizophrenia were administered RLAI intramuscularly into the dorsogluteal muscle. The standard procedure required inserting 80% of the two inch needle. By using data collected by ultrasonography, the findings confirmed that the median needle insertion lengths for subjects with normal and high BMI were 39.0 and 45.5 mm, respectively. To deliver RLAI effectively and safely, the authors strongly recommend that a specialized needle be used that is “marked” at the 40 mm point from the tip of the needle to the base. In this way regardless of subcutaneous fat content, the RLAI can be safely delivered into the muscle without causing untoward or side effects.