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

Abstract

Risperidone long-acting injectable (RLAI) is ap-proved for the treatment of schizophrenia in many countries. The suggested site is the glu-teal muscle with a needle length of two inches (50 mm) in Japan, which is longer than the or-dinarily used needle for intramuscular injections. The aim of this study was to determine the op-timal needle insertion length for accurate deliv-ery of RLAI procedure among subjects who have normal body mass index (BMI: 18 to 25) and high BMI (>25). Thirty-seven patients with schizo-phrenia were administered RLAI intramuscularly into the dorsogluteal muscle. The standard pro-cedure required inserting 80% of the two inch needle. By using data collected by ultrasono-graphy, the findings confirmed that the median needle insertion lengths for subjects with nor-mal and high BMI were 39.0 and 45.5 mm, re-spectively. To deliver RLAI effectively and safely, the authors strongly recommend that a special-ized 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 con-tent, the RLAI can be safely delivered into the muscle without causing untoward or side ef-fects.