Vol.5, No.12, 1939-1945 (2013) Health
http://dx.doi.org/10.4236/health.2013.512262
Optimal needle insertion length for intramuscular
injection of risperidone long-acting injectable (RLAI)*
Tetsuya Tanioka1#, Sakiko Sakamaki2, Yuko Yasuhara1, Masahito Tomotake1,
Kensaku Takase3, Chie Watari4, Kouichi Makiguchi4, Rozzano Locsin5,
Kazushi Motoki3, Tatsuya Inui6
1Department of Nursing Management, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima,
Japan; #Corresponding Author:
2Graduate School of Health Biosciences, The University of Tokushima, Tokushima, Japan
3Tokushima Prefectural Central Hospital, Tokushima, Japan
4Fujishiro Kensei Hospital, Hirosaki, Japan
5Department of Nursing, Christine E. Lynn College of Nursing, Florida Atlantic University, Boca Raton, USA
6Fujii Hospital, Tokushima, Japan
Received 6 October 2013; revised 16 November 2013; accepted 28 November 2013
Copyright © 2013 Tetsuya Tanioka et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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 am ong subject s who have
normal body mass index (BM I: 18 to 25) an d 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 deliv er RLAI effec tively 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.
Keywords: Risperidone Long-Acting Injectable;
Gluteal Muscle; Intramuscular Injection; Optimal
Needle Insertion Length; Body Muss Index;
Ultrasonography
1. INTRODUCTION
Patients with schizophrenia are almost always treated
with antipsychotic medications. However, many patients
cannot tolerate taking the regular oral medication, and
adhere to the treatment regimen such as in situations
when they experience side effects, lack of social support
and insight into the disease pathology, and poor adher-
ence to medication protocol, resulting in symptom re-
currence [1-3]. Therefore, long-acting injectable antip-
sychotics are often used in the treatment of these patients.
The first atypical antipsychotic long acting injectable
medication was the Risperidone long acting injection
(RLAI) launched in Japan and used to treat not only non-
adherent patients but also those who are able to partially
adhere to the protocol. RLAI is a water-based suspension,
whereas other antipsychotic medications are oil-based
solutions [4-6].
Intramuscular (IM) injection of medications is usually
administered into the deltoid muscle and/or the gluteal
muscles [7-9]. The most common reasons for preferring
the deltoid muscle for IM injections include ease of ac-
cess allowing for increased patient privacy and less em-
barrassment to the patient, and faster delivery of medica-
tion with lesser observed untoward or side effects such as
painful reactions. IM injection in the gluteal muscle is
less painful than injection into the deltoid muscle [10].
Because the gluteal muscles are dense enough to per-
mit the injection of larger volumes of fluid, these were
*Disclosure of interest: The authors report no conflicts of interest.

T. Tanioka et al. / Health 5 (2013) 1939-1945
1940
found to be the best areas for IM injections of high-
volume medications [11]. Larger volumes of fluid may
induce more pain and the volume limit for IM injection
into the deltoid muscles is approximated to be only 1 mL
[12,13].
Most muscles are adjacent to nerves, blood vessels and
other important anatomical structures. The gluteus mini-
mus muscle and the nearby sciatic nerve are less likely to
be injured by injection of medication into the gluteus
medius muscle. This can be located externally in the up-
per outer quadrant of the buttocks [14,15].
In a study by Chan et al. [16] fifty Irish patients who
were to undergo Computerized Tomography (CT) pro-
cedure were injected with 1 mL of air into the upper
outer quadrant of the buttocks. CT images were subse-
quently analyzed to determine the position of the injected
air bubble and to assess whether it was within the muscle
or not. Results showed that only 32% (n = 16/50) of the
air bubble were in the intramuscular area, while majority
(68%, n = 34/50) showed that the air bubbles were at the
subcutaneous area. This indicated that widely held as-
sumption of intramuscular injections are actually subcu-
taneous injections.
Problems can arise if drugs designed to be absorbed
from the muscle are only delivered into the subcutaneous
tissue. With increasing obesity in all developed and
many developing countries, this may pose as an increas-
ing concern. A study [17] of 119 healthy adults with a
body mass index (BMI) of more than 24.9 kg/m2 consid-
ered to be overweight, obese, or extremely obese was
conducted to determine the optimal needle length inser-
tion at the dorsogluteal and ventrogluteal IM injection
sites. Using ultrasonography, the findings revealed that
the standard 1.5 inch (38 mm) needle is not long enough
to deliver medications to the dorsogluteal and ventro-
gluteal muscles of healthy adults with a BMI of more
than 24.9 kg/m2. Furthermore, the results also revealed
that neither site should be used in women whose BMI is
more than 24.9 kg/m2, although the dorsogluteal site may
be used for overweight and obese men, and the ventro-
gluteal site only for overweight men. Zaybak et al. [17]
concluded that if alternative routes are not possible,
longer specialized needles should be produced by manu-
facturers and recommended for use among obese indi-
viduals.
Based on this recommendation, a study of four sub-
jects with schizophrenia who received the RLAI medica-
tion was conducted. Using a specialized (2-inch) needle
designed for RLAI medication, ultrasonography data
revealed that the location (gluteus medius or maximus)
and diffusion of the RLAI medications administered in-
tramuscularly can be visualized, illustrating depth of
needle injection, location of needle, and diffusion of
medication [18]. Moreover, through ultrasonography,
this study revealed that in some cases, the drug was
shown to be injected into the gluteus maximus instead of
the gluteus medius, affirming that IM injection to the
accurate muscle is critical to ensuring the desired effects
of medications.
Visualizing through ultrasonography is possible since
the microspheres of RLAI have characteristics like a
contrast medium, thereby allowing a picture to be ultra-
sonically and simultaneously seen when medications are
injected into the muscles. Ultrasonography data also re-
vealed that injection sites hardened when typical antip-
sychotics are injected into areas other than the desired
muscle for example into the subcutaneous layer. This
was visible through ultrasonography at 16 days post in-
jection.
These results confirmed that the gluteus muscle was
the ideal muscle for IM injection as evidenced by the dis-
persion/absorption of the medication solution. With the
use of ultrasonography, injection sites and drug disper-
sions can be evaluated under a direct visual guidance, af-
firming that ultrasonography is a useful method for es-
tablishing evidence for determining correct insertion of
IM injection, diffusion of medications, and the effective
administration of IM injections.
In Japan, with the RLAI, (as it cannot be administered
in the deltoid muscle Ministry of Health, Labour and
Welfare of Japan [19]) being recognized as a medication
that can only be administered intramuscularly and in the
gluteal region, a new standardized protocol for its ad-
ministration was sought. The major consideration is safe-
ty because the RLAI is an approved medication for treat-
ment of schizophrenia given as a biweekly injection and
only in the gluteal muscle.
It is critical therefore that, avoiding injection into the
subcutaneous fatty tissue [20] is assured. RLAI was ap-
proved to be administered to patients in the gluteal mus-
cle using a 2-inch needle length. In addition, considering
the volume of the RLAI (in Japan, it is distributed as 25
mg, 37.5 mg, or 50 mg risperidone/2 mL IM Syringe)
and its properties such as absorption and its safety (such
as possible damage to tissues including subcutaneous,
blood vessels, or nerve-endings), the appropriate proto-
col for the administration of the RLAI is to use the
gluteal muscles as the primary injection site.
Subcutaneous fat tissue and muscular thickness are
critical determinants to establishing the adequate length
of needle to use and the accurate angle of injection into
muscle areas. Currently, about 50% of clinical nurses do
not assess subcutaneous fat level when they administer
an IM injection [21]. Furthermore, it was pointed out that
standardized needles commonly used for IM injections
are the 20 - 23 gauge needles (1 to 1 1/2 inches: 25 - 38
mm) that do not always reach their intended target—the
gluteal muscles in a considerable number of patients [16,

T. Tanioka et al . / Health 5 (2013) 1939-1945 1941
17,22-24].
Cocoman and Murray [25] strongly advised that to
adequately, accurately, and safely administer IM injec-
tions, the upper outer quadrant region should be the site
of choice. To be effective, an imaginary division of the
area into quadrants is suggested. Injection, therefore, is
given in the upper outer quadrant of the upper outer
quadrant (land marking is done by making a double cross.
(See Figure 1(a) ).
However, like the recommendation by Cocoman and
Murray [25], in Japan, it is the “four- and three-way
split” method that is most commonly used for IM injec-
tion [26]. When the nurses perform IM injection, com-
petent assessment of the hypodermic site area is critical
especially because most nurses tend to hesitate to insert
the needle deep enough for patients who have less sub-
cutaneous fat at the injection site areas, such as of pa-
tients who are thin.
Based on the findings described in the aforementioned
(a)
probe 90 degree
Iliac bone
muscles
subcutaneous
surfa ce skin
dermis
(b)
Figure 1. Intramuscular Injection Part and Ultrasonographic
Images. (a) Intramuscular site in the buttocks by “four- and
three-way split” method; (b) An illustration of sagittal section
with IM injection site and ultrasonograph probe.
research studies and the standards of IM injections estab-
lished in Japan for administering the RLAI, it is critical
that the size and length of needle and the identification of
respective areas of choice for particular injection sites be
determined using empirical data. Other than the study by
Chan et al. [16], no other research studies have been re-
ported that answered the question whether or not medi-
cations administered through IM injections are actually
administered to the gluteus medius or to the subcutane-
ous layer. Furthermore, the avoidable consequences of
using inaccurate needle size and length must be assured
so that if the needle length is too short to reach the in-
tended muscle, then the drug will be injected into the
subcutaneous tissue, decreasing absorption rate and de-
creasing efficacy of the drug and thereby providing in-
adequate effect. Important as well is the possible pain,
abscess or granuloma formation at the injection site [17].
2. AIM
The aim of this study is to determine the optimal in-
sertion length of the specialized (2-inch) needle indica-
ted for administering the RLAI among Japanese subjects
with normal BMI (between 18 and 25) and those with
high BMI (>25).
3. METHODS
3.1. Subjects
There were thirty seven adult subjects diagnosed with
schizophrenia of whom twenty-two were men and fifteen
were women. They were all prescribed to receive RLAI.
These subjects were recruited from two hospitals within
the Tokushima and Aomori prefectures in Japan.
3.2. Data Collection
The study was conducted from June 2010 to January
2011. Body weight and height were measured, and BMI
was calculated in all patients. Just before RLAI injection,
the distance from the epidermis to the under-fascia
(DEUF), and distance from the epidermis to the iliac
bone (DEI) at bilateral gluteal sites were assessed using a
standardized ultrasonography. Similarly, needle-length
insertion (INL) was also identified guided by the mark
up on the needle using a felt-tip pen before withdrawal of
the needle.
To identify the injection site by the “four- and three-
way split”, the buttocks area was imaginarily divided
into four quadrants. The proper injection site was located
at the upper outer quadrant, and at one third the distance
from the iliac crest on the imaginary 45 degree line (See
Figure 1(a)).
All ultrasonographic measurements were performed
by an experienced Sonographer using a 7.5 MHz linear

T. Tanioka et al . / Health 5 (2013) 1939-1945
1942
and convex array transducer and real-time-B-mode ul-
trasonograph diagnostic system (Hitachi Medical Corpo-
ration, Japan). Ultrasonograph images were made at the
dorsogluteal injection site. Gluteus maximus, medius and
minimus muscles are commonly used as regions for IM
injection. DEUF and DEI measurements were made
above and outside a line drawn from the posterior supe-
rior iliac spine to the greater trochanter of the femur.
Ultrasonograph probe was held at right angle to the skin
at the gluteal region (See Figure 1(b)).
Two measurements were made: the internally inserted
length of the two-inch needle from the epidermis to the
muscle, and the remaining (exposed) needle length ex-
ternal to the injection site. Thereafter, ultrasonography
was used to determine whether the length of the inter-
nally inserted needle was adequately inserted into the
gluteus muscle.
Nurse investigators who have used the “four- and
three-way split” method to determine the gluteal muscle
injection site, performed the procedure to ensure consis-
tency in the insertion method. Results of ultrasonogra-
phic measurements were done based on the recorded
ultrasonographic images.
3.3. Ethical Considerations
This study was conducted after approval was received
from Tokushima University Hospital’s Ethics Committee.
Both verbal and written consents were obtained from the
prospective subjects of the study. Patient consent for
ultrasonography images was also obtained. The consent
also included a statement of understanding that images
may be used for educational purposes, lectures, and pub-
lications.
3.4. Data Analysis
Statistical analysis of data was performed using
PASW Statistics (Ver. 18.0J). All collected data were
stratified by normal BMI (between 18 and 25) and high
BMI (>25), and the median, lower and upper quartile,
and range were calculated. The Mann-Whitney U test
was used to test for differences between stratified groups
with normal and high BMI.
4. RESULTS
Table 1 provides description of the subjects’ BMI dis-
tribution. In the group with normal BMI, there were 5
men and 5 women. In the group with high BMI there
were 17 men and 10 women. Both left gluteus (p < 0.001)
and right gluteus (p < 0.01) DEIs were significantly dif-
ferent between the groups with high and normal BMIs.
No significant differences were observed in the left and
right DEUF.
Table 1. Distribution of BMI.
Sample (n) Median Lower quartile Upper quartileRange
Overall (37) 26.8 24.7 31.2 19.1 - 35.7
Normal BMI (10)21.2 19.6 23.6 19.1 - 24.8
High BMI (27)27.3 26.2 31.7 25.0 - 35.7
BMI: body mass index (kg/m2), Normal BMI: 18 - 25, High BMI: >25.
In the group with normal BMI, median distance from
the epidermis to the under-fascia (DEUF) was 16.0 mm
(left), 15.7 mm (right). Distance from the epidermis to
the iliac bone (DEI) was 54.7 mm (left), 55.9 mm (right).
Median of needle-length insertion (INL) was 39.0 mm
and range was 27.0 - 47.0 mm. On the other hand in a
high BMI group, median DEUF was 20.2 mm (left), 16.5
mm (right). DEI was 71.9 mm (left) 75.9 mm (right).
INL was 45.5 mm and range was 30.0 - 50.0 mm (Table
2). It was confirmed ultrasonographically that RLAI had
been injected under the fascias and into the gluteus mus-
cle, in all cases.
Figure 2(a) shows the typical example of a man pa-
tient with a high BMI, diagnosis of schizophrenia and
age of 50 years. Height: 158 cm. Weight: 79 kg. BMI:
31.6 Kg/m2. The injection site was on the left side, and
the INL was 42.0 mm. Also, the DEUF was 16.9 mm,
and the distance from epidermis to the ilium was 84.8
mm.
Figure 2(b) shows the typical example of a woman
patient with a normal BMI schizophrenia, aged 52.
Height: 165.5 cm. Weight: 53 kg. BMI: 19.4 Kg/m2. The
injection site in this situation was on the left side, and the
INL was 30.0 mm. Also, the distance from the epidermis
to subcutaneous area was 13.4 mm, and the distance
from epidermis to the ilium was 55.9 mm.
5. DISCUSSION
Cocoman and Murray [25] recommended that to pro-
vide appropriate estimate of correct muscle location, the
buttocks be viewed divided into four equal areas and the
IM injection selected as the top outside quarter (See
Figure 1(a)). The upper outer quadrant must be used to
avoid any damage to the sciatic nerve. The gluteus me-
dius is distributed directly under the epidermis, the sub-
cutaneous fat tissue and the gluteus maximus [27]. The
“four- and three-way split” method procedure ensures the
estimation of the correct location for the insertion of the
injection needle to a depth that extends through the
thickness of the subcutaneous tissue and into the gluteus
maximus. It is important to inject to the level of the glu-
teus medius during IM injection because it is thick
enough to hold the volume of the medication and prevent
damage to the nerves or prevent insertion of the needle to

T. Tanioka et al . / Health 5 (2013) 1939-1945 1943
Table 2. Body mass index-based differences in patients with schizophrenia.
Normal BMI (kg/m2), n = 10 High BMI (kg/m2), n = 27
Variable
Median Lower quartile Upper quartileRange Median Lower quartileUpper quartile Range z p
INL (mm) 39.0 34.8 40.8 27.0 - 47.045.5 37.5 46.0 30.0 - 50.0 −1.34 n.s.
DEUF/left (mm) 16.0 13.6 20.0 10.5 - 19.020.2 12.6 21.3 10.3 - 27.1 −0.48 n.s.
DEUF/right (mm) 15.7 12.5 15.9 10.3 - 19.716.5 13.1 19.5 11.1 - 25.0 −0.27 n.s.
DEI/left (mm)ţ 54.7 51.3 61.1 42.7 - 64.271.9 68.8 74.6 62.1 - 87.3 −3.06 ***
DEI/right (mm)ţ 55.9 51.6 67.3 42.7 - 71.975.9 68.8 78.0 60.5 - 94.1 −2.63 **
BMI: body mass index (kg/m2), Normal BMI: 18 - 25, High BMI: >25, INL: Inserted needle length; DEUF: distance from the epidermis to the under-fascia;
DEI: distance from the epidermis to the iliac bone; ţ: number of subjects (normal BMI: n = 5, high BMI: n = 17) that was able to be measured in DEI; Mann-
Whitney U test, ***p < 0.001, **p < 0.01, n.s.: not significant.
fascia
Gluteusmedius
(a)
fas cia
Gluteusmedius
(b)
Figure 2. Intramuscular injection part and ultrasono-
graphic images. (a) Representative ultrasonographic im-
ages of patients with schizophrenia after RLAI injection;
a man patient with a high body mass index (BMI) and (b)
A woman patient with a normal BMI. Circle is the area
which the dedicated needle of RLAI reached in the glu-
teus medius.
a blood vessel [28].
The range and average of the hypodermic thickness
was reflected well when using the “four- and three-way
split” procedure. Kikuchi et al. [29] examined the thick-
ness of the hypodermis by the ultrasonography. The
thickness of the subcutaneous tissue was found to vary
from a mean score of 1.03, range 0.32 to 3.08 cm in adult
Japanese men, and a mean of 1.42, range 0.86 to 3.66 cm
in adult Japanese women. Thus, if the needle length was
too short, the injected solution may not reach the gluteus
muscle.
In the current study, a case of one male subject indi-
cated that the insertion needle length was 32.0 mm and
the DEUF was 20.0 mm. Nonetheless, the ultrasono-
graphic data indicated that the RLAI was administered in
the gluteus maximus muscle. Given this data, it seems
that the needle must have been inserted obliquely against
the skin surface.
One of the significant findings of this study was de-
termining the appropriate length of needle using ultra-
sonography data. Patients with high BMI (31.6 Kg/m2),
showed DEUF of 16.9 mm, DEI 84.8 mm, and INL 42.0
mm. In contrast, patients with normal BMI (19.7 Kg/m2),
showed DEUF 13.4 mm, DEI 55.9 mm, and INL 30.0
mm. These findings show that in both high and normal
BMI groups, the inserted needle did not reach the iliac
bone. This indicated that the RLAI was and can be ad-
ministered appropriately into the muscle even in patients
with normal or very high BMI when using a specialized
RLAI needle. This is because as illustrated using the
ultrasonographic data, the RLAI needle was inserted at
the injection site into the intended gluteal muscle after
using the “four- and three-way split” method to find the
correct gluteal muscle injection site.
The ideal is to inject the RLAI into the gluteus medius
muscle. Nevertheless, even with the “four- and three-way
split” method, there is a possibility that the medication
may be administered into the gluteus maximus muscle
when the needle is inserted obliquely. There is also the
possibility that significant differences may be found
when patients have varying BMI and/or when needles
other than the specialized needles for RLAI are used.
Generally, in Japan, a 23-gauge (1.25 inch) needle is

T. Tanioka et al . / Health 5 (2013) 1939-1945
1944
used for IM injection [26]. Also, the recommendation is
to leave about 1/2 or 1/3 of the injection needle from the
skin surface. For RLAI, however, the result indicates that
it was necessary to insert 80% of the IM needle, leaving
only 20% exposed at the skin level. It was found that the
RLAI can be safely delivered into the muscle without
untoward or side effects such as reaching the iliac bone.
To ensure that the intended effect of using RLAI for
patients with schizophrenia is achieved the study indi-
cated that a specialized needle be manufactured that is
marked at the 40 mm level to indicate the insertion limits.
These marked needles should guide the nurse when
administering RLAI to patients with either high or low
BMI. While these specialized needles may be marked to
ensure depth of insertion considering BMI, an important
consideration is the correct estimation of the location of
the gluteus muscle using the “four- and three-way split”
method to determine the insertion site as the method of
choice to find the ideal gluteus muscle.
6. CONCLUSIONS
This is the first study which is based on the sonogra-
phic diagnosis that is carried out to confirm by ultraso-
nography data the use of a marked needle specially for
administering RLAI, assuring that indeed it is injected
into the ideal muscle. However, even with this study,
there remains a possibility that injection site untoward
reactions and side effects can occur as a result of RLAI
being injected into the subcutaneous tissue instead of the
gluteal muscles. Therefore, it is critical to assure injec-
tion of the RLAI into the gluteus muscle by using the
four- and three-way split method technique to find the
site, and to use the specialized and marked two-inch
RLAI needle.
With 37 subjects, it was confirmed by ultrasonogra-
phic images that using a two-inch RLAI needle could
ensure IM administration at the injection site when using
the “four- and three-way split” method and the speciali-
zed needle marked at 40 mm level. With the “four- and
three-way split” method, the RLAI was administered into
the gluteus maximus muscle even when the injection
needle was not inserted at a vertical angle. It is recom-
mended that RLAI can be safely delivered into the
muscle, if the two-inch specialized needle is marked at
the 40 mm point indicating that the needle must only be
inserted up to this level. As shown by ultrasonographic
data, insertion up to this level assures insertion of the
needle past the subcutaneous level and into the gluteus
muscle regardless of the patients’ BMI.
7. LIMITATIONS
The study has several limitations. One of these is the
small sample size which may limit the generalization de-
rived from the findings. Likewise, the researchers failed
to equalize the numbers of people in the gender groups.
Oftentimes, men and women have significantly different
BMIs which may influence their dermal (skin) thickness,
thereby significantly affecting the difference between the
thickness of subcutaneous fat and the subsequent muscle.
These differences may have influence on the outcomes
of the study.
Because of the limited number of subjects, the resear-
chers suggest that studies using larger samples may be
needed to re-affirm the results and recommendations of
the study. Finally, this study was conducted to confirm
the use of specialized 2-inch needles in RLAI by pro-
viding evidence using ultrasonography data.
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