REPLY
I thank Cossu et al. (1) for reporting the two cases of off-label administration of long-acting (LA) cabotegravir and rilpivirine via deltoid intramuscular (IM) injections for maintaining HIV-1 virologic suppression. Gluteal IM injection of cabotegravir LA (3mL/600mg) and rilpivirine LA (3mL/900mg) once every 2 months (Q2M) was approved and distributed in European Union for maintaining HIV-1 virologic suppression (2, 3). Cossu et al. (1) reported that gluteal IM injection was switched to deltoid IM injection in two transgender women, who had been receiving gluteal IM injections for>3 years. Trough concentrations of both cabotegravir and rilpivirine immediately before versus 24 weeks after the switch to the deltoid route were similar in both cases. Optimal immune-virologic control (HIV-RNA< 20 copies/mL) was maintained, and no side effects to LA treatment were reported in both cases.
The tolerability of deltoid and gluteal IM injections of rilpivirine LA was studied and compared in study TMC278-TiDP15-C146 (4). The assessment of injection site reaction consisting of redness, bruising, pain, and sometimes indurations demonstrated that 3mL of gluteal IM injections was better tolerated than 2mL of deltoid IM injections. Deltoid IM injections of 2mL induced more spontaneous pain and pain at touch (6/6 volunteers), albeit of moderate severity, than after gluteal IM injection (2/6 volunteers). Therefore, deltoid IM injection of rilpivirine LA was not further investigated.
Maximum volumes of IM injection have been assessed across the various IM sites for various drugs in adults (5). Overall, 2mL has been cited as the maximum volume for deltoid IM injections in adults (6–8), while up to 5mL of gluteal IM injections has been reported to be tolerable in adults (5). For recipients with less developed or small muscle mass, the maximum volume for deltoid IM injections is likely reduced.
In conclusion, the totality of information suggested that IM injection of 3mL would be better tolerated in the larger gluteus muscle in a broad range of individuals with varying body habitus.
Contributor Information
Kelong Han, Email: kelong.x.han@gsk.com.
James E. Leggett, Providence Portland Medical Center, Portland, Oregon, USA
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