Pain following depot intramuscular (IM) injection of oil vehicle-based drugs has been little studied. This study aimed to determine prospectively the prevalence, determinants, severity and functional consequences of
pain during the week after IM injection of 1 000 mg
testosterone undecanoate (TU) in a 4-mL
castor oil vehicle.
Androgen-deficient men receiving regular T replacement
therapy at an academic andrology clinic were recruited to report
pain scores using a coloured visual linear analogue scale at seven times over the first day and daily for a week after a deep IM gluteal injection. The time course and covariables influencing
pain scores were analysed by mixed model analysis of variance (ANOVA). Following 168
injections in 125 men,
pain was reported by 80% of men, peaking immediately after injection, reaching only moderate severity, lasting 1-2 days and returning to baseline by day 4. The
pain required little
analgesic use and produced minimal interference in daily activities. The time course of
pain scores was reproducible in the 43 men who underwent two consecutive
injections.
Pain was more severe in men who had an earlier painful injection, but less severe in older and more obese men. There were negligible differences in post-injection
pain experience between experienced nurses administering
injections. Deep IM gluteal injection of depot TU in 4-mL
castor oil is well tolerated and post-injection
pain is influenced by earlier painful injection experience, as well as age and
obesity.