Factors associated with severity and resolution of intramuscular injection site pain following treatment for uncomplicated gonorrhoea: a prospective cohort study of GToG trial participants.

Intramuscular injection (IMI) pain reduces the acceptability of treatment, but data identifying those at highest risk of severe pain following an injection are limited. This study identified factors associated with the severity, duration and resolution of IMI pain following treatment for uncomplicated gonorrhoea. Data from a subset of participants (aged 16-70 years) recruited between October 2014 and November 2016 into the 'Gentamicin for the treatment of gonorrhoea' trial in England were analysed. Pain was measured using a visual analogue scale (VAS) immediately after injection. Self-reported duration of pain was collected at a scheduled 2-week follow-up visit. Overall, 688 participants (82% male), reported a median pain VAS score of 23.5 (range 0-100), which was moderate-severe (VAS score >30) in 38% (262/688) of participants. Age [adjusted odds ratio (aOR) 0.86 per 5-yearly increase, (0.78-0.94)], gender [female cf. male, aOR 1.62 (1.18-2.24)], ethnicity [Asian cf. Caucasian, aOR 2.79 (1.72-4.51)], body mass index [aOR 0.80 per 5 kgm-2 increase, (0.72-0.89)] and antibiotic regimen [gentamicin cf. ceftriaxone, aOR 3.92, (3.12-4.93)] were associated with moderate-severe injection pain. The median duration of pain was 2 h (range 0-648). Gender [female cf. male, adjusted hazard ratio (aHR) 0.76 (0.57-1.00)], ethnicity [Mixed race cf. Caucasian, aHR 0.64 (0.45-0.92)], self-reported pain [aHR 0.97 per 10 mm VAS score increase, (0.95-0.99)] and symptom status [asymptomatic cf. symptomatic aHR 1.35 (1.12-1.64)] were associated with pain resolution. IMI pain is influenced by specific demographic, anthropometric and clinical factors. Knowledge of these factors will help identify those most at risk of pain.