Cumulative Efficacy of Longitudinal Repeat Salivary Gland OnabotulinumtoxinA Injection: A Retrospective Study

Aim We hypothesized that repeat onabotulinumtoxinA (BTX-A) injections to salivary glands would have a cumulative effect on drooling, leading to prolonged efficacy duration. Methods We retrospectively reviewed medical records and conducted a telephone survey of individuals treated with BTX-A to the salivary glands to investigate ongoing efficacy or adverse effects. Outcome measures were duration of decrease in drooling and adverse events. The main independent variable was the number of injections. We identified 52 consecutive individuals (26 females) with cerebral palsy with an average age of 9 yrs, 3 mos ± 5 yrs 2 mos, who had received BTX-A for sialorrhea. Results Linear regression analysis showed that each additional injection resulted in the duration of efficacy being 0.68 mos longer (P < 0.001, R2 = 0.47). Age, sex, Gross Motor Function Classification System level, presence of tube feeding, presence of tracheostomy, gastroesophageal reflex, seizures, and concurrent intramuscular injections seizures were not significant contributors to the association between injection number and efficacy duration (F (6, 45) = 1.01, P = 0.431). Interpretation There may be a cumulative effect of BTX-A injections to the salivary glands, resulting in longer periods of efficacy with consecutive injection.