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Introduction Onabotulinumtoxin type A (BoNTA) is manufactured as powder that requires reconstitution with normal saline prior to injection. Previous literature has suggested that preserved saline (PS) exerts a local anaesthetic effect, and reduces the procedure discomfort when used in reconstitution in lieu of preservative‐free saline (PFS). However, this was mainly studied in the aesthetics indications of BoNTA, and never in its use for the treatment of chronic migraine. The distinction is important as chronic migraine population suffers high incidence of scalp allodynia which makes it more prone to injection site pain. In addition, the pain of the procedure itself may be related to the spike of migraine frequency in the immediate postprocedural period which can occur in up to 5% of patients receiving the treatment. Our trial aimed to study the difference in procedural pain scale, and postprocedural headache rating with the use of PS vs PFS in constitution of BoNTA when used as a treatment for chronic migraine. Methods 68 subjects were consecutively enrolled in an outpatient setting at a large tertiary headache centre over a period of 6 months. Subjects were randomised into PS or PFS group. BoNTA was administered as per standard protocol in both groups. Injection site pain scores and frequency of headache days in the immediate following week were recorded. Wilcoxon rank sum tests were used to compare differences in between groups using SPSS software. Results Analysis (SAS V 9.4) revealed that those receiving [PF] had significantly higher procedure pain scores than those receiving [P] (5.3 vs 3.2, respectively). There was no difference in the headache or migraine frequency in the immediate postprocedural period. Conclusion This study supports the use of PS (bacteriostatic) over PFS for reconstitution of BoNTA in chronic migraine as it reduces the discomfort of the injection sites.

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