Conflicts of interest: Varan Perananthan was the Clinical Pharmacology Trainee participant on the Australian Prescriber Editorial Executive Committee at the time of writing. He was excluded from editorial decision-making related to the acceptance and publication of this case study. Miles Sparrow has received research support from Gilead and Celltrion, and speaker fees from Janssen, AbbVie, Ferring Pharmaceuticals, Takeda Pharmaceuticals, Pfizer, Celltrion Healthcare, Eli Lilly and Dr. Falk Pharma. He has been on advisory boards for Janssen, Takeda Pharmaceuticals, Pfizer, Celgene, AbbVie, MSD, Emerge Health, Gilead, Bristol Myers Squibb, Celltrion Healthcare and Eli Lilly. Anna Foley has no conflicts of interest to declare.