Would you switch to bimekizumab if a patient with psoriatic arthritis who is already on an IL-17 inhibitor has breakthrough skin or joint disease?   

Yes. An abstract at this year's ACR Meeting showed that patients who had failed secukinumab, ixekizumab, or brodalumab did respond to bimekizumab. Although the study included only 43 patients, it still provides solid evidence for a response.

If this was a 'secondary failure' (loss of response after initial good response) of the original IL-17i, then yes. If this was a primary failure ('lack of response'), then no.