Thank you for sharing your patient experience with the group.
Personally, I find it very interesting, and highly unusual that your patient lost 20 lbs with simply changing his ART from DRV/c + TAF/FTC to CAB + RPV (Cabenuva). To my knowledge and experience, an M184V mutation does not cause HIV-related wasting.
I would suggest that you look for other causes of weight loss., e.g., concomitant illness (e.g., neoplasm), change in food access, intentional weight loss, appetite suppressants (e.g., stimulant use) or others.
Also, did he gain weight on DRV/c + TAF/FTC originally? Perhaps discontinuing TAF/FTC has an effect on weight loss?
Eager to hear your thoughts and learn more.