Real-world data on HIV drug resistance (HIVDR) after transitioning to tenofovir disoproxil fumarate/lamivudine/dolutegravir (TLD) are limited. We assessed HIVDR rates and patterns in clients with virological failure (VF) after switching from an NNRTI-based regimen to TLD. A cross-sectional study was conducted in Gaza, Mozambique (August 2021–February 2022), including adults on first-line ART for ≥12 months who transitioned to TLD and had unsuppressed viral load (VL) ≥ 1000 copies/mL six months post-transition. After three adherence counseling sessions, participants with VF underwent genotyping for drug resistance mutations (DRMs) using the Stanford HIVdb Program. Of 717 participants (median age 39.2 years, 70.7% female), 217 (30.2%) had VF, 193 (88.9%) underwent genotyping, with 183 (94.8%) successfully genotyped. Intermediate–high dolutegravir (DTG) resistance was found in 19.6% (36/183). Unsuppressed VL before DTG transition was independently associated with VF (aOR: 2.14). Resistance patterns included 33.3% (12/36; 95% CI: 14.6–46.3) to all three TLD drugs, 55.6% (20/36; 95% CI: 39.3–71.9) to DTG and 3TC, and 11% (4/36; 95% CI: 0.8–21.3) to DTG only. Major drug resistance mutations to DTG included G118R (9.3%), R263K (6.6%), and Q148H/R/K (4.4%). This study highlights the need to consider virologic status before transitioning PLHIV to TLD and suggests that adherence counseling may not prevent resistance in those with unknown or prior VF.
