Weight gain in treatment-naive HIV-1 infected patients starting abacavir/lamivudine/dolutegravir or tenofovir alafenamide/emtricitabine/bictegravir Recent evidence suggests that initial combination antiretroviral therapy (cART), including integrase strand transfer inhibitors (INSTIs), is associated with greater weight gain than initial regimens including other antiretroviral classes, and this correlation has led to an increasing concern, because international guidelines recommend the INSTI-based regimens as the preferred first-line treatment for HIV infection [1][2][3].An unexpected excess in weight gain has been reported mostly in the course of dolutegravir-based treatments [3][4][5], but a comparison in weight gain associated with dolutegravir and bictegravir-based cART is still lacking.We performed a retrospective, observational, cohort analysis of HIV-1-infected adult patients naive to antiretroviral therapy and initiating a first antiretroviral treatment in our Division of Infectious Diseases from June 2018 through June 2020. Patients starting the coformulated antiretroviral regimen abacavir/lamivudine/dolutegravir (ABC/3TC/DOL) or tenofovir alafenamide/emtricitabine/bictegravir (TAF/FTC/BIC), and with a follow-up of at least 12 months were enrolled into the study.Demographic, clinical and laboratory data were extracted from the medical records and included weight, BMI, waist circumference, lipids, glucose and insulin. BMI classes were 18 kg/m 2 or less (class I), 18.1-25 kg/m 2 (class II), 25.1-30 kg/m 2 (class III) and more than 30 kg/m 2 (class IV). The homeostasis model assessment-estimated insulin resistance (HOMA-IR) index was calculated multiplying fasting plasma insulin (mUI/l) by fasting plasma glucose (mg/dl), then dividing by the constant 405, and insulin resistance is defined by HOMA-IR more than 2.5 [6].Study inclusion criteria were met by 141 patients who were enrolled in the study: 68 patients starting abacavir/ lamivudine/dolutegravir (ABC/3TC/DOL group) and 73 starting tenofovir alafenamide/emtricitabine/bictegravir (TAF/FTC/BIC group). Demographic, clinical and laboratory characteristics of study patients at baseline were comparable in both groups and are summarized in Table 1.The baseline mean (AE SD) weight was 72.8 (AE 10.7) kg, waist circumference 87.9 (AE 14.9) cm and BMI 24.3 (AE 3.6) kg/m 2 . In detail, BMI was 18 kg/m 2 or less (class I) in eight (5.7%) patients, ranging between 18 and 25 kg/m 2 (class II) in 79 (56%), ranging between 25 and 30 kg/m 2 (class III) in 35 (24.8%), and more than 30 kg/m 2 (class IV) in 19 (13.5%). Patients with baseline HOMA-IR index more than 2.5 were five (7.3%) in ABC/3TC/DOL group and four (5.5%) in TAF/FTC/BIC group.