Abstract Disclosure: S. Hudson: None. J. Aurora: None. K. Grossman: None. L. Kogelman: None. A.G. Pittas: None. Background: Antiretroviral therapy (ART) containing bictegravir (BIC), a second-generation integrase strand transfer inhibitor (INSTI), is a first-line treatment for HIV. There are mixed reports of INSTIs causing adverse metabolic effects, such as weight gain and hyperglycemia. There are cases of BIC causing hyperglycemia and diabetic ketoacidosis (DKA) within weeks to months following initiation; however, this has not been reported in clinical trials (1). It is unclear whether discontinuing BIC resolves hyperglycemia. We report a case of a patient with prediabetes who developed severe hyperglycemia after switching to a BIC-containing ART. The discontinuation of BIC resulted in significant improvement in glycemia, leading to the de-escalation of diabetes pharmacotherapy. Clinical Case: A 36-year-old woman with obesity was diagnosed with HIV during pregnancy, which was complicated by gestational diabetes mellitus. After pregnancy, she had prediabetes. Her initial ART was darunavir/cobicistat/emtricitabine/tenofovir alafenamide. Due to intolerable GI side effects, six years later, she was switched to bictegravir/emtricitabine/tenofovir alafenamide (BIC/FTC/TAF). Laboratory tests four months before starting BIC/FTC/TAF were consistent with prediabetes (HbA1c 6.4%, non-fasting blood glucose of 118 mg/dL). After one month, she was started on metformin when her HbA1c increased to 9.1% with a non-fasting blood glucose of 332 mg/dL. Another month later, HbA1c increased to 12.8% with a non-fasting blood glucose of 685 mg/dL without DKA. She was hospitalized for diabetes management. There were no significant changes in weight, viral load, or CD4 count. A search for secondary causes of hyperglycemia (diabetogenic medications, hypercortisolism, and autoimmune diabetes) was not revealing. She was discharged on metformin and insulin glargine. Her HIV regimen was switched to FTC/TAF and doravirine due to suspicion of BIC-induced hyperglycemia. After five months, she developed symptoms of hypoglycemia, and her estimated HbA1c by continuous glucose monitoring was 6.3%. Insulin glargine was discontinued. While on metformin, HbA1c three months later was 6.3%. Two years later on metformin and linagliptin: HbA1c was 6.1% and beta-cell function did not reveal insulin deficiency or resistance (non-fasting blood glucose 96 mg/dL, insulin 13.5 uIU/mL [RR 2.6-24.9 mIU/mL], C-peptide 3.7 ng/mL [RR 1.1-4.4 ng/mL]). Conclusion: Patients with HIV and a history of obesity and/or dysglycemia who are switched to a BIC-containing ART regimen should be educated and monitored for acute hyperglycemia. This may be due to impaired beta-cell function and/or insulin resistance; however, further research is needed to understand the mechanism. An alternative ART regimen should be considered if hyperglycemia develops. Reference: 1. Nolan NS, et al. Open Forum Infect Dis. 2021;16;8(5): ofab077. Presentation: 6/3/2024