Abstract
Of the approximately 40 million people living with human immunodeficiency virus (HIV) globally as of 2022, a clinically significant subset harbours multidrug-resistant (MDR) HIV-1, leaving them with few viable antiretroviral options. Ibalizumab (Trogarzo), a recombinant humanised IgG4 monoclonal antibody, received FDA approval in March 2018 as the first monoclonal antibody for HIV-1 therapy and the first agent of a novel mechanistic class approved in over a decade. This review critically appraises ibalizumab across its discovery, mechanism of action, pharmacology, clinical trial evidence, safety profile, special populations, and access considerations. A narrative review of peer-reviewed literature was conducted using PubMed and Embase, supplemented by data from ClinicalTrials.gov, FDA and European Medicines Agency (EMA) regulatory documents, and relevant conference proceedings published up to March 2026. Ibalizumab binds domain 2 (D2) of the extracellular CD4 receptor, sterically blocking post-attachment conformational changes required for co-receptor engagement without impairing MHC class II immune signalling. In the pivotal Phase III TMB-301 trial, 83% of heavily treatment-experienced adults achieved a clinically meaningful viral load reduction at week 24, while extended-access studies demonstrated durable virological suppression and sustained immunological recovery. The drug is generally well tolerated, with diarrhoea, headache, and nausea being the most frequently reported adverse events. Resistance develops rapidly when ibalizumab is used as monotherapy, underscoring the necessity of combining it with an optimised background antiretroviral regimen. Ibalizumab represents a genuine therapeutic advance for patients with MDR HIV-1 who have exhausted conventional regimens. Its unique mechanism, established efficacy, and favourable safety profile make it an indispensable salvage therapy component. Key barriers to broader uptake include intravenous administration, biweekly clinic attendance, high cost, and limited availability in resource-constrained settings. Long-acting formulations and bispecific antibody strategies offer promise for expanding its clinical reach.