P088

1:Research Institute for Medicines, Faculdade de Farmácia, Universidade de Lisboa, Lisboa, Portugal; 2:Serviço de Doenças Infecciosas, Hospital Curry Cabral, Centro Hospitalar Universitário de Lisboa Central, Lisboa, Portugal; 3:SYNLAB Portugal, Lisboa, Portugal; 4:Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; 5:Global Health and Tropical Medicine, GHTM, LA-REAL, Instituto de Higiene e Medicina Tropical, IHMT, Universidade NOVA de Lisboa, Lisboa, Portugal

Globally, endemic multidrug-resistant (MDR) strains of Mycobacterium tuberculosis pose a significant risk to tuberculosis (TB) management and control. Its continued circulation enables compensatory evolution and accumulation of additional mutations, potentially impacting resistance levels and clinical outcome. In Portugal, MDR-TB has been historically linked with two unusual endemic clades: Lisboa3 and Q1, whose microevolutionary trajectory over the last five decades is herein studied and integrated into pharmacokinetic models. This study comprises 40 representative clinical isolates, all of which were subjected to whole-genome sequencing and for which the minimum inhibitory concentration (MIC) of 12 anti-TB drugs was determined by broth microdilution. Pharmacokinetic (PK) models were generated to ascertain the maximum concentration to which each drug remains efficacious according to previously established targets. Drug resistance phenotypes were quantified and compared across distinct allelic configurations. Strains harboring dual mutations in inhA and embA/B loci exhibited significantly elevated MICs for isoniazid and ethambutol, respectively, relative to isolates with single-site mutations. Statistically significant intergroup differences in resistance levels were observed across phylogenetic lineages for rifamycin, streptomycin, and ethionamide, largely attributable to the differential distribution of high-level resistance-conferring genotypes. Pharmacokinetic/pharmacodynamic (PK/PD) simulations for isoniazid and moxifloxacin indicated that increased dosing regimens are unlikely to overcome resistance in strains possessing double inhA mutations or gyrA/B alterations. Only cycloserine and para-aminosalicylic acid maintained predicted efficacy against most clinical isolates. Comprehensive genotypic profiling of resistance-associated mutations is essential for optimizing therapeutic strategies in TB, as discrete allelic profiles markedly influence resistance levels and treatment outcomes.