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Oral L-carnitine supplementation increases trimethylamine-N-oxide but reduces markers of vascular injury in hemodialysis patients.Journal of cardiovascular pharmacology,65(3), 289-295

Integrative computational approach identifies drug targets in CD4 + T-cell-mediated immune disorders
doi:10.1186/s12864-020-06944-w 19

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The key mechanism for this seems to be renal re-absorption that displays saturation kinetics