Hypoprothrombinemia (OR 1.676, 95% CI 1.275–2.203) and prothrombin time (PT) prolongation (OR 2.050, 95% CI 1.398–3.005) were significantly associated with NMTT-cephalosporins, whereas bleeding was not (OR 1.359, 95% CI 0.920–2.009). This evidence concerns the gene F2 and Congenital factor II deficiency.