Emphasis added.

“The intracellular VC concentration is strictly regulated in order to maintain levels of 80–100 μM in the plasma [2, 3]. However, intravenous injection bypasses this strict regulation, allowing specific VC concentrations to be maintained within a specified period, thereby providing a pharmacological basis for its therapeutic application [4]. Several pioneering studies have demonstrated the efficacy of pharmacological VC in improving the survival of patients with advanced cancers [5, 6]. In contrast, two randomized double-blind controlled trials failed to demonstrate any benefit of VC against advanced malignant disease [7, 8]. Therefore, the route of administration is important for high-dose VC to have a therapeutic effect, and only intravenous administration results in sufficiently high plasma and urine concentrations to allow potential antitumor activity [9].”