Fractionated high-dose vitamin c sustains higher plasma trough concentrations in advanced solid tumors: a phase I clinical study

Highlights

• •Fractionated HDVC dosing achieves higher trough levels than once-daily dosing.
• •Further dose escalation provides no additional trough concentration benefit.
• •All regimens are safe and well tolerated in advanced solid tumors.
• •Provides a PK rationale for future phase II trials in solid tumor patients.

Abstract

High-dose vitamin C (HDVC) has a short half‑life of approximately 2 h, and once‑daily dosing results in sub‑therapeutic plasma concentrations for most of the dosing interval, potentially limiting its pro‑oxidant antitumor activity. In this phase I study, 18 patients with advanced solid tumors were assigned to three cohorts (n = 6 each): Group A (0.5 g/kg once daily, total daily dose 0.5 g/kg), Group B (0.5 g/kg every 12 h, total daily dose 1.0 g/kg), and Group C (0.75 g/kg every 12 h, total daily dose 1.5 g/kg). Plasma trough concentrations were measured daily for 7 days. Compared to Group A, Group B exhibited significantly higher trough concentrations throughout the study (P < 0.05), demonstrating superior maintenance of therapeutic levels. Further dose escalation to 0.75 g/kg twice daily (Group C) provided no additional trough concentration benefit versus Group B (P > 0.05), consistent with the plateau in peak concentrations at single doses above approximately 70 g/m² (∼1.0 g/kg). All regimens were well tolerated, with only one mild nausea (5.6%) and no serious adverse events. Fractionated dosing (0.5 g/kg every 12 h) significantly improves trough concentration maintenance with good tolerability. This optimized regimen (total daily dose 1.0 g/kg) provides a rational pharmacokinetic basis for future phase II trials designed to evaluate whether sustained pro‑oxidant levels translate into enhanced clinical efficacy.

Introduction

Vitamin C (ascorbic acid) is an essential water‑soluble nutrient with well‑known antioxidant properties. However, at pharmacological concentrations that can only be achieved by intravenous administration (typically >1 mM), vitamin C paradoxically acts as a pro‑oxidant. Through Fenton chemistry, it generates hydrogen peroxide (H₂O₂) in the extracellular fluid, which selectively induces oxidative stress and cell death in cancer cells while sparing most normal cells [1,2]. This redox‑based mechanism has attracted substantial interest in oncology over the past two decades. Preclinical studies have demonstrated that high‑dose vitamin C (HDVC) can synergize with chemotherapy (e.g., gemcitabine, platinum agents) and radiotherapy in a variety of malignancies [[3], [4], [5], [6], [7]].

Despite the robust preclinical rationale, clinical trials of HDVC have yielded inconsistent results. Early non‑controlled studies by Cameron and Pauling suggested survival benefits in advanced cancer patients [8,9], but subsequent randomized controlled trials at the Mayo Clinic using oral vitamin C showed no benefit [10,11]. The failure of oral administration is now well understood: oral vitamin C absorption is tightly regulated by intestinal sodium‑dependent vitamin C transporters, and plasma concentrations plateau at about 70–80 µM even with very high oral doses [12]. In contrast, intravenous administration bypasses intestinal absorption and can achieve millimolar plasma levels that are required for pro‑oxidant activity.

Several phase I trials have established the safety and pharmacokinetics of intravenous HDVC. Hoffer et al. [13] treated patients with advanced malignancies using doses up to 1.5 g/kg (approximately 56 g/m²) and reported peak plasma concentrations of about 26 mM, with no dose‑limiting toxicities. Stephenson et al. [14] escalated doses to 110 g/m² (approximately 1.5–2.0 g/kg) and achieved peak concentrations of 49 mM, again showing good tolerability. In pancreatic cancer, Welsh et al. [15] combined HDVC with gemcitabine in a phase I/II trial and reported disease stabilization in several patients without added toxicity.

More recently, important clinical studies have highlighted the importance of dosing frequency. In metastatic pancreatic cancer, Bodeker et al. [16] conducted a randomized phase II trial comparing gemcitabine plus nab‑paclitaxel with or without HDVC (75 g three times weekly). The addition of HDVC significantly improved median overall survival from 8.3 to 16.0 months (hazard ratio 0.46, P = 0.030) and progression‑free survival from 3.9 to 6.2 months (hazard ratio 0.43, P = 0.029), without increasing toxicity or impairing quality of life. This represents a highly encouraging result. In contrast, the phase III VITALITY trial in metastatic colorectal cancer [17] administered HDVC (1.5 g/kg on days 1–3 of each 14‑day cycle) and found no improvement in progression‑free survival, although post‑hoc analyses suggested potential activity in KRAS‑mutant tumors [18]. A randomized placebo‑controlled phase II trial in metastatic castration‑resistant prostate cancer using docetaxel with or without HDVC (1 g/kg every 3 weeks) was negative, with a trend toward shorter survival in the HDVC arm [19]. Our own institution has reported feasibility and safety of HDVC combined with neoadjuvant chemoradiotherapy in locally advanced rectal cancer, as well as efficacy in treating severe radiation proctitis [20,21].

These heterogeneous outcomes underscore the critical need for optimized dosing strategies. A key pharmacokinetic factor limiting efficacy is the short half‑life of vitamin C at pharmacological doses. Unlike physiological concentrations (where half‑life is 8–40 days due to renal reabsorption), intravenous millimolar doses saturate the renal sodium‑dependent vitamin C transporters, shifting elimination to first‑order kinetics with a half‑life of approximately 2 h [12,14,[22], [23], [24]]. After a single infusion, plasma concentrations decline exponentially and return to near‑baseline levels within 12–16 h [14]. Consequently, once‑daily or intermittent dosing schedules may leave most of the dosing interval with sub‑therapeutic levels that are insufficient to sustain continuous H₂O₂ generation and pro‑oxidant pressure on tumors.

We therefore hypothesized that increasing dosing frequency to every 12 h could better maintain trough concentrations of vitamin C, thereby providing a more sustained pro‑oxidant environment. This phase I clinical study was designed to compare the pharmacokinetic profiles of three dosing regimens in patients with advanced solid tumors: (1) once‑daily 0.5 g/kg, (2) twice‑daily 0.5 g/kg, and (3) twice‑daily 0.75 g/kg. The primary objective was to determine whether fractionated dosing improves trough concentration maintenance; secondary objectives were to assess safety and explore tumor marker responses.

Materials and methods

Study design and ethical approval

This was a single‑center, open‑label, phase I clinical trial conducted at xxxxxx between April 2025 and October 2025. The study protocol was approved by the Institutional Ethics Committee (approval number xxxxx) and registered at ClinicalTrials.gov (NCTxxxxxx). All procedures were performed in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. Written informed consent was obtained from every patient before any study‑related procedures.

Patient eligibility

Inclusion criteria: (1) histologically or cytologically confirmed advanced solid tumors (unresectable or metastatic); (2) age 18–75 years; (3) Eastern Cooperative Oncology Group performance status 0–2; (4) life expectancy ≥3 months; (5) adequate bone marrow, liver, and renal function: absolute neutrophil count ≥1.5 × 10⁹/L, platelets ≥80 × 10⁹/L, hemoglobin ≥90 g/L, total bilirubin ≤2.0 × upper limit of normal (ULN), alanine aminotransferase and aspartate aminotransferase ≤3.0 × ULN (≤5.0 × ULN in the presence of liver metastases), serum creatinine ≤1.5 × ULN or creatinine clearance ≥60 mL/min.

Exclusion criteria: (1) known glucose‑6‑phosphate dehydrogenase (G6PD) deficiency (mandatory screening); (2) renal insufficiency (estimated glomerular filtration rate <60 mL/min); (3) history of oxalate nephropathy or nephrolithiasis; (4) concomitant use of warfarin or other anticoagulants; (5) pregnancy or lactation; (6) known hypersensitivity to vitamin C or any component of the formulation; (7) any other condition judged by the investigator to interfere with compliance or safety.

Dosing regimens

Patients were sequentially enrolled into three cohorts of 6 patients each. Group A: Vitamin C 0.5 g/kg once daily (total daily dose 0.5 g/kg) for 7 consecutive days. Group B: Vitamin C 0.5 g/kg every 12 h (total daily dose 1.0 g/kg) for 7 consecutive days. Group C: Vitamin C 0.75 g/kg every 12 h (total daily dose 1.5 g/kg) for 7 consecutive days.

All patients had a central venous catheter placed for safe infusion of hyperosmolar solutions. The calculated dose of vitamin C (commercial injection, 0.5 g/mL) was diluted in 250 mL of 0.9% sodium chloride and infused using an infusion pump at a constant rate over 60–90 min. Patients were closely monitored during the infusion and for 30 min afterward. Concomitant standard antitumor therapies (chemotherapy, targeted therapy, or immunotherapy) were continued as per the treating physician’s discretion, and all concomitant medications were recorded.

Blood sampling and vitamin C assay

Blood samples were collected at the following time points. Baseline: fasting venous blood immediately before the first dose. Early post‑dose: 1 hour after completion of the first infusion (approximating peak concentration, since infusion duration was 60–90 min). Trough concentration: every morning before the first daily dose for 7 consecutive days (reflecting the minimum concentration at the end of the dosing interval).

For each sample, 4 mL of blood was drawn into heparinized tubes and immediately centrifuged at 4 °C (3000 rpm, 10 min). The plasma was then mixed with an equal volume of 10% metaphosphoric acid to stabilize vitamin C and prevent oxidation. Stabilized plasma was stored at –80 °C until analysis.

Plasma vitamin C concentrations were measured by high‑performance liquid chromatography (HPLC) using a C18 reversed‑phase column. The mobile phase consisted of phosphate buffer and methanol (85:15, v/v) at a flow rate of 1.0 mL/min. Detection was performed at 245 nm, and the column temperature was maintained at 25 °C. The assay was validated for linearity, precision, and recovery according to published methods [25,26].

Safety monitoring

Adverse events were recorded from the time of informed consent until 7 days after the last dose and were graded using the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Special attention was given to HDVC‑related adverse events, including nausea, vomiting, diarrhea, headache, flushing, injection site pain, hypercalcemia, hypotension, and hemolysis. All patients underwent mandatory G6PD screening before enrollment.

Statistical analysis

All statistical analyses were performed using SPSS version 26.0. Continuous variables are presented as mean ± standard deviation (SD) or median (range), and categorical variables as numbers (percentages). Baseline demographic and clinical characteristics were summarized descriptively; no formal statistical comparisons were performed due to the small sample size (n = 6 per group). Comparisons of plasma ascorbate concentrations among the three groups at a single time point were performed using one-way analysis of variance (ANOVA), followed by multiple-comparison tests for pairwise comparisons. Dynamic changes in plasma ascorbate concentrations over time and between-group differences during the study period were analyzed using two-way ANOVA, followed by multiple comparisons. All statistical tests were two-sided, and a P value < 0.05 was considered statistically significant. Adverse events were tabulated without statistical comparisons.

Results

Patient characteristics

A total of 18 eligible patients with advanced solid tumors were enrolled. Baseline characteristics are summarized in Table 1. The cohort consisted of pancreatic cancer (n = 9, 50%), hepatocellular carcinoma (n = 3, 16.7%), cholangiocarcinoma (n = 3, 16.7%), colorectal cancer (n = 1, 5.6%), and soft tissue sarcoma (n = 2, 11.1%). Baseline plasma vitamin C concentrations did not differ significantly among the three groups (P > 0.05; Fig. 1).

Table 1.

Baseline demographic and clinical characteristics.

Characteristic	Group A (n = 6)	Group B (n = 6)	Group C (n = 6)
Age (years)
Mean ± SD	60.3 ± 6.1	60.7 ± 7.8	54.3 ± 11.7
Gender [n (%)]
Female	2 (33.3%)	4 (66.7%)	2 (33.3%)
Male	4 (66.7%)	2 (33.3%)	4 (66.7%)
Tumor types [n (%)]
Hepatocellular carcinoma	2 (33.3%)	0 (0%)	1 (16.7%)
Cholangiocarcinoma	0 (0%)	2 (33.3%)	1 (16.7%)
Pancreatic cancer	4 (66.7%)	2 (33.3%)	3 (50.0%)
Colonic adenocarcinoma	0 (0%)	1 (16.7%)	0 (0%)
Soft tissue sarcoma	0 (0%)	1 (16.7%)	1 (16.7%)
ECOG PS [n (%)]
1	6 (100.0%)	5 (83.3%)	5 (83.3%)
2	0 (0%)	1 (16.7%)	1 (16.7%)
Current line of therapy [n (%)]
1	2 (33.3%)	3 (50.0%)	1 (16.7%)
2	4 (66.7%)	2 (33.3%)	4 (66.7%)
3	0 (0%)	1 (16.7%)	0 (0%)
4	0 (0%)	0 (0%)	1 (16.7%)

Data are presented as mean ± SD or n (%). SD, standard deviation; ECOG PS, Eastern Cooperative Oncology Group performance status.

Fig. 1.

Baseline plasma vitamin C concentrations in the three groups. Data are presented as mean ± SD (n = 6 per group). Group differences were analyzed by one-way ANOVA, followed by multiple-comparison tests for pairwise comparisons. HPLC-DAD, high-performance liquid chromatography with diode-array detection; SD, standard deviation. ns, not significant.

Study timeline and peak concentrations

The experimental timeline for vitamin C infusion and blood sample collection is illustrated in Fig. 2. Plasma vitamin C concentrations measured at 1 hour after completion of the first infusion are shown in Fig. 3. Group C (0.75 g/kg) achieved significantly higher peak concentrations compared to Group A (0.5 g/kg once daily, P < 0.05) and Group B (0.5 g/kg every 12 h, P < 0.05). There was no significant difference between Group A and Group B (P > 0.05). These results demonstrate that peak concentration is primarily determined by the single‑dose amount rather than dosing frequency.

Fig. 2.

Schematic diagram of the study timeline for intravenous vitamin C infusion and blood sample collection from Day 1 to Day 7.

Fig. 3.

Plasma ascorbate concentrations at 1 h after completion of the first infusion. Data are presented as mean ± SD. Group comparisons were performed using one-way ANOVA, followed by multiple-comparison tests for pairwise comparisons. n = 6 per group. ns, not significant; *P < 0.05; **P < 0.01.

Steady‑state trough concentrations

Plasma vitamin C concentrations measured before the first daily infusion on Day 1 represented baseline levels. For Days 2–7, concentrations measured before the first daily infusion reflected the steady‑state trough concentrations achieved after the previous day’s infusions. Plasma ascorbate concentrations increased markedly after intravenous vitamin C infusion in all three groups (Table 2).

Table 2.

Summary of plasma ascorbate concentrations.

Parameter	Group A (n = 6)	Group B (n = 6)	Group C (n = 6)
Total daily dose (g/kg)	0.5	1.0	1.5
Baseline concentration (mg/dL)	0.84 ± 0.54	0.83 ± 0.35	0.49 ± 0.25
Steady-state trough concentration (mg/dL, mean ± SD)
Day 1	1.94 ± 0.49	8.89 ± 3.31	5.21 ± 2.42
Day 2	2.03 ± 0.60	8.42 ± 4.10	5.27 ± 1.43
Day 3	1.90 ± 0.46	7.53 ± 2.97	5.39 ± 2.21
Day 4	2.01 ± 0.41	7.26 ± 3.40	6.42 ± 4.42
Day 5	2.02 ± 0.43	7.19 ± 3.40	6.98 ± 6.60
Day 6	1.89 ± 0.36	6.84 ± 2.58	7.12 ± 5.69*
concentrations at 1 h after completion of the first infusion (mg/dL, mean ± SD)	116.34 ± 33.70	105.66 ± 7.94	152.58 ± 7.79

* Group C, Day 6: n = 5. And the concentrations on Days 2–7 represent plasma ascorbate levels measured before the first daily infusion on each study day and correspond to the trough concentrations achieved after the previous infusion on Days 1–6, respectively.

As shown in Fig. 4, all groups exhibited increased plasma vitamin C concentrations after HDVC infusion compared to baseline. Group B consistently maintained higher trough concentrations than Group A throughout the study period (P < 0.05 for all days). In the early phase of treatment, there were no significant differences in trough concentrations between Group C and Group A (all P > 0.05). However, starting from the Day 5 measurement, Group C exhibited significantly higher trough concentrations compared to Group A (P < 0.05), and this difference persisted through the final measurement (all P < 0.01). In contrast, there were no significant differences in trough concentrations between Group B and Group C at any time point (all P > 0.05).

Fig. 4.

Changes in plasma ascorbate concentrations from Days 1 to 7. The Day 1 concentration represents the baseline level before the first infusion. Concentrations on Days 2–7 reflect steady‑state trough levels achieved after the infusions on Days 1–6, respectively. Data are presented as mean ± SD and analyzed using two-way ANOVA, followed by multiple-comparison tests for pairwise comparisons. The sample size was n = 6 for all groups, except for Group C on Day 7 (n = 5).ns, not significant; *P < 0.05; **P < 0.01.

These findings indicate that dosing frequency significantly influences steady‑state trough concentrations, and increasing administration frequency improves concentration maintenance. Under the same twice‑daily frequency, increasing the single dose from 0.5 to 0.75 g/kg did not translate into higher trough levels. This observation is consistent with the well‑established fact that peak concentrations reach a plateau at single doses above approximately 70 g/m² (∼1.0 g/kg) [14,24]. Moreover, the short half‑life of vitamin C (∼2 h) means that after a 12‑hour interval, the plasma concentration decays to only about 1.5% of the peak value; thus, once a certain dose threshold is exceeded, trough concentrations become primarily determined by the dosing interval rather than by the single‑dose amount.

Safety

High‑dose vitamin C was very well tolerated across all three dosing regimens. Only one patient (in Group C) experienced mild nausea (Grade 1), which occurred shortly after an infusion and resolved spontaneously without intervention. This corresponds to an overall incidence of treatment‑related adverse events of 5.6%. No other HDVC‑related adverse events were observed. Specifically, there were no cases of hemolysis (all patients had normal G6PD activity), hypotension, renal impairment, or electrolyte disturbances. No serious adverse events occurred during the study period.

Exploratory observations of tumor marker changes

During the study, we observed interesting tumor marker changes in two patients. Both patients had demonstrated progressively rising tumor markers while on stable systemic therapy prior to enrollment. Notably, during the 7‑day HDVC intervention, without any change to their concomitant antitumor regimens, both patients exhibited declines in their respective tumor markers.

Patient A‑03 (Group A, pancreatic cancer): CEA decreased from 10.3 to 7.99 ng/mL (↓22.4%), and CA19‑9 decreased from 1020 to 844.7 U/mL (↓17.2%) over the treatment week.

Patient B‑02 (Group B, hilar cholangiocarcinoma): CA125 decreased dramatically from 790 to 129.1 U/mL (↓83.7%) during the week of HDVC infusion.

These anecdotal observations, while not statistically evaluable, suggest potential antitumor activity of HDVC in some patients and warrant further investigation.

Discussion

This phase I clinical study provides direct pharmacokinetic evidence that fractionated dosing (0.5 g/kg every 12 h) significantly improves the maintenance of trough plasma concentrations of high‑dose vitamin C compared to once‑daily dosing in patients with advanced solid tumors. Moreover, further dose escalation to 0.75 g/kg twice daily (total daily dose 1.5 g/kg) did not yield any additional trough concentration benefit. The safety profile was excellent, with only one case of mild nausea and no serious adverse events.

Pharmacokinetic rationale for twice‑daily dosing

The short half‑life of vitamin C at pharmacological doses (approximately 2 h) is the key determinant of its elimination [12,14,[22], [23], [24]]. With a half‑life of 2 h, after a single infusion the plasma concentration falls by 50% every 2 h, reaching near‑baseline levels after about 12–16 h. Therefore, once‑daily dosing results in a “peak‑and‑trough” pattern with a long drug‑free interval during which plasma levels are likely too low to generate sufficient H₂O₂ for antitumor effects. By shortening the dosing interval to 12 h, we effectively prevented the excessive decline and maintained trough concentrations that were significantly higher than those achieved with once‑daily dosing. This finding is consistent with basic pharmacokinetic principles and supports the use of more frequent administration to sustain pro‑oxidant pressure.

Why further dose escalation did not increase trough concentrations

The lack of a significant increase in trough concentrations when escalating the twice‑daily dose from 0.5 to 0.75 g/kg can be explained by the pharmacokinetic characteristics of vitamin C at pharmacological doses. First, previous studies have demonstrated that peak concentrations reach a plateau at single doses above approximately 70 g/m² (∼1.0 g/kg) [14,24]. Our single‑dose of 0.5 g/kg (∼35 g for a 70‑kg patient) is well within the linear range, but the higher dose of 0.75 g/kg (∼52.5 g) approaches this plateau. Second, vitamin C distributes primarily in extracellular fluid with an apparent volume of distribution of approximately 0.2 L/kg [24]; this limited distribution space contributes to the non‑linear increase in peak concentrations at higher doses. Third, and most importantly, the short elimination half‑life (∼2 h) means that after a 12‑hour dosing interval, the plasma concentration decays to only about 1.5% of the peak value. Therefore, even though a higher single dose produces a higher peak, the trough concentration is predominantly determined by the dosing interval and the terminal half‑life, not by the single‑dose amount once a certain threshold is exceeded. Consequently, under a twice‑daily schedule, increasing the single dose from 0.5 to 0.75 g/kg provides minimal additional benefit in terms of trough concentration maintenance. This mechanistic understanding supports the recommendation of 0.5 g/kg every 12 h as the optimized regimen.

Redox implications

The antitumor activity of HDVC is believed to depend on sustained generation of H₂O₂ in the extracellular space, which in turn depends on maintaining millimolar concentrations of vitamin C [1,2,27]. Our pharmacokinetic data show that twice‑daily dosing provides significantly higher trough levels, which should translate into more continuous H₂O₂ production and therefore a more sustained pro‑oxidant insult to tumor cells. This is particularly relevant for tumors with defective antioxidant defenses, such as those with KRAS or BRAF mutations [5,18]. Recent studies have demonstrated that pharmacological ascorbate can induce oxidative stress in cancer cells by depleting intracellular glutathione and impairing the pentose phosphate pathway [28,29]. By maintaining higher trough concentrations, the twice‑daily regimen may enhance these effects.

Relationship to recent clinical trials

Our optimized regimen (0.5 g/kg every 12 h) is distinct from the intermittent schedules used in recent pivotal trials. The successful pancreatic cancer trial by Bodeker et al. [16] used a thrice‑weekly schedule (75 g per infusion), which still allows for 24‑ to 48‑hour intervals between doses. The negative VITALITY trial [17] used a regimen of 1.5 g/kg on days 1–3 of each cycle, which is also intermittent. Both of these schedules are likely to produce large fluctuations in plasma vitamin C levels, with long periods of sub‑therapeutic concentrations. In contrast, our twice‑daily regimen aims to provide a more continuous pro‑oxidant environment, which might be pharmacologically superior. The exploratory tumor marker responses we observed suggest that this strategy deserves further investigation, especially in tumors with KRAS mutations where synthetic lethality with HDVC has been proposed [5,18,30].

Safety in context of published literature

The excellent safety profile of HDVC in our study is consistent with a large body of published evidence. A systematic review by Yanase et al. [31] encompassing 74 studies and 2801 patients concluded that high‑dose intravenous vitamin C is safe when G6PD deficiency is excluded and appropriate monitoring is performed. The most common adverse events are mild gastrointestinal symptoms and transient electrolyte disturbances. Serious adverse events such as hemolysis, oxalate nephropathy, and hypernatremia are very rare and can be avoided by proper screening and fluid management.

Limitations and future directions

Several limitations should be acknowledged. First, the sample size is small (n = 6 per group), typical for a phase I trial, which precludes definitive conclusions about efficacy or rare adverse events. Second, the tumor types were heterogeneous, reflecting the real‑world population of a phase I study, but this limits tumor‑specific conclusions. Third, we did not collect urine samples to measure vitamin C and oxalate excretion. Fourth, our sampling schedule was limited to daily trough concentrations; more intensive sampling would be needed to fully characterize the concentration‑time profile and calculate individual half‑lives. However, trough concentration is a clinically meaningful metric for assessing drug level maintenance. Fifth, the observation period was only 7 days, and long‑term steady‑state kinetics remain unknown. Sixth, the tumor marker responses are anecdotal and must be interpreted with extreme caution; they are not proof of efficacy and could be due to natural fluctuations. Seventh, the multiple comparisons performed for daily trough concentrations were not corrected, and the nominal P values should be considered exploratory. Confirmatory studies are needed to validate these findings.

Future research should build on these findings by: (i) conducting larger phase II trials with efficacy endpoints using the optimized twice‑daily regimen, particularly in pancreatic cancer and cholangiocarcinoma; (ii) incorporating real‑time oxidative stress biomarkers to establish a pharmacokinetic/pharmacodynamic relationship; (iii) exploring whether even shorter intervals (e.g., 8‑hourly) could further improve trough concentrations; and (iv) prospectively collecting KRAS mutation status and other biomarkers to identify patients most likely to benefit.

Conclusion

In patients with advanced solid tumors, fractionated high‑dose vitamin C (0.5 g/kg every 12 h) sustains higher trough plasma concentrations compared to once‑daily dosing, with a favorable safety profile. Further dose escalation to 0.75 g/kg twice daily provides no additional benefit in trough concentration maintenance. The sustained trough concentrations achieved with the twice‑daily regimen may offer a pharmacological advantage over intermittent schedules by providing more continuous pro‑oxidant pressure. Exploratory tumor marker reductions in a pancreatic cancer patient and a cholangiocarcinoma patient provide preliminary signals of potential antitumor activity. The optimized regimen (0.5 g/kg every 12 h, total daily dose 1.0 g/kg) is recommended for future phase II trials designed to test whether sustained pro‑oxidant levels translate into enhanced clinical efficacy, particularly in KRAS‑mutant tumors. Such trials should incorporate oxidative stress biomarkers and efficacy endpoints to definitively address this question.

CRediT authorship contribution statement

Qing Yin: Conceptualization, Data curation, Formal analysis, Writing – original draft, Writing – review & editing. You Wang: Data curation, Formal analysis, Investigation, Project administration, Writing – original draft, Writing – review & editing. Han Wu: Conceptualization, Data curation, Formal analysis, Funding acquisition, Writing – original draft, Writing – review & editing. Qingqing Wang: Data curation, Conceptualization, Formal analysis, Writing – original draft, Writing – review & editing. Hui Xu: Conceptualization, Data curation, Formal analysis, Writing – original draft, Writing – review & editing. Xin long: Conceptualization, Data curation, Formal analysis, Writing – original draft, Writing – review & editing. Jin Peng: Conceptualization, Data curation, Formal analysis, Resources, Writing – original draft, Writing – review & editing. Jianyuan Wu: Conceptualization, Data curation, Formal analysis, Supervision, Writing – original draft, Writing – review & editing. Fuxiang Zhou: Conceptualization, Data curation, Formal analysis, Supervision, Writing – original draft, Writing – review & editing. Lei Yang: Conceptualization, Data curation, Formal analysis, Funding acquisition, Writing – original draft, Writing – review & editing.

Declaration of competing interest

None.