Reviews/Iron Status/Intravenous iron beats oral in inflammatory bowel disease
Ivd · IRON-IVD-02 · v2
Five head-to-head trials compared intravenous iron with oral iron in people with inflammatory bowel disease, and they do not all point the same way. Modern intravenous iron (ferric carboxymaltose) worked faster and restored iron stores better in some trials [2],[10], and higher ferritin with intravenous iron also appeared in [5] and [7]. But the largest direct comparison [5] failed to prove the intravenous agent even matched oral iron, and actually leaned toward oral for raising haemoglobin. Over longer follow-up the haemoglobin results tended to even out between the two routes [2],[7],[10], and by one measure of lost work time oral iron came out ahead [9]. So the panel found real but uneven support: an advantage that depends on the specific agent, the outcome measured, and how early it is measured, rather than a clean across-the-board win.
The on-claim corpus consists of five randomised intravenous-vs-oral trials in inflammatory bowel disease [2],[5],[7],[9],[10]. Intravenous ferric carboxymaltose beat oral ferric maltol on 12-week haemoglobin responder rate (67% and 68% vs 84% and 85%) with oral failing non-inferiority [2], and intravenous ferric carboxymaltose was superior for quick improvement of physical fitness in children [10]. Higher ferritin with intravenous iron was reported in [5] and [7]. However [5], the largest comparison (N=327), could not demonstrate non-inferiority and showed a trend for oral iron sulfate being more effective on haemoglobin, while long-term haemoglobin converged in [2] (comparable over 52 weeks), [7] and [10] (comparable Hb increase). On productivity, oral ferric maltol carried no treatment-linked loss whereas intravenous administration did [9]. The contested point: The evidence divides on whether intravenous iron's advantage is genuine and general or narrow and agent-specific. The direction flips with the agent used — ferric carboxymaltose favoured intravenous [2],[10] while iron isomaltoside trended toward oral [5] — and the haemoglobin benefit that appears early does not persist as the trials mature [2],[7],[10].
All 10 papers behind this claim with their DOIs and what each does to it, the panel’s arbitration, the evidence gap map and the open research questions. Free, and sent to your inbox.
We’ll also send you other claims from Iron Status, one at a time, and tell you when a release or a pivotal trial changes a grade. Unsubscribe by replying.
One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
PROCEED [5], the largest IV-vs-oral trial in the corpus (N=327), failed to demonstrate IV non-inferiority and trended toward oral iron sulfate being more effective on haemoglobin — a direct contradiction of the superiority claim.
'IV iron' is not one entity: superiority appears with ferric carboxymaltose ([2],[10]) but not with iron isomaltoside ([5]). The claim over-generalises across agents that behave differently.
Where it remains uncertain. The largest trial [5] failed to show intravenous non-inferiority and trended toward oral on haemoglobin, and long-term haemoglobin converged across [2], [7] and [10].
Aleatory
Several on-claim trials are small (N=72 in [7], N=64 in [10]), leaving outcome estimates sensitive to chance.
The load-bearing papers from a corpus of 10, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
IV FCM had a markedly higher early responder rate than oral ferric maltol, which failed non-inferiority — supports early IV superiority.
“Both treatments had comparable long-term effectiveness for hemoglobin and ferritin over 52 weeks and were well tolerated.”
Panel auditInternal validity: medium · scope of inference: Adults with nonseverely active IBD and iron-deficiency anemia, Hb response over 12 to 52 weeks.Key limitations: open-label · IV dose not standardized across centers · advantage at wk12 attenuated to comparable by 52 weeks
Similar clinical benefit by route; IV superiority limited to iron stores.
“Both PO and IV treatments ameliorated iron deficiency, but higher ferritin levels were observed with IV. Changes in disease activity were independent of iron treatment types.”
Panel auditInternal validity: low · scope of inference: IBD and iron-deficient patients, effect of oral vs IV iron on gut microbiota, metabolome, and clinical iron correction.Key limitations: open-label · small n · primary focus microbiome not clinical efficacy · IV gave higher ferritin
IV superiority is early and transient; haemoglobin outcomes are comparable by route.
“a single dose of IV ferric carboxymaltose was superior to oral ferrous fumarate with respect to quick improvement of physical fitness. At 3 and 6 months after initiation of therapy, no differences were discovered between oral and IV therapies. The increase of Hb over time was comparable in both treatment groups.”
Panel auditInternal validity: medium · scope of inference: Anemic children aged 8-18 with IBD, physical fitness and Hb over 6 months.Key limitations: small n · advantage only at 1 month, gone by 3 and 6 months · Hb increase comparable between groups · pediatric population
Largest IV-vs-oral trial here contradicts the claim on haemoglobin — a direct counter.
Panel auditInternal validity: medium · scope of inference: IBD patients in remission or mild disease tolerant of oral iron, change in Hb to week 8.Key limitations: open-label · excluded oral-iron-intolerant patients · authors suggest IV dose underestimated by Ganzoni formula · IV raised ferritin more despite Hb trend favouring oral
4 of 10 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
Genuine but inconsistent head-to-head support — IV wins on speed and iron stores yet not durably on haemoglobin and not with every agent — warrants an Uncertain tier.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Ferric carboxymaltose vs oral iron on durable haemoglobin. The intravenous win is concentrated early [2],[10] and converges long-term, so a trial powered on 6-12 month haemoglobin would test durability. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: Adequately powered randomised trial of ferric carboxymaltose vs an oral iron with a primary endpoint at 6-12 months.
Open question: Does the early haemoglobin and fitness advantage of ferric carboxymaltose persist beyond 3-6 months? Why it is still open: Advantage seen early in [2],[10] but haemoglobin converges by 52 weeks [2] and at 3-6 months [10].
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 18 Sep 2026 · protocol v0.19