Ferrous Sulfate Supplementation Causes Significant Gastrointestinal Side-Effects in Adults: A Systematic Review and Meta-Analysis

<div><p>Background</p><p>The tolerability of oral iron supplementation for the treatment of iron deficiency anemia is disputed.</p><p>Objective</p><p>Our aim was to quantify the odds of GI side-effects in adults related to current gold standard oral iron therapy, namely ferrous sulfate.</p><p>Methods</p><p>Systematic review and meta-analysis of randomized controlled trials (RCTs) evaluating GI side-effects that included ferrous sulfate and a comparator that was either placebo or intravenous (IV) iron. Random effects meta-analysis modelling was undertaken and study heterogeneity was summarised using <i>I²</i> statistics.</p><p>Results</p><p>Forty three trials comprising 6831 adult participants were included. Twenty trials (n = 3168) had a placebo arm and twenty three trials (n = 3663) had an active comparator arm of IV iron. Ferrous sulfate supplementation significantly increased risk of GI side-effects versus placebo with an odds ratio (OR) of 2.32 [95% CI 1.74–3.08, <i>p</i><0.0001, <i>I²</i> = 53.6%] and versus IV iron with an OR of 3.05 [95% CI 2.07-4.48, <i>p</i><0.0001, <i>I²</i> = 41.6%]. Subgroup analysis in IBD patients showed a similar effect versus IV iron (OR = 3.14, 95% CI 1.34-7.36, <i>p</i> = 0.008, <i>I²</i> = 0%). Likewise, subgroup analysis of pooled data from 7 RCTs in pregnant women (n = 1028) showed a statistically significant increased risk of GI side-effects for ferrous sulfate although there was marked heterogeneity in the data (OR = 3.33, 95% CI 1.19-9.28, <i>p</i> = 0.02, <i>I²</i> = 66.1%). Meta-regression did not provide significant evidence of an association between the study OR and the iron dose.</p><p>Conclusions</p><p>Our meta-analysis confirms that ferrous sulfate is associated with a significant increase in gastrointestinal-specific side-effects but does not find a relationship with dose.</p></div

Meta-regression analysis of the association between daily iron dose and the odds ratio of gastrointestinal side-effects.

<p><b>A,</b> data from 20 placebo-controlled RCTs (n = 3168); <b>B,</b> data from 23 IV iron-controlled RCTs (n = 3663). Individual studies are represented by circles, with the size of the circle being inversely proportional to the variance of the estimated effect (i.e the larger the circle, the more precise the estimated effect). The dotted lines represent the regression line for the analysis. Closed circles, studies with modified release ferrous sulfate; open circles, studies with conventional ferrous sulfate (i.e. not modified-release). All studies used daily posology.</p

Forest plot for the effect of daily ferrous sulfate supplementation on the incidence of gastrointestinal side-effects in placebo-controlled RCTs.

<p>Data for random-effects meta-analysis are shown. For each study the closed diamond represents the mean estimated effect and the horizontal lines the 95% CI. The grey shaded area surrounding each closed diamond represents the weight of each study in the analysis. Weight was assigned based on the (inverse of) the sum of the within-study variance and between study variance. Open diamonds represent the subgroup mean difference and pooled overall mean differences as shown. Test for overall effect: z-score = 7.54 (other), 0.20 (pregnant), 5.79 (overall); <i>p</i>-value <0.0001 (other), = 0.8 (pregnant), <0.0001 (overall). OR, odds ratio; CI, confidence interval. Data shown for 20 RCTs (n = 3168).</p

Study flow diagram.

<p>RCT, randomized controlled trial; ICU, intensive care unit. (1) This study was carried out by the co-authors and is currently submitted for publication and under review. A list compiling the 88 references that were not obtained is provided in Table A in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117383#pone.0117383.s002" target="_blank">S1 File</a>.</p

Randomized controlled trials with an intravenous iron comparator arm/group included in the meta-analysis.

<p>Six out of the 23 studies contained a co-intervention in both arms as indicated.</p><p>Abbreviations: M, male; F, female; CKD, chronic kidney disease; IBD, inflammatory bowel disease; NR, not reported or unclear; GISEs, gastrointestinal side effects shown as percentage of patients that experience gastrointestinal side-effects; Hb, hemoglobin;FeSO₄, ferrous sulfate group; IV, intravenous iron group; slow-Fe, modified-release ferrous sulfate.</p><p>⁽¹⁾ Iron dose in the FeSO4 group, unless indicated all trials used standard ferrous sulfate (i.e. not modified-release) and daily posology. Tardyferon® used in studies [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117383#pone.0117383.ref056" target="_blank">56</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117383#pone.0117383.ref057" target="_blank">57</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117383#pone.0117383.ref061" target="_blank">61</a>] and Ferrogradumet-Abbot used in study [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117383#pone.0117383.ref058" target="_blank">58</a>].</p><p>⁽²⁾ There was no statistically significant difference in baseline hemoglobin between the ferrous sulfate and the IV iron arms/groups.</p><p>⁽³⁾ Co-intervention: recombinant erythropoietin.</p><p>⁽⁴⁾ Co-intervention: mebendazole and folic acid.</p><p>⁽⁵⁾ Co-intervention: vitamin B12 and folic acid.</p><p>⁽⁶⁾ Co-intervention: folic acid.</p><p>Randomized controlled trials with an intravenous iron comparator arm/group included in the meta-analysis.</p

Individual side-effects reported in the FeSO₄ group/arm for the studies where this information was available.

<p>Data show for number of subjects reporting each individual symptom.</p><p>Individual side-effects reported in the FeSO₄ group/arm for the studies where this information was available.</p

Effect of daily ferrous sulfate supplementation on the incidence of gastrointestinal side-effects and hemoglobin repletion in intravenous iron-controlled RCTs.

<p><b>A,</b> Forest plot for random-effects meta-analysis of the effect of ferrous sulfate supplementation on the incidence of gastrointestinal side-effects against intravenous iron. For each study the closed diamond represents the mean estimated effect and the horizontal lines the 95% CI. The grey shaded area surrounding each closed diamond represents the weight of each study in the analysis. Weight was assigned based on (inverse of) the sum of the within-study variance and between study variance. Open diamonds represent the subgroup mean difference and pooled overall mean differences as shown. Test for overall effect: z-score = 4.36 (other), 3.05 (pregnant), 2.63 (IBD), 5.67(overall); <i>p</i>-value <0.0001 (other), = 0.002 (pregnant), = 0.008 (IBD), <0.0001 (overall). OR, odds ratio; CI, confidence interval. <b>B,</b> Hemoglobin increase in both ferrous sulfate (FeSO₄) and intravenous iron (IV iron) arms from baseline (open circles) to end of study intervention (closed circles). Data shown for 20 RCTs (n = 3261).</p

Ferritin-protein levels in Caco-2 cells following exposure to LM Fe(III) poly oxo-hydroxide (nano Fe), Fe(III) maltol (FeM) or Fe(II) sulphate-ascorbate (FeSO₄ + AA).

<p><b>A</b>, Ferritin-protein regulation in differentiated and undifferentiated cells. ***, <i>p</i>=0.0003. Cells were incubated for 1 h with 200 μM Fe plus a further 23 h in fresh, non-supplemented MEM to allow for ferritin formation. <b>B</b>, Phase distribution of Fe in the BSS uptake medium: i.e. fractional percentage of microparticulate (black bars), nanoparticulate (red bars) and soluble Fe (open bars) for each Fe material. Values are mean ± s.d. of 3 independent experiments. <b>C</b>, Effect of LM Fe(III) poly oxo-hydroxide particle dispersion (in BSS medium, closed bars) or agglomeration (in MEM medium, open bars) on ferritin-protein levels in differentiated cells: the LM Fe(III) poly oxo-hydroxide was dispersed in its nano-form (99 ± 2% nano) using BSS or agglomerated (97 ± 2% microparticulate) using MEM. Data are mean of 3 independent experiments (each experiment with 3 replicate wells). FeM: soluble iron control, Fe(III) maltol. ***, <i>p</i>=0.0002 for the comparison between BSS and MEM. <b>D</b>, TEER changes in differentiated Caco-2 cell monolayer at different time points during incubation with BSS supplemented with LM Fe(III) poly oxo-hydroxide (open circles) or non-supplemented BSS control (closed inverted triangles). Incubations were for 3 h with 200 μM Fe (measurements at 1, 2 & 3 h) plus a further 21 h in fresh, non-supplemented MEM (24-h). Values are expressed as a percentage of the initial measurement and are shown as mean ± s.d. of 3 independent experiments (each experiment with 3 replicate wells). Experimental points are connected with a solid line to aid visualization and not because a linear relationship is assumed between time and TEER measurement. Detailed methodology is available in the Methods Section and in Methods S1.</p

Lysososmal dissolution of LM Fe(III) poly oxo-hydroxide.

<p><b>A</b>, Solubility in simulated lysosomal conditions at pH 5.0 with 10 mM citric acid and 0.15 M NaCl. Soluble Fe was measured by ICP-OES following 5 min ultrafiltration (3000 Da MWCO) for the LM Fe(III) poly oxo-hydroxide (black) and for un-modified Fe(III) poly oxo-hydroxide (solid blue). Nanoparticulate Fe was obtained from the Fe in the supernatant following centrifugation excluding the soluble (ultrafilterable) Fe, and is shown for LM Fe(III) poly oxo-hydroxide (red) and for un-modified Fe(III) poly oxo-hydroxide (dotted blue). Values are plotted as mean ± s.d. of 3 independent experiments (each experiment with 3 replicates). <b>B</b>, Effect of inhibition of lysosomal acidification using monensin on Fe utilization by differentiated Caco-2 cells. Data are shown as a percentage of the control (without monensin) at 24 h: i.e. 1 h exposure to 200 µM nanoparticulate LM Fe(III) poly oxo-hydroxide (open circles) or Fe(III) maltol (closed squares) ± 5-30 µM monensin followed by 23 h in non-supplemented MEM. Results are means ± s.d. of 3 independent experiments (each experiment with 3 replicate wells). **, <i>p</i><0.005; ***, <i>p</i><0.001 in relation to the soluble Fe control (Fe(III)maltol). <b>C</b>, Change in TEER in the Caco-2 cell monolayer following 1 h exposure to 10 μM monensin (closed squares), 30 μM monensin (open diamonds) or non-supplemented BSS control (closed inverted triangles) and with 23 h further incubation in fresh MEM (24 h in total). Values are expressed as a percentage of the initial measurement at the start of the exposure time (corresponding to 0 h) and are shown as mean ± s.d. of 2 independent experiments (each experiment with 3 replicate wells). Experimental points are connected with a solid line to aid visualization and not because a linear relationship is assumed between time and TEER measurement. ***, <i>p</i>=0.0003; ****, <i>p</i><0.0001 in relation to the non-supplemented BSS control.</p

Characterisation of hydrolysed Fe(III) with simulated digestion and of aquated LM Fe(III) poly oxo-hydroxide.

<p><b>A</b>, Transmission Electron Microscopy (TEM) images collected from a drop of suspension after simulated digestion of 1 mM Fe(III) chloride in the presence of 2 g/L mucin and low molecular weight ligands. The boxed regions are shown magnified below and highlight the presence of fine, poorly crystalline nanoparticles dispersed in an amorphous gel. Crystallinity is indicated by the spots in the inset diffractograms (fast Fourier transforms) in the boxed regions and lattice spacings are discussed in the main text. Scale bar represents 5 nm. <b>B</b>, Whole area EDX analysis of a particle agglomerate similar to those in ‘A’ shows elemental compositions (the specimen support film and grid produce the background C and Cu signals respectively). <b>C</b>, Hydrodynamic size distribution of nanoparticulate 500 µM LM Fe(III) poly oxo-hydroxide in balanced salt solution (BSS) measured by Dynamic Light Scattering (DLS). Values are expressed as mean diameter ± s.d. (3 independent measurements) on a log₁₀ scale.</p