Every so often, you see a medication order that just makes you tilt your head and think, “Huh?” One order that I recently encountered that made me scratch my head was (ferrous sulfate) iron 2 tablets once daily. On the surface, it’s straightforward – take two tablets at the same time and call it a day. But for iron, that’s not always the best approach, and in this post, I’ll explain why this dosing is a bad idea.
Iron Absorption
Iron absorption is saturable, which means that even if you increase the dose, it isn’t going to help the patient. Once you hit a certain dose, your gut can’t take up much more in a single sitting. This means if a patient takes two full tablets (often totaling 130–150 mg of elemental iron) at once, they’re likely not getting the full benefit. Ferrous sulfate contains approximately 65 mg of elemental iron per tablet (great board exam question!). Splitting the dose into two separate times can improve absorption and iron replenishment over the long haul.
Side Effects
Tolerability of iron is often a concern we have in practice. Iron is notorious for causing constipation, nausea, and abdominal cramping. Giving a big dose all at once increases the risk of those side effects. Patients who feel lousy from their iron are more likely to skip doses, making treatment less effective. Smaller, divided doses tend to be better tolerated.
Anemia Response Blunted
If iron isn’t absorbed optimally because of the “two-at-once” approach, you might see slower improvement in hemoglobin and ferritin levels. This could lead to prolonged anemia, extra lab draws, and even unnecessary workups if clinicians suspect treatment failure.
Consider splitting the dose into one tablet twice daily or even alternate-day dosing, which some newer evidence supports for maximizing absorption. Review the timing with meals – iron is better absorbed on an empty stomach, but tolerability may require taking it with a small amount of food.
Bottom line: iron 2 tablets once daily may be easier and more convenient for the patient, but comes at the cost of poor absorption and an increased risk for GI adverse effects.
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