Iron deficiency anaemia is a relatively common condition affecting up to 5% of men and postmenopausal women (Goddard et al, 2011). It has a higher prevalence in women of childbearing age due to menstrual losses. Other than blood loss, there are common causative, or aggravating factors, which include poor dietary intake, medications and difficulty absorbing iron (Shokrgozar and Golafshan, 2019).
Fortunately, in many cases oral treatment with iron supplements can successfully treat the condition. However, humans have difficulty absorbing iron from non-haem sources so pharmacological doses of iron salts (which are non-haem) can seem relatively high compared to recommended daily intakes.
QUESTION 1
A common dose for treating iron deficiency anaemia in adults is ferrous sulfate 200 mg three times daily (Joint Formulary Committee, 2019).
- Ferrous sulfate monohydrate 172 g/mole (each mole contains 1 mole of iron)
- Iron 55.8 g/mole
To the nearest whole milligram, how many moles of elemental iron are there in each 200 mg ferrous sulfate tablet?
QUESTION 2
Given that the absorption of iron from ferrous sulfate is only around 5–15% (electronic Medicines Compendium (eMC), 2018a), how much elemental iron can be expected to be absorbed from a normal treatment dose per day?
QUESTION 3
In addition to poor absorption, dietary iron is slowly incorporated into haemoglobin (Hb). For patients on therapeutic doses of iron, it is expected that their Hb will increase at a rate of 2 g/dL every 3–4 weeks (National Institute for Health and Care Excellence, 2018).
If a patient is started on therapeutic iron when their Hb was 6 g/dL, how long would you expect it to take to reach a target concentration of 12 g/dL?
QUESTION 4
Hb is often reported in different units depending on the laboratory performing the test.
Given that 1dL is 100 ml, convert the patient's current Hb level (6g/dL) to g/L.
QUESTION 5
For patients unable to take oral iron, an injectable product such as CosmoFer, may be a suitable alternative. A treatment course may be given as a series of injections or as a single total dose infusion. For CosmoFer, the dose for a total dose infusion is calculated using the formula (eMC, 2018b):
Total dose (in mg of elemental iron) = (Body weight (kg) x (target Hb - actual Hb) (g/L) x 0.24) + mg iron for iron stores Up to a maximum single dose of 20 mg/kg
For the patient in question 3, how much CosmoFer would need to be added to a 500 mL bag of saline to give the total single dose infusion if they weighed 45 kg? The assumed iron stores for an adult are 500 mg; Cosmofer contains 50 mg/mL of elemental iron.