What you’ll need to know
You will need to know your patient’s:
- Current iron level (mg)
- Current haemoglobin concentration (g/dL)
- Target haemoglobin concentration (g/dL) based on diagnosis
- Body weight
- Patient’s height (in inches or centimetres)
- Age (in years)
Use a tool
Use a BMI calculator to obtain a value.
Whether you use actual body weight or ideal body weight in your subsequent Cosmofer® dose calculation depends on the BMI value.
BMI less than 30kg/m2
If the body mass index (BMI) is less than 30kg/m2, use actual body weight in your subsequent Cosmofer® dose calculations.
BMI more than 30kg/m2
If the body mass index (BMI) is more than 30kg/m2, use ideal body weight (IBW) in your subsequent Cosmofer® dose calculations. Use an IBW calculator to obtain a value.
Use pre-pregnancy weight
Oral iron is the preferred method of iron supplementation for anaemia in pregnancy. However, if oral iron is not tolerated or is ineffective, then parenteral iron can be considered. In these circumstances, use the pre-pregnancy weight in any dose calculations.
Using your patient’s target haemoglobin (g/dL) and ideal or actual body weight (as determined previously), you can use the manufacturer’s dosing tables to calculate the total dose of Cosmofer®. The manufacturer’s tables present a dose rounded to the nearest ampoule volume to reduce Comosfer® wastage.
Our article on Cosmofer dosing tables will guide you through the process.
To calculate total iron requirement (in mg ferrous iron) using the Ganzoni formula, undertake the following calculation:
[10 × (target Hb (g/dL)–actual Hb (g/dL)) × (0.24 × bodyweight [kg])] + mg of iron for body stores
Where the iron for body stores (mg) is determined by the person’s weight:
- Estimate the iron body-stores using 15mg iron/kg if actual body weight less than 35kg.
- Use 500mg for iron body-stores if actual body weight is more than 35kg.
A 50kg woman with current haemoglobin level of 5g/dL requires a target haemoglobin concentration of 11g/dL.
Using the Ganzoni formula, the total iron requirement is calculated as:
[10 x (11g/dL-5g/dL) x (0.24x50kg)] + 500 = 1220mg of iron
The calculated iron requirement in the worked example is close to the estimated total iron requirement in the manufacturer’s dosing table. For the worked example, the iron requirement is estimated as 1200mg using corresponding dosing table. A dose of 1200mg would be given to reduce Cosmofer® wastage.
The Royal College of Nursing (RCN) advise that large doses require separate infusions:
- Doses of iron greater than 20mg/kg must be given as two CosmoFer® infusions.
- The manufacturers advise that the second dose be given a week later.
- There is no need for haemoglobin monitoring in between the two infusions unless there are specific concerns, e.g. relapse.
CosmoFer® is available in ampoules of 2ml, 5ml or 10ml containing 50mg/ml iron solution for infusion or injection. The total dose must be diluted in either 500ml of 0.9% sodium chloride or 5% glucose before intravenous infusion.
The total dose infusion is given intravenously over 4 to 6 hours. However, the full dose should be preceded by a test dose, after which the rate of infusion may be increased progressively to 45 to 60 drops per minute.
Giving a test dose
The first 25mg of iron should be infused over a period of 15 minutes as a test dose. The MHRA advises that a test dose is required for every dose.
Monitoring during a test dose
Observe the patient and include pulse and blood pressure checks before and after infusion. If no adverse reactions occur during the test dose, then the remaining portion of the infusion can be given.
Observe the patient for signs of hypersensitivity for at least 30 minutes after each total dose infusion in an area where resuscitation facilities are available.
The manufacturers of Cosmofer® state that hypersensitivity reactions have also been reported after previously uneventful doses of intravenous iron. In the event of a hypersensitivity reaction, stop treatment immediately and initiate appropriate management.