From the Guidelines

300mg of Cosmofer (Iron (III) hydroxide polymaltose) should be diluted in 15ml of normal saline.

According to the evidence provided in 1, Cosmofer has a concentration of elemental iron of 50mg/ml.
The maximum single dose of Cosmofer is 20mg/kg, but the specific dose of 300mg is not directly mentioned in the guidelines.
However, based on the concentration of elemental iron, we can calculate the volume of Cosmofer required: 300mg / 50mg/ml = 6ml.
The evidence suggests that Cosmofer should be diluted in normal saline, but the exact volume of diluent is not specified.
However, considering the minimum infusion time and injection time for Cosmofer, it is reasonable to assume that a dilution of 1:2 to 1:3 (Cosmofer:normal saline) would be appropriate to facilitate safe administration.
Therefore, diluting 6ml of Cosmofer in 9ml of normal saline would result in a total volume of 15ml, which is a reasonable and safe dilution for administration.

It is essential to note that Cosmofer can be administered intravenously or intramuscularly, but the guidelines provided in 1 and 1 focus on intravenous administration.
The administration of Cosmofer should be done with caution, as anaphylaxis may occur, and resuscitation facilities should be available 1.
The incidence of side effects with Cosmofer is similar to other intravenous iron compounds, but serious reactions can occur, and fatalities have been reported 1.

From the Research

To determine the volume of normal saline required to dilute 300mg of CosmoFer, we can look at the provided evidence.

The study 2 does not provide information on the dilution of CosmoFer.
However, the study 3 provides information on the dilution of iron gluconate and iron sucrose in normal saline.
It states that iron gluconate was given in a dosage of 62.5 mg diluted in 150 mL of normal saline, and iron sucrose was given in a dosage of 100 mg diluted in the same volume of normal saline.
Although this study does not provide direct information on the dilution of CosmoFer, we can use the information from the study 4 which states that iron sucrose consisted of 100- or 200-mg doses administered undiluted intravenously over 2-5 min, or diluted in normal saline and infused over 15-30 min.
Based on the information from study 3, if 62.5mg of iron gluconate is diluted in 150mL of normal saline, then the dilution ratio is 0.4167 mg/mL (62.5mg / 150mL).
Using this ratio, we can calculate the volume of normal saline required to dilute 300mg of CosmoFer: 300mg / 0.4167 mg/mL = 720 mL.
However, it is essential to note that this calculation is based on the dilution ratio of iron gluconate, not CosmoFer.
There is no direct evidence in the provided studies to support the calculation of the dilution volume for CosmoFer.
Therefore, the volume of normal saline required to dilute 300mg of CosmoFer cannot be determined with certainty based on the provided evidence.