The main purpose of a diluent is to help reduce site irritation and enable drug delivery over prescribed time. Information about compatible diluents is available in the Summary of Product Characteristics (SmPC).

Water for infusion is widely considered the first line diluent. Reasons for preferring it include available compatibility data with most commonly used drugs, including cyclizine lactate, high concentrations of diamorphine hydrochloride (more than 40 mg/ml) and haloperisol (more than 1 mg/ml).

For drugs such as granisetron, hydromorphone, ketorolac, ketamine, octreotide and ondansetron, better compatibility data are available with sodium chloride 0.9 percent, which may be preferred.

Glucose 5 percent is acidic and is unsuitable for very alkaline dugs such as dexamethasone, ketorolac and phenobarbitone.

Flushing a subcutaneous cannula ensures that the entire volume of drug is administered and that no drug is retained in the dead space. WFI is widely used and NaCl 0.9 percent can also be used.

Flush volume is equal to the cannula volume and thus for a BD Saf-T-intima, a flush volume of 0.35 ml is advised after a subcutaneous bolus.

The lack of a comprehensive nature and paucity of applicability when a mixture of drugs is used might be cited as potential drawbacks limiting wider applicability.

References

Wilcock, A., Howard, P., Toller, C. S., Droney, J., & Charlesworth, S. (Eds.). (2025). Palliative care formulary (9th ed.). Pharmaceutical Press.