Nurses and other healthcare workers are being issued with urgent guidance on using intravenous amphotericin, following two patient deaths.
Both fatalities and a number of 'near misses' involved confusion when administering different formulations of the fungal infection treatment, the National Patient Safety Agency said.
Mix-ups between the lipid and non-lipid formulations, which have different dose recommendations, can lead to potentially fatal side effects or result in sub-therapeutic treatment.
The agency has advised NHS and independent sector organisations to carry out an immediate risk assessment of amphotericin products and procedures to be completed by 1 October.
NPSA chief executive Martin Fletcher, the NPSA's Chief Executive, said: 'These are practical actions which, when implemented, will make it more difficult for mistakes to occur.'