The maker of melanoma drug Keytruda says the drug is more effective than Pharmac is letting on.
The Government's pharmaceutical agency has been under intense pressure to fund the treatment since it was approved for use in New Zealand last year.
It declined to do so, calling it a 'low priority' and saying it needed more evidence of its efficacy.
Now a letter has been released, revealing Merck Sharp & Dohme complained to Health Minister Jonathan Coleman, accusing Pharmac of not using the most "up-to-date and correct clinical data".
"This is of significant concern as the use of incorrect data gives a misleading and false impression of how effective this breakthrough drug is, in the treatment of melanoma," writes Paul Smith, Merck Sharp & Dohme NZ director.
It says the findings showed Keytruda offered a much greater benefit to patients than the clinical paper reviewed by the agency.
Last week, rival melanoma drug Opdivo was given Medsafe approval. It too is very expensive, but may offer competition to help Pharmac negotiate a better price.