The Danish national is no longer suffering from the illness and is not displaying symptoms, the Danish Institute of Serology said in a statement.
"It does not constitute a risk to public health and does not cause changes to the recommendations for the use of oseltamivir (Tamiflu)," the institute said in a statement.
A spokesman for the Swiss company Roche, which manufactures Tamiflu, said the patient's resistance was likely to be an individual case.
David Reddy, Roche's pandemic task force leader, said the case was within the 0.5 per cent rate of case resistance to Tamiflu that had been established in clinical trials.
The World Health Organisation declared an influenza pandemic earlier this month and advised governments to prepare for a long-term battle against the new flu virus. The WHO had no immediate comment on the case of Tamiflu resistance.
The United Nations agency has raised its pandemic flu alert to its highest alert level of 6, indicating the first influenza pandemic since 1968 is under way.
We have stocked Tamiflu antiviral at home. Ideally within 6 hours and at the very latest within 48 hours of flu symptoms we will commence Tamiflu treatment. I bought Tamiflu online (£50 per dose) from pimsreg.com registered with the Royal Pharmaceutical Society of Great Britain (RPSGB) and listed in "websites displaying the internet pharmacy logo".
Update 26 July 2009: Tamiflu - currently one dose is free to people exhibiting swine flu symptons - get Tamiflu from the UK Government Pandemic Flu site.
On 1 September my son went down with, what our doctor said 'ticked all the boxes' as swine flu. After 102F, vomiting, diarohea, headaches ... and taking tamiflu (our emergency stock) and on Thursday Relenza, he seems on the mend (4 September 8pm).
Diagram of influenza virus nomenclature (for a Fujian flu virus)
Structure of the influenza virion. The hemagglutinin (HA) and neuraminidase (NA) proteins are shown on the surface of the particle. The viral RNAs that make up the genome are shown as red coils inside the particle and bound to Ribonuclear Proteins (RNPs).