Kao, 75, who won the physics prize earlier this month for his work on fiber-optic cables, suffers from the disease.

He was previously vice chancellor of the Chinese University of Hong Kong.

In a newspaper advert, headed "Letter to Professor Kao," Danish drugmaker Lundbeck said it is "deeply sorry" about Kao's diagnosis before detailing Ebixa (memantine) as a "new" treatment for Alzheimer's.

Kao and his wife, Gwen Kao May-wan, who hold British and US passports, are unaware of the advertisement.

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Ebixa was registered with the Department of Health in 2003 and launched in Hong kong the following year.

Lundbeck product manager for Ebixa in Hong Kong Chris Chow Kai-cheong said: "I am not sure if Professor Kao is taking Ebixa at this moment. It is an open letter. If he can reply, that's great."

Lundbeck education and training manager Edgar Liu Shiu-lam said Ebixa belongs to a "new class" of anti-Alzheimer's drugs that targets another neurotransmitter glutamate.

"Its transmission is important for memory building and learning," said Liu, adding that it costs around HK$800 a month.

The Hospital Authority has been asked to include Ebixa in the standard formulary "so patients can have another choice."

A Chinese University staffer described the open letter to Kao as "very creative."

Benjamin Kwong Yiu-sum, president of the Pharmaceutical Society of Hong Kong, said Ebixa is used for severe dementia but is not a cure. "It only offers a very marginal benefit for the patient but it has quite a premium to pay for."

Kwong added: "It all depends whether the caregiver needs it to make it easier to take care of the patient. But dementia is still progressing. It will not stop the disease progression."