Zanamivir (Relenza), an antiviral agent specifically designed for the treatment of influenza A and B, was launched by Glaxo Wellcome on September 6 (see p400). It is the first of a new class of antiviral drugs — the neuraminidase inhibitors.
The drug is administered via a dry powder inhaler and works by directly targeting the respiratory tract. Glaxo Wellcome says that treatment should be started within two days of the onset of symptoms, although the sooner it is started, the better. The recommended dose is two inhalations twice a day for five days.
Glaxo Wellcome says that, in clinical trials involving 6,100 patients, zanamivir reduced the severity of major symptoms (eg, fever, myalgia, weakness, cough and loss of appetite) by a maximum of 44 per cent. It shortened the duration of illness by a median of 1.5 days (range 1 to 2.5 days). Some high risk patients (eg, the elderly and patients with asthma) were included in the trials and appeared to have no major safety problems while taking zanamivir. However, efficacy data for these patient groups are limited.
Dr Rob Pearson (medical director, Glaxo Wellcome) said at a press briefing to launch zanamivir that resistance to the drug had not been seen in trials. One resistant mutant was found in an immunocompromised child but viruses with mutated neuraminidases seemed to be less infectious than “normal” strains, he said.
However, at the same briefing, Dr Jonathan Van Tam (senior lecturer in public health and epidemiology, University of Nottingham medical school) emphasised that vaccination against influenza was still the number one priority, as it prevented 40 to 60 per cent of deaths and hospital admissions due to influenza in high risk patients. Glaxo Wellcome says that, to ensure appropriate use of zanamivir, it has set up an influenza management programme for health professionals and patients. This offers suggestions on providing influenza services, as well as patient information on influenza symptoms. In addition, patient information leaflets and posters will be distributed to general practitioners’ surgeries and community pharmacists.
In a press release issued by Glaxo Wellcome, Mr Tony Schofield (community pharmacist, South Shields) is quoted as saying that pharmacists would play a key role in managing influenza this winter, through helping customers understand the difference between influenza and a common cold. “Time and time again, people mistakenly say they have influenza, when they simply have a cold. The pharmacist is ideally placed to help educate customers on the different symptoms of influenza and a cold to ensure that they receive the most appropriate treatment for their illness”, he said.
Zanamivir has been included in the list of first investigations to be carried out by the National Institute for Clinical Excellence (PJ, August 14, p225) and is to be “fast-tracked” through the review process. Glaxo Wellcome estimates the annual cost to the NHS at between £10-15m. This figure is based on the number of patients who might consult their general practitioner within the first two days of symptoms. A National Prescribing Centre estimate, quoted in the newspapers as £115m, is based on significant usage of zanamivir for both treatment and prophylaxis of influenza in an epidemic year. Zanamivir is not currently licensed for prophylaxis and Dr Pearson said that they had no plans, at this stage, to make an application for this indication.
Roche told The Journal on September 7 that it hopes to launch oseltamivir, its neuraminidase inhibitor, for treatment of influenza A and B in time for next year’s influenza season. It will be a 75mg oral capsule and should be taken within 36 hours of the onset of symptoms. The neuraminidase inhibitors are the first drugs to be effective against both influenza A and B. However, amantadine (Symmetrel) has been licensed for treatment and prophylaxis of influenza A for some time.
The influenza virus, normally penetrates epithelial cells in the respiratory tract. Each virus makes its way to the cell nucleus, where viral RNA is replicated. Once new viral particles are formed, they leave the epithelial cell and disperse to other cells, where the infective process is repeated.
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