THE HEALTH Service Executive last week repeated its advice to doctors not to use the anti-viral Tamiflu as a preventative treatment against swine flu, writes EOIN BURKE KENNEDY
The HSE says it has received reports that GPs are coming under increasing pressure to prescribe the drug to those who are not ill or who have only mild symptoms.
Following sustained human-to-human transmissions within Ireland in June and July, the authorities shifted their policy from one of containment to mitigation, mirroring strategies adopted in other countries.
In practice, this means the use of Tamiflu is no longer advised in all cases of infection or as a prophylactic for people who have come in contact with the virus.
GPs are advised to administer the drug only to high-risk groups, such as pregnant women, young children and adults with chronic underlying conditions or those at risk of developing complications.
While a more selective use of anti-virals is consistent with World Health Organisation (WHO) guidelines and sensible to preserve limited supplies for vulnerable groups and concentrated pockets of infection, it comes at a time when public concern over the virus has heightened noticeably.
Inevitably, this has resulted in more pressure on GPs to prescribe the drug. There has also been anecdotal evidence that some people are bypassing the need for a prescription and buying the drug over the internet.
Tamiflu is now one of the most “spammed” medicines on the internet.
But the UK’s Royal Pharmaceutical Society recently warned that the Tamiflu being sold online is, in most cases, fake and may be adulterated with anything from sugar to rat poison.
The Canadian authorities have also warned that products claiming to be “generic” Tamiflu were being sold on the internet even though there are no authorised generic versions of the anti-viral on the market.
The incidence of people buying these medicines over the internet is likely to increase in the coming weeks with experts predicting an increased level of infection as schools return and a second wave of cases during the winter influenza season.
Just as the overuse of antibiotics has led to drug-resistant strains of certain bacteria, health authorities fear the overuse of anti-virals will precipitate more virulent drug-resistant strains of the H1N1 virus.
According to Swiss drug manufacturer Roche, the maker of Tamiflu, studies have shown that 0.4 per cent of adults and 4 per cent of children with seasonal influenza develop resistance to the drug.
So far there have been only isolated cases of Tamiflu-resistant infections with the WHO reporting cases in Canada, Hong Kong, Japan, Egypt and Denmark.
The WHO said it had logged a number of such cases, while stating that there was no evidence the H1N1 virus was mutating into a more dangerous form.
Nevertheless, fears remain that resistance could become a problem and the WHO only last week issued a statement dismissing speculation that a cluster of anti-viral-resistant cases had emerged along the US-Mexico border near where the outbreak was first identified in April.
Kingston Mills, professor of biochemistry at University of Dublin, Trinity College, said anti-viral drugs such as Tamiflu and Relenza work by targeting a glycoprotein on the surface of influenza cells called neuraminidase which the virus needs to penetrate healthy cells and cement the infective process.
Prof Mills said the flu virus initially enters cells along the respiratory tract. Once inside the cell it makes copies of itself which then go on to infect other healthy host cells.
By inhibiting the function of the neuraminidase enzyme, the anti-virals limit the spread of the virus, slowing the disease process and lessening its severity. Unlike a vaccine which prevents disease by stopping the virus getting into the host cell, Prof Mills said anti-virals help the body fight off disease, provided they are given within the first 48 hours.
“Tamiflu is not as effective as an antibody in stopping the disease but has been shown to significantly slow down the disease process.
“But it is absolutely pointless taking it if you’re not infected and it’s counterproductive because the more people that have the anti-viral, the greater chance of a mutation in the virus, rendering the current batch of anti-virals less effective.
“Viruses are very clever and they can mutate and influenza is particularly prone to mutations, and that is why we need to get the vaccine jab every year against seasonal flu,” he said.
“To date, a significant resistant strain of the virus does not appeared to have developed, but that may change in the coming months.
“Fortunately, this is a fairly mild virus in most people and outside of high-risk groups or immune-compromised patients most people do not require Tamiflu,” Prof Mills said.
According to the HSE, the State has sufficient stocks of the anti-viral drugs oseltamivir (Tamiflu) and zanamivir (Relenza) for more than 50 per cent of the population.
It says it has one million packs of Tamiflu for adults, Tamiflu in a paediatric preparation form to treat 63,000 children, and 70,000 packs of Relenza for adults.
Last week, US pharmaceutical manufacturer Baxter announced it had completed its first commercial batches of a vaccine for the H1N1 virus and that it had entered into discussions with various health authorities, including Ireland, concerning distribution plans.
While a successful vaccination programme should limit the spread of the virus, there will still be a need for anti-virals for those not covered by the programme.
In addition, as most vaccines are 80-90 per cent effective, some people could, in theory at least, contract the virus after vaccination and require anti-viral treatment.
Dr Sinead Murphy, of the Irish College of General Practitioners and a Galway-based physician, said most doctors were now only giving Tamiflu to patients with more severe symptoms and those in the defined risk groups, such as people with chronic respiratory conditions or immuno-suppression issues.
“We are also giving Tamiflu to people who are aged 65 and older even though these are less likely to get this flu.”
She said about 70 per cent of cases in Ireland so far have involved people aged under 30.
Dr Murphy said Tamiflu could also be prescribed for young children who may be at a higher risk of developing complications.
However, she said there were specific side effects to Tamiflu and the decision to prescribe must be weighed against the severity of symptoms and the age of the patient.
The most common side effects are nausea and vomiting especially in the hours immediately after the dose, but some patients can develop diarrhoea and stomach ache, she said.
A UK study, published yesterday, found Tamiflu caused vomiting in some children, which led to dehydration, and warned the side effects of giving the drug may outweigh benefits.
It has even been linked to insomnia and nightmares in children. Although it is mainly given in tablet form to adults, some pharmacies are mixing the medicine with liquid for children. A typical adult treatment involves 75mg tablets taken twice daily for five days, with children receiving smaller doses.
The five-day course of 10 capsules, which would normally cost in the region of €40, is currently dispensed free with prescription under the HSE’s current pandemic control plan.
Dr Murphy admitted that panic and misinformation among the public may lead some to purchase medicines on the internet, but she warned that “you cannot be sure of the safety and efficacy of what you are buying”.
“When taking an unprescribed drug, you run the risk of getting side effects without any benefit,” she said.
Anti-viral facts
Unlike vaccines, anti-virals do not prevent illness by providing immunity. An anti-viral is a medicine which destroys a virus or inhibits its ability to grow and multiply.
The most common anti-viral drugs used in the treatment of swine flu are oseltamivir (Tamiflu) and zanamivir (Relenza).
According to the HSE, the State has sufficient stocks of these drugs to treat 55 per cent of the population.
Since the outbreak began, Tamiflu has become one of the most “spammed” medicines on the internet.
Experts warn the Tamiflu being sold on the internet is, in most instances, fake.
Antivirals, such as Tamiflu, can cause side effects like nausea, vomiting and diarrhoea and have even been linked to insomnia and nightmares in children.