Available Flu Drugs »
Tamiflu
The drug Tamiflu (oseltamivir phosphate) developed by Roche was approved
by the FDA in October 1999 for the treatment
of uncomplicated acute illness caused due to influenza infection
in adults. Tamiflu belongs to the family of medicines called antivirals
which are used to treat infections caused by viruses.
Tamiflu helps in reducing common flu and bird flu symptoms such as weakness,
headache, fever, cough, and sore throat by 1 day. Tamiflu (Oseltamivir
phosphate) has also been shown to prevent influenza infection if you
have come into close contact with someone who has the flu. Tamiflu,
one of the most sought after drug for treating flu is the only antiviral
available in the United States for both the treatment and prevention
of the most common strains of influenza types A and B.
The flu drug belongs to the latest breed of the neuraminidase inhibitor
(NI) class of medicines designed specifically to prevent the influenza
virus from spreading and infecting other cells. It is immensely effective
against all common strains of influenza (types A and B). The medication
targets one of two major surface structures on the influenza virus -
the neuraminidase protein. The neuraminidase protein is virtually the
same in all common strains of influenza. If neuraminidase is inhibited,
the virus is not able to infect new cells.
Roche Tamiflu is meant for treating adults, adolescents, and pediatric
patients of 1 year of age and older suffering from the flu and whose
flu symptoms started within the last day or two. Tamiflu is also used
to reduce the chance of getting the flu in people aged 13 and older
who have a higher chance of getting the flu because they’ve been
spending time with someone who has been inflicted with the flu. Tamiflu
has multiple benefits as it can also reduce the chance of getting the
flu if there is a flu outbreak in the community.
As per the pre-clinical testing, Tamiflu demonstrated activity against
the influenza virus responsible for the 1997 Hong Kong outbreak, (a
type of ‘H5N1’ strain),
at concentrations equivalent to those of the 75 mg twice daily dose
approved for treating influenza in humans. If taken properly, it can
be of immense use in fighting the dreaded avian flu.
In adults, if taken within 36 hours of the onset of influenza, Tamiflu
reduces the severity of symptoms and the duration of illness to a large
extent as compared to standard care. Tamiflu has been shown to significantly
reduce the incidence of influenza-associated chest infections requiring
antibiotic therapy by over 50% in adults. Treatment with Tamiflu also
significantly reduces hospitalizations as compared to standard care.
Children can also benefit from the effectiveness of Tamiflu as it helps
in reducing the severity and duration of influenza symptoms.
For best results, Tamiflu should be taken within 2 days after the onset
of the symptoms. Tamiflu is generally well tolerated by its users. The
most frequently reported adverse side effects are mild to moderate such
as transient nausea or vomiting. Tamiflu is usually recommended for
pediatric use as it’s capable of reducing the duration of influenza
by 1.5 days (26%) in children aged 1 to12 when given within 2 days of
onset of symptoms.
Tamiflu is used for treating adults, adolescents, and pediatric patients
of 1 year of age and older suffering from flu whose flu symptoms started
within the last day or two. Tamiflu is also used to reduce the chance
of getting the flu in people aged 13 and older who have a higher chance
of getting the flu because of spending time with someone who has the
flu. Tamiflu can also reduce the chances of getting the flu if there
is a flu outbreak in the community.
Special Warnings Pertaining to Tamiflu:
Tamiflu’s safety and effectiveness have not been determined in
people with chronic heart or lung disease, kidney failure, or in people
with high-risk underlying medical conditions.
Precautions:
• Tamiflu has not been shown to treat flu-like illnesses caused
by any virus other than influenza A and B (e.g., stomach flu, common
cold, or other respiratory illnesses not caused by influenza).
• Other kinds of infections can appear like influenza or occur
along with influenza, and need different types of treatment. Contact
your health care provider if you feel worse or develop new symptoms
during or after treatment, or if your influenza symptoms do not start
to get better.
• Taking Tamiflu should not affect your decision to have an annual
influenza vaccination.
• The safety and efficacy of repeated courses of treatment have
not been established.
• Tamiflu is not indicated for treatment or prevention of the
flu in patients less than 1 year of age.
Action Mechanism
Oseltamivir is an ethyl ester prodrug requiring ester hydrolysis for
conversion to the active form, oseltamivir carboxylate. The proposed
mechanism of action of oseltamivir is inhibition of influenza virus
neuraminidase with the possibility of alteration of virus particle aggregation
and release.
Antiviral Activity
The antiviral activity of oseltamivir carboxylate against laboratory
strains and clinical isolates of influenza virus was determined in cell
culture assays. The concentrations of oseltamivir carboxylate required
for inhibition of influenza virus were highly variable depending on
the assay method used and the virus tested. The 50% and 90% inhibitory
concentrations (IC50 and IC90) were in the range of 0.0008 µM
to >35 µM and 0.004 µM to >100 µM, respectively
(1 µM=0.284 µg/mL). The relationship between the in vitro
antiviral activity in cell culture and the inhibition of influenza virus
replication in humans has not been established.
Resistance
Influenza A virus isolates with reduced susceptibility to oseltamivir
carboxylate has been recovered in vitro by passage of virus in the presence
of increasing concentrations of oseltamivir carboxylate. Genetic analysis
of these isolates showed that reduced susceptibility to oseltamivir
carboxylate is associated with mutations that result in amino acid changes
in the viral neuraminidase or viral 274Y in influenza A N1 and I222T
and R292K in influenza A N2. Mutations E119V, R292K and R305Q have been
selected in avian influenza A neuraminidase N9. Mutations A28T and R124M
have been selected in the hemagglutinin of influenza A H3N2 and mutation
H154Q in the hemagglutinin of a reassortant human/avian virus H1N9.
In clinical studies in the treatment of naturally acquired infection
with influenza virus, 1.3% (4/301) of post treatment isolates in adult
patients and adolescents, and 8.6% (9/105) in pediatric patients aged
1 to 12 years showed emergence of influenza variants with decreased
neuraminidase susceptibility in vitro to oseltamivir carboxylate. Mutations
in influenza A resulting in decreased susceptibility were H274Y in neuraminidase
N1 and E119V and R292K in neuraminidase N2. Insufficient information
is available to fully characterize the risk of emergence of TAMIFLU
resistance in clinical use.
In clinical studies of post exposure and seasonal prophylaxis, determination
of resistance was limited by the low overall incidence rate of influenza
infection and prophylactic effect of Tamiflu.
Cross-resistance
Cross-resistance between zanamivir-resistant influenza mutants and oseltamivir-resistant
influenza mutants has been observed in vitro. Due to limitations in
the assays available to detect drug-induced shifts in virus susceptibility,
an estimate of the incidence of oseltamivir resistance and possible
cross-resistance to zanamivir in clinical isolates cannot be made. However,
two of the three oseltamivir-induced mutations (E119V, H274Y and R292K)
in the viral neuraminidase from clinical isolates occur at the same
amino acid residues as two of the three mutations (E119G/A/D, R152K
and R292K) observed in zanamivir-resistant virus.
Tamiflu Dosage
Tamiflu dosage will be different for different patients. You’re
required to follow your doctor's orders or the directions on the label.
The following information includes only the average doses of Tamiflu.
If your dose is different, do not change it unless your doctor tells
you to do so.
For oral dosage forms (capsules and oral suspension):
Tamiflu dosage for treatment of the flu:
• Adults: 75 milligrams (mg) two times a day for five days.
• Children 1 year of age or older: Dose is based on body weight
and must be determined by your doctor. It is usually between 30 and
75 mg two times a day for five days.
• Children up to 1 year of age: Use and dose must be determined
by your doctor.
Tamiflu dosage for prevention of the flu:
• Adults and teenagers 13 years of age or older: 75 mg once a
day for at least seven days.
• Children up to 13 years of age: Use and dose must be determined
by your doctor.
Missed Dose
This medicine works best when there is a constant amount in the body.
To help keep the amount constant, do not miss any doses. If you miss
a dose, take as soon as possible, except if it is near the next dose
(within 2 hours). Then go back to your regular dosing schedule. Do not
double doses. If you have missed several doses, inform your doctor and
follow the advice given to you.
Tamiflu Side Effects
Along with its needed effects, a medicine may cause some unwanted effects.
Although not all of these side effects may occur, if they do occur they
may need medical attention. Mentioned below are some of the Tamiflu
side effects:
Less common Tamiflu side effects include phlegm producing cough or wheezing.
Other side effects may occur that usually do not need medical attention.
These side effects may go away during treatment as your body adjusts
to the medicine. However, check with your doctor if any of the following
side effects continue or are bothersome:
More common side effects may include diarrhea; nausea and vomiting.
These events were generally of mild to moderate degree and usually occurred
on the first 2 days of administration.
Other Tamiflu side effects include abdominal or stomach pain; bloody
nose or unexplained nosebleeds (occurs mainly in children); burning,
dry or itching eyes, redness, pain, swelling of eye or eyelid, or excessive
tearing (occurs mainly in children); cough; dizziness; ear disorder
(occurs mainly in children); fatigue; headache; trouble in sleeping.
Additional adverse events occurring in less than 1% of patients receiving
Tamiflu for treatment includes unstable angina, anemia, pseudo membranous
colitis, humerus fracture, pneumonia, pyrexia, and peritonsillar abscess.
Some side effects not listed above may also occur in some patients.
If you notice any other effects, check with your doctor.
Tamiflu and Bird Flu
Roche, the maker of Tamiflu confirms that oral anti-influenza drug Tamiflu
(oseltamivir) could be effective in the treatment and post-contact prevention
of avian influenza that is circulating in the Far East therefore Tamiflu
and bird flu are associated with each other.
Tamiflu has been tested in a pre-clinical setting against a wide range
of influenza virus strains. Despite the lack of clinical data, these
pre-clinical findings provide reassurance that Tamiflu can be expected
to be active against any influenza virus neuraminidase enzyme subtype,
including the H5N1 strain. This strain is associated with the recent
outbreak of avian influenza in Asia.
The WHO in its interim recommendations for the protection of persons
in contact with animals potentially infected with highly pathogenic
avian influenza viruses, advises that ‘Oseltamivir be readily
available for the treatment of suspected H5N1 respiratory infections
in cullers and farm workers involved in the mass culling.
Therefore in the event of an epidemic, oseltamivir, the active ingredient
of Tamiflu can be supplied to national authorities in bulk for arresting
flu.
Tamiflu (oseltamivir phosphate) is available as a capsule containing
75 mg oseltamivir for oral use, in the form of oseltamivir phosphate,
and as a powder for oral suspension, which when constituted with water
as directed contains 12 mg/mL oseltamivir base. In addition to the active
ingredient, each capsule contains pregelatinized starch, talc, povidone
K 30, croscarmellose sodium, and sodium stearyl fumarate. You can buy
Tamiflu online from any of the FDA approved online pharmacies.
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