Oseltamivir (Tamiflu)

Has protective effect against the H5N1 strain of avian influenza virus.

Originally less than 1% of influenza viruses tested worldwide were resistant, but levels of resistance to Oseltamivir increased in 2007 and 2008, with increasing levels of such resistance in 2009.

Osetamivir can be used for chemoprophylaxis and treatment of influenza.

When used for prophylaxis after susceptible A or B strains of seasonal influenza are 70-90% effective.

Usual Adult Dose for Influenza:

75 mg orally twice a day for 5 days

Approved indication: Treatment of acute, uncomplicated influenza infection in patients symptomatic no more than 48 hours

Usual Adult Dose for Influenza Prophylaxis:

Following close contact with an infected individual: 75 mg orally once a day for at least 10 days

During a community outbreak of influenza: 75 mg orally once a day.

Trade name Tamiflu

Oral agent with >80% bioavailability.

Extensively metabolised to its active form upon first-pass through the liver. I Protein binding about 42% and 3% for active metabolite.

Hepatic metabolism.

Half-life of 1-3 hours, and 6-10 hours for the active metabolite.

Excretion in urine of greater than 90%.

An antiviral medication used to prevent and treat influenza A and influenza B.

A neuraminidase inhibitor.

A competitive inhibitor of the activity of the viral neuraminidase enzyme upon sialic acid, that is found on glycoproteins on the surface of normal host cells.

Blocks the activity of the enzyme neuramidase and prevents new viral particles from being released through the cleaving of terminal sialic acid on glycosylated hemagglutinin .

Use results in the failure of virus release.

Recommend use of oseltamavir for people who have complications or are at high risk for complications who present within 48 hours of first symptoms of infection.

Recommend use to prevent infection in at-risk people but not the general population.

Some recommend to treat those at lower risk who present within 48 hours of first symptoms of infection.

A Cochrane review concluded: does not reduce hospitalizations, and that there is no evidence of reduction in complications of influenza, or reduction of the spread of the virus.

Two meta-analyses have concluded that benefits in those who are otherwise healthy do not outweigh its risks, with little evidence regarding whether treatment changes the risk of hospitalization or death in high risk populations.

One meta-analysis found that oseltamivir was effective for prevention of influenza at the individual and household levels.

Risk-benefit ratio is controversial.

Side effects include: psychiatric symptoms, vomiting, and headaches.

It is pregnancy category C in the United States.

Dose adjustment may be needed in renal disease.

Recommended for the use in people who have complications or are at high risk for complications,including those who are hospitalized, young children, those over the age of 65, people with other significant health problems, and those who are pregnant.

It is recommended that all people admitted to intensive care units during influenza outbreaks with a diagnosis of community-acquired pneumonia receive oseltamivir until the absence of influenza infection is established by PCR testing.

Studies suggest that oseltamivir reduces the duration of symptoms by 0.5–1 day.

A 2014 Cochrane Collaboration concluded that oseltamivir does not affect the need for hospitalizations, no proof of reduction of complications of influenza, or reduction of the spread of the virus.

Some evidence exists that oseltamivir prevents some people from producing sufficient numbers of their own antibodies to fight infection.

The CDC does not recommend the general use for prevention due to concerns that widespread use will encourage resistance, but they do recommend it be considered in those at high risk who have been exposed to the disease within 48 hours but have not received or only recently received the flu shot, and also recommended it during outbreaks in long term care homes and in those who are significantly immunosuppressed.

Systematic reviews found low to moderate evidence that it decreases the risk of getting symptomatic influenza by 1% to 12%.

It recommended against its use in healthy, low risk individuals due to cost, risk of resistance , and side effects.

Common adverse drug reactions:associated with oseltamivir include nausea and vomiting. headaches, kidney, and psychiatric events.

It is pregnancy category C.

Dose adjustment may be needed in those with kidney impairment.

The majority of mutations conf2242ing resistance are single amino acid residue substitutions in the neuraminidase enzyme.

Meta-analysis finds incidence rate for oseltamivir resistance of 2.6%, with a higher incidence rates among influenza A patients, especially for H1N1 subtype influenza.

Resistance may be associated with pneumonia.

A prodrug that is hydrolysed to its active metabolite – the free oseltamivir carboxylate.

Has a volume of distribution of 23-26 litres, with Its half-life is about 1–3 hours

Its active metabolite has a half-life of 6–10 hours.

Eliminated in the urine as the active carboxylate metabolite with greater than 90% of oral dose.

Reduces the risk of lower respiratory tract infections resulting in antibiotic use and hospital admissions in adults.

In 2006 a Cochrane review concluded that oseltamivir should not be used during routine seasonal influenza because of its low effectiveness.


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