Tamiflu

Uses

Tamiflu is used for prevention of flu (influenza) in adults and adolescents aged 13 years and over who have been in contact with someone diagnosed with flu; treatment of flu (influenza) in adults and in children over one year of age when the influenza virus is circulating in the community

Tamiflu is also used to associated treatment for these conditions: Flu caused by Influenza, Influenza A Virus Infection, Influenza A, Influenza B, Influenza Type B

How Tamiflu works

Tamiflu phosphate is a pro-drug of the active metabolite (oseltamivir carboxylate) which is a potent and selective inhibitor of influenza virus neuraminidase enzymes, which are glycoproteins found on the virion surface. Viral neuraminidase enzyme activity is important for viral entry into uninfected cells, for the release of recently formed virus particles from infected cells, and for the further spread of the infectious virus in the body. Tamiflu activity reduces viral shedding and infectivity.

Tamiflu is effective agaisnt viral neuraminidases of influenza A (including pandemic H1N1) and influenza B.

Dosage

Tamiflu dosage

Tamiflu Phosphate may be taken with or without food. However, when taken with food, tolerability may be enhanced in some patients.Standard oral dose for the treatment of influenza:

• Adults and Adolescents: The recommended oral dose of Tamiflu for treatment of influenza in adults and adolescents 13 years and older is 75 mg twice daily for 5 days. Treatment should begin within 2 days of onset of symptoms of influenza.
• Pediatric patients: The safety and efficacy of Tamiflu for prophylaxis of influenza in pediatric patients younger than 13 years of age have not been established.

Recommended oral dose for the treatment of influenza:

• For prophylaxis of influenza in adults and adolescents 13 years and older following close contact with an infected individual: 75 mg once daily for at least 7 days. Therapyshould begin within 2 days of exposure.
• For prophylaxis during a community outbreak of influenza: 75 mg once daily. Safety and efficacy have been demonstrated for up to 6 weeks. The duration of protection lasts for as long as dosing is continued.

May be taken with or without food. May be taken with meals to reduce GI discomfort. Cap may be opened & mixed with sweetened food products eg chocolate syr, sweetened condensed milk, apple sauce or yogurt. Swallow mixture immediately after preparation.

Side Effects

The most frequently reported adverse events are nausea and vomiting. These events generally of mild to moderate degree and usually are occurred on the first 2 days of administration. Additional adverse events occurring in <1% of patients receiving Tamiflu for treatment include unstable angina, anemia, pseudomembranous colitis, humerus fracture, pneumonia, pyrexia, and peritonsillar abscess.

Toxicity

Reports of overdoses with oseltamivir have been received from clinical trials and during postmarketing experience. In the majority of cases reporting overdose, no adverse reactions were reported. Adverse reactions reported following overdose were similar in nature to those observed with therapeutic doses of oseltamivir.

Precaution

There is no evidence for efficacy of Tamiflu Phosphate in any illness caused by agents other than influenza viruses Types A and B. Efficacy of Tamiflu Phosphate in patients who begin treatment after 40 hours of symptoms has not been established.

Interaction

Information derived from pharmacology and pharmacokinetic studies of Tamiflu suggests that clinically significant drug interactions are unlikely. Co-administration with amoxicillin does not alter plasma levels of either compound.

Food Interaction

• Take with or without food. Co-administration with food does not affect pharmacokinetics but may enhance tolerability.

Tamiflu Disease Interaction

Moderate: hepatic impairment, renal impairment

Volume of Distribution

The mean volume of distribution at steady state of the oseltamivir carboxylate ranges approximately between 23 and 26 liters in humans, a volume that is roughly equivalent to extracellular body fluid. Since neuraminidase activity is extracellular, oseltamivir carboxylate distributes to all sites of influenza virus spread.

Elimination Route

Tamiflu is readily absorbed from the gastrointestinal tract after oral administration of oseltamivir phosphate and is extensively converted by predominantly hepatic esterases to the active metabolite oseltamivir carboxylate. At least 75 % of an oral dose reaches the systemic circulation as the active metabolite. Exposure to the pro-drug is less than 5 % relative to the active metabolite. Plasma concentrations of both pro-drug and active metabolite are proportional to dose and are unaffected by co-administration with food. Pharmacokinetic parameters following twice daily dosing of oseltamivir 75mg capsules are as follows: Cmax of oseltamivir and oseltamivir carboxylate were found to be 65ng/mL and 348ng/mL, respectively, while AUC (0-12h) of oseltamivir and oseltamivir carboxylate were found to be 112ng·h/mL and 2719ng·h/mL, respectively.

Half Life

Plasma concentrations of oseltamivir declined with a half-life of 1 to 3 hours in most subjects after oral administration, although plasma concentrations of oseltamivir carboxylate declined with a half-life of 6 to 10 hours in most subjects after oral administration.

Clearance

Renal clearance (18.8 l/h) of the drug exceeds glomerular filtration rate (7.5 l/h) indicating that tubular secretion occurs in addition to glomerular filtration.

Elimination Route

Following absorption, oseltamivir is more than 90 % eliminated through conversion to oseltamivir carboxylate and subsequent elimination entirely through renal excretion. During clinical studies, less than 20 % of oral radiolabelled dose was found to be eliminated in faeces.

Pregnancy & Breastfeeding use

Pregnancy Category C: There are insufficient human data upon which to base an evaluation of risk of Tamiflu Phosphate to the pregnant woman or developing fetus.

Nursing Mothers: It is not known whether oseltamivir or oseltamivir carboxylate is excreted in human milk. Tamiflu Phosphate should, therefore, be used only if the potential benefit for the lactating mother justifies the potential risk to the breast-fed infant.

Contraindication

Tamiflu is contraindicated in patients with known hypersensitivity to any of the components of the product.

Special Warning

Hepatic Impairment: The safety and pharmacokinetics in patients with hepatic impairment have not been evaluated.

Renal Impairment: Dose adjustment is recommended for patients with a serum creatinine clearance <30 mL/min.

Geriatric Use: The safety of Tamiflu Phosphate has been established in clinical studies.

Pediatric Use: The safety and efficacy of Tamiflu Phosphate in pediatric patients younger than 1 year of age have not been studied. Tamiflu Phosphate is not indicated for either treatment or prophylaxis of influenza in pediatric patients younger than 1 year of age.

Acute Overdose

At present there has been no experience of over dose. Single dose of up to 1000 mg of Tamiflu have been associated with nausea and/or vomiting.

Storage Condition

Store at 25°C. Reconstituted susp: Store between 2-8°C for up to 17 days or at 25°C for up to 10 days. Do not freeze.

Innovators Monograph

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