Welcome to the CDC Seasonal Flu website.
Skip directly to the search box, site navigation, or .

  • Contact Us
  • 800–CDC–INFO
  • (800-232-4636)
  • 888–232–6348 (TTY)
  • cdcinfo@cdc.gov

Antiviral Agents for Seasonal Influenza: Dosage

On this page:

















Dosage recommendations vary by age group and medical conditions:

Children

Zanamivir
Zanamivir is licensed for treatment of influenza among children aged 7 years and older. The recommended dosage of zanamivir for treatment of influenza is 2 inhalations (one 5-mg blister per inhalation for a total dose of 10 mg) twice daily (approximately 12 hours apart). Zanamivir is licensed for chemoprophylaxis of influenza among children aged 5 years and older; the chemoprophylaxis dosage of zanamivir for children aged 5 years and older is 10 mg (2 inhalations) once a day.

Oseltamivir
Oseltamivir is licensed for treatment and chemoprophylaxis among children aged 1 year and older. Recommended treatment dosages vary by the weight of the child: 30 mg twice a day for children who weigh less than or equal to 15 kg, 45 mg twice a day for children who weigh more than 15—23 kg, 60 mg twice a day for those who weigh more than 23—40 kg, and 75 mg twice a day for those who weigh more than 40 kg. Dosages for chemoprophylaxis are the same for each weight group, but doses are administered only once per day rather than twice.

Amantadine
Use of amantadine among children aged 1 year and younger has not been adequately evaluated. The FDA-approved dosage for children aged 1 through 9 years for treatment and prophylaxis is 4.4--8.8 mg/kg body weight/day, not to exceed 150 mg/day. Although further studies are needed to determine the optimal dosage for children aged 1--9 years, physicians should consider prescribing only 5 mg/kg body weight/day (not to exceed 150 mg/day) to reduce the risk for toxicity. The approved dosage for children 10 years and younger is 200 mg/day (100 mg twice a day); however, for children weighing <40 kg, prescribing 5 mg/kg body weight/day, regardless of age, is advisable.

Rimantadine
Rimantadine is approved for prophylaxis among children aged 1 year and older and for treatment and prophylaxis among adults. Although rimantadine is approved only for prophylaxis of infection among children, certain specialists in the management of influenza consider it appropriate for treatment among children. Use of rimantadine among children aged 1 year and younger has not been adequately evaluated. Rimantadine should be administered in 1 or 2 divided doses at a dosage of 5 mg/kg body weight/day, not to exceed 150 mg/day for children aged 1 through 9 years. The approved dosage for children aged >10 years is 200 mg/day (100 mg twice a day); however, for children weighing <40 kg, prescribing 5 mg/kg body weight/day, regardless of age, is recommended.

People Aged 65 Years and Older

Zanamivir and Oseltamivir
No reduction in dosage for oseltamivir or zanamivir is recommended on the basis of age alone.

Amantadine. The daily dosage of amantadine for persons aged 65 years and older should not exceed 100 mg for prophylaxis or treatment, because renal function declines with increasing age. For certain older persons, the dose should be further reduced.

Rimantadine. Among older persons, the incidence and severity of central nervous system (CNS) side effects are substantially lower among those taking rimantadine at a dosage of 100 mg/day than among those taking amantadine at dosages adjusted for estimated renal clearance. However, chronically ill older persons have had a higher incidence of CNS and gastrointestinal symptoms and serum concentrations 2--4 times higher than among healthy, younger persons when rimantadine has been administered at a dosage of 200 mg/day.

For prophylaxis among persons older than 65 years, the recommended dosage is 100 mg/day. For treatment of older persons in the community, a reduction in dosage to 100 mg/day should be considered if they experience side effects when taking a dosage of 200 mg/day. For treatment of older nursing home residents, the dosage of rimantadine should be reduced to 100 mg/day.

People with Impaired Renal Function

Zanamivir
Limited data are available regarding the safety and efficacy of zanamivir for patients with impaired renal function. Among patients with renal failure who were administered a single intravenous dose of zanamivir, decreases in renal clearance, increases in half-life, and increased systemic exposure to zanamivir were reported. However, a limited number of healthy volunteers who were administered high doses of intravenous zanamivir tolerated systemic levels of zanamivir that were substantially higher than those resulting from administration of zanamivir by oral inhalation at the recommended dose. On the basis of these considerations, the manufacturer recommends no dose adjustment for inhaled zanamivir for a 5-day course of treatment for patients with either mild-to-moderate or severe impairment in renal function.

Oseltamivir
Serum concentrations of oseltamivir carboxylate, the active metabolite of oseltamivir, increase with declining renal function. For patients with creatinine clearance of 10—30 mL per minute, a reduction of the treatment dosage of oseltamivir to 75 mg once daily and in the chemoprophylaxis dosage to 75 mg every other day is recommended. No treatment or chemoprophylaxis dosing recommendations are available for patients undergoing routine renal dialysis treatment.

Amantadine.
A reduction in dosage is recommended for patients with creatinine clearance <50 mL/min. Guidelines for amantadine dosage on the basis of creatinine clearance are located in the package insert. Because recommended dosages on the basis of creatinine clearance might provide only an approximation of the optimal dose for a given patient, such persons should be observed carefully for adverse reactions. If necessary, further reduction in the dose or discontinuation of the drug might be indicated because of side effects. Hemodialysis contributes minimally to amantadine clearance.

Rimantadine.
A reduction in dosage to 100 mg/day is recommended for persons with creatinine clearance <10 mL/min. Because of the potential for accumulation of rimantadine and its metabolites, patients with any degree of renal insufficiency, including older persons, should be monitored for adverse effects, and either the dosage should be reduced or the drug should be discontinued, if necessary. Hemodialysis contributes minimally to drug clearance.

People with Liver Disease

Zanamivir and Oseltamivir
Use of zanamivir or oseltamivir has not been studied among persons with hepatic dysfunction.

Amantadine
No increase in adverse reactions to amantadine has been observed among persons with liver disease. Rare instances of reversible elevation of liver enzymes among patients receiving amantadine have been reported, although a specific relation between the drug and such changes has not been established.

Rimantadine
A reduction in dosage to 100 mg/day is recommended for persons with severe hepatic dysfunction.

People with Seizure Disorders

Zanamivir and Oseltamivir
Seizure events have been reported during postmarketing use of zanamivir and oseltamivir, although no epidemiologic studies have reported any increased risk for seizures with either zanamivir or oseltamivir use.

Amantadine
An increased incidence of seizures has been reported among patients with a history of seizure disorders who have received amantadine. Patients with seizure disorders should be observed closely for possible increased seizure activity when taking amantadine.

Rimantadine
Seizures (or seizure-like activity) have been reported among persons with a history of seizures who were not receiving anticonvulsant medication while taking rimantadine. The extent to which rimantadine might increase the incidence of seizures among persons with seizure disorders has not been adequately evaluated.

People with Weakened Immune Systems

Oseltamivir
A recent retrospective case-control study demonstrated that oseltamivir was safe and well tolerated when used during the control of an influenza outbreak among hematopoietic stem cell transplant recipients living in a residential facility.

Route

Oseltamivir is administered orally in capsule or oral suspension form.

Zanamivir is available as a dry powder that is self-administered via oral inhalation by using a plastic device included in the package with the medication. Patients should be instructed about the correct use of this device.

Amantadine and rimantadine are administered orally. They are available in tablet or syrup form

Table: Recommended Daily Dosage of Seasonal Influenza Antiviral Medications for Treatment and Chemoprophylaxis—United States
Antiviral agent Age group (yrs)
1-6 7-9 10-12 13-64 65 and older
Zanamivir* Treatment, influenza A and B N/A† 10 mg (2 inhalations) twice daily 10 mg (2 inhalations) twice daily 10 mg (2 inhalations) twice daily 10 mg (2 inhalations) twice daily
Chemoprophylaxis, influenza A and B Ages 1-4
N/A		 Ages 5-9
10 mg (2 inhalations) once daily		 10 mg (2 inhalations) once daily 10 mg (2 inhalations) once daily 10 mg (2 inhalations) once daily
Oseltamivir Treatment†, influenza A and B Dose varies by child's weight§ Dose varies by child's weight§ Dose varies by child's weight§ 75 mg twice daily 75 mg twice daily
Chemoprophylaxis, influenza A and B Dose varies by child's weight¶ Dose varies by child's weight¶ Dose varies by child's weight¶ 75 mg/day 75 mg/day
Amantadine** Treatment, influenza A Dose varies by child's weight§ Dose varies by child's weight§ Dose varies by child's weight§ 75 mg twice daily 75 mg twice daily
Prophylaxis, influenza A 5 mg/kg body weight/day up to 150 mg in 2 divided doses†† 5 mg/kg body weight/day up to 150 mg in 2 divided doses†† 100 mg twice daily§§ 100 mg twice daily§ less than or equal to 100 mg/day
Rimantadine¶¶ Treatment#, influenza A N/A## N/A N/A 100 mg twice daily§§$  100 mg/day
Prophylaxis, influenza A 5 mg/kg body weight/day up to 150 mg in 2 divided doses†† 5 mg/kg body weight/day up to 150 mg in 2 divided doses†† 100 mg twice daily§§ 100 mg twice daily§ 100 mg/day$$
NOTE: Zanamivir is manufactured by GlaxoSmithKline (Relenza — inhaled powder). Zanamivir is approved for treatment of persons aged 7 years and older and approved for chemoprophylaxis of persons aged 5 years and older. Oseltamivir is manufactured by Roche Pharmaceuticals (Tamiflu® — tablet) Oseltamivir is approved for treatment or chemoprophylaxis of persons aged 1 year and older. Amantadine manufacturers include Endo Pharmaceuticals (Symmetrel® — tablet and syrup); Geneva Pharms Tech (Amantadine HCL — capsule);
USL Pharma (Amantadine HCL — capsule and tablet); and Alpharma, Carolina Medical, Copley Pharmaceutical, HiTech Pharma, Mikart, Morton Grove, and Pharmaceutical Associates (Amantadine HCL — syrup), and Sandoz. Rimantadine is manufactured by Forest Laboratories (Flumadine® — tablet and syrup); Corepharma, Impax Labs (Rimantadine HCL — tablet), and Amide Pharmaceuticals (Rimantadine HCL — tablet). No antiviral medications are approved for treatment or chemoprophylaxis of influenza among children younger than 1 year of age. This information is based on data published by the Food and Drug Administration (FDA).

* Zanamivir is administered through oral inhalation by using a plastic device included in the medication package. Patients will benefit from instruction and demonstration of the correct use of the device. Zanamivir is not recommended for those persons with underlying airway disease.

† A reduction in the dose of oseltamivir is recommended for persons with creatinine clearance less than 30 mL/min.

§ The treatment dosing recommendation for children who weigh 15 kg or less is 30 mg twice a day. For children who weigh more than 15 kg and up to 23 kg, the dose is 45 mg twice a day. For children who weigh more than 23 kg and up to 40 kg, the dose is 60 mg twice a day. For children who weigh more than 40 kg, the dose is 75 mg twice a day.

¶ The chemoprophylaxis dosing recommendation for children who weigh less than 15 kg is 30 mg once a day. For who weigh more than 15 kg and up to 23 kg, the dose is 45 mg once a day. For children who weigh more than 23 kg and up to 40 kg, the dose is 60 mg once a day. For children who weigh more than 40 kg, the dose is 75 mg once a day.

** The drug package insert should be consulted for dosage recommendations for administering amantadine to persons with creatinine clearance less than or equal to 50 mL/ min/1.73m2.

†† 5 mg/kg body weight of amantadine or rimantadine syrup = 1 tsp/2.2 lbs.

§§ Children aged 10 years and older who weigh less than 40 kg should be administered amantadine or rimantadine at a dosage of 5 mg/kg body weight/day.

¶¶ A reduction in dosage to 100 mg/day of rimantadine is recommended for persons who have severe hepatic dysfunction or those with creatinine clearance less than 10 mL/min. Other persons with less severe hepatic or renal dysfunction taking 100 mg/day of rimantadine should be observed closely, and the dosage should be reduced or the drug discontinued, if necessary.

# Only approved by FDA for treatment among adults.

## Not applicable.

$ Rimantadine is approved by FDA for treatment among adults. However, certain specialists in the management of influenza consider rimantadine appropriate for treatment among children. Studies evaluating the efficacy of amantadine and rimantadine in children are limited, but they indicate that treatment with either drug diminishes the severity of influenza A infection when administered within 48 hours of illness onset.

$$ Older nursing-home residents should be administered only 100 mg/day of rimantadine. A reduction in dosage to 100 mg/day should be considered for all persons aged 65 years and older, if they experience possible side effects when taking 200 mg/day.

NOTE: The text above on zanamivir and oseltamivir is taken from Prevention & Control of Influenza - Recommendations of the Advisory Committee on Immunization Practices (ACIP) 2008. MMWR 2008 Jul 17; Early Release:1-60. (Also available as PDF, 586K).. MMWR 2008 Jul 17; Early Release:1-60.

The text on amantadine and rimantadine is taken from Prevention & Control of Influenza – Recemmendations of the Advisory Committee on Immunization Practices (ACIP) 2005. MMWR 2005 Jul 29; 54(RR08);1-40.

CDC logo
USA.gov: The U.S. Government's Official Web Portal Department of Health and Human Services