Antiviral Drugs and H1N1 Flu
Antiviral Drugs
Antiviral drugs are prescription medicines (pills, liquid or an inhaler) with activity against influenza viruses, including swine influenza viruses. Antiviral drugs can be used to treat swine flu or to prevent infection with swine flu viruses. These medications must be prescribed by a health care professional. Influenza antiviral drugs only work against influenza viruses -- they will not help treat or prevent symptoms caused by infection from other viruses that can cause symptoms similar to the flu. There are four influenza antiviral drugs approved for use in the United States (oseltamivir, zanamivir, amantadine and rimantadine). The swine influenza A (H1N1) viruses that have been detected in humans in the United States and Mexico are resistant to amantadine and rimantadine so these drugs will not work against these swine influenza viruses. Laboratory testing on these swine influenza A (H1N1) viruses so far indicate that they are susceptible (sensitive) to oseltamivir and zanamivir.
Until June 29, all of the novel H1N1 viruses tested were sensitive to the anti-viral drugs oseltamivir (Tamiflu, produced by Roche U.S. Pharmaceuticals) and zanamivir (Relenza, licensed by United Kingdom-based GlaxoSmithKline).
These drugs are called neuraminidase inhibitors and they work by blocking the function of neuraminidase (the N in H1N1), a protein on the surface of flu viruses that allows copies of the virus to be released into the body from the infected host cell.
H1N1 is resistant to two other anti-viral drugs that are available to treat or prevent flu, amantadine and rimantadine, which work by blocking a pathway into the healthy cell that the virus creates using a protein called M2.
On July 8, WHO announced that health authorities in Denmark, Japan and Hong Kong had reported the appearance of H1N1 viruses that were resistant to oseltamivir. The viruses were found in three patients who had mild disease and have recovered. The viruses are still sensitive to zanamivir.
Laboratories in the WHO Global Influenza Surveillance Network have evaluated nearly 1,000 pandemic H1N1 viruses for anti-viral drug resistance and found all other viruses are sensitive to oseltamivir and zanamivir. WHO and its partners continue to monitor flu viruses for anti-viral drug resistance.
The instances of drug resistance seem to be sporadic, according to WHO, and there is no evidence to indicate the development of widespread anti-viral resistance among pandemic H1N1 viruses.
| 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 | 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 |
| 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$$ | |
| Duration of Treatment | Treatment | Recommended duration for antiviral treatment is 5 days. | ||||
| Chemoprophylaxis |
Recommended duration is 5-7 days after the last known exposure. |
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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);
* 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. †† 55 mg/kg body weight of amantadine or rimantadine syrup = 1 tsp/22 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.
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Treatment
If you get sick, antiviral drugs can make your illness milder and make you feel better faster. They may also prevent serious influenza complications. Influenza antiviral drugs work best when started soon after illness onset (within two [2] days), but treatment with antiviral drugs should still be considered after 48 hours of symptom onset, particularly for hospitalized patients or people at high risk for influenza-related complications.
Prevention
Influenza antiviral drugs also can be used to prevent influenza when they are given to a person who is not ill, but who has been or may be near a person with swine influenza. When used to prevent the flu, antiviral drugs are about 70% to 90% effective. When used for prevention, the number of days that they should be used will vary depending on a person’s particular situation.