New Engl J Med 2005;353:1363-73.
Vaccination is the primary means for prevention of influenza, however antigenic drift in the virus may render the vaccine less protective and outbreaks can occur more easily among high-risk population. Hence antiviral agents may form an important role in management of this virus.
Four drugs are currently available for management of influenza infection namely:
- Amantadine } Adamantanes
- Rimantadine }
- Oseltamivir } Neuraminidase inhibitors
- Zanamivir }
The Adamantanes inhibit viral uncoating within the cell, are effective only against influenza, are associated with severe side effects and new strains of H5N1 are already resistant to this class of drugs. Hence they are not recommended for treatment of bird flu.
The neuraminidase inhibitors interfere with release of progeny influenza virus from infected host cells and thus prevent infection of new host cells. Hence, these drugs should be administered as early in the disease cause as possible. They are effective against all neuraminidase subtypes and this effective against all strains of influenza and hence are the drug of choice for the recent bird flu.
Pharmacokinetics :- Zanamivir is not orally effective and is available as a dry powder for inhalation which delivers the drug directly to the respiratory tract. The concentration of the drug in the respiratory tract has been estimated to be more than 1000 times higher than IC 50 (50 percent inhibitory concentration) with action starting within 10 seconds of administration.
Oseltamivir is available as capsule or powder for liquid suspension with good oral absorption. Half life is 6 to 10 hours. The drug is primarily excreted in the kidney. It is useful in extrapulmonary disease manifestation.
Adverse Effects :-
Zanamivir – Cough, bronchospasm and reversible decrease in pulmonary functions.
Oseltamivir – Transient nausea, vomiting and abdominal pain.
Dosage :- See Table 1. Oseltamivir dose needs to be adjusted in patients with renal disease.
Table 1: Treatment of BIRD FLU (1)
| Drug
|
1-6 years
|
7-12 years
|
> 13 years
|
| Treatment Zanamivir
|
- |
10 mg twice daily for 5 days
|
10 mg twice daily for 5 days
|
| Oseltamivir
|
75 mg twice daily for 5 days irrespective of weight
|
| < 15kg
|
30 mg twice daily for 5 days
|
30 mg twice daily for 5 days
|
|
| 15-23 kg
|
45 mg twice daily for 5 days
|
45 mg twice daily for 5 days
|
| 23-40 kg
|
60 mg twice daily for 5 days
|
60 mg twice daily for 5 days
|
| > 40 kg
|
75 mg twice daily for 5 days
|
75 mg twice daily for 5 days
|
| Prevention Oseltamivir
|
- |
- |
75 mg once daily for 7-10 days
|
Resistance: Resistance though rare with neuraminidase inhibitors has been reported recently with Oseltamivir more commonly in children and hence these drugs need to be given with caution to prevent emergence of drug resistance.
Last updated on 01-04-06
