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Australian Journal of Pharmacy : October 2006
cdi: drug news • approved CPE pharmacy ed u complications have included Reye’s syndrome, lung haemorrhage, pancytopaenia and sepsis.19 Mortality The fatality rate among hospitalised patients has been high—62 per cent in all patients but 89 per cent in patients aged less than 15 years.16,19 Death has occurred at an average of nine-to-10 days after onset of the illness (with a range of six to 30 days).19 Table One: Adverse effects of the neuraminidase inhibitors Drug and use Zanamivir treatment Adverse effects Serious: Allergic reaction, arrhythmia, bronchospasm, difficulty breathing, facial oedema, rash, seizure, fainting, itching (<1.5 per cent) Minor: Headache (2 per cent), dizziness (2 per cent), nausea (3 per cent), diarrhoea (3 per cent), vomiting (1 per cent), sinusitis (3 per cent), bronchitis (2 per cent), cough (2 per cent), infection—ear, nose, throat (2 per cent) Oseltamivir treatment Serious: Aggravation of diabetes, arrhythmia, confusion, hepatitis, pseudomembranous colitis, fever, rash, seizure, swelling of face or tongue, toxic epidermal necrolysis, unstable angina (<1 per cent) Minor: Insomnia (1 per cent), dizziness (1 per cent), nausea (10 per cent), vomiting (9 per cent) Oseltamivir prophylaxis Similar to those reported during treatment but generally with a lower incidence Treatment Hospitalised patients Most hospitalised patients need ventilatory support within 48 hours of admission.19 Intensive care for multi-organ failure and hypotension is also required.19 Treatment with broad-spectrum antibiotics, antiviral agents and corticosteroids has also been utilised but their usefulness has not been rigorously assessed.19 Initiation of oseltamivir in some patients has resulted in disappearance of the virus within two-to-three days but progression of disease and death has also been reported in patients who have received early therapy with oseltamivir.19 Antivirals Three drugs are available for treatment or prophylaxis of influenza infections: • Amantadine (Symmetrel); • Zanamivir (Relenza); and • Oseltamivir (Tamiflu) Unfortunately, future pandemic strains are likely to be resistant to amantadine. Studies done in nursing homes where amantadine was used as prophylactic treatment for outbreaks of influenza showed that there was a rapid development of resistance to the drug.23 Zanamivir is not bioavailable orally and is marketed as a dry powder for inhalation. Ten-to-twenty per cent of the inhaled powder reaches the lungs with the remainder deposited in the oropharynx.23 The concentration of the drug in the lungs has been estimated to be 1,000 times the 50 per cent inhibitory concentration needed to inhibit neuraminidase.23 It also works within 10 seconds to inhibit neuraminidase.23 Both these factors are favourable in terms of limiting the development of resistance to zanamivir. Oseltamivir is available as a capsule or powder for liquid Table Two: Dosing schedule of neuraminidase inhibitors Drug 1-6 years Treatment Zanamivir Oseltamivir – <15kg:30mg bd for 5 days 15–23kg:45mg bd for 5 days 23–40kg:60mg bd for 5 days >40kg:75mg bd for 5 days Prevention Oseltamivir – 7-12 years Dose according to age 13-64 years <15kg:30mg bd for 5 days 15–23kg:45mg bd for 5 days 23–40kg:60mg bd for 5 days >40kg:75mg bd for 5 days – bd for 5 days 75mg bd Renal impairment >64 years 10mg (2 inhalations) 10mg (2 inhalations) 10mg (2 inhalations) bd for 5 days bd for 5 days 75mg bd for 5 days for 5 days 10mg (2 inhalations) bd for 5 days Creatinine clearance 10–30ml/min, 75mg once daily 75mg once daily for >7 days (up to 6 weeks) 86 ? THE AUSTRALIAN JOURNAL OF PHARMACY, VOL.87 OCTOBER 2006 75mg once daily for >7 days (up to 6 weeks) Creatinine clearance 10–30mL/min, 75mg every second day