Oseltamivir

Oseltamivir: a review of its use in influenza

Oseltamivir is a prodrug of oseltamivir carboxylate (Ro 64-0802, GS4071), a potent and selective inhibitor of the neuraminidase glycoprotein essential for replication of influenza A and B viruses. Studies in volunteers with experimental human influenza A or B showed that administration of oral oseltamivir 20 to 200 mg twice daily for 5 days reduced both the quantity and duration of viral shedding compared with placebo. Subsequent assessment of the drug at a dosage of 75 mg twice daily for 5 days in otherwise healthy adults with naturally acquired febrile influenza showed that oseltamivir reduced the duration of the disease by up to 1.5 days and the severity of illness by up to 38% compared with placebo when initiated within 36 hours of symptom onset (earlier initiation of therapy was associated with faster resolution). The incidence of secondary complications and the use of antibacterials were also reduced significantly in oseltamivir recipients. A liquid formulation of oseltamivir (2 mg/kg twice daily for 5 days) has been shown to be effective in the treatment of children with influenza, and data presented in abstracts suggest that the drug may also be of use in high-risk populations such as the elderly or those with chronic cardiac or respiratory disease. In addition to treatment efficacy, the drug has demonstrated efficacy when used for seasonal or household prophylaxis. Oral oseltamivir (75 mg once or twice daily for 6 weeks) during a period of local influenza activity significantly prevented the development of naturally acquired influenza by >70% compared with placebo in unvaccinated otherwise healthy adults. The drug also demonstrated efficacy when used adjunctively in previously vaccinated high-risk elderly patients (92% protective efficacy). Short term administration of oseltamivir (75 mg once daily for 7 days) may significantly reduce the risk of illness in household contacts of infected persons when administered within 48 hours of symptom onset in the infected person. Oseltamivir 75 mg twice daily for 5 days was well tolerated in clinical trials in healthy adults and high-risk patients, with nausea and vomiting being the most commonly reported events. Gastrointestinal events were mild and transient and both nausea and vomiting were less likely when oseltamivir was taken with food.

CONCLUSIONS

Oseltamivir is a well tolerated orally active neuraminidase inhibitor which significantly reduces the duration of symptomatic illness and hastens the return to normal levels of activity when initiated promptly in patients with naturally acquired influenza. It therefore represents a useful therapeutic alternative to zanamivir (especially in patients who prefer oral administration or who have an underlying respiratory disorder) and the M2 inhibitors amantadine and rimantadine (because of its broader spectrum of anti-influenza activity and lower likelihood of resistance) in patients with influenza. In addition, although annual vaccination remains the best means of influenza prevention, there may be a place for oseltamivir in providing household prophylaxis or adjunctive prophylaxis in high-risk vaccinated patients during an outbreak of the disease or for use in patients in whom vaccination is unsuitable or ineffective.

Fatores de risco e medidas profiláticas nas pneumonias adquiridas na comunidade

Este artigo revisa os efeitos do envelhecimento, tabagismo, DPOC, insuficiência cardíaca, colonização da orofaringe, aspiração (micro e macro), alcoolismo, cirrose hepática, deficiência nutricional, imunossupressão e fatores ambientais sobre o risco de adquirir pneumonia na comunidade e sua gravidade. Na segunda parte, é feita revisão sobre a ação profilática das vacinas antiinfluenza e antipneumococo, assim como a ação das drogas antivirais, na profilaxia e tratamento das pneumonias adquiridas na comunidade.

Prevention, diagnosis, and treatment of influenza: current and future options

Because influenza significantly affects the health of children, this review describes the current and future options for preventing, diagnosing, and treating influenza infections. Currently, the inactivated influenza vaccine is recommended for prevention of influenza; however, the live, attenuated, intranasal influenza vaccine is a potential future option. For diagnosis, viral culture is the gold standard, although four rapid diagnostic tests are available for more immediate results. The impetus for rapid results is the availability of effective antiviral agents indicated for early influenza infection. The four currently approved antiviral agents are amantadine, rimantadine, zanamivir [Relenza, Glaxo Wellcome, Inc., Research Triangle Park, NC] and oseltamivir [Tamiflu, Roche Pharmaceuticals, Nutley, NJ]. The indications, benefits, side effects and ages for which each drug is approved are reviewed.

Neuraminidase inhibitors: zanamivir and oseltamivir

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and safety of zanamivir and oseltamivir for the prophylaxis and treatment of influenza.

DATA SOURCES

A MEDLINE search restricted to English-language journals was conducted (1980-May 2000).

STUDY SELECTION AND DATA EXTRACTION

All efficacy and safety trials were included if conducted in humans and published in a journal. Abstracts were included if no other data source was available.

DATA SYNTHESIS

Zanamivir and oseltamivir block influenza neuraminidase and prevent the cleavage of sialic acid residues, thus interfering with progeny virus dispersement within the mucosal secretions and reducing viral infectivity. The neuraminidase trials for prophylaxis and treatment of influenza enrolled predominantly young (mean age 29-37 y), healthy, mostly unvaccinated individuals who were at the lowest risk of influenza and its complications. When zanamivir 10 mg inhaled twice daily or oseltamivir 75 mg orally twice daily were used for treatment, systemic symptoms such as myalgias, fever, and headache were reduced by approximately 0.7-1.5 days. Greater efficacy (symptom reduction by 1.5-2.0 d) was noted in proven cases of influenza infection, in febrile patients, and in patients who received the treatment medication within 30 hours of symptom onset. Clinical efficacy did not increase when doses higher than the treatment dose approved by the Food and Drug Administration were used. When given for prophylaxis, zanamivir 10 mg inhaled once daily or oseltamivir 75 mg orally once daily was used for four to six weeks and achieved protective clinical efficacy for laboratory-confirmed influenza ranging from 67% to 74%, depending on whether culture or serologic tests were performed. The most common adverse effects (usually < 5%) included upper respiratory tract symptoms. Patients with asthma or chronic obstructive pulmonary disease who received zanamivir had an increased incidence of a > 20% decline in forced expiratory volume in one second or peak expiratory flow rates. Headaches, nausea, and vomiting were more frequent in the oseltamivir groups than in placebo groups. The most common gastrointestinal adverse effects, nausea and vomiting, were reduced to approximately 10% by administering the medication with food.

CONCLUSIONS

Zanamivir and oseltamivir are more effective in preventing culture-positive influenza or for treatment of culture-positive influenza in febrile (> or = 37.8 degrees C) individuals. Treatment is more effective if initiated within 30 hours of symptom onset in febrile individuals; however, it is difficult to meet these criteria. More realistically, clinical efficacy is closer to 60-70% and, for treatment started within 48 hours for laboratory-confirmed influenza, symptom reduction is approximately 0.7-1.5 days. If used appropriately to minimize the development of resistance, the neuraminidase inhibitors represent a new and unique class of antiinfluenza agents that can potentially reduce the morbidity associated with influenza.