Neuraminidase inhibitors for preventing and treating influenza in children

BACKGROUND

During epidemics, influenza attack rates in children may exceed 40%. Options for prevention and treatment currently include the neuraminidase inhibitors zanamivir and oseltamivir. Laninamivir octanoate, the prodrug of laninamivir, is currently being developed.

OBJECTIVES

To assess the efficacy, safety and tolerability of neuraminidase inhibitors in the treatment and prevention of influenza in children.

SEARCH METHODS

For this update we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1) which includes the Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to January week 2, 2011) and EMBASE (January 2010 to January 2011).

SELECTION CRITERIA

Double-blind, randomised controlled trials (RCTs) comparing neuraminidase inhibitors with placebo or other antiviral drugs in children aged up to and including 12 years. We also included safety and tolerability data from other types of studies.

DATA COLLECTION AND ANALYSIS

Four review authors selected studies, assessed study quality and extracted data for the current and previous versions of this review. We analysed data separately for oseltamivir versus placebo, zanamivir versus placebo and laninamivir octanoate versus oseltamivir.

MAIN RESULTS

Six treatment trials involving 1906 children with clinical influenza and 450 children with influenza diagnosed on rapid near-patient influenza testing were included. Of these 2356 children, 1255 had laboratory-confirmed influenza. Three prophylaxis trials involving 863 children exposed to influenza were also included. In children with laboratory-confirmed influenza oseltamivir reduced median duration of illness by 36 hours (26%, P < 0.001). One trial of oseltamivir in children with asthma who had laboratory-confirmed influenza showed only a small reduction in illness duration (10.4 hours, 8%), which was not statistically significant (P = 0.542). Laninamivir octanoate 20 mg reduced symptom duration by 2.8 days (60%, P < 0.001) in children with oseltamivir-resistant influenza A/H1N1. Zanamivir reduced median duration of illness by 1.3 days (24%, P < 0.001). Oseltamivir significantly reduced acute otitis media in children aged one to five years with laboratory-confirmed influenza (risk difference (RD) -0.14, 95% confidence interval (CI) -0.24 to -0.04). Prophylaxis with either zanamivir or oseltamivir was associated with an 8% absolute reduction in developing influenza after the introduction of a case into a household (RD -0.08, 95% CI -0.12 to -0.05, P < 0.001). The adverse event profile of zanamivir was no worse than placebo but vomiting was more commonly associated with oseltamivir (number needed to harm = 17, 95% CI 10 to 34). The adverse event profiles of laninamivir octanoate and oseltamivir were similar.

AUTHORS' CONCLUSIONS

Oseltamivir and zanamivir appear to have modest benefit in reducing duration of illness in children with influenza. However, our analysis was limited by small sample sizes and an inability to pool data from different studies. Oseltamivir reduces the incidence of acute otitis media in children aged one to five years but is associated with a significantly increased risk of vomiting. One study demonstrated that laninamivir octanoate was more effective than oseltamivir in shortening duration of illness in children with oseltamivir-resistant influenza A/H1N1. The benefit of oseltamivir and zanamivir in preventing the transmission of influenza in households is modest and based on weak evidence. However, the clinical efficacy of neuraminidase inhibitors in 'at risk' children is still uncertain. Larger high-quality trials are needed with sufficient power to determine the efficacy of neuraminidase inhibitors in preventing serious complications of influenza (such as pneumonia or hospital admission), particularly in 'at risk' groups.

Neuraminidase inhibitors for preventing and treating influenza in children

BACKGROUND

During epidemic years, influenza attack rates in children exceed 40%. Options for prevention and treatment include the neuraminidase inhibitors: zanamivir and oseltamivir.

OBJECTIVES

To assess the efficacy, safety and tolerability of neuraminidase inhibitors in the treatment and prevention of influenza infection in children.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 1, 2005); MEDLINE (1966 to April 2005); EMBASE (January 1980 to December 2004); the on-line GlaxoSmithKline Clinical Trials Register; the on-line Roche Clinical Trial Protocol Registry and Clinical Trial Results Database (August 2005); and reference lists of articles. We also scrutinised web sites of European and US regulatory bodies and contacted manufacturers and authors.

SELECTION CRITERIA

Double-blind, randomised, controlled trials comparing neuraminidase inhibitors with placebo or other antiviral drugs in children less than 12 years of age. Additional safety and tolerability data from other sources were also included.

DATA COLLECTION AND ANALYSIS

Four authors applied the inclusion criteria to the retrieved studies, assessed trial quality and extracted data. Data were analysed separately for oseltamivir and zanamivir.

MAIN RESULTS

Three trials involving 1500 children with a clinical case definition of influenza were included, of whom 977 had laboratory-confirmed influenza. Overall, trial quality was good. Oseltamivir reduced the median duration of illness by 26% (36 hours) in healthy children with laboratory-confirmed influenza (P value less than 0.0001). The reduction was only 7.7% (10 hours) in 'at risk' (asthmatic) children, and this did not reach statistical significance (P value = 0.54). Zanamivir reduced the median duration of illness by 24% (1.25 days) in healthy children with laboratory-confirmed influenza (P value less than 0.001). No data in 'at risk' children were available. Only oseltamivir produced a significant reduction in the complications of influenza (particularly otitis media), although there was a trend to benefit for zanamivir. We identified one randomised, controlled trial of oseltamivir for the prevention of influenza transmission in households, reporting data from 222 paediatric contacts. Where index cases had laboratory-confirmed influenza, a protective efficacy of 55% was observed, but this did not reach statistical significance (P value = 0.089). The adverse events profile of zanamivir was no worse than placebo, but vomiting was more common in children treated with oseltamivir.

AUTHORS' CONCLUSIONS

Neuraminidase inhibitors are effective in shortening illness duration in healthy children with influenza, but efficacy in 'at risk' children remains to be proven. Oseltamivir is also effective in reducing the incidence of secondary complications, and may be effective for influenza prophylaxis.

Safety of neuraminidase inhibitors for influenza

Neuraminidase inhibitors, oseltamivir and zanamivir, are used for the treatment of, and protection from, influenza. The safety of these compounds has been assessed in systematic reviews. However, the data presented are somewhat limited by the paucity of good quality adverse event data available. The majority of safety outcomes are based on evidence from just one or two randomised controlled trials. The results of the systematic reviews suggest that neuraminidase inhibitors have a reasonable side effect and adverse effect profile if they are to be used to treat or protect patients against a life-threatening disease. However, if these compounds are to be prescribed in situations in which avoidance of inconvenience or minor discomfort is hoped for, then the balance of harms to benefits will be more difficult to judge.

Antiviral drugs in influenza: an adjunct to vaccination in some situations

(1) Influenza is a common acute respiratory disease due to a virus that causes annual seasonal epidemics. Three major pandemics occurred in the 20th century, in 1918-1919, 1957 and 1968, mainly due to genetic variants of type A influenza virus. (2) In temperate regions the incidence of hospitalisation increases during annual influenza epidemics. More than 90% of deaths linked to influenza involve people over 65 years of age. (3) The clinical manifestations of influenza virus infection are non specific. The main complications are secondary bacterial respiratory tract infections (especially pneumonia); those most at risk are people over 65, infants less than one year old, and people with underlying chronic disorders (pulmonary, cardiac, renal or metabolic) or immune deficiencies. (4) Vaccination is the main preventive measure. During most years the vaccine strain closely matches the epidemic strain. In relative terms, vaccination of people over 65 reduces the number of deaths linked to influenza by about 80%, hospitalisation and pneumonia by about 50%, and symptomatic influenza by about 30%. Yearly vaccination is recommended for younger people with serious chronic disease. (5) Three antiviral drugs are currently approved in France for prevention or treatment of influenza: amantadine and the neuraminidase inhibitors zanamivir and oseltamivir. (6) Efficacy of antiviral drugs has not been evaluated in comparative randomised trials in which death and influenza complications were the primary outcome measures. (7) A systematic review of 20 comparative randomised trials involving about 2500 healthy people showed that amantadine reduced the frequency of flu-like syndromes by about 7% in absolute terms (26.3% versus 33.1% with placebo). Zanamivir and oseltamivir have only been shown to reduce the frequency of serologically confirmed episodes of influenza (0.4% to 2.5%, compared to 4.4% to 14.9% with placebo). (8) In a randomised placebo-controlled trial of oseltamivir, involving 548 institutionalised subjects over 65 years of age, more than 80% of whom had been vaccinated, respiratory tract infections were less frequent in the oseltamivir group, but the relevance of this result is undermined by the small number of observed cases. (9) Efficacy of antiviral drugs on avian influenza (bird flu) was studied during a 2003 Dutch outbreak due to a type A/H7N7 virus. Among the 38 exposed persons who were treated, about 3% developed symptoms, compared with about 10% of 52 exposed persons who refused treatment (p = 0.38). The low statistical power and the lack of randomisation rule out any firm conclusions on preventive effects. (10) The three antiviral drugs have different profiles of adverse effects and drug interactions. Amantadine carries a risk of neuropsychological, atropinic and dopaminergic adverse effects, and can interact with drugs that have similar effects. Zanamivir carries a risk of life-threatening bronchospasm. Oseltamivir was approved relatively recently and its full spectrum of adverse effects is not yet known; its main adverse effects appear to be mild gastrointestinal disturbances, although a few cases of serious cutaneous reactions have been reported. (11) In vitro resistance to the three drugs has been demonstrated, but the possible clinical and epidemiological consequences are unclear. (12) In situations warranting antiviral therapy for the prevention of influenza, oseltamivir, at a dose of 75 mg/day for 10 days, is the drug with the best risk-benefit balance. Its use should be limited to situations where a major potential benefit exists in order to avoid selection for resistant strains. (13) Testing of oseltamivir in children is limited. Oseltamivir should be avoided during pregnancy, because of evidence that it may harm the unborn child. (14) In practice, the use of antiviral drugs in otherwise healthy adults and children is not generally recommended. (15) Despite the lack of convincing data regarding the efficacy of oseltamivir in preventing complications of influenza, its effect on documented infections suggests it may be useful for unvaccinated individuals who are at high risk of infection and severe complications. Under these conditions, treatment should be started within 48 hours after contact with a person who has flu-like symptoms during a seasonal epidemic; residents in institutions in which influenza cases occur may also qualify for preventive treatment. Other preventive measures should also be used, including immediate vaccination, case isolation, use of face masks, and more frequent hand washing. (16) During seasonal influenza epidemics due to viral strains against which the current vaccine is of limited effectiveness, the utility, target populations and optimal duration of preventive antiviral treatment must be determined by examining the groups most at risk and the severity of complications. (17) Most flu-like syndromes are not due to the influenza virus, and the preventive effect of antiviral drugs on complications in persons at risk has not yet been demonstrated. (18) In practice, antiviral drugs are not an alternative to influenza vaccination, but may be a useful adjunct in some situations. It is best to limit their use to short-term prophylaxis of vulnerable persons in situations where the risk of contracting influenza virus infection is high.

[Anti-virals for influenza virus infection]

Dramatic advances in the diagnosis and treatment of influenza in Japan has been made in recent years. Rapid diagnosis tests for influenza are routinely performed in Japanese hospitals. Both zanamivir and oseltamivir have been approved for the treatment of influenza since 2001, in addition to amantadine. Japan has the highest figure of neuraminidase inhibitor-use in the world because the treatment of influenza with neuraminidase inhibitors is covered by Japan's National Health Insurance program. Therefore, we should carefully observe the appearance of resistance strains and side effects to neuraminidase inhibitors.

A side effect of neuraminidase inhibitor in a patient with liver cirrhosis

Neuraminidase inhibitors have been widely used in Japan since 2001, and several side-effects of their use have been reported. However, erythema toxicum has rarely been described as a side-effect of these drugs in patients with liver function disorder. Here, we report a case of generalized rash after treatment with the neuraminidase inhibitors zanamivir and oseltamivir administered prophylactically to prevent influenza infection in two patients with hepatoma associated with liver cirrhosis.

Is sialic acid an independent risk factor for cardiovascular disease? A 17-year follow-up study in Busselton, Western Australia

PURPOSE

To investigate the relationship between serum sialic acid level and risk of coronary heart disease (CHD) and stroke in men and women without diagnosed cardiovascular disease.

METHODS

A prospective case-cohort study over the period 1981 to 1998 involving 151 CHD cases, 87 stroke cases, and a random sub-cohort of 340 was used. Sialic acid levels were determined by enzymatic method from frozen serum. Cox proportional hazards regression was used to estimate the relative risks of CHD and stroke for sialic acid tertiles and for continuous sialic acid level after adjustment for age, blood pressure, body mass index, cholesterol, triglycerides, diabetes, and smoking.

RESULTS

The multivariate-adjusted relative risk of CHD associated with a 25 mg/dl increase in sialic acid was 1.22 (95% CI: 1.02-1.45) overall, 1.40 (95% CI: 1.11-1.76) in women, and 1.06 (95% CI: 0.82-1.37) in men. The overall relative risk for stroke was 1.13 (95% CI: 0.87-1.46) and for CHD and stroke combined it was 1.17 (95% CI: 0.99-1.37)

CONCLUSIONS

Serum sialic acid may be a long-term predictor of CHD events in adults (especially women) who are currently clinically free of cardiovascular disease. Further studies are needed to determine whether this association can be explained by sialic acid being a marker of accelerated atherosclerosis or inflammation.

Neuraminidase inhibitors in patients with underlying airways disease

Influenza virus infection accounts for significant morbidity, mortality, and healthcare expenditures among persons worldwide. Approximately 20,000 to 40,000 people in the US die each year as a result of influenza. Individuals most susceptible to adverse outcomes include the elderly and those with asthma, chronic obstructive pulmonary disease (COPD), heart disease, renal failure, malignancy, or immunosuppression. Prior to the AIDS epidemic, underlying respiratory disease was the greatest risk factor for influenza-related hospitalization ranking third to heart disease and malignancy for risk of mortality. Although the influenza vaccine can help prevent pneumonia and hospitalization, it is limited by less than ideal immunization rates and the possibility of viral antigenic shifts that render the vaccine ineffective. Pharmacologic interventions play an important role in the management of influenza virus infection by shortening the duration of symptoms. The advent of the neuraminidase inhibitors (NAIs) zanamivir and oseltamivir has significantly affected the treatment of influenza. Unlike NAIs, the older therapeutic options amantadine and rimantadine may cause significant central nervous system adverse effects. In addition, amantadine and rimantadine are not active against influenza B viruses, whereas NAIs are active against both influenza A and B. Post-marketing surveillance of the NAIs has revealed that bronchospasm may occur in patients with underlying respiratory disease treated with the NAI zanamivir. Recent data suggest zanamivir is effective in patients with underlying respiratory disease, but the data are insufficient to elucidate the true risk of bronchospasm. Based on post-marketing reports, zanamivir should be used with caution in patients with asthma or COPD. Although oseltamivir has not been associated with any significant respiratory adverse effects, no data exist on the safety and efficacy of this NAI in patients with underlying respiratory disease.

Spotlight on zanamivir in influenza

Zanamivir is a potent competitive inhibitor of the neuraminidase glycoprotein, which is essential in the infective cycle of influenza A and B viruses. Zanamivir (10 mg by inhalation via the Diskhaler twice daily, or 10 mg inhaled plus 6.4 mg intranasally 2 or 4 times daily, for 5 days) reduced the median time to alleviation of major influenza symptoms by up to 2.5 days compared with placebo. Significant reductions of 1 to 2.5 days versus placebo were observed with inhaled zanamivir in phase III trials involving otherwise healthy adults, high-risk patients or children aged 5 to 12 years. Accelerated return to normal activities, and reduced interference with sleep, consumption of relief medication and incidence of complications leading to antibacterial use were also observed with zanamivir. When used for prophylaxis, inhaled zanamivir 10 to 20 mg/day for 10 days to 4 weeks (plus 6.4 mg/day intranasally in one trial) prevented influenza A in 67% of recipients in a university community, significantly reduced the number of families with new cases of influenza compared with placebo or prevented new cases of influenza in long-term care facilities. The tolerability of inhaled or intranasal zanamivir was similar to that of placebo in otherwise healthy adults, high-risk and elderly patients, and children. Recommended dosages of zanamivir did not adversely affect pulmonary function in patients with respiratory disorders in a well-controlled trial, although there have been rare reports of bronchospasm and/or a decline in respiratory function. In conclusion, zanamivir (used within 48 hours of symptom development) reduces the duration of symptomatic illness, causes accelerated return to normal activities or reduces complications requiring antibacterial use in adults, high-risk individuals and children with influenza. Vaccination remains the intervention of choice for prophylaxis in selected populations. However, the efficacy, good tolerability profile and lack of resistance with zanamivir make it a useful option, particularly in those not covered or inadequately protected by vaccination, who are able to use the inhalation device. The use of zanamivir in patients with respiratory disorders remains unclear because of concerns regarding its potential for bronchospasm. Prospective cost-effectiveness analyses and investigations of efficacy in preventing serious complications of influenza, particularly in high-risk patients, are required. Zanamivir shows potential for prophylaxis in persons for whom vaccination is contraindicated or ineffective, in elderly or high-risk patients in long-term care facilities and in households.

[Neuraminidase inhibitor, anti-influenzal agent--mechanism of action, and how to use clinically]

Neuraminidase inhibitor has changed the treatment of influenza dramatically. The drug is effective for both influenza A and B whereas amantadine, another anti-influenzal agent, inhibits influenza A virus infection but not B. Neuraminidase inhibitor blocks the process of release of influenza virus from infected cells and inhibit the virus transmission to the neighboring cells. Neuraminidase inhibitor improves the symptoms of influenza and shortens the duration of illness. It is emphasized that this drug should be given within forty-eight hours after the onset, and it must be not noted that the possibility of the drug resistant virus although it is observed infrequently. Prophylactic use of the drug is also discussed.

Safety and efficacy of nebulized zanamivir in hospitalized patients with serious influenza

Influenza is an important cause of hospitalization due to lower respiratory tract involvement for which there is no specific antiviral treatment with proven efficacy. We conducted a double-blind, randomized, placebo-controlled trial to assess the tolerability and efficacy of nebulized zanamivir (16 mg four times a day) in combination with rimantadine compared to rimantadine with nebulized saline for treating influenza in adults hospitalized with influenza. Twenty patients tolerated the inhaled zanamivir (ZNV) plus rimantadine without decline in peak expiratory flow rates compared to the 21 who received inhaled saline. The study was terminated early because the approval of ZNV made further enrollment untenable. No significant differences were observed in the proportion of patients shedding virus by treatment day 3 (57% ZNV plus rimantadine, 67% placebo plus rimantadine), or in the durations of hospitalization and supplemental oxygen use. More ZNV plus rimantadine recipients exhibited no or mild cough on day 3 of treatment (94 vs 55%, P=0.01). Two rimantadine-resistant viruses emerged during rimantadine monotherapy; no ZNV resistance was observed. Nebulized ZNV appears to be well tolerated in this hospitalized population but further studies are needed to assess its efficacy.

Antivirals for influenza: what is their role in the older patient?

Influenza infection is a cause of high morbidity and mortality in the elderly living in the community or in long-term care facilities. Yearly immunisation is the most important means for prevention of infection. However, protection by vaccination in the elderly is incomplete, and influenza infections and outbreaks in long-term care facilities still occur. Symptoms of influenza include fever, chills, headache, myalgia and respiratory symptoms. These clinical features overlap considerably with other co-circulating respiratory viruses such as respiratory syncytial virus and parainfluenza virus. Elderly and debilitated patients with influenza may present with less prominent respiratory symptoms and may present only with fever, lassitude and confusion. Antiviral prophylaxis and treatment with amantadine and rimantadine have been given in the past but adverse effects and early development of drug resistance have limited their use. The newer antivirals zanamivir and oseltamivir are equally effective and have the advantage of being well tolerated and active against both influenza A and B without the development of resistance. However, they are costly. Early identification and diagnosis of influenza illnesses are crucial since treatment with antiviral agents should be started within 48 hours of the beginning of illness.

Safety and efficacy of once daily intranasal zanamivir in preventing experimental human influenza A infection

Zanamivir, a potent inhibitor of influenza A and B virus neuraminidases, is protective against experimental human influenza when given intranasally twice daily. We conducted two studies to assess the pharmacokinetics and protective efficacy of a reduced frequency dosing regimen of topical zanamivir. In the first study, 36 uninfected volunteers received a single dose of zanamivir by intranasal spray (6.4 mg), intranasal drops (16 mg) or dry powder oral inhalation (10 mg). At 4 h, median nasal wash concentrations were 50-fold higher after intranasal dosing than after inhalation. Substantial levels (spray group, median 4,596 ng/ml; drop group, 1,239 ng/ml) were detected in nasal wash 48 h after intranasal dosing. In the double-blinded efficacy study, 47 sero-susceptible volunteers were randomized to receive either placebo or zanamivir intranasal spray (6.4 mg). Among the 43 subjects evaluated, decreases in viral shedding occurred in the group receiving one dose of zanamivir 4 h prior to inoculation, whereas no significant benefit was observed in those receiving a single dose 48 h prior to challenge. In the group given three daily doses, reductions were seen in viral shedding and infection. In the two regimens providing zanamivir 4 h prior to inoculation, significant reductions in nasal mucus weight were observed. Decreases in total symptom scores and the incidence of upper respiratory illness also occurred, but they did not reach statistical significance. The efficacy of a single dose of zanamivir given 4 h prior to inoculation supports the hypothesis that influenza virus neuraminidase is essential for initial virus spread through respiratory secretions. These findings indicate that once daily dosing of zanamivir is protective against experimental influenza A infection.

Neuraminidase inhibitors for preventing and treating influenza in children

BACKGROUND

During epidemic years, influenza attack rates in children exceed 40%. Options for prevention and treatment include immunisation, amantadine and rimantadine, and the neuraminidase inhibitors: zanamivir and oseltamivir.

OBJECTIVES

Our objective was to assess the efficacy, safety and tolerability of neuraminidase inhibitors in the treatment and prophylaxis of influenza infection in children.

SEARCH STRATEGY

We searched the Cochrane Acute Respiratory Infections Group Specialised Trials Register, the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, and the GlaxoSmithKline Clinical Trials Register, generally from inception through to December 2002. We also screened the references of retrieved articles and scrutinised relevant web sites. We also screened references of retrieved articles and other systematic reviews, scrutinised web sites of European and US regulatory bodies, and contacted manufacturers and authors.

SELECTION CRITERIA

Double-blind randomised controlled trials comparing neuraminidase inhibitors with placebo or other antiviral drugs in children less than 12 years of age. Additional safety and tolerability data from other sources were also included.

DATA COLLECTION AND ANALYSIS

Four reviewers applied the inclusion criteria to the retrieved studies, assessed trial quality and extracted data. Data were analysed separately for oseltamivir and zanamivir.

MAIN RESULTS

We identified three randomised controlled trials reporting data from 1500 children with a clinical case definition of influenza, of whom 798 had laboratory confirmed influenza infection. Two were trials of oseltamivir (in healthy children and in children with asthma) and one was a trial of zanamivir (in healthy children). Overall, trial quality was good. Oseltamivir reduced the median duration of illness by 26% (36 hours) in previously healthy children with laboratory confirmed influenza (p < 0.0001) and by 17% (21 hours) in the intention-to-treat population (p = 0.0002). Zanamivir reduced the median duration of illness by 24% (1.25 days) in previously healthy children with laboratory confirmed influenza (p < 0.001) and by 10% (0.5 days) in the intention-to-treat population (p = 0.011). Both drugs also significantly reduced the time to return to normal activity. Only oseltamivir produced a significant reduction in the complications of influenza (particularly otitis media), although there was a trend to benefit for zanamivir. No data on the use of zanamivir in 'at risk' children were available. The reduction in time to resolution of illness in 'at risk' children (with asthma) treated with oseltamivir was not statistically significant. Although we identified three trials of neuraminidase inhibitors in the prevention of influenza in families (including children), Roche and GlaxoSmithKline were not willing to break-out data for paediatric populations, and so no data were eligible for inclusion in the review. The adverse events profile of zanamivir was no worse than placebo and we found no reports of zanamivir-induced bronchospasm in children. Vomiting was more common in children treated with oseltamivir (p = 0.008), but study withdrawals were similar (<2%) between oseltamivir and placebo.

REVIEWER'S CONCLUSIONS

Neuraminidase inhibitors were effective in shortening illness duration and hastening return to normal activity in previously healthy children with a clinical or laboratory diagnosis of influenza. Oseltamivir was effective in reducing the incidence of secondary complications. Efficacy in 'at risk' children remains to be proven. The drugs are safe, but oseltamivir can cause vomiting.

Zanamivir prophylaxis: an effective strategy for the prevention of influenza types A and B within households

A double-blind, randomized study of inhaled zanamivir for the prevention of influenza in families was conducted. Once a person with a suspected case of influenza was identified (index patient), treatment of all other household members (contacts) > or =5 years old was initiated. Contacts received either 10 mg zanamivir or placebo inhaled once daily for 10 days. Index patients received relief medication only. In total, 487 households (242 placebo and 245 zanamivir) were enrolled, with 1291 contacts randomly assigned to receive prophylaxis. Four percent of zanamivir versus 19% of placebo households (P<.001) had at least 1 contact who developed symptomatic, laboratory-confirmed influenza, representing 81% protective efficacy (95% confidence interval, 64%-90%). Protective efficacy was similarly high for individuals (82%) and against both influenza types A and B (78% and 85%, respectively, for households). Zanamivir was well tolerated and was effective in preventing influenza types A and B within households where the index patient was not treated.

Efficacy and safety of zanamivir in patients with influenza--impact of age, severity of infections and specific risk factors

Influenza infections occur primarily in the winter season and may lead to serious morbidity and mortality, predominantly in patients with increased risk of complications; these include those with advanced age or with chronic clinical conditions. In this group, the rate of influenza-related hospitalization or death is considerably increased. New treatment options have been introduced for treatment of influenza infection, with the neuraminidase inhibitors zanamivir and oseltamivir being the most promising substances for treatment and prevention of influenza. Numerous double-blind, randomized, placebo-controlled trials in otherwise healthy individuals have demonstrated that zanamivir, when administered orally inhaled for 5 days, produced a statistically significant reduction (by 1.5 days) in the time to alleviation of influenza-related symptoms by compared to inhaled placebo (lactose). The time to alleviation was reduced by 2.5 days in high-risk patients and by 3.25 days in these patients with fever at enrollment. Likewise, the time to alleviation could be reduced by 2 days in patients with severe influenza-related symptoms aged under 50 years and by 7 days in the patient population aged over 50 years compared to placebo. In patients with asthma or chronic pulmonary disease, zanamivir demonstrated a comparable efficacy, reduced the rate of pulmonary complications and did not adversely affect pulmonary function. Zanamivir was well tolerated. In conclusion, zanamivir has proven to be efficacious in treating influenza infection: this was true especially in high-risk patient groups, e.g., patients with advanced age, underlying chronic medical conditions or presenting with severe influenza-related symptoms.

Drug under test: influenza--Relenza in daily practice. Experience during the influenza season 1999/2000

A total of 5-7 million cases of the disease, 4.5 million medical certificates, 25,000 admissions to hospital, 15,000 mortalities and direct and indirect costs amounting to several billions - that is the outcome of a "normal" influenza season (data provided by the Influenza Study Group, AGI, of Germany on the 1998/99 season). With zanamivir (Relenza), a selective inhibitor of the influenza-specific neuraminidase, a pharmaceutical product against influenza A and B is now available in Germany for the very first time. In clinical studies, zanamivir reduced not only the duration of the illness and the severity of symptoms, but also the rate of complications and the need for antibiotics. Under practice conditions, the efficacy and tolerability of the anti-influenza product were studied during the 1999/2000 influenza season. In a large observational study in over 1,900 patients, including many patients at risk of asthma and/or chronic obstructive bronchitis, zanamivir (Relenza) improved the symptoms quickly and reliably, and was tolerated very well. The diagnosis of influenza was established clinically to discriminate the disease from colds.

Risk for respiratory events in a cohort of patients receiving inhaled zanamivir: a retrospective study

BACKGROUND

Inhaled zanamivir is indicated for treatment of uncomplicated acute illness due to influenza A and B viruses in patients aged > or = 12 years who have been symptomatic for no more than 2 days.

OBJECTIVE

The primary objective of this study was to estimate the incidence of adverse respiratory events among zanamivir-treated patients under conditions of usual care.

METHODS

The Ingenix research database includes insurance claims for all dispensations, inpatient and outpatient services, and procedures including the associated diagnoses and costs for a subset of all enrolled UnitedHealthcare members. We identified all persons with a dispensation of zanamivir recorded between October 1, 1999, and April 30, 2000. We captured medical and pharmaceutical claims data for the 6 months before the dispensation to obtain information about comorbidities, overall health status, and respiratory events. Medical and hospital record abstraction and clinical review served to confirm inpatient/emergency department (ED) events. We also examined the records of an approximately 10% random sample of patients treated for a potential respiratory event in an outpatient/ physician office visit during the 10-day follow-up period. Respiratory events not sufficiently severe to result in medical care were not captured in this study.

RESULTS

A total of 5498 eligible zanamivir dispensations contributed by 5450 patients (2911 females, 2539 males; mean age, 38.8 years), with 40 confirmed inpatient/ED respiratory events, were included in the study. Of these 40 events, 31 were pneumonia, bronchitis, or exacerbations of existing chronic respiratory disease; none required intubation or ventilation. No events occurred on the dispensation date. The overall risk for an inpatient/ ED respiratory event was 0.7 per 100 episodes (95% CI, 0.5-1.0). Seven events of wheezing or shortness of breath were not an obvious extension of the original influenza-like illness or of a complicating bronchitis (risk = 0.13 per 100 episodes; 95% CI, 0.06-0.26).

CONCLUSIONS

No immediate or severe bronchoconstrictive responses occurred among 5498 zanamivir dispensations. The overall risk for any respiratory event was low, and none was sufficiently severe to suggest respiratory failure.

Utility of zanamivir for chemoprophylaxis of concomitant influenza A and B in a complex continuing care population

OBJECTIVE

To describe compliance with and the safety and prophylactic efficacy of zanamivir among patients at risk of developing influenza-related complications after exposure to both influenza A and B viruses.

DESIGN

Nonrandomized trial using both historical and contemporaneous controls from ward populations within the same facility.

SETTING

A 547-bed urban hospital providing complex continuing care and rehabiltation.

PATIENTS

Fifty patients on a single ward concomitantly exposed to both influenza A and B during an influenza outbreak.

INTERVENTIONS

All patients were screened for symptoms of influenza and nasopharyngeal swabs were sent for viral culture prior to treatment (two oral inhalations [2 x 5 mg] twice daily for 5 days) or prophylaxis (two oral inhalations [2 x 5 mg] once daily for 14 days) with zanamivir. Patient symptoms, compliance, and drug tolerance were monitored daily. Demographic data, comorbidities, vaccination status, and functional status (Katz score) were collected for all patients.

RESULTS

The mean age of the patients was 70.6 years (standard deviation, +/- 16.4 years). Ninety-four percent had two or more comorbidities, 71% were dependent in two or more activities of daily living, 63% had been vaccinated for influenza, and 82% had received amantadine. Zanamivir was well tolerated, with 93% of the patients completing their course. The efficacy for preventing symptomatic infection was 82% and 91% (95% confidence interval, 62% to 98%) based on historical and contemporaneous controls, respectively.

CONCLUSION

These data suggest that zanamivir can be used safely and effectively as a prophylactic agent in the management of influenza outbreaks in a complex continuing care population with multiple comorbidities.

Economic analysis of influenza vaccination and antiviral treatment for healthy working adults

BACKGROUND

Physicians have several treatment options for influenza, including vaccination and various antiviral therapies. However, the optimal influenza prevention and treatment strategy is unknown.

OBJECTIVE

To compare the relative health values of contemporary treatment strategies for influenza in a healthy sample of working adults.

DESIGN

Cost-benefit analysis using a decision model.

DATA SOURCES

Previously published data.

TARGET POPULATION

Healthy employed adults 18 to 50 years of age.

TIME HORIZON

A complete influenza season.

PERSPECTIVE

Societal.

INTERVENTIONS

Eight treatment options (yes or no) based on the possible combinations of vaccination and antiviral therapy (rimantadine, oseltamivir, or zanamivir or no treatment) should infection develop.

OUTCOME MEASURES

Cost in U.S. dollars, including the value of symptom relief and medication side effects, which was assigned a monetary value through a conjoint analysis that used a "willingness-to-pay" approach.

RESULTS

In the base-case analysis, all strategies for influenza vaccination had a higher net benefit than the nonvaccination strategies. Vaccination and use of rimantadine, the most cost-beneficial strategy, was $30.97 more cost-beneficial than nonvaccination and no use of antiviral medication. The health benefits of most antiviral treatments equaled or exceeded their costs for most scenarios. The choice of the most cost-beneficial antiviral strategy was sensitive to the prevalence of influenza B and to the comparative workdays gained by each antiviral therapy.

CONCLUSIONS

Vaccination is cost-beneficial in most influenza seasons in healthy working adults. Although the benefits of antiviral therapy for persons with influenza infection appear to justify its cost, head-to-head trials of the various antiviral therapies are needed to determine the optimal treatment strategy.

Zanamivir: a review of clinical safety in individuals at high risk of developing influenza-related complications

Post-marketing experience shows zanamivir to be well tolerated in the general population for the treatment and prophylaxis of influenza type A and B infections. Individuals at high-risk of influenza have potentially more to gain from zanamivir therapy. We assessed safety and tolerability findings from treatment and prophylaxis studies in over 982 high-risk subjects. Eight treatment studies involving high-risk subjects have been conducted with zanamivir 10 mg twice daily for 5 days. The incidence and pattern of adverse events was similar in zanamivir and placebo recipients. Lower respiratory adverse events reported by recipients receiving zanamivir occurred at similar or lower frequencies to those receiving placebo. In one treatment study involving 525 patients with asthma or chronic obstructive pulmonary disease, zanamivir recipients had a small but significantly increased mean morning peak expiratory flow rate (PEFR) and evening PEFR compared with placebo during the treatment period (days 1 to 5). Eight prophylaxis studies have been conducted, five in family or community settings and three in nursing homes. Data from these studies demonstrate that zanamivir is well tolerated for prophylaxis. In nursing home studies, where 90% of participants were high risk, the pattern and incidence of adverse events were similar to that reported in otherwise healthy individuals, and similar to both placebo and rimantadine, a comparator in one study. In treatment and prophylaxis studies the incidence and pattern of adverse events in participants > or =65 years or with chronic underlying respiratory disorders was similar for zanamivir or placebo recipients. Overall, zanamivir was well tolerated and study drug discontinuations were low. A small number of deaths have been reported in studies of high-risk elderly individuals, but none were considered to be related to zanamivir. Thus clinical studies have demonstrated that zanamivir has a comparable safety profile in high-risk and otherwise healthy recipients. Approximately 1.72 million treatment courses of zanamivir were prescribed up to the end of January 2001. Many spontaneous adverse event reports received since marketing, a third of these from non-healthcare professionals, reflect the underlying condition being treated. However, a number of events have resulted in changes to the zanamivir prescribing information, including rare reports of bronchospasm, dyspnoea, rash, urticaria and allergic type reactions including facial and oropharyngeal oedema. The reported safety profile of zanamivir, for treatment and prophylaxis of high risk subjects with influenza type A and B infections supports its continued use in these individuals who are likely to benefit most.

Zanamivir: an update of its use in influenza

Zanamivir is a potent competitive inhibitor of the neuraminidase glycoprotein, which is essential in the infective cycle of influenza A and B viruses. Zanamivir (10mg by inhalation via the Diskhaler twice daily, or 10mg inhaled plus 6.4mg intranasally two or four times daily, for 5 days) reduced the median time to alleviation of major influenza symptoms by up to 2.5 days compared with placebo. Significant reductions of 1 to 2.5 days versus placebo were observed with inhaled zanamivir in phase III trials involving otherwise healthy adults, high-risk patients or children aged 5 to 12 years. Accelerated return to normal activities, and reduced interference with sleep, consumption of relief medication and incidence of complications leading to antibacterial use were also observed with zanamivir. When used for prophylaxis, inhaled zanamivir 10 to 20 mg/day for 10 days to 4 weeks (plus 6.4 mg/day intranasally in one trial) prevented influenza A in 67% of recipients in a university community, significantly reduced the number of families with new cases of influenza compared with placebo or prevented new cases of influenza in long-term care facilities. The tolerability of inhaled or intranasal zanamivir was similar to that of placebo in otherwise healthy adults, high-risk and elderly patients, and children. Recommended dosages of zanamivir did not adversely affect pulmonary function in patients with respiratory disorders in a well-controlled trial, although there have been rare reports of bronchospasm and/or a decline in respiratory function.

CONCLUSION

Zanamivir (used within 48 hours of symptom development) reduces the duration of symptomatic illness, causes accelerated return to normal activities or reduces complications requiring antibacterial use in adults, high-risk individuals and children with influenza. Vaccination remains the intervention of choice for prophylaxis in selected populations. However, the efficacy, good tolerability profile and lack of resistance with zanamivir make it a useful option, particularly in those not covered or inadequately protected by vaccination, who are able to use the inhalation device. The use of zanamivir in patients with respiratory disorders remains unclear because of concerns regarding its potential for bronchospasm. Prospective cost-effectiveness analyses and investigations of efficacy in preventing serious complications of influenza, particularly in high-risk patients, are required. Zanamivir shows potential for prophylaxis in persons for whom vaccination is contraindicated or ineffective, in elderly or high-risk patients in long-term care facilities and in households.

The use of zanamivir to treat influenza A and B infection after allogeneic stem cell transplantation

The use of zanamivir in seven patients with influenza (three A and four B) post allograft is described. Inhaled zanamivir (10 mg twice daily) was continued from the diagnosis of influenza until excretion of virus ceased (median duration 15 days, range 5 to 44 days). There was no toxicity attributable to zanamivir and rapid resolution of influenza symptoms was seen. There was no mortality due to influenza in the seven patients. The good outcome of 30 previous patients with influenza post transplant is described. A randomised multicentre study would be required to demonstrate efficacy.

Diagnosis of influenza in the community: relationship of clinical diagnosis to confirmed virological, serologic, or molecular detection of influenza

BACKGROUND

Successful treatment of influenza depends on an accurate diagnosis of the illness and prompt intervention. However, there is a lack of data comparing clinical diagnosis vs laboratory diagnostic techniques.

OBJECTIVE

To compare the clinical diagnosis of community cases of influenza with various laboratory diagnostic techniques including multiplex, reverse transcription polymerase chain reaction.

METHODS

Clinical diagnosis, viral isolation, hemagglutinin inhibition serology, and multiplex, reverse transcription polymerase chain reaction were used to diagnose influenza in patients enrolled in international phase 3 studies designed to investigate the efficacy and safety of an anti-influenza drug (inhaled zanamivir). Patients clinically diagnosed with influenza were enrolled at centers across North America and Europe.

RESULTS

A total of 791 (77%) of 1033 patients with laboratory results from all 3 methods were confirmed positive for influenza by 1 or more test results. For 692 patients (67%), the results of all 3 tests agreed. Total symptom scores at baseline showed a significant association toward greater severity of symptoms with an increasing number of positive test results (P<.001). An increasing number of positive test results also showed a significant correlation with a longer time to alleviation of symptoms of influenza in the placebo group (P =.001).

CONCLUSIONS

During a time when influenza was known to be circulating and clinical diagnostic criteria were applied, diagnosis of influenza in these trials was accurate in approximately 77% of adults on clinical grounds alone. This highlights the need for primary care physicians to be alerted to circulating influenza and to be aware that presentation with cough and fever provide the most predictive symptoms.

Zanamivir and oseltamivir: two new options for the treatment and prevention of influenza

BACKGROUND

Influenza infection is responsible for thousands of hospitalizations and deaths in the United States each year. Until recently, management options were limited to vaccination or use of the antiviral agents amantadine and rimantadine. Two antiviral drugs, zanamivir and oseltamivir, have recently been approved by the US Food and Drug Administration for the treatment of influenza A and influenza B.

OBJECTIVE

This article reviews the published data on the pharmacology and clinical utility of zanamivir and oseltamivir in the treatment and prevention of influenza A and influenza B illness.

METHODS

To identify relevant literature, a search of MEDLINE, International Pharmaceutical Abstracts, and the Iowa Drug Information Service was conducted for the period from 1969 to 2000. The search terms used were influenza, neuraminidase, zanamivir, oseltamivir; amantadine, and rimantadine. The reference lists of the articles so obtained were used to identify additional publications.

RESULTS

Zanamivir and oseltamivir inactivate viral neuraminidase, an enzyme responsible for cleaving sialic acid residues on newly formed virions as they bud off from the host cell. This inhibition results in aggregation of virions on the surface of the host cell, which limits the extent of infection and speeds recovery from illness. Clinical studies have shown that neuraminidase inhibitors can decrease the median duration of influenza-related symptoms by approximately 1 day if initiated within 48 hours of the onset of symptoms of influenza.

CONCLUSIONS

Evidence supports the use of zanamivir and oseltamivir in the treatment of influenza; however, additional studies are needed to clarify their utility and tolerability in pediatric and high-risk patients, as well as their utility in the prevention of influenza.

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.

Effect of zanamivir on duration and resolution of influenza symptoms

BACKGROUND

Zanamivir is a neuraminidase inhibitor, the first of a new class of drugs with potent, specific antiviral activity against influenza A and B. Administration by inhalation results in direct delivery to the respiratory tract, the principal site of viral replication.

OBJECTIVE

This study was undertaken to determine the effectiveness of zanamivir on duration and resolution of influenza symptoms.

METHODS

Using a method similar to that employed in amantadine treatment studies to obtain supporting evidence of efficacy for US Food and Drug Administration consideration, pooled data from 6 zanamivir phase II and III clinical trials involving primarily previously healthy adults were analyzed to categorize patients as accelerated resolvers (temperature <37.8 degrees C < or = 24 hours after dosing, plus a > or = 50% reduction in symptom score by 36 hours), early resolvers (temperature <37.8 degrees C < or = 36 hours after dosing), and nonaccelerated resolvers (febrile >36 hours after dosing). Patients in the accelerated and early categories were termed rapid resolvers; the others were slow resolvers. Patients recorded their symptom severity, temperature, ability to perform normal daily activities, and use of relief medication on a diary card. The primary end point of median time to alleviation of symptoms was also reexamined, with the additional requirement that patients were not taking relief medication when their symptoms were alleviated. This analysis was intended to control for the possible effect of relief medication on the primary end point.

RESULTS

In the influenza-positive population (n = 1572), significantly more zanamivir-treated patients were rapid resolvers compared with those receiving placebo (807 [72%] vs 765 [64%], P < 0.001). Significant benefits of zanamivir treatment were observed in patients with a baseline temperature of > or = 37.8 degrees C (630 [68%] vs 595 [57%], P < 0.001) or > or = 38.3 degrees C (382 [67%] vs 365 [52%], P < 0.001) and in patients considered by their physi- cian to have severe symptoms at the start of therapy (252 [70%] vs 222 [63%], P = 0.02). Differences were even more apparent in patients with high-risk conditions (74% vs 53%, P = 0.014) and in those aged > or = 50 years (70% vs 54%, P = 0.005). Zanamivir treatment was also associated with a significant reduction in time to alleviation of symptoms with no use of relief medication. This was particularly noticeable in those aged > or = 50 years; time to alleviation was 13 days in patients receiving placebo and 6 days in patients receiving zanamivir (P < 0.001). In these trials, adverse events were reported at a similar frequency in patients receiving zanamivir and those receiving placebo.

CONCLUSIONS

Zanamivir is more effective than placebo in patients with influenza at providing early symptom relief and a reduced duration of illness at a time when use of relief medication has ended. These benefits are seen across different patient groups but appear to be particularly marked in patients who are aged > or = 50 years, who have underlying illnesses, who are considered high risk, or who are more severely ill at the beginning of therapy.

Direct measurement of the anti-influenza agent zanamivir in the respiratory tract following inhalation

In a single-center, randomized study, zanamivir (Relenza) concentrations in induced sputum samples and nasal washings of healthy adults following oral inhalation were measured. Concentrations in sputum exceeded the median viral neuraminidase 50% inhibitory concentration at 6, 12, and 24 h, and those in nasal washings did so at 6 and 12 h. There were no zanamivir-related adverse events or laboratory abnormalities.

Zanamivir for treatment of symptomatic influenza A and B infection in children five to twelve years of age: a randomized controlled trial

BACKGROUND

Influenza infection rates are higher in children than in other age groups. This study evaluated the efficacy, safety and tolerability of a 5-day course of twice daily inhaled zanamivir, 10 mg, compared with placebo in the treatment of symptomatic influenza A and B viral infections among children 5 to 12 years of age.

METHODS

This double blind, randomized, placebo-controlled, parallel group, multicenter study conducted in the Northern Hemisphere during the 1998 and 1999 influenza season enrolled 471 patients with influenza-like symptoms for < or = 36 h. Patients were randomly assigned to zanamivir (n = 224) or placebo (n = 247). Symptoms were recorded on diary cards twice daily during treatment, for 9 days after treatment and for 14 additional days (if still reporting moderate/severe cough and/or taking relief medication).

FINDINGS

A total of 346 (73%) patients were influenza-positive by culture, serology or polymerase chain reaction (65% influenza A, 35% influenza B). Zanamivir reduced the median time to symptom alleviation by 1.25 days compared with placebo among patients with confirmed influenza infection (P < 0.001). Zanamivir-treated patients returned to normal activities significantly faster and took significantly fewer relief medications than placebo-treated patients. Zanamivir was well-tolerated, demonstrating adverse event profiles similar to those of placebo and no clinically significant changes in laboratory findings. Viral susceptibility testing revealed no zanamivir-resistant strains of influenza A or B.

CONCLUSIONS

Zanamivir was effective in shortening the duration and severity of influenza symptoms and was well-tolerated among children 5 to 12 years of age.

Safety and efficacy of the neuraminidase inhibitor zanamivir in treating influenza virus infection in adults: results from Japan. GG167 Group

The study was carried out to evaluate the therapeutic effects of zanamivir, a highly selective, potent and specific inhibitor of influenza A and B virus neuraminidases, in adult patients with acute influenza-like illness. Patients who presented within 36 h of the onset of influenza-like symptoms were randomly assigned to receive one of three treatments, twice daily, for 5 days: 10 mg zanamivir powder for inhalation (zanamivir inhalation group), 10 mg zanamivir powder for inhalation plus 6.4 mg zanamivir nasal spray (zanamivir inhalation plus intranasal group) or placebo (placebo group). The primary end point was the time to alleviation of the three major symptoms (fever, headache and myalgia). The secondary end point was the time to alleviation of five influenza symptoms (fever, headache, myalgia, cough and sore throat). One hundred and sixteen patients with influenza-like illness were recruited to the study. No differences were observed between the two groups of patients who received zanamivir (inhalation group or inhalation plus intranasal group). Patients who received zanamivir recovered significantly faster (median 3 days to recovery) than the patients in the placebo group (median 4 days to recovery; P < 0.01). Topically administered zanamivir was well tolerated. This study confirms that in adults, topically administered zanamivir is well tolerated and is effective in reducing the time to alleviation of influenza symptoms.

Influenza virus neuraminidase inhibitors

Neuraminidase promotes influenza virus release from infected cells and facilitates virus spread within the respiratory tract. Several potent and specific inhibitors of this enzyme have been developed, and two (zanamivir and oseltamivir) have been approved for human use. Unlike amantadine and rimantadine that target the M2 protein of influenza A viruses, these drugs inhibit replication of both influenza A and B viruses. Zanamivir is delivered by inhalation because of its low oral bioavailability whereas oseltamivir is administered by mouth. Early treatment with either drug reduces the severity and duration of influenza symptoms and associated complications. Both agents are effective for chemoprophylaxis. Because of a broader antiviral spectrum, better tolerance, and less potential for emergence of resistance than is seen with the M2 inhibitors, the neuraminidase inhibitors represent an important advance in the treatment of influenza.

Short-term treatment with zanamivir to prevent influenza: results of a placebo-controlled study

We explored the prophylactic activity of zanamivir after presumed exposure to influenza in the community. After close contacts with index cases of influenza-like illnesses, 575 subjects were randomized in 4 treatment groups: 144 received placebo, 141 received intranasal zanamivir, 144 received inhaled zanamivir, and 146 received inhaled plus intranasal zanamivir for 5 days. Of 25 subjects (4%) who developed symptomatic influenza during the 5 days of prophylaxis, 9 (36%) were in the placebo group, 8 (32%) were in the intranasal zanamivir group (odds ratio [OR], 0.90; 95% confidence interval [CI], 0.30-2.72; P=.855), 3 (12%) were in the inhaled zanamivir group (OR, 0.27; 95% CI, 0.07-1.05; P=.058), and 5 (20%) were in the inhaled plus intranasal zanamivir group (OR, 0.52; 95% CI, 0.17-1.58; P=.247). Short-term treatment with intranasal zanamivir was ineffective. However, inhaled zanamivir treatment reduced the rate of influenza, which was 2%-3% among zanamivir recipients versus 6% among placebo recipients. Additional studies assessing a longer duration of postcontact prophylaxis are warranted.