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

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1 Safety and efficacy of nebulized zanamivir in hospitalized patients with serious influenza Michael G Ison 1, John W Gnann Jr 2, Stephanie Nagy-Agren 3, John Treanor 4, Carlos Paya 5, Roy Steigbigel 6, Michael Elliott 7, Heidi L Weiss 2 and Frederick G Hayden 1 * for the NIAID Collaborative Antiviral Study Group 1 University of Virginia, Charlottesville, Va., USA 2 University of Alabama-Birmingham, Birmingham, Ala., USA 3 Salem Veterans Administration Medical Center, Salem, Va., USA 4 University of Rochester, Rochester, NY, USA 5 Mayo Clinic, Rochester, Minn., USA 6 State University of New York, Stony Brook, NY, USA 7 GlaxoSmithKline, Research Triangle Park, NC, USA Antiviral Therapy 8: *Corresponding author: Tel: ; Fax: 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, placebocontrolled 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 enrolment 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. Introduction Influenza epidemics, particularly those due to influenza A/H3N2 subtype viruses, are associated with excess mortality rates, two- to threefold increases in pneumonia rates, and two- to fivefold increases in hospitalizations for high-risk adults patients [1]. Although influenza virus infection is associated with acute, self-limited, febrile illness in most persons, serious lower respiratory complications occur including viral tracheobronchitis, exacerbation of preexisting airways disease, primary viral pneumonia, and secondary bacterial or mixed viral-bacterial pneumonias [2]. Excess mortality is primarily attributable to lower respiratory complications and cardiovascular disease. Mortality rates are highest in older adults (particularly those over 65 years) and in those with underlying cardiopulmonary disease. Up to a half of deaths have occurred in persons who were functionally independent [2]. No specific antiviral therapy of proven value currently exists for the lower respiratory tract complications of influenza. Orally administered amantadine and its congener, rimantadine, provide antiviral effects and moderate clinical benefits in uncomplicated influenza when treatment can be initiated within 2days of symptom onset. Amantadine has also been found to shorten the duration of peripheral airway functional abnormalities, although not the associated airway hyperactivity, in such patients. One uncontrolled study of high-dose oral amantadine ( mg/day) found a 55% survival rate in 11 patients with primary influenza A pneumonia [3]. There are several shortcomings for the M2 inhibitors, amantadine and rimantadine, that include the lack of controlled data in severe influenza, antiviral spectrum limited to influenza A viruses, development of drug resistance during therapeutic use, lack of a parenteral formulation for seriously ill patients, and dose-related central nervous system and gastrointestinal toxicities. Recently, controlled clinical studies showed that the neuraminidase inhibitors, zanamivir (ZNV) and oseltamivir, were effective for the treatment of uncomplicated influenza A and B infections in ambulatory 2003 International Medical Press /02/$

2 MG Ison et al. adults and children [4 13]. Prior to the availability of oral oseltamivir, we initiated a study to examine the tolerability and antiviral effects of aerosolized ZNV plus rimantadine in hospitalized influenza patients. This is the first prospective controlled trial of a neuraminidase inhibitor in patients with serious influenza infection with lower respiratory tract involvement. ZNV is not orally bioavailable and has been given as an inhaled dry powder aerosol in most studies. In order to treat seriously ill patients hospitalized with lower respiratory tract influenza disease, a nebulized formulation was tested in combination with rimantadine in a controlled study. Methods Study design The study was a randomized, placebo-controlled, double-blinded evaluation of the treatment of influenza infection with nebulized ZNV and oral rimantadine in hospitalized patients. The study was conducted at seven centres throughout the USA from January 1998 to April 1999 (see list at end). The primary goals of the study were to assess the safety and antiviral efficacy of nebulized ZNV in patients hospitalized with serious influenza infections. This study protocol was approved by the National Institute of Allergy and Infectious Diseases Collaborative Antiviral Study Group and by the institutional review boards of each of the seven study centres. Written consent was obtained from all study participants or an appropriate decision maker when the patient was unable to give consent. An interim safety analysis was performed in July 1998 after a total of 24 patients had been enrolled into the study, and an independent data and safety monitoring board decided to continue the study. The study was terminated prior to full enrollment as the approval and the widespread availability of both neuraminidase inhibitors in 1999 made accrual of additional patients unfeasible. Patients Male or female patients 10 years of age that were hospitalized with influenza A or B virus infection with symptoms of 4 days duration or less were eligible for participation. In addition, they had to manifest at least one of the following lower respiratory tract signs: new infiltrate on chest radiograph; new onset of respiratory distress (dyspnea, severe cough); 15 mmhg or greater decrease in alveolar-arterial oxygen gradient compared to the patient s known or expected baseline gradient; and/or arterial oxygen saturation 90% by transcutaneous (fingertip) oximetry on room air. Prior to drug administration, influenza virus infection was established by conventional viral cultures and/or by detection of influenza viral antigens or nucleic acids in respiratory secretions, as previously described [14 16]. Female patients were required to have a negative urine or serum pregnancy test prior to enrollment. Any compatible influenza-related clinical syndrome (such as, viral or mixed viral-bacterial pneumonia, severe bronchitis, exacerbations of asthma or chronic obstructive pulmonary disease) was eligible, and the use of antibiotics or other treatment was not restricted. Patients with known hypersensitivity to neuraminidase inhibitors, pregnant or breastfeeding patients, patients who were intubated or had an expectation of imminent demise were excluded. Drug administration ZNV 16 mg (as 16 mg/ml in normal saline) or placebo (normal saline) was administered by the Medic-Aid Sidestream Disposable Nebulizer (Medic-Aid, West Sussex, UK) with a mouthpiece attachment at an airflow of 6 7 l/min and completed within 10 min. Previous studies have shown that this system delivers 80% of the output volume below the critical size of 5 µm for lower respiratory tract disposition. Doses were given four times a day for 5 days. No dosage adjustment was made for renal or hepatic impairment. Patients discharged early were continued on the same treatment schedule with dry powder-inhaled ZNV plus rimantadine (n=3) or placebo plus rimantadine (n=2) under blinded conditions to complete the 5-day course. A computer-generated block randomization scheme was utilized and the sites were provided with the study drug and randomization envelopes. The research pharmacist at each site, who was unblinded, prepared the study medication for dispensing in a blinded fashion to the patient care area. The investigators, nursing and respiratory therapy staff remained blinded. All patients with influenza A virus infection (40/41) also received rimantadine orally for 5 days. For patients 10 to 64 years of age, the dose of rimantadine was 100 mg twice daily. For persons with severe hepatic dysfunction or renal failure (CrCl 10 ml/min) and for persons 65 years of age or older, the dose was reduced to 100 mg once daily. Clinical monitoring Patients were followed daily with recording of basic clinical information (maximum temperature, respiratory rate, arterial oxygen saturation by transcutaneous oximetry, supplemental oxygen use, concomitant medications and intercurrent infections). Results of arterial blood gas determinations and chest radiography (if done) were also recorded. Severity of cough was assessed on a daily basis using a 4-point scale (Table 1) International Medical Press

3 Nebulized zanamivir for serious influenza Table 1. Enrolment characteristics Characteristic Placebo (n=21) Zanamivir (n=20) P-value* Age, years Median (range) 61 (22 80) 67 (24 93) 0.24 Gender, male (%) 14 (67) 18 (90) 0.13 Weight, pounds Median (range) ( ) ( ) 0.99 Temperature, F Median (range) 99.7 ( ) 99.5 ( ) 0.56 Respiratory rate Median (range) 22 (16 32) 24 (18 32) 0.97 Heart rate Median (range) 91 (60 125) 92 (65-118) 0.57 Pulse oximetry, % saturation Median (range) 94.5 (44 98) 95 (87 98) 0.54 Supplemental O 2, no. (%) patients 16 (76) 14 (70) 0.66 Cough, no. (%) None 1 (5) Mild 5 (2) 6 (30) Moderate 12 (57) 11 (55) Severe 3 (14) 3 (15) Activity level, no. (%) Bed rest 8 (38) 8 (40) 0.39 Limited ambulation 11 (52) 12 (60) Unrestricted 2 (10) 0 ICU 3 (14) 3 (15) 0.99 Influenza, no. (%) A 19 (90) 19 (95) 0.99 B 1 (5) 0 (0) *P-value based on Fisher s exact test; P-value based on Wilcoxon rank-sum test. For safety studies, blood samples were obtained at baseline and at the end of treatment for routine clinical laboratory tests (complete blood count with differential, electrolytes, blood urea nitrogen, creatinine, uric acid, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, creatinine phosphokinase). The blood was obtained within 48 h of initiation of treatment and within 48 h of completion of therapy. Assessment of symptoms and activity patterns related to the influenza episode were monitored on treatment days 1 5 and on days 7 and 9, if the patient remained hospitalized. Peak expiratory flow rates (PEFRs) were measured before and after the first dose of nebulized medication. The patients then had a follow-up evaluation on day 28, which included a physical examination and assessments of influenza symptom resolution and functional status. Virological monitoring During hospitalization, daily samples of upper (nose swabs and separate throat swabs) and lower (sputum) respiratory secretions (if available) were collected into viral transport media and frozen at 70 C and submitted for viral culture, determination of influenza virus titres and antiviral susceptibility testing, as previously described [17 19]. Samples were collected daily on treatment days 1 5, 7 and 9 if the patient remained hospitalized. The type of sample depended on the clinical status of the patient, but reasonable effort was made to obtain consistently the same type of sample on a particular patient and to extend the period of sampling for 3 days after the end of treatment in order to be able to detect a rebound in virus shedding. Throat swabs were collected from all patients. Antiviral susceptibility to rimantadine was screened by phenotypic assays in Madin-Darby canine kidney cell monolayers. A previously described ELISA was used to assess M2 inhibitor susceptibility [20]. If a phenotypically resistant isolate was found, the M2 region of RNA segment 7 was sequenced for presence of defined mutations linked to resistance [19]. The possibility of neuraminidase inhibitor-resistant variants was assessed by a previously described neuraminidase inhibition assay [21]. The virological analyses were conducted at the core laboratory located at the University of Virginia, Charlottesville, Va., USA. Antiviral Therapy 8:3 185

4 MG Ison et al. Acute serum (obtained at the time of study entry) and convalescent serum (obtained approximately 3 4 weeks post-enrolment) were collected for measurement of haemagglutination-inhibition (HAI) antibodies to the prevalent influenza virus strain. All samples from the day of enrolment were collected prior to initiation of study medication. Study end-points The primary end-point of the study was the absence of pharyngeal influenza viral shedding on day 3 of treatment. Secondary virological end-points were duration and quantity of viral shedding in respiratory samples, and emergence of rimantadine-resistant or ZNVvariant virus. Secondary clinical end-points included durations of fever, supplemental oxygen use and hospitalization; time to recovery of arterial oxygen saturation to 95% or to known baseline while breathing room air; severity of cough; frequency of complications; and time to full resumption of usual activities based on outpatient follow-up. Data analysis The biostatistics unit of the Collaborative Antiviral Study Group at the University of Alabama at Birmingham provided statistical support for the study. The comparability of the two treatment groups was determined by the χ 2 test or Fisher s exact test for categorical variables and by Wilcoxon rank-sum test for continuous variables. Kaplan-Meier survival curves were calculated to evaluate duration of viral shedding by treatment group and compared using the log-rank test. Drug safety was evaluated based on laboratory test results and adverse events as reported. Samples size Initial sample size calculations indicated that 50 patients in each study arm would be needed to yield >80% power in detecting at least a 25% absolute reduction in the proportion of patients shedding virus on day 3 in the ZNV plus rimantadine group compared to the placebo plus rimantadine group. Although the study was designed to enrol 50 patients in each study arm, it was terminated early (41 enrolled subjects from two influenza seasons), as discussed previously. Results Patient population and disposition During two influenza seasons (January 1998 April 1999), 41 infected patients were enrolled in the trial from seven institutions. Two patients were negative for influenza by culture and serology (likely false-positive antigen test; one in each arm) and were excluded from Table 2. Underlying medical conditions Disease Placebo Zanamivir Total Heart disease (CAD, CHF) Pulmonary disease Renal insufficiency Diabetes mellitus Active cancer Any cancer Rheumatoid arthritis Transplant Any immunocompromise the analyses of efficacy, but were included in the tolerability and safety analyses. Baseline characteristics of the ZNV plus rimantadine and placebo plus rimantadine-treated groups were broadly comparable and did not differ statistically (Tables 1 & 2). All but one patient was infected with an influenza A virus. Most patients presented with respiratory symptoms and required supplemental oxygen. There were slightly more transplant recipients in the placebo plus rimantadine arm and slightly more patients with underlying heart disease in the ZNV plus rimantadine arm. Sixty-one percent completed the study and received treatment for 5 days and follow-up at day 28 (11 ZNV plus rimantadine and 14 placebo plus rimantadinetreated patients). Six patients withdrew from the study without completing 5 days of therapy, three patients died, and five patients were lost to follow-up. Six other patients (ZNV plus rimantadine, n=4; placebo plus rimantadine, n=2) left the hospital prior to completion the 5-day dosing regimen because they were clinically improved. All of the patients discharged early, except for one of the ZNV plus rimantadine-treated patients, completed the protocol using inhaled drug as an outpatient and are thus not considered withdrawals. Tolerance Most patients tolerated the nebulized study medication without difficulty. There were no significant differences in the number of patients reporting adverse events between placebo plus rimantadine (76%) or ZNV plus rimantadine (70%) (P=0.66). Seven serious adverse events were observed (Table 3), but only one episode of retrosternal burning with dyspnea (patient 1, Table 3) was felt to be caused by the study medication. The symptoms resolved rapidly after inhaled ZNV was discontinued. The patient refused further evaluation and withdrew from the study. One placebo plus rimantadine patient withdrew consent at day 4 while three additional patients (ZNV plus rimantadine, n=1; placebo plus rimantadine, n=2) refused treatment on day 2, 3 and 5, respectively, all without reporting any specific adverse effects of the medication. One other ZNV plus rimantadine patient International Medical Press

5 Nebulized zanamivir for serious influenza Table 3. Serious adverse events Patient (study drug) Study day Event Related to test agent Resolution 1 (ZNV) 1 Retrosternal burning with dyspnea Probable Resolved 2 (Placebo) 1 Overdose of study medication Yes Resolved* 3 (Placebo) 9 Back injury No Resolved 4 (Placebo) 20 Tracheobronchitis staphylococcal infection No Resolved 5 (Placebo) 9 Viral pneumonia No Death 6 (ZNV) 12 Coronary artery disease and congestive heart failure No Death 7 (ZNV) 33 Pneumonia, cerebrovascular accident No Death AE, adverse event; ZNV, zanamivir plus rimantadine; placebo, placebo plus rimantadine; *removed from protocol, asymptomatic. withdrew from the study after the second study day due to an adverse event (patient 1, Table 3). Three deaths occurred (8%; ZNV plus rimantadine, n=2; placebo plus rimantadine, n=1) (Table 3). PEFRs were similar between treatment groups with only one patient in each group (5%) exhibiting a 20% decrease in PEFR after treatment on day 1 (P=0.23, Table 4). Most patients had a small improvement in PEFRs after the first dose. Virological outcomes Kaplan-Meier estimates indicate that nebulized ZNV plus rimantadine did not significantly reduce the rate of pharyngeal viral shedding compared to placebo plus rimantadine, although there was a tendency towards shorter time to cessation of viral shedding in the ZNV plus rimantadine arm (P=0.37, Figure 1). The median time to no pharyngeal viral shedding was 4 days [95% confidence interval (CI): 2 5 days] in the placebo plus rimantadine group and 2 days (95% CI: 2 5 days) in the ZNV plus rimantadine group (Table 5). No significant differences were noted between the groups in pharyngeal or nasal virus titres (median titres day 1, 2.75 vs 2.21 log 10 /ml; day 3, 0.83 vs 0.42 log 10 /ml; and day 5, 0 vs 0 log 10 /ml, placebo + rimantadine and ZNV+rimantadine, respectively). Table 4. Peak expiratory flow rates related to the first dose Placebo Zanamivir P-value Pre-dose PEFR (ml/s) 165 (40 450) 175 ( ) 0.51 Median (range) Post-dose PEFR (ml/s) 190 (40 440) 205 ( ) 0.90 Median (range) Difference between 0.23 pre-post PEFR 20% Decrease 1 (5%) 1 (5%) <20% Decrease 4 (19%) 8 (40%) No change 7 (33%) 2 (10%) Increased 8 (38%) 7 (35%) Data unavailable 1 (5%) 2 (10%) Clinical outcomes On treatment day 3, no statistically significant differences existed in the proportion of patients still hospitalized (95 vs 94%), receiving supplemental oxygen (65 vs 62%) or having resumed full ambulation. A higher proportion of patients in the ZNV plus rimantadine group reported no/mild cough on day 3 of treatment (94 vs 55%, P=0.01). There are no significant differences between the two groups on other clinical outcomes on day 3 of treatment or at followup on day 28 (Table 5). Viral resistance For 21 patients, sequential viral isolates were available for susceptibility testing. All 43 viral isolates were sensitive to ZNV in the neuraminidase-inhibition assay; there was no significant difference between inhibitory concentration of 50% (IC 50 ) values for ZNV on the first and last day isolates, or in comparison to sensitive controls [day 1 median and range IC 50 =1.9 ng/ml ( ) for ZNV plus rimantadine and 2.2 ng/ml ( ) for placebo plus rimantadine; last isolate 2.1 ng/ml ( ) and 2.1 ng/ml ( ), respectively]. The 43 viral isolates were screened for M2 inhibitor resistance. Three resistant isolates were found by ELISA; they were all from patients on rimantadine monotherapy. Sequence analysis of the M gene (the region encoding the M2 protein) of the three viruses with presumed resistance found that one isolate had a Ala30Thr mutation and another had a Ser31Asn mutation. These two variants developed during rimantadine monotherapy on days 3 and 4, respectively. One of the viruses that screened resistant by ELISA had no documented M2 mutations and was presumed to be a false-positive phenotypic screening assay. Discussion This study is the first prospective, controlled trial of antiviral therapy in seriously ill adults hospitalized with lower respiratory tract manifestations of influenza. Although the study was stopped prematurely and was, Antiviral Therapy 8:3 187

6 MG Ison et al. Figure 1. Kaplan-Meier curve: percent shedding virus Percent shedding virus Any site: ZNV + rimantadine Any site: placebo + rimantadine Pharynx: placebo + rimantadine Pharnyx: ZNV + rimantadine 2 3 Study day Solid lines represent the percentage of virus isolates [placebo n=17, zanamivir (ZNV) n=17] that had positive virus cultures of pharynx by day. No significant difference in curves (log-rank P=0.37). Dashed lines represent the percentage of virus isolates (placebo n=19, ZNV n=19) that were positive from any site by day. Trend to faster recovery in the zanamivir-treated patient (log-rank P=0.49). therefore, underpowered to assess efficacy, it provides important information about the tolerability of nebulized ZNV and the course of influenza in hospitalized adults. Nebulized ZNV was generally well tolerated, without significant declines in PEFRs, by these severely ill patients and was relatively easy to administer. Treatment with nebulized ZNV significantly reduced the severity of cough by day 3 of treatment, but did not have a statistically significant effect on other signs and symptoms of influenza in this hospitalized population. Of note, the study used an investigational nebulized formulation of ZNV for inpatient treatment and did not address the tolerability of the dry powder inhalation formulation currently approved for therapeutic use. Despite being underpowered, several findings of this study suggest that nebulized ZNV combined with rimantadine may be superior to rimantadine monotherapy treatment for patients with lower respiratory tract manifestations of influenza. The beneficial effect on cough suggests that nebulized ZNV may be clinically effective and was well tolerated. Most patients who discontinued the study medication early did so because they had improved sufficiently that they wanted to leave the hospital. This event tended to occur more often in the ZNV plus rimantadine recipients (4/20, 20%) than placebo plus rimantadine (2/21, 10%). ZNV plus rimantadine-treated patients also had a trend toward faster cessation of viral shedding. 4 5 There are no published data on the time course of viral shedding in hospitalized patients treated with rimantadine/amantadine, except for small numbers of immunocompromised individuals [20]. In elderly nursing home residents with acute influenza, rimantadine treatment modestly reduced viral titres in the upper respiratory tract during the first several days of administration, but did not significantly shorten the duration of shedding or reduce titres on later treatment days [25]. This study provides new information about the virological and clinical course of influenza infections in hospitalized adult patients receiving rimantadine therapy. First, the patients in this study had prolonged viral shedding, with a majority still manifesting pharyngeal shedding after day 3. Even 5 days following enrollment, over 25% of patients still hospitalized continued to shed virus from one or more sites. Such data may be useful in determining the length of time patients pose a threat for nosocomial transmission of influenza to other patients. Most patients with severe influenza required supplemental oxygen for >3 days and maintained abnormal pulse oximetry beyond 3 days. As a result of the sequelae of infection, patients had restricted activity and often required hospitalizations in excess of 5 days. One limitation of M2 inhibitors is the frequent emergence of highly resistant transmissible variants during therapy [26]. An interesting observation was that two of the rimantadine monotherapy recipients developed M2 inhibitor-resistant virus, whereas none of those receiving combination of inhaled ZNV and oral rimantadine shed M2 inhibitor-resistant virus. Although the numbers are too small for definitive conclusions, these observations suggest that combination therapy may be able to limit emergence of M2 inhibitor resistance. Consistent with earlier reports from ZNV treatment studies [27], we did not observe resistance to this neuraminidase inhibitor. To date, only one case of ZNV resistance in a highly immunocompromised patient has been reported [21]. This study had several limitations that may impact the findings of the study. The study was stopped early because further recruitment of patients was found to be untenable because of the wide spread availability and use of the two approved neuraminidase inhibitors. As a result, the study was underpowered to definitively assess clinical and virological efficacy of ZNV plus rimantadine in patients hospitalized with lower respiratory tract disease due to influenza. The enrolled patients, although similar in both arms, were very heterogeneous in their baseline characteristics. This study also allowed patients to be enrolled for up to 4 days after onset of symptoms. Previous studies have suggested that otherwise healthy outpatients who received a neuraminidase inhibitor within the first International Medical Press

7 Nebulized zanamivir for serious influenza Table 5. Outcome measures Outcome Placebo, n (%) Zanamivir, n (%) P-value Hospitalized at day 3 18 (95) 15 (94) 0.99 Activity at day Bed rest 4 (20) 3 (19) Limited activity 13 (65) 11 (69) Unrestricted 3 (15) 2 (13) Supplemental O 2 use 13 (65) 10 (62) 0.88 at day 3 Severity of cough at day 3 No cough 4 (20%) 2 (13) 0.01 Mild 7 (35) 13 (81) Moderate 9 (45) 1 (6) Severe 0 0 Pulse oximetry normal 10 (55) 11 (73) 0.96 at day 3 Days of hospitalization* 5.2 ±2.3 (5) 4.7 ±2.3 (5) 0.52 Days of supplemental O 2 * 3.6 ±2.8 (3) 2.9 ±2.8 (2) 0.37 Days with fever* 1.3 ±1.9 (1) 0.6 ±0.8 (0) 0.17 *Mean ±standard deviation (median), number of days; from Fisher s exact test for categorical outcomes and Wilcoxon rank-sum test for continuous outcome measures h had the greatest benefit [4,13]. In our study of hospitalized adults, viral replication continued for a median of 4 days after enrollment in patients receiving rimantadine alone. These patients theoretically would have benefited from institution of a more potent antiviral regimen. This study used an investigational nebulized formulation of ZNV for inpatient treatment and did not address the tolerability of the dry powder inhalation formulation currently approved for therapeutic use. Although well tolerated in controlled studies of outpatients with influenza [4 11], the marketed dry powder formulation has been associated with reports of bronchospasm [22]; studies of the dry powder would be needed in hospitalized patients to establish safety. Nebulized ZNV is a generally well tolerated therapy that may provide clinical benefit in hospitalized patients, although further studies are needed to more completely assess the efficacy and safety of nebulized ZNV in the treatment of this setting. Oral oseltamivir is another therapeutic option in hospitalized adults and children, but also remains unstudied with regard to its oral absorption and antiviral efficacy in severely ill patients. In the event of pandemic influenza, the number of severely ill influenza patients will present a serious challenge to the current armamentarium of anti-influenza agents. Further studies of combinations of antiviral agents to enhance antiviral efficacy and perhaps reduce resistance emergence are needed. Disclaimer Written informed consent was obtained from all participants or their guardians; the clinical research was conducted in accordance with guidelines for human experimentation as specified by the US Department of Health and Human Services. The results of this study have been presented at the 40th Interscience Conference on Antimicrobial Agents & Chemotherapy, Chicago, Ill., USA, 2001 (Abstract #664) and the International Conference on Antiviral Research, Prague, Czech Republic, 2002 (Abstract #102). Study centres included: University of Virginia (FG Hayden), Salem Veteran s Affairs Medical Center (S Nagy-Agren), Rochester School of Medicine and Dentistry (J Treanor, R Betts), Mayo Clinic (C Paya), SUNY Stony Brook (RT Steigbigel), Hackensack (PA Gross), University of New Mexico (G Mertz). References 1. Simonsen L, Fukuda K, Schonberger LB & Cox NJ. The impact of influenza epidemics on hospitalizations. Journal of Infectious Diseases 2000; 181: Barker WH & Mullooly JP. Pneumonia and influenza deaths during epidemics: implications for prevention. Archives of Internal Medicine 1982; 142: Couch RB & Jackson GG. Antiviral agents in influenza. Summary of Influenza Workshop VIII. Journal of Infectious Diseases 1976; 134: Hayden FG, Osterhaus AD, Treanor JJ, Fleming DM, Aoki FY, Nicholson KG, Bohnen AM, Hirst HM, Keene O & Wightman K. Efficacy and safety of the neuraminidase inhibitor zanamivir in the treatment of influenzavirus infections. GG167 Influenza Study Group. New England Journal of Medicine 1997; 337: Management of Influenza in the Southern Hemisphere Trial (MIST). Randomised trial of efficacy and safety of inhaled zanamivir in treatment of influenza A and B virus infections. MIST Study Group. Lancet 1998; 352: Osterhaus ADME, Tisdale M & Elliott M. A double blind randomized trial of zanamivir in the treatment of acute influenza-clinical and virological efficacy results. 38th Interscience Conference on Antimicrobial Agents & Chemotherapy, 1998, San Diego, Calif., USA. 7. Monto AS, Fleming DM, Henry D, de Groot R, Makela M, Klein T, Elliott M, Keene ON & Man CY. Efficacy and safety of the neuraminidase inhibitor zanamivirin the treatment of influenza A and B virus infections. Journal of Infectious Diseases 1999; 180: Boivin G, Goyette N, Hardy I, Aoki F, Wagner A & Trottier S. Rapid antiviral effect of inhaled zanamivir in the treatment of naturally occurring influenza in otherwise healthy adults. Journal of Infectious Diseases 2000; 181: Makela MJ, Pauksens K, Rostila T, Fleming DM, Man CY, Keene ON & Webster A. Clinical efficacy and safety of the orally inhaled neuraminidase inhibitor zanamivir in the Antiviral Therapy 8:3 189

8 MG Ison et al. treatment of influenza: a randomized, double-blind, placebo-controlled European study. Journal of Infection 2000; 40: Kaiser L, Keene ON, Hammond JM, Elliott M & Hayden FG. Impact of zanamivir on antibiotic use for respiratory events following acute influenza in adolescents and adults. Archives of Internal Medicine 2000; 160: Murphy KR, A. E, Pauksen K, Stein WJ, Tellier G, Watts R, Léophonte P, Sharp SJ & Loeschel E. Efficacy and safety of inhaled zanamivir for the treatment of influenza in patients with asthma or chronic obstructive pulmonary disease: a double-blind, randomized, placebo-controlled multicentre study. Clinical Drug Investigation 2000; 20: Treanor JJ, Hayden FG, Vrooman PS, Barbarash R, Bettis R, Riff D, Singh S, Kinnersley N, Ward P & Mills RG. Efficacy and safety of the oral neuraminidase inhibitor oseltamivir in treating acute influenza: a randomized controlled trial. US Oral Neuraminidase Study Group [see comments]. Journal of the American Medical Association 2000; 283: Nicholson KG, Aoki FY, Osterhaus AD, Trottier S, Carewicz O, Mercier CH, Rode A, Kinnersley N & Ward P. Efficacy and safety of oseltamivir in treatment of acute influenza: a randomised controlled trial. Neuraminidase Inhibitor Flu Treatment Investigator Group. Lancet 2000; 355: Stokes CE, Bernstein JM, Kyger SA & Hayden FG. Rapid diagnosis of influenza A and B by 24-h fluorescent focus assays. Journal of Clinical Microbiology 1988; 26: Mills RD, Cain KJ & Woods GL. Detection of influenza virus by centrifugal inoculation of MDCK cells and staining with monoclonal antibodies. Journal of Clinical Microbiology 1989; 27: Waner JL, Todd SJ, Shalaby H, Murphy P & Wall LV. Comparison of Directigen FLU-A with viral isolation and direct immunofluorescence for the rapid detection and identification of influenza A virus. Journal of Clinical Microbiology 1991; 29: Gubareva LV, Kaiser L, Matrosovich MN, Soo-Hoo Y & Hayden FG. Selection of influenza virus mutants in experimentally infected volunteers treated with oseltamivir. Journal of Infectious Diseases 2001; 183: Klimov AI, Rocha E, Hayden FG, Shult PA, Roumillat LF & Cox NJ. Prolonged shedding of amantadine-resistant influenzae A viruses by immunodeficient patients: detection by polymerase chain reaction-restriction analysis. Journal of Infectious Diseases 1995; 172: Rollins BS, Elkhatieb AH & Hayden FG. Comparative anti-influenza virus activity of 2 -deoxy-2 -fluororibosides in vitro. Antiviral Research 1993; 21: Englund JA, Champlin RE, Wyde PR, Kantarjian H, Atmar RL, Tarrand J, Yousuf H, Regnery H, Klimov AI, Cox NJ & Whimbey E. Common emergence of amantadine- and rimantadine-resistant influenza A viruses in symptomatic immunocompromised adults. Clinical Infectious Diseases 1998; 26: Gubareva LV, Matrosovich MN, Brenner MK, Bethell RC & Webster RG. Evidence for zanamivir resistance in an immunocompromised child infected with influenza B virus. Journal of Infectious Diseases 1998; 178: Kent RS. Important revisions to safety labeling for Relenza (zanamivir for inhalation). Letter to Physicians July ; Research Triangle Park, NC, USA: GlaxoWellcome Monto AS, Moult AB & Sharp SJ. Effect of zanamivir on duration and resolution of influenza symptoms. Clinical Therapeutics 2000; 22: Van Voris LP, Betts RF, Hayden FG, Christmas WA & Douglas RG Jr. Successful treatment of naturally occurring influenza A/USSR/77 H1N1. Journal of the American Medical Association 1981; 245: Betts RF, Treanor JJ, Graman PS, Bentley DW & Dolin R. Antiviral agents to prevent or treat influenza in the elderly. Journal of Respiratory Diseases 1987; s56 s Hayden FG. Combination antiviral therapy for respiratory virus infections. Antiviral Research 1996; 29: Hayden FG, Gubareva LV, Monto AS, Klein TC, Elliot MJ, Hammond JM, Sharp SJ & Ossi MJ for the Zanamivir Family Study G. Inhaled zanamivir for the prevention of influenza in families. Zanamivir Family Study Group. New England Journal of Medicine 2000; 343: Received 28 August 2002; accepted 6 January International Medical Press