Use of Intravenous Zanamivir after Development of Oseltamivir Resistance in a Critically Ill Immunosuppressed Child Infected with 2009 Pandemic Influenza A (H1N1) Virus

Abstract

An 18-month-old female patient was admitted for allogeneic matched related stem cell transplant for relapsed hematologic malignancy. The patient was without respiratory symptoms at the time of hospital admission. Results of polymerase chain reaction (PCR) assay for a panel of respiratory viruses, including influenza A and B, obtained 1 week prior to admission were negative. She developed cough on hospital day 1 following the initiation of myeloablative therapy. On hospital day 2, she experienced fever (maximum temperature, 38.7°C) with continued cough but exhibited no signs or symptoms of respiratory distress. No abnormalities were identified on chest radiography. PCR assay performed on a nasopharyngeal specimen for influenza A and B (obtained hospital day 2) returned a positive result for influenza A on hospital day 6. Treatment with 45-mg oseltamivir (3 mg/kg per dose) every 12 h was initiated.

Because myeloablative therapy had been initiated prior to onset of illness, the patient received bone marrow infusion on hospital day 10 without complication. Fever recurred on day 15 and persisted until day 21 in association with new radiographic opacities in the left upper and right lower lobes of the lungs. On hospital day 20, the patient developed respiratory distress requiring mechanical ventilation, intermittently using oscillatory mode, with high peak pressure and FiO₂ settings. Results of viral culture and PCR assay performed on endotracheal and nasopharyngeal aspirates for influenza A remained positive from day 13 to day 33 in the context of persistent neutropenia and lymphopenia (Figure 1). PCR assay of an endotracheal aspirate specimen collected on day 22 confirmed infection with 2009 pandemic influenza A (H1N1) virus, and all subsequent specimens positive for influenza A by PCR were confirmed to be pandemic influenza A (H1N1) virus. Influenza B was detected by viral culture of a nasopharyngeal specimen obtained on day 29 and PCR assay of an endotracheal aspirate obtained on day 30, but no further culture or PCR evidence of influenza B infection was found in any specimen. No culture or other laboratory indications of bacterial or fungal infection were identified. However, broad-spectrum antimicrobial therapy (vancomycin, meropenem, and micafungin) was administered throughout the illness because of the continued fever, neutropenia, and respiratory failure. Immunosuppression was maintained with cyclosporine (entire posttransplantation course), methylprednisolone (initiation on day 34 and transition to weaning on day 48), and etanercept (days 27–51) (Figure 1). Consideration was given to decreasing the intensity of immunosuppression, but this action was deferred because of concern for severe graft-versus-host disease in the early posttransplantation setting.

Figure 1

Treatment history, laboratory findings, and virologic course in a critically ill immunosuppressed pediatric patient infected with oseltamivir-resistant novel H1N1 influenza. H275Y is a mutation in the neuraminidase protein of H1N1 associated with oseltamivir resistance. ALC, absolute lymphocyte count; C_t, polymerase chain reaction cycle detection threshold for novel H1N1 RNA; G, granulocyte colony-stimulating factor; IVIG, intravenous immune globulin; WBC, white blood cell count. *Indicates detection of influenza B.

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Treatment with zanamivir was considered because of continued viral shedding in conjunction with clinical deterioration and concerns for possible oseltamivir resistance. However, the patient's age and intubated status contraindicated use of the standard powdered formulation of zanamivir [1]. Therefore, intravenous therapy with zanamivir (provided on a compassionate use basis by GlaxoSmithKline), 320 mg (20 mg/kg per dose, based on weight and creatinine clearance rate) every 12 h, was initiated on day 35 following consent from the patient's mother and approval by the local Institutional Review Board. Oseltamivir treatment was continued throughout the remainder of the hospitalization (total course, 52 days) because of possible influenza B coinfection and the investigational nature of zanamivir treatment.

Endotracheal aspirates collected on days 5 and 9 of intravenous zanamivir therapy (corresponding to hospital days 39 and 43, respectively) did not contain PCR-detectable influenza A, although virus was again detected on days 11–20 of treatment (hospital days 45–54). Granulocyte colony-stimulating factor was administered on hospital days 46–48 (Figure 1), but the patient's clinical condition continued to worsen despite improvement in the total white blood cell and absolute neutrophil counts. Intravenous zanamivir therapy was completed on hospital day 54 following a 20-day course. A single occurrence of fever (maximum temperature, 38.6°C) on hospital day 44 was documented during the period of zanamivir treatment. Laboratory abnormalities occurring during zanamivir therapy were explainable by the patient's underlying condition; no sustained changes in creatinine, alanine aminotransferase, or total bilirubin levels were observed (Table 1). The patient experienced progressive decrease in respiratory status despite maximal ventilator support and died on hospital day 57. Autopsy findings of the lungs revealed diffuse alveolar damage with extensive intra-alveolar hemorrhage, organizing pneumonia, and focal acute inflammation. Scattered cytomegalovirus-positive cells were identified on the basis of characteristic cytopathic effect and immunohistochemical staining. No fungal elements or other microorganisms were detected in lung sections, and postmortem viral, bacterial, and fungal cultures of lung tissue were negative.

Table 1

Laboratory Data by Hospital Day Referenced to Clinical Data and Antiviral Treatment

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Subsequent sequence- and real-time PCR–based analysis of the novel H1N1 virus neuraminidase (NA) gene conducted at our institution, the Centers for Disease Control and Prevention, and IntelligentMDx demonstrated the presence of the oseltamivir resistance–associated H275Y mutation [2–4] in specimens obtained on hospital days 13, 29, 30, and 33. The wild-type NA sequence at position 275 was detected in the influenza A–positive specimen collected on day 2 (Figure 1). The C_t values determined from reverse transcription real-time PCR assay data revealed a logarithmic decrease in novel H1N1 viral RNA level coincident with zanamivir treatment.

Novel H1N1 influenza A has been shown to target children and young adults with the potential for severe morbidity and mortality, and immunosuppressed patients are considered to be at additional increased risk [5–7]. Our patient demonstrated prolonged viral shedding and progressive pulmonary disease following H1N1 virus infection in the setting of extreme leukopenia due to myeloablative therapy. Development of oseltamivir resistance in novel H1N1 virus is documented in immunosuppressed patients and healthy children receiving oseltamivir treatment and prophylaxis [4, 8, 9]. Because the resistance-associated H275Y mutation in NA was not detected in our patient prior to introduction of oseltamivir (sample obtained on hospital day 2) but had appeared by the seventh day of therapy, oseltamivir resistance appears to have evolved during treatment. Consistent with earlier reports, antiviral resistance arose early in the treatment course [8]. Early development of oseltamivir resistance has serious implications for the care of immunosuppressed patients infected with novel H1N1 influenza A. Clinicians should consider viral resistance testing early in the management of immunosuppressed patients who fail to demonstrate clinical improvement or develop prolonged viral shedding detected by PCR assay or culture.

In the present case, oseltamivir dosing was initiated as recommended by the Centers for Disease Control and Prevention guidelines [10]. The optimal dose of oseltamivir in immunosuppressed and critically ill patients has not been established. Some experts advocate higher dosing at onset of therapy in this population to prevent selection of antiviral resistance [11]. Although it is possible that early selection of oseltamivir resistance in this patient occurred using the standard dose of drug, the patient was not critically ill at the time that therapy was initiated and, therefore, likely would have had adequate drug absorption by the oral route. It must be emphasized that peramivir, an intravenous formulation of influenza virus neuraminidase inhibitor now available through Emergency Use Authorization from the Centers for Disease Control, appears to not be effective in this clinical setting because of crossresistance between oseltamivir and peramivir conferred by the H275Y mutation [12, 13].

Intravenous zanamivir has been evaluated in healthy adults, and its use in a critically ill immunosuppressed adult patient has been reported elsewhere [14–16]. One report addressed the use of intravenous zanamivir in children [17]. The pediatric literature regarding safety and efficacy of this formulation remains sparse. The present report of intravenous zanamivir therapy for a confirmed infection with oseltamivir-resistant novel H1N1 influenza A in a child with complicated influenza infection provides further evidence that intravenous zanamivir is well tolerated with no apparent adverse events or laboratory abnormalities attributable to its use. Intravenous zanamivir was associated with evidence of major virologic improvement, manifested as a logarithmic decrease in viral load during therapy based on changes in C_t values. Although specimen type and collection methods may affect the amount and integrity of viral RNA template available for amplification, these variables are unlikely to account for a decrease of this magnitude. Several clinical factors also may have contributed to the decrease in viral load. Administration of intravenous immune globulin occurred prior to the use of zanamivir. A possible role for intravenous immune globulin in this setting is suggested by the presence of preexisting crossreactive antibodies to 2009 novel H1N1 influenza A in up to 34% of adults [18]. Additionally, a slight rebound in immune function, evidenced by an increase in the total white blood cell count, following administration of granulocyte colony-stimulating factor may have contributed to the reduction in viral load. However, persistent and severe lymphopenia likely limited any positive impact of leukocyte recovery on the control of influenza infection. Though initiation of intravenous zanamivir was temporally associated with transient clinical and radiographic improvement, these effects were not sustained, presumably because of extensive lung injury and unremitting lymphopenia.

The provenance and role of concurrent influenza B infection in the patient's clinical course is unclear because this virus was detected in only 2 specimens obtained on hospital days 29 and 30. It is possible that she acquired a transient influenza B superinfection that was promptly eradicated by oseltamivir therapy. A testing artifact seems unlikely because influenza B was identified in independent laboratories by complementary methods (Vanderbilt and Tennessee State Department of Health). Though we cannot exclude a role for cytomegalovirus infection in this patient's illness, the histopathologic changes most likely reflect only local reactivation of cytomegalovirus replication on the basis of the limited extent of tissue involvement and absence of PCR-detectable circulating virus at any point during hospitalization. Pathology findings in the present case were similar to those previously described for novel H1N1 influenza A [19].

The present case underscores the risk for selection of oseltamivir resistance in an immunosuppressed patient after a short period of antiviral therapy and provides empiric data on the use of intravenous zanamivir as an alternative treatment for oseltamivir-resistant novel H1N1 influenza A in an intubated pediatric patient for whom conventional inhaled zanamivir therapy is contraindicated. Although multiple factors may have played a role in the virologic improvement noted in this case, our observations are concordant with recent reports describing use of intravenous zanamivir to treat pneumonia due to oseltamivir-resistant novel H1N1 influenza A [16, 17]. The present case extends the duration of well-tolerated intravenous zanamivir in pediatric patients from 15 days, as reported previously, to 20 days [17]. Although progressive deterioration of our patient's respiratory status could not be reversed, the marked reduction in viral load concurrent with intravenous zanamivir therapy provides additional evidence for the efficacy of this treatment strategy to limit oseltamivir-resistant novel H1N1 virus replication in severely ill individuals.

At present, insufficient evidence exists to specifically define the clinical and virologic triggers to alter antiviral therapy in individual immunosuppressed patients. Therefore, we urge vigilant monitoring of these fragile patients for early indications of treatment failure and development of oseltamivir resistance in patients who are immunosuppressed, shed virus for prolonged periods, or experience progressive or especially severe disease while receiving oseltamivir. There is an urgent need for widely available, rapid laboratory diagnostic methods to detect drug-resistant viruses and for intravenous formulations of neuraminidase inhibitors that can be used to treat critically ill children and adults infected with oseltamivir-resistant strains of novel H1N1 influenza A.

Acknowledgments

We thank GlaxoSmithKline for providing the intravenous preparation of zanamivir.

Financial support.The Southeast Regional Center of Excellence for Emerging Infections and Biodefense and from the National Institute of Allergy and Infectious Diseases (U54 AI57157 to M.R.D.).

Potential conflicts of interest.C.B.C. has received grant support from Pfizer, Merck, and Cubist Pharmaceuticals unrelated to this report and has served as a consultant for Pfizer and Novartis Vaccines. All other authors: no conflicts.

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