Adenovirus (ADV) is a common cause of respiratory infection in childhood. ADV infections are usually self-limited and asymptomatic in the immunocompetent host but have been recognized as a cause of significant morbidity and mortality in immunocompromised pediatric patients such as recipients of hematopoietic stem cell transplant (HSCT) and solid organ transplant (SOT) ¹ . In these patients, ADV is an opportunistic pathogen that may lead to severe localized disease including pneumonia/pneumonitis, hepatitis, hemorrhagic cystitis or disseminated disease with multiorgan failure ^{2– 4} . Case fatality rates in immunocompromised patients with ADV pneumonia have been reported to be as high as 60% ⁵ . Currently, there is no FDA-labeled product available for treatment of ADV infection though several agents have been administered for this indication including ribavirin ^{6, 7} , ganciclovir ⁸ , vidarabine ^{9, 10} , immune globulin ¹¹ and cidofovir ^{12– 21} .

Cidofovir (CDV), a nucleoside and phosphonate analogue is a broad-spectrum antiviral agent that inhibits viral DNA polymerase and has broad activity in vitro against multiple viruses including all serotypes of ADV ^{22, 23} . CDV has an FDA indication for the treatment of cytomegalovirus (CMV) retinitis in patients with AIDS. Although this drug does not have an FDA indication for treating ADV, there is evidence of in vivo efficacy of CDV against ADV ^{12, 14} . While CDV at a standard dose of 5mg/kg has been reported as primary therapy for treatment of ADV infection in pediatric and adult hematopoietic stem cell transplantation (HSCT) patients ^{12, 21} , concern exists regarding potential nephrotoxicity. These associated adverse effects have limited the use of CDV for treatment of ADV infections in pediatric patients. To minimize potential toxicity of CDV, modified dosing regimens such as the use of 1 mg/kg three times have been utilized ¹⁴ .

Limited information regarding safety and efficacy of CDV in pediatric patients prompted us to review prior published studies in the literature and conduct a retrospective review of our inpatient use of CDV at Boston Children’s Hospital (BCH).

Following Institutional Review Board (IRB) approval (IRB-P00015576), a retrospective chart review was conducted for all hospitalized patients at Boston Children’s Hospital (BCH), who were prescribed CDV for adenovirus infection from January 2006 through December 2010. The following data were collected: (1) demographic information, (2) underlying disease state, (3) type of transplant, (4) duration of cidofovir therapy, (6) serum creatinine (SCr) (baseline, peak during therapy, and level up to 2 weeks post last dose), (7) concomitant nephrotoxins prescribed (acyclovir, amikacin, cyclosporine, foscarnet, gentamicin, liposomal amphotericin B, tacrolimus, tobramycin, vancomycin, and intravenous contrast media), (8) sites of ADV detection by viral direct fluorescent antibody (DFA), nucleic acid test, and/or culture, (9) viral quantitative PCR surveillance in blood and other sites of infection (all specimens were tested at least weekly before, during and to two weeks post last dose of CDV to evaluate for changes in viral load with a minimum three serial values being obtained before, during and at end of therapy); (10) symptoms of infection, and clinical course including response to therapy, (11) concomitant reduction of immunosuppression and (12) mortality and cause(s) of mortality. All blood sample testing for adenovirus quantitative PCR in blood was performed at the Boston Children’s Hospital Virology Laboratory using our laboratory developed test, the Argene adenovirus assay (bioMerieux, Cambridge, MA). The Argene adenovirus assay contains primers and probes selective for a 138 base pair (bp) sequence in the Hexon gene of the adenovirus. Using a 5’ nuclease assay, viral DNA is detected using the primers and fluorescent probes from the Argene assay kit by means of real time PCR in a Cepheid SmartCycler (Cepheid, Sunnyvale, CA).

From January 1, 2006 to December 31, 2010, a total of 16 pediatric patients received CDV for adenovirus infection at our hospital. These 16 patients received 19 courses (three patients received two separate CDV courses). The standard CDV dose of 5mg/kg weekly was used in all courses unless there was concern for renal dysfunction at the start of therapy in which case a dosing regimen of 1mg/kg three times a week was used. Patient demographics, primary diagnosis, clinical symptoms and course, and sites of adenovirus detection appear in Table 1. Patient age ranged from 0.75–20 years (mean 6.5 years). Seven (44%) patients were male. Underlying primary diagnosis included 8 (50%) HSCT (1 autologous), 4 (25%) SOT, 2 (12.5%) leukemia, and 2 (6.5%) defined as other. Duration of CDV therapy ranged from 5–82 days (median 33.5 days).

Of the 19 courses prescribed ( Table 1), two courses were prescribed in a patient with definite adenovirus disease of the gastrointestinal tract, 15 courses were prescribed in patients with probable disease and two courses were prescribed in patients with asymptomatic infection. Sixteen courses (84%) were in patients who had a positive blood ADV PCR either in whole blood only or in combination with positive ADV PCR of sputum, stool, urine, broncho-alveolar lavage (BAL) fluid, pericardial fluid or positive sputum adenoviral DFA sample. Respiratory symptoms were the most common presentation in 10 courses (53%) of which six courses were prescribed for patients with respiratory symptoms and radiological evidence of pneumonia. Two courses were prescribed in patients who presented with prolonged fevers; four courses were prescribed in patients who had worsening diarrhea and colitis, two of which were biopsy proven adenovirus infection; four courses were prescribed in patients with viral sepsis with or without pneumonia; and two courses were administered in patients with severe hemorrhagic cystitis. Two courses were prescribed in patients with asymptomatic respiratory tract infection and asymptomatic gastrointestinal infection respectively.

We further examined the 16 blood-positive courses to assess trends in ADV viral load pre-, during and post- CDV therapy ( Figure 1). A quantitative reduction in viral load was seen in 15 blood positive courses (94%) with viral clearance achieved in 14 (88%). Of note, all solid organ transplant recipients treated with CDV also had concomitant decrease in their immunosuppression. A single patient (Patient 6) did not demonstrate viral response to therapy and expired. The majority of adenovirus blood-positive CDV courses (10/16, 63%) were associated with clinical improvement with viral clearance, however this was not the case in four courses. Patients 7, 10, 11 and 16 expired despite demonstrating viral clearance. Patients 6, 7 and 16 had multiple other co-infections. Patients 11 and 16 developed severe hemorrhagic cystitis. Patient 11 experienced significant complications of hemorrhagic cystitis including urinary tract obstruction, renal failure and bladder perforation. Patient 16 also had concomitant BK Polyoma virus detected in the urine.

Each patient’s medication profile was assessed to determine the number of additional nephrotoxic agents concomitantly prescribed during CDV therapy (from Day 1 to 7 days post last CDV dose). All 19 courses prescribed had at least one additional nephrotoxic agent prescribed during CDV therapy ( Table 2). Four courses (21%) had only one additional nephrotoxic medication prescribed, five courses (26%) had two such medications prescribed, six courses (32%) had three prescribed, two courses (11%) had four prescribed, and two courses (11%) had five prescribed.

Administration of CDV was significantly associated with occurrence of renal dysfunction when comparing the peak Cr measured during CDV therapy to the baseline serum Cr (p=0.0016). Eleven courses (58%) were associated with development of renal dysfunction. Cr increased by a mean of ~50% from baseline during CDV therapy ( Figure 2). Of the courses with elevation in serum creatinine, 64% demonstrated return to pre-treatment creatinine levels following cessation of CDV therapy. There was no statistically significant difference when assessing for increased risk of renal dysfunction if patients received ≤ 1 additional nephrotoxic agent or ≥ 2 additional nephrotoxic agents.

In this retrospective review of patients treated with CDV for adenovirus infection at our hospital during a 5-year period, we assessed the safety and potential efficacy of the medication in pediatric patients. Our review yielded a case series of 16 patients. While the number of patients is modest, this series adds to the existing literature describing the use of CDV in pediatric recipients of HSCT, SOT and chemotherapy for oncologic diagnoses ( Table 3).

Similar to other studies the majority of our patients had received a HSCT or had an oncologic diagnosis and received chemotherapy. We identified eight publications describing the use of CDV for adenovirus infection in the setting of HSCT or oncologic diagnoses treated with chemotherapy ( Table 3). Three of these studies ^{14, 17, 27} reported viral clearance in 89–100% of their patients. We observed similar rates of viral clearance (88%) but this was not consistently associated with clinical improvement.

There are very few reports on the use of CDV for adenovirus infection in pediatric SOT recipients, which have largely been restricted to reports of children receiving liver or lung transplants ^{16, 20, 24, 25} . We identified four publications reporting the use of CDV for adenovirus infection in pediatric SOT recipients limited to one to four per report and all of these children having received liver or lung transplants ^{16, 20, 24, 25} . Doan et al. ²⁵ described children who had received lung transplants with reported viral clearance in three of their four patients. Our case series contributes patients who received several types of SOT including lung, heart, combined kidney and liver, and multi-visceral transplants. All patients with SOT in our series demonstrated viral clearance as well as resolution of symptoms, which may have reflected a combination of both the antiviral effect of CDV coupled with reduced immunosuppression.

Two-thirds of our patients experienced resolution of their symptoms and had an overall favorable clinical course with recovery. However, one-third died all of which were stem cell transplant recipients. With the exception of one patient it is unclear whether adenovirus was the direct cause of mortality in these patients. Our observations are consistent with what has been reported in the literature pertaining to outcomes in stem cell transplant recipients with adenovirus infections who have been treated with CDV ^{9, 12, 14, 18, 23, 27} . Among SCT patients mortality remains high (10%–70%) even when clearance from blood is seen.

In our case series, renal dysfunction was common during CDV therapy with patients experiencing an average 50% increase of serum creatinine from their baseline. However, renal dysfunction was transient in the majority of patients with serum creatinine returning to baseline after cessation of CDV therapy. While some studies have reported no toxicities related to the use of CDV ^{14, 16, 17, 19, 25} , the transient nature of nephrotoxicity observed has been reported by other studies ^{20, 24} . We were unable to detect any increased risk of nephrotoxicity associated with concomitant administration of additional nephrotoxic agents but this may reflect our small number of study participants.

Our study has several limitations. Most notably, the small number of patients precluded evaluation of other factors that may impact infection resolution such as immunosuppressive regimens, and additional factors that may impact degree of renal dysfunction. Nevertheless, our study adds to the limited reported literature of pediatric ADV patients treated with CDV.

The data referenced by this article are under copyright with the following copyright statement: Copyright: � 2016 Ganapathi L et al.

Data associated with the article are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

F1000Research: Dataset 1. Raw data for Figure 1, 10.5256/f1000research.8374.d117321 ²⁸

F1000Research: Dataset 2. Raw data for Figure 2, 10.5256/f1000research.8374.d117322 ²⁹