Protective role of γδ T cells in cigarette smoke and influenza infection.

Airborne pathogens commonly trigger severe respiratory failure or death in smokers with lung disease. Cigarette smoking compromises the effectiveness of innate immunity against infections but the underlying mechanisms responsible for defective acquired immune responses in smokers remains less clear. We found that mice exposed to chronic cigarette smoke recovered poorly from primary Influenza A pneumonia with reduced type I and II interferons (IFNs) and viral-specific immunoglobulins, but recruited γδ T cells to the lungs that predominantly expressed interleukin 17A (IL-17A). Il-17a-/- mice exposed to smoke and infected with Influenza A also recruited γδ T cells to the lungs, but in contrast to wild-type mice, expressed increased IFNs, made protective influenza-specific antibodies, and recovered from infection. Depletion of IL-17A with blocking antibodies significantly increased T-bet expression in γδ T cells and improved recovery from acute Influenza A infection in air, but not smoke-exposed mice. In contrast, when exposed to smoke, γδ T cell deficient mice failed to mount an effective immune response to Influenza A and showed increased mortality. Our findings demonstrate a protective role for γδ T cells in smokers and suggest that smoke-induced increase in IL-17A inhibits the transcriptional programs required for their optimal anti-viral responses. Cigarette smoke induces IL-17A expression in the lungs and inhibits γδ T-cell-mediated protective anti-viral immune responses.

Supercoiled Minivector DNA resists shear forces associated with gene therapy delivery.

Supercoiled DNAs varying from 281 to 5302 bp were subjected to shear forces generated by aerosolization or sonication. DNA shearing strongly correlated with length. Typical sized plasmids (≥ 3000 bp) degraded rapidly. DNAs 2000-3000 bp persisted ~10 min. Even in the absence of condensing agents, supercoiled DNA <1200 bp survived nebulization, and increased forces of sonication were necessary to shear it. Circular vectors were considerably more resistant to shearing than linear vectors of the same length. DNA supercoiling afforded additional protection. These results show the potential of shear-resistant Minivector DNAs to overcome one of the major challenges associated with gene therapy delivery.

Cyclosporin A aerosol improves the anticancer effect of paclitaxel aerosol in mice.

Paclitaxel (PTX) is a lipophilic agent with broad anticancer activity. In the present study we examined the antitumor effect and toxicity of co-administration of cyclosporine A (CsA) and PTX in liposomal aerosol using the Renca lung metastases mouse model. The untreated and PTX-only groups exhibited cancer growth while CsA aerosol plus PTX had more favorable effects on tumor growth. Weight loss was seen in mice treated with CsA/PTX+CsA by day 9 to 22. Histopathological examination showed no toxicity following treatment. The findings offer evidence that a combination of CsA and PTX may be suitable for aerosol treatment of lung cancer if it is possible to control toxicity of the therapy.

Improved respiratory delivery of the anticancer drugs, camptothecin and paclitaxel, with 5% CO2-enriched air: pharmacokinetic studies.

PURPOSE: To increase pulmonary deposition of anticancer liposome aerosols in mice by modulation of respiratory physiology through the addition of 5% CO2 to the air source used to generate the aerosols. Breathing CO2-enriched aerosol increases pulmonary ventilation with concurrent increased deposition of inhaled particles. METHODS: Dilauroylphosphatidylcholine liposome formulations of two anticancer drugs, paclitaxel (PTX) and camptothecin (CPT), were investigated. The aerosol droplet size was measured using an Andersen cascade impactor. Drug concentrations in aerosol droplet fractions and tissues were determined by HPLC analysis. ICR mice were exposed to each liposome aerosol for 30 min. For each drug, one group of mice inhaled the drug-liposome aerosol generated with a mixture of 5% CO2 in air and another group inhaled the drug-liposome aerosols produced with normal air. Tissue distribution and pharmacokinetics were determined for both drug delivery systems. RESULTS: Significantly higher concentrations of PTX and CPT were found in organs of mice exposed to 5% CO2-air aerosols compared to organs of mice exposed to normal air aerosols. The highest concentrations of drug were detected in the lungs and were two- to fourfold higher with 5% CO2-air aerosols than with aerosols generated with normal air. Higher concentrations were also detected in liver, spleen, kidneys, blood, and brain. CONCLUSION: 5% CO2 enrichment of air increased respiratory tract deposition of inhaled aerosol particles containing PTX and CPT.

Use of cotton rats for preclinical evaluation of measles vaccines.

The continued prevalence and medical impact of measles worldwide has created interest in the development of new generations of measles vaccines. Monkeys can be used for preclinical testing of these vaccines. However, a more practical and less expensive animal model is highly desirable, particularly for initial vaccine development and evaluation. Cotton rats have been shown to support the replication of different strains of measles virus (MV), and thus may be useful for these purposes. To test this concept, the immunogenicity and protective efficacy of two standard (Moraten and trivalent measles, mumps, rubella) and four experimental (two recombinant ALVAC, one ISCOM subunit and live attenuated Edmonston-Zagreb) MV vaccines were evaluated in naïve cotton rats, and cotton rats with passively acquired MV-specific neutralizing serum antibodies. All of the test vaccines were immunogenic and protected naíve animals from pulmonary infection and viral dissemination. However, under the conditions utilized, only the Edmonston-Zagreb vaccine provided such protection to animals with significant levels of passively acquired MV-specific neutralizing antibodies. The results of these tests and the potential of using cotton rats as an animal model for preliminary testing of MV vaccines are discussed.

9-Nitrocamptothecin liposome aerosol treatment of melanoma and osteosarcoma lung metastases in mice.

The response rates of relapsed osteosarcoma and melanoma pulmonary metastases to traditional i.v. chemotherapeutic regimens have been disappointing. Direct drug delivery of chemotherapy to the lungs could increase the drug concentration in the tumor area and may offer a new therapeutic approach for these patients. Previous studies demonstrated that drugs delivered to the respiratory tract in liposomal formulation resulted in high pulmonary drug concentration, reduced systemic toxicity, and reduced dosage requirements compared with parenteral and oral administration. To determine whether this approach has utility against pulmonary metastases, the efficacy of aerosol therapy with liposome-encapsulated 9-nitrocamptothecin (L-9NC) was determined using two different experimental lung metastasis models. C57BL/6 mice were treated the day after the i.v. injection of B16 melanoma cells with aerosol L-9NC for 1 h (153 microg 9-nitrocamptothecin/kg) for 5 days per week for up to 3 weeks. Aerosol L-9NC treatment resulted in a reduction in lung weights (P = 0.005) and number of tumor foci (P < 0.001). Visible tumor nodules were fewer and smaller in the 9-nitrocamptothecin-treated group than in untreated control mice (P < 0.001). Using a newly developed human osteosarcoma experimental metastasis model in nude mice, we demonstrated that aerosol L-9NC was also effective against established lung metastases. Aerosol therapy initiated on the ninth week after i.v. tumor injection and continued for 8 or 10 weeks produced highly significant reductions in the number of animals with both visible and microscopic disease (P < 0.02), the total number of tumor foci in the lungs (P < 0.005), and the size of the individual tumor nodules (P < 0.02). These data suggest that L-9NC aerosol therapy may offer significant advantage over existing methods in the treatment of melanoma and osteosarcoma pulmonary metastases.

Use of cotton rats to evaluate the efficacy of antivirals in treatment of measles virus infections.

No practical animal models for the testing of chemotherapeutic or biologic agents identified in cell culture assays as being active against measles virus (MV) are currently available. Cotton rats may serve this purpose. To evaluate this possibility, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) and poly(acrylamidomethyl propanesulfonate) (PAMPS), two compounds that have been reported to inhibit MV in vitro, and ribavirin, an established antiviral drug with MV-inhibitory activity, were evaluated for their antiviral activities against MV and respiratory syncytial virus (RSV) in tissue culture and in hispid cotton rats. A single administration of PAMPS markedly inhibited pulmonary RSV or MV replication (>3 log(10) reduction in pulmonary titer compared to that for controls), but only if this compound was administered intranasally at about the time of virus inoculation. Both EICAR and ribavirin exhibited therapeutic activity against RSV and MV in cotton rats when they were administered parenterally. However, both of these compounds were less effective against MV. On the basis of the pulmonary virus titers on day 4 after virus inoculation, the minimal efficacious dose of EICAR against MV (120 mg/kg of body weight/day when delivered intraperitoneally twice daily) appeared to be three times lower against this virus than that of ribavirin delivered at a similar dose (i.e., 360 mg/kg/day). These findings correlated with those obtained in vitro. The data obtained suggest that cotton rats may indeed be useful for the initial evaluation of the activities of antiviral agents against MV.

9-Nitrocamptothecin liposome aerosol treatment of human cancer subcutaneous xenografts and pulmonary cancer metastases in mice.

The purpose of this study was to test the anticancer properties of the water-insoluble derivative of camptothecin, 9-nitrocamptothecin (9NC), administered in a liposome formulation (L-9NC) in aerosol to mice with subcutaneous xenografts of three human cancers and in mice with murine melanoma and human osteosarcoma pulmonary metastases. The drug was formulated with dilauroylphosphatidylcholine and nebulized in particle sizes of 1.2-1.6 microns mass median aerodynamic diameter and a geometric standard deviation of 2.0. The aerosol was generated with the nebulizer flowing at 10 l/min and delivered to mice in sealed plastic cages or in a nose-only exposure chamber. Aerosol was administered for 15 min to 2 hr daily, delivering deposited doses in the respiratory tract of 8.1-306.7 micrograms of 9NC/kg. With subcutaneous tumors, growth was greatly inhibited or tumors were undetectable after several weeks of treatment. We also showed that oral dosage with L-9NC had no detectable effect on cancer growth, and thus the benefit from aerosol treatment was due to pulmonary deposition and not the larger fraction of drug deposited in the nose of mice during aerosol treatment which is promptly swallowed. Intramuscular L-9NC in slightly larger doses than given in the aerosol had detectable anticancer activity, but it was significantly less than in mice receiving the drug by aerosol. With metastatic pulmonary cancers, treated animals showed highly significantly less cancer growth than control animals. L-9NC aerosol showed a major therapeutic benefit in the treatment of subcutaneous human cancer xenografts in nude mice, suggesting that cancers at systemic sites might be responsive to this treatment. In addition, the strong anticancer effect of L-9NC aerosol on pulmonary metastases offers a therapeutic approach for treatment of pulmonary cancers. Thus, L-9NC aerosol may have applicability in the treatment of cancers throughout the body.

Alternative administration of camptothecin analogues.

The binding of camptothecin (CPT) to the DNA-topoisomerase complex is reversible, but it needs to be maintained for maximal inhibitory activity. It is also dependent on the chemical structure of CPT. The lactone form is thought to be necessary for the activity. In human serum, the equilibrium between lactone and carboxylate is in favor of the latter. For these reasons, alternative administration of CPT analogues is being evaluated. The ideal compound would remain in lactone form and would expose the host for long periods of time to its effects. Oral administration of irinotecan (CPT-11) and topotecan (TPT) is discussed by other investigators. We studied oral rubitecan and reported a low lactone to total drug area under the plasma concentration-time curve (AUCP) ratio (14.7%), with low plasma concentration over time despite repeated administrations and the presence of an enterohepatic cycle. Aerosolization of a liposomal formulation of rubitecan is currently under study. Six patients have been treated once a day for 5 days every 3 weeks. The dose was 6.7 micrograms/kg/day. Plasma levels are dose for dose higher than those after oral administration, but the ratio of lactone versus total drug is low. No toxicity was observed. The study will continue with increasing doses and lengths of administration. Intrathecal administration of topotecan has been studied in a phase I trial in children. Doses of 0.4 mg are tolerated without toxicity, and clinical responses have been seen in patients with refractory meningial carcinomatosis. Phase II studies are planned. Intraperitoneal (i.p.) administration of topotecan has been studied in a phase I trial as a 24-hour infusion in 5% dextrose at pH 3.5 every 21 days. Dose-limiting toxicity is 4 mg/m2. Toxic effects are neutropenia, anemia, emesis, fever, and pain. Five of 10 patients with ascites had symptomatic relief. Pharmacokinetic analysis demonstrates a second-order kinetics with elimination half-lives of 0.49 and 2.7 hours. The peritoneal to plasma AUC ratio was 31.2. Intramuscular, transdermal, and subcutaneous administrations have been extensively studied in the mouse.

Anticancer effect of 9-nitrocamptothecin liposome aerosol on human cancer xenografts in nude mice.

PURPOSE: To test the anticancer properties of the water-insoluble derivative of camptothecin, 9-nitrocamptothecin (9-NC) against human breast, colon and lung cancer xenografts in nude mice when administered in liposome aerosol. METHODS: The drug was formulated with dilauroylphosphatidylcholine and nebulized in a particle size of 1.6 microm +/- 2.0 mass median diameter to deliver doses of usually less than 200 microg/kg daily, 5 days per week. 9-NC liposome aerosols were generated with a Aerotech II nebulizer (CIS-USA) flowing at 101/min from a compressed air source and delivered to mice in sealed plastic cages or in a nose-only exposure chamber. RESULTS: Tumor growth was greatly reduced or tumors were undetectable after several weeks of treatment. Colon tumor was least responsive. 9-NC was better than the parent compound, camptothecin, also water-insoluble, tested by aerosol in a similar liposomal preparation. Equivalent doses of 9-NC liposome preparations administered by mouth were substantially without effect while there was some effect, but limited, of the liposome preparation given intramuscularly. CONCLUSIONS: 9-NC liposome aerosol was strikingly effective in the treatment of three human cancer xenografts growing subcutaneously over the thorax in nude mice at doses much smaller than those traditionally used in mice administered by other routes.

Distribution of camptothecin after delivery as a liposome aerosol or following intramuscular injection in mice.

PURPOSE: The plant alkaloid camptothecin (CPT) has shown significant antitumor activity against a wide variety of human tumors xenografted in nude mice. In previous studies we have found that administration of dilauroylphosphatidylcholine (DLPC) liposome aerosols containing 9-nitrocamptothecin (9-NC) inhibits the growth of human breast, colon and lung cancer xenografts. The purpose of this study was to analyze the pharmacokinetics and tissue distribution of inhaled CPT formulated in DLPC liposomes. METHODS: C57BL/6 mice with subcutaneous Lewis lung carcinoma, Swiss nu/nu mice with human lung carcinoma xenografts and BALB/c mice without tumors were used for pharmacokinetic studies of CPT administered as a liposome aerosol and BALB/c mice were given CPT intramuscularly. RESULTS: After 30 min inhalation of CPT liposome aerosol, drug was deposited in the lungs (310 ng/g) and was followed promptly by the appearance of high concentrations in the liver (192 ng/g) and with lesser amounts appearing in other organs. Drug concentration in the brain was 61 ng/g. After intramuscular injection of CPT dissolved in DMSO, drug was released from the site of injection very slowly and accumulated mainly in the liver (136 ng/g). Only trace amounts appeared in the lungs (2-4 ng/g). These results demonstrate a prompt pulmonary and later systemic distribution of CPT following liposome aerosol administration. CONCLUSIONS: The substantial concentrations of CPT in lungs and other organs following inhalation of liposome aerosol suggest the possible benefit of it and of its more active derivative, 9-NC, in the treatment of lung, liver, kidney and brain cancer in humans.

Pharmacokinetics of liposomal aerosolized cyclosporine A for pulmonary immunosuppression.

BACKGROUND: The results of pulmonary transplantation are compromised by acute and chronic rejection. We hypothesized that a liposomal form of aerosolized cyclosporine A (CsA) would be selectively deposited and concentrated in the lungs. The theoretical advantage of this therapy is selective pulmonary immunosuppression with prolonged utilization. METHODS: Eighteen dogs were endotracheally intubated; aerosolized liposomal CsA was administered for 15 min. CsA levels were measured in whole blood, lung, trachea, heart, kidney, liver, and spleen at various times after treatment. RESULTS: The lung rapidly absorbs aerosolized liposomal CsA; other organs have much lower concentrations. The retention of pulmonary CsA delivered by liposome aerosol is approximately 120 min in this model. CONCLUSIONS: Aerosolized liposomal CsA is selectively deposited and concentrated in the lungs; other organs absorb less CsA.

CL387626 exhibits marked and unusual antiviral activity against respiratory syncytial virus in tissue culture and in cotton rats.

CL387626 (4,4'-Bis[4,6-di[3-aminophenyl-N,N-bis(2-carbamoylethyl)-sulfon ilimino]-1,3,5-triazine-2-ylamino-bi-phenyl-2,2'-disulfonic acid, disodium salt), a compound synthesized by Wyeth-Ayerst Research Laboratories, was tested for its cytotoxicity and antiviral activity against respiratory syncytial virus (RSV) in tissue culture and in cotton rats. The median cell inhibitory (IC50) and median efficacious (EC50) concentrations of CL387626 against RSV in proliferating HEp2 or Vero tissue culture cells were determined to be 375 and 0.25 microg/ml, respectively, giving the compound an apparent selective index (S.I.) of 1500. This compound also exhibited uncommon antiviral activity against RSV in cotton rats. In multiple experiments, a single 30 mg/kg dose of CL387626 administered intranasally 4 or 5 days prior to virus challenge, significantly inhibited pulmonary replication of RSV compared to that seen in control animals inoculated similarly with placebo (i.e. water). In contrast to these results, most lots of CL387626 failed to significantly inhibit pulmonary RSV replication when administered utilizing therapeutic administration schedules. Although some cytotoxicity was noted in tissue culture assays, no overt toxic effects were noted in any test animal, including those inoculated with > 300 mg CL387626/kg, a dose approximately 150 times the apparent minimal efficacious dose (i.e. 1.9 mg/kg).

Tolerance of volunteers to cyclosporine A-dilauroylphosphatidylcholine liposome aerosol.

Cyclosporine A (CsA) in liposomes of dilauroylphosphatidylcholine (DLPC), containing 118 micrograms of CsA/L of aerosol with a particle size of 1.6 to 1.7 micron diameter, was inhaled by 10 nonsmoking, normal volunteers each for 45 min. Aerosol was administered through an Aerotech II nebulizer (CIS-US, Inc., Bedford, MA) mouthpiece. Eight of the 10 volunteers had tracheal irritation and intermittent coughing following exposure. FEV1 and FVC values were mildly reduced, but returned to normal in 1 h. Blood chemical and hematologic values were unchanged at any time point after as opposed to before inhalation. Nine of the 10 volunteers later inhaled DLPC only, administered through the nebulizer mouthpiece. There was no change in FEV1 or FVC values, and there was no coughing or tracheal irritation. Subsequently, five of the volunteers who had previously had respiratory reactions inhaled CsA-DLPC liposome aerosol for 45-min, but through a mouth-only face mask. There was no tracheal irritation, coughing, or changes in spirometric measures. Blood concentrations of CsA at 15 min after the 45-min inhalation with a face mask averaged 83 +/- 42 ng/ml (mean +/- SD). At 24 h after treatment, CsA was undetectable in blood of the initial 10 volunteers. These studies indicate that CsA-DLPC liposome aerosol can be safely explored as a treatment for patients with moderately severe asthma.

Pulmonary delivery of beclomethasone liposome aerosol in volunteers. Tolerance and safety.

STUDY OBJECTIVE: To test the tolerance and safety of single doses of beclomethasone dipropionate (Bec)-dilauroylphosphatidylcholine (DLPC) liposome aerosol in volunteers. DESIGN: Single-dose inhalations of liposome preparations of Bec-DLPC and DLPC alone were administered for 15 min from a jet nebulizer (Puritan-Bennett, modified twin jet; mass median aerodynamic diameter of 1.6 microns) under close clinical and laboratory surveillance. Two dose levels (0.5 mg Bec/12.5 mg DLPC per milliliter, and 1.0 mg Bec and 25 mg DLPC per milliliter in the reservoirs, respectively) were administered. The Bec doses were selected to approximate the dosages of this glucocorticoid used with metered-dose inhalers (MDIs). First, four volunteers were exposed to an initial low dose; the mean (+/-SD) inhaled doses were 0.56 +/- 0.07 mg of Bec and/or 14.0 +/- 1.8 mg of DLPC. Subsequently, a second group of six volunteers was exposed to a higher dose; the mean (+/-SD) inhaled doses were 1.29 +/- 0.14 mg of Bec and/or 34.6 +/- 6.8 mg of DLPC. SETTING: Outpatient and inpatient. PATIENTS: Normal male (n = 6) and female (n = 4) adult volunteers. INTERVENTIONS: Inhalation of Bec-DLPC and DLPC liposome aerosols in a single-dose tolerance study involving 10 normal volunteers. MEASUREMENTS AND RESULTS: Spirometry, clinical observations, clinical chemistry, and hematology were monitored. No adverse clinical or laboratory events were observed. CONCLUSIONS: Bec-DLPC liposome aqueous aerosol was well tolerated in doses equivalent to those currently administered by MDIs and dry powder inhalers for treatment of asthma.

Recombinant superoxide dismutase (SOD) administered by aerosol inhibits respiratory syncytial virus infection in cotton rats.

Recombinant (r) human (hu) manganese (Mn) and copper-zinc (CuZn) superoxide dismutase (SOD) were evaluated for their cytotoxicity and antiviral activity against respiratory syncytial virus (RSV) in tissue culture and in cotton rats. No apparent cytotoxicity or inhibition of RSV was observed in the tissue culture studies (both compounds had IC50 and EC50 values > or = 1000 micrograms/ml and a selective index = 1). However, significant reductions in mean pulmonary RSV titers (ranging between 0.5 and 1.9 log10/g of lung compared with the mean pulmonary viral titers detected in similarly inoculated, placebo-treated control animals) were seen in most of the experiments, in which experimentally infected cotton rats were exposed to continuous small-particle aerosols (reservoir concentrations > or = 20 mg/ml) containing either rhuMnSOD or rhuCuZnSOD. This protective effect was dose dependent and not observed when either rSOD compound was administered parenterally (intraperitoneally) or intranasally. No toxic effects were noted in any of the cotton rats exposed to aerosols of either rhuMn or CuZnSOD; nor was any evidence of drug-induced histopathology observed in sections of lung prepared from these animals.

Liposomal aerosols in the management of pulmonary infections.

The combination of liposomes and aerosols has been utilized to directly target the lungs with chemotherapeutic agents that might not have been used because of low solubility or toxicity. There are a variety of antibacterials, antifungals, and antivirals that have good in vitro activity, but are not effective because of their systemic toxicity and/or poor penetration into the lungs. Incorporation of many lipophilic drugs into liposomes decreases their toxicity without affecting effectiveness, thus increasing the therapeutic index. We have focused on aerosol delivery of amphotericin B (ampB) for the treatment of pulmonary and systemic fungal diseases. We have tested a variety of ampB-lipid formulations for the optimal treatment regimen for Cryptococcus and Candida infections in mouse models. The AeroTech II nebulizer (MMADs of 1.8-2.2 microns) produced aerosols with the highest concentrations in the breathable range. Pharmacokinetic studies revealed that pulmonary drug was present for hours to weeks. AmBisome retained its anticryptococcal activity even when animals were challenged 14 days after aerosol treatment. Aerosols may also be effective in systemic diseases. In our Candida-mouse model, systemic candidiasis and mortality were reduced by aerosolized ampB-liposome treatment. The ability to utilize lipophilic drugs, to deliver high concentrations of drug directly to the site of infection, and to reduce toxicity makes aerosol liposomes an attractive, alternative route of administration.

Aerosol delivery of a beta-galactosidase adenoviral vector to the lungs of rodents.

Aerosol delivery of adenoviral vectors is of particular interest in regard to gene therapy for cystic fibrosis (CF), with potential advantages of more uniform respiratory delivery, a less invasive approach, and ease of repetition. The AdHCMVsp1LacZ (AdLacZ) adenoviral vector was used to evaluate the feasibility of aerosol delivery to the respiratory epithelium in rodents. The adenoviral vector tolerated aerosol generation as measured by recovery in an all-glass impinger. Using an Andersen sampler to mimic the human respiratory tract, aerosol particles were found to have an average mass mean aerodynamic diameter of 1.6 microns and a geometric standard deviation of 1.7 microns. Cotton rats and mice exposed to viral aerosols demonstrated beta-galactosidase expression in up to 10-30% of the epithelial surface of the small and large airways, whereas expression in Sprague Dawley rats was largely limited to the alveolar epithelium. Transgene expression was distributed uniformly through both lungs in animals treated by aerosol. The variables for aerosol delivery are complex and include viral titer, aerosol device, duration of exposure, species of recipient, and respiratory behavior among other factors. Species differences in expression in airways as compared to alveolar epithelium have important implications for clinical application.

High-dose, short-duration ribavirin aerosol therapy compared with standard ribavirin therapy in children with suspected respiratory syncytial virus infection.

Children with suspected respiratory syncytial virus infection were examined prospectively in a randomized evaluation of standard ribavirin aerosol therapy (6 gm/300 ml water for 18 hours daily) compared with high-dose, short-duration ribavirin aerosol therapy (6 gm/100 ml water given for a period of 2 hours three times a day) by means of an oxygen hood (n = 20) or a ventilator (n = 12). Viral shedding was quantitated daily; clinical observations were recorded daily by 2 physicians aware and one unaware of treatment assignments. Study characteristics evaluated at entry were not significantly different in the high-dose and the standard-dose groups. Viral titers and clinical scores decreased similarly in both groups during the study; pulmonary function test results were also similar at discharge in children not receiving mechanical ventilation. Potential complications related to aerosol therapy were noted in three patients (one hood patient who was receiving standard therapy; two patients with an endotracheal tube in place who were receiving high-dose therapy); substantial crystallization was noted in the tubing of the patients undergoing intubation and receiving high-dose therapy. Environmental sampling revealed that ribavirin was nearly undetectable near patients supported by mechanical ventilation who were receiving either form of therapy, and was significantly decreased on a daily basis in patients without an endotracheal tube who were receiving high-dose therapy compared with those receiving standard therapy. The effects of high-dose, short-duration aerosol ribavirin therapy were similar to those of standard-dose therapy in our study patients and resulted in a decreased release of ribavirin into the room of patients receiving therapy by means of an oxygen hood.