Background

Eosinophilic pneumonia is a rare, but serious respiratory syndrome that occurs when eosinophils accumulate in the lungs [1, 2]. It has been associated with several medications and chemicals, with antibiotics and nonsteroidal anti-inflammatory drugs among the most common [3, 4].

The pathophysiology of acute eosinophilic pneumonia is thought to be caused by detection of an antigen by alveolar macrophages which leads to recruitment of T-helper 2 lymphocytes and subsequent release of interleukin 5. Interleukin 5 promotes eosinophil production and migration to the lung. Additionally, eotaxin (a potent eosinophil chemoattractant) production by alveolar macrophages, pulmonary endothelial cells, airway smooth muscle cells, and alveolar epithelial cells leads to further accumulation of eosinophils in the lungs [5].

Daptomycin is a cyclic lipopeptide antibiotic derived from the fermentation of Streptomyces roseosporus. Daptomycin has activity against Gram-positive organisms including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) [6]. In 2007, pulmonary eosinophilia was added to the “Adverse Reactions, Post-Marketing Experience” section of the product label for daptomycin [2]. A review of the literature and the US FDA Adverse Event Reporting System database in 2012 revealed 7 definite, 13 probable, and 38 possible cases of daptomycin-induced eosinophilic pneumonia [1]. While the mechanism of daptomycin’s pulmonary toxicity is not known, the drug undergoes conformational change through interaction with calcium which allows binding to the cytoplasmic membrane, increased membrane permeability, and intracellular ion escape [7]. The antibacterial activity of daptomycin is decreased because of its binding to pulmonary surfactant. Some have speculated two potential mechanisms for daptomycin’s pulmonary toxicity: 1) chronic daptomycin administration results in drug accumulation near the epithelial alveolar surface causing epithelial injury and pneumonia and 2) the daptomycin-surfactant interaction could alter lipid integrity which may stimulate an inflammatory response [3, 7, 8].

Per the FDA guidance, eosinophilic pneumonia is attributed to daptomycin when the following criteria are met: 1) concurrent exposure to daptomycin, 2) fever, 3) dyspnea with increased oxygen requirement or requiring mechanical ventilation, 4) new infiltrates on chest x-ray or computed tomography (CT) scan, 5) bronchoalveolar lavage (BAL) with > 25% eosinophils, and 6) clinical improvement following daptomycin withdrawal [2]. Solomon and Schwartz [4] have also developed criteria for drug- or toxin-induced eosinophilic pneumonia that is similar and includes 1) presence of simple, acute, or chronic eosinophilic pneumonia by diagnostic criteria which includes excess of eosinophils either on lung biopsy or BAL (usually ≥25%) in the setting of parenchymal infiltrates 2) presence of a potential candidate drug or toxin in an appropriate time frame 3) no other cause of eosinophilic pneumonia such as fungal or parasitic infection 4) clinical improvement after cessation of the drug or toxin, and 5) recurrence of eosinophilic pneumonia with re-challenge to the drug or toxin. However, re-challenge is often not recommended as it can be dangerous [4, 5].

Although the mechanism of daptomycin-induced eosinophilic pneumonia is unknown, some have speculated that daptomycin may bind to human surfactant and accumulate in the alveolar space causing injury to the epithelium with resulting inflammation [7, 8]. The purpose of this review is to systematically evaluate the published literature describing daptomycin-induced eosinophilic pneumonia.

Methods

All relevant cases and studies were identified by systematically searching of the PubMed, EMBASE, Google Scholar, Cochrane Database of Systematic Reviews, and Clin-Alert databases by two reviewers from inception through May 2016. The truncated terms “daptomycin”, “eosinophil*”, and “pneumon*” were searched in each database. All case reports that included information regarding patient age, indication, clinical and objective findings, treatment, and outcome were evaluated. Reports not published in English were excluded as well as abstracts from conference proceedings. Descriptive analysis was used to present pooled demographic information and other data where applicable.

Results

No clinical or observational trials assess daptomycin-induced eosinophilic pneumonia; only case reports and case series are published. In 2012, Kim et al. identified 7 definite, 13 probable, and 38 possible cases of daptomycin-induced eosinophilic pneumonia via review of literature and FDA Adverse Event Reporting System Reports (AERS) as defined in Table 1 [1]. Details regarding the 38 possible cases reported through AERS were not described. Of the 20 cases that were identified as definite or probable, 9 have been published in the literature, the remaining 11 were summarized by Kim [1, 3, 9–13]. We also identified 39 additional cases of eosinophilic pneumonia attributed to daptomycin for a total of 59 cases described in the literature [7, 14–24]. Of those, 21 were excluded from this systematic review because they were abstract presentations at international meetings and did not go through the peer review publishing process [25–41]. Another three were excluded because they were not published in English [42–44]. Currently available data on a total of 35 cases of daptomycin-induced eosinophilic pneumonia is summarized in Table 2.

Table 1 Criteria for inclusion as definite, probably, possible, and unlikely cases of daptomycin-induced eosinophilic pneumonia [1, 2]
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Table 2 Summary of 35 cases of presumed daptomycin-induced eosinophilic pneumonia
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Analysis of the 35 cases shows eosinophilic pneumonia resulting from daptomycin use is most likely to be reported in males with a mean age of 65.4 ± 15 years and a mean length of therapy of 2.8 ± 1.6 weeks at symptom onset. The most common indication for daptomycin use was osteomyelitis and/or diabetic foot infection closely followed by prosthetic joint infection. Daptomycin dose ranged from 4 to 10 mg/kg/day depending on renal function; therefore, the adverse effect does not appear to be dose dependent, but time dependent exposure. The most common symptoms of eosinophilic pneumonia included fever and dyspnea often requiring either oxygen supplementation or mechanical ventilation. Other clinical findings included malaise, elevated ESR (4/35 cases), or elevated C-reactive protein (11/35 cases). Peripheral eosinophilia was also present in approximately 77% (27/35 cases) of patients. Many cases also had computed tomography scans or chest x-rays which revealed opacities (12/35 cases) and bilateral infiltrates (13/35 cases). Symptom improvement was seen within 24 h through one week after daptomycin discontinuation. The majority of patients were also prescribed treatment with corticosteroids (23/35 cases); however, all patients were reported to recover (See Table 3).

Table 3 Compilation of available data on 35 cases of daptomycin-induced eosinophilic pneumonia
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Discussion

While the criteria developed by Solomon and Schwartz differ from the FDA guidance, they are largely similar in that an offending agent (here, daptomycin) must be present, >25% eosinophils are present, and that clinical improvement is seen after discontinuation of the drug. The FDA guidance also includes some measures of symptomatology such as fever and dyspnea [2, 4].

Overall, dyspnea was the most common documented symptom associated with eosinophilic pneumonia followed by the presence of either pulmonary infiltrates or opacities on chest x-ray or CT. A total of 10 cases specifically mentioned the characteristic finding of ground glass opacities on CT. A potential limitation of this review is that some of the daptomycin-induced eosinophilic pneumonia used lung biopsy in place of BAL as part of the diagnostic criteria which is not part of the FDA guidance, but is included in the Solomon and Schwartz criteria. In addition, since some patients had BAL < 25% eosinophils but lung biopsy revealed eosinophilia [1, 13], a 25% cut off may be too strict in certain situations.

Corticosteroids are believed to be beneficial at halting clinical manifestations of daptomycin-induced eosinophilic pneumonia and were used in the majority of reported cases. Steroids exert action through eosinophilic apoptosis and through accelerating intracellular signaling involved in eosinophil death [45]. No dose or length of corticosteroid treatment is established in guidelines for eosinophilic pneumonia; however, a commonly employed regimen is intravenous methylprednisolone 60–125 mg every 6 h, with conversion to prednisone 40–60 mg oral daily and taper over 2–6 weeks. Use of a 2- or 4-week course appears to have similar time to resolution of clinical symptoms and radiological abnormalities [46].

Conclusion

As use of daptomycin continues to increase, it is important for clinicians to recognize and appropriately manage daptomycin-induced eosinophilic pneumonia. Although symptoms may resolve upon discontinuation of daptomycin, use of corticosteroid may be beneficial for recovery. Further research is needed to determine the exact mechanism of daptomycin-induced eosinophilic pneumonia and identify the optimal treatment course.