2434. Review of Linezolid (LZD) Use and Onset of Toxicity in 4 Belgian Hospital Centers: A Retrospective Study

Background

LZD is approved (FDA label and Belgian Summary of Product Characteristics [SmPC]) for the treatment of SSSTI and pneumonia caused by Gram-positive organisms (mainly MRSA and VRE) only. Yet IDSA recommendations for MRSA infections also position LZD for osteomyelitis and as an alternative for CNS infections and bacteremia (CID 2011;52:e18–55). LZD use is limited by adverse events, the incidence of which may vary according to the length and conditions of therapy. The aim of this study was to document LZD actual use and onset of adverse events in real life clinical practice.

Methods

Observational, retrospective study in 4 Belgian hospital centers (about 4,000 beds) over 1 year (2016). Analysis of medical files (222 treatments) to collect information on (i) patient’s characteristics and treatment modalities and indications, (ii) occurrence, causality and severity of adverse drug reactions (ADR), and (iii) concomitant medications (increasing the risk of developing a serotonin syndrome [SS]).

Results

Key data are shown in the figure. 18% of prescriptions matched the indications approved in the United States and in Belgium and 47% those mentioned in the IDSA recommendations. 54% of the patients were infected by bacteria resistant to first choice drugs. Decreases in platelet counts (DPC) were observed in 30% of patients (compared with <1% thrombocytopenia in the Belgian SmPC or 25% DPC in 3% of patients in FDA label) and was observed in 15/39 cases (patients with in-Belgian label indications), 35/105 cases (patients with IDSA indications), 30/117 (other indications). Treatment duration > 10 days was the only significant risk factor for DPC (Kaplan Meyer; P < 0.005 [Mann–Whitney]). 7 cases of CNS ADR were reported. Although 41% of patients were prescribed at least 1 drug increasing SS risk, SS was actually observed in only 1 patient.

Conclusion

LZD is mainly used in off-Belgian label indications, some of which, however, are in the IDSA recommendations. The high incidence of ADR (40%) as well as the frequent use of co-medications putting patients at risk of SS highlight the importance of follow-up for LZD-treated patients. A prospective study is now needed to better assess the severity of these ADR and identify more associated risk factors.

Disclosures

All authors: No reported disclosures.

Activity of fusidic acid against extracellular and intracellular Staphylococcus aureus: influence of pH and comparison with linezolid and clindamycin

BACKGROUND

Emergence of multidrug-resistant Staphylococcus aureus has triggered a reassessment of fusidic acid (CEM-102, sodium fusidate).

METHODS

Fusidic acid was examined for (1) activity against recent methicillin-resistant S. aureus (MRSA) isolates; (2) modulation of activity by acidic pH; and (3) accumulation by phagocytic cells and intracellular activity against methicillin-susceptible S. aureus (MSSA) and MRSA.

RESULTS

About 96% of strains (N = 94) were susceptible (European Committee on Antimicrobial Susceptibility Testing breakpoint [≤ 1 mg/L]). Activity was enhanced at pH 5.5 (6 dilutions decrease for minimum inhibitory concentration) in parallel with an increase of drug bacterial accumulation (opposite effects for clindamycin; linezolid remained unaffected). Fusidic acid accumulated in THP-1 cells (about 5.5 fold), with further accumulation at pH 5.5 vs pH 7.4. The intracellular activity of Fusidic acid was similar to that of clindamycin and linezolid (maximal relative activity, 0.4-0.6 log(10) colony-forming unit decrease). No cross-resistance to vancomycin or daptomycin was observed.

CONCLUSIONS

Fusidic acid is active against S. aureus in broth as well as intracellularly, with no cross-resistance to other antibiotics.

Intracellular activity of the peptide antibiotic NZ2114: studies with Staphylococcus aureus and human THP-1 monocytes, and comparison with daptomycin and vancomycin

OBJECTIVES

Staphylococcus aureus survives inside eukaryotic cells. Our objective was to assess the activity of NZ2114, a novel peptidic antibiotic, against intracellular S. aureus in comparison with established antistaphylococcal agents acting on the bacterial envelope with a distinct mechanism.

METHODS

The extracellular (broth) and intracellular (THP-1 monocytes) activities of NZ2114 were compared with those of vancomycin and daptomycin against methicillin-susceptible S. aureus (MSSA), methicillin-resistant S. aureus (MRSA) and vancomycin-resistant S. aureus (VRSA).

RESULTS

All three compounds showed an extracellular bactericidal effect (>3 log(10) kill) against MSSA and MRSA. Daptomycin and NZ2114 also exhibited bactericidal activity against VRSA. The extracellular killing was concentration dependent for all three compounds within the range of drug concentrations tested. The intracellular experiments demonstrated a maximal intracellular effect of NZ2114 after 24 h as a 5 log(10) cfu reduction against MSSA (ATCC 25923), while the activity was a 0.9 log(10) cfu reduction against MRSA and a 0.2 log(10) cfu reduction against VRSA. For comparison, the intracellular activity of daptomycin was a 1.0 log(10) cfu reduction against MSSA, a 0.8 log(10) cfu reduction against MRSA and a 0.3 log(10) cfu reduction against VRSA. Vancomycin showed activity against both MSSA and MRSA (0.6 log(10) cfu reduction), whereas VRSA was resistant to vancomycin.

CONCLUSIONS

NZ2114 displayed similar extracellular and intracellular activities as daptomycin, and was more effective than vancomycin against the intracellular forms of susceptible bacteria. However, the study also showed that the intracellular activities of NZ2114 and daptomycin are weaker than their extracellular activities.