Compatibility of corticosteroids and antibiotics in combination

Use of in vitro assays to identify antibiotics that are cytotoxic to normal equine chondrocytes and synovial cells

BACKGROUND

Intra-articular (IA) antibiotic usage is prevalent in equine practice. However, recent emergence of antimicrobial resistance prompts re-evaluation of antibiotic selection, particularly when used prophylactically. Furthermore, many commonly used antibiotics exert direct cytotoxicity to equine cells, and appropriate IA doses have not been defined.

OBJECTIVES

To screen antibiotics in vitro as an initial assessment of cytotoxicity against normal equine joint cells in monolayer culture and explant tissues.

STUDY DESIGN

In vitro experimental study.

METHODS

Chondrocytes and synovial cells were harvested from three horses and plated on 24-well plates (100 000 cells/wells in triplicate) for 48 hours prior to addition of antibiotics. Joint cells were exposed to antibiotics (n = 15) at various doses (25-0.39 mg/mL in complete DMEM media) for 24 hours and viability was assessed by trypan blue dye exclusion. The half maximal inhibitory concentration (IC50) was determined for each antibiotic. Cartilage explants were obtained from 3 horses, minced and exposed to antibiotics (n = 5) for 72 hours. Live/dead staining was performed, and fluorescence was visualised using Olympus IX83 spinning disk confocal microscope. Percentage of live vs dead cells was quantified.

RESULTS

Antibiotics from different antimicrobial classes expressed dose-dependent but variable cytotoxicity to equine joint cells in vitro. Aminoglycosides and doxycycline had the lowest IC50 (most toxic). Ampicillin sulbactam, imipenem, tobramycin, ceftiofur sodium and amoxicillin had IC50 > 25 mg/mL for at least one cell line, representing potentially less cytotoxic alternatives.

MAIN LIMITATIONS

Further studies are necessary to extrapolate these in vitro data results to the in vivo joint environment.

CONCLUSIONS

Targeted IA antibiotic therapy would involve selection of the safest antibiotics (highest IC50) with efficacy based on bacterial culture/sensitivity. Antimicrobial selection and evidence-based dosing may minimise damage to native articular cartilage and synovial cells and development of antimicrobial resistance when IA antibiotics are used in equine practice.

Indecision about corticosteroids for bacterial keratitis: an evidence-based update

PURPOSE

To quantify the effect of topical corticosteroids on bacterial keratitis.

CLINICAL RELEVANCE

Bacterial keratitis is an economically important infection affecting 1 in 10,000 Americans annually. The predisposing factors, prior ocular health, infecting microorganisms, inflammatory severity, and therapeutic choices can affect the course and outcome. Antibacterial treatment is often curative but does not guarantee good vision. Because many treated patients develop a sight-limiting corneal problem, antiinflammatory therapy has sometimes been recommended.

LITERATURE REVIEWED

Publications from 1950 to 2000 that evaluated the effect of corticosteroids on bacterial keratitis in animal experiments, case reports and series, case-comparison and cohort studies, and clinical trials were systematically identified by electronic and manual search strategies.

RESULTS

The use of a topical corticosteroid before the diagnosis of bacterial keratitis significantly predisposed to ulcerative keratitis in eyes with preexisting corneal disease (odds ratio [OR], 2.63; 95% confidence limits [CL], 1.41, 4.91). Once microbial keratitis occurred, prior corticosteroid use significantly increased the odds of antibiotic treatment failure or other infectious complications (OR, 3.75; 95% CL, 2.52, 5.58). However, the effect of a topical corticosteroid with antibiotics after the onset of bacterial keratitis was unclear. Experimental models suggested likely advantages, but clinical studies did not show a significant effect of topical corticosteroid therapy on the outcome of bacterial keratitis (OR, 0.62; 95% CL, 0.25, 1.54).

CONCLUSIONS

Topical corticosteroids increase the risk of infectious complications affecting the cornea but may or may not have an effect during antibacterial therapy. The unproven role of corticosteroids in the adjunctive treatment of bacterial keratitis highlights the need to collect prospective information that would guide appropriate management for this common eye disease.