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Original Investigation |

Concentration Accuracy of Compounded Mitomycin C for Ophthalmic Surgery

Robert M. Kinast, MD1; Kiran K. Akula, PhD2; Steve L. Mansberger, MD, MPH1; Gordon T. Barker, MS1; Stuart K. Gardiner, PhD1; Emily Whitson, BA1; Andrea E. DeBarber, PhD3
[+] Author Affiliations
1Devers Eye Institute, Legacy Health, Portland, Oregon
2RS Dow Neurobiology Laboratories, Legacy Research Institute, Portland, Oregon
3Oregon Health and Science University, Portland
JAMA Ophthalmol. 2016;134(2):191-195. doi:10.1001/jamaophthalmol.2015.4970.
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Importance  Ophthalmologists rely on accurate concentrations of mitomycin C (MMC) to prevent scarring with trabeculectomy surgery. To our knowledge, the concentration accuracy and variability of compounded MMC are unknown.

Objective  To determine whether the measured concentration differs from the expected concentration of 0.4 mg/mL of MMC used in ophthalmic surgery.

Design, Setting, and Participants  Laboratory experimental investigation conducted in July 2013. We acquired 60 samples of 0.4 mg/mL of MMC from a spectrum of common compounding and storage techniques (refrigeration, freezing, and immediately compounded dry powder) and a variety of pharmacies (an academic hospital, a community hospital, and an independent Pharmacy Compounding Accreditation Board–accredited pharmacy). We used C18 reversed-phase high-performance liquid chromatography to measure the MMC concentration of all samples. We used pure MMC (Medisca Inc) to generate calibration curves and sulfanilamide as an internal standard.

Main Outcomes and Measures  We calculated MMC concentration using a calibration curve (range, 0.3-0.5 mg/mL) generated by dividing MMC peak area by internal standard peak area and plotting the area ratio against the calibrant concentrations. We compared the measured concentration against the expected 0.4 mg/mL concentration for all samples.

Results  Measurement of MMC using the high-performance liquid chromatography method demonstrated acceptable accuracy (92%-100%), precision (2%-6% coefficient of variation), and linearity (mean correlation coefficient of r2 = 0.99). The measured MMC concentration determined using the high-performance liquid chromatography method for all samples was 12.5% lower than the expected 0.4 mg/mL value (mean [SD], 0.35 [0.04] mg/mL; 95% CI, 0.34-0.36; P < .001) with a wide concentration range between 0.26 and 0.46 mg/mL.

Conclusions and Relevance  Common compounding and storage techniques for MMC resulted in a lower accuracy and wider range of concentration than expected. These differences in concentration may result from compounding techniques and/or MMC degradation. Variability in MMC concentration could cause inconsistency in glaucoma surgical results, but the clinical relevance of such findings on glaucoma surgery outcomes remains unknown.

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Figure 1.
Representative High-Performance Liquid Chromatrography of Mitomycin C Sample

Peaks are analytes demonstrating absorbance at 210nM: sulphanilamide internal standard (4.8 minutes), unknown minor degradants (7.3 and 10.7 minutes), cis-hydroxymitosene (11.7 minutes), trans-hydroxymitosene (17.1 minutes), and mitomycin C (28.9 minutes). The expanded region, indicated by the dashed lines, shows 4 through 20 minutes.

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Figure 2.
Box Plots of Measured Concentrations of Expected 0.4 mg/mL of Mitomycin C Using a Variety of Storage Techniques and Sources

Shaded box areas indicate 25th and 75th percentiles. Error bars show concentration ranges of the 60 samples (12 samples per storage method).

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