Rapid fluorimetric assay of minocycline in plasma or serum: comparison with microbiological assay.

1. Plasma concentrations of minocycline were assayed by measuring the fluorescence emission of an aluminum-minocycline chelate in a spectrofluorimeter. 2. The assay gives reproducible results over the concentration range 0.05-5.0 mug ml-1, and compared favourably with results achieved using a conventional large plate agar diffusion microbiological assay in a double-blind comparison of the two methods. 3. Fluorimetric assay of minocycline in plasma was found to correlate closely with antibiotic activity (r = 0.95). The method is easy and economical to perform, results being obtained in 1 h.