Effects of serum lipid content on the binding of minocycline

Minocycline was added to normal and hyperlipemic serum samples in concentrations of 1 approximately 10 mcg/ml. These specimens had similar protein contents. Chemically extractable minocycline was quantitated fluorometrically. Hyperlipemic serum (cholesterol 480 mg/100 ml; triglycerides 321 mg/100 ml) yielded an average of 50% less minocycline than did normal serum (cholesterol 170 mg/100 ml; triglycerides 114 mg/100 ml). When ultrafiltrates of serum containing 6, 12 and 20 mcg/ml minocycline were assayed microbiologically, it was evident that variations in serum triglyceride and cholesterol levels did not alter the ratio of bound to free drug. Minocycline appears to be reversibly associated with, and/or soluble in, triglyceride-cholesterol components of serum.