Fluorometric TLC determination of free and conjugated propranolol, naphthoxylactic acid, and p-hydroxypropranolol in human plasma and urine.

Sensitive, specific, and reproducible TLC methods are described for the determination of propranolol and its major metabolites in humans, conjugated propranolol, free and conjugated naphthoxylactic acid, and free and conjugated p-hydroxypropranolol. The drug or metabolites are extracted from plasma or urine with ether and applied to TLC plates of silica gel or microcrystalline cellulose. After development, the plates are scanned in a spectrodensitometer equipped to measure fluorescence in the UV and blue regions of the light spectrum. Quantitation is achieved by comparing the areas under the peaks obtained from the unknowns to those obtained from standards applied to the same plate. Limits of quantitation in plasma are: free propranolol, 2 ng/ml; free p-hydroxypropranolol, 10 ng/ml; conjugated propranolol, 15 ng/ml; total (free and conjugated) naphthoxylactic acid, 25 ng/ml; and conjugated p-hydroxypropranolol, 50 ng/ml. These methods were used to obtain plasma level data in a volunteer after one single dose of propranolol and in patients under propranolol therapy. The Rf values of some known metabolites of propranolol obtained in various TLC developing systems are also presented.