Simultaneous determination of physostigmine and tetrahydroaminoacridine in a transdermal permeation study by...

A selective and stability-indicating high-performance liquid chromatographic assay with diazepam as the internal standard was developed for simultaneously analyzing physostigmine and tetrahydroaminoacridine in skin samples, permeation diffusates and dosage form. Baseline resolution was achieved with an octadecyl column for physostigmine, its two degradation products and tetrahydroaminoacridine. Peak homogeneity of physostigmine and tetrahydroaminoacridine was confirmed. The calibration curves for both drugs in skin samples were established at 1-50 micrograms per 200 mg skin. Those for diffusate samples were at 10-50 ng per 50 microliters for physostigmine and 30-150 ng per 50 microliters for tetrahydroaminoacridine. The assay was reproducible with within-day and between-day variations of 5-6 and 4-10%, respectively. Application of the assay for in vitro transdermal permeation study was demonstrated.