Determination of Phenobarbital and Phenytoin in Serum by Ultraviolet Spectrophotometry

Abstract

A modification of the method of Svensmark & Kristensen for the spectrophotometric determination of phenobarbital and phenytoin in serum has been described. By means of small alterations the method was made more suitable for routine use. It was shown that recovery of both drugs was 7–9 per cent higher when known amounts were added to water instead of serum. Some not previously described interfering drugs, ethoxybenzamid, trimethadione, sulthiame, sulphadimethoxine and sulphamethoxipyridazine, were investigated. It was shown that recording of the extinction curve in the range 220–300 nm offers a possibility to recognize interfering drugs, except other barbiturates. Phenytoin can only be determined by this method if interfering drugs or metabolites are not present, i.e. the intake of other drugs should be known not to interfere; otherwise the analysis must be carried out by a specific method (thin-layer chromatography).

Key Words:

• Diphenylhydantoin
• phenobarbital
• spectrophotometry
• ultraviolet rays