Is there a climatic influence on the blood level of anticonvulsive drugs?

The diphenylhydantoin concentration in ten treated epileptics was determined during a period of two years in Tel-Aviv, Israel where subtropical climate prevails. The data collected showed a significant decrease at the end of Summer and a significant increase at the end of Winter. Since diphenylhydantoin is excreted in the sweat and sweating is excessive during the Summer months in the area where the study was undertaken, it is suggested that the increase of perspiration is responsible for the drop of diphenylhydantoin serum concentration. No other seasonal biological rhythms are known to us which could be incriminating.