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Circadian rhythmicity is present in almost every aspect of the living world and effects of drugs on various life forms are no exception. This study was undertaken to find out the circadian variation in the analgesic activity of aspirin and to correlate the variations with the blood levels of salicylate at that time. The model used was the application of radiant heat to the tail of rats for analgesic activity. Aspirin exhibited maximum activity when administered at 12:00 h, although this difference was not statistically significant. Also, there was no correlation between the levels of salicylate in the blood and the activity of aspirin. Due to the presence of this trend towards increased activity at 12:00 h, it may thus be worthwhile to conduct similar studies, in patients of chronic arthritis, in order to find out the time(s) at which, aspirin if administered will be most useful. [ABSTRACT FROM AUTHOR]

The role of the time of administration of phenytoin on its serum levels and pharmacodynamic parameters was studied in two comparable groups of patients of grand mal—epilepsy stabilized on serum phenytoin therapy. In these patients, phenytoin was advised to be taken as a single daily dose either at 08.00 (Group M) or 20.00 (Group E) every day. A serum phenytoin level profile over 24 hours was obtained and all patients were clinically followed up for six months. Maximum serum concentration (C-max) of phenytoin was achieved significantly faster (p < 0.001) in patients of Group E. The total number of serum samples having toxic concentrations and also the incidence and severity of toxic effects of phenytoin was less in Group E. The study suggests that bedtime administration of phenytoin in patients of grand mal—epilepsy may lead to faster absorption of the drug and less side effects as compared with drug administration in the morning. [ABSTRACT FROM AUTHOR]