[Circannual rhythm of drug use by a psychiatric clinic]

The total number per month of prescribed antibiotics or psychiatric drugs during one year (1998) was assessed by means of sine wave models [Y(t) = M + A x sin(2 x pi x t/tau + phi)]. M (no. of prescriptions per month) denotes mean frequency over one period, A (no. per month) denotes amplitude, tau (month) corresponds to the period and phi (month) to the phase of the fitted curve. Data were evaluated descriptively and chronograms including 95%-confidence limits were given. Significant nonlinear regression models could be calculated for amoxicillin, paroxetine, citalopram, amitriptyline and buspirone prescription behaviour. Both circannual and ultra-annual (period shorter than one year) rhythms of prescription were found. Peak values for antibiotic drug prescription during fall and winter is probably associated with higher incidence of infectious diseases. Antidepressant drug prescription has maxima in spring and fall, which is in keeping with the epidemiology of depressive disorders. The seasonality of buspirone prescription may reflect a basic periodicity of anxiety disorders. In conclusion, the chronopharmaco-epidemiological data of antibiotic and antidepressant drug prescription with circannual and ultra-annual rhythms may reflect the periodicity of infectious and psychiatric diseases.