Les troubles dépressifs du sujet âgé, du fait de leur importante prévalence et du vieillissement constant de notre population constituent un réel enjeu thérapeutique. Il est classiquement recommandé de prescrire les antidépresseurs tricycliques chez le sujet âgé à des posologies inférieures ou égales à 75 mg/j pour éviter l'apparition d'effets secondaires. Afin de tester la validité de cette recommandation, une population de 61 patients âgés de plus de 65 ans, présentant le diagnostic CIM-10 d'épisode dépressif majeur caractérisé d'intensité moyenne ou sévère et ayant bénéficié avec succès d'un traitement par antidépresseur tricycliques a été constituée rétrospectivement. La posologie dépassait 75 mg/jour (140 mg/j 30) pour 79 % des patients. 22 % d'entre eux ont présenté un dosage plasmatique supérieur à la valeur maximale de la zone thérapeutique recommandée par le laboratoire. Aucun signe d'intolérance, évaluée à partir de la révision des dossiers cliniques, n'a été retrouvé. En conclusion, nos résultats ne s'opposent pas à l'utilisation de posologies de tricycliques identiques, chez le sujet âgé déprimé hospitalisé, à celles classiquement prescrites chez le sujet jeune.

It is recommended to reduce by one half the dosages of tricyclic antidepressants for patients over 65 years of age, in order to avert the occurrence of side-effects. The question we studied was : is it rightful to prescribe tricyclic antidepressants at half-dose to hospitalized elderly people ? It is important, for the following reasons, to specify the rules of prescription of tricyclics in elderly patients : 1) The elderly population is on the increase ; 2) There is a high prevalence of depression in elderly patients ; 3) Depression exposes the elderly person to an increased risk of suicide ; 4) Depression influences the prognosis of associated organic disorders 5) Recourse to tricyclic antidepressants is often necessary within this population group because of treatment resistant forms of depression which impose the use of different families of antidepressants and thus resort to tricyclics despite their lower tolerance. Objectives and methods : The aim of our study is to evaluate whether the half doses of tricyclics recommended for an elderly person are sufficient in the case of an hospitalized patient. In order to provide some answer to this question, we have carried out a retrospective study. We have studied a sample of patients over-65, hospitalized at the Clinique des Maladies Mentales et de l'Encéphale, over a period of two years, with a ICD 10 diagnosis of moderate or severe intensity major depressive episode, and treated effectively with return to the euthymia. Creatinemia was prescribed systematically to each patient on entry. Only patients with normal renal function were retained. Laboratory norms are between 45 and 120 micromol/liter. The routine practice of imipraminic blood dosages allowed the comparison of blood levels obtained among patients treated with posologies inferior or equal to 75 mg/day imipraminic, to those treated with more than 75 mg/day imipraminic for a least a week. The percentage observed were compared using the Khi ² test with Yates correction. We retained the blood concentrations of the mother molecule for tertiary amines (imipramine, clomipramine and amitriptyline). The samples were taken after at least seven days of treatment at the same dose, and twelve to thirteen hours after the last taking. The maxima of blood levels were respectively : desipramine 200 ng/ml, clomipramine 258 ng/ml, imipramine 163 ng/ml, amitriptyline 129 ng/ml. Research for evidence in favor of toxicity (fall, delirium, convulsion, reduction of dosage before discharge), was done through revision of patients' clinical files. Results : The test group consisted of 87 individuals. The average age was 71.3 years (SD : 5.09). Mean creatinemia was 83.73 mmol/l (SD : 26.89). The population thus selected divided into 4 groups : 61 (70.1 %) were given imipraminics, 10 (11.5 %) serotonin recapture inhibitors, 11 (12.7 %) other antidepressants essentially of mianserine and 5 (5.7 %) treatment by electroconvulsivotherapy. The imipraminics prescribed were desipramine, imipramine, clomipramine and amitriptyline. Among the 61 patients treated with imipramine, blood level dosage was practised on 48 patients (79 %). Two subgroup were distinguished : 13 (21 %) received dosages inferior ou equal to 75 mg/day and 48 (79 %) superior to 75 mg/day. The mean dosage found in the sub-group of patients treated with dosages superior to 75 mg/day was 140 mg/day (SD : 30). The subgroup treated with dosages superior to 75 mg/day was more frenquently monitored than the subgroup receiving dosages inferior or equal to 75 mg/day, respectively 40/48 (83 %), and 8/13 (62 %). This difference is statistically non-signifiant (p > 0.10). The analysis of dosages used showed that : - among the dosages effected upon patients receiving doses inferior or equal to 75 mg/day, 1 (12.5 %) exceeded the maximal value of therapeutic range. - Among the dosages effected upon patients receiving dosages superior to 75 mg/day, 9 (22 %) exceeded the maximal value of the therapeutic range. The difference is statistically significiant (p < 0.001). On revision of clinical files, no patient presented any element that might lead one to suspect toxicity such as defined in « Objectives and Methods ». Conclusion : In our study, patients were hospitalized and so benefited from closer observation than one can expect in outpatients. In this particular context, the dosages used are close to those advocated for the general population. With the elderly subject, the systematic prescription of half-dose tricyclics runs the risk of infratherapeutic dosage. It is thus preferable to resort to blood level dosage and to look for a maximum dose tolerance before concluding ineffectuality. This allows one to monitor whether the blood levels obtained are included in the therapeutic range ; to avoid toxic doses and to check weak compliance in the elderly patient. Our findings do not oppose the use, for the elderly hospitalized depressive, of doses of imipraminics close to those of a young subject. To confirm these results it would be desirable to carry out o prospective study, including a systematised evaluation of adverse effects and a comparison of clinical effectiveness for parallel groups of elderly patients receiving different doses of imipraminic antidepressants.