Correlates of low-dosage treatment with antidepressants by psychiatrists and general practitioners

The prescribing of low dosages of antidepressants has for many years been a matter of concern in the scientific literature. There is a little understanding of why physicians do not follow dosage recommendations and what factors influence medical decision-making.

In a drug utilisation observation study, treatment of 692 patients was monitored who were prescribed the tricyclic antidepressant doxepin by 80 general practitioners and 85 psychiatrists.

The mean maximum dosage per day was 83 mg/d. One hundred and fifty milligrams per day or more were prescribed for only 6.1% of the patients. There were significant differences between dosage groups: patients older than 65 received lower dosages (68 mg/d) as younger patients (84 mg/d), male patients higher dosages (94 mg/d) than females (79 mg/d), patients who had a mild depression with a score of 1-35 on the depression symptom scale received on average 68 mg/d, while patients with 36-74 got 100 mg/d. Physician speciality was not significantly related to dosage levels. In a logistic regression analysis, gender and Clinical Global Impression (CGI) at first examination remained factors that significantly predicted dosages of >or=125 mg/d.

Low-dosage treatment with antidepressants is a rule rather than an exception. The prescribing pattern is not indiscriminate, but physicians follow an adaptive strategy and there is medical and theoretical evidence which supports their practice. Outcome research will have to be clarified in future studies as to what extent reference to such intervening variables can help to optimise individual dosage finding.