Dr Kao Replies

See letter by Doruk and article by Lee et al

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Dr Kao Replies

To the Editor: My colleagues and I appreciate the critique of our study by Dr Doruk and would like to clarify the issues he raised about its design.

First, we identified patients newly diagnosed with dementia from the Registry of Catastrophic Illnesses Patient Database (CIPD) of the Taiwan National Health Insurance Research Database (NHIRD) as the case group to confirm the accuracy of the dementia diagnosis, because the approval of a catastrophic illness certificate is a rigorous process. Since patients without a dementia diagnosis in CIPD usually have other severe diseases that may confound the analysis, our control group comprised patients without dementia selected from the Longitudinal Health Insurance Database 2000 of NHIRD, a sampling file of 1 million people with almost identical distributions of sex, age, and health care cost as the total population of 23 million in Taiwan. Each dementia patient was matched with a nondementia patient on age, sex, year of major depression diagnosis, and year of index date, ie, the date at first diagnosis of dementia. Therefore, the duration of antidepressant use is the same in both groups. Yet, we do agree with Dr Doruk’s comment that selecting cases and controls from different subsets of NHIRD may introduce some unknown bias.

Second, the antidepressants included in our study are tricyclic antidepressants (amitriptyline, clomipramine, desipramine, doxepin, imipramine, and nortriptyline), selective serotonin reuptake inhibitors (SSRIs; fluoxetine, fluvoxamine, paroxetine, sertraline, citalopram, and escitalopram), monoamine oxidase inhibitors (MAOIs; tranylcypromine, phenelzine, selegiline, and isocarboxazid), heterocyclic antidepressants (nefazodone and trazodone), and others (bupropion, venlafaxine, and mirtazapine). We decided not to show cumulative doses of individual drugs, but to list only the partition of quartile or median doses of each group of antidepressants, in order to improve the readability of the article. Indeed, this may obscure specific pharmacologic properties of individual drugs, and the results should be interpreted carefully.

In conclusion, we found an association between antidepressant use and the risk of dementia in our population-based study. As mentioned in our article, the quality of evidence derived from retrospective case-control studies is generally lower than that from randomized trials, so large-scale randomized clinical trials are required any definitive conclusions can be drawn.

Chia-Hung Kao, MDa

d10040@mail.cmuh.org.tw

aGraduate Institute of Clinical Medical Science and School of Medicine, College of Medicine, China Medical University, Taichung, Taiwan.

Potential conflicts of interest: None.

Funding/support: None.

J Clin Psychiatry 2016;77(9):e1152

dx.doi.org/10.4088/JCP.16lr10742a

© Copyright 2016 Physicians Postgraduate Press, Inc.