Ketamine treatments are meant to be temporary and augmented with proper existing long-term treatments like SSRIs/SNRIs/TCAs/etc. After a few treatments, the long term antidepressants have had time to start working.
Do you have a source for that? The article seems to contradict this, from what I understand Ketamine is used for cases of treatment-resistant depression, i.e. many kinds of medications have been tried and failed.