If lithium augmentation is ineffective, it should be discontinued and the antidepressant changed (Table 5). A lack of response to one of the newer agents in a class, such as the selective serotonin reuptake inhibitors (SSRIs), does not predict lack of response to others in that class. If the first drug used was a reversible inhibitors of monoamine oxidase A (RIMA) with only one drug in the class, the switch should be to an SSRI. If the original drug was an SSRI, a second SSRI, a RIMA, or other newer agents should be tried. If a TCA or MAOI was used first, the switch should also be to one of the new classes of antidepressants.

The tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs) should be kept as third-line antidepressants. Evidence shows that response to an SSRI does not determine response to a TCA. One study has shown that 60.5% of patients who failed to respond to SSRI monotherapy responded when switched to a noradrenergic TCA. Most tricyclic antidepressants (TCAs) have both serotonergic and noradrenergic properties. Desipramine and nortriptyline are somewhat more noradrenergic than the others. Venlafaxine, a new selective serotonin and noradrenaline reuptake inhibitor (SSNRI) might also be considered.

If atypical symptoms, such as panic attacks or anxiety, are present, an MAOI or reversible inhibitors of monoamine oxidase A (RIMA) should be considered after a suitable washout period for the previously used antidepressant (10 to 14 days for most antidepressants; up to 5 weeks for fluoxetine because of an active metabolite).

If the second antidepressant is not effective, lithium augmentation should be tried once more before the antidepressant is changed again.

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