Esketamine Monotherapy: Label vs. Payer Policy
Intranasal esketamine has been approvable as monotherapy since 2025 — but her payer's criteria still require a concurrent oral antidepressant, and the only dose she can tolerate may not be doing anything at all.
R.K., a 58-year-old woman who has spent the past two decades doing tax accounting for a small firm, is living through her third depressive episode in six years, and this one has not lifted with anything tried so far. Her HTN has been well-controlled on lisinopril for over a decade, and she has no other chronic illness — nothing about her general health explains why this episode has outlasted the others.
Over the past sixteen months she completed adequate trials of sertraline, then venlafaxine titrated to 225mg, then bupropion XL, each carried a full six to eight weeks at a real target dose before being judged a failure. Duloxetine came next, and it was the first drug that touched her mood at all — irritability easing, sleep improving — but 60mg produced nausea severe enough that she lost eleven pounds in five weeks and could not sustain it. The only dose she can actually tolerate is 20mg, roughly a third of the usual effective range, and at that dose duloxetine's own antidepressant contribution is genuinely doubtful.
Intranasal esketamine, started eight weeks ago under REMS-monitored administration, is the first intervention that has produced a real response: her PHQ-9 has fallen from 22 to 9, and she has returned to spending weekends with her mother, whom she helps care for, without the flat exhaustion that had made even that feel impossible. The original esketamine approval covered use only alongside an oral antidepressant, and every pivotal trial behind it tested add-on therapy; in January 2025 the FDA approved esketamine as monotherapy for treatment-resistant depression on the strength of a dedicated monotherapy trial, so the label itself no longer requires a partner drug. Her payer's continued-authorization criteria, written before that change, still do — treating the 20mg duloxetine as the qualifying concurrent agent regardless of whether it is doing anything at that dose. The question in front of the team is whether to push the dose back toward 60mg and risk losing the tolerability that kept her in treatment at all, switch to an oral agent she can actually stay on, or challenge the criterion directly on the ground that the label it was built around no longer says what it said.
At the medication-management visit
The original approval was built entirely on add-on trials — TRANSFORM-2 and SUSTAIN-1 both started patients on a newly initiated oral antidepressant at randomization rather than continuing one they were already stable on, and the monoaminergic contribution of that background agent was never isolated out. That gap is the one the 2025 monotherapy trial was run to close, and it closed it: esketamine alone beat placebo. So the pharmacologic question her payer is still asking has actually been answered.
Twenty milligrams of duloxetine sits well below the 40-60mg range where receptor-occupancy data put meaningful norepinephrine-reuptake inhibition, so on paper she is already getting glutamatergic monotherapy dressed up as combination therapy — which the label now permits outright and only her payer still objects to.
I'd push back on treating dose escalation as the default fix. She lost eleven pounds at 60mg — that's not a mild tolerability complaint, and forcing her back onto a dose she couldn't sustain the first time risks losing the oral agent entirely, which would jeopardize the esketamine authorization outright rather than protect it.
Mirtazapine at a modest starting dose gives real noradrenergic and serotonergic activity through a completely different receptor profile, tends to help sleep and appetite rather than working against them, and would give the payer a genuinely active concurrent agent instead of a dose she is tolerating only on paper.
Agreed — the honest read of the duloxetine dose is that it isn't carrying real weight, and I'd rather build the concurrent-agent case on a drug we can actually keep her on.
Switching to mirtazapine 15mg at bedtime, titrating as tolerated, gives us both a real pharmacologic rationale and a documentation trail that doesn't require anyone to argue that twenty milligrams of duloxetine is doing something it probably isn't.
The team elected to cross-taper duloxetine off over roughly two weeks rather than stop it outright — even 20mg can produce a discontinuation syndrome — while starting mirtazapine 15mg at bedtime and continuing intranasal esketamine on its existing weekly maintenance schedule.
What remains genuinely unresolved is how the payer's utilization-management criteria will treat a therapy change made mid-authorization — nothing about the new regimen guarantees smoother sailing than the current renewal, only a more defensible clinical rationale behind it.
Esketamine coverage continues on the new combination, and the record shows a genuinely active second agent rather than a dose maintained mostly for documentation.
The team will need to decide between a formal appeal, expedited external review, or bridging esketamine access out of pocket while the oral agent stabilizes — a real access problem with no drug-only fix.
Everyone agreed on one point without dispute: whatever the payer decides, the twenty-milligram duloxetine was never going to hold up if this ever needed explaining to anyone outside billing.