Nursing Field Notes / Psych-Mental Health Pharmacology · Antidepressant Ladder — Rungs 2 & 3 of 3
SNRI vs. TCA
Two older or dual-acting antidepressant classes — one modern & broad, one older & risky
NG-187PSYCH PHARMADHD-friendly visual edition
SNRIs block reuptake of two neurotransmitters — serotonin AND norepinephrine — and double as neuropathic pain drugs. TCAs are an older class that also boosts serotonin & norepinephrine, but drags a heavy anticholinergic side-effect profile and a genuinely dangerous overdose behind it. Same neurotransmitter targets, very different safety margins — that's the whole point of this comparison.
🎯 SNRI = dual + painSerotonin AND norepinephrine reuptake blocked — also treats neuropathic/fibromyalgia pain.
💀 TCA = narrow marginCardiotoxic in overdose — QT prolongation, arrhythmia. A small extra dose can kill.
🥴 TCA = anticholinergic"Can't see, can't pee, can't spit, can't poop" — the classic tetrad.
🚨 Serotonin syndromeAgitation, hyperthermia, clonus/hyperreflexia, diaphoresis, tremor — same 5 signs, same risk, both classes.
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SIDE A · SNRI
STEP 1 · DUAL & MODERN
Rung 2 of the ladder — same serotonin trick as an SSRI, plus norepinephrine, plus a second job treating chronic pain.
🔬 Blocks TWO reuptake pumps at once
MOA Like an SSRI, an SNRI blocks the serotonin reuptake pump — but it also blocks the norepinephrine reuptake pump, so both neurotransmitters build up in the synapse. That second target is what gives SNRIs their extra job: treating neuropathic pain, not just mood.
🧠 “SNRI = double duty.” One drug, two pumps blocked, two jobs done: mood and pain.
🧠 "If a fibromyalgia patient on duloxetine says they're not depressed, they need education" — it's still the right drug. It's treating their pain, not (only) their mood.
⭐ Key point — pain AND sleep
Duloxetine helps with chronic pain and improves sleep quality in fibromyalgia patients — a two-for-one benefit worth pointing out in patient teaching.
🧠 SNRIs are often reached for second, after an SSRI trial, or first when chronic pain is part of the picture.
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SIDE B · TCA
STEP 2 · OLDER & RISKIER
Rung 3 of the ladder — an older class that hits more receptors than it needs to, and that's exactly the problem.
🥴 The anticholinergic tetrad — "dry body"
TCAs don't just block serotonin/norepinephrine reuptake — they also block acetylcholine receptors, causing a predictable dry-everything picture.
🧠 "Amy trips on things" — Amitriptyline causes orthostatic hypotension: teach slow position changes to avoid a dizzy fall. Imipramine — "Inhibit my PEEing" = urinary retention is its stand-out anticholinergic effect.
💊 Know the names
Amitriptyline — orthostatic hypotension
Imipramine — urinary retention
Indications: depression, anxiety, and neuropathic pain (diabetics & fibromyalgia) — TCAs treat pain too, like SNRIs, just with a rougher side-effect trade-off.
🧠 Two drugs, two classic teaching points: Amitriptyline = slow rise. Imipramine = slow stream.
💀 Cardiotoxicity — the reason TCAs fell out of favor
Narrow safety margin — in overdose, TCAs cause QT prolongation and life-threatening cardiac arrhythmias. Unlike SSRIs/SNRIs, a TCA overdose is a genuine cardiac emergency.
🧠 "TCAs can stop a heart before they stop a headache." A small dose miscalculation or an overdose attempt with a narrow-margin drug like this is a true cardiac emergency — assess for arrhythmia, monitor ECG.
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TELL THEM APART
STEP 3 · SIDE BY SIDE
Same neurotransmitter targets, very different risk profile — this is the table the "vs." title is asking for.
Ladder position: older, generally reserved when newer agents fail
🧠 "Same targets, different manners." Both hit serotonin + norepinephrine — the TCA just also grabs receptors it didn't need to, and that's where all its side effects and its overdose danger come from.
🚨 Both interact with MAOIs the same dangerous way
Never combine an SNRI or a TCA with an MAOI — risk of serotonin syndrome. A 2-week washout period is required when switching to or from an MAOI.
🧠 "MAOI = Anti... depressant STOP." Whichever antidepressant a patient is switching away from or onto an MAOI, count two weeks first. See NG-154 for the full MAOI washout rule.
🪜 Where these two sit on the antidepressant ladder
🪜 This page = Rungs 2 & 3 · see NG-205 (SSRI) and NG-154 (MAOI) for the rest of the ladder