Adverse drug reactions from - antidepressants

Reactions by class

SSRI/SNRI hyponatraemia - elderly, female, concurrent diuretics, low body weight
GI bleeding risk inc with concurrent NSAID/antiplatelet/anticoagulant use

SIADH: serotonergic effect on hypothalamic ADH release -> hyponatraemia, typically within first weeks of therapy
inc bleeding risk: platelets rely on serotonin for aggregation - SSRIs deplete platelet serotonin stores
QT prolongation: hERG channel effects, most notable with citalopram/escitalopram (dose-dependent) and TCAs
Serotonin syndrome: excess synaptic 5-HT with combination therapy or overdose (see poisoning-from-antidepressants)

Hyponatraemia - UEC within first 2-4 weeks of starting SSRI/SNRI in at-risk patients, or with new confusion/falls
ECG if starting citalopram/escitalopram in patients with other QT-prolonging risk factors, or on TCA
Clinical diagnosis of serotonin syndrome vs discontinuation syndrome (flu-like, dizziness, "brain zaps" on stopping/missing doses - resolves with reinstatement or slow taper)

Discontinuation syndrome: taper slowly rather than stopping abruptly, esp. with short half-life agents (paroxetine, venlafaxine)
Hyponatraemia: stop or switch agent, fluid restriction; rarely severe enough to need hypertonic saline
Serotonin syndrome: stop causative agent(s), benzodiazepines, cyproheptadine if moderate-severe - see poisoning-from-antidepressants
Bleeding risk: caution/gastroprotection when combining SSRI with NSAID/antiplatelet/anticoagulant
Citalopram/escitalopram: respect maximum daily dose limits in the elderly given dose-dependent QT effect

Falls and fractures in the elderly (sedation, postural hypotension, hyponatraemia)
Sexual dysfunction - major cause of non-adherence, often under-reported
Neonatal adaptation syndrome / persistent pulmonary hypertension of the newborn with late-pregnancy SSRI exposure

Most adverse effects (GI, sexual) persist for the duration of therapy rather than resolving with tolerance
Discontinuation syndrome - self-limiting over 1-2 weeks if not reinstated
Hyponatraemia typically resolves within days to weeks of stopping the causative agent

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