9 - Psychiatric Drug Reactions Flashcards
If a patient asks you if antidepressants are addictive what should your response be?
No
Only criteria of addiction it fits is ‘withdrawal’ symptoms which is discontinuation syndrome.
e.g no increased tolerance, no cravings
What is discontinuation syndrome?
- Onset is within 5 days of stopping, sometimes after cross-tapering or missing doses
- Usually mild and self-limiting but can be prolonged and severe
- Warn patients about this and explain it is normal
- SSRIs: ’Flu-like symptoms, headaches, dizziness, insomnia, tears, irritability, vivid dreams
- MAOIS: Agitation, irritability, ataxia, movement disorders, insomnia
- TCAS: ’Flu symptoms; insomnia
Which antidepressants are associated with the worst discontinuation syndrome?
- Paroxetine
- Venlaxafine
How can the effects of discontinuation syndrome be avoided?
- Slow taper down dose
- Snap tablets in half or take on alternate days
- Switch to Fluoxetine (long half-life) and taper down from that
How does the half-life of an antidepressant determine the likelihood of serotonin syndrome and discontinuation syndrome?
Long Half-Life: More likely to have serotonin syndrome
Short half life: More likely to have discontinuation syndrome
What is Serotonin Syndrome and how does it present?
Life-threatening neurological disorder due to increased serotonergic activity in the CNS
Triad of:
-Mental status changes
-Autonomic hyperactivity e.g HTN, Hyperthermia, Tachycardia
-Neuromuscular abnormalities e.g rigidity, clonus, hyperreflexia
Which antidepressants are most associated with serotonin syndrome?
SSRIs
Can be due to a single drug or a combination that increase serotonergic activity
What are some signs and symptoms of serotonin syndrome?
DILATED PUPILS
What is the criteria for a diagnosis of serotonin syndrome?
Hunter Criteria
Patient taking serotonergic agent presents with one of:
- Spontaneous clonus
- Inducible/ocular clonus and agitation or diaphoresis
- Tremor and hyperreflexia
- Hyperthermia, hypertonia, and ocular/inducible clonus
What are some differential diagnoses for serotonin syndrome?
- Neuroleptic malignant syndrome
- Malignant Hyperthermia
- Encephalitis
- Drug intoxication (MDMA and Cocaine)
- Phaeochromocytoma
What investigations should you do if you suspect serotonin syndrome?
- Bedside: ECG, cardiac monitoring (particularly if profound autonomic symptoms), blood glucose, urine dip
- Bloods: CK, FBC, U+ES, LFTs, and blood gas. Patients may have features of neutrophilia, acute kidney injury, or elevated CK levels
- Imaging: cerebral imaging (i.e. CT/MRI) may be needed in patients with new-onset altered mental status to exclude an alternative cause
- Special: a lumbar puncture may be needed to exclude an intracerebral infection or investigate for an alternative cause of confusion (e.g. autoimmune encephalopathy).
How is serotonin syndrome managed?
- Stop serotonergic agent
- Monitor for 4-6 hours. Resolves in 24 hours
- Supportive: fluids for AKI, cooling blankets, benzos for agitation,
- Medical: if supportive and benzos fail give Serotonin antagonist Cyproheptadine
What are some complications of serotonin syndrome?
- Cardiac arrest
- Cardiac arrhythmias
- AKI
- Rhabdomyolysis
- DIC
- Seizures
- Respiratory failure
- VTE
When is the QT interval prolonged?
- 450 ms for men
- 470ms for women
What is Neuroleptic Malignant Syndrome?
Life-threatening neurological disorder characterised by confusion, fever, muscle rigidity and autonomic instability
Affects up to 3% of patients on antipsychotics (neuroleptics), more men
How long after taking an antipsychotic can NMS occur?
Within first 2 weeks
Usually recovers within 2 weeks of stopping agent
What blood test should you do for NMS?
Elevated CK due to muscle rigidity (e.g. >1000-100,000 IU/L)
May be normal if rigidity not profound or if early in the presentation
How is NMS managed?
Supportive:
- Stop antipsychotic
- Cardiac monitoring
- Give benzodiazepines for agitation
- Fluid resus
- Cooling blankets
Specific
- Dantrolene or Lorazepam or Bromocriptine to relax muscles
- Fluids and Sodium Bicarbonate for rhabdomyolysis
- Clonidine for profound HTN
What are the complications with NMS?
- Cardiac arrest
- Cardiac arrhythmias
- Acute kidney injury
- Rhabdomyolysis
- Disseminated intravascular coagulation
- Seizures
- Respiratory failure
- Venous thromboembolism
How can you tell the difference between NMS and SS?
What is an acute dystonia?
Sustained often painful muscle spasms producing abnormal postures common with antipsychotics
Occur in first 48 hours to 5 days of taking antipsychotic
Most common: neck, tongue, jaw, oculogyric crisis
How is Clozapine agranulocytosis managed?
- Stop Clozapine
- Stop other bone marrow suppressing drugs e.g Valproate
- Avoid antipsychotics for a few weeks
- Contact haematologist
- Avoid infection (e.g isolate) and consider prophylactic broad spectrum antibiotics
- Give lithium or G-CSF to raise WCC and neutrophils
