💊 SSRIs
Drug Class & Overview
Selective Serotonin Reuptake Inhibitors (SSRIs) are a class of antidepressant medications primarily used to treat major depressive disorder and various anxiety disorders.
Mechanism of Action
SSRIs work by blocking the reuptake of serotonin (5-HT) into the presynaptic neuron in the central nervous system. This increases the concentration of serotonin in the synaptic cleft, enhancing serotonergic neurotransmission.
Key Indications
Major Depressive Disorder is a primary indication. They are also widely used for anxiety disorders including Generalised Anxiety Disorder, Panic Disorder, Obsessive-Compulsive Disorder (OCD), and Post-Traumatic Stress Disorder (PTSD). Some SSRIs are indicated for bulimia nervosa and premenstrual dysphoric disorder.
Contraindications
Absolute contraindications include concomitant use with MAO inhibitors due to the risk of serotonin syndrome. Caution is required in patients with epilepsy, a history of bleeding disorders, or angle-closure glaucoma. They should be used with caution in patients with cardiac disease, particularly those with prolonged QT interval.
Adverse Effects
Common side effects include gastrointestinal disturbances (nausea, diarrhoea), headache, insomnia, and sexual dysfunction (decreased libido, anorgasmia). Serotonin syndrome is a rare but serious adverse effect, characterised by mental status changes, autonomic hyperactivity, and neuromuscular abnormalities. Hyponatraemia, particularly in older adults, and increased risk of bleeding are also concerns.
Monitoring
Baseline renal and liver function tests may be considered, especially in older adults or those with pre-existing conditions. Regular monitoring for clinical response and adverse effects is crucial, particularly during the initial weeks of treatment. Electrolyte monitoring may be warranted in at-risk patients for hyponatraemia.
Prescribing Safety (OSCE)
When prescribing SSRIs, always check for drug allergies and current medications to identify potential interactions, especially with MAOIs, triptans, or other serotonergic drugs. Counsel patients on the delayed onset of therapeutic effect, potential initial worsening of anxiety, and common side effects. Emphasise the importance of not stopping treatment abruptly due to withdrawal symptoms.
MLA High-Yield Notes
SSRIs are first-line antidepressants due to their efficacy and generally favourable side effect profile compared to older agents. Citalopram and escitalopram carry a dose-dependent risk of QT prolongation. Fluoxetine has a long half-life, making it less prone to discontinuation syndrome but also prolonging drug interactions. Paroxetine is associated with a higher risk of discontinuation symptoms.
Common SBA Themes
Classic SBA questions often focus on identifying serotonin syndrome, differentiating it from neuroleptic malignant syndrome, or recognising common side effects like sexual dysfunction. Another common theme is the management of antidepressant discontinuation syndrome or the appropriate choice of SSRI in specific patient populations (e.g., those with cardiac issues).
References
- BNF (British National Formulary)
- NICE (National Institute for Health and Care Excellence) Guidelines
- MHRA (Medicines and Healthcare products Regulatory Agency) Guidance