Antidepressants Flashcards
How do you give a patient an adequate trial of an antidepressant?
Usually between 1 and 2 months at full dose, before considering changing medications
What are the major categories of antidepressants?
SSRIs (selective serotonin reuptake inhibitors), Heterocyclic antidepressants, including TCAs and tetracyclic antidepressants, Monoamine oxidase inhibitors (MAOIs), Miscellaneous antidepressants
Response rates of antidepressants
All have similar response rates in treating major depression but differ in safety and side effect profiles.
How many patients will respond to antidepressants?
About 70 percent of patients with major depression. About 30 percent of this is placebo response.
How long do antidepressants need to work?
Most require a trial of at least 3-4 weeks for effect, with some people requiring as little as 1-2 weeks and some 6-8 weeks for noticeable effects.
Withdrawal phenomenon:
Most antidepressants have this. Characterized by dizziness, headaches, nausea, insomnia and malaise. Depending on dose and half-life, they may need to be tapered.
SSRIs and related antidepressants:
Because of safety and tolerability, they have become the most common agents used to treat major depression.
The choice of a particular medication used for a given patient should be based on:
- Patient’s symptoms
- Previous treatment responses by the patient or a family member to a particular drug
- Medication side effect profile
- Comorbid conditions
- Risk of suicide
- Cost
SSRIs Mechanism:
Inhibit presynaptic serotonin pumps that take up serotonin, leads to increased availability of serotonin in synaptic clefts. However, research indicates that the mechanism of action may be more complex.
Response to SSRIs:
Although structural differences are minimal, patients often respond differently in terms of both efficacy and side effects to different SSRIs.
Dosing of SSRIs:
Based on their half lives, most are dosed daily, Fluoxetine also has a weekly dosing form available.
SSRI Plasma Levels:
There is no correlation between plasma levels and efficacy or side effects.
SSRIs are most commonly prescribed antidepressants due to several distinct advantages:
- Low incidence of side effects, most of which resolve with time
- No food restrictions
- Much safer in overdose
6 Examples of SSRIs:
Fluoxetine (Prozac), Sertraline (Zoloft), Paroxetine (Paxil), Fluvoxamine (Luvox), Citalopram (Celexa), Escitalopram (Lexapro)
Fluoxetine (Prozac)
- Longest half-life with active metabolites; therefore, no need to taper
- Safe in pregnancy, approved for use in children
- More common sleep changes and anxiety
- Can elevate levels of neuroleptics, leading to Inc. side effects
Sertraline (Zoloft)
- Highest risk for GI disturbances
- Very few drug interactions
- More common sleep changes
Paroxetine (Paxil)
- Highly protein bound leads to several drug interactions
- More anticholinergic effects like sedation, constipation, weight gain
- Short half-life leading to withdrawal phenomena if not taken consistently
Fluvoxamine (Luvox)
- Currently approved only for use in obsessive-compulsive disorder (OCD)
- Nausea and vomiting more common
- Lots of drug interactions
Citalopram (Celexa)
- Fewest drug-drug interactions
- Possibly fewer sexual side effects
Escitalopram (Lexapro)
- Levo-Enantiomer of citalopram; similar efficacy, possibly fewer side effects
- More expensive than citalopram
Comparative Side Effects SSRIs
SSRIs have significantly fewer side effects than TCAs and MAOIs due to serotonin selectivity (they do not act on histamine, adrenergic, or muscarinic receptors)
SSRIs in Overdose
SSRIs are much safer in overdose. Most side effects occur because of the extensive number of serotonin receptors throughout the body, including the GI tract.
When do SSRI side effects usually resolve?
Mostly resolve within a few weeks.
What are the SSRI side effects?
- Sexual dysfunction (25-30 percent), decreased interest, anorgasmia, delayed ejaculation. These typically do not resolve in a few weeks.
- GI disturbance: Mostly nausea and diarrhea, giving with food can help
- Insomnia: also vivid dreams, often resolves over time
- Headache
- Anorexia, weight loss
- Restlessness: an akathisia-like state has been reported at initiation and termination of SSRIs
- Seizures: Rate of 0.2%, slightly lower than TCAs
OTC drugs that increase serotonin:
Drugs that inc. serotonin may be found in OTC cold remedies, possibly leading to serotonin syndrome. A classic example is someone on a high-dose antidepressant taking cough medicine.
How do you treat the sexual side effects of SSRIs?
Augment the regimen with buproprion, change to a non-SSRI antidepressant, or add medications like sildenafil for men
FDA Black Box Warning against all SSRIs for…
“increased suicidal thinking and behavior.” This is most documented in children and adolescents, but may be accurate for adults as well.
Serotonin Syndrome
Caused by taking two drugs, both of which increase serotonin and lead to too much serotonin in the brain. An example is triptans used with SSRIs. This is characterized by fever, diaphoresis, shivering, tachycardia, hypertension, delirium and neuromuscular excitability (especially hyperreflexia and “electric jolt” limb movements), potentially leads to death.