Intro

The chapter on SSRI drugs is a key part of the pharmacy exam by the PEBC. It talks about what SSRIs do, when to use them, the side effects they can have, and how they react with other drugs. This chapter helps future pharmacists learn how to use these common depression medications carefully and correctly in their work. The SSRI chapter is made to meet the PEBC requirements. It's not just about passing the test; it's also about learning to make good decisions as a pharmacist. By studying this chapter, you'll get ready for the exam and also learn how to better help patients with mental health treatments.

Mechanism:

SSRIs are antidepressants with a high selectivity for the serotonin transporter over the norepinephrine transporter. They are preferred over TCAs and MAOIs due to fewer side effects and higher safety in overdose. Examples include fluoxetine, citalopram, escitalopram, fluvoxamine, paroxetine, and sertraline. Escitalopram is the pure S-enantiomer of citalopram.

Indications: 

 • Major depression

 • OCD

 • Anxiety disorders 

 • panic attacks

 • Bulimia

 • Premenstrual dysphoric disorder (PMDD)

Actions:

SSRIs increase serotonin levels in the brain by blocking its reuptake, enhancing mood. Significant mood improvement takes at least 2 weeks, with maximum benefits taking up to 12 weeks. Initial side effects occur quickly, but some may adjust or change over long-term use. Dosage adjustment may be necessary due to individual metabolism differences.

Pharmacokinetics: 

SSRIs are well absorbed orally, with peak levels in 2 to 8 hours. Food impact varies for example taking sertralin with food increases its absorbtion upto %30. Metabolism occurs through CYP450 enzymes, with significant variation in half-lives among SSRIs. Fluoxetine has the longest half-life. Some SSRIs inhibit specific CYP450 isoenzymes, affecting metabolism and drug interactions.

Adverse Effects

• Increased Risk of QTc Prolongation: Certain medications may interact with Escitalopram & Citalopram to prolong the QT interval on an EKG, which can affect heart rhythm.
  
• Increased Risk of Bleeding: There's a greater risk of bleeding when SSRIs are taken with blood thinners, nonsteroidal anti-inflammatory drugs (NSAIDs), or other medications that affect bleeding. For example a patient on Escitalopram who takes NSAIDs for arthritis pain, the combined effect could increase the chances of gastrointestinal bleeding, necessitating close monitoring or adjustments to medication.
  
• Serotonin Syndrome: A potentially life-threatening condition that can occur when SSRIs increase serotonin levels too much. Example: If someone takes an SSRI with another serotonergic drug, like an MAOI, they could experience rapid heart rate, high fever, or muscle rigidity, which are signs of serotonin syndrome.
• Hyponatremia: Low sodium levels in the blood, which can lead to confusion and seizures.
• Sleep-related issues: Including insomnia and somnolence (excessive sleepiness).
• Gastrointestinal Problems: Such as nausea (common), diarrhea, or dry mouth (xerostomia) also GI bleeding.
• Sexual Dysfunction: Difficulty achieving sexual satisfaction, which is a persistent and limiting side effect.
• Headache, 
• Sweating, 
• Anxiety, 
• Agitation, 
• Fatigue, 
• Weight changes, 
• Paroxetine and fluvoxamine are more sedating
• Neuromuscular and Skeletal:  fluvoxamine may cause a general sense of bodily weakness 
  
• Fluoxetine and sertraline are more activating
• SSRIs increase insulin secretion, which can lead low blood sugar or hypoglycemia in patients using other hypoglycemic medications
  

Special Considerations: Children and Teenagers: Use cautiously due to risks of suicidal ideation. Monitor for worsening depression and suicidality. 

Contraindications:

• Known Allergy: Individuals with a known hypersensitivity to SSRIs should not take these medications.
• Concurrent MAOI Use: Due to the risk of serotonin syndrome, SSRIs are contraindicated in patients taking monoamine oxidase inhibitors (MAOIs) or within 14 days of discontinuing an MAOI.
• Pimozide and Thioridazine: SSRIs can interact with certain drugs like pimozide and thioridazine, leading to increased plasma concentrations, which can cause serious cardiac arrhythmias.
• Pregnancy and Breastfeeding: Some SSRIs are contraindicated or used with caution during pregnancy and breastfeeding due to potential risks to the fetus or infant.
• Severe Liver or Kidney Disease: SSRIs are metabolized in the liver and excreted by the kidneys. Patients with severe liver or kidney disease may require dose adjustments or may be advised to avoid certain SSRIs altogether.
• Bleeding Disorders: SSRIs have been associated with an increased risk of bleeding. They are contraindicated or used with caution in individuals with bleeding disorders or those on anticoagulant therapy.
• Unstable Epilepsy: Due to the potential for SSRIs to lower the seizure threshold, they should be used with caution in patients with unstable epilepsy.
• Bipolar Disorder: Without concurrent mood-stabilizing medication, SSRIs may induce mania or rapid cycling in patients with bipolar disorder.
• Severe Hyponatremia: SSRIs can cause or exacerbate hyponatremia, particularly in the elderly or those taking diuretics.
• Alcohol Use: SSRIs may interact with alcohol, and their use is generally discouraged in individuals with alcohol use disorder.

Overdose and Toxicity: SSRIs are relatively safe but can cause QT prolongation (citalopram) or lower seizure thresholds. Serotonin syndrome is a risk with drug interactions. 

Discontinuation Syndrome: Abrupt withdrawal can lead to discontinuation syndrome, especially with short-half-life SSRIs. Gradual tapering is recommended. Fluoxetine has the lowest discontinuation risk. 

Drug Interactions: SSRIs, especially fluoxetine and paroxetine, can interact with other drugs metabolized by CYP2D6, potentially leading to serotonin syndrome or enhancing the effects of other drugs.

Exam Notes:

Note 1. Fluoxetine as Primary Treatment: Fluoxetine is often the preferred initial treatment for both adults and children experiencing depression.The therapeutic effects of fluoxetine typically start to become noticeable after 2 to 4 weeks following the start of the treatment. Drug Interaction Precautions: It is strongly advised not to use two SSRIs or an SSRI in combination with a TCA (Tricyclic Antidepressant) or an MAOi (Monoamine Oxidase Inhibitor) due to potential adverse interactions.

Note 2.  Managing Medication Changes: If there's a need to switch from one SSRI to another or to a TCA or MAOi, it is crucial to have a waiting period, commonly referred to as a 'washout period'. This period allows the medication to clear from the body to prevent withdrawal symptoms. For most SSRIs, this period is 2 weeks; however, for fluoxetine, a longer period of 5 weeks is required due to its longer activity in the body. For Moclobemide, a different type of antidepressant, the washout period is 5 days.

Note 3. Special Considerations for the Elderly and NSAID Users: Extra care should be taken when prescribing SSRIs to elderly patients or those taking NSAIDs (Nonsteroidal Anti-inflammatory Drugs), as there is an increased risk of gastrointestinal bleeding.

Note 4. Paroxetine has the shortest half-life among SSRIs, leading to its infrequent prescription due to the severity of withdrawal symptoms experienced by patients when they stop taking it.

Note 5. Fluoxetine’s Half-life and Withdrawal Symptoms: Fluoxetine has a notably long half-life, ranging from 6 to 9 days, and is known for not causing withdrawal symptoms, which can be a considerable advantage in some treatment plans.   For example, in practice, a patient being treated with fluoxetine may report feeling better after a month of therapy. However, if the treatment needs to be switched to another SSRI or a different class of antidepressants, a healthcare professional must ensure an appropriate washout period to avoid withdrawal effects. This is especially true when transitioning away from fluoxetine due to its long half-life, making careful planning essential to maintain patient safety and comfort.

Note 6. Citalopram and Escitalopram Characteristics: These two SSRIs are known for their high selectivity and are generally better tolerated by patients, making them a favourable choice in certain cases.

Note 7. Optimal Intake of Sertraline: To enhance its effectiveness, sertraline should be taken with food.

Serotonin Syndrome

Serotoninergic syndrome, more commonly known as serotonin syndrome, is a potentially life-threatening medical condition that arises from excessively high levels of the neurotransmitter serotonin in the nervous system. This can happen shortly after beginning a new medication that affects serotonin levels, increasing the dosage too rapidly, or accidentally overdosing on such medications. The onset is typically rapid, often occurring within 6 hours after the change in medication.

Symptoms of Serotonin Syndrome:

• Elevated body temperature (hyperpyrexia): A sudden, dangerous increase in body heat.
•  Restlessness and agitation: Patients may feel extremely anxious and unable to stay still.
•  Muscle symptoms: This includes muscle pain, uncontrollable twitching or jerking (myoclonus), and excessive muscle reflexes (hyperreflexia).
•  Blood pressure changes: Either an increase (hypertension) or a decrease (hypotension).
•  Neurological symptoms: Shaky movements (tremors), muscle shivers, seizures, and in severe cases, a loss of consciousness or coma can ensue.
  

Treatment and Antagonists: The management of serotonin syndrome involves the administration of medications to counteract the excess serotonin. These include benzodiazepines, which are sedatives that help relieve agitation and seizures. Propranolol is used to mitigate symptoms like tremors, while cyproheptadine specifically blocks serotonin effects.

Medications Leading to Serotonin Syndrome: The risk of serotonin syndrome increases when SSRIs are taken in combination with other drugs that elevate serotonin levels, including MAOIs, TCAs, as well as certain pain relievers like meperidine and pentazocine, and the cough suppressant dextromethorphan.

Withdrawal Symptoms: On the other hand, when a person discontinues a serotonin-affecting medication abruptly, they may experience what's known as discontinuation syndrome. This condition presents with symptoms resembling the flu, such as body aches and fever, sleep disturbances (insomnia), stomach upsets (nausea), a general feeling of being unsteady or off-balance, sensory anomalies like "electric shock" sensations, and heightened energy or restlessness. For example, discontinuation syndrome might occur in someone who suddenly stops taking their long-term SSRI medication without tapering off, leading to several days or weeks of uncomfortable and distressing symptoms as their body readjusts to the absence of the drug.