What are the potential side effects of Pristiq (desvenlafaxine)?

Pristiq (Desvenlafaxine) Side Effects

Pristiq commonly causes nausea, dizziness, insomnia, sweating, constipation, and sexual dysfunction, with the most serious risks being serotonin syndrome, elevated blood pressure, increased bleeding risk, and discontinuation syndrome upon abrupt cessation. 1

Most Common Side Effects

The most frequently reported adverse effects occurring in ≥5% of patients and at least twice the rate of placebo include: 1

• Nausea (most common, occurring in up to 22% at higher doses) 1
• Dizziness (up to 13%) 1
• Insomnia (6-15% depending on dose) 1
• Hyperhidrosis/excessive sweating (4-21% depending on dose) 1
• Constipation 1
• Somnolence/drowsiness (4-12%) 1
• Decreased appetite 1
• Anxiety (2-5%) 1

Sexual Dysfunction

Sexual side effects are common and dose-dependent, occurring more frequently in men: 1

In men:

• Erectile dysfunction (1-11% depending on dose) 1
• Ejaculation delayed (1-7%) 1
• Decreased libido (1-6%) 1
• Anorgasmia (0-8%) 1
• Ejaculation disorder/failure (0-5%) 1

In women:

• Anorgasmia (0-3%) 1

Serious Side Effects Requiring Immediate Medical Attention

Serotonin Syndrome

A potentially life-threatening condition that requires emergency treatment, particularly when combined with other serotonergic medications: 1

Signs include: 1

• Agitation, confusion, hallucinations
• Fast heart rate, blood pressure changes
• High body temperature, sweating, flushing
• Tremors, stiff muscles, muscle twitching, loss of coordination
• Seizures
• Nausea, vomiting, diarrhea

Elevated Blood Pressure

Blood pressure increases were observed in clinical studies and require regular monitoring. 1 Cases of elevated blood pressure requiring immediate treatment have been reported, and sustained increases could have adverse cardiovascular consequences. 1

Increased Bleeding Risk

Pristiq increases bleeding risk, particularly when combined with aspirin, NSAIDs, or anticoagulants. 1 Bleeding events range from ecchymosis and epistaxis to life-threatening hemorrhages. 1

Discontinuation Syndrome

Abrupt cessation, particularly at higher doses, causes serious withdrawal symptoms: 1

Symptoms include: 1

• Dizziness, nausea, headache
• Irritability, agitation, anxiety
• Insomnia, abnormal dreams
• Electric shock sensations (paresthesia)
• Sweating, confusion
• Seizures (in severe cases)

Gradual dose reduction is mandatory when discontinuing. 1

Hyponatremia

Low sodium levels can occur, particularly in elderly patients and those taking diuretics. 1 Severe cases (sodium <110 mmol/L) have been reported. 1

Signs include: 1

• Headache, difficulty concentrating, memory impairment, confusion
• Weakness and unsteadiness leading to falls
• In severe cases: hallucinations, syncope, seizures, coma, respiratory arrest, death

Other Significant Adverse Effects

Angle-Closure Glaucoma

Pupillary dilation can trigger angle-closure glaucoma in susceptible patients. 1 Avoid use in patients with untreated anatomically narrow angles. 1

Seizures

Cases of seizures have been reported. 1 Use with caution in patients with seizure history. 1

Activation of Mania/Hypomania

Mania occurred in approximately 0.02% of patients in clinical trials. 1 Use cautiously in patients with personal or family history of bipolar disorder. 1

Interstitial Lung Disease

Rare cases of interstitial lung disease and eosinophilic pneumonia have been reported with venlafaxine (parent drug). 1 Patients presenting with progressive dyspnea, cough, or chest discomfort should undergo prompt evaluation and discontinuation should be considered. 1

Cardiovascular Effects

• Tachycardia 1
• Hot flushes (1-2%) 1
• Palpitations 1

Neurological Effects

• Tremor (2-9% depending on dose) 1
• Disturbance in attention (up to 2%) 1
• Vertigo (1-5%) 1
• Tinnitus (1-2%) 1

Sensory Effects

• Blurred vision (1-4%) 1
• Mydriasis/pupil dilation (up to 6%) 1
• Dysgeusia/taste disturbance (1-2%) 1

Urinary Effects

• Urinary hesitation (up to 2%) 1

Other Effects

• Yawning (1-4%) 1
• Abnormal dreams (1-4%) 1
• Nervousness (1-2%) 1

Important Clinical Considerations

The recommended dose is 50 mg daily, as doses above 100 mg show no additional therapeutic benefit but significantly increase adverse effects. 1, 2 At the 50 mg dose, the discontinuation rate due to adverse reactions (4.1%) was similar to placebo (3.8%), but increased to 8.7% at 100 mg. 1

Nausea is dose-dependent and the most common reason for discontinuation (4% of patients). 1 Other common reasons for discontinuation include dizziness, headache, and vomiting (2% each). 1

Desvenlafaxine has minimal CYP450 interactions compared to its parent drug venlafaxine, which may reduce drug-drug interaction risks. 3, 4, 5