From the FDA Drug Label
In all US Prozac clinical trials as of May 8,1995,0. 7% of 10,782 patients reported mania/hypomania (see also Pediatric Use under PRECAUTIONS). Hyponatremia — Hyponatremia may occur as a result of treatment with SSRIs and SNRIs, including Prozac. In many cases, this hyponatremia appears to be the result of the syndrome of inappropriate antidiuretic hormone secretion (SIADH) Cases with serum sodium lower than 110 mmol/L have been reported and appeared to be reversible when Prozac was discontinued. Elderly patients may be at greater risk of developing hyponatremia with SSRIs and SNRIs. Also, patients taking diuretics or who are otherwise volume depleted may be at greater risk (see Geriatric Use) Discontinuation of Prozac should be considered in patients with symptomatic hyponatremia and appropriate medical intervention should be instituted. Signs and symptoms of hyponatremia include headache, difficulty concentrating, memory impairment, confusion, weakness, and unsteadiness, which may lead to falls More severe and/or acute cases have been associated with hallucination, syncope, seizure, coma, respiratory arrest, and death.
Among 633 adult patients who overdosed on fluoxetine hydrochloride alone, 34 resulted in a fatal outcome, 378 completely recovered, and 15 patients experienced sequelae after overdosage, including abnormal accommodation, abnormal gait, confusion, unresponsiveness, nervousness, pulmonary dysfunction, vertigo, tremor, elevated blood pressure, impotence, movement disorder, and hypomania The remaining 206 patients had an unknown outcome. The most common signs and symptoms associated with non–fatal overdosage were seizures, somnolence, nausea, tachycardia, and vomiting. Other important adverse events reported with fluoxetine overdose (single or multiple drugs) include coma, delirium, ECG abnormalities (such as QT interval prolongation and ventricular tachycardia, including torsades de pointes–type arrhythmias), hypotension, mania, neuroleptic malignant syndrome–like events, pyrexia, stupor, and syncope
Presyncope is not explicitly mentioned in the provided drug labels. However, syncope is mentioned as a possible adverse event associated with hyponatremia and overdose. Since presyncope is a feeling of lightheadedness or a sensation of almost passing out, which may be a precursor to syncope, and syncope is a reported adverse event, it is possible that presyncope could occur. However, the FDA drug label does not directly answer the question regarding presyncope. Therefore, a conservative clinical decision would be to monitor patients for signs and symptoms of presyncope, especially in patients at risk of hyponatremia or those who have overdosed on fluoxetine. 1 1
From the Research
Presyncope and Prozac (Fluoxetine)
- Presyncope, a feeling of lightheadedness or faintness, can be a concern for individuals taking Prozac (Fluoxetine) as there is evidence suggesting a potential link between the two 2, 3, 4, 5, 6.
- A study published in 2006 found that Fluoxetine may be more effective in reducing presyncopes and total vasovagal events in some patients with recurrent vasovagal syncope (VVS) 2.
- Another study from 2017 reported that Fluoxetine exerted beneficial effects regarding VVS prevention in patients with anxiety sensitivity, with a significant difference observed between patients receiving Fluoxetine and those with placebo regarding presyncopal events 5.
- However, there are also reports of Fluoxetine-induced bradycardia and syncope, suggesting a potential direct central nervous system effect of increased serotonin on medullary cardiovascular regulation 3, 4.
- A review of cardiovascular effects of Fluoxetine published in 1998 noted that while the drug may cause fewer anticholinergic, antihistaminergic, and cardiotoxic side effects compared to tricyclic antidepressants, there is still a risk of dysrhythmia, bradycardia, and syncope associated with Fluoxetine treatment and overdose 6.
Key Findings
- Fluoxetine may reduce presyncopes and total vasovagal events in patients with recurrent VVS 2, 5.
- Fluoxetine can cause bradycardia and syncope in some individuals, potentially due to a direct central nervous system effect 3, 4.
- The drug has a lower incidence of cardiovascular complications compared to tricyclic antidepressants, but still carries a risk of dysrhythmia, bradycardia, and syncope 6.