Hypothesis: antiplatelet effects of selective serotonin reuptake inhibitors cause clinical benefits on cardiovascular disease and increase risks of bleeding

Citalopram inhibits platelet function independently of SERT-mediated 5-HT transport

Citalopram prevents serotonin (5-HT) uptake into platelets by blocking the serotonin reuptake transporter (SERT). Although some clinical data suggest that selective serotonin reuptake inhibitors (SSRIs) may affect haemostasis and thrombosis, these poorly-characterised effects are not well understood mechanistically and useful in vitro data is limited. We sought to determine whether the inhibitory effects of citalopram on platelets are mediated via its pharmacological inhibition of 5-HT transport. We quantified the inhibitory potency of (RS)-, (R)- and (S)-citalopram on platelet function. If SERT blockade is the primary mechanism for citalopram-mediated platelet inhibition, these potencies should show quantitative congruence with inhibition of 5-HT uptake. Our data show that citalopram inhibits platelet aggregation, adhesion and thromboxane production with no difference in potency between (R)- and (S)-isomers. By contrast, citalopram had a eudysmic ratio of approximately 17 (S > R) for SERT blockade. Furthermore, nanomolar concentrations of citalopram inhibited 5-HT uptake into platelets but had no effect on other platelet functions, which were inhibited by micromolar concentrations. Our data indicate that citalopram-induced inhibition of platelets in vitro is not mediated by blockade of 5-HT transport. This raises a new question for future investigation: by what mechanism(s) does citalopram inhibit platelets?

Risk of Bleeding in Patients on Full-Dose Enoxaparin With Venous Thromboembolism and Selective Serotonin Reuptake Inhibitors

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are very commonly prescribed agents that are also potent antiplatelet agents.

OBJECTIVE

This study was designed compare the rate of major bleeding events between patients who were treated with low-molecular-weight heparin (LMWH) for venous thromboembolism (VTE) on SSRIs and those not on chronic SSRI therapy.

METHODS

This was a retrospective cohort study of 575 patients with a primary or secondary diagnosis of an acute VTE initiated on full-dose enoxaparin with or without an SSRI between October 1, 2009, and October 1, 2014, in a 443-bed, single tertiary care referral county teaching hospital.

RESULTS

No significant difference was found in the incidence of major bleeding in the SSRI versus non-SSRI group (19.6% vs 17.0%, P = 0.548). Ad hoc analysis demonstrated an elevated risk of major bleeding in patients on escitalopram compared with those on any of the other SSRIs (46.2% vs 15.2%, P = 0.018). Multivariate analysis demonstrated that escitalopram use-OR (95% CI) = 18.85 (1.84-193.6)-was associated with increased major bleeding, and acid suppressive therapy-0.24 (0.07-0.90); P = 0.014-was associated with decreased major bleeding in patients reporting alcohol use.

CONCLUSION

No difference was found in the incidence of major bleeding in patients on LMWH and SSRIs versus those on LMWH but not on SSRIs. However, ad hoc findings showed a significantly higher rate of major bleeding events in patients who received escitalopram and alcohol among patients on full-dose enoxaparin for VTE. These findings merit further exploration.

Incident user cohort study of risk for gastrointestinal bleed and stroke in individuals with major depressive disorder treated with antidepressants

OBJECTIVE

To examine the association between exposure to newer antidepressants and risk of gastrointestinal (GI) and other bleeding complications among individuals with major depressive disorder (MDD).

DESIGN

This study uses an incident user cohort design to compare associations between incidence of vascular/bleeding events and the relative affinity (low, moderate or high) of the antidepressant for the serotonin transporter during an exposure risk period for each patient.

SETTING

New England healthcare system electronic medical record database.

PARTICIPANTS

36 389 individuals with a diagnosis of MDD and monotherapy with a selective serotonin reuptake inhibitor, serotonin-norepinephrine reuptake inhibitor or other new-generation antidepressant were identified from among 3.1 million patients in a New England healthcare system.

PRIMARY AND SECONDARY OUTCOME MEASURES

Rates of bleeding or other vascular complications, including acute liver failure, acute renal failure, asthma, breast cancer and hip fractures.

RESULTS

601 GI bleeds were observed in the 21 462 subjects in the high-affinity group versus 333 among the 14 927 subjects in the lower affinity group (adjusted RR: 1.17, 95% CI 1.02 to 1.34). Similarly, 776 strokes were observed in the high-affinity group versus 434 in the lower affinity treatment group (adjusted RR: 1.18, 95% CI 1.06 to 1.32). No significant association with risk for a priori negative control outcomes, including acute liver failure, acute renal failure, asthma, breast cancer and hip fractures, was identified.

CONCLUSIONS

Use of antidepressants with high affinity for the serotonin transporter may confer modestly elevated risk for GI and other bleeding complications. While multiple methodologic limitations must be considered, these results suggest that antidepressants with lower serotonin receptor affinity may be preferred in patients at greater risk for such complications.

Effects of selective serotonin reuptake inhibitors on platelet function: mechanisms, clinical outcomes and implications for use in elderly patients

Among the antidepressants, the selective serotonin reuptake inhibitors (SSRIs) are often preferred to other classes of antidepressants in the treatment of depression in the elderly because of their better safety profile. Most of the known effects of SSRIs, either beneficial or adverse, are linked to their inhibitory action on the serotonin reuptake transporter (5-HTT). This reuptake mechanism is present not only in neurons but also in other cells such as platelets. Serotoninergic mechanisms seem to play an important role in haemostasis, and their importance in this regard has long been underestimated. Abnormal activation may lead to a pro-thrombotic state, as may occur in patients with major depressive disorder, whilst downregulation, as occurs in patients treated with SSRIs, may have two clinical consequences, both of particular interest in the elderly. On the one hand, there may be an increased risk of bleeding; on the other hand, a reduction in thrombotic risk may be possible. Polymorphism in the promoter region of the gene that transcribes the 5-HTT has been shown to have a relevant impact on its function and, in turn, on the beneficial and adverse effects of SSRIs. Bleeding has been a concern since the introduction of SSRIs, with multiple case reports published and communicated to the pharmacovigilance systems. The first epidemiological study was published in 1999 and since then, 34 epidemiological studies from different areas, most of them including elderly patients in their study populations, have been published with a variety of results. Broadly, the epidemiological evidence supports a moderately increased risk of bleeding associated with the use of SSRIs, which may be critically dependent on patient susceptibility and the presence of risk factors. The impairment of primary haemostasis induced by SSRIs may result, as a beneficial counterpart, in a reduction in the thrombotic risk. A small number of clinical trials and an increasing number of epidemiological studies that include elderly patients have been conducted to clarify whether SSRIs reduce the risk of primary and secondary ischaemic disorders. However, the results have been inconclusive with some studies suggesting a preventive effect and others no effect or even an increased risk. Behind such contradictory results may be the role of depression itself as a cardiovascular risk factor and, therefore, a major confounding factor. How to disentangle its effect from that of the antidepressants is the methodological challenge to be overcome in future studies. In this complex scenario, the elderly seem to be at a crossroads, because they are the group in which both the risks and the benefits can be the greatest. Studies performed to date have provided us with some clues that can help orient clinicians in taking the most appropriate course of action. For instance, as the gastrointestinal bleeding risk appears to increase with age, prudent advice in patients with a previous history of upper-gastrointestinal bleeding or peptic ulcer, and in those who take NSAIDs, oral anticoagulants, antiplatelet drugs or corticosteroids, would be to suggest addition of an acid-suppressing agent to the drug regimen in those elderly patients in whom SSRIs are indicated.

Clinical impact of selective serotonin reuptake inhibitors therapy with bleeding risks

The selective serotonin reuptake inhibitors (SSRIs) are extensively used for the treatment of multiple psychiatric conditions. In vitro and ex vivo data with these agents indicate they may have varying degrees of antiplatelet activity via multiple receptors. Reports of bleeding in patients receiving SSRIs appeared soon after their introduction. A review of the literature suggests SSRI therapy may increase the risk of bleeding especially with concomitant aspirin or nonsteroidal anti-inflammatory agents. Clinicians should exercise caution when prescribing these agents in high risk patients and maintain awareness of the potential contribution of SSRIs to unexplained bleeding episodes.