The inability of tegaserod to affect platelet aggregation and coronary artery tone at supratherapeutic concentrations

Re-evaluation of the Cardiovascular Safety Profile of Tegaserod: A Review of the Clinical Data

BACKGROUND AND AIMS

Tegaserod is a 5-HT₄ receptor agonist approved for irritable bowel syndrome with constipation in women <65 years of age without a history of cardiovascular ischemic events. Safety data are presented from 2 external adjudications from the 2018 Gastrointestinal Drugs Advisory Committee meeting supporting tegaserod's reintroduction after its voluntary 2007 withdrawal. Withdrawal was based on an internal adjudication using pooled placebo-controlled tegaserod data to identify potential cardiovascular ischemic signals.

METHODS

An independent committee conducted an external adjudication to evaluate 24 possible cardiovascular ischemic events (tegaserod: n = 20; placebo: n = 4) identified internally. A second independent external adjudication further evaluated these events.

RESULTS

A total of 18,645 patients were included (tegaserod: n = 11,614; placebo: n = 7031). The first adjudication identified 14 (0.075%) events (tegaserod: n = 13 [0.11%]; placebo: n = 1 [0.014%]). All patients had ≥1 cardiovascular risk factor, and 11 had ≥2. The second adjudication identified 390 events, 24 (0.13%) were classified as probable new or worsening events (tegaserod: 18 [0.16%]; placebo: 6 [0.09%]). For tegaserod, 7 (0.06%) were coronary or cerebrovascular ischemic events compared with 1 (0.01%) for placebo (odds ratio, 4.24; 95% confidence interval, 0.52-34.74; P = .273). All tegaserod patients reporting cardiovascular events had ≥1 risk, including cardiovascular disease, hyperlipidemia, ≥55 years of age, hypertension, diabetes, obesity, and smoking. Women <65 years of age without a history of cardiovascular ischemic events and ≤1 cardiovascular risk factor receiving tegaserod experienced no major adverse cardiovascular event(s).

CONCLUSIONS

Two independent, external adjudications suggest that tegaserod is safe for women <65 years of age with irritable bowel syndrome with constipation, no history of cardiovascular ischemic events, and ≤1 cardiovascular risk factor.

Targeting the 5-HT system: Potential side effects

Targeting the serotonin (5-HT) system is no simple task: there are at least 15 5-HT receptors, in addition to a number of transporters and metabolizing enzymes. Multiple 5-HT receptor variants exist due to genetic variations and/or post translational modifications, splice variants or editing variants. Some receptors may form homo and heteromers. The 5-HT system is targeted by multiple drugs to treat a variety of diseases. Given the homology amongst the 5-HT and neighbouring receptor classes, only few drugs are actually selective for a single target. In fact, many 5-HT drugs act on a combination of targets, i.e. several receptors and/or transporters or enzymes. For instance, a number of antidepressants or antipsychotics act on 5-HT and other transmitter systems. Recently developed drugs may show target selectivity by design, based on the current state of knowledge, whereas many older compounds hit multiple targets since they were developed using phenotypic screens, as was done well into the 1980's. Ergot analogues, antipsychotics or antidepressants, fall into this category. As our knowledge developed over the last 25-30 years, some targets have very well-defined liabilities: for instance, 5HT_2B or 5-HT_2A receptor agonists, will produce valvulopathies or hallucinations, respectively, whereas 5-HT₃ receptor antagonists, may lead to constipation. This short review will be limited in scope as there are multiple targets and even more compounds to discuss. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

An Ex Vivo Study to Evaluate the Effect of Tegaserod on Platelet Activation and Aggregation

INTRODUCTION

Tegaserod, an orally active, potent 5-hydroxytryptamine-4 serotonin receptor agonist, was previously indicated for irritable bowel syndrome but was voluntarily withdrawn due to potential cardiovascular side effects. In vitro studies suggested that tegaserod increased platelet aggregation, but these results were not reproduced or were inconclusive. We sought to assess ex vivo effects of tegaserod on platelet aggregation.

METHODS

In this double-blind, placebo-controlled, crossover study, we randomized a majority of healthy patients with no history of cardiovascular risk factors (n = 21) to receive tegaserod or matching placebo for 7 + 2 days followed by a 7- to 10-day washout period, and then patients were crossed over to the other study drug for the next 7 + 2 days. Unstimulated and agonist-stimulated platelet aggregation; P-selectin expression; serum thromboxane (Tx)B₂ and urinary 11-dehydro (11-dh) TxB₂; and tegaserod and M29.0 concentrations were serially assessed.

RESULTS

There was no significant difference in percentage change in unstimulated or adenosine diphosphate (ADP)- and ADP + serotonin-, collagen- and thrombin receptor activating peptide-induced maximum platelet aggregation and in platelet P-selectin expression in the presence of tegaserod at any time point when compared to placebo. Similarly, there was no significant difference in percentage change in serum TxB₂ or urinary 11-dhTxB₂ levels between placebo and tegaserod. No new or unexpected findings were observed in evaluations of safety or pharmacokinetic parameters.

CONCLUSION

This comprehensive pharmacodynamic study, by employing established markers used in prior investigations, which have been considered by the Food and Drug Administration to indicate drug-related platelet effects, does not demonstrate any influence of tegaserod treatment on platelet function.

The in vitro pharmacology and non-clinical cardiovascular safety studies of a novel 5-HT4 receptor agonist, DSP-6952

The pharmacological activity of DSP-6952, a novel compound was investigated, compared to that of clinically efficacious gastrointestinal (GI) prokinetic 5-hydroxytryptamine₄ (5-HT₄) receptor agonists. DSP-6952 had a strong affinity of Ki = 51.9 nM for 5-HT_4(b) receptor, and produced contraction in the isolated guinea pig colon with EC₅₀ of 271.6 nM and low intrinsic activity of 57%, similar to tegaserod and mosapride. In the development of the 5-HT₄ receptor agonists, cardiovascular risk was deliberately evaluated, because some related prokinetics were reported to cause with cardiovascular adverse events, such as ventricular arrhythmias or ischemia. DSP-6952 showed minimal effects up to 100 μM in human ether-a-go-go-related gene (hERG) channels or guinea pig cardiomyocytes. In telemetered conscious monkeys, DSP-6952 did not affect blood pressure or any electrocardiogram (ECG) up to 180 mg/kg, p.o.; however, DSP-6952 transiently increased heart rate, as well as in anesthetized dogs. The positive chronotropic effects of DSP-6952 were completely antagonized by a 5-HT₄ receptor antagonist, and another 5-HT₄ receptor agonist, TD-5108 also increased heart rate. These effects are considered a class effect seen in clinically developing and marketed 5-HT₄ receptor agonists, and have not been regarded as a critical issue in clinical use. DSP-6952 did not induce contraction in the rabbit coronary artery up to 100 μM, which differed from tegaserod or sumatriptan. These results show that DSP-6952 does not have cardiac ischemic risk via coronary vasoconstriction. In conclusion, DSP-6952 is a promising GI prokinetic compound with partial 5-HT₄ receptor agonistic activity as well as a favorable cardiovascular safety profile.

An update on prucalopride in the treatment of chronic constipation

Chronic constipation (CC) is a highly prevalent and often under-appreciated gastrointestinal disorder associated with significant impairment in quality of life. Symptoms of constipation are typically present for a number of years prior to a patient seeking help. Lifestyle modifications followed by, or coupled with, over-the-counter laxatives represent the initial treatment option; however, relief for many is limited and dissatisfaction rates for these approaches remain high. Over recent years, therefore, considerable effort has been exerted on the development of novel pharmacological approaches. Two major targets have emerged, motility and secretion. Research on the former led to the development of a number of prokinetic agents capable of stimulating colonic motility and, thus, accelerating colonic transit. Of these, earlier prototypes such as cisapride and tegaserod, though effective, were ultimately withdrawn due to cardiovascular adverse events due in part to receptor non-selectivity. Highly selective serotonergic receptor agonists have since emerged which appear to be equally effective in stimulating gut motility but are devoid of cardiac side effects. One such agent is prucalopride, which has now been approved for the management of chronic idiopathic constipation in several countries, but not in the United States. Multiple multicenter, randomized placebo-controlled clinical trials have demonstrated superiority for prucalopride compared to placebo in the short to medium term in relieving the major symptoms of constipation in both men and women across a broad spectrum of ages, ethnicities and geographic locations. To date, prucalopride has enjoyed a favorable safety profile and there have been no signals to suggest arrythmogenicity. Efficacy over longer periods of treatment remains to be confirmed. Evidence for efficacy in other forms of constipation, such as opioid-induced constipation and that related to Parkinson's disease is beginning to emerge; its status in the management of constipation-predominant irritable bowel syndrome or foregut motility disorders, such as gastroparesis, remains to be established.

Ischemic Colitis as a Complication of Medication Use: An Analysis of the Federal Adverse Event Reporting System

BACKGROUND

More than one decade ago, rising cases of ischemic colitis (IC) prompted the Federal Drug Administration to revoke alosetron's approval as treatment of irritable bowel syndrome (IBS). The aim of this study was to identify medical therapies associated with development of IC.

METHODS

The Federal Adverse Event Reporting System was queried for the time between January 2004 and September 2015. We identified reports listing IC as treatment complication and extracted suspected causative and concomitantly administered drugs, indications for their use and outcomes.

RESULTS

After eliminating duplicates, we found 2811 cases of IC (68.4 % women; 59.4 ± 0.4 years). Patients with IBS accounted for 3.9 % of the cases, mostly attributed to tegaserod or alosetron. Chemotherapeutic and immunosuppressive drugs, sex hormones, and anticoagulants were the most commonly suspected causes. Bisphosphonates, nonsteroidal anti-inflammatory drugs, antipsychotics, triptans, interferon therapy, and laxative use prior to colonoscopy were among the more commonly listed treatments. In 8 %, the adverse event contributed to the patient's death with male sex and older age predicting fatal outcomes.

CONCLUSION

Beyond confirming known risks of IC, the results identified several potential culprits of ischemic colitis. This information may not only explain the development of this serious adverse event, but could also guide treatment decisions, cautioning healthcare providers when considering these agents in persons with known risk factors or other drugs that may increase their risk of IC.

An in vitro investigation of the cardiovascular effects of the 5-HT(4) receptor selective agonists, velusetrag and TD-8954

The 5-HT(4) receptor agonists, and gastrointestinal (GI) prokinetic agents, cisapride and tegaserod, lack selectivity for the 5-HT(4) receptor. Cisapride is a potent human ether-à-go-go-related gene (hERG) potassium channel inhibitor while cisapride and tegaserod have significant affinity for 5-HT(1) and 5-HT(2) receptor subtypes. Marketing of both compounds was discontinued due to cardiovascular concerns (cardiac arrhythmias with cisapride and ischemic events with tegaserod). The reported association of tegaserod with ischemia has been postulated to involve coronary artery constriction or augmentation of platelet aggregation. This in vitro study investigated the effects of two of the new generation of highly selective 5-HT(4) receptor agonists, velusetrag and TD-8954, on canine, porcine and human coronary artery tone, human platelet aggregation and hERG potassium channel conductance. No significant off-target actions of velusetrag or TD-8954 were identified in these, and prior, studies. While cisapride inhibited potently the hERG channel currents, tegaserod failed to affect platelet aggregation, and had only a small contractile effect on the canine coronary artery at high concentrations. Tegaserod inhibited the 5-HT-induced contractile response in the porcine coronary artery. New generation 5-HT(4) receptor agonists hold promise for the treatment of patients suffering from GI motility disorders with a reduced cardiovascular risk.

The role of pharmacogenetics in nonmalignant gastrointestinal diseases

Genetic variation influences the absorption and efflux of drugs in the intestine, the metabolism of drugs in the liver and the effects of these drugs on their target proteins. Indeed, variations in genes whose products have a role in the pathophysiology of nonmalignant gastrointestinal diseases, such as IBD, have been shown to affect the response of patients to therapy. This Review provides an overview of pharmacogenetics in the management of nonmalignant gastrointestinal diseases on the basis of data from clinical trials. Genetic variants that have the greatest effect on the management of patients with IBD involve the metabolism of thiopurines. Variation in drug metabolism by cytochrome P450 enzymes also requires attention so as to avoid drug interactions in patients receiving tricyclic antidepressants and PPIs. Few genotyping tests are currently used in the clinical management of patients with nonmalignant gastrointestinal diseases, owing to a lack of data from clinical trials showing their effectiveness in predicting nonresponse or adverse outcomes. However, pharmacogenetics could have a beneficial role in enabling pharmacotherapy for nonmalignant gastrointestinal diseases to be targeted to the individual patient.