Tegaserod

Tegaserod is a selective serotonin 5-HT₄ receptor agonist used for the treatment of irritable bowel syndrome with constipation (IBS-C). It enhances gastrointestinal motility and secretion by stimulating 5-HT₄ receptors in the gastrointestinal tract, promoting peristalsis, intestinal secretion, and esophageal relaxation.

Tegaserod is indicated for the treatment of IBS-C in selected adult women who are at low cardiovascular risk. Due to the potential risk of cardiovascular adverse events, its use is restricted to appropriate patients after careful risk assessment.

Tegaserod is a serotonin-4 (5-HT4) receptor agonist indicated for the treatment of constipation predominant irritable bowel syndrome (IBS-C) specifically in women under the age of 65. There is currently no safety or efficacy data for use of tegaserol in men.

Tegaserod is a serotonin-4 (5-HT4) receptor agonist indicated for the treatment of adult women less than 65 years of age with irritable bowel syndrome with constipation (IBS-C) . The safety and effectiveness of tegaserod in men with IBS-C have not been established .

• Constipation-predominant Irritable Bowel Syndrome (IBS-C)

In general, it has been determined that tegaserod is an agonist of serotonin type-4 (5-HT(4)) receptors, an antagonist at 5-HT(2B) receptors, but is expected to possess minimal binding to 5-HT(1) receptors, and virtually no affinity for 5-HT(3) or dopamine receptors .

In clinical trials with tegaserod, centrally analyzed ECGs were recorded in 4,605 male and female patients receiving tegaserod 6 mg twice daily or placebo for IBS-C and other related motility disorders . No subject receiving the agent had an absolute QTcF above 480 ms . An increase in QTcF of 30 to 60 ms was observed in 7% of patients receiving tegaserod and 8% receiving placebo . An increase in QTcF of greater than 60 ms was observed in 0.3% and 0.2% of subjects, respectively . The effects of tegaserod on the QTcF interval were ultimately not considered to be clinically meaningful .

Furthermore, it was determined that there is a potential for tegaserod and its main metabolite (the M29 metabolite) to increase platelet aggregation in vitro . In one in vitro study, at concentrations up to 10-times the maximum plasma concentration (Cmax) at the recommended dose, tegaserod significantly increased platelet aggregation in a concentration-dependent manner up to 74% (range 11% to 74%) compared to a control vehicle (with potentiation by various agonists) . In another in vitro study, the M29 metabolite, at concentrations up to 0.6-times the Cmax of M29 also showed a 5% to 16% increase in platelet aggregation compared to the control vehicle . The clinical implications of these in vitro platelet aggregation results remain unclear .

Irritable bowel syndrome (IBS) is a complex functional disorder comprised of various abnormal and discomforting effects on the gastrointestinal tract and bowel function . Although the cause of IBS has yet to be formally elucidated, patient experience has demonstrated that the disorder is typically associated with abdominal pain, abdominal distension, cramping or bloating, variations in urgency for bowel movements, feelings of incomplete evacuation, gastroesophageal reflux, and various other effects . In particular, IBS that features constipation as a predominant effect is categorized as constipation-predominant IBS, or IBS-C .

Concurrently, 5-Hydroxytryptamine (5-HT, or serotonin) has demonstrated the ability to elicit significant regulatory actions on gastrointestinal motility . Specifically, it has been shown that the activation of 5-HT(4) receptors located on motor neurons and interneurons in the gastrointestinal wall can cause the release of acetylcholine, substance P, and calcitonin gene-related peptide that can all facilitate the propulsion of material through the gut . Moreover, when 5-HT(4) receptors located in smooth muscle cells are also activated, activities that may alleviate symptoms of IBS-C like esophageal relaxation and the inhibition of human colonic circular muscle contraction can also occur . Additionally, activating 5-HT(4) on enteric neurons and enterocytes also cause natural fluid secretion in the gut - an action which also strongly assists in promoting the movement of content along the gastrointestinal tract .

Alternatively, it has also been observed that 5-HT may participate in generating visceral hyperalgesia in IBS, an observation supported in part by the finding of increased amounts of 5-HT and its metabolites in the plasma of patients experiencing IBS It has therefore also been proposed that antagonism of 5-HT(2B) receptors can lead to inhibition of both 5-HT mediated gastrointestinal motility and visceral hypersensitivity .

Subsequently, because tegaserod is considered to be an agonist of the 5-HT(4) receptor and an antagonist of the 5-HT(2B) receptor at clinically relevant levels, it is believed that tegaserod may elicit its mechanism of action by facilitating activities associated with the activation and antagonism of the 5-HT(4) and 5-HT(2B) receptors, like stimulating peristaltic gastrointestinal reflexes and intestinal secretion, inhibiting visceral sensitivity, enhancing basal motor activity, and normalizing impaired motility throughout the gastrointestinal tract, among other actions .

The absolute bioavailability of tegaserod is approximately 10% when administered to fasting subjects. The median time of peak tegaserod plasma concentration (Tmax) is approximately one hour (range 0.7 to 2 hours) .

Nevertheless, when tegaserod was given to individuals thirty minutes before a meal of high-fat and high-calorie content (about 150 calories from protein, 250 calories from carbohydrates, and 500 calories from fat), the AUC was reduced by 40% to 65%, the Cmax was reduced by approximately 20% to 40%, and the median Tmax was 0.7 hours . Additionally, plasma concentrations were similar when tegaserod was administered within thirty minutes before a meal or even two and a half hours after a meal .

Although tegaserod is not approved for intravenous administration, data regarding the mean volume of distribution of tegaserod at steady-state is recorded as 368 ± 223 L following research of tegaserod administered intravenously .

The protein binding recorded for tegaserod is about 98% .

Approximately two-thirds of an orally administered dose of tegaserod is excreted unchanged in the feces, with the remaining one-third excreted in the urine as metabolites .

The mean terminal elimination half-life documented for tegaserod ranges from 4.6 to 8.1 hours following oral administration .

Although tegaserod is not approved for intravenous administration, data regarding the mean plasma clearance of tegaserod is documented as 77 ± 15 L/h following research of tegaserod administered intravenously .

Single oral doses of 120 mg (which is 20 times the recommended dose) of tegaserod were administered to three healthy subjects in one study . All three subjects developed diarrhea and headache. Two of these subjects also reported intermittent abdominal pain and one developed orthostatic hypotension . In 28 healthy subjects exposed to 90 to 180 mg per day of tegaserod (which is 7.5 to 15 times the recommended daily dosage) for several days, adverse reactions were diarrhea (100%), headache (57%), abdominal pain (18%), flatulence (18%), nausea (7%), and vomiting (7%) .

Although available data from case reports with tegaserod use in pregnant women have not identified a drug-associated risk of major birth defects, miscarriage, or adverse maternal or fetal outcomes, animal studies involving maternal dietary administration of tegaserod with doses 45 to 71 times the recommended dose demonstrated decreased body weight, delays in developmental landmarks, and decreased survival in rat pups . Caution and careful consideration of risks versus benefits are recommended before administering tegaserod to a pregnant woman.

Despite there being little if any data available regarding the presence of tegaserod in human milk, the effects on the breastfed infant, or the effects on milk production, tegaserod and its metabolites are present in rat milk and the milk to plasma concentration ratio is very high in rats . Subsequently, because of the potential for serious reactions in the breastfed infant, including tumorigenicity, breastfeeding is not recommended during treatment with tegaserod .

The safety and effectiveness of tegaserod in pediatric patients has not yet been established .

Tegaserod is not indicated in patients that are aged 65 years or older .

Tegaserod was not carcinogenic in rats given oral dietary doses up to 180 mg/kg/day (approximately 93 to 111 times the recommended dose based on AUC) for 110 to 124 weeks . In mice, dietary administration of tegaserod for 104 weeks produced mucosal hyperplasia and adenocarcinoma of the small intestine at 600 mg/kg/day (approximately 83 to 110 times the recommended dose based on AUC) . There was no evidence of carcinogenicity at lower doses (3 to 35 times the recommended dose based on AUC) . Tegaserod was not genotoxic in the in vitro Chinese hamster lung fibroblast (CHL/V79) cell chromosomal aberration and forward mutation test, the in vitro rat hepatocyte unscheduled DNA synthesis (UDS) test or the in vivo mouse micronucleus test . The results of the Ames test for mutagenicity were equivocal. Tegaserod at oral (dietary) doses up to 240 mg/kg/day (approximately 57 times the recommended dose based on AUC) in male rats and 150 mg/kg/day (approximately 42 times the recommended dose based on AUC) in female rats was found to have no effect on fertility and reproductive performance .

Inhibition of the hERG (human Ether-a-go-go-Related Gene) channel was evident only in the micromolar concentration range with an IC50 of 13 micromolar (approximately 1300 times the Cmax in humans at the recommended dose) . In in vitro studies, tegaserod had no effects on impulse conduction in isolated guinea pig papillary muscle at up to 100 times the Cmax in humans, Langendorff-perfused isolated rabbit heart (QT interval) at up to 1000 times the Cmax in humans, or human atrial myocytes at multiples up to 10 times the Cmax in humans . The major metabolite, M29, had no effect on QT in the Langendorff-perfused isolated rabbit heart at multiples up to 323 times the Cmax in humans .

In anesthetized and conscious dogs, tegaserod at doses up to 92 to 134 times the recommended dose based on Cmax did not alter heart rate, QRS interval duration, QTc or other ECG parameters . In chronic toxicology studies in rats and dogs, there were no treatment-related changes in cardiac morphology after tegaserod administration at doses up to 660 times the recommended dose based on AUC .

Although tegaserod is expected to bind to 5-HT2B receptors in humans at the recommended dose, there does not appear to be any potential for heart valve injury based on functional evidence of 5-HT2B receptor antagonism .

Studies with isolated coronary and mesenteric blood vessels from non-human primates and humans showed no vasoconstrictor effect at concentrations approximately 100 times the human Cmax . Tegaserod exhibited antagonism of 5-HT-mediated vasoconstriction via 5-HT1B receptors . In rat thoracic aortic rings that were pre-constricted with phenylephrine or norepinephrine, tegaserod produced vasorelaxation, with IC50 values 6 and 64 times the Cmax plasma concentrations in humans, respectively . No effects were observed in the basal tone of aortic rings at concentrations up to 1000 times the human Cmax .

In studies with an anesthetized rat model for measuring macro- and micro-circulation of the colon, intraduodenal dosing with tegaserod (approximately 7 times the recommended dose based on Cmax) produced no clinically relevant effect on blood pressure, heart rate, or vascular conductance .

• Take before a meal. To increase absorption, take 30 minutes before a meal.