ESOMEPRAZOLE.

Esomeprazole is described chemically as 6-methoxy-2-[(S)-(4-methoxy-3,5-dimethylpyridin-2-yl) methylsulfinyl]-1H-benzimidazole. The empirical formula is C17H19N3O3S and the molecular weight is 345.4.

 The structural formula is:

ESGIFIX is available as an Enteric coated tablet for oral administration containing the equivalent of 40 mg Esomeprazole as Esomeprazole Magnesium Trihydrate

Mechanism of Action

Esomeprazole is a proton pump inhibitor that suppresses gastric acid secretion by specific inhibition of the H+/K+-ATPase in the gastric parietal cell. The S- and R-isomers of omeprazole are protonated and converted in the acidic compartment of the parietal cell forming the active inhibitor, the achiral sulphonamide. By acting specifically on the proton pump, esomeprazole blocks the final step in acid production, thus reducing gastric acidity. This effect is dose-related up to a daily dose of 20 to 40 mg and leads to inhibition of gastric acid secretion.

 Pharmacodynamics

Esomeprazole is a compound that inhibits gastric acid secretion and is indicated in the treatment of gastroesophageal reflux disease (GERD), the healing of erosive esophagitis, and H. pylori eradication to reduce the risk of duodenal ulcer recurrence. Esomeprazole belongs to a new class of antisecretory compounds, the substituted benzimidazoles, that do not exhibit anticholinergic or H2 histamine antagonistic properties, but that suppress gastric acid secretion by specific inhibition of the H⁺/K⁺ ATPase at the secretory surface of the gastric parietal cell. By doing so, it inhibits acid secretion into the gsatric lumen. This effect is dose-related and leads to inhibition of both basal and stimulated acid secretion irrespective of the stimulus. Esomeprazole is the s-isomer of [DB00338], which is a racemate of the S- and R-enantiomer. Esomeprazole has been shown to inhibit acid secretion to a similar extent as [DB00338], without any significant differences between the two compounds _in vitro_. PPIs such as esomeprazole have also been shown to inhibit the activity of dimethylarginine dimethylaminohydrolase (DDAH), an enzyme necessary for cardiovascular health. DDAH inhibition causes a consequent accumulation of the nitric oxide synthase inhibitor asymmetric dimethylarginie (ADMA), which is thought to cause the association of PPIs with increased risk of cardiovascular events in patients with unstable coronary syndromes. Due to their good safety profile and as several PPIs are available over the counter without a prescription, their current use in North America is widespread. Long term use of PPIs such as esomeprazole has been associated with possible adverse effects, however, including increased susceptibility to bacterial infections (including gastrointestinal _C. difficile_), reduced absorption of micronutrients including iron and B12, and an increased risk of developing hypomagnesemia and hypocalcemia which may contribute to osteoporosis and bone fractures later in life.

 Pharmacokinetics

Absorption

After oral administration, peak plasma levels (Cmax) occur at approximately 1.5 hours (Tmax). The Cmax increases proportionally when the dose is increased, and there is a three-fold increase in the area under the plasma concentration-time curve (AUC) from 20 to 40 mg. At repeated once-daily dosing with 40 mg, the systemic bioavailability is approximately 90% compared to 64% after a single dose of 40 mg. The mean exposure (AUC) to esomeprazole increases from 4.32 μmol*hr/L on Day 1 to 11.2 μmol*hr/L on Day 5 after 40 mg once daily dosing. The AUC after administration of a single 40 mg dose of Esomeprazole is decreased by 43% to 53% after food intake compared to fasting conditions. Esomeprazole should be taken at least one hour before meals. _Combination Therapy with Antimicrobials:_ Esomeprazole magnesium 40 mg once daily was given in combination with [DB01211] 500 mg twice daily and [DB01060] 1000 mg twice daily for 7 days to 17 healthy male and female subjects. The mean steady state AUC and Cmax of esomeprazole increased by 70% and 18%, respectively during triple combination therapy compared to treatment with esomeprazole alone. The observed increase in esomeprazole exposure during co-administration with clarithromycin and amoxicillin is not expected to produce significant safety concerns.

Metabolism

Esomeprazole is extensively metabolized in the liver by the cytochrome P450 (CYP) enzyme system. The metabolites of esomeprazole lack antisecretory activity. The major part of esomeprazole's metabolism is dependent upon the CYP 2C19 isoenzyme, which forms the hydroxy and desmethyl metabolites. The remaining amount is dependent on CYP 3A4 which forms the sulphone metabolite. CYP 2C19 isoenzyme exhibits polymorphism in the metabolism of esomeprazole, since some 3% of Caucasians and 15 to 20% of Asians lack CYP 2C19 and are termed Poor Metabolizers. At steady state, the ratio of AUC in Poor Metabolizers to AUC in the rest of the population (Extensive Metabolizers) is approximately 2. Following administration of equimolar doses, the S- and R-isomers are metabolized differently by the liver, resulting in higher plasma levels of the S- than of the R-isomer.

Elimination

The plasma elimination half-life of esomeprazole is approximately 1 to 1.5 hours. Less than 1% of parent drug is excreted in the urine. Approximately 80% of an oral dose of esomeprazole is excreted as inactive metabolites in the urine, and the remainder is found as inactive metabolites in the feces.

Drug Interactions

 It is unknown whether esomeprazole is distributed into milk. However, omeprazole is distributed into human milk; discontinue nursing or drug because of potential risk in nursing infants.

FDA Pregnancy Category: B /NO EVIDENCE OF RISK IN HUMANS. Adequate, well controlled studies in pregnant women have not shown increased risk of fetal abnormalities despite adverse findings in animals, or, in the absents of adequate human studies, animal studies show no fetal risk. The chance of fetal harm is remote but remains a possibility

When esomeprazole is used in fixed combination with naproxen, the usual cautions, precautions, and contraindications associated with naproxen must be considered in addition to those associated with esomeprazole.

Administration of proton-pump inhibitors has been associated with an increased risk for developing certain infections (e.g., community-acquired pneumonia).

 PRESCRIBING INFORMATION

INDICATIONS AND USAGE

Esomeprazole is indicated for the treatment of acid-reflux disorders including healing and maintenance of erosive esophagitis, and symptomatic gastroesophageal reflux disease (GERD), peptic ulcer disease, H. pylori eradication, prevention of gastrointestinal bleeds with NSAID use, and for the long-term treatment of pathological hypersecretory conditions including Zollinger-Ellison Syndrome.

DOSAGE AND ADMINISTRATION

Recommended Dosing

As directed by physician

CONTRAINDICATIONS

• Hypersensitivity to the active component, other proton pump inhibitors (PPIs), substituted benzimidazoles or any other ingredient of the formulation
• Use with rilpivirine-containing products (IV formulations)

For the treatment of H pylori (as combination therapy): Refer to the contraindications section of the other antibacterial agents for further information.

Safety and efficacy have not been established in patients younger than 1 month (esomeprazole magnesium prescription formulations and esomeprazole sodium) and 18 years (esomeprazole magnesium OTC tablets and esomeprazole strontium).

ADVERSE REACTIONS

Common side effects include headache, diarrhea, nausea, flatulence, decreased appetite, constipation, dry mouth, and abdominal pain. More severe side effects are severe allergic reactions, chest pain, dark urine, fast heartbeat, fever, paresthesia, persistent sore throat, severe stomach pain, unusual bruising or bleeding, unusual tiredness, and yellowing of the eyes or skin.^[24]

Proton pump inhibitors may be associated with a greater risk of hip fractures^[25] and Clostridium difficile-associated diarrhoea.^[26] Patients are frequently administered the drugs in intensive care as a protective measure against ulcers, but this use is also associated with a 30% increase in occurrence of pneumonia.^[27]

Long-term use of proton pump inhibitors in patients treated for Helicobacter pylori has been shown to dramatically increase the risk of gastric cancer.^[28]

Acute tubulointerstitial nephritis is a possible adverse reaction when using proton pump inhibitors.