Amflee

Pharmacodynamics. Mechanism of action. Pantoprazole is a substituted benzimidazole that inhibits gastric hydrochloric acid secretion through specific blockade of the proton pumps of parietal cells. Pantoprazole is converted to its active form in the acidic environment of parietal cells, where it inhibits the H⁺/K⁺-ATPase enzyme, thereby blocking the final step of hydrochloric acid production in the stomach. The inhibition is dose-dependent and affects both basal and stimulated acid secretion. Most patients achieve symptom relief within 2 weeks. Administration of pantoprazole, as with other proton pump inhibitors (PPIs) and H₂-receptor antagonists, reduces gastric acidity and consequently increases gastrin secretion in proportion to the reduction in acidity. The increase in gastrin secretion is reversible. Since pantoprazole binds to the enzyme distal to the cellular receptor, it can inhibit hydrochloric acid secretion regardless of stimulation by other substances (acetylcholine, histamine, gastrin). The effect is the same whether the drug is administered orally or intravenously. Fasting gastrin levels increase during pantoprazole treatment. With short-term use, they generally do not exceed the upper limit of normal. During long-term treatment, gastrin levels double in most cases. Excessive increases occur only in isolated cases. As a result, in a small number of cases during long-term treatment, a mild to moderate increase in specific enterochromaffin-like (ECL) cells in the stomach is observed (similar to adenomatoid hyperplasia). However, according to studies conducted to date, the formation of carcinoid precursor cells (atypical hyperplasia) or gastric neuroendocrine tumours, as observed in animal studies, has not been found in humans. Based on animal study results, an effect of long-term (more than one year) pantoprazole treatment on endocrine parameters of the thyroid gland cannot be excluded. During treatment with antisecretory medicinal products, serum gastrin levels increase in response to decreased acid secretion. Furthermore, chromogranin A (CgA) levels increase due to decreased gastric acidity. Elevated CgA levels may interfere with diagnostic investigations for neuroendocrine tumours. Available published data suggest that PPI therapy should be discontinued between 5 days and 2 weeks prior to CgA measurements. This allows CgA levels to return to the normal range, which may be falsely elevated following PPI treatment. Pharmacokinetics. Absorption. Pantoprazole is rapidly absorbed, and peak plasma concentrations are achieved after a single oral dose of 40 mg. The maximum serum concentration of approximately 2–3 µg/ml is reached on average 2.5 hours after administration; this concentration remains constant after repeated dosing. Pharmacokinetic properties do not change after single or repeated administration. In the dose range of 10 to 80 mg, plasma pharmacokinetics of pantoprazole are linear after both oral and intravenous administration. The absolute bioavailability of the tablets is approximately 77%. Concomitant food intake does not affect AUC (area under the concentration-time curve) or maximum serum concentration, and therefore does not affect bioavailability. Only the variability of the lag time is increased with concomitant food intake. Distribution. Pantoprazole serum protein binding is approximately 98%. The volume of distribution is approximately 0.15 L/kg. Biotransformation. The substance is metabolised almost exclusively in the liver. The main metabolic pathway is demethylation by CYP2C19 followed by sulfate conjugation; other metabolic pathways include oxidation by CYP3A4. Elimination. The terminal elimination half-life is approximately 1 hour, and clearance is 0.1 L/h/kg. A few cases of delayed elimination have been noted. Due to the specific binding of pantoprazole to parietal cell proton pumps, the elimination half-life does not correlate with the much longer duration of action (acid secretion inhibition). The majority of pantoprazole metabolites are excreted renally (approximately 80%); the remainder is excreted in faeces. The main metabolite in both serum and urine is desmethylpantoprazole conjugated with sulfate. The half-life of the main metabolite (approximately 1.5 hours) is not much longer than that of pantoprazole. Special patient populations. Poor metabolisers. Approximately 3% of the European population lacks functional CYP2C19 enzyme activity; these individuals are referred to as poor metabolisers. In these subjects, pantoprazole metabolism is probably mainly catalysed by CYP3A4. After a single 40 mg dose of pantoprazole, the mean area under the plasma concentration-time curve was approximately 6 times greater in poor metabolisers than in subjects with functional CYP2C19 enzyme activity (extensive metabolisers). The mean peak plasma concentration was increased by approximately 60%. These findings do not affect the dosing recommendations for pantoprazole. Renal impairment. No dose reduction is recommended when pantoprazole is administered to patients with impaired renal function (including patients on dialysis). As in healthy subjects, the half-life of pantoprazole is short. Only very small amounts of pantoprazole are dialysed. Although the main metabolite has a moderately prolonged half-life (2–3 hours), elimination is still rapid, and therefore accumulation does not occur. Hepatic impairment. Although the half-life increases to 7–9 hours and the AUC increases 5- to 7-fold in patients with hepatic cirrhosis (Child-Pugh classes A and B), the maximum serum concentration is only slightly increased by a factor of 1.5 compared with healthy volunteers. Elderly patients. The slight increase in AUC and Cmax in elderly volunteers compared with younger volunteers is also of no clinical significance.