Genodom Mechanism of Action

Pharmacology: Pharmacodynamics: Mechanism of Action: Domperidone acts as a gastrointestinal emptying (delayed) adjunct and peristaltic stimulant. The gastroprokinetic properties of domperidone are related to its peripheral dopamine receptor blocking properties. Domperidone facilitates gastric emptying and decreases small bowel transit time by increasing esophageal and gastric peristalsis and by lowering esophageal sphincter pressure. Antiemetic: The antiemetic properties of domperidone are related to its dopamine receptor blocking activity at both the chemoreceptor trigger zone and at the gastric level. It has strong affinities for the D2 and D3 dopamine receptors, which are found in the chemoreceptor trigger zone, located just outside the blood brain barrier, which - among others - regulates nausea and vomiting.
Pharmacokinetics: DOMPERIDONE: Absorption: In fasting subjects, Domperidone is rapidly absorbed after oral administration, with peak plasma concentrations at 30 to 60 minutes. The low absolute bioavailability of oral Domperidone (approximately 15%) is due to an extensive first-pass metabolism in the gut wall and liver. Although Domperidone's bioavailability is enhanced in normal subjects when taken after a meal, patients with gastro-intestinal complaints should take Domperidone 15-30 minutes before a meal. Reduced gastric acidity impairs the absorption of Domperidone. Oral bioavailability is decreased by prior concomitant administration of cimetidine and sodium bicarbonate. The time of peak absorption is slightly delayed and the AUC somewhat increased when the oral drug is taken after a meal.
Distribution: Oral domperidone does not appear to accumulate or induce its own metabolism; a peak plasma level after 90 minutes of 21 ng/ml after two weeks oral administration of 30 mg per day was almost the same as that of 18 ng/ml after the first dose. Domperidone is 91-93% bound to plasma proteins. Distribution studies with radiolabelled drug in animals have shown wide tissue distribution, but low brain concentration. Small amounts of drug cross the placenta in rats.
Metabolism: Domperidone undergoes rapid and extensive hepatic metabolism by hydroxylation and N-dealkylation. In vitro metabolism experiments with diagnostic inhibitors revealed that CYP3A4 is a major form of cytochrome P-450 involved in the N-dealkylation of Domperidone, whereas CYP3A4, CYP1A2 and CYP2E1 are involved in Domperidone aromatic hydroxylation.
Excretion: Urinary and faecal excretions amount to 31 and 66% of the oral dose respectively. The proportion of the drug excreted unchanged is small (10% of faecal excretion and approximately 1% of urinary excretion). The plasma half-life after a single oral dose is 7-9 hours in healthy subjects but is prolonged in patients with severe renal insufficiency.
Toxicology: Preclinical Safety Data: Electrophysiological in vitro and in vivo studies indicate an overall moderate risk of Domperidone to prolong the QT interval in humans. In in vitro experiments on isolated cells transfected with HERG and on isolated guinea pig myocytes, ratios were about 10, based on IC50 values inhibiting currents through ion channels in comparison to the free plasma concentrations in humans after administration of the maximum daily dose of 20mg (q.i.d.). However, safety margins in in vitro experiments on isolated cardiac tissues in in vivo models (dog, guinea pig, rabbits sensitised for torsades de pointes) exceeded the free plasma concentrations in humans at maximum daily dose (20mg q.i.d.) by more than 50-fold. In the presence of inhibition of the metabolism via CYP3A4 free plasma concentrations of Domperidone can rise up to 10-fold.
At a high, maternally toxic dose (more than 40 times the recommended human dose), teratogenic effects were seen in the rat. No teratogenicity was observed in mice and rabbits.