Prokinetic agents are specialized medications that stimulate gastrointestinal (GI) motility, promoting food movement through the GI tract. Dopamine, an inhibitory neurotransmitter, plays a significant role in this process, reducing GI motility and indirectly controlling the speed of digestion. Dopamine receptor antagonists, such as metoclopramide and domperidone, offer a unique advantage as prokinetic agents. By blocking the dopamine receptors, these drugs increase GI motility, improving food transit.
Metoclopramide (Primperan) enhances GI motility, both by blocking dopamine receptors and increasing the release of acetylcholine, another neurotransmitter that promotes GI motility. It is absorbed quickly and acts within 1-2 hours of oral intake. It has a half-life of 4-6 hours. It undergoes hepatic sulfation and glucuronide conjugation and is excreted in the urine. It treats gastroparesis, gastroesophageal reflux disease (GERD), and nausea/vomiting but can lead to side effects like extrapyramidal symptoms, dystonias, dyskinesias, sedation, and hyperprolactinemia.
Domperidone (Motilium) also increases GI motility by blocking dopamine receptors but has fewer central nervous system side effects than metoclopramide. However, it may increase the risk of cardiac arrhythmias. It is metabolized by hepatic CYP3A4, N-dealkylation, and hydroxylation pathways. It is primarily used to treat nausea and vomiting. Notably, it is available through expanded access to investigational drugs with the FDA.
Dopamine, a neurotransmitter abundant in the gastrointestinal or GI tract, is involved in GI motility. It binds to D2 receptors, lowering intragastric pressures, thereby relaxing the lower esophageal sphincter and inhibiting GI motility.
Dopamine receptor antagonists, such as metoclopramide and domperidone, are useful for treating GI motility disorders.
These agents block D2 receptors in the GI tract, neutralizing dopamine's inhibitory effects. The resulting increase in the lower esophageal sphincter pressure leads to coordinated GI contractions.
Additionally, they block D2 receptors in the brain's chemoreceptor trigger zone, mitigating nausea and vomiting.
Metoclopramide, specifically, aids gastric emptying in individuals with gastroparesis and serves as an adjuvant for GI diagnostic procedures like endoscopy.
Their common adverse effects include elevated prolactin levels resulting in galactorrhea or breastmilk production and gynecomastia or swollen breasts in men.
Furthermore, metoclopramide may induce insomnia, anxiety, tremors, involuntary muscle contractions or dystonia, and uncontrollable body movements or dyskinesia.
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