The present invention relates to deuterium-enriched pyridinonecarboxamides and their derivatives of the formula 1, and pharmaceutically acceptable salts thereof, are partial or full agonists of serotonin (5-Hydroxytryptamine or 5-HT) receptor subtype 4 (5-HT4), and are useful compounds for the prevention and treatment of Alzheimer's disease, cognitive and memory dysfunction, mild cognition impairment, memory decline, cognitive impairment associated with schizophrenia, cognitive impairment associated with age-related dementia or Alzheimer's disease, cognitive impairment associated with post-coronary bypass surgery, attention deficit hyperactivity disorder, Obsessive compulsive disorder, depression, speech improvement in autistic children, sleep apnea in Alzheimer's patients, Age-related macular degeneration (AMD), irritable bowel syndrome, gastroesophageal reflux disease, Crohn's disease, emesis, nausea, vomiting, prokinesia, non-ulcer dyspepcia, anxiety, depression, pain, migraine, urinary incontinence, arterial fibrillation, arrhythmia, ischemic stroke, gastric emptying disorders, gastritis, gastrointestinal disorders, feeding disorders, obesity, anorexia, constipation, respiratory depression, and erectile dysfunction.