Pharmacokinetics in Pediatric Patients: Overview and Drug Absorption

Neonates have a gastric pH greater than 4, which is significantly higher than infants' pH of 2–4. Children's gastric pH becomes comparable to adults by around age four. These differences directly affect how drugs are absorbed orally, particularly acid-labile medications and drugs like phenobarbital, necessitating age-specific dose adjustments.

Neonates experience faster and irregular gastric emptying and intestinal transit times compared to older children. This accelerated gastrointestinal transit reduces the time available for drug absorption in the intestines, decreasing the overall absorption rate and bioavailability of oral medications in this population.

The higher gastric pH in neonates (>4) increases the bioavailability of acid-labile drugs because these medications are less likely to be degraded in the stomach's less acidic environment. However, this same elevated pH decreases bioavailability of drugs such as phenobarbital, requiring careful dose adjustments for optimal therapeutic outcomes.

Neonates have immature biliary function, which significantly impairs their ability to absorb fat-soluble vitamins and essential lipophilic nutrients. This physiological limitation underscores the importance of considering biliary maturation when prescribing vitamins and other essential nutrients to ensure adequate absorption and nutritional status in this vulnerable population.

Gastric emptying and intestinal transit times in children continue to increase and reach maturity by around age four. By this developmental milestone, their gastric pH and biliary function become comparable to those of adults, though faster gastrointestinal transit during earlier childhood still affects medication absorption rates.

Infants display a gastric pH of 2–4, which is lower than neonates but higher than adults. They have increased gastric emptying and intestinal transit times compared to neonates, and their biliary function begins approaching the adult pattern. These developmental changes require different dosing strategies than those used for neonates.

Pediatric patients exhibit significant variations in gastric pH, gastric emptying, intestinal transit, and biliary function that profoundly affect oral drug absorption. Understanding these physiological differences allows healthcare professionals to optimize drug dosing and tailor pharmacological approaches, ensuring efficacy while minimizing adverse effects across different age groups.