13.11: Pharmacokinetics in Pediatric Patients: Overview and Drug Absorption

Understanding the physiological differences in the pediatric population is crucial for effective pharmacotherapy. Neonates, infants, and children exhibit significant variations in gastric pH, gastric emptying time, intestinal transit time, and biliary function. These variations profoundly affect oral drug absorption, necessitating a nuanced approach to pediatric dosing.

Neonates present with a unique physiological profile, having a gastric pH greater than 4 and faster and more irregular gastric emptying and intestinal transit times. Their biliary function is also immature. This higher gastric pH can enhance the bioavailability of acid-labile drugs but reduce the bioavailability of certain drugs like phenobarbital, requiring careful dose adjustments. A particular concern in neonates is their immature biliary function, which complicates the absorption of fat-soluble vitamins. This underscores the importance of considering these physiological factors when prescribing vitamins and other essential nutrients.

Conversely, infants display a slightly lower gastric pH ranging from 2 to 4, with increased gastric emptying and intestinal transit times. Their biliary function begins to approach the adult pattern during this stage of development. This adjustment in physiological functions influences how drugs are absorbed and metabolized compared to neonates, suggesting the need for different dosing strategies as infants grow.

Children continue to experience changes, with increasing gastric emptying and intestinal transit times extending to age 4. However, by this time, their gastric pH and biliary function have become similar to those of adults. Despite these developments, the pediatric population still faces challenges in drug absorption due to the faster gastrointestinal transit, which can decrease the overall absorption rate of medications.

In summary, the pediatric population's physiological diversity demands tailored pharmacological approaches. By understanding these differences, healthcare professionals can optimize drug dosing, ensuring efficacy while minimizing the risk of adverse effects.

Neonates, infants, and children exhibit significant physiological variations in gastric pH, gastric emptying time, intestinal transit time, and biliary function, which affect oral drug absorption.

Neonates have a gastric pH > 4, along with faster and irregular gastric emptying, intestinal transit times, and immature biliary function.

Meanwhile, infants display a gastric pH of 2–4, with increased emptying and transit times, and their biliary function approaching the adult pattern.

On the other hand, gastric emptying and intestinal transit times in children continue to increase, reaching maturity by around age four. However, their gastric pH and biliary function are comparable to those of adults.

The higher gastric pH in neonates and infants leads to increased bioavailability of acid-labile drugs and decreased bioavailability of drugs such as phenobarbital, necessitating dose adjustments.

The faster GI transit also reduces the drug absorption rate.

In addition to these challenges, neonates also experience difficulty in absorbing fat-soluble vitamins.