Pharmacokinetic variability occurs due to differences in drug absorption, distribution, metabolism, and excretion between individuals. Several factors influence this variability including age, body weight, pregnancy, and disease states. Drug metabolism and excretion are often lower in newborns compared to adults due to immature organ systems and lower enzyme levels. Plasma protein binding is also lower in newborns which increases drug distribution. Renal function is reduced in newborns leading to slower drug clearance. These developmental differences can increase the risk of adverse drug reactions in newborns if dosages are not appropriately adjusted.

7. Drug binding, metabolism, and excretion may change as a function of age.

8. The study panel was divided into 5 groups: Newborns (2 to 3 days) Infants (1 to 12 months) Children (4 to 9 years) Adults (16 to 37 years) Elderly subjects (more than 70 years)

10. Clearance increased from 0.9 to 2.5 ml/min. when comparing patient 1 to 8 days old with patient 9 to 30 days old.

11. The mean clearance of ceftriaxone in children ranging in age from 1 to 12 months and from 1 to 6 years was 6.2 ml/min. and 9.1 ml/min. respectively.

14. Most of the enzymatic microsomal systems required for drug metabolism are present at birth, but their concentration are usually lower than adult levels.

16. Sulfate conjugation seems to be as efficient in newborns as in adults, but conjugation with glucuronic acid is considerably reduced, reaching adult level only after 3 years of age.

19. In each case binding in plasma protein is level in the newborns than in the adults.

20. Increase in plasma protein binding is an increase in apparent volume of distribution in the newborn.

23. The difference process of renal excretion on mature at different rates,

24. Average glomerular filtration rate is 38.5 ml/min.

27. Older infants age (6 months to 12 years) has higher drug metabolism capacity rates compared to adults. for example, clindamycin theophylline valproic acid Has faster elimination rate.

29. Formula used to determine dosage form

30. Child dose= SA of child(m²) ------------------------------

32. The increase in gastric ph, the decrease in gastric emptying rate and the slower motility associated with pregnancy can affect the rate and extent of drug absorption.