Comparison of pharmacokinetics between Pediatric and Geriatric Group.

As we know before that Absorption, Distribution, Metabolism and Elimination are related to Pharamacokinetics so, we will compare the previous processes between infants and adults. 

Absorption:

Distribution:

*: The less lean body mass, the more percentage of fat and the more the drug can diffuse into tissues and prolong its action.

*: The less serum albumin, the more percentage of free drug in the blood.

*: The more alpha acid glycoprotein, the more distribution of drug in body. 

Factors affecting distribution of drug:

a)    Size of water body compartment.

b)    Plasma protein binding.

c)    Development of BBB.

d)    pH and composition of body fluids.

e)    Blood flow and tissue specificity for receptor site.

Size of water compartment:

1)    Is high ranging from 65% in older children to 80% in neonates.

2)    The more water content, the higher dose given to patient.

3)     There are some drugs, their dose is calculated based on body weight:

a)    Aminophylline

b)    Digoxin

c)    Aminoglycosides

d)    Frusemide

4)    There are some drugs, their dose is calculated based on body surface area:

a)    Anticancer

b)    Immunomodulators

c)    Ibuprofen (in hepatic disorders)

d)    Aminoglycosides (in renal disorders)

5)    Dose needs to be adjusted in cases of diarrhea and nephrotic syndrome.

Plasma Protein binding:

Albumin alpha glycoprotein and lipoprotein are the important plasma protein.

Reasons of high fraction of free drug in blood:

a)    Plasma protein concentration is reduced in infants.

b)   Decrease affinity of drug for binding as you can see in Digoxin and Theophylline.

c)    High concentration of endogenous compounds which compete with drug for binding such as bilirubin (a yellow compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates), hormones transferred through placenta and Free FA.

d)    Diseases that leads to reduction of plasma proteins and drug binding: PEM (protein-energy malnutrition) and nephrotic syndrome. 

Metabolism:

Elimination:

Wait for Pharmacodynamics and Adverse Effects!!!!!!!