Chapter 9 PHARMACOKINETICS VARIABILITY by Dr. Arshad Ali Khan Faculty of Engineering Technology arshad@ump.edu.my

PHARMACOKINETICS VARIABILITY Definition : Due to differences in drug concentration at the site of action because of inter-individual differences in drug absorption, distribution, metabolism and excretion. Also known as inter-individual variations of a drugs pharmacokinetic parameters, resulting in different pharmacokinetic profiles after administration of the same dose to different patients.

FACTORS AFFECTING THE PHARMACOKINETIC VARIABILITY IN DISEASES STATES

Body weight Same drug dose administration with different body weight individuals may results into different plasma profile The dose adjustment according to the body weigh individual (obese and thin) can reduce the pharmacokinetic variability. In the obese patients, it is difficult to reduce the pharmacokinetic variability of drug because the recommended dose of the drugs are normally based on the body weight of the normal individuals. This pharmacokinetic variability is due to the function of organs such as kidney and liver is different from the normal individuals.

Elderly subjects (more than 70 years) Age Age can affect the distribution and elimination of drugs Drug protein binding, drug metabolism and drug excretion may change according to age There are 5 groups : Infants (1-12 months) Newborns (-3 days) AGE Children (4-9 years) Adults (16-37years) Elderly subjects (more than 70 years)

Sex The body size are different for both men and women which led to different volume of distribution and different drug clearance. Higher body fat in female may enhance the volume of distribution for the lipophilic therapeutic agents. The oral bioavailability in somewhat higher in female in comparison to male. Bioavailability after transdermal drug administration does not appear to be significantly affected by gender; nor does protein binding. The transdermal drug administration are not affected by sex.

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