Pharmacokinetics

Active Transport System

Filtration of drugs through the nephrons. Glomeruli filtrate the blood drug molecules. The non polar or lipophilic molecules can easily reabsorbed back into blood whereas charged molecules can not be reabsorbed and excreted into urine. Active transport sy

Bioavailability And Intravenous Versus Oral Administration

Bioavailability is defined as the percentage of the drug which reach systematic circulation. At steady state the intravenous administration rate equal to clearance multiply by concentration. Bioavailability of the drug affect the rate of administration of

Dosing Interval

Continuous intravenous infusion reach the steady state concentration after around 4 half-lives. Single daily intravenous injection will reach steady state after four half-lives but with more peaks and troughs. More frequent administrations results in less

Loading Dose

In some serious clinical conditions there is need to reach the target plasma concentration rapidly. Therefore a high dose called loading dose is given for once followed by usual maintenance dose to avoid reaching the toxic concentration

Major Pharmacokinetic Processes

Different drugs pass through four major pharmacokinetic processes in the body; absorption, metabolism, distribution and finally elimination.

Phases Of Drug Metabolism

There are two major phases of drug metabolism; phase I and phase II. In phase I; a hydrophilic group is added or unmasked in the drug. Cytochrome P450 isozyme system play important role in phase I. In phase II more lipophilic groups are conjugated to the

Steady State Equation

At steady state the administration rate equals to elimination rate. Therefore the plasma concentration of the drug remain constant. At steady state concentration infusion rate equal to plasma concentration multiplied by clearance.

Therapeutic Window

For any drug to exert a proper therapeutic effect, its plasma concentration must lie in target therapeutic window above the minimum therapeutic concentration and below the toxic level

Volume Of Distribution

Volume of distribution measure the ability of various drugs with different sizes and charges to distribute through body fluids. Apparent volume of distribution Vd is calculated by dividing the amount of the drug administered on the plasma concentration of

Weak Acids And Bases

The charged molecules cannot cross the phospholipid bilayer of the cell membrane, whereas the noncharged molecule can easily pass this membrane. Weak acids at its protonated form is non charge and can pass the cell membrane. However its dissociated base i