First order kinetics

First order kinetics is related to way of acting of drug in the body system

1. FIRST ORDER KINETICS

2. First order kinetics The process that is directly proportional to the drug concentration available at that time. Linear kinetic process Concentration dependent process Rate of process increase linearly with increase in drug concentration Never comes to an end

3. Drug metabolism First order kinetics Constant fraction per unit time is metabolized Rate increases if drug conc. increases

4. General expression dC / dt = - kC Here , dC = The change in concentration dt = Time interval dC / dt = The velocity of the reaction k = Rate constant C = Concentration

5. General equation: Log C = Log C - kt / 2.303 Half-life : t 1/2 = 0.693 / K - Concentration independent - Constant value Rate constant units : Time‾ 1

6. www.chem.purdue.edu

7. This is the same curve as the one above but the y-axis is the natural logarithm of conc. This allows the calculation of t½. http://schoolbag.info/chemistry/mcat_2/mcat_2.files/image252.jpg

8. Pseudo-order reaction Following administration of a drug, it may be eliminated from the body only after reacting with tissue components. -Tissue components present in high concentration. -Are not used up to any degree. -Show pseudo-monomolecular reactions -Drug eliminates from the body according to first order kinetics.

9. Example: 100 mg drug orally Absorption rate: 10% per hour First hour : 10 % of 100 mg(10 mg) Second hour: 10% of remaining 90mg (9 mg ) Third hour : 10 % 0f remaining 81 mg (8.1 mg) and will continue in this process. http://www.aboutkidshealth.ca//En/Assets/PST_child_medicine_syringe_EN.jpg

10. References IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006) http://www.pharmainfo.net http://www.chemteam.info http://chem.libretexts.org