The document summarizes key concepts in pharmacokinetics including biological half-life, volume of distribution, renal clearance, total body clearance, plasma protein binding, absorption and elimination rate constants. Pharmacokinetics is the study of the movement of drugs in the body over time, including absorption, distribution, metabolism and excretion. It involves experimental measurement of drug concentrations as well as theoretical modeling of drug disposition.

1. PHARMACOKINETICS
Prepared By : Guided By :
Parth Patel Dr. Hitesh Jain
(M. Pharm Sem.1) M.pharm ,Ph.D
Forwarded By:
Dr.U.M. Upadhyay
M.pharm ,Ph.D
Sigma Institute Of Pharmacy, Vadodara

2. CONTENTS
Biological Half Life
Volume Of Distribution
Renal Clearance
Total Body Clearance
Plasma Protein Binding
Absorption Rate Constant
Elimination Rate Constant
Conclusion
References

3. PHARMACOKINETICS:
 Definition: the activity or fate of drugs in the body over a period of
time, including the processes of absorption, distribution, localization in
tissues, biotransformation and excretion.
 The study of pharmacokinetics involves both experimental and
theoretical approaches. The experimental aspect of pharmacokinetics
involves the development of biologic sampling techniques, analytical
methods for the measurement of drugs and metabolites, and procedures
that facilitate data collection and manipulation. The theoretical aspect
of pharmacokinetics involves the development of pharmacokinetic
models that predict drug disposition after drug administration.

4. BIOLOGICAL HALF LIFE
 Basic Concept And Importance Of Biological Half Life :
 Half-life is the time taken for the drug concentration to fall to half its original value
 ZERO ORDER t1/2 = 0.5Co
Ko
Co = initial drug concentration
Ko = zero order rate constant

5. VOLUME OF DISTRIBUTION
 It is defined as the hypothetical volume of body fluid into which a drug is dissolved or
distributed. It is also known as apparent volume of distribution because all parts of the body
equilibrated with the drug do not have equal drug concentration.
 Drug in circulation distributes to various organs and tissues. When the process of distribution
is complete ,different organs and tissues contain varying concentrations of drugs which can
be determined by the volume of tissues in which the drug is present.
 There is a relationship between concentration of drug in plasma (C)and amount of drug in
the body (X).
𝜲 𝜶 𝑪 so 𝜲= Vd•c
where 𝜲 = amount of drug in the body
Vd = volume of distribution
c = concentration of drug in plasma

6. amount of drug in the body(X)
Apparent volume of distribution(Vd)=
plasma drug concentration(C)
Vd = X
C

7. RENAL CLEARANCE
 Renal clearance CLR is defined as the volume of plasma that is cleared of drug per unit of
time through the kidney. Similarly, renal clearance may be defined as a constant fraction of
the V D in which the drug is contained that is excreted by the kidney per unit of time. More
simply, renal clearance is defined as the urinary drug excretion rate divided by the plasma
drug concentration .
 An alternative approach to obtaining equation is to consider the mass balance of drug
cleared by the kidney and ultimately excreted in the urine. For any drug cleared through
the kidney, the rate of the drug passing through kidney (via filtration, reabsorption, and/or
active secretion) must equal the rate of drug excreted in the urine.
 Rate of drug passing through kidney = rate of drug excreted

8. CL renal = [(Glomerular filtration rate + Tubular secretion rate) – Tubular reabsorption rate] / Cp
If the renal clearance of the drug is higher than the physiological creatinine
clearance (120-130 ml/min), that time we can say that the tubular secretion
helps and contributes the elimination of the drug additionally to filtration.
In early newborns and newborns, glomerular filtration and tubular
secretion mechanisms
are immature and not sufficient.
Renal Clearence (CLR) =
V x CU
t x CP
V= collected urine volume
t= duration to collect the urine
CP= plasma concentration of the drug
CU= urine concentration of the drug

9. TOTAL BODY CLEARANCE
 Total body clearance is a pharmacokinetic term for describing drug elimination from
the body without identifying the mechanism of the process. Total body clearance
(body clearance, total body clearance, or cl T) considers the entire body as a single
drug-eliminating system from which many unidentified elimination processes may
occur. Instead of describing the drug elimination rate in terms of amount of drug
removed per time unit (eg, mg/min), Total body clearance is described in terms of
volume of fluid clear of drug per time unit (eg, ml/min).
 There are several definitions of clearance, which are similarly based on volume of
drug removed per unit time. The simplest concept of clearance regards the body as
a space that contains a definite volume of body fluid (apparent volume of
distribution, V D) in which the drug is dissolved. Total body clearance is defined as
the fixed volume of fluid (containing the drug) cleared of drug per unit of time.

10.  The units for clearance are volume/time (eg, ml/min, L/hr). For example, if the cl
T of penicillin is 15 ml/min in a patient and penicillin has a V D of 12 L, then from
the clearance definition, 15 ml of the 12 L will be cleared of drug per minute.
 Alternatively, cl t may be defined as the rate of drug elimination divided by the
plasma drug concentration. This definition expresses drug elimination in terms of
the volume of plasma eliminated of drug per unit time. This definition is a practical
way to calculate clearance based on plasma drug concentration data.
 Where d e is the amount of drug eliminated and dd e/dt is the rate of elimination.

11. PLASMA PROTEIN BINDING

12. ABSORPTION RATE CONSTANT

13. ELIMINATION RATE CONSTANT
 The elimination rate constant (k) is the fraction of drug in the body which is removed
per unit time.
 The rate of elimination for most drugs from a tissue or from the body is a first-order
process, in which the rate of elimination is dependent on the amount or concentration
of drug present. The elimination rate constant, k, is a first-order elimination rate
constant with units of time– 1 (eg, hr– 1 or 1/hr). Generally, the parent or active drug is
measured in the vascular compartment. Total removal or elimination of the parent drug
from this compartment is effected by metabolism (biotransformation) and excretion.
The elimination rate constant represents the sum of each of these processes:

14. References
1. Martin’s physical pharmacy and pharmaceutical sciences ; 6th edition ; by Patrick
J.Sinko and Yashveer Singh ; Lippincott Williams and wilkins ; P.No ;258-299
2. Pharmaceutical calculations ;13th edition ;by Howard C.Ansel ;Lippincott Williams
and wilkins ; P.No. ;
3. Pharmaceutics; the sciences of dosage form design ; 2nd edition; edited by m.e.
Aulton ;Churchill Livingstone; P.No.; 211-289
4. Applied biopharmaceutics and pharmacokinetics ; 5th edition ;by Leon Shargel ,
Susanna wu pong, Andrew B.C. Yu ; P.No.
5. R brahmankar, s jaiswal