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Volume of distribution (Vd)It is the proportionality constant that relates

drug concentration in a reference fluid, typicallyplasma, to the amount of drug distributed

throughout the body.

Vd =

ClearanceIt is the most useful pharmacokinetic

indicator of irreversible loss of drug from the

body and refers to a volume of fluid from which

drug appears to be removed in a given amountof time.

Clearance =

amount of drug in the bodydrug concentration

Rate of distributionConcentration

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Zero-Order KineticIt is typically found when an enzyme or

transport system becomes saturated & the rateprocess becomes constant & cannot be increased

by increases in the concentration of substrate.

Zero- order rate processes are typically of

constant rate intravenous infusions andprolonged release dosage forms.

If the amount of the drug that is converted to

a metabolite is constant with respect to time, the

reaction is said to be zero-order and expressedas:

-dD/dt = koWhere Ko is the zero-order rate constant with

the units as mass per time (mg/ml).

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First Order KineticIt is when the amount of the drug in the body

is converted to a metabolite at a rate that is aconstant fraction of the amount of the drug in

the body, the conversion of D to M.

kD= dD/ dtwhere k is the first order rate constant

expressed in units of reciprocal time (min-1)

Loading DoseIt is a dose of medication administered for

the purpose of establishing a therapeutic level of

the mediaction.

Loading Dose =(C) (V)F

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Steady-State ConcentrationThe concentration of a drug or chemical in a

body fluid usually plasma at the time asteady state has been achieved, and rates of

drug administration and drug elimination are

equal. It is a value approached as a limit and is

achieved, theoretically, following the last of aninfinite number of equal doses given at equal

intervals.

Css= Km x RVmax - R

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pH negative logarithm of Hyrdronium ionconcentration

pH Normality interms ofHydroniumIonNormality interms ofHyrdroxyl Ion

0 1 10-14

1 10-1 10-132 10-2 10-12Increasing 3 10-3 10-11acidity 4 10-4 10-105 10-5 10-9

6 10-6 108Neutral point 7 10-7 10-78 10-8 10-6

9 10-9 10-5

10 10-10

10-4

11 10-11 10-3Increasing 12 10-12 10-2alkalinity 13 10-13 10-114 10-14 1

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pKa Values of Some Common DrugsDrugs pKa value

Acidic drugsAspirin 3.5

Paracetamol 9.5

phenobarbital 7.4 (first

ionization)

Basic drugs

Cocaine 8.6

Diazepam 3.3Diphynhydramine 90

Amphoteric drugs

Morphine 8.0 (amine),

9.9 (phenol)Adrenaline

(epinephrine)

8.7 (amine),

10.2, 12.0

(phenols)

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FOR WEAK ACIDS

pH = pKa compound is approximately 50%

ionized

pH = pKa +1 compound is approximately 90%

ionized

pH = pKa + 2 compound is approximately 99%

ionized

pH = pKa +3 compound is approximately 99.9%

ionizedPh = pKa + 4 compound is approximately 99.99%

ionized

FOR WEAK BASES

pH = pKa compound is approximately 50%ionized

pH =pKa compound is approximately 90%

ionized

pH = pKa compound is approximately 99%

ionized

pH = pKa compound is approximately 99.9%ionised

pH = pKa compound is approximately

99.99% ionised

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Percent IonizationIt is the percentage of weak electrolyte that

ionizes in a solution of given concentration.

Partition CoefficientIt is the ratio of the concentration of a

chemical species absorbed or dissolved by 1

phase to the concentration of the species in

other phase.

K= [Organic acid in oil][ Organic acid in water] by mass