Pharmacology for Dentistry

Pharmacokinetics 29

under the curve (AUC) represents the total
amount of drug absorbed into the
circulation.
The percent availability can also be
calculated from urine data:

Percent availability =

  





 

 



        




  







       



      

        

×

From blood data:

Percentage availability =

    








×

AUC = Area under the curve (Total amount of
drug absorbed into the circulation).

DISTRIBUTION OF DRUG

After absorption, the drug may be
distributed into various body fluids
like intestinal fluid, transcellular fluids
e.g. fluids in the gastrointestinal tract,
CSF etc.

The drug is distributed in such a pattern

which reflects physiological factors and

physicochemical nature of drug. These

patterns of distribution depend on various

factors.

PLASMA PROTEIN BINDING

Most of the drugs are transported bound

to nonspecific sites on plasma proteins, mostly

to albumin (for acidic drugs) and to α 1 -acid

glycoprotein (for basic drugs). Binding to other

proteins like ceruloplasmin and transcortin

generally occurs to a much smaller extent. The

binding is usually reversible and depends on

the individual compound.

The binding of drugs to plasma proteins

limit its concentration in tissue and

glomerular filtration of the drug. Since only

unbound drug is in equilibrium across

membranes and this process does not

immediately change the concentration of

free drug in the plasma. The free drug is

cleared from the plasma by the liver and

kidneys, which is rapidly replaced by

Fig. 1.4.2: Drug concentration in the plasma after oral administration (area under the curve versus time plot).

Drug

concentration

(μg/ml)

5.0

4.0

3.0

2.0

1.0

123 45 678

Time after drug administration (hours)

Peak height concentration

Peak

Time of real concentration

Area under curve = Total

amount of drug absorbed

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