Pharmacology for Dentistry

Pharmacokinetics 37

The figure shows the different types of
drugs with different plasma half life, but the
steady state concentration is maintained on
repetitive dosing in all the three type of drug.

A B C

Toxic level

Steady state

concentration

Therapeutic

level

Blood concentration

Time (hour)

Fig. 1.4.3: Drug concentration vs time curve of
repeated dosing.

Drug : A = Drug with long plasma half life given
in initial loading dose followed by
constant maintenance dose.
B = Drug with short plasma half life given
in constant repetitive dose.
C = Drug with long plasma half life given
in constant repetitive dose.

LOADING DOSE

It is a single or many quickly repeated
doses given in the beginning of treatment
to achieve target concentration rapidly.

DOSAGE INTERNAL

Most of the drugs are given in divided
dose daily, the dosing interval is determined
by the plasma half life. The drugs with long
half lives may be given once or twice daily
while drugs with shorter plasma half lives
may require constant dosing or with short
dosing interval.

When any drug is administered, it

produces its desired effect in a particular

time at receptor site and remain there at

therapeutic level for particular time and

after that its therapeutic efficacy declines.

So the next dose should be given in

between this period so that the steady state

concentration is maintained and no toxic

effects are produced due to high dose.

The graph shows that the drug reaches

at the therapeutic level in 3½ hours after oral

administration and achieve its peak

concentration in 4½ hours and decreases

below the mini-mum effective concentration

(MEC) in 10 hours.

1

2

3

4

5

6

7

2468 10 12 14 16 18 20

Toxic level

[Minimum toxic

concentration (MTC)]

Therapeutic level

[Minimum effective

concentration (MEC)]

Plasma concentration (μg/ml)

Time (hr.)

Fig. 1.4.4: Drug concentration in plasma vs time curve

of drug administered orally.

Now for maintaining the serum concen-

tration above the MEC for longer duration,

the second dose of drug should be given

about 7 to 8 hours after the first dose,

otherwise when it is given after 7 to 8 hours

it will take extra time to reach the MEC or if

it is given prior to 7 to 8 hours the second

dose in combination with the first dose effect

crosses the minimum toxic concentration

(MTC).