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Abstract

Pharmacokinetics for nursing students in brief
Pharmacology for nursing students
General principles of pharmacology
3rd lecture
د .نودعس دولخ
Pharmacokinetics(PK)
It is what the body does to the drug, it is
quantitative study of ADME.
A= Absorption,D= Distribution, M= Metabolism,
E= Excretion.
These four processes are important to
determine the onset of drug action, intensity of
its effect, &the duration of drug action
Absorption of drugs
It is the transfer of a drug from its site of
administration to the blood stream.
The rate & extent of absorption depends on
many factors.
Factors affecting drug absorption
A- Factors related to drugs:
1- Properties of drugs( physical chemical, dosage forms---).
2- Routes of administration.
B- Factors related to patient:
1- Blood flow to the absorbing site.
2-Absorption surface( intestine larger area than stomach).
3- PH of the medium( acidic drugs absorb from stomach).
4- Gastrointestinal contents(food or drugs) and diseases.
Drug distribution
It is the process by which a drug leaves the blood stream & enters the
extracellular fluid and /or the cells of the tissues. Sites of drug
accumulation are( fats, bones, plasma protein, and tissues).
Volume of distribution (Vd): It is a hypothetical volume of fluid into
which the total body content of the drug appears to distribute with a
concentration equal to that in plasma.
D( total dose in the body)
Vd=------------------------------------
C( plasma concentration of drug)
Factors affecting distribution of drugs
1- Physico-chemical properties of drugs
( molecular weight, polarity, lipid solubility).
2- Binding to plasma proteins: Highly plasma
protein binding drugs have low Vd. They mainly
remain in the circulation(less pharmacological
actions).
Drug metabolism(biotransformation)
It is the changes that occur to drugs after absorption
until excretion. The liver is the major site for the drug
metabolism because of the presences of enzymes, but
some drugs may metabolized in other tissues(
intestine, lung, plasma, skin & kidney)
Metabolism processes change the drug from active
into inactive form( there are exceptions when inactive
drug changed to active drug, it is called pro-drug).
Rate of metabolism
It is important in the pharmacological actions of
drugs.
Increase in the rate leads to decrease in its action.
Decrease in the rate leads t increase in its action or
accumulation of the drugs( toxicity).
There are many factors that affect on drug
metabolism.
Factors affecting rate of metabolism
1- Enzyme induction: It is the stimulation of enzyme activity by some
drugs or other substances this lead to increase the rate of metabolism
of other drugs. Such as phenytoin or cigarette smoking or alcohol
intake.
2- Enzyme inhibition: It is the reduction in enzyme activity after
exposure to some drugs such as chloramphenicol and cimetidine.
Result of enzyme induction and inhibition is a serious drug- drug
interactions when the patients takes two drugs together.
3- Other factors such as age, liver disease and genetic factors.
Drug excretion
It is the process whereby drugs or their metabolites are eliminated
from the body. Water soluble drugs are more easily excreted.
Site of excretion:
1- Kidneys(most important).
2-Liver(bile) e.g steroids and ampicillin.
3-GIT feces e.g neomycin.
4- Lungs e.g inhalational general anesthetics.
5-Other routes( sweat, milk, skin, saliva, vagina, seminal fluid)
Factors affecting renal excretion
1- PH of the urine.
2- Presence of disease in kidneys such as kidney failure,
in this case the dose of the drug should be decreased
to avoid accumultion of it or its metabolites and cause
toxicity.
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