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I- Routes of drug administration :
2 major routes
Oral
*the most common route.
*the most variable mode in amount of drugs reach the target tissues .
*some drugs are absorbed from the stomachmost drugs are absorbed from the duodenum.
*most drugs
absorbed from GIT enter the portal circulation and encounter the liver
before they are distributed in the general circulation first pass metabolism by intestine or liver limits the efficacy of many drugs when taken orally
Sublingual
the drug diffuses to the systemic circulation directly
Rectal
fifty percntage of the drug bypass the portal circulation
Useful if the drug
destructed by the intestinal enzymes.
destructed by the low pH of the stomach.
induce vomitting or the patient himself is vomitting
B- Parenteral
I.V
the most common parenteral routedrugs avoid first pass
metabolismpermit a rapid effectpermit the maximal
degree of control over the circulating levels of drug the
rate of infusion must be carefully controlled.
I.M
main route used for depot preparations which dissolves
slowly providing a sustained dose over an extended
period of time.
used also for many aquous solutions of drugs
S.C
as I.M it requires absorbtion slower than I.V
minimizes the risks associated with I.V injections
Others
Inhalation
provides rapid delivery of drug producing rapid effect
almost as that of I.V
Intranasal
e.g salmon calcitonin used in osteoporosis
Intrathecal
e.g methotrexate in leukemia
Intraventricular
Topical
when local effect of the drug is required
Transdermal
e.g nitroglycerine when used as antianginal
II- Absorbtion of drugs
the transfer of a drug from its site of administration to
blood stream.
the rate and the efficiency of absorbtion depend on the
route of administration so in
I.V : Complete absorbtion
Other routes : partial absorbtion which lowers the
bioavailability
A- Transport of drugs from GIT
depending on their chemical properities drugs may be
absorbed from GIT by
Passive diffusion
Active transport
B- physical factors influencing absorbtion
blood flow to the absorbtion site.
total surface area available for absorbtion.
contact time at the absorbtion surface.
III-Bioavailability
the fraction of administerd drug that reaches the
systemic circulation in a chemically unchanged form
ex : if 100 mg of the drug is administrated orally and
70mg of this drug is absorbed unchanged so
..the bioavailability is 70%
Factors that influence bioavailability
first pass hepatic metabolism.
solubility of the drug.
chemical instability.
[size=16]the nature of the drug formulation.
2 major routes
A- Enteral
Oral
*the most common route.
*the most variable mode in amount of drugs reach the target tissues .
*some drugs are absorbed from the stomachmost drugs are absorbed from the duodenum.
*most drugs
absorbed from GIT enter the portal circulation and encounter the liver
before they are distributed in the general circulation first pass metabolism by intestine or liver limits the efficacy of many drugs when taken orally
Sublingual
the drug diffuses to the systemic circulation directly
Rectal
fifty percntage of the drug bypass the portal circulation
Useful if the drug
destructed by the intestinal enzymes.
destructed by the low pH of the stomach.
induce vomitting or the patient himself is vomitting
B- Parenteral
I.V
the most common parenteral routedrugs avoid first pass
metabolismpermit a rapid effectpermit the maximal
degree of control over the circulating levels of drug the
rate of infusion must be carefully controlled.
I.M
main route used for depot preparations which dissolves
slowly providing a sustained dose over an extended
period of time.
used also for many aquous solutions of drugs
S.C
as I.M it requires absorbtion slower than I.V
minimizes the risks associated with I.V injections
Others
Inhalation
provides rapid delivery of drug producing rapid effect
almost as that of I.V
Intranasal
e.g salmon calcitonin used in osteoporosis
Intrathecal
e.g methotrexate in leukemia
Intraventricular
Topical
when local effect of the drug is required
Transdermal
e.g nitroglycerine when used as antianginal
II- Absorbtion of drugs
the transfer of a drug from its site of administration to
blood stream.
the rate and the efficiency of absorbtion depend on the
route of administration so in
I.V : Complete absorbtion
Other routes : partial absorbtion which lowers the
bioavailability
A- Transport of drugs from GIT
depending on their chemical properities drugs may be
absorbed from GIT by
Passive diffusion
Active transport
B- physical factors influencing absorbtion
blood flow to the absorbtion site.
total surface area available for absorbtion.
contact time at the absorbtion surface.
III-Bioavailability
the fraction of administerd drug that reaches the
systemic circulation in a chemically unchanged form
ex : if 100 mg of the drug is administrated orally and
70mg of this drug is absorbed unchanged so
..the bioavailability is 70%
Factors that influence bioavailability
first pass hepatic metabolism.
solubility of the drug.
chemical instability.
[size=16]the nature of the drug formulation.
