I- Routes of drug administration : 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 stomach
most 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 route
drugs avoid first pass metabolism
permit a rapid effect
permit 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
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