To obtain a general effect, the drug is usually given by oral or parenteral route. The choice depends on the drug i.e. the existence of preparations appropriate for these uses and on the state of the patient. Emergency or the impossibility of intake by mouth makes the parenteral route necessary.
To obtain a local effect, special preparations like the ophthalmic solutions, but it should be remembered that a systemic diffusion is always possible after local administration. Parenteral route
A drug to be injected by parenteral route, must be sterile and little irritant. The injection requires a syringe and a needle or a device of administration already set up.
Intradermal route, especially used for intradermal reactions. Subcutaneous route
The volume of fluid injected is limited and the rate of resorption variable, depending on local factors: sclerosis, circulatory state (vasodilation, vasoconstriction). Heparin and insulin are among the drugs generally administered drugs by subcutaneous route. Intramuscular route
The rate of resorption is fast and it is possible to inject aqueous or oily solutions. There are delayed preparations gradually releasing over one or many weeks the active product from the anatomic site of injection into the circulation, sexual hormones or neuroleptic agents for example. The intramuscular injection should not be made in a vessel, nor in contact with a nerve. It is contra-indicated if the patient is undergoing anticoagulant therapy. Intravenous route
There are two possibilities: direct injection with the syringe or administration by perfusion. The bioavailability is by definition 100%; it is necessary however to pay attention to the speed of administration because it should not be: too rapid, which can be the case with direct administration by a syringe, with risk of severe reactions. too slow, as observed during certain perfusions, because if the rate of elimination is rapid, the effective...
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