Fastest route of absorption is:
A. inhalation***
B. intravenous (IV).
Absorption corresponds to all the phenomena involved in the transfer of the active drug ingredient from its site of administration to the bloodstream. This stage of drug development in humans is essential to study because it can cause significant variability in the response to drugs, particularly through significant drug interactions.
1. THE DIFFERENT ROUTES OF ADMINISTRATION
Several routes of administration are possible:
• General or systemic:
- intravenous and intra-arterial
- subcutaneous and intramuscular
- nasal, sub-lingual, oral (or per os), rectal
• By local or in situ:
- inhaled, ocular and intraocular, cutaneous or transdermal
- intra-articular and intra-thecal
The choice of the route of administration depends on the therapeutic objective (rapidity of effect, limitation of the systemic effects), the possibilities of administration in the patient, the physico-chemical properties and the size of the molecules (resistance to gastric acidity and digestive enzymes, facilitated to pass the capillary or digestive barriers ...) and processes of elimination of these drugs (intestinal, hepatic biotransformation).
Generally speaking, two types of administration route can be distinguished in a simple manner: on the one hand, the routes of administration where the drug reaches the general circulation either directly or through the capillary wall and the routes of administration where the drugs join the general circulation through the digestive barrier then by the system carries and thus a first passage forced by the liver.
Intravenous way:
The intravenous route represents the reference route of administration for absorption as the drug directly affects the systemic circulation. Absorption is complete and rapid, the only limiting factor being the rate of administration of the drug.
Subcutaneous and intramuscular routes:
The subcutaneous and intramuscular administration routes require the drugs to cross the capillary barrier. By these ways, the drug reaches the general circulation without passage forced by the portal system and the liver. Absorption will be more or less complete and more or less fast depending on the physicochemical properties of the drugs.
Oral way:
The oral or oral route of administration imposes on the drug a passage through the digestive barrier and then the passage of the capillary wall. This passage can be done by simple passive diffusion or involve more complex phenomena involving a system of transporters favoring or otherwise limiting absorption.
Finally, the intestinal cells (enterocytes) are provided with enzymatic systems and the drug can undergo biotransformations at this level, the drug being destroyed even before reaching the blood compartment.
Once the digestive barrier is crossed, to reach the general circulation the drug must pass through the portal system and the liver where it can undergo biotransformations by the enzymatic systems of hepatocytes. In some cases, the metabolism of the drugs may be sufficiently large that the amount of drug reaching the general circulation is significantly reduced. This is called first-pass effect (EPPh) (eg propranolol).
Absorption corresponds to all the phenomena involved in the transfer of the active drug ingredient from its site of administration to the bloodstream. This stage of drug development in humans is essential to study because it can cause significant variability in the response to drugs, particularly through significant drug interactions.
1. THE DIFFERENT ROUTES OF ADMINISTRATION
Several routes of administration are possible:
• General or systemic:
- intravenous and intra-arterial
- subcutaneous and intramuscular
- nasal, sub-lingual, oral (or per os), rectal
• By local or in situ:
- inhaled, ocular and intraocular, cutaneous or transdermal
- intra-articular and intra-thecal
The choice of the route of administration depends on the therapeutic objective (rapidity of effect, limitation of the systemic effects), the possibilities of administration in the patient, the physico-chemical properties and the size of the molecules (resistance to gastric acidity and digestive enzymes, facilitated to pass the capillary or digestive barriers ...) and processes of elimination of these drugs (intestinal, hepatic biotransformation).
Generally speaking, two types of administration route can be distinguished in a simple manner: on the one hand, the routes of administration where the drug reaches the general circulation either directly or through the capillary wall and the routes of administration where the drugs join the general circulation through the digestive barrier then by the system carries and thus a first passage forced by the liver.
Intravenous way:
The intravenous route represents the reference route of administration for absorption as the drug directly affects the systemic circulation. Absorption is complete and rapid, the only limiting factor being the rate of administration of the drug.
Subcutaneous and intramuscular routes:
The subcutaneous and intramuscular administration routes require the drugs to cross the capillary barrier. By these ways, the drug reaches the general circulation without passage forced by the portal system and the liver. Absorption will be more or less complete and more or less fast depending on the physicochemical properties of the drugs.
Oral way:
The oral or oral route of administration imposes on the drug a passage through the digestive barrier and then the passage of the capillary wall. This passage can be done by simple passive diffusion or involve more complex phenomena involving a system of transporters favoring or otherwise limiting absorption.
Finally, the intestinal cells (enterocytes) are provided with enzymatic systems and the drug can undergo biotransformations at this level, the drug being destroyed even before reaching the blood compartment.
Once the digestive barrier is crossed, to reach the general circulation the drug must pass through the portal system and the liver where it can undergo biotransformations by the enzymatic systems of hepatocytes. In some cases, the metabolism of the drugs may be sufficiently large that the amount of drug reaching the general circulation is significantly reduced. This is called first-pass effect (EPPh) (eg propranolol).
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