3.3
Administration de médicaments : aperçu
Le choix de la voie d'administration d'un médicament dépend de ses propriétés physicochimiques, notamment de sa solubilité dans les lipides ou l'eau e…
Le choix de la voie d'administration d'un médicament dépend de ses caractéristiques physico-chimiques, telles que la solubilité dans les lipides ou l'eau et l'ionisation, ainsi que du besoin thérapeutique, tel qu'une action immédiate ou prolongée.
Les médicaments peuvent être administrés par les voies entérale, parentérale et topique.
La voie entérale est une voie d’administration de médicament couramment utilisée, où un médicament peut être avalé directement, conservé sous la langue ou entre les gencives et les joues. Les médicaments oraux traversent principalement le tractus gastro-intestinal pour une absorption systémique.
L’administration entérale présente des inconvénients, notamment une mauvaise absorption, une irritation gastrique, une instabilité du pH gastrique bas et un métabolisme par la flore intestinale.
La voie parentérale consiste à injecter des médicaments directement dans la circulation sanguine, les muscles ou sous la peau, assurant ainsi une biodisponibilité variable.
Parmi eux, l’administration intraveineuse permet d’obtenir une biodisponibilité élevée et un début d’action rapide.
La voie topique consiste à appliquer un médicament directement sur la peau ou les muqueuses pour un effet localisé avec une toxicité minimale.
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Q1: What factors determine which drug delivery route to use?
Drug delivery route selection depends on the drug's physicochemical features, including lipid or water solubility and ionization, as well as therapeutic needs such as immediate or prolonged action. These factors determine whether enteral, parenteral, or topical administration is most appropriate for achieving desired therapeutic outcomes.
Q2: What are the main limitations of enteral drug delivery?
Enteral delivery has several drawbacks: poor absorption, gastric irritation, drug instability in low gastric pH, and metabolism by intestinal flora. However, most enteral drugs are designed with protective coatings and formulations to overcome these limitations and ultimately achieve good absorption in the gastrointestinal tract.
Q3: Why does intravenous administration provide faster drug effects than other routes?
Intravenous administration yields the highest bioavailability and fastest onset of action because drugs are injected directly into the bloodstream, bypassing absorption barriers. This parenteral route ensures rapid systemic distribution and therapeutic response compared to enteral routes that require gastrointestinal absorption and processing.
Q4: How do topical drugs achieve systemic effects?
While topical administration typically targets local effects on skin or mucous membranes with minimal toxicity, some drugs applied topically can achieve systemic effects. For example, transdermal fentanyl patches deliver drugs systemically over time through skin absorption into the bloodstream for widespread therapeutic distribution.
Q5: What are the different types of parenteral drug administration?
Parenteral delivery involves injecting drugs directly into the bloodstream, muscles, dermis, or subcutaneous tissue, providing varying degrees of bioavailability. Intravenous injection offers the highest bioavailability and fastest onset, while intramuscular and subcutaneous routes provide different absorption rates and therapeutic profiles for various clinical needs.
Q6: How do enteral drugs enter systemic circulation?
Orally administered drugs primarily traverse the gastrointestinal tract for systemic absorption. The drug must dissolve, be absorbed through the intestinal epithelium via mechanisms like paracellular transcellular and vesicular transport, and enter the bloodstream for distribution throughout the body and therapeutic action.
Q7: Why is drug formulation design important for enteral delivery?
Drug formulations are specifically designed to address enteral delivery challenges such as gastric degradation and poor absorption. Protective coatings limit drug degradation in the stomach's low pH environment, allowing drugs to reach the intestines intact for better systemic absorption and improved therapeutic efficacy.