3.3
Administração de Medicamentos: Visão Geral
A seleção da via de administração de um medicamento depende de suas propriedades físico-químicas, incluindo solubilidade em lipídios ou água e ionizaç…
A escolha da via de entrega de um medicamento depende de suas características físico-químicas, como lipossolubilidade e ionização em lipídios ou água, bem como da necessidade terapêutica, como ação imediata ou prolongada.
Os medicamentos podem ser administrados por via enteral, parenteral e tópica.
A via enteral é uma via de entrega de medicamentos comumente usada, onde um medicamento pode ser engolido diretamente, mantido sob a língua ou entre gengivas e bochechas. Os medicamentos orais atravessam principalmente o trato gastrointestinal para absorção sistêmica.
A administração enteral tem desvantagens, incluindo má absorção, irritação gástrica, instabilidade em pH gástrico baixo e metabolismo pela flora intestinal.
A via parenteral envolve a injeção de drogas diretamente na corrente sanguínea, nos músculos ou sob a pele, garantindo biodisponibilidade variável.
Entre eles, a administração intravenosa produz alta biodisponibilidade e um rápido início de ação.
A via tópica envolve a aplicação de medicamentos diretamente na pele ou nas membranas mucosas para um efeito localizado com toxicidade mínima.
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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.