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Non-Oral Extravascular Drug Absorption Routes
Non-oral extravascular routes, which encompass sublingual, buccal, topical, intramuscular, and inhalation methods, primarily utilize passive diffusion…
Non-oral extravascular routes mainly diffuse drugs passively to reach the systemic circulation. Factors influencing extravascular drug absorption include the drug's physicochemical properties and the anatomy and pathophysiology of the patient.
Lipophilic drugs, stable at salivary pH 6 and poorly binding to the oral mucosa, are absorbed better through sublingual and buccal delivery. Sublingual nitroglycerin drains from the mouth's venous system into the superior vena cava, bypasses first-pass hepatic metabolism, and improves blood flow to the heart.
Drugs applied topically on the foot and palm are absorbed slowly because of the thick stratum corneum. However, medications for burned or injured skin exhibit rapid absorption, aided by occlusive dressing to maintain skin moisture.
Intramuscular injections yield rapid absorption from arms, rich in blood supply, compared to thighs, and slowest from the buttocks.
Gaseous and aerosol drugs given by inhalation are absorbed rapidly because of the lung's large surface area and high vascularity.
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Q1: Why are lipophilic drugs better absorbed through sublingual and buccal routes?
Lipophilic drugs are better absorbed sublingually and buccally because they are stable at salivary pH 6 and exhibit minimal binding to the oral mucosa, allowing efficient passive diffusion across mucosal membranes. These routes bypass first-pass hepatic metabolism, enabling rapid systemic delivery.
Q2: How does sublingual nitroglycerin reach the heart so quickly?
Sublingual nitroglycerin is absorbed from the mouth's venous system and drains directly into the superior vena cava, bypassing first-pass hepatic metabolism. This direct route to systemic circulation allows rapid delivery to the failing heart, improving blood flow efficiently and providing immediate therapeutic benefit.
Q3: What determines absorption rates for intramuscular injections at different injection sites?
Intramuscular injection absorption rates depend on blood supply at the injection site. The arms, with rich vascular networks, yield faster absorption than the thighs, while the buttocks register the slowest absorption due to lower blood perfusion and reduced factors influencing drug absorption anatomical parameters.
Q4: Why is topical absorption slow on the foot and palm compared to other skin areas?
Topical absorption is slow on the foot and palm because these areas have a thick stratum corneum, the skin's outermost layer, which creates a significant barrier to drug diffusion. This dense layer limits passive diffusion of drugs across the skin barrier.
Q5: How do occlusive dressings accelerate drug absorption on burned or injured skin?
Occlusive dressings accelerate drug absorption on burned or injured skin by maintaining skin moisture and preventing water loss. Damaged skin has a compromised stratum corneum, and the moist environment created by occlusive dressings further enhances passive diffusion of medications into systemic circulation.
Q6: Why are gaseous and aerosol drugs absorbed so rapidly through inhalation?
Gaseous and aerosol drugs are absorbed rapidly via inhalation because the lungs possess an extensive surface area and rich vascular network. This large absorptive surface combined with high blood perfusion enables quick drug uptake, making inhalation ideal for emergency treatments like bronchodilators.
Q7: What physicochemical and anatomical factors control non-oral extravascular drug absorption?
Non-oral extravascular drug absorption is controlled by the drug's physicochemical properties, such as lipophilicity and pH stability, and the patient's anatomical and pathophysiological state. These factors collectively determine whether drugs undergo passive diffusion effectively across different tissue barriers to reach systemic circulation.