Advantages of aerosol: 1 easy to use and quick to take effect; 2. It can keep drugs clean and sterile, and improve the stability of drugs. Because the medicine is packed in a closed container, it can avoid contact with air, moisture and light, thus reducing the possibility of pollution and deterioration; 3. Relieve pain (such as burns and patients with sensitive skin diseases) and infection caused by local application; 4 The sprayed fog particles are tiny, which can directly reach the action site or absorption site, and are evenly distributed, and the dosage is small, so the side effects are also small.
Aerosol also has disadvantages: 1 needs pressure-resistant container and valve system, and the cost is high; Mechanical equipment that needs cooling and filling. The preparation operation is troublesome; Aerosol has a certain internal pressure and is easy to explode when heated or hit; Aerosol works by the pressure of vapor pressure of propellant, but it may also fail because of the leakage of propellant; Inhaled aerosol, as the main use, is often not fully absorbed because of many interference factors in lung absorption.
Drugs in aerosol are absorbed in respiratory organs, mainly through the lungs.
The respiratory organs of human body are composed of mouth, nose, throat, trachea, bronchi, bronchioles, alveolar ducts, alveolar sacs and alveoli. Alveola is the main absorption site. The distance between alveolar surface and capillary is only 0.5 ~ 65438 0 μ m; Moreover, the total number of human alveoli is estimated to be 300-400 million, and the total surface area is estimated to be about 200m2. . The total capillary area to the alveoli is estimated to be1100m2, and such a large breathing surface is an important factor for good lung absorption. In particular, the amount of blood circulating through the lungs is very large, and almost all the blood output by the heart passes through the lungs. The above structural characteristics and hemodynamic characteristics constitute the rapid absorption of drugs in the lungs.
The absorption rate of drugs in the lungs is directly proportional to the lipid solubility of drugs and inversely proportional to the molecular weight of drugs. When applying aerosol, all atomized particles may not reach the main absorption site-alveoli. The best local effect on lung is n 1 fried 3 ~ 10. However, if you want to absorb it quickly and play a systemic role, it is best to fry it as small as 1 ~ 0.5 m, and it is not good if the particles are too small, because it can still be discharged with exhalation after inhalation.
When bronchodilators are administered in aerosol, if they contain a large number of large particles, the proportion of them reaching the main site of action is very small. When asthma patients have an attack, if they inhale repeatedly and inhale too much in the upper trachea, it will have side effects, increase the burden on the heart and even report fatal cases. This is especially dangerous for drugs with a therapeutic dose close to side effects, that is, drugs with a small safety index.
Whether aerosol reaches or stays in alveoli mainly depends on particle size; But as far as lung absorption is concerned, the fat solubility of drugs is more important than the molecular weight of drugs. When aerosol is administered, due to the loss of drugs in the mouth and pharynx, the deposition in the cavities of various parts of respiratory organs, and the escape during exhalation and inhalation, the percentage of main drugs actually entering the alveoli and being absorbed is not high, which is a major deficiency of aerosol.
Other gaseous solvents:
Besides aerosol, there are several similar preparations, such as barometric preparation, inhalant, aerosol and fumigant.