Clin Pharmacokinet. ;39 Suppl Absorption kinetics after inhalation of fluticasone propionate via the Diskhaler, Diskus and metered-dose inhaler in. 2Pharmacokinetic evaluation of drug absorption from the lungs provides an accurate and reproducible method for comparing different inhaler delivery systems. Drug Metab Dispos. Jan-Feb;14(1) Species comparison of drug absorption from the lung after aerosol inhalation or intratracheal injection. Schanker.
After Inhalation Absorption
Here, the large absorption area, thin epithelium, and pulmonary circulation supply mean that absorptive clearance occurs more quickly compared with other regions of the lung [ 10 , 73 ]. By contrast, perfusion is much slower in the conducting airways, which have a smaller surface area available for absorption and are supplied by the systemic circulation instead of the pulmonary circulation [ 72 , 73 ].
In the alveoli, a high perfusion rate confers rapid equilibration with the systemic circulation and a very short half-life of drug distribution in this region. This was discussed for fluticasone propionate and salmeterol, resulting in reduced airway selectivity in the alveolar space compared with the conducting airways [ 73 , 74 ].
Faster drug absorption as a general observation in the alveolar space was suggested by Brown and Schanker [ 75 ]. For this reason, and even though tissue retention in the alveolar space might not be completely absent, the tissue retention in the alveolar space was not included in Figure 1. In the tracheobronchial region, a lower perfusion rate combined with higher tissue retention offers a longer equilibration time and increased local airway selectivity [ 73 , 74 ]. To minimize systemic exposure after drug inhalation, inhaled drugs should have low oral bioavailability and high systemic clearance [ 76 , 77 ].
High oral bioavailability of an inhaled drug would result in efficient absorption of swallowed fractions and lead to higher systemic exposure. Therefore, to maximize airway selectivity, oral bioavailability should remain low, as this can affect the bioavailable fraction of swallowed drug and impact negatively on airway selectivity, thereby increasing the risk of systemic side effects.
In addition, the systemic clearance of inhaled drugs should be high, as drugs with high systemic clearance have lower systemic exposure and are associated with high airway selectivity [ 26 , 77 ]. These aspects further highlight the difference between inhaled drugs and orally administered drugs, as these are often characterized by a high oral bioavailability and a low systemic clearance. It has also been discussed that high plasma protein binding might reduce initial high free plasma concentrations after pulmonary drug absorption, which are potentially associated with systemic adverse effects [ 78 ].
However, high plasma protein binding would likely correlate to lower free pulmonary concentrations, and so this hypothesis requires further evaluation. Overall, inhaled drugs are most effective when they are designed for, and delivered to, their target location in the airways.
An optimal inhaled drug combined with a well-designed inhalation device would confer the largest difference between pulmonary drug concentrations and systemic drug concentrations. This difference is known as PK airway selectivity, a concept that underpins the aim of respiratory treatment to specifically target the airways [ 77 ].
Ultimately, airway selectivity should also result in a high pulmonary PD selectivity. Airway selectivity can be further enhanced by optimizing particle size, which, as discussed, is a key determinant of the pulmonary regions in which inhaled drugs are deposited [ 21 , 26 — 29 , 79 ]. Drug concentrations in the lung typically cannot be directly measured. Therefore, to indirectly infer on the pulmonary concentration-time profiles, a combination of PK data after inhalation, oral and IV administration is required.
Furthermore, a mathematical approach to simultaneously integrate all these data and to infer on the relevant pulmonary and systemic kinetic processes is required. Often, it can also be of importance to base these mathematic modelling approaches not only on in vivo PK data but additionally consider high-quality in vitro data, for example, about pulmonary drug deposition or pulmonary drug dissolution [ 80 ].
Even though this integration of data has provided valuable insights into the overall pulmonary PK profile for inhaled drugs, our understanding of the intricacies of the inhalation route remains more limited in comparison to traditional oral and IV routes [ 25 ].
Further PK evaluations have also been published for inhaled drugs such as glycopyrronium [ 61 ], a LAMA, and AZD, a nonsteroidal glucocorticoid receptor modulator [ 86 ]. However, these are beyond the scope of this review. As outlined before, particle size is a key determinant of overall drug deposition in the airways and therefore has a major impact on efficacy [ 21 , 26 ].
Larger particles are deposited to a higher extent in the mouth-throat area, and subsequently a higher fraction of the inhaled drug is swallowed. In a study of monodisperse albuterol aerosols 1. Predicted deposition patterns of the three investigated particle sizes are highlighted in Figure 3.
This example shows that, while a higher lung dose is typically considered to improve lung selectivity, a lower lung dose with an optimal deposition pattern resulted in higher efficacy and lower systemic exposure. In contrast, for idiopathic pulmonary fibrosis patients, a more peripheral deposition pattern was considered valuable, as potential targets are located more peripherally in the lung [ 88 ].
However, as outlined before, it remains to be demonstrated that the pulmonary selectivity in peripheral areas of the lung can be sufficient for future drug targets. In summary, the local pulmonary deposition patterns should be optimized with regard to the target location and the diseased area rather than just the lung dose or the fine particle fraction.
Disease-related factors have been shown to have strong effects on drug PK and PD behavior. In patients with obstructive pulmonary diseases e. In multiple studies comparing the PK of fluticasone propionate and budesonide following inhalation by asthma or COPD patients with healthy volunteers, plasma concentrations of fluticasone propionate were lower in asthma and COPD patients compared with healthy volunteers, whereas those for budesonide were similar between patients and healthy volunteers [ 82 — 84 ].
A potential explanation is the combination of the slow dissolution of fluticasone propionate combined with a high central deposition in patients. This could lead to a higher fraction of the drug to be cleared by the mucociliary clearance in patients compared with healthy volunteers, and consequently, a lower fraction of deposited drug being absorbed in the lung. For bronchodilating drugs or quickly dissolving corticosteroids, as in this case budesonide, the difference in pulmonary PK and resulting systemic concentrations is less pronounced [ 82 , 85 ].
These drugs dissolve faster in the lung fluids compared with fluticasone propionate and might, therefore, already be absorbed to the pulmonary tissue before a substantial amount of particles can be cleared by the mucociliary clearance. This would also result in a higher fraction of the initially deposited lung dose being available in a dissolved state at the target site. These findings suggest superior availability of budesonide compared with fluticasone propionate in acute asthma, in which the airways are markedly narrowed.
This hypothesis is supported by the finding that inhaled fluticasone propionate confers a poor response in children with acute severe asthma [ 90 ]. On first sight, this might be surprising given that fluticasone propionate is considered to be an optimized drug for inhalation. Furthermore, the higher cleared fraction of fluticasone propionate in patients compared with healthy volunteers might be unexpected given that mucociliary clearance is typically slower in patients with airway diseases [ 91 ].
Olodaterol is another inhaled drug reported to have interesting PK characteristics in patients. Here, despite the decreased lung function in asthma and COPD patients, pulmonary bioavailable fractions of inhaled olodaterol were comparable with healthy volunteers [ 85 ].
Although this result is consistent with the established lung dose for the soft mist inhaler used [ 92 ], overall pulmonary absorption was slower in patients [ 85 ]. This is unexpected given that airway epithelia are typically damaged in asthma patients [ 93 ], and the integrity of tight junctions is compromised in COPD patients [ 94 ]. The overall slower absorption was discussed to be a result of the more central deposition in patients, which confers an extended pulmonary residence time.
This suggests preferable lung targeting of inhaled olodaterol in asthma and COPD patients compared with healthy volunteers [ 85 ].
Inhaled drugs are the mainstay of treatment in the care of pulmonary diseases such as asthma and COPD [ 2 — 4 ]. Compared with other routes of administration, respiratory drugs that are specifically designed for inhalation can offer significant benefits, including direct delivery to the disease target site, rapid onset of action, high and long-term pulmonary efficacy, and reduced risk of systemic side effects [ 7 ].
These benefits can be achieved in drug design by considering the physiochemical properties of inhaled drugs e. Overall, a sound understanding of the lung and its associated kinetic processes is necessary to overcome the complex challenges of the inhalational route of administration. Furthermore, the interplay between all pulmonary kinetic processes is highly complex.
All pulmonary kinetic processes must be simultaneously considered as consideration of only a single process or parameter, such as lung dose, can lead to incorrect assumptions or inferences regarding pulmonary efficacy of inhaled drugs. Indexed in Science Citation Index Expanded. Subscribe to Table of Contents Alerts.
Table of Contents Alerts. Abstract The inhalation route is frequently used to administer drugs for the management of respiratory diseases such as asthma or chronic obstructive pulmonary disease. Introduction Inhalation therapy has gained importance in recent decades [ 1 ]. Summary of the lung-specific PK processes for inhaled drugs.
If CBD oil is held under the tongue for 60 to 90 seconds before being swallowed, the mucus membranes in the mouth can absorb the compounds. This sublingual method allows CBD to completely bypass the digestive system and liver metabolism, so the compounds can avoid being broken down by enzymes and reach the bloodstream more quickly.
When CBD oil in inhaled, such as through vaporization, the compounds are absorbed through the alveoli in the lungs, which offer a large absorptive surface area. Once through the alveoli, the CBD molecules are immediately transferred into the bloodstream. Compared to ingestion, the inhalation method allows more CBD to be absorbed and offers faster absorption. Human skin in general has low permeability, which means it blocks most substances from entering. The skin has a particularly low absorption rate for cannabinoids, so application of CBD balms, salves, and lotions need to be heavy enough to overcome this barrier.
However, when applied liberally, CBD is permeable to the skin through its pores. Now that you know that the way that CBD is absorbed varies depends on the administration method, you may decide that one method is more ideal than another depending on your needs. Elimination half-life is about 4 hours. Contraindications and precautions Contraindicated in patients hypersensitive to drug or any component of its formulation.
Use cautiously in patients with CV disorders, including coronary insufficiency and hypertension; in patients with hyperthyroidism or diabetes mellitus; and in those who are unusually responsive to adrenergics. Epinephrin, other orally inhaled sympathomimetic amines: May increase sympathomimetic effects and risk of toxicity. MAO inhibitors, tricyclic antidepressants: Serious CV effects may follow use. Propranolol, other beta blockers: May antagonize effects of albuterol. Overdose and treatment Signs and symptoms of overdose include exaggeration of common adverse reactions, particularly angina, hypertension, hypokalemia, and seizures.
Cardiac arrest may occur. To treat, use selective beta blockers such as metoprolol with extreme caution; they may induce asthmatic attack. Monitor vital signs and electrolyte levels closely. Monitor patient for worsening symptoms or loss of control. These drugs sound and look alike. Tell him to read directions before use, that dryness of mouth and throat may occur, and that rinsing with water after each dose may help.
Shake canister thoroughly to activate it, and place the mouthpiece well into mouth, aimed at back of throat.
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tantly variation in the rate of absorption after inhalation. Oral bioavailability is lowest for fluticasone propionate, indi- cating a low potential for unwanted systemic. Oct 18, Objective The aim of this analysis was to assess the rate and extent of systemic availability of inhaled fluticasone propionate (FP) from 2 dry. Sep 30, Small peptides and proteins are absorbed more rapidly after inhalation than after subcutaneous injection. For other small molecules, inhalation.