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In medicine, the effectiveness and safety of many therapies, especially drug delivery methods, depend on the size of the medication particles. This is a crucial factor in determining the so-called 'd50 particle size', which refers to the median diameter of a particle population, meaning that when d50 is measured, 50% of the particles are smaller than that size, while the other 50% are larger. In pharmacology, the dose is the quantity of medicine that a physician prescribes to be taken by the patient to achieve the desired health benefits.
There are two d50 particle size, namely the volume d50 (or 'fine mass median aerodynamic diameter') and the surface area d50 (or 'effective mass median aerodynamic diameter'). The volume d50 size is important in medicinal aerosols. Large d50 sizes can lead to drugs accumulating in large airways and not penetrating them for deep lung diseases like COPD and cystic fibrosis. Small d50 sizes promote better drug dispersion and deeper lung drug delivery; hence, effective padeck in these conditions. On the other hand, the surface area d50 is of interest for formulations exposed to high surface shear during processing, such as dry powder inhalers (DPIs). Notice that DPIs are dry powder inhalation devices; they are instruments that are used to administer medication to the lungs using dry powder as the medication. Shear force is the force responsible for the deformation of solid materials, and it can affect their size and release. Reduction in effective e median aerodynamic diameter force results in smoother and more fine particles, ultimately achieving better lung padek
Pharmacy is about the only medical area where the d50 particle size is primarily used. However, it's worth noting that in other industries, such as food, cosmetics, and manufacturing, its values are also championed for functional assessments. For instance, in foods such as eggs, chicken, and vegetables that are eaten raw or are prepared with untreated water, geometric mean diameter measurement and monitoring can be key to pathogen intervention success, as pathogens can be associated with food particles, including those much finer than d50.
Cosmetics such as deodorants, home inhalers, nasal sprays, and eye drop preparations, where active ingredients and excipients are contained, and their physicochemical characteristics can determine drug delivery system effectiveness and safety. Likewise, the large dimension of dietary supplements such as powdered herbs and vitamins, drugs, and d50 sizes can affect their solubility, bioavailability, and cascade effect onset.
In the medicinal aerosol and powder industry, there is a concern that measuring only the d50 is not sufficient to determine the lung deposition of inhaled drugs. There are also metrics such as d90 (the diameter below which 90% of the particles fall), and cystic fibrosis refers to the percentage of particles below a certain size and the particle size distribution span (the difference between the smallest and the largest particle). These metrics and the d50 are often measured together as a set so that one is not solely dependent on the d50 alone. For example, the average effective size based on surface versus volume and the spread of particle size distribution provide little or no aerodynamic consequence due to lung deposition. Hence, measuring a particle size distribution without considering surface area-effective and d50 metrics, for example, only measuring the diameter without considering the surface area effective, is not sufficient.
Measurement techniques
The most commonly used techniques to measure the d50 of aerosols are laser diffraction and electrozone sensing. Note that laser diffraction is the gold standard because it allows rapid and high-throughput measurement over a wide range of particle sizes. Electrozone sensing provides high-resolution measurement over a narrow particle size range but can be time-consuming. Also, laser diffraction can only measure what can be seen but cannot see what cannot be seen.
Granulometry
Measurement of d50 requires a granulometer or particle sizer, a dedicated instrument used to measure the particle size distribution of a powder or suspension. Granulometers come in a number of sizes and shapes, including laser diffraction instruments like the Malvern Mastersizer, which uses laser interference to quantify the sizes of the particles. There are also smaller particle size analyzers, such as the Horiba LA-950, constrained only to the fine end of the distribution.
Test sieves
Test sieves are a relatively simple and low-tech method that utilizes a series of woven wiremesh screens to give the relative proportion of particles retained on each sieve, hence giving the d50.
Inhalation
Measurements of d50 mean that non-hydroscopic drugs may undergo restructuring by inhalation. In theory, this could affect deposition. Doses that are taken should be small amounts within the range of micrograms to milligrams. However, larger d50s and smaller doses should also be allowed because less energy is required for larger-sized particles to break the surface tension and deposit in the lungs.
Oral administration
Orally administered drugs may have d50s because they affect the rate and degree of absorption; hence, they should not be very large or too small. Only small particle sizes are preferred for enhanced bioavailability. Conferring to non-invasive substitute medicines, for instance, vitamin B12, d50s exert an important role since they determine whether such drugs pass through biological barriers such as membranes and are absorbed.
Quality and safety regarding the d50 particle size are quite intertwined with those of the pharmaceutical product, aerosol, or spray in their related fields. Here are some important considerations:
Quality control of inhaled medicines
Inhaled medicines, especially those meant for lung diseases, undergo rigorous quality control. Key size and d50 metrics monitor drug delivery efficiency and safety. For example, effective metered e median aerodynamic diameter and particle size distribution are crucial for deep lung drug delivery to be effective and efficient. Furthermore, consistent d50 values ensure that each dose of the medicine is delivered with precision. Inadequately sized particles may cause poor drug distribution, resulting in underdose in target lungs or overdose in other potentially dangerous areas such as the bloodstream.
Formulation stability
Quality also comes in the form of stability. Inhaled therapies are particularly delicate, requiring stable formulations where d50 sizes must remain consistent with the shelf life. If particle sizes change, the formulation may become ineffective due to variations in lung deposition. Quality d50 measurements help ensure that products maintain their therapeutic potency and efficacy over time.
Safety concerns
Inhaled medicines, especially those used in lung diseases, are mass median aerodynamic diameter measured for safety concerns. Particles that are too large can become lodged in major airways resulting in airway obstruction; on the other hand, particles that are too small can penetrate deep respiratory tract and interact with blood; hence the sizes must be constrained within safe limits.
A1: D50 means that 50% of the particles have a diameter less than D and 50% have a diameter greater than D.
A2: The ideal average particle size for inhalable drugs is between 1 and 5 micrometers.
A3: Inhaled drugs whose particles are greater than 10 micrometers are generally deposited in the mouth or taken to the bronchial tubes and are unable to reach the lungs.
A4: Laser diffraction and cascade impactor are the most commonly used methods to assess the particle size distribution of pharmaceutical aerosols.
