Lactose monohydrate, or alpha-lactose monohydrate, is a crystalline milk powder. It has various properties that make it useful as a pharmaceutical filler in the manufacture of capsules and tablets. The powder is available in different grades, depending on particle size distribution, density and how easily it flows. It is also used to make infant formulas, freeze-dried products and dry powder inhalers.
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Alpha-lactose monohydrate is the most commonly used form of lactose, or milk sugar, in making medications for a number of reasons. It is affordable, widely available, physically and chemically stable and easy to mix with other ingredients. It also has a bland taste and does not absorb water. Rather, it dissolves readily in water. For this reason, formulations that include the powder as an ingredient do not contain much water.
The commercial manufacture of the powder consists of chilling a concentrated solution of lactose to a low enough temperature that it forms crystals. A centrifuge is then used to separate out the crystals, which are then dried. Because the manufacture of tablets in high-speed presses requires a consistent flow of powder, flowability is essential for efficient production. Low flowability may cause uneven feed and unreliable filling of die cavities. Manufacturers must develop a powder that results in tablets whose weights are as uniform as possible.
Factors such as the size and shape of the particles in the powder, as well as the distribution of particle size and humidity help determine flowability. Coarse powders with undamaged particles that are spherical, regular in shape and close in size have greater flowability. However, a coarse powder dissolves more slowly than a fine powder since that particles are larger, though final solubility is not affected. Heat will increase solubility.
Lactose monohydrate powder and other forms of lactose in pharmaceutical formulations are usually present in quantities of 1 g or less per pill. Lactose-sensitive individuals seem to tolerate the small amounts well. Also, because lactose is absorbed more slowly than glucose and sucrose, diabetics can also take the pills safely. In addition, bacteria in the mouth that cause dental caries by fermenting sucrose are less able to use lactose.