A Modest Excipient with an Outsized Role
Lactose is the sugar naturally found in mammalian milk. Mildly sweet, inexpensive, chemically inert and widely available, it has become the most widely used filler excipient in tablet and capsule manufacturing.
Its history is a textbook case in pharmaceutical formulation: from its isolation out of whey to the modern pharmaceutical grades engineered for direct compression, lactose has evolved across several centuries of chemistry and pharmacy.
A Discovery Spanning Three Centuries
Since milk is the primary carbohydrate source for mammals, lactose has been known empirically since the dawn of animal husbandry. Its isolation as a distinct substance, however, is credited to the Italian physician Fabrizio Bartoletti, who in the early seventeenth century obtained a "milk salt" by evaporating whey.
In the eighteenth century, Swedish chemist Carl Wilhelm Scheele identified its sweet nature in 1780. It was French chemist Jean-Baptiste Dumas who finally named it lactose in 1843, from the Latin lac, meaning milk. Its structure as a disaccharide made up of galactose and glucose would only be fully elucidated by sugar chemistry at the turn of the twentieth century.
Crystalline Forms, Distinct Technological Properties
Lactose is a mildly sweet sugar, soluble in water and chemically stable. It exists in several crystalline forms, each with distinct technological properties:
- Lactose monohydrate (α), obtained by crystallization followed by milling or sieving, widely used in wet granulation.
- Anhydrous lactose (β), less sensitive to moisture.
- Spray-dried lactose, with excellent flow and compression properties, specifically engineered for direct compression.
This diversity of forms and grades explains the many commercial references — Pharmatose, Flowlac, SuperTab, Tablettose, among others — found in raw material catalogs.
Digestion and Tolerance: What to Know
Lactose is digested through an intestinal enzyme, lactase, which breaks it down into absorbable glucose and galactose. Part of the population has a lactase deficiency, known as lactose intolerance.
At the quantities present in medicines, the lactose load is generally very low and well tolerated. This characteristic must nonetheless appear in product information, since some patients are sensitive to it.
A Multifunctional Pharmaceutical Excipient
Lactose serves several functions in the formulation of solid dosage forms and powders:
- Diluent / filler for tablets and capsules, valued for its low cost, availability, inertness and neutral taste.
- Carrier for direct compression, in its spray-dried or co-processed grades.
- Granulating agent, in wet granulation processes.
- Carrier for inhalation powders in dry powder inhalers, where large lactose particles carry the micronized active ingredient to the respiratory tract.
Owing to its compatibility and versatility, lactose is paired with a very large number of active pharmaceutical ingredients. However, its Maillard reactivity with amine-bearing molecules — including certain active ingredients — must be taken into account, as it can lead to browning or degradation. Hence the importance of compatibility studies conducted during formulation development.