What are Small and Large Molecules?

  • An essential facet of determining the right approach for a new treatment is choosing the best technology platform. Molecules that serve as active substances can be divided into two classes – small and large molecules. These two do not only differ in terms of size, but also in how they are prepared, how they work or function, their mechanism of action in the body and their suitability for certain drug dosage forms. 
  • Small, chemically manufactured molecules (or sMOLs) are the typical active substances that make up about 90% of the drugs in the market today. On the other hand, large molecules or biologics, are regarded as therapeutic proteins with an increasing significance in the medical field.
  • Small molecules are the basis of classic drug development. These small molecules can be processed into drug dosage forms like tablets, capsules or syrups. Because of their small structure and chemical composition, they are able to easily penetrate cell membranes. These drugs are synthesized the standard way, which is by chemical reactions between different organic and/or inorganic compounds.  
  • Biologics or biopharmaceuticals are innovative drugs made of proteins. These large protein molecules are basically augmented versions of endogenous human proteins. They are able to bind to specific cell receptors that are associated with the disease process. They are generally prepared in genetically engineered cells making its manufacturing more challenging than traditional small molecule drugs. Minor changes during processing can cause substantial changes to their efficacy and immunogenicity.
  • Selected categories of biologic agent structure:
    Growth factor: A substance, usually a polypeptide, promotes growth, especially cellular growth. (Examples are erythropoietin, colony-stimulating factors)
    • — Interferons: Proteins that are normally produced by cells in response to viral infection and other stimuli. They usually have a property of inhibiting virus replication.
    • — Interleukins: A large group of cytokine proteins. Most are involved in directing other immune cells to divide and differentiate. They are produced by leukocytes for regulating immune responses.
    • — Monoclonal antibodies (MAbs): An antibody produced by a single clone of cells or cell line and consisting of identical antibody molecules. MAbs recognize only one chemical structure, i.e., they are directed against a single epitope of the antigenic substance used to raise the antibody.
    • — Polypeptides: Peptides containing ten or more amino acids. Typically, a peptide consists of fewer than 50 amino acids, while a protein has more than 50 amino acids.
    • — Vaccine: a biological preparation that provides active acquired immunity to a particular disease. It contains antigens produced from killed, attenuated or live pathogenic microorganisms, synthetic peptides, or by recombinant organisms. These are used for stimulating the immune system of the recipient to produce specific antibodies providing active immunity and/or passive immunity in the progeny.