The Differences Between Small Molecule Drugs and Biological Drugs?

Posted onAuthorLinda Kesselring

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What are small molecule drugs?
Small molecule drugs, as their name suggests, are chemical compounds that have low molecular weight – a single molecule of a small molecular drug typically contains only 20 to 100 atoms. They can enter cells easily where they interact with molecules within the cell.

What are some examples of small molecule drugs?
Despite the development of more targeted drugs, small molecule drugs are immensely popular, and account for 90% of drugs in the market. Examples of common small molecule drugs include aspirin, penicillin, paracetamol, and esomeprazole (sold under the brand name Nexium and helps reducing stomach acid).

What are biological drugs?
Biological drugs are drugs that are manufactured or extracted from living organisms. These drugs can consist of genetic material or proteins such as hormones or antibodies. These are typically larger in size than small molecule drugs, with a single molecule consisting of anywhere between 200 to 50,000 atoms.

Unlike small molecule drugs that are characterized by their specific chemical composition, it can be difficult to determine the exact chemical composition of biological drugs because they are often large, complex molecules. Instead, these are characterized by the process by which they are obtained.

What are some examples of biological drugs?
Some examples of biological drugs include:

  • Insulin
  • Vaccines
  • Trastuzumab, a drug used to treat breast cancer. Trastuzumab is an antibody that binds to a receptor involved in the development of breast cancer and prevents it from firing cellular signals.
  • Adalimumab, also an antibody, that is used to treat rheumatoid arthritis.

How does drug delivery differ between the two types of drugs?
Small molecule drugs are typically administered orally. Biological drugs, on the other hand, are not as stable as small molecule drugs. If they are consumed orally, they degrade in the gastrointestinal tract. As a result, biological drugs are typically administered by injection or infusion.  

What are some of the pros and cons of the two types of drugs?

  • Small molecule drugs are a lot easier to administer than biological drugs.
  • Biological drugs are highly targeted drugs. They don’t bind to non-target molecules, and as a result, lead to fewer side effects.
  • Biological drugs are much more expensive to develop and hence are much more expensive for patients.
  • Innovations are assisting the development of both small molecule and biological drugs. Sophisticated gene editing tools such as CRISPR/Cas9 have transformed medical research, and have pushed the boundaries of the kinds of targeted therapies and drugs that can be discovered. At the same time, small molecule drugs are likely going to remain important, and their discovery is projected to be aided by the use of technologies like artificial intelligence.

What are generic drugs and biosimilars and how are they regulated?
A generic drug is a drug that has the same active ingredients as the drug that was originally patented. Generic drugs have the same dosage, intended use, and method of administration as the brand-name drug, although the manufacturing process might differ.
Biosimilars are drugs that are “highly similar” to biological drugs but are not necessarily identical to them. Because of the large size and complexity of biological drugs, biosimilars do not have to be exact copies of the original biological drug in order to have the same therapeutic function.

The regulations governing generic drugs are fairly straight forward: the Hatch-Waxman Act of 1984 provides drug innovators with 5 years of market exclusivity. After this period expires, generic drugs can enter the market, as long as clinical trials are conducted, and the FDA had ensured that manufacture of drugs is consistent. These regulations have been vital in lowering prescription drug costs. Today, nearly 90% of prescription drugs are generic drugs which can cost up to 80% lesser than brand-name drugs.

Regulations governing biosimilars are more complicated. These regulations were signed into law in 2010 under the Biologics Price Competition and Innovation Act (BPCIA) give 12 years of market exclusivity to the drug innovator. Additionally, for biosimilars to be approved, manufacturers have to conduct more rigorous clinical trials compared to those required for generic drugs. These stricter regulations have led to an increase in biological drug costs – Medicare and Medicaid spending biological drugs has ballooned from $5.3 billion in 2012 to $10.3 billion in 2016.

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