Biologics and nucleic acid medicines
Medicines made from proteins, cells or genetic material: antibodies, hormones, antisense and siRNA drugs, gene and cell therapies.
Biologics are large, complex medicines made from or by living systems: proteins such as insulin and monoclonal antibodies, and newer products built from nucleic acids or cells. They reach targets small molecules cannot, but they are usually injected, can trigger immune responses and are costly to make.
Therapeutic proteins
Recombinant proteins replace or add a natural protein: insulin, growth hormone, erythropoietin, coagulation factors and enzymes. Insulin illustrates the shift: once regulated as a chemical drug, it is now regulated as a biologic. Because biologics come from living sources, small batch-to-batch differences are normal, which is why copies are biosimilars rather than generics.
Monoclonal antibodies
Antibodies bind a single antigen. They can block a ligand or receptor (anti-TNF, anti-VEGF, anti-PCSK9), mark cells for immune destruction (anti-CD20), release the brakes on immunity (checkpoint inhibitors) or carry a toxin to a tumour (antibody-drug conjugates). They are large proteins, so they are given by injection or infusion. Examples on DurgiPedia include adalimumab (anti-TNF), rituximab (anti-CD20) and pembrolizumab (a checkpoint inhibitor).
Nucleic acid medicines
- Antisense oligonucleotides (ASO): short synthetic strands that bind a target RNA; nusinersen, injected into the fluid of the spinal canal, increases a protein that muscles and nerves need in spinal muscular atrophy.
- Small interfering RNA (siRNA): double-stranded RNA that silences a target mRNA; inclisiran, a PCSK9-interfering RNA medicine, lowers LDL cholesterol with injections given only a few times a year.
- Both act on RNA, changing how much of a protein the cell makes rather than blocking the protein itself.
Gene and cell therapies
Gene therapy modifies genes to treat disease by replacing a faulty gene with a working copy, inactivating a harmful gene or adding a new or modified gene. Products include plasmid DNA, modified viruses that can no longer cause infection (viral vectors), bacterial vectors and gene-editing tools. In patient-derived cell therapies, a person's cells are removed, modified (often with a viral vector) and returned; CAR-T cells, engineered to attack cancer cells, are an example. In the US these products are regulated as biologics, and FDA guidance covers long-term follow-up after treatment.
Practical differences from small molecules
- Route: injection or infusion; oral absorption is negligible for large molecules.
- Immunogenicity: biosimilars must match the reference product in immunogenicity, because the immune response to a biologic matters for safety and effect.
- Manufacturing: purification and processing are more complex than for chemical drugs.
- Copies: approved as biosimilars rather than generics.
- Cost: biosimilar competition can lower prices and widen coverage.
Test yourself
Think of the answer, then tap the question to see it.
Why are most biologics given by injection?
They are large proteins or nucleic acids that are digested or poorly absorbed in the gut.
How does an antisense oligonucleotide differ from an siRNA?
An ASO is a single synthetic strand that binds target RNA; an siRNA is double-stranded and silences a target mRNA through the RNA interference machinery.
What are the three basic ways gene therapy can treat disease?
Replacing a faulty gene with a healthy copy, inactivating a harmful gene, or introducing a new or modified gene.
Why can a biologic not be copied as an exact generic?
It is made in living systems with natural batch-to-batch variability, so copies are approved as highly similar biosimilars.
Example drugs
- Regular human insulin
- Adalimumab
- Rituximab
- Pembrolizumab
- Nusinersen
- Tofersen
- Inclisiran
- Onasemnogene abeparvovec
- Tisagenlecleucel
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: What is Gene Therapy? | FDA (U.S. Food and Drug Administration, 2026); Biosimilars Basics for Patients | FDA (U.S. Food and Drug Administration, 2026); Nusinersen Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); Inclisiran injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026).
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Representative model, for educational purposes only.