Classification and Pharmacodynamics
There are three main types of interferons (IFNs), which differ in their producing cells, induction stimuli, and predominant pharmacological effects:
- IFN-alpha (produced predominantly by leukocytes) and IFN-beta (synthesized by fibroblasts). Viral infections and cytokines (IL-1, IL-2, TNF) serve as stimuli for their synthesis. These types feature predominantly antiviral and antiproliferative activity. They actively stimulate the cytotoxicity of immunocompetent cells (macrophages, lymphocytes, natural killer cells).
- IFN-gamma (produced by T lymphocytes and natural killer cells). It is produced in response to antigenic stimulation. Here, the immunomodulatory effect comes to the fore, whereas the antiviral effect is relatively weak.
Molecular Mechanism of Antiviral Action
Interferon itself does not destroy the virus directly. The effect is realized at various stages of viral reproduction through a complex intracellular reaction cascade:
- The interferon molecule binds to specific receptors on the cell surface.
- Protein synthesis is induced — genes encoding protective effector enzymes are activated.
- The synthesized proteins block viral DNA and RNA replication.
Key IFN-induced enzymes:
- Oligoadenylate 2'-5' (A) synthetase — activates endoribonucleases that degrade single-stranded RNA (both viral and cellular). This enzyme is used as a marker of interferon biological activity.
- Protein kinase R — phosphorylates cellular translation initiation factors, leading to their inactivation and complete blockade of viral protein synthesis.
Main Drug Groups
Pharmacological agents are divided into natural (derived from biological material — blood leukocytes) and recombinant (created via genetic engineering methods).
Natural preparations:
- Human leukocyte interferon (a mixture of IFN-alpha subtypes) — used intranasally for the prevention and treatment of influenza and ARVI.
- Lockferon — used topically for viral eye diseases.
Recombinant preparations (systemic and topical):
- IFN-alpha-2a: Roferon-A (systemic for hepatitis B and C, chronic myelogenous leukemia, Kaposi sarcoma), Reaferon-ES, Ophthalmoferon (eye drops combining IFN with the antihistamine diphenhydramine).
- IFN-alpha-2b: Differs from 2a by the presence of the amino acid arginine at position 23. Includes parenteral formulations (Altevir, Intron-A), oral forms (Reaferon-ES-Lipint), intranasal drops (Gripeferon), and rectal suppositories (Genferon Light, Viferon).
- IFN-beta-1a: Rebif, Avonex. Used for multiple sclerosis, herpes, HPV, and hepatitis (often in combination therapy with ribavirin).
Pegylation and Pharmacokinetics
Standard parenteral formulations of interferons have a bioavailability of about 80%, are metabolized in the liver and kidneys, and have a half-life ($t_{1/2}$) of only 3–8 hours.
To improve pharmacokinetic properties, pegylation is applied — attaching a monomethoxypolyethylene glycol (PEG) moiety to the interferon molecule. This prolongs the drug's action: $t_{1/2}$ increases to 80–90 hours. Due to this, pegylated interferons (Pegasys, PegIntron) can be administered subcutaneously just once a week. They are effective in treating hepatitis B and C, including cases resistant to conventional interferons.
Safety Profile
Interferon therapy is frequently accompanied by adverse reactions. The most common is flu-like syndrome, occurring a few hours after injection. It manifests as fever (usually resolving within 12 hours), myalgia, arthralgia, headache, and gastrointestinal disturbances (nausea, vomiting, diarrhea).
Hematological toxicity is also characteristic (thrombocytopenia, neutropenia — especially frequent with pegylated forms). Organ toxicity may occur: central nervous system and cardiovascular disorders, nephritis, pneumonia, and hepatotoxicity.