Interferons

Interferons

A family of naturally occurring glycoproteins, interferons are so named because of their ability to interfere with viral replication. These drugs exhibit anticancer activity as well as activity against condylomata acuminata (soft, wartlike growths on the skin and mucous membrane of the genitalia caused by a virus). The three types of interferons are:

• alfa interferons derived from leukocytes
• beta interferons derived from fibroblasts (connective tissue cells)
• gamma interferons derived from fibroblasts and lymphocytes.

Pharmacokinetics

After I.M. or subcutaneous administration, interferons are usually well absorbed. Information about their distribution is unavailable.

Metabolism and excretion

Alfa interferons are filtered by the kidneys, where they’re degraded. Liver metabolism and biliary excretion of interferons are negligible.

Pharmacodynamics

Although their exact mechanism of action is unknown, interferons appear to bind to specific membrane receptors on the cell surface. When bound, they initiate a sequence of intracellular events that includes the induction of certain enzymes.

Running interference

This process may account for the ability of interferons to:

• inhibit viral replication
• suppress cell proliferation
• enhance macrophage activity (engulfing and destroying microorganisms and other debris)
• increase cytotoxicity of lymphocytes for target cells.

Pharmacotherapeutics

Alfa interferons have shown their most promising activity in treating blood malignancies, especially hairy cell leukemia. Their approved indications currently include:

• hairy cell leukemia
  
  
• AIDS-related Kaposi’s sarcoma
• condylomata acuminata.

Interfering in these areas as well…

Alfa interferons also demonstrate some activity against chronic myelogenous leukemia, malignant lymphoma, multiple myeloma, melanoma, and renal cell carcinoma.

Drug interactions

Interferons interact with other drugs:

• They may enhance the CNS effects of CNS depressants and substantially increase the half-life of methylxanthines (including theophylline and aminophylline).
• Concurrent use with a live virus vaccine may potentiate replication of the virus, increasing the adverse effects of the vaccine and decreasing the patient’s antibody response.
• Bone marrow suppression may be increased when an interferon is used with radiation therapy or a drug that causes blood abnormalities or bone marrow suppression.
• Alfa interferons increase the risk of kidney failure from interleukin-2. 

Warning!

Adverse reactions to interferons

Blood toxicity occurs in up to one-half of patients taking interferons and may produce leukopenia, neutropenia, thrombocytopenia, and anemia. Adverse GI reactions include anorexia, nausea, and diarrhea.

Alfa concerns

The most common adverse reaction to alfa interferons is the development of flulike symptoms, which may produce fever, fatigue, muscle pain, headache, chills, and joint pain.

It catches your breath

Coughing, difficulty breathing, hypotension, edema, chest pain, and heart failure have also been associated with interferon therapy.