growth. They are classified as alfa, beta or gamma according to their antigenic and physical properties. Alfa interferons (subclassified -2a, -2b and -Nl) are effective against conditions that include hairy cell leukaemia, chronic myelogenous leukaemia, recurrent or metastatic renal cell carcinoma, Kaposi's sarcoma in AIDS patients (an effect that may be partly due to its activity against HIV) and condylomata acuminata (genital warts).
Interferon alfa-2a and -2b also improve the manifestations of viral hepatitis, but responses differ according to the infecting agent (see p. 658). Whereas patients with hepatitis B and C may respond to interferon alfa, those with hepatitis C have a higher rate of relapse and may need prolonged therapy. Interferon alfa-2b has been used in combination with ribavirin for moderate to severe, chronic hepatitis C infection, but not in patients who are heavy imbibers of alcohol because of the risks of liver damage. Successful treatment results in the serum concentration of viral RNA becoming undetectable by polymerase chain reaction (PCR). Hepatitis D requires a much larger dose of interferon to obtain a response and yet relapse may occur if the drug is withdrawn.
Adverse reactions are common and include an influenza-like syndrome (naturally-produced interferon may cause symptoms in natural influenza infection), fatigue and depression which respond to lowering the dose. Other effects are anorexia (sufficient to induce weight loss), convulsions, hypotension, hypertension, cardiac arrhythmias and bone marrow depression. Interferons inhibit the metabolism of theophylline, increasing its effect.
This drug is reported to stimulate the host immune response to virus infection and has been used for mucocutaneous herpes simplex and genital warts (but aciclovir is superior). It is administered by mouth and metabolised to uric acid, so should be used with caution in patients with hyperuricaemia or gout.
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