Clinical pharmacology The interferons

are a family of naturally occurring small proteins and glycoproteins produced and secreted by cells in response to viral infections and to synthetic or biological inducers. Interferons as a class possess antitumor, antiviral, and immunomodulating activity. Interferon alfa-2b recombinant is similar to interferon alfa-2a recombinant in that both are pure clones of single interferon subspecies; they differ by the sequence of two amino acids.

Pharmacokinetics The elimination half-life of interferon alfa-2b after subcutaneous or intramuscular administration is 2 to 3 hours.

Dispostion Interferon alfa-2b undergoes extensive proteolytic degradation in the kidney (during tubular reabsorption); hepatic metabolism is minimal.

Drug Interactions According to the product label, interactions between Intron A and other drugs have not been fully evaluated. Caution should be exercised when administering Intron A therapy in combination with other potentially myelo-suppressive agents such as zidovudine. Concomitant use of alfa interferon and theophylline decreases theophylline clearance, resulting in a 100% increase in serum theophylline levels.

E. Therapeutic response The percentage of patients with hairy-cell leukemia who required red blood cell or platelet transfusions decreased significantly during treatment with Intron A, and the percentage of patients with confirmed and serious infections declined as granulocyte counts improved. Intron A therapy produced a significant increase in relapse-free and overall survival in patients with malignant melanoma. Patients receiving the combination of Intron A therapy plus che motherapy had a significantly longer progression-free survival than patients who received chemotherapy alone. Intron A treatment of condylomata was significantly more effective than placebo, as measured by disappearance of lesions, decreases in lesion size, and by an overall change in disease status. Studies in patients with chronic hepatitis C demonstrated that Intron A therapy can produce meaningful effects on this disease, manifested by normalization of serum alanine aminotrans-ferase and reduction in liver necrosis and degeneration.

F. Role in therapy According to Micromedex, Intron A is the agent of choice for the treatment of malignant melanoma (surgical adjuvant) and chronic hepatitis B. It is also the drug of choice for chronic hepatitis C in combination with ribavirin. The combination is available under the name Rebetron. Intron A is an alternative (unresponsive/intolerant patients) to pentostatin in hairy-cell leukemia, topical podophyllin regimens in condyloma acuminata, and standard regimens in multiple myeloma.

G. Other applications Intron A has been used in the treatment of many viral infections and malignancies, but documentation of safety and efficacy is poor.

H. Other considerations Interferon alfa-2b has been designated an orphan product for use in the treatment of Kaposi's sarcoma.

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