Increase in platelet count based on inosine triphosphatase genotype during interferon beta plus ribavirin combination therapy.

BACKGROUND AND AIM: The inosine triphosphatase (ITPA) genotype is associated with ribavirin-induced anemia and pegylated interferon α (PEG IFN-α)-induced platelet reduction during PEG IFN-α plus ribavirin combination therapy. Natural IFN-β plus ribavirin therapy is associated with increases in platelet counts during treatment. We investigated decreases in platelet counts according to ITPA genotype during natural IFN-β/ribavirin therapy to determine if patients with low platelet counts were eligible for this combination therapy.

METHODS: A total of 187 patients with chronic hepatitis C received PEG IFN-α/ribavirin or natural IFN-β/ribavirin therapy. Decreases in platelet counts based on ITPA genotype were investigated during treatment through 24 weeks.

RESULTS: Platelet counts decreased during week 1 of PEG IFN-α/ribavirin therapy, but increased during week 2, after which platelet counts decreased gradually. Platelet counts decreased until week 4 of natural IFN-β/ribavirin therapy, after which platelet counts increased. Platelet counts after week 8 were higher relative to pretreatment platelet counts. Patients with the ITPA-CC genotype showed a smaller decrease in platelet counts during natural IFN-β/ribavirin therapy than those with the ITPA-CA/AA genotype; platelet counts after week 8 of this therapy were higher than pretreatment platelet counts, regardless of pretreatment platelet counts. Multivariate logistic regression analyses showed that natural INF-β/ribavirin therapy was the only significant independent predictor for an increase in platelets through week 8.

CONCLUSION: Natural IFN-β/ribavirin therapy is safe for patients with the ITPA-CC genotype, even if their pretreatment platelet counts are low.