The majority of injection drug users (IDUs) are infected with hepatitis C virus (HCV) and are often treated with methadone maintenance therapy (MMT). Data suggests that methadone may suppress interferon-mediated antiviral activity. Studies are needed to evaluate the clinical and pharmacological interaction of Pegasys (peginterferon (40KD) alfa-2a/PEG-IFN) and methadone.

The primary objective of the present study was to evaluate the potential for pharmacokinetic (PK), pharmacodynamic (PD) and clinical drug interactions with the concomitant use of 180 microgram PEG-IFN and methadone in CHC patients on MMT.

The PK and PD of PEG-IFN were evaluated after single and multiple weekly 180 microgram doses in 24 CHC patients on MMT. PEG-IFN's effect on methadone pharmacokinetics was assessed by the comparison of methadone's PK before and after multiple doses of PEG-IFN.

The PD effects of PEG-IFN were assessed by measuring 2',5'-oligoadenylate synthetase (2',5'-OAS) serum activity and HCV kinetics. Non-compartmental PK and PD analyses, including descriptive statistics and an ANOVA, were completed.

The majority of patients enrolled were male (63%), Caucasian (63%), 50 to 124 kg, and 34 to 57 years old. Patients received stable daily methadone doses of 30 to 150 mg. PEG-IFN PK at week 1 and week 4 was similar to PEG-IFN PK determined from historic data in CHC patients not receiving MMT.

Methadone PK was similar at baseline and after 4 weeks of PEG-IFN treatment. PEG-IFN-induced 2',5'-OAS activity after a single dose was similar to that seen in healthy subjects.

Twelve of 20 (60%) patients demonstrated a virological response (undetectable [<600 IU/mL] or a 2-log10 drop in HCV RNA serum concentrations) by treatment week 4.

The most frequently reported adverse events included headache, myalgia, pyrexia, fatigue and anorexia; most were mild or moderate in intensity. No signs of opioid withdrawal were observed. No patient modified methadone or PEG-IFN doses during the study. One subject withdrew prematurely due to poor venous access.

Conclusions:

- PEG-IFN monotherapy is well tolerated by CHC patients receiving MMT;

- PEG-IFN and methadone do not significantly alter the PK of each respective therapy;

- Biologic response as assessed by 2',5'-OAS activity was similar to that in healthy subjects;

- HCV RNA decline was similar to that seen in CHC patients not receiving MMT;

- These data suggest that MMT does not impair the antiviral activity of PEG-IFN.

Reference
MS Sulknowsi and others. Pharmacokinetics, Pharmacodynamics and Antiviral Response in Patients with Chronic Hepatitis C Infection on Methadone Maintenance Therapy Receiving Peginterferon (40KD) Alfa-2a (Pegasys®). Abstract 231. Abstracts of Digestive Disease Week 2003. May 17-22, 2003. Orlando, FL, USA.