Interactions : אינטראקציות

4.5   Interaction with other medicinal products and other forms of interaction

Interaction studies have only been performed in adults.
Administration of Pegasys 180 micrograms once weekly for 4 weeks in healthy male subjects did not show any effect on mephenytoin, dapsone, debrisoquine and tolbutamide pharmacokinetics profiles, suggesting that Pegasys has no effect on in vivo metabolic activity of cytochrome P450 3A4, 2C9, 2C19 and 2D6 isozymes.

In the same study, a 25% increase in the AUC of theophylline (marker of cytochrome P450 1A2 activity) was observed, demonstrating that Pegasys is an inhibitor of cytochrome P450 1A2 activity. Serum concentrations of theophylline should be monitored and appropriate dose adjustments of theophylline made for patients taking theophylline and Pegasys concomitantly.
The interaction between theophylline and Pegasys is likely to be maximal after more than 4 weeks of Pegasys therapy.

HCV monoinfected patients and HBV monoinfected patients

In a pharmacokinetic study of 24 HCV patients concomitantly receiving methadone maintenance therapy (median dose 95 mg; range 30 mg to 150 mg), treatment with Pegasys 180 micrograms sc once weekly for 4 weeks was associated with mean methadone levels that were 10% to 15% higher than at baseline. The clinical significance of this finding is unknown; nonetheless, patients should be monitored for the signs and symptoms of methadone toxicity. Especially in patients on a high dose of methadone, the risk for QTc prolongation should be considered.

Ribavirin, by having an inhibitory effect on inosine monophosphate dehydrogenase, may interfere with azathioprine metabolism possibly leading to an accumulation of 6- methylthioinosine monophosphate (6-MTIMP), which has been associated with myelotoxicity in patients treated with azathioprine. The use of peginterferon alfa-2a and ribavirin concomitantly with azathioprin should be avoided. In individual cases where the benefit of administering ribavirin concomitantly with azathioprine warrants the potential risk, it is recommended that close haematologic monitoring be done during concomitant azathioprine use to identify signs of myelotoxicity, at which time treatment with these medicinal products should be stopped (see section 4.4).

Results from pharmacokinetic substudies of pivotal phase III trials demonstrated no pharmacokinetic interaction of lamivudine on Pegasys in HBV patients or between Pegasys and ribavirin in HCV patients.

A clinical trial investigating the combination of telbivudine 600 mg daily, with pegylated interferon alfa-2a, 180 micrograms once weekly by subcutaneous administration for the treatment of HBV, indicates that the combination is associated with an increased risk for developing peripheral neuropathy. The mechanism behind these events is not known; thus, co-treatment with telbivudine and other interferons (pegylated or standard) may also entail an excess risk. Moreover, the benefit of the combination of telbivudine with interferon alfa (pegylated or standard) is not currently established.
Therefore, the combination of Pegasys with telbivudine is contraindicated (see section 4.3).



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PEGASYS                                                      MoH Approved Prescribing Information Pre-Filled Syringe, Pre-Filled Pen 135 & 180 mcg                                 December 2015 HIV-HCV co-infected patients
No apparent evidence of drug interaction was observed in 47 HIV-HCV co-infected patients who completed a 12 week pharmacokinetic substudy to examine the effect of ribavirin on the intracellular phosphorylation of some nucleoside reverse transcriptase inhibitors (lamivudine and zidovudine or stavudine). However, due to high variability, the confidence intervals were quite wide. Plasma exposure of ribavirin did not appear to be affected by concomitant administration of nucleoside reverse transcriptase inhibitors (NRTIs).

Co-administration of ribavirin and didanosine is not recommended. Exposure to didanosine or its active metabolite (dideoxyadenosine 5’-triphosphate) is increased in vitro when didanosine is co-administered with ribavirin. Reports of fatal hepatic failure as well as peripheral neuropathy, pancreatitis, and symptomatic hyperlactataemia/lactic acidosis have been reported with use of ribavirin.

Exacerbation of anaemia due to ribavirin has been reported when zidovudine is part of the regimen used to treat HIV although the exact mechanism remains to be elucidated. The concomitant use of ribavirin with zidovudine is not recommended due to an increased risk of anaemia (see section 4.4). Consideration should be given to replacing zidovudine in a combination anti-retroviral therapy regimen if this is already established. This would be particularly important in patients with a known history of zidovudine induced anaemia.