Concurrent use of drugs that alter concentrations of boceprevir
(Victrelis) or telaprevir (Incivek or Incivo) in the body may contribute to
poor response to interferon-based triple therapy for chronic hepatitis C virus (HCV),
according to study findings presented at the Digestive Disease Week meeting
(DDW 2013) last month in Orlando.
Boceprevir and telaprevir are both HCV protease inhibitors metabolised
by the cytochrome P450 enzyme system in the liver. Many different types of
medication – ranging from statins to antiretroviral drugs for HIV – are
processed by the CYP3A4 enzyme. Agents that inhibit or slow down processing can
raise levels of other drugs, while agents that induce or speed up processing
can lower drug levels.
Manie Juneja from Georgetown University Hospital and colleagues
evaluated the effects of "polypharmacy", or use of multiple drugs, on
outcomes of hepatitis C treatment using boceprevir or telaprevir in combination
with pegylated interferon and ribavirin.
As described in the study abstract, this retrospective analysis included
74 people (46 men and 28 women) treated at a hepatitis clinic. Most (85%)
used telaprevir, the rest boceprevir; nearly 60% had previously been treated
with interferon-based therapy. The abstract reported rates of rapid virological
response (RVR), or undetectable HCV RNA at week 4 of treatment, according to
use of concurrent drugs.
About one-third of participants were classified as having "minor
polypharmacy", defined as concurrent use of three to five medications, while 70% had
"major polypharmacy", defined as six or more medications. The average
number of drugs used by people on hepatitis C triple therapy was 7.35.
Nearly half of participants were taking CYP3A4 inhibitors – most
commonly statins for elevated blood lipids and SSRIs for depression – and 3
people were on CYP3A4 inducers. Eight per cent were taking drugs considered contraindicated
with hepatitis C triple therapy and therefore discontinued. In addition, six
people were using milk thistle or silymarin, an over-the-counter supplement.