The latest data from a European trial using
boosted darunavir (DRV/r) as the sole HIV drug have found no evidence of increased
treatment failure or of viral loads increasing over time, even when viral loads
below the usual limit of detectability were investigated with an ultrasensitive
assay.
The latest results from the MONET trial,
presented at the recent
Tenth International Congress on Drug Therapy in HIV Infection (HIV10) in Glasgow, contrast with an
African trial using boosted lopinavir monotherapy (LPV/r) also presented which,
in the absence of viral load testing, found increased rates of viral failure
over time.
The
MONET trial randomised 256 patients who had had a viral load under 50 copies/ml for at
least six months either to take DRV/r monotherapy or to take monotherapy plus the
two most suitable NRTI drugs. The 48-week results, presented this time last year at the European AIDS
Conference, found that 87% of people on monotherapy and 89% on combination
therapy maintained a viral load under 50 copies/ml – a non-significant difference and the
most successful result from a PI monotherapy trial.
Other monotherapy trials have found that
while the numbers of patients with detectable viral loads may be similar, a
larger number of patients on monotherapy had ‘subliminal’ viral loads – ones below
50 but detectable by ultrasensitive tests – which another
study reported this week found that monotherapy was associated with some risk of eventual
failure.
The 96-week results from this study were
presented at the Vienna International AIDS Conference this year. They showed that after nearly
two years, the study found that 75% of people on monotherapy and 81% on combination
therapy had maintained a viral load under 50 copies/ml without changing therapy; when NRTIs
were added back in or patients switched to new ones, then 91% on combination
therapy and 92% who had taken monotherapy had a viral load under 50 copies.
The Glasgow conference heard that, using an
ultrasensitive test that could detect viral loads down to five copies/ml, the
investigators found that the proportion of people with low-but-detectable viral
loads varied little over the study. At baseline the proportion of patients with
a viral load between five and 50 copies/ml was 13% in the monotherapy arm and
17% in the combination therapy arm. At week 96 these proportions were 17% and
15% respectively.
The proportion with viral loads under five
copies/ml hardly changed at all. Eighty per cent of patients started monotherapy
with viral loads under five copies; the proportion by 96 weeks was 79%. In the
combination therapy arm the proportion of patients with viral loads under five
copies/ml rose from 79 to 81%.
None of these differences in viral load were
statistically significant, and there is thus no sign of a rise in ‘subliminal’
viral loads in patients taking monotherapy. There was very little drug
resistance observed during the trial. Three patients acquired protease inhibitor
resistance during the trial, one of them on combination therapy, and one
acquired a new NRTI mutation.
At the Glasgow conference lead investigator
Jose Arribas also presented a new cost-effectiveness analysis showing that if
all patients in Spain who would have been eligible for the MONET trial – which means
more than six months with undetectable viral load with no history of treatment failure, amounting
to 15% of all patients in care – then a year’s drug costs for each patient
would be €12,250 rather than €20,650. This would save a total of €46 million a
year in drug costs, though the analysis did not take viral load testing, overheads
such as healthcare worker costs, or the cost of possible future illness into
account.
Another study at Glasgow looked at the
efficacy of LPV/r (Kaletra) monotherapy
in the clinic, as opposed to on a randomised clinical trial.
The study looked at
77 patients at three Spanish hospitals who were switched to LPV/r monotherapy.
They had been virally undetectable for an average of three years, had taken an
average of seven previous ARV drugs, had a high average CD4 count (519). After a
mean follow-up of 22 months (eleven as a minimum), 88% had maintained a viral load under
50 copies/ml. Of the nine patients who failed, seven admitted to poor adherence,
and eight successfully re-suppressed their HIV after re-introducing NRTIs.