Snail venom leads to effective analgesic
Ziconotide, a synthetic version of a peptide found in the venom of Conus
magus, a marine snail, is an effective analgesic in patients with severe chronic pain, data from two new studies indicate.
Research published last week in JAMA confirms the drug’s efficacy
in treating pain caused by cancer or AIDS (2004;291:63). At the same
time, data issued by Elan, the company developing the drug, reveal that
ziconotide reduces neuropathic pain at lower doses than have been used
in previous trials.
The first study involved 111 patients with pain caused by cancer or AIDS
that was not effectively eased by systemic or intrathecal analgesics.
Patients were assigned to receive ziconotide or placebo for five to six
days followed by a five-day maintenance phase for responders and crossover
to the opposite treatment group for non-responders. Pain intensity was
assessed using a visual analogue scale.
The researchers found that pain intensity scores improved by 53.1 per
cent in patients treated with ziconotide compared with 18.1 per cent
for patients given placebo (P<0.001). The effects of ziconotide did
not diminish during the maintenance phase of treatment. More than half
the patients in the ziconotide group reported moderate to complete pain
relief, whereas less than a fifth of the placebo group reported similar
responses. Opioid use decreased in the ziconotide group by 9.9 per cent
but increased in the placebo group by 5.1 per cent.
There were several adverse events associated with ziconotide use, including
14 involving the nervous system. However, the researchers say that starting
at a lower dosage, using smaller increments, and increasing the interval
between dose titrations tended to reduce their frequency.
These points were dealt with in the second, as yet unpublished, trial.
Elan reports that in this study, there were few serious side effects,
with an incidence similar to placebo.
The company expects ziconotide, an N-type calcium channel blocker, to
reach the US market by early 2005. |
The
Pharmaceutical Journal