|
At the Danish
University of Pharmaceutical Sciences the following ULLA
lecture took place at the Day
of Research Tuesday 28 January 2003 from 9-10 a.m. (Benzon
Auditorium):
 Cannabis
- From Plant to Patient
Cannabis comes from the plant Cannabis sativa and contains
about 60 different cannabinoids including tetrahydrocannabinol
(THC), cannabinol, cannabidiol, cannabigerol and cannabichromene.
It is the THC that is the psychoactive constituent and gives
the "high" normally associated with the use of Cannabis.
The relative and absolute amounts of the various cannabinoids
in any sample of Cannabis depend not only on the variety of
Cannabis grown, but also on part of the World where it is
grown, its growing conditions, and on the storage and treatment
of the plant material.
Cannabis has been used for thousands of years and appears
in Assyrian tablets around 700 BC and its medicinal use included
the treatment of muscle spasms, menstrual cramps, rheumatism,
tetanus convulsions, rabies and epilepsy. Its modern day therapeutic
potential is still in the area of muscle relaxation and cannabinoids
are currently advocated for the treatment of anorexia, bronchial
asthma, epilepsy, glaucoma, hypertension, muscle spasticity,
nausea, vomiting and pain. The cannabinoids work through CB1
receptors centrally and CB2 receptors peripherally.
There are two cannabinoids currently licensed for medicinal
use. The first is THC (licensed in the USA for the treatment
of nausea following cancer chemotherapy and appetite enhancement
in patients with AIDS) and the second is Nabilone (licensed
in the UK for the treatment of nausea caused by chemotherapy).
There has been a lot of discussion as to whether THC alone
or an extract of Cannabis (containing a mixture of cannabinoids)
has a greater therapeutic effect. However, some recent research
showed that an extract of Cannabis has a far greater muscle
relaxant effect in mice than the same dose of THC on its own.
Because there is no good scientific evidence that Cannabis
has therapeutic benefit, the World Health Organisation lists
it under their Schedule 1 drugs so that medical practitioners
may not prescribe them. To provide that evidence, there are
two clinical trials in progress. The first is a double blind,
placebo controlled, multicentre clinical trial for the treatment
of multiple sclerosis and the second trial is a double blind,
placebo controlled, multicentre clinical trial for the relief
of post-surgical pain. GW Pharmaceuticals are also conducting
clinical trials on Cannabis derived medicines.
The legal position of Cannabis has changed in different parts
of the world. Canada permits its medicinal use whilst USA
federal law still prohibits it with The Netherlands tolerating
its controlled sale in Cannabis cafes.
Smoking gives the risks of cancer and the oral route has
low and variable bioavailability (6-10%). Therefore, other
routes of delivery are being investigated. For example, GW
Pharmaceuticals are using a sub-lingual spray which has a
fast absorption and is not subject to first-pass metabolism
by the liver. Other companies are investigating the pulmonary
delivery of cannabinoid solutions via metered dose inhalers
for immediate pain relief. Patches may also be a suitable
form for delivery if constant blood concentrations are required,
eg in the treatment of chronic pain.
|
