Page 103 - Pagetit

NEUROSCIENCE OF PSYCHOACTIVE SUBSTANCE USE AND DEPENDENCE

BOX 4.1

Substitution therapy
Substitution therapy is defined as the administration under medical supervision of
a prescribed psychoactive substance – pharmacologically related to the one
producing dependence – to people with substance dependence, for achieving
defined treatment aims (usually improved health and well-being). Substitution therapy
is widely used in the management of opioid dependence and is often referred to as
“opioid substitution treatment,” “opioid replacement therapy”, or “opioid
pharmacotherapy”. Agents suitable for substitution therapy of opioid dependence
are those with some opioid properties, so that they have the capacity to prevent
the emergence of withdrawal symptoms and reduce craving. At the same time
they diminish the effects of heroin or other opioid drugs because they bind to
opioid receptors in the brain. In general, it is desirable for opioid substitution drugs
to have a longer duration of action than the drug they are replacing so as to delay
the emergence of withdrawal and reduce the frequency of administration. As a
result there is less disruption of normal life activities from the need to obtain and
administer drugs, thereby facilitating rehabilitation efforts. Whereas non-prescribed
opioids are usually injected or inhaled by drug users, these prescribed medicines
are usually administered orally in the form of a solution or a tablet. Agents used in
substitution therapy can also be prescribed in decreasing doses over short periods
of time (usually less than one month) for detoxification purposes. Substitution
maintenance treatment is associated with prescription of relatively stable doses of
opioid agonists (e.g. methadone and buprenorphine) over a long period of time
(usually more than 6 months). The mechanisms of action of opioid substitution
maintenance therapy include prevention of disruption of molecular, cellular and
physiological events and, in fact, normalization of those functions already disrupted
by chronic use of usually short-acting opiates such as heroin. The context of delivery
of substitution therapy has important implications for the quality of the interventions,
both to maintain adequate control and to ensure responsible prescribing.

Since 1970, methadone maintenance treatment has grown substantially to
become the dominant form of opioid substitution treatment globally. Because
the treatment was initially controversial, it has been more rigorously evaluated
than any other treatment for opioid dependence. The weight of evidence for
benefits is substantial.
Source: WHO, 1998; Kreek, 2000.

A newer drug, Levo-alpha-acetyl-methadol (LAAM) resembles methadone:
it is a synthetic opioid that can be used to treat heroin dependence, but it
needs only to be taken three times per week, thus making it even easier for
people to use this therapy.
Buprenorphine is another prescribed drug for management of opioid
dependence that has the potential of improving access to drug treatment by
bringing more people into treatment in primary health care settings (see
Box 4.2). It has been widely used in France and is now being trialed in the USA.

82

Chapter_4 82 19.1.2004, 11:42