BACLOFEN
Baclofen(Lioresal) is a GABA-agonist, although its exact mechanism of
action remains uncertain. It is known to reduce release of excitatory
neurotransmitters.
Baclofen does not affect neuromuscular transmission. It is primarily a
drug used to treat spasticity (i.e. increased muscle tone) and spasm of
skeletal muscles seen in neurological conditions but has also proved to
be effective in the treatment of trigeminal neuralgia and has since been
found useful in all types of neuropathic pain, especially if paroxysmal
. It is now widely used.
Baclofen is partially metabolized by the liver (15%) and excreted by
the kidney, therefore the dose should be decreased in patients with
known liver or kidney impairment. There have been reports of elevated
liver enzymes, so screening liver function tests should be performed
before commencing treatment and then at six month intervals. A starting
dose of 5 mg once a day, increasing to two to three times per day is
gradually escalated by increments of 5mg per day as tolerated to 30-90
mg per day, and possibly higher if side effects permit. It may be
helpful to time the increase of dose for the bedtime dose, to minimise
the impact of side-effects. The most common adverse effects are sedation
and confusion, which are due to the central nervous system depressant
action of baclofen. However, a further problem may be
hypotonia(decreased muscle tone) and weakness, which can compound
pre-exisiting weakness due to the neurological condition being treated.
Conversely, Baclofen-induced dyskinesia (abnormal movements)may occur .
Although mostly used orally, baclofen may also be given intrathecally,
often using a pump, either alone of with intrathecal opioids. Indeed,
Intrathecal baclofen, is widely used to treat spasticity( ) and also
used to treat neuropathic pain of central origin.
This use of baclofen will be discussed further in a future article
about invasive therapies. However, please note that The Arachnoiditis
Trust does not endorse the use of intraspinal medication due to the lack
of data on safety in long-term use; also, invasive procedures carry the
potential risk of causing/exacerbating arachnoiditis which is incurable
and extremely difficult to treat even palliatively.
NOTE: Abrupt withdrawal must be avoided as this may result in a
hyperactive state with rapid, uncontrollable spasms and possibly
hallucinations, convulsions (status epilepticus) and disordered mental
state (confusion, psychosis); insomnia and "rebound" spasticity. In
order to avoid this, baclofen should always be discontinued by gradual
dose reduction over at least 1-2 weeks. If symptoms occur, it may be
necessary to prolong the gradual reduction.

OTHER SKELETAL MUSCLE RELAXANTS
DANTROLENE;(Dantrium): acts directly on skeletal muscle and therefore
has fewer central adverse effects.
CARISOPRODOL (Soma)
CYCLOBENZAPRINE(Flexeril)
METAXALONE (Skelaxin)
METHOCARBAMOL: (Robaxin/Robaxisal)
ORPHENADRINE (Norflex/Norgesic/ Norgesic Forte) : a derivative of the
antihistamine diphenydramine (Benadryl).
DIAZEPAM (see above under BENZODIAZEPINES)
QUININE SULFATE (Quinam): particularly for nocturnal cramps
TIZANIDINE(Zanaflex): a new drug ; a short-acting alpha-2 adrenergic
agonist; reduces spasticity by increasing inhibition of motor neurons.
Chemically related to clonidine so it may cause hypotension(low blood
pressure). Side effects are minimal: slight sleepiness and dry mouth.





These drugs are primarily used for their muscle relaxant properties
which may of course confer relief of pain due to muscle tension and
painful muscle spasms. However, it is not in the remit of this article
to cover this in detail and it will be addressed in a future article.
In summary, whilst some of these muscle relaxants may contribute to
analgesia, there is insufficient published literature to which
clinicians can refer as regards the long-term safety and efficacy of
these drugs. Therefore, although their use in treating cancer patients
is well established, treatment of the muscle spasm component of
musculoskeletal pain associated with chronic non-malignant neuropathic
pain is less common.

Dr.S. A. Andreae-Jones MB BS
Patron of the Arachnoiditis Trust
July 2000