Methocarbamol is a potent skeletal muscle relaxant
which has an unusually selective action on the central nervous system,
specifically on the internuncial neurons of the spinal cord. This specific
action results in a diminution of skeletal muscle hyperactivity without
concomitant alteration in normal muscle tone. It is long-acting and
essentially non-toxic, and has proved effective in a wide range of disorders
involving acute muscle spasm.
PHARMACOLOGY
Animal studies have shown that methocarbamol
acts primarily on the internuncial neurons of the spinal cord. It exerts
a prolonged blocking effect on polysynaptic reflex pathways at dosages
which do not significantly alter transmission through monosynaptic
reflex arcs and interrupts abnormal impulses from areas of disturbed
muscle. It has no direct action on the contractile mechanism of striated
muscle, the motor end-plate or the nerve fiber.
Methocarbamol affords a marked protective action
against the effects of strychnine in rats, cats and dogs. It prevents
both convulsions and death when administered prior to strychnine in the
rodent. In dogs and cats, it promptly controls the classical and severe
symptoms of strychnine poisoning. Methocarbamol is more potent than
mephenesin or mephenesin carbamate in blocking convulsions induced with
pentylenetetrazol or electroshock.
Signs of central nervous system
depression are produced by large doses of methocarbamol. Included are
loss of righting reflex, prostration and ataxia. Also indicative of CNS
depression is the finding that methocarbamol potentiates barbiturate
hypnosis in mice.
The results of acute and subchronic studies
emphasize that methocarbamol is relatively non-toxic. It does not
significantly alter hematologic or biochemical values. Similarly, gross
and microscopic tissue examinations revealed no significant findings
attributable to it.
INDICATIONS
Dogs and Cats, oral -
METHOCARBAMOL is indicated as an adjunct to therapy of acute
inflammatory and traumatic conditions of the skeletal muscle and to
reduce muscular spasms. The efficacy of tablets in the treatment of
acute skeletal muscle hyperactivity secondary to the following
conditions has been demonstrated:
1. Intervertebral disc syndrome, compressive
myelitis, spinal cord injury where cord remains intact.
2. Traumatism causing muscular and ligamentous
sprains and strains.
3. Myositis, fibrositis, bursitis, synovitis.
4. Muscular spasm prior to or following surgical
procedures.
5. Miscellaneous conditions: To maintain
therapeutic benefits of the injectable relaxants in strychnine poisoning
and tetanus.
Horses - As an adjunct
to therapy of acute inflammatory and traumatic conditions of the
skeletal muscle to reduce muscular spasms, and effect striated muscle
relaxation. The efficacy in the treatment of acute skeletal muscle
hyperactivity secondary to the following conditions has been
demonstrated:
1. Trauma, muscular and ligamentous sprains and
strains.
2. Myositis, fibrositis, bursitis and synovitis.
3. Tying up syndrome.
4. Muscular spasm prior to or following surgical
procedures.
5. Maintenance of muscle relaxation in tetanus.
Methocarbamol can be used concurrently with
adrenal corticosteroids and other medications usually employed in these
cases without untoward effects.
CONTRAINDICATIONS
Although rat studies have indicated no adverse
effects on the pregnant female, fetus or neonate, methocarbamol should
not be used during pregnancy unless in the judgment of the veterinarian
the potential benefits outweigh the possible hazards.
Methocarbamol is contraindicated in patients
hypersensitive to the ingredients.
WARNING
Not to be used in horses intended for food.
ADMINISTRATION AND DOSAGE
Methocarbamol is compatible with general
anesthetics, causing no depression of vital body functions or no
prolonging of anesthesia.
Horses:
Give drug to effect: moderate conditions, a dose of 2 to 10 mg/lb; for
severe conditions (tetanus), a dose of 10 to 25 mg/lb.
Dogs and Cats - Tablets: Dosage and
frequency of administration should be based on the severity of symptoms
and on the therapeutic response noted. The usual canine and feline dose
of methocarbamol is 60 mg/lb body weight in divided doses followed by 30
or 60 mg/lb body weight each following day. The total dose should be
divided into two or three equal doses (given at twelve or eight hour
intervals respectively).
Due to the nature of the conditions for which
methocarbamol therapy is recommended, it is important that an accurate
diagnosis is made. If no response is evident within five days of the
initiation of treatment, the diagnosis should be redetermined.
RECOMMENDED DOSAGE SCHEDULE FOR TABLETS
Load dose - 1st day, 60 mg/lb
Maintenance dose - 2nd day, 30 mg to 60 mg/lb.
|
Wt. of Dog
|
1st Day Load Dose
|
2nd Day Maintenance Dose
|
|
12 1/2 lbs
|
1/2 tablet t.i.d.
|
1/4 to 1/2 tablet t.i.d.
|
|
25 lbs
|
1 tablet t.i.d.
|
1/2 to 1 tablet t.i.d.
|
|
50 lbs
|
2 tablets t.i.d.
|
1 to 2 tablets t.i.d.
|
Toxicity studies have shown methocarbamol to be well
tolerated at doses of 400 mg/kg divided in two daily doses given 5 days
a week for 26 weeks. The usual treatment during clinical trials did not
exceed 14 to 21 days.
CAUTION
Federal law restricts this drug to use by or on
the order of a licensed veterinarian.