Nuxvomica

Strychnine is an alkaloid obtained from the seeds and bark of the strychnine tree ( Nuxvomica).

Kinetics :

 Strychnine is rapidly absorbed from the small intestine .

 It is metabolized in the liver, but up to 20% of the dose may be excreted in the urine unchanged .

It rapidly distributes to many different tissues and has a half – life of about 6 hours .

Mechanism of Action :

Strychnine competitively blocks the effects of the amino acid glycine, an inhibitory neurotransmitter in the spinal cord.

 Normally, glycine prevents repetitive nerve activity that stimulates muscle contractions. Without this inhibition, the nerve continues to fire rapidly and leads to muscle spasms. Eventually, the animal develops muscle rigidity (tetanic spasms) . Because extensor muscles are stronger than flexor muscles in limbs and neck, an extensor rigidity develops.

 Clinical  Signs:

 Signs can occur from 10 minutes to 2 hours after ingestion depending on when the stomach empties since strychnine is better absorbed in the intestines .

Vomiting is uncommon .

Initially, the animal may be anxious, tachypneic, and salivating heavily.

Signs then progress to ataxia followed by collapse with violent muscular seizures. The legs will be extended and rigid and the neck may be arched.

 Stimulation by noise or lights typically causes signs to worsen. The animal can be hyperthermic due to extreme muscle activity. Death is likely due to respiratory arrest from paralysis of the diaphragm .

Diagnosis:

 Antemortem :

Strychnine can be detected in urine and stomach contents from gastric lavage . However, some animals die so quickly that strychnine can ’ t be detected in their urine .

In addition, the results of the tests are not likely to be available before the patient has either died or recovered.

Postmortem :

There are no specific lesions associated with strychnine toxicosis. Strychnine can be detected in stomach contents, urine, bile, liver, and kidney to confim exposure.

Treatment:

Emesis can be induced before the animal is symptomatic; however, due to rapid onset of signs in most cases, this may not be practical.

Activated charcoal may be useful but care should be taken to avoid aspiration .

 In general, treatment is aimed at controlling the tremors and seizures. Barbiturates, methocarbamol, propofol, and gas anesthesia may be used to control signs.

 In severe cases, the patient may need to be kept under anesthesia for 24 – 48 hours.

 IV  fluids to support hydration should be administered.

 Sensory stimulation should be kept to a minimum to prevent worsening of the signs.

 Treatment should be continued until signs have resolved, which may take 24 – 72 hours .

 Prognosis :Prognosis is guarded once signs have begun.