Uses of phenytoin



Phenytoin is used as both an abortive and preventive medication in seizure management. Intravenous administration of phenytoin ceased seizure activity in 60%-80% of patients in status epilepticus within 20 minutes. Prophylactic indications include pregnancy-induced hypertension, postneurosurgery, cerebrovascular accidents, and traumatic brain injury. Of these, there is inconsistent evidence to support the routine use of phenytoin in patients who have undergone craniectomy.

Less-common uses of phenytoin include the treatment of neuropathic pain, motion sickness, muscular dystrophy, and arrhythmia.

Phenytoin levels



Phenytoin is used as both an abortive and preventive medication in seizure management.
The total phenytoin reference range varies by age, as follows:

• Children and adults: 10-20 µg/mL
• Neonates: 8-15 µg/mL

Toxic phenytoin levels are defined as greater than 30 µg/mL.
Lethal levels are defined as greater than 100 µg/mL.
The reference range of free phenytoin is 1-2.5 µg/mL.
In patients with renal failure associated with hypoalbuminemia, free phenytoin levels may be more accurate than total phenytoin levels.However, the Sheiner-Tozer formula (below) can be used to correct the phenytoin level.
Adjusted concentration = measured total concentration / [(0.2 x albumin) + 0.1].
Administration of phenytoin and interpretation of serum phenytoin levels vary depending on the clinical scenario. Loading doses to achieve rapid therapeutic levels should be checked 1 hour after an intravenous loading dose and 24 hours after an oral loading dose.
Patients who are on long-term phenytoin therapy generally do not need to be monitored at intervals less than 3-12 months after a steady state has been reached unless clinically indicated, for example in patients who may have intentionally or unintentionally taken a toxic dose.
Although the reference range is between 10 and 20 µg/mL, about half of patients’ seizures are controlled at values lower and higher than the therapeutic range.
Some adverse effects of phenytoin are related to specific serum levels. Nystagmus is frequently observed at levels greater than 20 µg/mL.At greater than 30 µg/mL, patients may exhibit slurring of speech, ataxia, and movement disorders such as tremor, choreoathetosis, and orofacial dyskinesia.At serum levels that exceed 40 µg/mL, patients are often lethargic, stuporous, and confused and may require aggressive supportive measures.

Anatomy of Speech

Language processes have a clear neuroanatomical basis. 

In simplest terms, the reception and processing of spoken language take place in the auditory system, beginning with the cochlea and proceeding through a series of way stations to the auditory cortex, the Heschl gyrus, in each superior temporal gyrus. Decoding sounds into linguistic information involves the posterior part of the left superior temporal gyrus, the Wernicke area or Brodmann area 22, which gives access to a network of cortical associations to assign word meanings. For both repetition and spontaneous speech, auditory information is transmitted to the Broca area in the posterior inferior frontal gyrus. This area of cortex “programs” the neurons infrom which descending axons travel to the brainstem cranial nerve nuclei. The inferior parietal lobule, especially the supramarginal gyrus, also may be involved in phoneme processing in language comprehension and in phoneme production for repetition and speech. 

Reading requires perception of visual language stimuli by theoccipital cortex, followed by processing into auditory language information via the heteromodal association cortex of the angular gyrus. Writing involves activation of motor neurons projecting to the arm and hand.

Lateral Ventricle- Parts

There are several areas in the lateral ventricle:
• the frontal horn, which is bounded by the caudate nucleus, Corpus callosum and septum pellucidum
• the body of the lateral ventricle is bounded by the caudate nucleus / thalamus, corpus callosum and fornix
• the atrium: this is the focal point of the occipital and temporal horns
• the occipital horn
• the temporal horn

The two lateral ventricles (right, left) communicate with each other via the third ventricle.

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