USMLE Forum Archives - USMLE Step 3 - Phenytoin toxicity:
Phenytoin toxicity:
meduploader - 05-15-09 14:07
The earliest sign is the presence of nystagmus of fal lateral gaze. Some other facts include blurred vision, diplopica, ataxia, slurred speech, dizziness, drowsiness, lethargy and decreased mentation, which progress to coma. Systemic side effects and neurotoxicity is one of the major limitations to the use of phenytoin.
Usuall therapeutic range of phenytoin is between 10 – 20 mcg/mL and most patients will experience adverse dose related neurotoxic effects with levels greater than 20 mcg/mL. however the serum levels associated with neurotoxixty vary from patient to patient. Some patients can experience toxic effects even when the measured levels are well within the normal range.
The first step in the management of the side effects due to higher drug levels is t reduce the dose or alter the treatment schedule to minimize the peak drug levels.
meduploader - 05-15-09 14:07
The earliest sign is the presence of nystagmus of fal lateral gaze. Some other facts include blurred vision, diplopica, ataxia, slurred speech, dizziness, drowsiness, lethargy and decreased mentation, which progress to coma. Systemic side effects and neurotoxicity is one of the major limitations to the use of phenytoin.
Usuall therapeutic range of phenytoin is between 10 – 20 mcg/mL and most patients will experience adverse dose related neurotoxic effects with levels greater than 20 mcg/mL. however the serum levels associated with neurotoxixty vary from patient to patient. Some patients can experience toxic effects even when the measured levels are well within the normal range.
The first step in the management of the side effects due to higher drug levels is t reduce the dose or alter the treatment schedule to minimize the peak drug levels.
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Re: Phenytoin toxicity: mtniharika - 10-05-09 14:34 ADVERSE EFFECTS OF PHENYTOIN:
-Phenytoin may cause a febrile reaction, hypotension (during intravenous infusion), or bradycardia.
-Mouth -Gingival hyperplasia (chronic use), the most common adverse effect (20%)
-Neurologic
Hyperreflexia or hyporeflexia
Abnormal gait (bradykinesia, truncal ataxia is a very typical presntation of overdose)
Respiratory distress
Encephalopathy
Meningeal irritation with pleocytosis
Tremor (intention)
Irritability or agitation
Confusion
Hallucinations
Mental status varies from completely normal to the extremes of stupor and coma
Peripheral neuropathy (chronic use)
Priapism
Urinary incontinence
Choreoathetoid movements
Dysarthria
Dysphagia
Seizures (rare)
Death (rare)
-Eyes
Nystagmus (horizontal, vertical)
Ophthalmoplegia
Diplopia
Miosis or mydriasis
-Hypersensitivity reactions (usually 1-4 wk after exposure)
Fever, rash, and lymphadenopathy, commonly observed together
Hepatitis
Myocarditis
Systemic lupus erythematosus (SLE)
Polyarteritis
Polymyositis
Eosinophilia
Megaloblastic anemia
Pseudolymphoma
Lymphadenopathy
-Cardiovascular
Hypotension, bradycardia , myocardial depression, ventricular fibrillation, asystole, and tissue necrosis all have been associated with the IV formulation.
Phlebitis, necrosis, even gangrene
"Purple glove syndrome"
Distal limb edema, discoloration, and pain after IV administration
Usually in elderly and after massive/multiple doses
-Skin
Hirsutism
Acne
Rashes, can be mild, morbilliform, scarlatinoid or as severe as Stevens-Johnson syndrome
Jaundice
Facial or periorbital edema
Erythema multiforme (EM)
Toxic epidermal necrolysis (TEN)
-GI/abdomen
Right upper quadrant tenderness
Hepatomegaly
Splenomegaly
Nausea
Vomiting
Hepatitis
-Fetal hydantoin syndrome is manifested by broad nasal bridge, wide fontanelle, low hairline, cleft lip/palate, epicanthal folds, short neck, microcephaly, low-set ears, small or absent nails, dislocated hip, hypoplasia of distal phalanges, impaired growth, and congenital heart defects.
-Metabolic symptoms may include osteomalacia and hypothyroidism (chronic toxicity).
-Trauma - Patients suffer from ataxia and consequently falling.
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