0071643192.pdf

TOXICOLOGY

HORMONAL AGENTS

Thyroid Hormones

Thyroid hormones are used as replacement therapy in hypothyroidism.

Levothyroxine (T 4 , Synthroid) is the most commonly used agent, though

levothyronine (T 3 ) is also available.

Onset of symptoms from levothyroxine (T 4 ) overdose may be delayed by several

days as T 4 requires in vivo conversion to the active hormone, T 3. Hence, T 3

ingestions will produce symptoms more quickly.

MECHANISM/TOXICITY

■ Excessive sympathetic activity

SYMPTOMS/EXAM

■ Tremor, confusion, agitation, hyperreflexia

■ Tachycardia, hypertension, palpitations, flushing, diaphoresis

■ Mydriasis

■ Diarrhea

■ Patient may report fever, weight loss, and heat intolerance with chronic

overdose (facticious hyperthyroidism).

DIFFERENTIAL

■ Primary hyperthyroid states (Graves disease)

■ Sympathomimetic toxicity (cocaine, amphetamines)

■ Methylxanthine toxicity (theophylline, caffeine)

DIAGNOSIS

■ Clinical diagnosis based on history and physical examination.

■ Elevated serum T 4 and T 3 levels

■ An elevated T 4 :T 3 ratio is suggestive of chronic, excess levothyroxine

intake.

TREATMENT

■ β-Antagonists, such as propranolol or esmolol, to control the effects of exces-

sive sympathetic activity

■ Agents that block endogenous thyroid hormone production (PTU, methi-

mazole) have limited utility.

INDUSTRIAL TOXINS

Hydrogen Fluoride

Hydrogen fluoride (HF, hydrofluoric acid) is a water soluble gas that is most

commonly encountered as a solution.

HF is encountered commonly in rust removers, oven cleaners, and automo-

tive wheel cleaners. Commercial uses include glass etching, graffiti removal,

and manufacture of semiconductors and certain fuels.

Acute ingestions of

levothyroxine will not produce

symptoms for several days.