Lithium
Lithium
Lithium carbonate and lithium citrate are used to prevent or treat mania. The discovery of lithium was a milestone in treating mania and bipolar disorders.
Pharmacokinetics
When taken orally, lithium is absorbed rapidly and completely and is distributed to body tissues.
Metabolism and excretion
An active drug, lithium isn’t metabolized and is excreted from the body unchanged.
Pharmacodynamics
It’s theorized that in mania, the patient experiences excessive catecholamine stimulation. In bipolar disorder, the patient is affected by swings between the excessive catecholamine stimulation of mania and the diminished catecholamine stimulation of depression.
Returning to normal
Lithium’s exact mechanism of action is unknown. It may regulate catecholamine release in the CNS by:
- increasing norepinephrine and serotonin uptake
- reducing the release of norepinephrine from the synaptic vesicles (where neurotransmitters are stored) in the presynaptic neuron
- inhibiting norepinephrine’s action in the postsynaptic neuron.
Getting more of the message
Researchers are also examining lithium’s effects on electrolyte and ion transport. Lithium may also modify the actions of second messengers such as cyclic adenosine monophosphate.
Pharmacotherapeutics
Lithium is used primarily to treat acute episodes of mania and to prevent relapses of bipolar disorders.
Under investigation
Other uses of lithium being researched include preventing unipolar depression and migraine headaches and treating depression, alcohol dependence, anorexia nervosa, syndrome of inappropriate antidiuretic hormone, and neutropenia.
No margin for error
Lithium has a narrow therapeutic margin of safety. A blood level that is even slightly higher than the therapeutic level can be dangerous.
Drug interactions
Serious interactions with other drugs can occur because of lithium’s narrow therapeutic range:
- The risk of lithium toxicity increases when lithium is taken with thiazide and loop diuretics and nonsteroidal anti-inflammatory drugs.
- Administration of lithium with haloperidol, phenothiazines, or carbamazepine may increase the risk of neurotoxicity.
- Lithium may increase the hypothyroid effects of potassium iodide.
- Sodium bicarbonate may increase lithium excretion, reducing its effects.
- Lithium’s effects are reduced when lithium is taken with theophylline.
Warning!Adverse reactions to lithium
Common adverse reactions to lithium include:
- reversible electrocardiogram changes
- thirst
- polyuria
- elevated white blood cell count.
A flood in the blood
Elevated toxic blood levels of lithium may produce:
- confusion
- lethargy
- slurred speech
- increased reflex reactions
- seizures.
Take this with a grain (or more) of salt
A patient on a severe salt-restricted diet is susceptible to lithium toxicity. On the other hand, an increased intake of sodium may reduce the therapeutic effects of lithium.
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