Lithium

Lithium

Lithium carbonate and lithium citrate are used to prevent ortreat 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 cat-echolamine stimulation. In bipolar disorder, the patient is affected by swings between the excessive catecholamine stimulation of mania and the diminished catecholamine stimulation of depres-sion.

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 vesi-cles (where neurotransmitters are stored) in the presynaptic neu-ron

§    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 unipo-lar 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 dan-gerous.

Drug interactions

Serious interactions with other drugs can occur because of lithi-um’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 io-dide.

§    Sodium bicarbonate may increase lithium excretion, reducing its effects.

§    Lithium’s effects are reduced when lithium is taken with the-ophylline.

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 thetherapeutic effects of lithium. (See Adverse re-actions to lithium.)