Lithium pharmacology

Lithium in pharmacology refers to the lithium ion, Li+, used as a drug. Lithium is administered in a number of chemical salts of lithium, which are used primarily in the treatment of bipolar disorder as mood stabilizing drugs. In bipolar disorder they have a role in the treatment of depression and particularly of mania - acutely and in the long term. As a mood stabiliser, lithium is probably more effective in preventing mania than depression, and may reduce the risk of suicide. In depression alone (unipolar disorder) lithium can be used to augment other antidepressants. Lithium carbonate (Li2CO3), sold as Carbolith®, Cibalith-S®, Duralith®, Eskalith®, Lithane®, Lithizine®, Lithobid®, Lithonate®, Lithotabs® and Maniprex®, is the most commonly prescribed, whilst the citrate salt lithium citrate (Li3C6H5O7), the sulfate salt lithium sulfate (Li2SO4) sold as Lithionit®, aspartate and the orotate salt lithium orotate are alternatives.

Upon ingestion Lithium becomes widely distributed in the central nervous system and interacts with a number of neurotransmitters and receptors, decreasing norepinephrine release and increasing serotonin synthesis.

History
Solutions of lithium will dissolve uric acid crystals. Against the background of nineteenth century theories linking excess uric acid to a range of disorders, including manic disorders, Carl Lange in Denmark and William Alexander Hammond in New York used lithium to treat mania from the 1870s onwards.

However, by the turn of the century, the use of lithium in this way died out and was seemingly forgotten. This was also due to the reluctance of the pharmaceutical industry to invest in a drug that could not be patented. The use of lithium salts to treat mania was rediscovered by the Australian psychiatrist John Cade in 1949, who proposed lithium as a tranquilizer, and soon succeeded in controlling mania in chronically hospitalized patients. This was one of the first successful applications of a drug to treat mental illness, and it opened the door for the development of medicines for other mental problems in the next decades.

The rest of the world was slow to adopt this revolutionary treatment, largely because of deaths which resulted from even relatively minor overdosing, and from use of lithium chloride as a substitute for table salt. Largely through the research and other efforts of Denmark's Mogens Schou in Europe, and Samuel Gershon in the U.S., this resistance was slowly overcome. The application of lithium for manic illness was approved by the United States Food and Drug Administration in 1970.

Treatment
Lithium treatment is used to treat mania in bipolar disorder. Initially, lithium is often used in conjunction with antipsychotic drugs as it can take up to a week for lithium to have an effect. Lithium is also used as prophylaxis for depression and mania in bipolar disorder. Also, it is sometimes used for other disorders, like cycloid psychosis, unipolar depression, migraine and others. It is sometimes used as an "augmenting" agent, to increase the benefits of standard drugs used for unipolar depression. Lithium treatment was previously considered to be unsuitable for children, however more recent studies show its effectiveness for treatment of early-onset bipolar disorder in children as young as eight.The required dosage (15-20mg per kg of body weight) is slightly less than the toxic level, requiring blood levels of lithium to be monitored closely during treatment. In order to prescribe the correct dosage, the patient's entire medical history, both physical and psychological, is sometimes taken into consideration. Blood tests are carried out every 3 months to ensure the level of lithium is appropriate and to prevent toxicity, along with kidney and thyroid tests.

Those who use lithium should receive regular (generally monthly once stable) blood tests and should monitor thyroid function annually and kidney function every three to six months for abnormalities. As it interferes with the regulation of sodium and water levels in the body, lithium can cause dehydration. Dehydration, which is compounded by heat, can result in increasing lithium levels.

High doses of haloperidol, fluphenazine, or flupenthixol may be hazardous when used with lithium; irreversible toxic encephalopathy has been reported.

Lithium salts have a narrow therapeutic/toxic ratio and should therefore not be prescribed unless facilities for monitoring plasma concentrations are available. Patients should be carefully selected. Doses are adjusted to achieve plasma concentrations of 0.6 to 1.2mmol Li+/litre (lower end of the range for maintenance therapy and elderly patients, higher end for pediatric patients) on samples taken 12 hours after the preceding dose. Overdosage, usually with plasma concentrations over 1.5mmol Li+/litre, may be fatal and toxic effects include tremor, ataxia, dysarthria, nystagmus, renal impairment, and convulsions. If these potentially hazardous signs occur, treatment should be stopped, plasma lithium concentrations redetermined, and steps taken to reverse lithium toxicity. The most common side effects end up being an overall dazed feeling and a fine hand tremor. These side effects are generally present during the length of the treatment but can sometimes disappear in certain patients. Other common side effects such as nausea and headache, can be generally remedied by a higher intake of water. Lithium unbalances electrolytes; to counteract this, increased water intake is suggested.

Lithium toxicity is compounded by sodium depletion. Concurrent use of diuretics that inhibit the uptake of sodium by the distal tubule (e.g. thiazides) is hazardous and should be avoided. In mild cases withdrawal of lithium and administration of generous amounts of sodium and fluid will reverse the toxicity. Plasma concentrations in excess of 2.5 mmol Li+/litre are usually associated with serious toxicity requiring emergency treatment. When toxic concentrations are reached there may be a delay of 1 or 2 days before maximum toxicity occurs.

In long-term use, therapeutic concentrations of lithium have been thought to cause histological and functional changes in the kidney. The significance of such changes is not clear but is of sufficient concern to discourage long-term use of lithium unless it is definitely indicated. Doctors may change a bipolar patient's medication from lithium to another mood stabilizing drug, such as Depakote (valproic acid), if problems with the kidneys arise. An important potential consequence of long-term lithium usage is the development of renal diabetes insipidus (inability to concentrate urine). Patients should therefore be maintained on lithium treatment after 3-5 years only if, on assessment, benefit persists. Conventional and sustained-release tablets are available. Preparations vary widely in bioavailability, and a change in the formulation used requires the same precautions as initiation of treatment. There are few reasons to prefer any one simple salt of lithium; the carbonate has been the more widely used, but the citrate is also available.

Mechanism of Action
The precise mechanism of action of Li+ as a mood-stabilizing agent is currently unknown. It is possible that Li+ produces its effects by interacting with the transport of monovalent or divalent cations in neurons. However, because it is a poor substrate at the sodium pump, it cannot maintain a membrane potential and only sustains a small gradient across biological membranes. Yet Li+ is similar enough to Na+ in that under experimental conditions, Li+ can replace Na+ for production of a single action potential in neurons.

Recent research suggests three different mechanisms which may act together to deliver the mood-stabilizing effect of this ion. An increasing number of scientists have come to the conclusion that the excitatory neurotransmitter glutamate is the key factor in understanding how lithium works. Other mood stabilizers such as valproate and lamotrigine exert influence over glutamate, suggesting a possible biological explanation for mania. The other mechanisms by which lithium might help to regulate mood include the alteration of gene expression and the non-competitive inhibition of an enzyme called inositol monophosphatase.

Unlike other psychoactive drugs, Li+ produces no obvious psychotropic effects (such as euphoria) in normal individuals at therapeutic concentrations.

Dr. Klein and his colleagues’ at the University of Pennsylvania discovered in 1996 that lithium ion deactivates the GSK-3B enzyme. The regulation of GSK-3B by lithium may affect the circadian clock -- and recent research (Feb 2006) seems to support this conclusion. When GSK-3B is activated, the protein Bmal1 is unable to reset the “master clock” inside the brain; as a result, the body’s natural cycle is disrupted. When the cycle is disrupted, the routine schedules of many functions (metabolism, sleep, body temperature) are disturbed. Lithium may thus restore normal brain function after it is disrupted in some people. The complete mechanism by which it treats mood disorders remains a mystery.

The time lithium takes to reach steady state is 2 to 3 weeks.

Harmful effects of lithium
Lithium is much less teratogenic than previously thought, though it does double the likelihood of Ebstein's anomaly (a cardiac defect), occurring at 0.1% when used during the first trimester of pregnancy.

The average developmental score for the lithium-exposed group of children was 7-8 points lower than the control group (siblings).

There have also been long term effects on the kidney, including diabetes insipidus with secondary distortion of bladder and urinary tract. Animal studies show long-term physical and behavioural effects extending beyond the first generation.

Lithium is known to be responsible for (sometimes significant) weight gain, acne with scarring, thinning of hair, and pronounced tremor, usually in the hands but extending to lips and tongue when the person is stressed, or after prolonged use. 

Lithium and culture
As with many other drugs, songs have been written about its effects, "Lithium Sunset" by Sting, and "Lithium]]" by Nirvana are some examples. The song "Lithium" by Evanescence, though titled like the drug, has been stated to be a metaphor about numbness and happiness.

The soft drink 7 Up, originally named "Bib-Label Lithiated Lemon-Lime Soda", contained lithium citrate until it was reformulated in 1950.

Hundreds of other soft drinks also included lithium salts or lithia waters. Additionally, Lithia light beer was brewed at the West Bend Lithia Company in Wisconsin. (All of these were forced to remove lithium in 1948).

An early version of Coca Cola available in pharmacies' soda fountains called Lithia Coke was a mixture of Coca Cola syrup and lithia water -- lithia waters are naturally occurring mineral waters with higher lithium amounts.

The amount of lithium in any of the commercially available soft drinks was hundreds of times less than a minimum psychiatric dose but the ban didn't make any distinctions on that basis.

Selected bibliography

 * McIntyre RS, Mancini DA, Parikh S, Kennedy SH. "Lithium revisited." Can J Psychiatry. 2001 May;46(4):322-7.
 * Bowden CL, Brugger AM, Swann AC, Calabrese JR, Janicak PG, Petty F, and others. Efficacy of divalproex vs lithium and placebo in the treatment of mania. JAMA 1994;271:918–24.