Lithium

The lithium test is requested to monitor the amount of lithium in the blood in order to find out whether drug concentrations are at a concentration where they can be effective. This is known as the "therapeutic range". Lithium tests may be requested every few days when a patient first begins taking lithium to help adjust the dose to the desired blood level. Subsequently the test may be requested at regular intervals or as needed to monitor blood concentrations. One or more lithium tests may be requested if a patient starts taking additional medications (to judge their effect, if any, on lithium levels) if the doctor suspects that levels are too high and causing symptoms of toxicity.

Lithium salts are potentially toxic and should not be prescribed unless facilities for monitoring serum lithium concentration are available (British National Formulary, 2022).

Lithium tests are often requested when a patient is starting lithium treatment or returning to it after an absence. Once stable blood concentrations in the therapeutic range have been achieved, then lithium should be monitored at regular intervals (3 monthly in the first year, 3-6 monthly thereafter) to ensure that the concentration remains in this range. Different brands of lithium release lithium into the stomach differently, and blood testing may be required if the brand of lithium is changed, to ensure that blood levels stay the same.

The test may also be requested when a patient’s condition does not appear to be responding to lithium to determine whether concentrations are too low, the medication is ineffective, or if the patient is taking the lithium as prescribed. It may also be requested when a patient experiences a troublesome level of side effects and/or exhibits symptoms that the doctor suspects may be due to toxicity.

Patients should talk to their doctor about the timing of the sample collection. Lithium blood levels must be performed at least 12 hours (usually 12-18 hours) after the last dose of lithium. Since dosage timing varies and some types of tablet release lithium more slowly, detailed collection instructions may vary.

The range of effective blood concentrations (the “therapeutic range”) for lithium has been established as 0.4 – 1.2 mmol/L (0.4 to 1.0 mmol/L in most patients; lower end of the range for maintenance therapy and in the elderly). Within this range, most people will respond to the drug without symptoms of toxicity. Response and side effects will be individual, however. Some people’s condition will not be adequately treated at the lower end of the therapeutic range and some people will experience excessive side effects at the upper end. Patients should work closely with their doctor to find the dosage and concentration that works the best for them.

In general, when lithium results are in the therapeutic range, the doctor and patient are satisfied that the patient’s condition is being appropriately managed and the patient is not experiencing significant side effects, then the dosage of lithium a patient is receiving is adequate. If the patient is below the therapeutic range, it is likely that they are not receiving adequate medication. If they are above the therapeutic range and/or are experiencing significant side effects at their current dose, then it is likely that they are taking too much medication. Patients should not decrease or stop taking their medication without consulting with their doctor, however, as abrupt withdrawal can worsen their symptoms. Dosage determinations and adjustments must be evaluated on a case-by-case basis.

Lithium is excreted mainly by the kidneys. Long-term use of lithium carries a risk of decreased kidney function. Patients with kidney disease may have increased lithium levels because of decreased elimination. Doctors will monitor kidney function over time with tests such as urea, and creatinine, before starting treatment and at intervals thereafter, usually every six months.

Lithium levels and side effects can increase with the loss of salt and water from the body, such as may occur with a low-salt or salt=-ree diet, excessive sweating, or with an illness that causes dehydration, vomiting or diarrhoea. If sickness and diarrhoea persists for a day or two, or if food or fluid intake is reduced, patients should contact their doctor urgently. Patients who take lithium may develop hypothyroidism (decreased thyroid function). Doctors will regularly monitor a patient’s thyroid function with a TSH and/or a T4 test before starting treatment and at intervals thereafter usually every six months.

Women who use lithium during pregnancy are at an increased risk of having their baby develop a rare heart valve defect. Women who want to become pregnant while taking lithium should talk to their doctors, but it is important not to stop taking lithium without medical advice.. There are two different types of lithium preparation – lithium carbonate and lithium citrate. Lithium citrate comes as a liquid and is usually only prescribed for patients who have difficulty swallowing tablets. It is important not to change to a different type of preparation unless recommended to do ao by a doctor.

A variety of prescribed drugs, over-the-counter medications, and supplements can increase, decrease, or interfere with the concentrations of lithium in the blood. Drugs that can increase lithium concentrations include anti-inflammatory agents such as aspirin, ibuprofen and naproxen and diuretics such as bendroflumethazide and furosemide. Drugs that can increase the side effects of lithium include antidepressants such as paroxetine fluoxetine and antipsychotics such as clozapine and olanzapine, blood pressure medications such as calcium channel blockers and angiotensin converting enzyme inhibitors (enalapril, lisinopril, ramipril) and antiseizure medications such as carbamazepine and phenytoin.

Drugs that can decrease lithium concentrations include theophylline and prescription levels of caffeine.

All patients on lithium therapy are recommended to carry a ‘Lithium Alert Card’ to alert health professionals that they are taking lithium, and to keep a ‘Lithium Record Book’ recording details of their treatment. In the UK, the Lithium Treatment Pack (“Purple Book” can be obtained from your doctor or your pharmacist.

Provided it is working well to control your condition, you will generally take lithium for a long time, Some people need to take it for many years.