Lithium

Clinical Chemistry

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Description

Lithium is used in the treatment of mania, bipolar effective disorder, depression, and aggressive/self-harming behaviour. It should be monitored (along with regular U&E, TFT, and BMI measurements) in accordance with the Safer Lithium Therapy guidelines. Patients should have a Lithium Alert Card and a lithium therapy record book. Where dose changes are being considered, the patient should ideally be at steady-state (a minimum of 4 to 7 days after initiation of therapy or after last dose change) prior to sample collection.

Different preparations have different bioavailability: maintenance on the same brand and same formulation is advised.

Renal impairment and drugs that effect the kidneys (such as angiotensin converting enzyme inhibitors (ACEIs), thiazide diuretics, non-steroidal anti-inflammatory drugs (NSAIDs), and sodium containing antacids) may reduce renal clearance of lithium and potentiate toxicity. Many other potentially severe interactions are possible, (including with some over-the-counter medication) and consultation of the BNF is recommended.

Altered fluid balance (including increased body fat in obesity) may alter lithium metabolism and thus the effectiveness of therapy. Fluid intake should be maintained.

Lithium therapy may also affect thyroid, parathyroid, and renal function, with patients at risk of hypothyroidism, hyperparathyroidism, and polyuria and polydipsia (effects similar to nephrogenic diabetes insipidus).

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Indications

Regular monitoring of lithium is mandated by the Safer lithium therapy Patient Safety Alert NPSA 2009/PSA005. Guidance on the frequency of lithium monitoring during initiation and maintenance of therapy is given in NICE clinical guideline 185 and the BNF. Measurement of lithium may also be useful in the following circumstances:

- dose optimisation

- poorly controlled symptoms or suspected toxicity

- in patient populations with greater metabolic variability/polypharmacy (pregnancy (lithium therapy not routinely recommended), elderly, severe intercurrent illness, especially in renal impairment)

- where the formulation of the drug is altered

- where there is the possibility of drug interactions

- where patients are at risk of hypothyroidism, renal impairment, hypercalcaemia, or other complications.

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Sample Type

Serum, SST/Gel, minimum 2 mL (1 mL separated serum), usually 12 hours post-dose, or pre-dose depending on formulation.

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Reference Range

Reference ranges are provided on the report. Alternatively, please contact the laboratory for current ranges.

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Turnaround Time

Within 1 day

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Testing Frequency

Daily

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External Notes

Generally, sample at least 12 hours post-dose for therapeutic drug monitoring (TDM) purposes. This may vary according to the preparation, and advice should be sought from Pharmacy. In cases of suspected toxicity, please indicate time of last dose and sample collection.

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Patient Preparation

For TDM purposes, take samples 12 hours post-dose. Taking samples at different post-dose intervals makes long term monitoring difficult. Patients should have attained steady-state (see below) prior to sample collection.

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.