Lithium is given under close supervision with regular monitoring of
serum concen- trations because there is a narrow margin between therapeutic concentrations and those that are toxic. The dosage of
lithium is adjusted to give therapeutic
serum concentrations of 0.4 to 1 mmol/L, although it should be noted that this is the range used in the UK, and other ranges have been quoted. Initially weekly monitoring is
advised, dropping to every 3 months for those on stable regimens. It is usual to take
serum lithium samples about 10 to 12 hours after the last oral dose. Adverse effects that are not usually considered serious include nausea, weakness, fine tremor, mild polydipsia and polyuria. If
serum concentrations rise into the 1.5 to 2 mmol/L range,
toxicity usually occurs, and may present as lethargy, drowsiness, coarse hand tremor, lack of coordination, muscular weakness, increased nausea and vomiting, or diarrhoea. Higher levels result in neurotoxicity, which manifests as ataxia, giddiness, tinnitus, confusion, dysarthria, muscle twitching, nystagmus, and even coma or seizures. Cardiovascular
symptoms may also develop and include ECG changes and circulatory problems, and there may be a worsening of polyuria. Virtually all of the reports are concerned with the carbonate, but sometimes
lithium is given as other compounds. There is no reason to believe that these
lithium compounds will interact any differently to
lithium carbonate.