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Lithium in General Practice

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Case 1

MT, a 35 year old male with bipolar disorder, has been stable on 800 mg daily of lithium carbonate and 10 mg daily of enalapril for six months with no apparent problems. His usual maintenance lithium concentration is 0.8 mmol/L. He presents to the surgery complaining of dizziness, ataxia and increased tremor. A lithium concentration of 1.6 mmol/L is reported and confirms drug toxicity. On questioning MT reveals that he has recently taken up strenuous exercise at the gym and has also been taking diclofenac, bought over-the-counter, for muscle aches.

Toxicity could have been precipitated by dehydration and excessive sweating which can increase lithium concentrations. In addition the NSAID can also increase the concentration, especially if MT is dehydrated. Enalapril can also interact but MT has been stable on this combination. The addition of the NSAID may have exacerbated the interaction.

The diclofenac was stopped and the lithium and enalapril withheld for 24 hours and re-checked. MT was advised to avoid dehydration while exercising and to take it a bit easier until his body adjusts. After 24 hours the lithium concentration was 0.9 mmol/L and re-stabilised on the same daily dose at 0.85 mmol/L. The enalapril was restarted when lithium concentrations stabilised and did not affect subsequent measurements.

Case 2

AG, a 56 year old woman with recurrent major depression, responded well to the addition of 500 mg of lithium carbonate to her previous 125 mg of nortriptyline. During initial follow-up after this change there appeared to be no new side effects due to the lithium. Some three years later AG disclosed that she had ceased the lithium, and found she was no longer having to rise four to five times during the night to pass urine, with resulting sleep disturbance.

Polyuria is generally a late side effect of treatment. Specific routine enquiry into such side effects is easily overlooked, but is important. Should continued treatment be indicated, consideration could be given to use of DDAVP nasal spray.

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