Toxic elevation of serum lithium concentration by non-steroidal anti-inflammatory drugs.

It is estimated that four million people in the United Kingdom have either osteo arthritis or rheumatoid arthritis. With the extension in lifespan seen in recent decades, the number is thought to be increasing. Many of the above will be treated with non-steroidal anti-inflammatory drugs. Lithium has been proven to be useful in the prophylaxis of affective disorders. It is also used in refractory depression and mania and has been advocated in those with aggressive outbursts. McCreadie et all found it being taken by 0-77/1,000 people in south west Scotland. Extrapolated to the United Kingdom this would mean lithium is taken by approximately 40,000 patients. With the increasing use of nonsteroidal anti-inflammatory drugs and lithium, the possibility of interactions are more likely. Seven reports of patients taking both agents detail interactions leading to a toxic elevation of the serum lithium level. The non steroidal anti -inflammatory drugs previously implicated have been piroxicam,2 3 4 mefanamic acid,5 6 indomethacin7 and phenylbutazone.8 We have recently observed two patients with affective disorders who were main tained on lithium carbonate but then developed lithium toxicity following inadvertent prescription of non steroidal anti inflammatory drugs by their general practitioner.