Lithium and drug interactions

The mutual enhancement of the side effects of muscular tremor and rigidity caused by lithium and neuroleptic drugs should be recognised. However, at present the 'case' for a neuroleptic-lithium interaction producing severe organic brain syndrome is arguably weak; in the absence of standardised sampling for monitoring lithium serum concentrations such reports may simply reflect 'pure' lithium intoxication rather than a drug interaction. Certainly it seems unwarranted in this connection to ascribe specific properties to haloperidol. A potentially high risk of interaction should be recognised between lithium and natriuretic diuretics, and other drugs and therapeutic measures affecting sodium balance. Such interactions may disturb stable treatment monitoring and give rise to the start of self-increasing lithium intoxication. The practical clinical importance of lithium interactions with neuromuscular blocking agents, phenytoin, carbamazepine, iodide salts and methyldopa is only weakly supported by the data available at this time. However, if simple prophylactic measures are available when such drugs are to be used in patients receiving lithium, for example temporary withdrawal of lithium, it may be prudent to take such steps.