A case of lisinopril-induced lithium toxicity We describe a patient who developed lithium toxicity when lisinopril was substituted for clonidine. Possible mechanisms of angiotensin-converting enzyme (ACE) inhibitor-induced lithium toxicity are discussed. Aggressive serum lithium concentration monitoring and a reduction in the dose of lithium is advised when using ACE inhibitors because of disturbances and shifts in fluid and electrolyte balance. 