When caring for a patient on lithium, which medication should be avoided to prevent toxicity?

Lithium is a mood stabilizer frequently used in the treatment of bipolar disorder. It has a narrow therapeutic index, which means that the difference between a therapeutic dose and a toxic dose is small. This makes monitoring levels and potential interactions with other medications critical.

Hydrochlorothiazide is a thiazide diuretic that can cause increased levels of lithium in the body. Thiazide diuretics decrease the renal clearance of lithium, leading to potential toxicity. This effect can occur due to dehydration, sodium depletion, or changes in fluid balance, which are common side effects seen with thiazide diuretics. Therefore, when a patient is taking lithium, healthcare providers often avoid or use caution when prescribing hydrochlorothiazide to prevent an increase in lithium levels that could lead to toxicity.

Other options, such as venlafaxine, gabapentin, and losartan, do not have the same direct interaction with lithium, and their use does not notably affect lithium levels in the body. Thus, while they may be suitable for certain conditions, they do not pose the same risk of lithium toxicity as hydrochlorothiazide does.