Final answer:
A client on lithium should discontinue ibuprofen, as it can increase lithium levels in the blood and lead to toxicity.
Step-by-step explanation:
A client on lithium should discontinue ibuprofen because it can increase the lithium levels in the blood, which may lead to lithium toxicity. Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that can interfere with the kidney's ability to eliminate lithium, thereby increasing its concentration.
On the other hand, acetaminophen, diphenhydramine, and calcium carbonate can generally be safely used with lithium. Acetaminophen is a pain reliever, diphenhydramine is an antihistamine, and calcium carbonate is a calcium supplement that are not known to interact with lithium.