Which of the following antihypertensive drugs is contraindicated in a patient on Lithium in order to prevent toxicity?
A. Clonidine
B. Beta blockers
C. Calcium channel blockers
D. Diuretics

ans: diuretics it increases lithium toxicity

DRUG INTERACTIONS: Non-steroidal anti-inflammatory drugs (NSAIDs), [for example, ibuprofen , naproxen , indomethacin, nabumetone, diclofenac , ketorolac , reduce the kidney's ability to eliminate lithium and lead to elevated levels of lithium in the blood and lithium side effects. Blood concentrations of lithium may need to be measured for 4 to 7 days after an NSAID is either added or stopped during lithium therapy. Aspirin and sulindac do not appear to affect lithium concentrations in the blood.

Diuretics should be used cautiously in patients receiving lithium. Diuretics that act at the distal renal tubule, [for example, hydrochlorothiazide, spironolactone triamterene , can increase blood concentrations of lithium. Diuretics that act at the proximal tubule, [for example, acetazolamide (Diamox)], are more likely to reduce blood concentrations of lithium. Diuretics such as furosemide and bumetanide may have no affect on lithium concentrations in blood.