Question

A patient on lithium therapy developed hypertension. He was started on Thiazide for hypertension. After a few days, he developed coarse tremors and other symptoms suggestive of lithium toxicity. What is the probable mechanism of interaction?

• A. Thiazide increases the tubular reabsorption of lithium
• B. Thiazide inhibits the metabolism of lithium
• C. Thiazides act as an add on the drug to lithium
• D. All of the above

Answer 1

The Correct Option is A

In this scenario, a patient receiving lithium therapy develops hypertension and begins treatment with thiazide diuretics. Subsequently, the patient shows signs of lithium toxicity, including coarse tremors. Let's explore the probable mechanism of this drug interaction.

Thiazides are a class of diuretics that work by inhibiting sodium reabsorption in the distal convoluted tubule of the nephron. This action reduces blood volume and arterial pressure. However, thiazides also cause compensatory mechanisms in the kidney. When sodium reabsorption decreases, the kidney attempts to retain sodium by increasing reabsorption at other sites, including the proximal convoluted tubule.

Because lithium is a monovalent cation similar to sodium, it is reabsorbed in the proximal tubule using similar pathways. Therefore, when thiazides increase sodium and lithium reabsorption by decreasing sodium delivery to the distal nephron, the renal clearance of lithium decreases, leading to higher serum lithium levels.

The answer to the question is that thiazides increase the tubular reabsorption of lithium, resulting in lithium accumulation and toxicity.

Therefore, the correct option is: Thiazide increases the tubular reabsorption of lithium.