On 2017 Mar 16, KEVIN BLACK commented:

This report gives some useful information but I interpret the results quite differently. The authors start with the assumption that the trough level is what one wants. I disagree. What one wants is to be able to compare a patient's lithium dosing to the large body of published knowledge about lithium treatment. Almost all of that data comes from standard 12-hour blood draws with plain (immediate-release) lithium carbonate or citrate. So the real question of interest is, with extended-release lithium formulations, at what time point do I draw the lithium level to compare most accurately with a standard 12-hour blood draw with plain lithium carbonate? The answer is not obvious because extended-release formulations affect only the absorption and not the excretion of lithium. Their primary benefit is reducing the transient peak lithium serum concentration, not delaying the (already relatively slow) elimination of lithium.

Emami J, 2004 provide the needed data. They show, first, that 90% of the administered dose of a commercial extended-release formulation (Eskalith CR®) is absorbed by 4 hours after a dose, and ~100% is absorbed by 8 hours (Fig. 2A). Second, they show that at 12 hours after a dose, the blood levels for immediate and extended release formulations are essentially identical (Fig. 3). Thus 12 hours after the last dose is the ideal time for drawing blood levels for extended-release lithium tablets.

On 2017 Mar 16, KEVIN BLACK commented:

This report gives some useful information but I interpret the results quite differently. The authors start with the assumption that the trough level is what one wants. I disagree. What one wants is to be able to compare a patient's lithium dosing to the large body of published knowledge about lithium treatment. Almost all of that data comes from standard 12-hour blood draws with plain (immediate-release) lithium carbonate or citrate. So the real question of interest is, with extended-release lithium formulations, at what time point do I draw the lithium level to compare most accurately with a standard 12-hour blood draw with plain lithium carbonate? The answer is not obvious because extended-release formulations affect only the absorption and not the excretion of lithium. Their primary benefit is reducing the transient peak lithium serum concentration, not delaying the (already relatively slow) elimination of lithium.

Emami J, 2004 provide the needed data. They show, first, that 90% of the administered dose of a commercial extended-release formulation (Eskalith CR®) is absorbed by 4 hours after a dose, and ~100% is absorbed by 8 hours (Fig. 2A). Second, they show that at 12 hours after a dose, the blood levels for immediate and extended release formulations are essentially identical (Fig. 3). Thus 12 hours after the last dose is the ideal time for drawing blood levels for extended-release lithium tablets.