Alex describes his experience of taking lithium and his search for information on its pharmacokinetic properties. He wanted to calculate his peak serum concentration and find out his approximate lithium half-life using the exponential decay formula. However, he found that there was no semi-log plot in the literature and no mention of the dual half-life of lithium. He searched for papers on simulations of the pharmacokinetic curve and found references to multi-compartmental models. Eventually, he found a chapter on lithium pharmacokinetics in a book and learned that the two half-lives he observed corresponded to the alpha and beta phases of lithium removal from blood vessels after peak concentration, which could be described using multicompartment models.

When I first started to take lithium, I wanted to calculate my peak serum concentration using my 12-hour sample value. I knew it was going to be a very rough estimation, but for me, doing the calculation made me feel less anxious about toxicity.

My plan was to use the exponential decay formula 1 to find the peak concentration (assuming the peak occurred around five hours). I wanted to find out, given I knew my serum creatinine levels, what my approximate lithium half-life was. I went looking for data in the lithium pharmacokinetic literature to figure this out.

Continue reading