PTH and Lithium

My wife has been on lithium treatment for bi-polar for over 18 yrs. In 2000 start of ESRD, highly suspect lithium !!. has been on PD since 2000, i have done a lot of reserch and keep up with as much as in can learn. She has a very high pth, MD keeps relating to meds, but i have seen several med. atricles on the need to adjust the PTH with a fomula to include the use of lithium. this could cause an abnormal result on calcium and pth. What is your input on this with people still requiring lithium and on PD. thanks, hubby of happyonpd

We have long known that lithium can cause chronic kidney disease (CKD). It causes chronic inflammation in the ‘interstitium’ of the kidney – or, so-called, chronic interstitial nephritis (CIN) … a condition with many, often medication-related causes. The interstitium of the kidney is the supportive cells that surround and provide a structure to the nephrons … rather like the packing and support we would wrap around valuable, breakable items before transport. That actually ‘demeans’ the interstitial cells a bit and I don’t really mean to do that - they have many important functions other than just architectural support - EPO production, for one - but for this discussion, consider the interstitium as a supportive and protective ‘bulk’ around the nephron tublues that run through it.

There is always a ‘damned if you do, damned if you don’t’ issue with lithium and CKD … it really still is the best drug, in most circumstances, to treat bipolar disease – but, in some patients, particularly if the lithium blood levels creep up too high, or an acute lithium toxic crisis (or repeated crises) occur, slow chronic damage can result. Stopping the lithium is sometimes the ideal answer – but then, the bipolar symptoms can re-surface … in other words: ‘damned if you do, damned if you don’t’.

Though several other agents are now proving as effective in many patients, they have only been about for a relatively short time … and these have their own set of side effects too. Some patients with a long history of bipolar disorder, dating back to when lithium was the only effective agent, will therefore now have either established lithium-induced CIN or have even moved on to CKD and dialysis dependence - like your wife has.

We have also known for a long time that lithium can cause both thyroid and parathyroid gland side-effects.

Lithium seems to do two potentially ‘bad’ things to the parathyroid glands … (1) it competes with the ways in which calcium normally gets from the blood into body cells, thus leading to higher than normal blood calcium levels and (2) it raises the threshold of the ‘calcium-sensing receptors’ in the parathyroid glands which normally sense a high blood calcium and, in response, shut off parathyroid production.

As a result, parathyroid hormone production is not ‘switched off’ as it should be by the high blood calcium (the lithium having ‘dulled’ the capacity (sensitivity) of the receptors in the glands to detect a high calcium level) and PTH secretion continues unabated.

I know that seems complex … but hopefully, re-reading will help you through the sequence.

As for there being a ‘formula’ to calculate the dose of lithium against the PTH or calcium level … not one that I know of - or at least one that reliably works. But, clearly, there may be something out there that I am unaware of that has been advocated or used. There are a range of corrective formulae for the blood calcium level in relationship to the blood albumin level – depending on the laboratory methods used – and maybe this is what you are thinking of … but for lithium? … not one that I know.

If the bipolar state is stable on lithium and dialysis is already underway (ie: CKD has supervened and progressed to dialysis dependence), then there is no compelling reason I know of not to continue the lithium once on dialysis.

HD removes lithium … indeed, it can actually be used in acute lithium poisoning to remove excess lithium … but PD transfers (or removes) lithium rather poorly and only a small dosage change should usually be needed. More importantly, the blood level of lithium should be monitored (as it should be in all patients on lithium – regardless of the presence of kidney disease or not) and adjusted to ensure that the level of lithium in the blood remains within the therapeutic range … the range where enough is given to ensure it is effective but not so much as to be toxic.

I hope that (sort of) helps and answers your questions.

John Agar