Calcium, Magnesium & Phosphate

Hypercalcaemia: Fluids, Bisphosphonates and the Calcium Axis

Calcium sits under a beautifully tight thermostat — the parathyroids and vitamin D nudging it up, calcitonin trimming it down — because both too much and too little of it stop nerves firing and hearts beating properly. When that thermostat breaks upward, the patient turns to stone: kidney stones, aching bones, a groaning gut, a moaning, confused mind. Two diagnoses cause almost all of it — an overactive parathyroid gland or a cancer — and the treatment is a satisfyingly logical cascade. You rehydrate first, then you turn off the bone. This chapter owns the calcium-homeostasis map, and every drug we use hangs off one of its arms.

Hypocalcaemia: Correcting the Excitable State

If hypercalcaemia sedates — "stones, bones, groans and psychiatric moans" — hypocalcaemia does the opposite: it winds nerve and muscle up until they fire on their own. The same ion, read from the other end of its axis. Tingling fingers, a cramping hand, a twitching face, and — at the sharp end — a spasming larynx, a seizure, or a heart with a dangerously long QT. The management is a story in two speeds: rescue the excitable patient now with intravenous calcium, then think slowly about why the calcium fell — and the answer, more often than students expect, is a missing hormone, an unactivated vitamin, or a low magnesium that quietly blocks every attempt to fix it.

Magnesium: The Forgotten Electrolyte That Runs the Others

Magnesium is the electrolyte nobody checks. It rarely appears on the routine panel, it hides inside cells where the blood level barely hints at the true deficit, and yet it quietly governs the two ions everyone does check — potassium and calcium. Miss it, and you chase a low potassium that refuses to correct and a low calcium that ignores your infusions, replacing bag after bag while the real culprit sits unmeasured. Learn one rule from this chapter and let it be this: when potassium or calcium won't come up, check the magnesium.

Phosphate and CKD Bone Disease: Binders and the Mineral Axis

Phosphate is the quietest of the electrolytes — rarely on the front page of a resuscitation, easy to forget on a drug chart. Yet it sits at the centre of a web that ties together the kidney, the parathyroid glands, vitamin D and bone. Pull one thread and the whole net moves. Let it fall too low in a starving patient being fed and the muscles that breathe can fail. Let it climb in a failing kidney and, over years, the bones soften while the arteries harden. Managing phosphate is never about phosphate alone — it is about the whole mineral axis, and the drugs that hold it together are among the few you deliberately time to a meal.