LET’S START WITH THE FACTS
- We know that calcium chloride (CaCl2) provides 3 times more elemental calcium than an equivalent amount of calcium gluconate.
- So, CaCl2 1 gm = calcium gluconate 3 gm.
- Does CaCl2 have better bioavailability than calcium gluconate?
- Does calcium gluconate have a slower onset of action because it needs hepatic metabolism to release the calcium?
Calcium gluconate does NOT require hepatic activation to exert its effect.
Liver transplant patients 
- Serum ionized calcium levels were measured in 15 hypocalcemic patients during the anhepatic stage of liver transplantation. Half received CaCl2 10 mg/kg, the other half received calcium gluconate 30 mg/kg.
- Serum concentrations of ionized calcium were determined before and up to 10 min after calcium therapy.
- Equally rapid increases in calcium concentration after administration of CaCl2 and gluconate were observed, suggesting that calcium gluconate does not require hepatic metabolism for the release of calcium and is as effective as CaCl2 in treating ionic hypocalcemia in the absence of hepatic function.
Children and dogs 
- A weird randomized prospective study in both children and dogs compared ionization of CaCl2 and calcium gluconate.
- The authors conclude that equal elemental calcium doses of calcium gluconate (10%) and CaCl2 (10%) (approximately 3:1), injected over the same period of time:
- Are equivalent in their ability to raise calcium concentration during normocalcemic states in children and dogs
- The changes in calcium concentration following calcium administration are short-lived (minutes)
- The rapidity of ionization seems to exclude hepatic metabolism as an important factor in the dissociation of calcium gluconate
Ferrets and in vitro human blood 
- Equimolar quantities of CaCl2 and calcium gluconate produced similar changes in plasma ionized calcium concentration when injected IV into anesthetized ferrets or when added to human blood in vitro.
- In vivo changes were followed with a calcium electrode positioned in the animal’s aorta, and this showed that the ionization of calcium gluconate on its first pass through the circulation is as great as that of CaCl2.
- This does not support the common suggestion that CaCl2 is preferable to calcium gluconate because of its greater ionization.
As long as equivalent doses are used, calcium gluconate works as quickly (and to the same degree) as CaCl2 to raise calcium concentration… without the same extravasation risk.
- Martin TJ, Kang Y, Robertson KM, Virji MA, Marquez JM. Ionization and hemodynamic effects of calcium chloride and calcium gluconate in the absence of hepatic function. Anesthesiology. 1990 Jul;73(1):62-5. PubMed PMID: 2360741.
- Cote’ CJ, Drop LJ, Daniels AL, Hoaglin DC. Calcium chloride versus calcium gluconate: comparison of ionization and cardiovascular effects in children and dogs. Anesthesiology. 1987 Apr;66(4):465-70. PubMed PMID: 3565811.
- Heining MP, Band DM, Linton RA. Choice of calcium salt. A comparison of the effects of calcium chloride and gluconate on plasma ionized calcium. Anaesthesia. 1984 Nov;39(11):1079-82. PubMed PMID: 6507824.