Bedside mixing of calcium gels for dermal hydrofluoric acid treatment leads to precipitate formation and loss of dissolved calcium

Hydrofluoric acid is a weak acid with the potential for local and systemic fluoride toxicity. Standard care for dermal exposures includes the application of a topical calcium gel. If a commercially produced 2.5% calcium gel is not available, bedside mixing of one is recommended. We sought to determine whether bedside mixing of a calcium gel can reliably produce a suitable product for the treatment of this exposure. A survey was sent to the medical directors of America’s Poison Centers^® to collect information on current treatment recommendations for dermal hydrofluoric acid exposures. Following this, bedside mixing of a 2.5% calcium gel was attempted with seven brands of water-based gels and one brand of petroleum-based gel. Each brand of gel was mixed in a 3:1 mL ratio with 10% calcium salt solutions (calcium gluconate or calcium chloride) in an attempt to create a 2.5% calcium gel solution. Mixtures were photographed and assessed visually for viscosity and precipitations and were analyzed for final calcium concentration. Five of seven water-based gels exhibited a rapid loss of gel-like viscosity and immediate development of gross precipitates upon mixing with calcium-containing salts. The mean calcium concentrations in these non-viscous, precipitate-containing mixtures were lower than the expected 2.5% for both calcium gluconate and calcium chloride mixtures. The petroleum-based gel failed to produce a usable mixture when combined with water-based calcium salt solutions. For the majority of gel brands tested in this study, the recommended practice of mixing a 2.5% calcium gel using 10% calcium salt solutions and water-based gels resulted in immediate precipitate formation, loss of gel viscosity, and a reduction in dissolved calcium concentration. The standard recommendation of mixing a calcium gel at the bedside may result in the production of a non-viscous mixture with a calcium concentration lower than the expected 2.5%.