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

Colleen P Cowdery; Steve C Kazmierczak; John A Thompson

doi:10.1080/15563650.2025.2519323

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

Clin Toxicol (Phila). 2025 Jun 30:1-6. doi: 10.1080/15563650.2025.2519323. Online ahead of print.

Authors

Colleen P Cowdery^{1

2}, Steve C Kazmierczak³, John A Thompson^{1

2}

Affiliations

¹ Department of Emergency Medicine, Oregon Health & Science University, Portland, Oregon, USA.
² Oregon Poison Center, Portland, Oregon, USA.
³ Department of Pathology and Laboratory Medicine, Oregon Health & Science University, Portland, Oregon, USA.

PMID: 40587120
DOI: 10.1080/15563650.2025.2519323

Abstract

Introduction: 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.

Methods: 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.

Results: 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.

Discussion: 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.

Conclusions: 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%.

Keywords: Calcium gel; dermal exposure; hydrofluoric acid; medication preparation; topical calcium.