Hong Fen

Hong Fen (HgO) and Qing Fen (Hg2Cl2) are two distinct pharmacopoeial drugs, and this database record has them crossed: its scientific_name gives calomel while its latin_name, category and functions all describe red mercuric oxide. The two are not interchangeable. Hong Fen is a red or orange-yellow escharotic used to debride and drain; Qing Fen is a white powder used for damp skin lesions, scabies and, historically, internally as a purgative and antisyphilitic, which is where most calomel poisoning came from. Mercurous mercury also disproportionates in vivo to the divalent form, so the distinction protects nobody from mercury; it only changes the dose, the corrosivity and the indication.

The substitution runs both ways and the reverse direction is the more damaging one. Qing Fen is applied to relatively intact skin for eczematous and parasitic conditions. Hong Fen is a debriding escharotic intended for necrotic ulcer beds. Applying Hong Fen to the skin surfaces Qing Fen is prescribed for burns viable tissue, creating the ulcer that then absorbs mercury far faster than the intact skin would have.

Bai Jiang Dan is made by the descending rather than the ascending method and its main components are mercuric chloride (HgCl2) with mercurous chloride. Mercuric chloride is freely water-soluble and strongly corrosive, and the preparation is used at very small quantities on sinus tracts and fistulae. In rats, topical Hydrargyrum Chloratum Compositum promoted wound healing at a middle dose without gross organ pathology, but atomic absorption still detected significant mercury accumulation in the kidney. The dan preparations look alike as powders and share overlapping indications.

Intact stratum corneum is a real barrier to mercury salts; an abraded surface is a weaker one; an ulcerated, exudative, well-perfused wound bed is barely a barrier at all, because there is no keratinised layer, the exudate solubilises the oxide, and the granulation tissue underneath is densely capillarised. That matters more here than for any other topical, because ulceration is the indication. In rabbits, a single 4 to 5 hour application to a 5 cm by 5 cm wound produced significant, dose-related rises in blood mercury, and after a month of daily 9 to 1 dilution blood mercury took 71 days and urine mercury about three months to return to baseline after the drug was stopped. Undiluted Sheng Dan at the same site raised creatinine, urea and AST within 24 to 72 hours and produced hepatic and renal pathological change. Human observation is consistent: urine mercury in ulcer patients treated with external mercury preparations has exceeded regulatory reference values across dose groups.

Mercury from a topical mercurial adds to whatever the patient is already carrying. Inorganic mercury concentrates in the renal proximal tubule with a biological half-life measured in weeks to months, and the brain fraction persists for years, so exposures separated in time still sum. Systemic poisoning from purely dermal mercury is well documented outside traditional medicine: inorganic mercury poisoning is a recognised consequence of skin-lightening cosmetics, and nephrotic syndrome has been reported from a skin ointment containing mercuric ammonium chloride. Cinnabar (HgS) in formulas such as An Gong Niu Huang Wan is a much less soluble species and a smaller contributor per gram, but it is not zero.

The proximal convoluted tubule is where inorganic mercury concentrates and where it does its damage; degenerative change in that segment can begin within an hour of exposure to inorganic mercurials. Mercury also causes an immune-mediated membranous nephropathy independent of dose-dependent tubular toxicity. Superimposing any other nephrotoxin on that is straightforwardly additive, and a patient with a chronic ulcer is often already on NSAIDs and has often already had contrast imaging.

Mercury preparations sit under specific legal controls, and their availability is not a guide to their legality. Within China, Hong Fen is a pharmacopoeial drug but is handled under the regulations governing medical toxic drugs, with restricted supply and record keeping. Internationally, the Minamata Convention on Mercury phases out mercury-added products, but products used in traditional or religious practices are excluded from the relevant annex for the time being, so the treaty does not currently prohibit this drug. That exclusion is explicitly provisional and does not override national medicines law: mercury-containing traditional remedies are restricted or effectively unavailable in many countries, and importing them can be an offence.