Shi Yan
StarFossilia Spiriferis (fossilized shells of Cyrtospirifer sinensis (Grabau) and allied spiriferid brachiopods)
Synonyms: Cyrtospirifer sinensis (Grabau), Spirifer fossil shell, Shi Yan Zi, 石燕
Traditionally used for
- Eye health
- Urinary & fluids
Cautions & contraindications
- Kidney conditions
☯ TCM Properties
Clears Damp-Heat, promotes diuresis and removes nebulae
Traditional Chinese Uses
Salty and cool, entering the Kidney and Bladder channels, Shi Yan is classed among the substances that clear Damp-Heat and promote urination. It is used for painful, difficult or turbid urination and stony/heat-type stranguria (lin syndrome), for chronic leucorrhoea, and for Damp-Heat lodged in the lower burner. Because it is salty and "removes nebulae," powdered Shi Yan (often levigated with water) was applied to the eyes for corneal opacities and superficial films, and taken internally for intestinal wind bleeding, haematochezia and anal fistula discharge. It is typically decocted 9–15 g, crushed and cooked first (or calcined and ground for topical/eye use). As a hard mineral fossil it is decocted long; use cautiously in the absence of genuine Damp-Heat.
Relationships
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Botanical Description
Shi Yan (石燕, "stone swallow") is a fossil, not a plant. The medicinal material is the petrified shell of extinct spiriferid brachiopods, chiefly Cyrtospirifer sinensis (Grabau) and related Devonian species, embedded in limestone or shale. The winged, ridged valves superficially resemble a swallow in flight, giving the drug its name. Specimens are grey, brownish-grey or yellowish, hard, heavy and stony, with a fan-shaped body bearing radiating plications and a hinge line drawn out into two lateral "wings." For use, the fossil shells are dug out, washed free of matrix, dried, and either ground to powder or, more often, calcined and quenched (cu zhi) to make them friable before decoction.
Occurs as fossilized brachiopod shells preserved in Devonian marine limestone and calcareous shale strata; collected from rock outcrops and quarries.
Active Constituents
Calcium carbonate
Carbonate mineral, calciteConcentration: The overwhelming bulk of the drug. Standard Chinese materia medica entries give the composition as principally calcium carbonate with small amounts of phosphorus and silicon dioxide; no modern quantitative mineralogical analysis of this specific drug has been published.
The fossil shell is recrystallised calcium carbonate, so on ingestion the drug behaves as an antacid and a slowly available calcium source, dissolving in gastric acid to calcium ion and carbon dioxide. Every clinically important interaction of Shi Yan follows from this single fact: divalent calcium in the gut lumen chelates and immobilises several drug classes. There is no organic pharmacology here at all.
Silicon dioxide
Oxide mineral, silicaConcentration: Small amounts, reported qualitatively in standard materia medica entries; not quantified in any published assay.
Silica derives from partial silicification of the fossil and from adherent sedimentary matrix. It is insoluble in gastric acid and pharmacologically inert, but it makes up part of the indigestible residue and is one reason a fossil drug delivers less calcium per gram than a pure carbonate would.
Phosphorus, present as phosphate
Inorganic phosphateConcentration: Small amounts, reported qualitatively; not quantified.
Phosphate is a normal minor component of marine carbonate fossils. At the amounts present in a 3 to 9 g dose it has no independent action, and it is noted here only because a mineral drug's composition is its whole pharmacology.
Calcium oxide and calcium acetate in the calcined vinegar-quenched drug
Alkaline earth oxide and organic acid saltConcentration: Formed during processing rather than present in the raw fossil; the proportion depends entirely on kiln temperature and the number of quenching cycles, which are not standardised.
Shi Yan is dispensed both raw and processed. The classical processing is calcination followed by quenching in vinegar, traditionally repeated seven times, which cracks the shell to a friable powder. Calcination at the temperatures used drives off carbon dioxide and converts part of the carbonate to calcium oxide, and the vinegar quench converts surface oxide to the far more soluble calcium acetate. The processed drug is therefore more alkalising and delivers more soluble calcium than the raw fossil, which matters because the interactions below scale with soluble calcium.
Adherent sedimentary matrix minerals
Clay and oxide mineralsConcentration: Variable and unquantified; a function of how thoroughly the collected fossil was cleaned.
The drug is dug out of Palaeozoic marine sediments, mainly in Hunan, Guangxi, Sichuan, Shanxi and Jiangxi, and cleaned by hand. Residual matrix carries whatever the host rock and its weathering products contain, which is the plausible route for any trace-element burden in the finished drug.
Toxic trace elements including lead, cadmium and arsenic
Toxic trace elementsConcentration: No published assay exists for this drug. Surveys of heavy metals in Chinese herbal medicine cover plant drugs and do not include Fossilia Spiriferis, so its contaminant load is unmeasured rather than measured and found low.
A geological drug dug from sedimentary rock has a contaminant profile set by its host rock, not by cultivation practice, and lead and arsenic are common in marine sedimentary sequences. Nothing here is a positive finding of contamination; the point is that the absence of an assay is not evidence of absence, and this drug is dispensed at 3 to 9 g a day.
⚠ Drug Interactions
Tetracycline and fluoroquinolone antibiotics
Shi Yan is essentially calcium carbonate. Calcium in the gut lumen forms insoluble chelates with the beta-diketone system of tetracyclines and with the 4-oxo and 3-carboxyl groups of fluoroquinolones, and the resulting complexes are not absorbed. This is a well-characterised effect of calcium salts generally, and the calcined vinegar-quenched form of the drug delivers more soluble calcium than the raw fossil does.
Clinical note: Separate the two by at least two hours before and four to six hours after the antibiotic dose, or better, suspend Shi Yan for the duration of the antibiotic course. This is the same rule as for antacids and dairy, and it applies to doxycycline, minocycline, ciprofloxacin, levofloxacin and moxifloxacin alike.
Levothyroxine
Calcium carbonate binds levothyroxine in the gastrointestinal tract and reduces its absorption, an interaction repeatedly documented for calcium supplements and antacids. Because the effect is on absorption rather than metabolism, it produces a slow drift in thyroid function tests rather than an acute event.
Clinical note: Give levothyroxine at least four hours apart from Shi Yan and keep the interval consistent, since it is variability rather than a fixed offset that destabilises the dose. If a patient on levothyroxine starts or stops the herb, arrange thyroid function testing six to eight weeks later.
Oral bisphosphonates
Oral bisphosphonates such as alendronate and risedronate are absorbed to well under one percent of the dose, and any polyvalent cation in the gut, calcium included, chelates them and abolishes what absorption there is. Calcium carbonate is the standard example in the product labelling.
Clinical note: Do not give Shi Yan on the same morning as a bisphosphonate. The bisphosphonate must be taken on an empty stomach with plain water and nothing else for at least 30 to 60 minutes; put the herbal decoction at the other end of the day.
Oral iron salts
Calcium and non-haem iron compete for absorption in the duodenum, and calcium carbonate taken with an iron salt measurably lowers iron uptake. A patient being actively repleted for iron-deficiency anaemia is the one who loses most.
Clinical note: Separate ferrous sulphate or fumarate from Shi Yan by at least two hours. If haemoglobin or ferritin is not responding as expected during iron repletion, review the herbal formula for calcium-bearing mineral drugs before increasing the iron dose.
Thiazide diuretics
Thiazides reduce renal calcium excretion. Combined with a sustained oral calcium carbonate load, and particularly with the calcined form which is more alkalising, this can raise serum calcium and produce the calcium-alkali picture of hypercalcaemia, metabolic alkalosis and renal impairment. The risk is well described for calcium carbonate antacids and supplements; Shi Yan is chemically the same load in a less predictable dose.
Clinical note: Check serum calcium and renal function before combining Shi Yan with a thiazide, and again after a few weeks. Warn the patient about nausea, constipation, thirst and confusion. Avoid the combination entirely in anyone with reduced renal function or a history of hypercalcaemia.
Herbs co-decocted with Shi Yan in the same pot
Work on Long Gu, the other fossil drug of this materia medica, showed that adding the fossil to a decoction changed both the inorganic and the organic profile of the extract, and that the fossil does not merely release ions but adsorbs organic compounds from the co-decocted herbs onto its macroporous surface. Nitrogen adsorption isotherms and terahertz spectrometry confirmed the porous structure and the adsorption. Shi Yan is likewise a porous fossil boiled with the rest of the formula, usually as a long pre-decoction, but no equivalent measurement has been made on it.
Clinical note: Treat a formula containing Shi Yan as chemically different from the same formula without it, not simply as the same formula plus a mineral. Where a narrow-therapeutic-index pharmaceutical or a critical herbal constituent is involved, decoct Shi Yan separately rather than in the same pot.
Fossil material of undetermined identity supplied as Shi Yan
Shi Yan is defined by trade description rather than by a determinable species: the crude drug is a mixed assemblage of Palaeozoic spiriferid brachiopod shells, and the binomial attached to it in materia medica entries is best read as a trade designation, not a determination made on the material in the packet. The precedent is direct: a taxonomic examination of 20,939 fossil fragments of market Long Gu found the Chinese-market material drawn from a considerably wider range of taxa than the Japanese-market material, across nine families. There is no reason to expect fossil brachiopod material to be sourced more carefully than fossil mammal bone, and there is no published survey of it.
Clinical note: Ask the supplier for the collection locality and geological horizon, not just the drug name, and reject material with heavy adherent matrix. Where the formula's intent is simply an alkalising calcium mineral, a pharmacopoeial mineral drug with a real assay is the more defensible choice.
Historical Texts
Xin Xiu Ben Cao, also known as Tang Ben Cao (Newly Revised Materia Medica)
Tang dynasty, 659 CEZhong Yao Da Ci Dian (Dictionary of Chinese Materia Medica), Jiangsu New Medical College
Modern China, first edition 1977References
- Oguri K, Nishioka Y, Kobayashi Y, Takahashi K. Taxonomic examination of longgu (Fossilia Ossis Mastodi, dragon bone) and a related crude drug, longchi (Dens Draconis, dragon tooth), from Japanese and Chinese crude drug markets . Journal of Natural Medicines (2017) [DOI]
- Oguri K, Kawase M, Harada K, Shimada-Takaura K, Takahashi T, Takahashi K. Longgu (Fossilia Ossis Mastodi) alters the profiles of organic and inorganic components in Keishikaryukotsuboreito . Journal of Natural Medicines (2016) [DOI]
- Oguri K, Ueda T, Takahashi K. Transition in Longgu Surface Associated with Decoction Process of Keishikaryukotsuboreito . Chemical and Pharmaceutical Bulletin (2019) [DOI]
- Yang CM, Chien MY, Chao PC, Huang CM, Chen CH. Investigation of toxic heavy metals content and estimation of potential health risks in Chinese herbal medicine . Journal of Hazardous Materials (2021) [DOI]
This information is for educational purposes only and is not intended to replace professional medical advice. Always consult a qualified healthcare provider before using any herbal remedy, especially if you are pregnant, nursing, or taking medications.
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