Cholecalciferol rodenticide toxicosis in dogs and cats: dose calculation, monitoring, and treatment

Bottom line

Cholecalciferol is one of the rodenticides with no antidote, and it has the narrowest margin and the longest tail of the three common classes. Merck's professional toxicology chapter reports clinical signs at doses as low as 0.1 mg/kg, with appreciable calcium and phosphorus elevations and metastatic soft-tissue mineralisation above 0.5 mg/kg — and a single 14–28 g bait block of the usual 0.075% product contains 10.5–21 mg of cholecalciferol [1]. Calculate mg/kg before you decide anything else: even the smallest block clears 0.5 mg/kg in any dog under about 20 kg. Decontaminate on the clock, then plan monitoring out to 72–96 hours after ingestion rather than overnight [1], because there is no rescue drug at the far end: "No antidote for cholecalciferol poisoning is available." [1]

Pathophysiology, presentation, and why the calcium moves late

Ingested cholecalciferol is hydroxylated in the liver to calcifediol (25-hydroxycholecalciferol) and then in the renal tubules to calcitriol (1,25-dihydroxycholecalciferol), the most bioactive form [1]. Peak calcitriol concentrations are reached 48–96 hours after ingestion, accounting for the delay in both clinical signs and laboratory changes; signs and laboratory changes often develop within 12–48 hours [1]. The patient in front of you at hour two can be entirely normal and still be on a trajectory.

When the patient does become clinical, Merck lists the signs and laboratory changes as "weakness, anorexia, vomiting, polyuria and polydipsia, dehydration, metastatic mineralization of the soft tissues, and consequent systemic effects" depending on the organ tissues affected [1]. That vomiting/PU-PD/anorexia/lethargy set is what an owner sent home on a monitoring plan needs to be told to watch for, and it is non-specific enough that it will not announce itself as a poisoning.

Duration is the second half of the problem. Persistent elevations in calcium and phosphorus leading to metastatic mineralisation commonly affect the kidneys and may lead to renal injury, dysfunction, or failure; any soft tissue, including that of the heart, lungs, and GI tract, may be affected [1]. Merck attributes the prolonged course to the extended half-life of cholecalciferol and its metabolites, which often results in prolonged clinical signs requiring weeks of consistent laboratory monitoring and sporadic adjustments to treatment [1].

Two reports put numbers on that tail. Gerhard and Jaffey described an 8.0 kg Shih Tzu mix with serum 25-hydroxyvitamin D of 3,625 nmol/L on day 1 (reference interval 109–423 nmol/L) rising to 6,091 nmol/L by day 26; their report is titled for the finding of "Serum 25(OH)D concentrations >500 nmol/L for 9 months following cholecalciferol rodenticide ingestion", and they state that concentrations "remained greater than the upper limit of the reference interval for almost a year after the dog in this report ingested cholecalciferol rodenticide" [2]. Fooshee and Forrester reported that serum calcium concentration did not stabilise for approximately one month in a treated dog [3]. Ionised calcium normalises long before 25(OH)D does, so a normal calcium is not proof the exposure is over; taper against repeat chemistry, not a calendar.

The dose calculation you have to do at the desk

This single step decides the case, and the unit error here is tenfold or worse. The inputs, from Merck's professional chapter: cholecalciferol in bait "is usually found in a concentration of 0.075% (0.75 mg/g)"; "soft bait or bait block products often weigh between 14 and 28 g, thus containing 10.5–21 mg"; clinical signs may be noted at doses as low as 0.1 mg/kg, with appreciable calcium and phosphorus elevations leading to metastatic soft-tissue mineralisation at doses exceeding 0.5 mg/kg; reported acute lethal dose is 13 mg/kg and LD50 is 88 mg/kg [1].

dose (mg/kg) = grams of bait ingested × mg cholecalciferol per gram ÷ body weight (kg)

Patient	Amount eaten	Cholecalciferol	Dose	Against the thresholds [1]
9 kg dog	one 28 g block	28 × 0.75 = 21 mg	21 ÷ 9 = 2.3 mg/kg	well above 0.5 mg/kg
30 kg dog	half a 14 g block (7 g)	7 × 0.75 = 5.25 mg	5.25 ÷ 30 = 0.18 mg/kg	above 0.1, below 0.5 mg/kg
4 kg cat	5 g of bait	5 × 0.75 = 3.75 mg	3.75 ÷ 4 = 0.94 mg/kg	above 0.5 mg/kg

Three traps. First, 0.075% is 0.75 mg per gram, not 0.075 mg per gram — a percentage is grams of active per 100 g of product [1], and reading it straight across as mg/g understates the dose tenfold. Second, the percentage describes the bait and the mg/kg figures describe the patient; you must pass through grams eaten and body weight before comparing them. Third, a label in International Units is not interchangeable with these figures: rodenticide labels state cholecalciferol as a percentage by weight [1], while supplements and foods state IU — the five-cat food-associated series by Vecchiato and colleagues reports the implicated diet at 273,000 IU/kg of food [4]. Confirm the milligram equivalent before applying any mg/kg threshold to an IU-labelled product.

A caution specific to cats. The 0.1 and 0.5 mg/kg figures are Merck's thresholds for animals generally [1], and they are not feline-derived. Voss and Chow state directly that "Cats are suspected to be more susceptible, but there is no established toxic dose for this species" [5]. Treat the canine thresholds in a cat as a floor for concern rather than a validated cut-off, and lower your threshold to hospitalise.

When the amount eaten is genuinely unknown, assume the whole container. The thresholds are low enough that partial-ingestion optimism has no margin in it.

Differential by bait class: you usually do not know which bait was eaten

Owners bring the dog, not the label, and the three common classes behave so differently that guessing wrong wastes the only window that matters.

	Cholecalciferol	Bromethalin	Second-generation anticoagulant
Mechanism	Conversion to calcifediol then calcitriol; hypercalcaemia and metastatic mineralisation of kidney, heart, lung, GI tract [1]	Uncouples oxidative phosphorylation in CNS mitochondria; cerebral and spinal cord oedema [6]	Inhibits vitamin K epoxide reductase; loss of factors II, VII, IX, X [7]
Typical bait strength	0.075% (0.75 mg/g) [1]	0.01% to 0.025% (0.1–0.25 mg/g) [6]	—
Onset	Signs and lab changes often within 12–48 h; calcitriol peaks 48–96 h [1]	Convulsant syndrome in dogs within 4–36 h at high doses; paralytic syndrome typically within 1–5 days; overall within 1–7 days [6]	Coagulation parameters elevated 2–5 days after ingestion; bleeding typically 3–7 days [7]
Cat sensitivity	No established feline toxic dose [5]	LD50 0.4–0.71 mg/kg in cats vs 2.38–5.6 mg/kg in dogs [6]	—
Bedside discriminator	Ionised calcium and phosphorus [1]	Neurological examination	PT [7]
Antidote	None [1]	"No antidote exists for bromethalin poisoning." [6]	Vitamin K1 2.5 mg/kg PO q12h for 28 days, or 5 mg/kg PO q24h for 28 days [7]

On product availability, the US EPA's rodenticide restrictions page (last updated September 2025) states registration facts only: second-generation anticoagulants are no longer registered for consumer products and are registered only for the commercial and structural pest control markets; the bait components of consumer-market ready-to-use bait station products contain bromethalin, chlorophacinone, or diphacinone; pelleted baits are no longer permitted in consumer products; cholecalciferol is among the rodenticides registered to control mice; and professional- and agricultural-use products containing cholecalciferol must be sold in containers holding at least four pounds of bait [8]. Do not read that as a rule about where cholecalciferol exposures come from — consumer-branded cholecalciferol bait stations do reach households, and the dog in Case 1 of Voss and Chow's series ingested a "d-Con Ready to Use Bait Station; Reckitt, Slough, England" [5]. A supermarket-box history does not lower cholecalciferol on the differential.

Decontamination

Emesis is appropriate if ingestion occurred within 4 hours; Merck lists apomorphine, ropinirole, or hydrogen peroxide in dogs and dexmedetomidine, hydromorphone, or xylazine in cats [1]. Adsorption is then stratified by the calculated dose [1]:

• 0.1–0.5 mg/kg: a single dose of activated charcoal, 1–2 g/kg PO as an aqueous slurry, with a cathartic.
• Above 0.5 mg/kg: the same initial dose, followed by cholestyramine 0.3–1 g/kg PO every 8 hours for 3–4 days. "If cholestyramine is not available, administer activated charcoal (1–2 g/kg, PO as aqueous slurry) with a cathartic, followed by activated charcoal without a cathartic, every 8 hours for up to two additional doses."

So repeat charcoal dosing is a fallback for when cholestyramine cannot be obtained, not a parallel option — and it is bounded: the cathartic accompanies the first dose only, and repeat charcoal is capped at two further doses [1]. Cholestyramine is a human bile-acid sequestrant used extra-label in dogs and cats.

Monitoring, recheck intervals, and stop criteria

Merck's baseline workup is "Baseline calcium concentration (ionized calcium concentration is ideal), phosphorus concentration, PCV, TP concentration, BUN concentration, creatinine concentration, electrolyte panel, and prefluid urinalysis" [1] — the electrolyte panel and the pre-fluid urinalysis matter, because both furosemide and diuresis will make them uninterpretable afterwards. Then follow the dose-stratified schedule [1]:

Calculated dose, not clinically affected	Initial support	Recheck schedule
0.1–0.5 mg/kg	SC fluid therapy and outpatient laboratory testing	Calcium, phosphorus, PCV, TP, BUN, creatinine and body weight at 72 hours after ingestion
Above 0.5 mg/kg	IV fluid therapy at twice the maintenance dose for 24 hours	The same panel every 24 hours until 72–96 hours after ingestion

The stop criterion is explicit: patients that remain clinically normal and maintain stable and normal calcium and phosphorus values 72–96 hours after ingestion would not be expected to develop clinical signs [1]. That, not a single overnight recheck, is the discharge decision for an asymptomatic ingestion. Once mineralisation is established the horizon lengthens to weeks of monitoring [1], with calcium in one dog not stabilising for approximately a month [3].

Track the calcium × phosphorus product alongside the individual values, with its limits in view. Vecchiato and colleagues state that "A Ca × P product of >60 mg/dl is reported by veterinary textbooks and guidelines for hypercalcemia management as the level considered as risky for soft tissue mineralization", but immediately add that "This value is not a specific threshold established for cats, but it has been simply extrapolated from human medicine", that other authors have not supported a real correlation between metastatic calcification and the level of the Ca × P product, and that "higher values of Ca × P should be considered physiologically normal for growing animals" [4]. Use it as a trend, not a trigger, and be especially careful applying it to a kitten or puppy. In the experimental pamidronate study by Rumbeiha and colleagues, total calcium × phosphorus concentration product was among the endpoints separating treated from untreated dogs [9].

Treating established hypercalcaemia

Merck gives the following for clinically affected patients [1]:

Agent	Dose	Purpose
Aluminium hydroxide	30–100 mg/kg every 24 hours, PO mixed with food, divided with each meal	Phosphate binding
Prednisone (dogs) or prednisolone (cats)	1 mg/kg, PO, every 12 hours, tapered as calcium concentration improves	Reduce calcium
Furosemide	"may be considered (2 mg/kg, SC, IV, or PO, every 8–12 hours) to aid in calcium excretion through the kidneys; however, it can be dehydrating and lead to electrolyte disturbances"	Calciuresis
Pamidronate or zoledronate	Single IV dose, with notably lower calcium concentrations within 1–3 days	Inhibit osteoclastic bone resorption
Salmon calcitonin	Listed but rarely used	Reduce calcium

IV crystalloid diuresis underpins all of it. Aluminium hydroxide, cholestyramine, the bisphosphonates and salmon calcitonin are all human products used extra-label in dogs and cats.

Bisphosphonate evidence. The controlled canine data come from an experimental study: Rumbeiha, Fitzgerald, Kruger, Braselton, Nachreiner, Kaneene and Frese gave 20 clinically normal 8- to 12-month-old male Beagles 8 mg of cholecalciferol/kg once orally, then IV saline or pamidronate at 0.65, 1.3, or 2.0 mg/kg on days 1 and 4 after cholecalciferol administration [9]. The 2.0 mg/kg group had significantly higher mean GFR (day 3), significantly lower mean serum creatinine and total calcium × phosphorus concentration product (days 4 and 7) than saline controls, and no abnormal findings on histological examination of renal tissue, while saline controls had moderate mineralisation and cellular necrosis of proximal renal tubules [9]. This is an experimental Beagle model at a fixed 8 mg/kg dose, not a clinical trial in naturally exposed pets.

Gerhard and Jaffey's clinical dog received zoledronate 0.3 mg/kg IV diluted in 100 mL saline over 2 hours, with 0.9% sodium chloride at 180 mL/kg/day, furosemide 2 mg/kg IV bolus then 1 mg/kg/h CRI, dexamethasone 0.1 mg/kg/day IV, prednisone 1.0 mg/kg PO q24h, and aluminium hydroxide 10 mg/kg PO q8h, later 16 mg/kg q12h; the dog "was discharged on day 8 with resolution of azotemia and ionized hypercalcemia" [2].

Intravenous lipid emulsion has preliminary support only. Voss and Chow reported 2 dogs and 2 cats with vitamin D toxicosis (ingested 0.39 and 2.54 mg/kg in the dogs, 2.55 and 3.18 mg/kg in the cats) given ILE in addition to standard treatment; their stated protocol is "A commonly used dosage is 1.5 mL/kg BW, IV, over 1 min; followed by 15 mL/kg BW, IV, over 1 h", and the doses actually administered differed between cases — Case 1 received 1.5 mL/kg BW IV then 15 mL/kg BW IV over 1 h, while Cases 2, 3 and 4 each received 2 mL/kg BW IV then 15 mL/kg BW IV over 1 h [5]. Ionised calcium was lower after ILE in all four, all four were discharged alive (Case 2 was subsequently lost to follow-up), and the authors concluded that IVLE may be a useful adjunctive treatment for ionised hypercalcaemia secondary to vitamin D toxicosis and that additional studies to verify the positive findings appear warranted [5]. Four animals is not a basis for routine use.

Prognosis and the renal injury that persists

Decontaminated patients who clear 72–96 hours with normal calcium and phosphorus are not expected to progress [1]. Those who reach the mineralisation stage face a longer, less certain course. In Vecchiato and colleagues' five-cat food-associated series, "All of the cats recovered, except for two persistent azotemic cats, which developed chronic kidney disease"; those two were classified as IRIS stage 2 [4]. All five survived the acute toxicosis, and the two with residual azotaemia are among them.

Residual azotaemia is the characteristic long-term injury — reduced functional reserve rather than relapsing illness. Counsel owners early that the discharge chemistry may not be the final one, and stage the kidney formally once the patient is stable and rehydrated.

A toxicology consultation is worth the call for anything above the emesis-only tier; the ASPCA Animal Poison Control Center is reachable at (888) 426-4435 [10]. Have the product name, label percentage, container weight, estimated grams missing, and patient weight to hand — that is everything needed to fix the mg/kg figure before treatment is committed.

Frequently Asked Questions

How do I convert a 0.075% bait to a mg/kg dose? Multiply grams eaten by 0.75 mg/g, then divide by body weight in kilograms. Merck's professional chapter states cholecalciferol bait is usually found in a concentration of 0.075% (0.75 mg/g), and that soft bait or bait block products often weigh between 14 and 28 g, thus containing 10.5–21 mg [1]. A 9 kg dog eating one 28 g block therefore received 21 mg, or 2.3 mg/kg. The classic error is reading 0.075% as 0.075 mg/g, which understates the dose tenfold.

At what dose do I have to treat, and does that change in cats? Merck reports clinical signs may be noted in doses as low as 0.1 mg/kg, with appreciable elevations in calcium and phosphorus concentrations leading to metastatic soft tissue mineralisation in doses exceeding 0.5 mg/kg [1]. Reported acute lethal dose is 13 mg/kg and LD50 is 88 mg/kg, both far above the thresholds that matter clinically [1]. Those figures are not feline-derived: Voss and Chow state that cats are suspected to be more susceptible, but there is no established toxic dose for this species [5]. In a cat, treat the canine numbers as a floor for concern.

Why is the patient normal at presentation, and what will it look like if it decompensates? Peak calcitriol concentrations are reached 48–96 hours after ingestion, and clinical signs and laboratory changes often develop within 12–48 hours [1]. Merck lists the signs as weakness, anorexia, vomiting, polyuria and polydipsia, dehydration, and metastatic mineralisation of the soft tissues with consequent systemic effects [1]. A normal calcium at hour two says nothing about hour thirty-six, which is why the monitoring schedule runs to 72–96 hours — and why the owner needs that sign list at discharge.

Is there an antidote? No. Merck's professional chapter states that no antidote for cholecalciferol poisoning is available [1]. Bromethalin has no antidote either [6], so a rodenticide exposure with an unknown bait class is not resolved by the absence of one. The class that does have an antidote is the anticoagulants, where Merck gives vitamin K1 at 2.5 mg/kg PO every 12 hours for 28 days, or 5 mg/kg PO every 24 hours for 28 days [7].

Does repeat activated charcoal help, and where does cholestyramine fit? Merck stratifies by dose: at 0.1–0.5 mg/kg, a single dose of activated charcoal at 1–2 g/kg PO as an aqueous slurry with a cathartic; above 0.5 mg/kg, that same initial dose followed by cholestyramine at 0.3–1 g/kg PO every 8 hours for 3–4 days [1]. Repeat charcoal is the fallback rather than an equal option — Merck's wording is "If cholestyramine is not available, administer activated charcoal (1–2 g/kg, PO as aqueous slurry) with a cathartic, followed by activated charcoal without a cathartic, every 8 hours for up to two additional doses" [1]. Cholestyramine is used extra-label in dogs and cats.

When can I stop monitoring an asymptomatic ingestion? Merck states that patients that remain clinically normal and maintain stable and normal calcium and phosphorus values 72–96 hours after ingestion would not be expected to develop clinical signs [1]. Its baseline workup is calcium (ionised ideal), phosphorus, PCV, TP, BUN, creatinine, an electrolyte panel and a pre-fluid urinalysis [1]. Above 0.5 mg/kg, recheck calcium, phosphorus, PCV, TP, BUN, creatinine and body weight every 24 hours until 72–96 hours after ingestion; at 0.1–0.5 mg/kg, a single recheck of the same panel at 72 hours [1].

How long does hypercalcaemia last once established, and what is the long-term outlook? Longer than most toxicoses. Merck attributes prolonged clinical signs to the extended half-life of cholecalciferol and its metabolites, often requiring weeks of consistent laboratory monitoring [1]. Fooshee and Forrester reported that serum calcium did not stabilise for approximately one month in a treated dog [3], and Gerhard and Jaffey documented serum 25-hydroxyvitamin D above 500 nmol/L for 9 months, remaining above the reference interval for almost a year [2]. In Vecchiato and colleagues' five-cat series all the cats recovered except two persistently azotaemic cats that developed chronic kidney disease, both classified IRIS stage 2 [4].

Which calcium-lowering drug has controlled canine data behind it? Pamidronate is the agent with a controlled canine experiment. Rumbeiha and colleagues dosed 20 male Beagles with 8 mg cholecalciferol/kg orally and treated them with IV pamidronate at 0.65, 1.3, or 2.0 mg/kg on days 1 and 4; the 2.0 mg/kg group had significantly lower serum creatinine and calcium × phosphorus product than saline controls and no abnormal renal histology, while controls had moderate renal mineralisation and proximal tubular necrosis [9]. That is an experimental Beagle model at a fixed dose, and bisphosphonate use in dogs is extra-label. Merck lists pamidronate or zoledronate as a single IV dose producing notably lower calcium concentrations within 1–3 days [1].