What the numbers mean
Merck gives one rule and is careful about how it words it: more than one grape or raisin per 10 lb of body weight may contain enough tartaric acid to put the kidneys at risk. That is a rule of thumb, not a dose, and the reason is in the fruit. Tartaric acid content swings from bunch to bunch, so two dogs can eat the same number of grapes and get different poisonings.
- Under the lineNot established as safe. Only not established as dangerous.
- Over the lineMerck’s risk threshold for kidney injury.
- 6–12 hoursVomiting or diarrhea, if it is coming.
- 24–72 hoursKidney failure. Once urine stops, the outlook is poor.
Why dogs and not us
Dogs lack the organic acid transporters other species have, so tartaric acid piles up in the cells of the kidney tubules instead of being cleared. It is the same reason tamarind is on the list. Raisins are the same fruit with the water taken out, so a raisin carries a whole grape’s worth of acid in something small enough to drop off a scone without noticing.
What to actually do
- Call whatever the count says. There is no established safe dose, so the profession’s default is to decontaminate first and argue about the arithmetic afterwards.
- The useful window for emptying the stomach is roughly the first two hours. That is the reason to call now rather than watch.
- Count what is missing, not what is left. Under the sofa counts as eaten.
- Fluids for 48 hours with the kidney values checked is the standard course. It is not cheap and it is what saves the kidney.
- Sultanas, currants, holiday fruitcake, fruit cake, granola, trail mix and cinnamon raisin bread are all the same problem in a costume.
What about cats
Established in dogs. There are anecdotal reports in cats and ferrets and no published case reports, so nobody can give you a number. Call anyway.