Reminder of a potential animal toxicity associated with making beer
Duncan KL, Hare WR, Buck WB. Malignant hyperthermia-like reaction secondary to ingestion of hops in five dogs. JAVMA 220(1):31-33, 1997.
This article, although not current, serves as a timely reminder of a potential animal toxicity associated with making beer. Many people receive home brew kits for Christmas and are just now trying them out. The article reviews five cases of hops ingestion and notes that ingestion of hops may result in a malignant hyperthermia type reaction in susceptible dogs. A key point, in terms of toxicity, is that hops plugs contain compressed whole leaves and are generally the culprits with little or no toxicity expected from the more popular processed hops pellets.
Article review :
The cases of five dogs (4 Greyhounds and 1 Labrador Retriever) known to ingest hops were reviewed. Three of the five dogs had no history of anesthesia. The onset of clinical signs occurred from 2.5 to 8 hours after ingestion. Signs included panting, restlessness, abdominal pain, tachycardia and tachypnea. Evidence of gaseous distension in the proximal SI and colon was present on X-Rays. Rectal temperature in all five dogs was elevated, with temperatures in three dogs > 41.7C. Four of the five dogs died despite aggressive therapy. Rigor mortis, when reported, occurred within 10 minutes. The surviving dog was treated early and aggressively with gastric lavage, removing about 250 ml of hops from the washings, and IV sodium bicarbonate.
Cultivated members of the genus Humulus are referred to as hop. Hops, used to provide flavor and aroma while brewing beer, are obtained from the flowers of the female Humulus lupulus . Resins, essential oils, phenols, and nitrogenous compounds are found in Humulus lupulus . Any of these can have a toxic effect on animals.
Resins, especially soft resins, contain acids that provide the bitter taste to beer. Soft resins are generally phenolic compounds that are unstable and their content decreases with the age of hops. Essential oils are present in 0.5 to 2.5% concentrations and include hydrocarbons, sulfur containing compounds, and oxygenated compounds. Essential oils impart the aroma to hops. Essential oils are also unstable and most are evaporated 10-15 minutes after boiling. Phenolic compounds vary from 2 to 4%. Included are tannins (coumaric acid, gallic acid, and caffeic acid) and many other polyphenolic compounds. Of the 20 different polyphenolic compounds identified, xanthohumol is the most widely recognized. It is rapidly oxidized, even in cold states. Nitrogenous compounds are present in 2 to 3.5 % concentrations; 0.5% are soluble. An “uncharacterized alkaloid” has been isolated. Betaine, adenine, hypoxanthine, choline, and most essential amino acids are other nitrogenous constituents present in hops.
Most of these biologically active compounds are volatile and would be lost during the boiling portion of brewing. The authors surmise, however, that if hops are steeped and not boiled, then one or more of the biologically active compounds would be present in used or discard hops plugs. They further postulate that ingestion of a hops plug containing one or more of these biologically active compounds was the cause of clinical signs in all five dogs. They suspected malignant hyperthermia in these dogs based on breed, presence of hyperthermia, lack of response to cooling measures, rapid onset of rigor mortis, and serum electrolyte/muscle enzyme abnormalities.
Malignant hyperthermia has been reported in human beings, pigs, dogs, cats, and horses. Stress, excitement, and anesthetic agents are the most common triggers in susceptible animals. Clinical signs develop from minutes to a few hours. The most common signs include hyperthermia, tachycardia, metabolic acidosis, and increases in serum magnesium potassium, calcium and phosphorous. A presumptive diagnosis is made based on clinical signs, familial history, and breed of dog. A definitive diagnosis can be obtained by using one or more of diagnostic tests (RBC fragility, muscle contracture, and halothane-succinylcholine challenge exposure test).
Any dog exposed to hops plugs that presents with an increased heart rate and elevated temperature should be treated aggressively. Treatment includes emesis, gastric lavage followed by activated charcoal with a cathartic, IV fluids to lower body temperature and increase urine output, and other cooling measures. Acid base status should be assessed and IV sodium bicarbonate administered as needed. Cardiac arrhythmias should be treated with procainamide and not lidocaine as lidocaine has an effect on the myoplasmic calcium concentration. Dantrolene, although not used in these dogs, is recommended (2-3 mg/kg IV or 3.5 mg/kg PO as soon as possible; followed by 100 mg PO every 12 hours for 3 days).
Any dog that survives should have a diagnostic test to confirm susceptibility to malignant hyperthermia. The authors suggest either an RBC fragility test or caffeine muscle contracture. Animal owners brewing beer should dispose of spent hops in a manner not likely to harm dogs. Hops plugs, which contain whole leaf hops, are generally felt to be the most toxic. The more popular hops pellets, with little or not particulate matter left for dogs to consume, are generally felt to be safer and less likely to result in toxicity.
Dr. Hovda's Comments: This article presents timely information regarding the potential for susceptible dogs to develop malignant hyperthermia when exposed to hops plugs. While recommended but not used in any of the dogs in this review, dantrolene has been used successfully in a number of more recent cases and should be considered in all cases similar to these. Finally, veterinarians should remember that the more popular and very processed hops pellets may not be as toxic as spent hops plugs.
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