You get a call at your clinic from owners who are frantic about their dog, which is panting excessively and has bright red gums. Earlier in the evening, the dog ingested spent hops that had been tossed on the soil of a potted houseplant. However, the owners do not think their dogs clinical signs are due to the ingestion because their other dog also ingested the hops but is asymptomatic.
Humulus lupulus, a member of the Cannabinaceae family, has male and female plants. The female plant produces seedless flowers (cones) known as hops, which are used in brewing beer to provide bitter flavors and aromas.1 Hops are also sometimes used as a calming agent in herbal supplements.2 Some dog treats contain small amounts of hops extract to help alleviate anxiety; however, in larger quantities, hops can be fatal to dogs. The median lethal dose of hops in dogs is unknown. This article provides an overview of hops toxicosis and its treatment in dogs.
Hops intoxication in dogs is rare but can be devastating for unsuspecting dog owners who home brew beer. Spent hops make a great fertilizer because of their nitrogen content and tendency to warm rapidly when wet.3 For these reasons, hops are often tossed into compost piles or gardens, to which curious dogs may have access.
When used in home brewing, hops come in several different forms: whole flowers, pellets, and plugs of whole flower.1 These chemically diverse mixtures contain essential oils (which produce aromas) and α- and β-hydroxyacids (which are bittering agents).1 The many varieties of hops have differing ratios of these components, contributing to the complexity of hops and the difficulty in determining the mechanism of action for toxicity in dogs. Fresh cones and pellets and even spent hops are considered toxic to dogs.4
Clinical Signs of Toxicosis
The primary clinical sign of hops intoxication is a malignant hyperthermia-like reaction resulting in a rapid increase in body temperature.4 Certain canine breeds are more prone to developing malignant hyperthermia because they have a genetic mutation that allows an increase in the calcium level in muscle cells. This results in increased muscle contractions and changes in metabolism.5 Malignant hyperthermia can be triggered by stress, certain anesthetic gases, and exercise.5 Initially, it seemed that greyhounds were more prone to developing the malignant hyperthermia-like reaction seen with hops ingestion.6 However, as more cases of hops ingestion were reported to the ASPCA Animal Poison Control Center, it became apparent that many other canine breeds are susceptible.
The onset of clinical signs varies from 30 minutes to 12 hours after ingestion. Most commonly, owners notice their pet panting heavily, which is sometimes preceded by vomiting. Clinical signs may include panting, agitation, vomiting, injected mucous membranes, and death.4,7 Physical examination findings may include tachycardia and elevated body temperature.
Treatment
Because the median lethal dose of hops in dogs is unknown, ingestion of brewing hops should be considered life-threatening. Asymptomatic dogs should be decontaminated by induction of emesis and administration of activated charcoal. The patient should be monitored for 8 to 12 hours while receiving intravenous fluids.4 Hydrogen peroxide (3%; 2 mL/kg up to 45 mL) or apomorphine (0.04 mg/kg IV) may be administered to induce emesis within 1 hour of exposure if the patient is asymptomatic.6 If more than 1 hour has passed since ingestion or if emesis does not recover all of the hops, gastric or enterogastric lavage may be considered.4,6 The effectiveness of gastric lavage may be limited if the form of hops ingested is too large to pass through the tube. If gastric lavage is used, it should be performed within 2 hours of exposure.4,8 Activated charcoal (1 to 2 g/kg PO) can be given with a cathartic for further decontamination.6 Intravenous fluids should be administered to reduce body temperature and increase urine output.6 Fans, cool baths, and external ice packs may also help to reduce body temperature.4 Diazepam (0.5 to 1 mg/kg IV) may be given to treat agitation.4
No specific antidote is available for hops intoxication. Dantrolene is a skeletal muscle relaxant that can be used to treat malignant hyperthermia.4,7 Once body temperature becomes elevated, dantrolene can be administered at an initial dose of 2 to 3 mg/kg IV or 3.5 mg/kg PO. Thereafter, the drug can be given at 100 mg q12h PO for 3 days.4,6 Dantrolene is not typically available at veterinary clinics, so it may need to be acquired from a local human hospital. If dantrolene is not available, cyproheptadine may be administered at 1.1 mg/kg PO q6h as needed. There is some evidence that malignant-like hyperthermia is a result of serotonin effects.4,9 The use of cyproheptadine has had successful results in some cases of hyperthermia triggered by hops.4
Laboratory Diagnostics
The patients acid-base status should be monitored, as the lactic acid and carbon dioxide levels may become elevated due to increases in anaerobic and aerobic metabolism within the muscle cells.4,5 Metabolic acidosis occurs when too much lactic acid has been produced in the body; it can be treated by administering sodium bicarbonate (1 to 2 mEq/kg IV).6 Respiratory acidosis occurs when the lungs cannot remove carbon dioxide fast enough; it can be managed using ventilator support.5 Muscle tissue may begin to break down in a process known as rhabdomyolysis.5 A complete blood count and a chemistry panel (including the creatine kinase level) should be obtained for a baseline.4,7 The creatine kinase level (normal: 50 to 554 U/L)10 may become markedly elevated. A tenfold increase above the high end of normal indicates rhabdomyolysis.11 Urinalysis is also recommended.4,7 The urine is often brown due to myoglobinuria. If rhabdomyolysis occurs, renal values should be monitored.4 The patient should be given intravenous fluids to prevent kidney failure due to myoglobin release from muscle cells. In patients with prolonged hyperthermia, a platelet count, a blood smear, and coagulation testing should be considered.4,12 With severe hyperthermia, disseminated intravascular coagulation may occur; in this condition, blood clots develop throughout the body, depleting platelets and clotting factors and possibly resulting in abnormal bleeding.12
Prognosis
Hops toxicosis can be lethal even if dantrolene is administered. Death may occur due to organ damage from elevated body temperature and associated metabolic changes.4 In cases resulting in death, death usually occurs within 3 to 12 hours after the onset of clinical signs.4 When treatment is successful, clinical signs can take 24 to 72 hours to resolve.4
Acknowledgments
The author thanks Safdar A. Khan, DVM, MS, PhD, DABVT; Tina Wismer, DVM, DABVT, DABT; and Marsha Hays, CVT, who are affiliated with the ASPCA Animal Poison Control Center, Urbana, Illinois, for their contributions to and review of this article.
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