An American woman who took phenylbutazone prescribed for her horse was admitted to hospital with a range of worrying symptoms.
The woman had thought the non-steroidal anti-inflammatory drug, commonly referred to as bute, would help her back troubles, because an over-the-counter painkiller was not helping.
She admitted to taking three doses of the drug at a rate suitable for a 181kg (400-pound) horse about three days before the start of her symptoms.
A case report in the journal Clinics and Practice describes the unusual case.
Khalid Sawalha and his colleagues said the 41-year-old woman, who had no significant past medical history, went to hospital complaining of nausea, vomiting, and generalized weakness over two weeks.
She had been doing well before developing the symptoms and had assumed they would resolve without seeking medical attention. She reported fevers with severe back pain during this period.
The patient said she often had mild back pain, usually controlled by naproxen over the counter, but it had provided little relief during this episode.
The patient said she felt progressively worse and had lost her appetite. Her husband suggested drinking large volumes of fluids. She reported drinking a gallon of cranberry juice, six 16-ounce bottles of water, and four cans of lemonade, leading to severe diarrhea and further weakness.
The woman also reported a tick bite around the time of her initial symptoms.
She denied smoking or illegal drug abuse.
On examination, the woman had a high heart rate and was borderline for low blood pressure, with normal oxygen saturations. She looked sick and lethargic, with dry mucous membranes, but otherwise appeared normal.
Her lab results revealed several areas of concern, including a low white blood count, low platelet levels, evidence of acute kidney injury, and elevated liver enzymes. Thyroid function was normal. There was no evidence of hepatitis.
Her urine drug screen was positive for amphetamines and marijuana. A CT scan revealed an enlarged spleen without any other abnormalities.
The case report team said the urine drug screen had been obtained because of suspicion of drug abuse, despite her initial denial.
They discussed the findings with the patient, and she later admitted to using both amphetamines and marijuana.
“This led us to take a detailed social history that revealed an unexpected event,” they reported.
The patient raises horses at her ranch, one of which was in pain. The vet prescribed phenylbutazone for the horse, and she saw that the horse had experienced pain relief.
“The patient was frustrated as naproxen did not help her (back) this time and took phenylbutazone to alleviate her pain. The patient admitted to taking three doses of a 400-pound horse equivalent dose of phenylbutazone about three days before the start of her symptoms.”
On learning that she had taken phenylbutazone, poison control and toxicology centers were notified but no antidote was recommended.
Her medical team put her a N-acetyl cysteine and sodium bicarbonate drip due to suspected acute liver damage from the phenylbutazone, as well as other treatments to improve her condition.
Her lab results improved during her three days in hospital and she was feeling better, but unfortunately decided to leave the hospital against medical advice before complete recovery occurred.
The case report team noted that phenylbutazone was first made available in 1949 for use in humans for the treatment of ankylosing spondylitis – inflammatory arthritis that affects the spine and large joints – gouty arthritis, and rheumatoid arthritis, but was withdrawn in the late 1970s due to an increased risk of agranulocytosis, a life-threatening blood disorder.
Phenylbutazone, they said, has now replaced chloramphenicol as the most common cause of fatal drug-related aplastic anemia and it must not be taken by people.
The drug is metabolized in the liver and excreted by the kidneys.
Phenylbutazone is widely available and is usually sprinkled as a powder over the food of horses requiring the drug.
Most cases of phenylbutazone toxicity are treated similarly to other cases of poisoning involving non-steroidal anti-inflammatory drugs (NSAIDs), with supportive therapy, including airway management, volume resuscitation, and correcting for metabolic acidosis.
“As with other NSAID toxicities, dialysis has not been shown to be an effective treatment option as it (the drug) is highly protein-bound,” they noted.
Activated charcoal in adolescents/adults or gastric lavage has also been used if the patient presents within an hour of ingestion.
“Our patient has ingested three doses of phenylbutazone in addition to using naproxen and possibly other over-the-counter NSAIDs. The dose she used was for a 400-pound horse, which is much bigger than her weight (170 pounds).
“Due to all of this, we believe that the patient’s presentation is most consistent with phenylbutazone toxicity leading to aplastic anemia, acute kidney, and liver injury.
“The long half-life that phenylbutazone exhibits in humans suggest that the medication had been in her blood for two to three weeks, given that medications take around four to five half-lives to be cleared from the body.”
The level of toxicity could have been further exacerbated by her use of other NSAIDs, they said.
The authors also noted that testing revealed evidence of Ehrlichia, a species of bacteria that is transmitted by ticks.
“We believe that she was exposed to it and her immune system was capable of clearing the infection on its own; therefore, explaining the positivity for both immunoglobulins.
“Yet, she could have had a mild infection which added symptoms to her clinical presentation,” they acknowledged.
The case, they said, was a great example of the importance of taking a proper history from a patient, including social and drug history.
“Patients may sometimes hide their usage of over-the-counter medications and herbal medicinal preparations from physicians.
“Multiple medications, such as antibiotics, anti-helminths, and anti-inflammatory agents, are used for humans and animals, but it is not recommended for humans to ingest the formulations made for animals as they have different pharmacokinetics and absorption properties.”
Sawalha is with the White River Health System in Arkansas. Others involved in the case report were Ryan James, Farah Mazahreh, Harmeen Goraya and Fuad Habash, all with the University of Arkansas.
Sawalha, K.; James, R.; Mazahreh, F.; Goraya, H.; Habash, F. “Ain’t She a Bute?”: The Importance of Proper History Taking in a Case of Inappropriate Use of Horse NSAID in a Human. Clin. Pract. 2021, 11, 455-458. https://doi.org/10.3390/clinpract11030060