Aspirin (Acetylsalicylic Acid)
Aspirin, also known as acetylsalicylic acid (ASA), belongs to the group of non-steroidal anti-inflammatory drugs (NSAIDs) and is commonly used in human medicine as a painkiller, anti-inflammatory, and blood thinner. However, in pets, especially dogs and cats, aspirin can cause severe poisoning. Aspirin poisoning (intoxication) occurs when animals ingest a toxic dose of this active substance.
The mechanism of action of aspirin is based on the inhibition of cyclooxygenase enzymes (COX-1 and COX-2), which are responsible for the formation of prostaglandins. Prostaglandins are endogenous signaling molecules that, among other things, influence inflammatory processes, pain perception, fever, as well as the protection of the gastric mucosa and the regulation of kidney function. By blocking these enzymes, aspirin has pain-relieving, fever-reducing, and anti-inflammatory effects, but at the same time impairs important protective mechanisms in the body.
Particularly noteworthy is the significant difference in aspirin metabolism between dogs and cats. While dogs can metabolize aspirin with a half-life of about 8 hours, cats lack a crucial enzyme for the glucuronidation of salicylic acid, which extends the half-life to about 40 hours. This species-specific peculiarity makes cats particularly susceptible to aspirin poisoning, as the active substance remains in the body significantly longer and can accumulate more easily.
The most important facts at a glance
Aspirin poisoning in dogs and cats represents a medical emergency that requires rapid and targeted veterinary intervention. Aspirin (acetylsalicylic acid) acts by inhibiting cyclooxygenase enzymes, thereby impairing the formation of prostaglandins, which leads to therapeutic effects but also to undesirable side effects.
Particularly noteworthy is the fundamental difference in metabolism between dogs and cats. While dogs can metabolize aspirin with a half-life of about 8 hours, cats lack a crucial enzyme for glucuronidation, which extends the half-life to about 40 hours. This makes cats particularly susceptible to poisoning.
The most common causes of aspirin poisoning are improper medication administration by pet owners and accidental ingestion of unsecured medications. Symptoms include gastrointestinal complaints (vomiting, diarrhea, bleeding), neurological abnormalities (apathy, ataxia, seizures), changes in the respiratory and circulatory systems, as well as kidney and liver damage.
Diagnosis is based on anamnesis, clinical examination, and laboratory diagnostic procedures, with the direct detection of salicylates in the blood being particularly conclusive. Therapy includes decontamination, specific antidote administration (misoprostol in dogs), and symptomatic measures such as fluid therapy, gastric protection, and control of vomiting and seizures.
The prognosis depends on the dose, the timing of treatment initiation, and pre-existing conditions. With early treatment, it is generally good, whereas with delayed therapy or pre-existing organ damage, complications are to be expected. Aftercare includes regular follow-up examinations and, if necessary, dietary measures.
Prevention measures such as the safe storage of medications and educating pet owners about the dangers of self-medication are crucial to avoid future poisoning cases.
Causes, development and progression
In small doses, aspirin already has an anticoagulant effect, and in higher doses, due to the inhibition of inflammatory mediators (prostaglandins), it has pain-relieving, fever-reducing, and anti-inflammatory properties.
The anticoagulant effect is partly used in cats.
Supplement
The causes of aspirin poisoning in pets can be divided into several categories. The most common cause is improper medication administration by pet owners who act with good intentions but administer human medical preparations without veterinary instruction. Many pet owners are unaware of the significant metabolic differences between humans and animals and mistakenly transfer human dosages or application recommendations to their pets.
Another common cause is the accidental ingestion of aspirin by curious animals who have access to unsecured medications. Dogs, in particular, who are less selective about what they eat, can swallow entire packages of painkillers if they are stored within their reach. Improper disposal of medications in household waste can also lead to accidental ingestion.
In rarer cases, overdoses can occur as part of a veterinary-prescribed therapy. This happens, for example, when pet owners misunderstand dosage instructions or when multiple family members unknowingly administer the same medication. Especially in cats, who can only tolerate very low dosages due to their limited metabolizing ability, even small deviations from the prescribed dose can lead to toxic reactions.
The minimum toxic dose for oral intake in dogs is approximately 50 mg/kg body weight three times daily, while in cats it is already 25 mg/kg body weight twice daily. The LD50 (dose at which 50% of animals die without treatment) is stated as approximately 700 mg/kg body weight for dogs. For cats, this value is significantly lower.
Mechanism of action
Prostaglandins are involved in regulating stomach acid and blood flow to the gastric mucosa. Prolonged intake or unintentional excessive intake of aspirin can lead to damage to the gastric mucosa, such as inflammatory irritation, bleeding, or local ulcers.
Simultaneous intake of glucocorticoids increases the risk of bleeding and ulcers in the gastrointestinal tract.
In dogs, high doses of aspirin stimulate the respiratory center and can thereby negatively affect the internal acid-base balance.
Aspirin in ointments is also almost completely absorbed through the skin.
Cats react significantly more sensitively. Due to a genetic change, cats of all breeds are hardly able to convert salicylic acid, which is formed immediately after aspirin intake, into a substance that can be excreted via the kidneys.
As a result of this special situation in cats, elimination from the body takes about five times longer in cats than in dogs. In dogs, a half-life of 8 hours can be assumed. In cats, it is approximately 40 hours.
This is also the reason why the therapeutic administration of aspirin in dogs is twice daily, while in cats it should only be once daily.
Supplement
Acetylsalicylic acid (ASA), internationally known as Aspirin, belongs to the group of non-steroidal anti-inflammatory drugs (NSAIDs) and is commonly used in humans for pain and fever reduction as well as blood thinning. However, in dogs and especially in cats, ASA can quickly become toxic – due to dose-dependent, multiple systemic effects.
The mechanism of poisoning is based on the inhibition of important enzymes, disturbances of the acid-base balance, and direct cell damage.
1. Inhibition of Cyclooxygenases (COX-1 and COX-2)
Acetylsalicylic acid irreversibly inhibits the enzymes cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), which are responsible for the synthesis of prostaglandins.
Consequences of toxic dose:
- Gastrointestinal damage:
- Prostaglandins protect the gastric mucosa. Their inhibition leads to ulcerations, erosions, bleeding, and perforations of the gastrointestinal tract.
- Kidney damage:
- In the kidneys, prostaglandins are important for blood flow regulation. Their inhibition can lead to acute kidney failure, especially in dehydrated animals.
- Coagulation disorders:
- COX-1 inhibition inhibits the formation of thromboxane A2 in platelets → reduced platelet aggregation → increased bleeding tendency.
2. Disturbance of Energy Metabolism and Cellular Respiration
In high doses, ASA uncouples oxidative phosphorylation in the mitochondria. This disrupts ATP formation.
Consequences:
- Metabolic acidosis: Increased anaerobic glycolysis leads to increased lactate formation → acidification of the blood
- Hyperthermia: Increased heat production due to uncoupling of cellular respiration
- Hypoglycemia: Increased energy demand with reduced energy production
3. CNS Effects at Toxic Dose
At high blood levels, ASA can directly affect the central nervous system.
- Initially: Stimulation of the respiratory center → hyperventilation, respiratory alkalosis
- Later: Exhaustion → respiratory depression, CO₂ increase
- Neurological symptoms: Ataxia, disorientation, seizures, coma
4. Species-dependent Differences
Dog:
- Metabolism: Dogs can metabolize ASA relatively slowly, but are less sensitive than cats.
- Toxic dose: 25–50 mg/kg with chronic administration; acute toxicity from approx. 200 mg/kg
Cat:
- Particular risk: Cats are highly sensitive to ASA because they largely lack the enzyme UDP-glucuronyltransferase, which is necessary for ASA metabolism.
- Half-life: up to 38 hours (vs. 8–12 h in dogs)
- Toxic dose: potentially toxic from approx. 10–25 mg/kg
Summary of Toxic Effects:
| System | Toxic effect |
| Gastrointestinal tract | Mucosal damage, bleeding, ulcers |
| Kidneys | Reduced blood flow, acute kidney failure |
| Blood clotting | Inhibition of platelet aggregation → bleeding tendency |
| Central nervous system | Stimulation and later depression → hyperventilation, seizures, coma |
| Metabolism | Acidosis, hypoglycemia, hyperthermia |
Symptoms of intoxication
The first symptoms, especially vomiting, appear as early as 4–6 hours after intoxication.
Young dogs are more sensitive than adult animals, as their conversion mechanisms are limited, similar to cats.
Characteristic is the development of acidosis (metabolic acidosis), which can be accompanied by respiratory paralysis and unconsciousness.
In cats, kidney and liver damage is also to be expected with aspirin poisoning. Effects on the brain are also possible.
The minimum toxic dose for oral intake in dogs is 50 mg/kg body weight 3 times daily, for cats 25 mg/kg body weight 2 times daily.
The LD50 (50% of animals die without treatment) in dogs is 700 mg/kg body weight.
In summary, the symptoms of intoxication are
generally:
- Lethargy
- Depression
- Loss of appetite
affecting the gastrointestinal tract and liver:
- Vomiting, sometimes bloody
- Diarrhea, sometimes bloody
- Anemia due to blood loss via the gastrointestinal tract
- Yellowing of the skin (jaundice) in case of liver damage
affecting brain function
- Balance disorders (ataxia)
- Tremor,
- generalized seizures or muscle weakness
affecting lung function and the cardiovascular system
- Increased respiratory rate
- Increased heart rate
- Hypothermia
- Coma
- Shock
Clinical signs of aspirin poisoning typically develop within 4–6 hours after ingestion and can vary depending on the dose ingested, the species, and the individual health status of the animal. The symptoms can be divided into several organ systems.
In the gastrointestinal tract, affected animals often show vomiting as the first sign, which can sometimes be bloody. This results from the direct irritating effect on the gastric mucosa and the reduced prostaglandin production, which normally contributes to the protection of the gastric mucosa. Other symptoms include loss of appetite, diarrhea (possibly with blood), abdominal pain, and increased salivation. In the long term, chronic bleeding can lead to anemia, which manifests as pale mucous membranes and increased fatigue.
At the neurological level, poisoning can lead to behavioral changes. Affected animals often show apathy, depression, or paradoxically, restlessness and hyperactivity. As the poisoning progresses, balance disorders (ataxia), tremors, and in severe cases, generalized seizures can occur. In highly severe poisonings, impaired consciousness up to coma can occur.
In the respiratory and circulatory systems, aspirin initially leads to stimulation of the respiratory center with an increased respiratory rate. In severe poisonings, metabolic acidosis develops, leading to compensatory hyperventilation. The heart rate is typically increased. In advanced stages, hypothermia and shock can occur.
Especially in cats, but also in dogs, kidney and liver damage can occur, which can manifest as increased drinking and urination, as well as yellowing of the mucous membranes (jaundice). Impairment of kidney function can lead to reduced urine production up to acute kidney failure.
Young animals and animals with pre-existing gastrointestinal, kidney, or liver diseases are particularly sensitive to aspirin and can develop severe symptoms even at lower doses.
Diagnosis
The diagnosis of aspirin poisoning is based on a combination of anamnesis, clinical examination, and laboratory diagnostic procedures. The first and often crucial step is a thorough collection of the patient’s history. Information about possible access to medications, observed ingestion of aspirin or other painkillers, as well as the approximate amount and time of ingestion, are of central importance. Documentation of symptoms that have already appeared and their temporal course also provides important diagnostic clues.
During the clinical examination, the veterinarian pays particular attention to signs of gastrointestinal irritation, neurological abnormalities, vital parameters, and mucous membrane color. Measuring body temperature, heart and respiratory rate, and assessing hydration status are fundamental components of this examination.
Several parameters are relevant for laboratory diagnostics. A blood gas analysis can detect metabolic acidosis, which is characteristic of advanced aspirin poisoning. A complete blood count can indicate anemia due to gastrointestinal bleeding, while the determination of liver and kidney values shows possible organ damage. Coagulation diagnostics are useful to assess the effects on blood clotting.
The direct detection of salicylates in blood or urine is the most specific diagnostic method. The blood concentration correlates with the severity of the poisoning and can be used for therapy planning. In cases of suspected gastrointestinal bleeding, an ultrasound examination of the abdomen can be helpful to assess the extent of mucosal damage.
Differentially, other intoxications (especially by other NSAIDs such as ibuprofen or paracetamol), acute gastroenteritis, pancreatitis, primary kidney diseases, and neurological diseases must be ruled out. The combination of typical symptoms, corresponding anamnesis, and elevated salicylate levels in the blood confirms the diagnosis.
Therapeutic principles
The therapeutic principles follow the measures described at the beginning.
Decontamination is carried out by:
- Inducing vomiting,
- Gastric lavage,
- Administration of activated charcoal,
- Bowel irrigation
- Stimulation of urine production (forced diuresis)
A synthetic prostaglandin (misoprostol) is available as an antidote for dogs.
Repeated administration of this preparation can counteract the toxic effect of anti-inflammatory drugs in dogs.
Otherwise, therapy in dogs is symptomatic.
No antidote is available for cats, so only symptomatic therapy can be used here.
The main focus of symptomatic therapy is the monitoring and stabilization of vital functions:
- Circulation
- Respiration
- Water, electrolyte, and acid-base balance
Further symptomatic therapy includes:
- Relieving seizures
- Optimizing body temperature
- Protecting the gastric mucosa
- Controlling vomiting
- Compensating for blood loss in critical anemia
Supplement
The treatment of aspirin poisoning requires a rapid and systematic approach. Therapeutic management can be divided into several phases: decontamination, specific antidote administration (if available), and symptomatic therapy.
Decontamination aims to prevent further absorption of the toxin. In cases of recent ingestion (within 1–2 hours), inducing vomiting by administering apomorphine in dogs or xylazine in cats may be indicated. However, this should only be done under veterinary supervision, as there is a risk of aspiration if neurological symptoms or impaired consciousness are already present. In animals that already show symptoms or if ingestion occurred longer ago, gastric lavage can be performed under anesthesia.
An essential part of decontamination is the administration of activated charcoal, which binds toxic substances in the gastrointestinal tract and prevents their absorption. In aspirin poisonings, activated charcoal is ideally administered multiple times at intervals of 4 to 6 hours, as aspirin undergoes enterohepatic circulation and can be repeatedly excreted into the intestine. The administration of laxatives can accelerate excretion.
Misoprostol, a synthetic prostaglandin E1 analogue, is available as a specific antidote for dogs. It can partially replace the prostaglandin production inhibited by aspirin. It protects the gastric mucosa and can reduce gastrointestinal bleeding. Unfortunately, no specific antidote exists for cats, which makes treatment in this species more complicated.
Symptomatic therapy includes several components. Intravenous fluid therapy is essential to promote renal blood flow and accelerate toxin excretion. In metabolic acidosis, sodium bicarbonate may be administered to correct the acid-base balance. Proton pump inhibitors such as omeprazole or H2 receptor antagonists such as ranitidine are used to protect the gastric mucosa. Antiemetics such as maropitant can control vomiting.
In severe bleeding, a blood transfusion may be necessary. Seizures are treated with anticonvulsants such as diazepam or phenobarbital. Monitoring and stabilizing vital functions, including body temperature, respiration, and circulation, are of utmost importance throughout the treatment.
The duration of therapy depends on the severity of the poisoning and can range from a few days to several weeks, especially if organ damage has occurred. Close monitoring of clinical parameters and regular checks of laboratory values are required throughout the treatment period.
Prognosis & follow-up care
With careful monitoring and appropriate therapy, the prognosis is good.
The prognosis for aspirin poisoning depends on several factors: the dose ingested, the time elapsed until therapy begins, the species of the affected animal, and the presence of co-existing diseases. Generally, the earlier treatment begins, the better the chances of full recovery.
In mild poisonings with prompt veterinary intervention, the prognosis is generally good. Animals treated within the first 4–6 hours after ingestion and who have not developed severe organ damage usually recover completely. In moderate to severe poisonings, especially if kidney or liver damage has already occurred, the prognosis is more cautious. Cats tend to have a poorer prognosis than dogs due to their limited metabolic capacity.
Aftercare plays a crucial role in long-term recovery. After the acute treatment phase, regular follow-up examinations are necessary to monitor organ functions. This includes blood tests to check liver and kidney values, and if necessary, ultrasound examinations to monitor the healing of gastrointestinal lesions.
Dietary recommendations for the convalescence phase include easily digestible, gentle diets that should be offered in small, frequent portions. In cases of persistent gastrointestinal problems, long-term medication with gastric protective agents may be necessary. Animals with kidney damage may require a special renal diet and regular monitoring of kidney function.
It is particularly important to educate pet owners about preventive measures to avoid future poisonings. This includes safely storing medications out of reach of pets, ideally in locked cabinets. Medications should never be administered without veterinary instruction, and expired or no longer needed medications must be disposed of properly.
In some cases, animals that have survived severe poisoning may have long-term damage that requires permanent adjustments to their living conditions. This particularly affects animals with permanent kidney function impairments who require lifelong monitoring and treatment.
Research outlook
Research in the field of aspirin poisoning in pets is currently focusing on several promising approaches. One focus is on the development of species-specific antidotes, especially for cats, which are particularly at risk due to their limited metabolic capacity. Scientists are investigating modified prostaglandin analogues that are specifically tailored to the needs and physiological peculiarities of cats.
Another research area deals with improved diagnostic methods. Point-of-care tests, which enable rapid and reliable detection of salicylates in small blood volumes, could revolutionize diagnosis in veterinary practice. Such tests would allow for immediate treatment decisions without delay due to laboratory examinations.
Innovative treatment approaches such as extracorporeal toxin elimination are gaining increasing importance. Hemodialysis and hemoperfusion have proven effective in severe cases to remove aspirin from the bloodstream. Current studies are focusing on optimizing these procedures for veterinary medicine and developing portable devices that could also be used in smaller practices.
Research into the long-term consequences of recovered aspirin poisoning is another important field. Longitudinal studies investigate whether and to what extent subclinical organ damage can occur after acute poisoning and what preventive measures are useful to minimize long-term effects.
Last but not least, research is dedicated to improving prevention strategies. These include the development of more pet-friendly packaging for human medications, the optimization of educational campaigns for pet owners, and the integration of poisoning prevention into basic veterinary care.
These research approaches promise to significantly improve the diagnosis and therapy of aspirin poisoning in pets in the coming years and to increase the survival rates and quality of life of affected animals.
Frequently asked questions (FAQs)
- How quickly do symptoms of aspirin poisoning appear in my pet?
The first symptoms, typically vomiting and lethargy, usually appear within 4–6 hours after ingestion. In cats, some symptoms may be delayed due to their slower metabolism. - Can I give my dog or cat aspirin myself for pain?
No, you should never administer aspirin or other human medications to your pets without veterinary instruction. The dosage, frequency of administration, and suitability must always be determined by a veterinarian. - What immediate measures can I take if my pet has ingested aspirin?
Contact your veterinarian or a veterinary emergency clinic immediately. Do not attempt to induce vomiting yourself, as this can be dangerous if symptoms are already present. Keep the packaging or remaining medication ready to estimate the ingested amount. - Are certain pet breeds or age groups particularly at risk?
Yes, young animals, small breeds, and older animals with impaired organ function are particularly sensitive to aspirin. Additionally, cats are generally more sensitive than dogs. - Can a single aspirin poisoning lead to permanent damage?
Yes, especially with severe poisoning or delayed treatment, permanent kidney or liver damage can remain. Chronic gastrointestinal problems are also possible. - How can I prevent aspirin poisoning in my pets?
Store all medications in locked cabinets out of reach of pets. Dispose of unused or expired medications safely and inform all household members about the dangers of human medications for animals. - Are there safe alternatives to aspirin for pets with pain?
Yes, there are pain medications specifically developed for animals that are significantly safer. Your veterinarian can prescribe a suitable preparation depending on the cause of pain and your pet’s individual situation. - How long does recovery take after aspirin poisoning?
In mild cases of poisoning and with prompt treatment, recovery can occur within a few days. In severe cases with organ damage, recovery can take weeks to months and require regular follow-up examinations. - What diagnostic tests are performed if aspirin poisoning is suspected?
Typically, a complete blood count (CBC), organ values, blood gas analysis, and specific tests for salicylate concentrations in the blood are performed. Depending on the symptoms, further examinations such as ultrasound or ECG may be necessary. - Is aspirin poisoning always an emergency?
Yes, any aspirin ingestion by pets should be considered a potential emergency requiring immediate veterinary assessment. The sooner treatment begins, the better the chances of success.
Literature
- https://www.msdmanuals.com/de-de/profi/verletzungen,-vergiftungen/vergiftung/vergiftungen-mit-acetylsalicyls%C3%A4ure-und-anderen-salicylaten
- Artner, J. Syn. ASA, Aspirin. Def. Platelet aggregation inhibitor, non-steroidal, antiphlogistic-antipyretic analgesic. The mechanism of action: Acetylsalicylic acid exerts its effect through non-specific, irreversible inhibition of cyclooxy.
- https://www.vetpharm.uzh.ch/clinitox/toxdb/klt_059.htm
- Löwe G, Löwe O. Poisoning in Dogs and Cats – A Veterinary Guide. 2nd edition. Kreuztal: Kynos-Verlag. 2021; 208 p.
- GWALTNEY-BRANT, S. M. (2021): Nonsteroidal Anti-inflammatory Drug Toxicosis. In: Veterinary Toxicology. 4th Ed. Academic Press, S. 325–337.
- KHAN, S. A., MCLEAN, M. K. (2023): Common toxicologic issues in small animals. Veterinary Clinics of North America: Small Animal Practice, 53(2), S. 417–438.
- JÄHNIG, P. (2024): Poisonings in dogs and cats – A retrospective analysis of empirical and evidence-based data from 2000 to 2020 on epidemiology, diagnostics and therapy. Dissertation, University of Leipzig.
- WISMER, T., MEANS, C. (2023): Toxicology of Commonly Used Analgesics in Companion Animals. Veterinary Clinics of North America: Small Animal Practice, 53(1), S. 75–89.