Parallel to the increasing trend in illicit drug use among humans, and in many cases multiple DA use, the intoxication of pets with recreational or illicit substances has become increasingly prevalent in the past decade. Such exposure can occur accidentally, intentionally, or through malicious means. Furthermore, dogs, known for their wandering tendencies and indiscriminate eating habits, are particularly vulnerable to various forms of poisoning, including that caused by illicit drugs (4). Other important exposure scenarios include active duty or training of drug detection dogs (7). and the use of animals, especially dogs, as “pack mules” for the illegal transport of drugs. In the latter scenario, dogs are either fed baggies filled with the drug or baggies are surgically implanted in the peritoneum. Death may occur from either the drug itself (leakage of drug from its container) or secondary to infection following a non-sterile surgical technique (8).

In the present study, in at least 32% of cases, the samples were submitted to CAHFS due to suspicion of cruelty to animals. In 75% of cases, the detected drug combinations included methamphetamine, amphetamine, or both. Methamphetamine, amphetamine, methylenedioxy-methamphetamine, and other designer amphetamines collectively belong to the group of drugs known as amphetamine-type stimulants (ATS) (9). Amphetamines are part of a class of psychotropic drugs initially developed for human use in the treatment of conditions such as attention deficit hyperactivity disorder (ADHD) and narcolepsy. Amphetamine is classified as α-methylphenethylamine (10). In contrast to some AST’s (e.g., amphetamine and methylphenidate) which have recognized clinical applications and advantages, methamphetamine and methamphetamine designer drugs are potent psychostimulants known for their high addiction potential (9, 11). Methamphetamine currently ranks as the second most widely abused drug worldwide and ATS have become the most popular illegal psychostimulants in the world (9, 11). Experiments investigating the disposition and fate of amphetamine and methamphetamine in the body confirm that approximately 30–40% of the ingested dose is excreted unchanged in the urine (12, 13). Other studies indicate that about 5–7% of methamphetamine undergoes N-demethylation to amphetamine as the primary metabolite, while amphetamine is not metabolized into methamphetamine (13–15). Consequently, when pure methamphetamine is consumed, the concentration ratio of methamphetamine to amphetamine should be greater than one (15). This may explain the reason for diagnosing both methamphetamine and amphetamine in most (85%) of the examinations verifying exposure to methamphetamine inhalation, although the CAHFS DA tests are qualitative rather than quantitative. ATS are quickly absorbed through the gastrointestinal tract, although for prescription ATS their absorption is delayed when using sustained-release products (SRP). The oral bioavailability of methamphetamine is estimated to be 67% with rapid, widespread distribution throughout most body tissues (16). Amphetamines may also be absorbed in dogs through inhalation or contact with mucous membranes (4, 8). Peak plasma concentrations of amphetamine are typically reached within 1–3 h following ingestion, except when a SRP has been taken. Amphetamine is highly lipophilic, allowing it to readily penetrate the blood–brain barrier (4, 8). In humans, approximately 70% of an oral methamphetamine dose is eliminated through urine within 24 h, with the parent drug accounting for 30–50% and the amphetamine metabolite contributing about 10%. Given that urine serves as the primary route for the elimination of methamphetamine and its primary metabolite, amphetamine, it is considered a suitable specimen for toxicological analysis, as well as serum/plasma. Unfortunately, urine may not be accessible during necropsy (11, 17, 18). Other samples that can be sent for LC–MS/MS analysis in dogs may include liver, kidney tissues, and stomach contents, which often have higher drug concentrations compared to other tissues. These samples may be especially useful for postmortem confirmation (11). Amphetamine is eliminated in dogs within approximately 6 h when the average urine pH is around 7.5, and within 3.3 h when the average urine pH is around 6.6 (8).

Given the abundant use of ATS as an illicit drug in humans in the US, there is no surprise in the finding that it was also the most common to be found among the pet samples submitted to CAHFS. The most common clinical signs reported for methamphetamine/amphetamine intoxication in the present study included seizures, agitation, hyperreactivity, tremors, ataxia, circling, mydriasis, tachypnea, tachycardia, and hyperthermia, all consistent with sympathomimetic effects. Forty-three percent of patients who tested positive for methamphetamine/amphetamine were dead when samples were submitted. Nevertheless, while considering these findings, it is important to remember that many of the patients were exposed to more than one drug. The prognosis for animals with ATS intoxication depends on the consumed dose, the time elapsed between exposure and presentation, and the severity of clinical signs, and is overall considered fair, but there is an information gap in formulating a prognosis (8). Differential diagnosis for ATS intoxication may include exposure to other drugs such as cocaine, ephedrine, pseudoephedrine, methylxanthines, caffeine, selective serotonin reuptake inhibitors (SSRIs), tremorgenic mycotoxins, metaldehyde, or strychnine, which may cause similar central nervous system and/or cardiovascular stimulation, as well as conditions like pheochromocytoma.

Specific treatments were rarely mentioned in the provided case histories. In general, the ideal approach should focus on prevention and/or controlling life-threatening central nervous system and cardiovascular signs. This may include decontamination methods, such as emesis, gastric lavage (depending on the timing and amount ingested), activated charcoal, hospitalization for intravenous fluid treatment, and addressing symptomatic signs. These treatments could involve the use of phenothiazines for agitation, cyproheptadine as a serotonin antagonist, beta-blockers for managing tachycardia and hypertension, and other antiarrhythmics (e.g., lidocaine, procainamide) for severe arrhythmias. Methocarbamol can be employed for tremors, barbiturates for seizures, and the use of propofol or inhaled anesthesia in cases of uncontrolled seizures. The use of diazepam is controversial in treating pets with ATS intoxication, as it may increase dysphoria, paradoxical stimulation, and morbidity. Unfortunately, there is no specific antidote available for ATS intoxication, so monitoring and prompt treatment for signs of hyperthermia, cardiac arrhythmias (including ECG monitoring), and blood pressure are crucial (4, 8, 19). The use of IV lipid emulsion (ILE) infusion has been mentioned in cases of ATS intoxication (20–22). However, its efficacy has not been definitively approved, and some authors state that ILE is not indicated for cases of amphetamine toxicosis, due to a lack of known efficacy and the potential for clinical signs to worsen with the administration because it can decrease the efficacy of some therapeutic medications (23).

Interestingly, despite the staggering increase in opioid-related morbidity and mortality among humans in the US that has earned the name “the opioid epidemic” (24), and that the prevalence of cocaine use has only increased modestly, cocaine-involved overdose mortality has risen dramatically (25). Opioids (16%), synthetic opioids (14%), and cocaine (21%) were presented in relatively small numbers in the present study, often in combination with other drugs, especially ATS.

Only 7 out of 175 specimens tested positive solely for Delta-9-Tetrahydrocannabinol (THC). These cases were not included in the study’s results. All in all, with current trends in cannabinoid legalization and reduced or eliminated state penalties for cannabis possession, the odds of a cannabis poisoning call to poison control centers have increased (26). Despite this fact, it appears that testing at CAHFS for THC as a recreational drug “intoxication” is less common. This is likely due to the fact that clinicians are more aware of the possibility of marijuana exposure, are familiar with the clinical signs of marijuana exposure, utilize the cost-effective urine drug screening test (UDST), and recognize that marijuana intoxication is a relatively mild clinical condition that resolves quickly with mostly no adverse effects (27). In 3 out of 57 cases in the present study, THC was found in conjunction with other drugs of abuse and was therefore reported.

Nicotine was found in 29% of samples, mostly (63% of nicotine exposures) as a trace exposure in the sample, and always in combination with other drugs. These exposures were probably not a “true” nicotine intoxication, but rather an indication of “passive smoking.” This finding would not be unexpected in a pet living in an environment that may contain illicit or recreational drugs (28). The significance of a “trace exposure in the sample” can be explained by the fact that LC–MS/MS was not designed as a quantitative test since detected concentrations do not contribute to the interpretation. The test is designed to determine exposure. A sample is spiked with a specific analyte (e.g., nicotine) concentration that is as low as possible but still readily detected. This is considered the “reporting limit.” If a signal is higher than the reporting limit for that analyte, the result is reported as “positive.” If a positive signal for an analyte is detected below the reporting limit but sufficiently above the analytical “background” signal (3–5 times the background signal), it is reported as a “trace.” If a signal is not detected or not detected sufficiently above the background signal, the result is considered “negative.”

In the present study, only 7 cases reported the use of point-of-care (POC) on-site urine multidrug tests or UDST. These cases seem to exhibit a reasonable correlation with the LC–MS/MS method. However, the limited number of reported cases is insufficient for making a precise assessment of false positive or negative rates. Research conducted using the UC Davis Veterinary Medical Teaching Hospital’s Small Animal Clinic database indicates that many cases are primarily diagnosed based on history, clinical signs, and human POC UDST. This preference for human POC UDST is likely because of its over-the-counter availability, rapid results, and affordability. It is estimated to be accurate in identifying barbiturates, opiates, benzodiazepines, and amphetamines/methamphetamines in dogs’ urine when these drugs are administered intravenously or orally. However, it is not as effective in identifying marijuana or methadone and has not been validated for phencyclidine or cocaine intoxication (29). In cases where POC UDST is used, the diagnosis is supported by a history and clinical examination findings consistent with drug exposure. Furthermore, LC–MS/MS test results require longer turnaround times, typically within 10–14 business days, and often do not alter the treatment plan or clinical course. However, it’s worth noting that the specificity and sensitivity of the POC UDST was conducted for only one kit and in a relatively small number of samples. POC UDSTs are qualitative and employ antibodies that may cross-react with structurally related compounds. For instance, a positive result for opiates may occur for all compounds in the same class, and there may be false positive results when some common medications or substances are used (as shown in Table 3, based on human data) (30, 31). It would be interesting to more thoroughly validate the commonly used POC UDSTs in dogs and cats.

At least one-third of the tests in this study were requested due to known or suspected cases of cruelty to animals. Violence is inherently linked to the culture of misuse of alcohol and drugs (32, 33). Unless these substances are used explicitly for medical purposes, any presence of illicit or recreational drugs in an animal specimen suggests an unintended exposure. Instances of malicious poisoning or various forms of animal abuse and cruelty, including involving pets in drug use, have been documented (34, 35). These are often exposures with the intent to harm. Finding these in animal specimens is a cause for concern and investigation. A pet owner who is aware that their animal may have ingested or been exposed to illegal substances may hesitate to acknowledge it (4, 8). Veterinarians should balance client confidentiality, best practice for the patients, and legal obligations.

It is important to remember that, given the large number of animal abuse or cruelty cases, the involvement of law enforcement, and the potential for criminal penalties, POC urine multidrug tests are merely screening tests (not confirmatory). Therefore, they might not be as useful to law enforcement. Samples should be sent to an established toxicological laboratory for the absolute confirmation of drugs of abuse (DA) in these cases.

This study has a few inherent limitations. First, the retrospective nature of the study, and the fact that it was based on information from referral forms or cases where the patient was found deceased, rather than comprehensive medical records, led to missing data. Moreover, cause-and-effect relationships often cannot be determined retrospectively. Second, the cohort size, although the largest yet, is nonetheless limited, which weakens the descriptive information and does not allow for statistical analyses. Third, the results of the DA screen test at CAHFS are qualitative rather than quantitative. For diagnostic purposes, this does not change the clinical course of the case since proof of exposure to these drugs is unequivocal. Nevertheless, it would have been interesting to compare drug concentrations to morbidity and mortality. Fourth, this study comprised clinical data from a single referral veterinary toxicological laboratory. Therefore, our results should be applied cautiously to other clinical settings.

In conclusion, in 75% of the drug-of-abuse screen tests conducted at CAHFS, the detected drug combinations included ATS. In 47% of cases, a combination of more than one drug group was found. In at least 32% of cases, the samples were submitted to CAHFS due to suspicion of cruelty against animals, and at least 41% of the patients were deceased when the samples were submitted. More studies on the prevalence of illicit drugs in small animals with confirmatory testing are warranted to fully understand the significance of this growing toxicological hazard in veterinary medicine.