Shih Tzu - Pentobarbital In Dog Food

The low levels of exposure to sodium pentobarbital (pentobarbital) that dogs might receive through food is unlikely to cause them any adverse health effects, Food and Drug Administration scientists concluded after conducting a risk assessment.

During the 1990s, FDA's Center for Veterinary Medicine (CVM) received reports from veterinarians that pentobarbital, an anesthetizing agent used for dogs and other animals, seemed to be losing its effectiveness in dogs. Based on these reports, CVM officials decided to investigate a plausible theory that the dogs were exposed to pentobarbital through dog food, and that this exposure was making them less responsive to pentobarbital when it was used as a drug.

The investigation consisted of two parts. First, CVM had to determine if dog food could contain residues of the drug. Second, if residues were found, the Center had to determine what risk, if any, the residues posed to dogs.

In conjunction with this investigation, the Center wanted to determine if pet food contained rendered remains of dogs and cats.

How pentobarbital can get into dog food

Because in addition to producing anesthesia, pentobarbital is routinely used to euthanize animals, the most likely way it could get into dog food would be in rendered animal products.

Rendered products come from a process that converts animal tissues to feed ingredients. Pentobarbital seems to be able to survive the rendering process. If animals are euthanized with pentobarbital and subsequently rendered, pentobarbital could be present in the rendered feed ingredients.

In order to determine if pentobarbital residues were present in animal feeds, CVM developed a sophisticated process to detect and quantify minute levels – down to 2 parts per billion of pentobarbital in dry dog food. To confirm that the methods they developed worked properly, CVM scientists used the methods to analyze dry commercial dog foods purchased from retail outlets near to their Laurel, MD, laboratories. The scientists purchased dog food as part of two surveys, one in 1998 and the second in 2000. They found some samples contained pentobarbital (see the attached tables).

Dogs, cats not found in dog food

Because pentobarbital is used to euthanize dogs and cats at animal shelters, finding pentobarbital in rendered feed ingredients could suggest that the pets were rendered and used in pet food.

CVM scientists, as part of their investigation, developed a test to detect dog and cat DNA in the protein of the dog food. All samples from the most recent dog food survey (2000) that tested positive for pentobarbital, as well as a subset of samples that tested negative, were examined for the presence of remains derived from dogs or cats. The results demonstrated a complete absence of material that would have been derived from euthanized dogs or cats. The sensitivity of this method is 0.005% on a weight/weight basis; that is, the method can detect a minimum of 5 pounds of rendered remains in 50 tons of finished feed. Presently, it is assumed that the pentobarbital residues are entering pet foods from euthanized, rendered cattle or even horses.

Finding levels of pentobarbital residues in dog food

Upon finding pentobarbital residues in dog food, the researchers undertook an assessment of the risk dogs might face. Dogs were given known quantities of pentobarbital for eight weeks to determine if consumption of small amounts of pentobarbital resulted in any physiological changes that could indicate potential effects on health. In short, the scientists wanted to find the level of pentobarbital dogs could be exposed to that would show no biological effects. The most sensitive indicator that pentobarbital had an effect is an increase in the production of certain enzymes collectively called cytochrome P450.

Virtually all animals produce enzymes as a normal response to metabolize naturally occurring and man-made chemicals in their environment. Barbituates, such as pentobarbital, are especially efficient at causing the liver to produce these enzymes. In dogs, the most sensitive biological response to pentobarbital is an increase in the production of cytochrome P450 enzymes, which is why the scientists chose that as the best indicator of biological effect. If a low level of pentobarbital did not cause a dog to produce additional cytochrome P450 enzymes, then scientists could assume that the pentobarbital at that low level had no significant effect on the dog.

In CVM's study, experimental animals were each dosed orally with either 50, 150, or 500 micrograms phenobarbital/day for eight weeks. The results were compared with control animals, which were not exposed to phenobarbital.

Several significant phenobarbital-associated effects were identified in this study:
1. Dogs that received 150 and 500 micrograms phenobarbital once daily for eight weeks had statistically higher liver weights (relative to their body weights) than the animals in the control groups. Increased liver weights are associated with the increased production by the liver of cytochrome P450 enzymes;

2. An analysis showed that the activity of at least three liver enzymes was statistically greater than that of the controls at doses of approximately 200 micrograms phenobarbital per day or greater.

But researchers found no statistical differences in relative liver weight or liver enzyme activity between the group receiving 50 micrograms phenobarbital per day and the controls. Based on the data from this study, CVM scientists were able to determine that the no-observable-effect level – which is the highest dose at which no effects of treatment were found – for phenobarbital was 50 micrograms of phenobarbital per day.

Adverse health effects unlikely
For the purposes of CVM's assessment the scientists assumed that at most, dogs would be exposed to no more than 4 micrograms/kilogram body weight/day based on the highest level of phenobarbital found in the survey of dog foods. In reality, dogs are not likely to consume that much. The high number was based on the assumption that the smallest dogs would eat dog food containing the greatest amount of phenobarbital detected in the survey of commercial pet foods-- 32 parts per billion.

However, to get to the exposure level of 50 micrograms of phenobarbital per day, which is the highest level at which no biological response was seen, a dog would have to consume between 5 to 10 micrograms of phenobarbital per kilogram of body weight. But the most any dog would consume, based on the survey results, was 4 micrograms phenobarbital per kilogram of body weight per day.

It should be emphasized that induction of cytochrome P450 enzymes is a normal response to many substances that are naturally found in foods. It is not an indication of harm, but was selected as the most sensitive indicator to detect any biological effect due to phenobarbital.

Thus, the results of the assessment led CVM to conclude that it is highly unlikely a dog consuming dry dog food will experience any adverse effects from exposures to the low levels of phenobarbital found in CVM's dog food surveys.

Dog Food Samples Used in CVM Phenobarbital Surveys and Analytical Results
CVM conducted two surveys of dry dog food samples. In survey #1, samples were analyzed to determine if any phenobarbital was present. In survey #2, other samples were analyzed to measure how much phenobarbital might be present.

THESE RESULTS NEED TO BE UNDERSTOOD WITHIN THE FOLLOWING CONTEXT:

Sampling was non-representative. Samples were purchased from retail outlets in the Laurel, MD, area. Only dry dog foods with certain animal-derived ingredients were sampled. This selection pattern meant that the samples were not representative of dog food nationwide or even locally. It also means that the data cannot be used to draw inferences about dog food being produced and sold in the U.S. today. The concentration of phenobarbital, if present in any U.S. pet food, may be different than the findings of these surveys. The results apply only to the specific lots analyzed.

Sampling focused on certain ingredients. The selection of products based on specific animal-derived ingredients would tend to increase the likelihood of finding phenobarbital given the assumption that phenobarbital in dog food comes from euthanized animals.

Ingredient sources vary geographically and temporally. Feed manufacturers have regional ingredient suppliers and manufacturing facilities. Samples available in a specific geographical region may not reflect the nation as a whole. Ingredient sources for pet foods vary based on such considerations as availability and cost. The surveys represent a snapshot in time, and no conclusions about dog food in general can be made. For reasons described above, the survey information does not predict the likelihood of phenobarbital in a particular brand of dog food on the market today or in the future. Pet food formulations that had detectable phenobarbital levels when the samples were collected may be free of phenobarbital now. FDA has no way to know whether pet food brands that were not sampled had phenobarbital residues.

Differences between different lots of the same dog food are not surprising.
In survey #1, two different lots for the same formulation were sampled in 37 cases, making up 74 samples. The different lots gave the same results in only 31 of 37 cases. One would not expect different lots to give the same outcome, because composition of the raw materials may vary, even if the formulations do not. In survey #2, only one lot of each formulation was analyzed.

The surveys are not comparable to each other. Comparisons between the two survey sets are not scientifically or statistically justifiable.

1. Survey #1 only detected the presence of phenobarbital, but did not indicate how much was present. Therefore, no quantitative comparison between the results of survey #1 and survey #2 is possible.

2. The surveys did not include the same brand names and formulations.

3. Survey #1 included more samples with rendered or hydrolyzed ingredients ranked higher on the ingredient statement. In survey #2, 25 of 60 samples (42%) contained rendered or hydrolyzed ingredients listed in the first, second, or third position in the ingredient statement, whereas in the survey #1 there were 56 such samples out of 87 (64%). Therefore, a direct comparison of the percent of confirmed samples in the two surveys would be misleading because the first sample set included 50% more feeds with rendered or hydrolyzed ingredients listed in the 1st, 2nd, or 3rd position on the ingredient list.

There appear to be associations between rendered or hydrolyzed ingredients and the presence of phenobarbital in dog food. The ingredients Meat and Bone Meal (MBM), Beef and Bone Meal (BBM), Animal Fat (AF), and Animal Digest (AD) are rendered or hydrolyzed from animal sources that could include euthanized animals.

1. Within the sample set for Survey #1, samples with certain ingredients near the 1st position in the ingredient list were more likely to be confirmed for presence of phenobarbital than samples with these ingredients listed near the last position or not included at all. The association appeared to be strongest for AF (of all rendered ingredients tested) and was somewhat weaker for AD, MBM, or either MBM or BBM (no product contained both). Corn Gluten Meal did not show an association between position on the ingredient list and the confirmed presence of phenobarbital. Corn Gluten Meal was selected as a reference ingredient because it was not likely to contain rendered or hydrolyzed animal tissue, and the results were as expected. The position of BBM in the ingredient list showed somewhat of an association with a failure to confirm the presence of phenobarbital. 2. In survey #2 fewer total samples contained detectable phenobarbital, so examination of associations between phenobarbital and ingredients was more limited. For the 25 samples with either MBM, BBM, AF, (or beef tallow (BT) listed 1st, 2nd, or 3rd in the ingredient list, 15 (60%) were found to contain phenobarbital in concentrations greater than 1 part per billion (ppb.) For the other 35 samples with MBM, BBM, AF, (or BT), AD listed 4th-7th in the ingredient statement, phenobarbital was found in concentrations greater than 1 ppb in only 2 (6%) of the samples.