Introduction

This backgrounder pertains to the use of Banamine (flunixin meglumine) Injectable Solution for the control of pyrexia and inflammation in beef and non-lactating dairy cattle. There are many diseases and conditions affecting cattle that can be favorably influenced by the proper application of Banamine. This backgrounder will discuss pyrexia, the inflammatory process, the pharmacology of flunixin meglumine in cattle, and specific diseases of cattle where the activity of Banamine has been demonstrated.

Pyrexia and Inflammation

Pyrexia

Pyrexia (fever) means the elevation of body temperature above the normal range. It may be caused by abnormalities in the brain itself or by toxic substances that affect the temperature regulating centers. Such causes include bacterial or viral infections, abnormalities as a brain tumor and/or a syndrome which causes a vicious cycle of heat production without heat loss, which may terminate in a heat stroke.

Normally, the temperature of the body is regulated almost entirely by nervous feedback mechanisms, and almost all of these operate through a temperature regulating center located in the hypothalamus at the base of the brain. Nerve receptors in the skin and spinal cord provide feedback that drives the body to either conserve heat (pilo-erection, or hairs standing on end), produce increased quantities of heat (shivering), or increase heat loss (sweating or panting). Changes in the heat regulating process are constantly undergoing modifications that go unnoticed. In other words, heat regulation is not a static process but an ever-moving one that is important to normal body function.

Substances that may cause the "set point" of the hypothalamic thermostat to rise are called pyrogens. Many proteins, breakdown products of proteins, and certain other substances, such as lipopolysaccharide toxins (LPS or endotoxin) secreted by bacteria, can act as pyrogens. It is pyrogens secreted by toxic bacteria or pyrogens released from degenerating tissues of the body that cause fever during disease conditions. Pyrogens are extremely potent since as little as a few nanograms (nano = one billionth) injected into animals can cause a fever.

There is some debate on how pyrogens affect temperature regulation in the hypothalmus. Some feel that there is a direct effect while others feel it is an indirect effect through byproducts of macrophages and lymphocytes destroyed by ingesting toxic products. These dying white blood cells (WBC) release an "endogenous pyrogen" which then affects the hypothalmus. Regardless of the method, it is the change in the hypothalamic thermostat that induces a fever.

When the setting of the thermostat is suddenly changed from the normal level to a higher-than-normal value as a result of tissue destruction, pyrogenic substances, or dehydration, the body temperature usually takes several hours to reach the new temperature setting. During this time there is a feeling of being cold, chills and shivering, and the skin may feel cold to the touch because of vasoconstriction to reduce heat loss. This process will continue until the new temperature is reached.

When the new temperature is reached, the animal no longer feels chills or any particular effects of being hot or cold. If the substance causing fever is removed, the body will react by setting a new lower temperature on the thermostat. In attempting to reduce body temperature, there will be sweating and "flushing" of the skin due to vasodilation or increasing blood flow to the skin resulting in heat loss. This is commonly referred to as "the fever has broken".

The dangers of fever are that excessively high temperatures destroy body cells, particularly nerve cells. Destruction of nerve cells is particularly dangerous because they do not regenerate. Once a nerve cell has died it is not replaced. Other body cells are damaged as well. The pathologic findings of death due to hyperpyrexia are localized hemorrhages and degeneration of cells throughout the body.

Inflammation

Literally volumes have been written about inflammation, the inflammatory process, and its control. It is beyond the scope of this document to cover all of that information. Inflammation is a complex process involving the circulatory system and blood-born cells. It is a natural body response to an injury, be it of physical, chemical or infectious origin, and it is a necessary prelude to healing. Despite the inherent protective nature of inflammation, its effect on body tissue and organs may be excessive and cause damage. Therefore, there are conditions or situations where control of excessive inflammation provides a significant benefit to the health and well being of the individual.

The cardinal signs of inflammation are heat, swelling, redness, and pain or loss of function. Heat and redness are the result of increased blood supply due to reflex dilation of the smaller arteries. Swelling is a result of increased blood flow and blood fluids leaking from the small blood vessels (capillaries, venules) into surrounding tissues. This leakage is due to increased permeability of the cells lining the capillaries and venules. Pain or loss of function is associated with various substances released by damaged tissues that act on local nerve endings.

As blood fluids (plasma) escape into tissue spaces, numerous chemical mediators are released. These further increase the permeability of the blood vessels, leading to more swelling, heat, redness, and pain. Blood cells migrate into the tissues and release various substances. One of these is histamine from white blood cells and mast cells. This phase of inflammation is often referred to as "histamine dependent", and it is the reason antihistamines work in the early phases of inflammation. This phase may only last 30 minutes.

A second wave soon follows and is characterized by the release of a host of mediators including kinins, complement, and prostaglandins. These substances are formed or released from damaged blood and tissue cells, which causes further damage and increases the inflammatory response. Particularly in the presence of infections, additional cells migrate to the area, releasing more mediators and furthering the process. The inflammatory process continues as long as the noxious agents persist. When the noxious agents are eliminated, local mediators are rapidly turned off by dilution, removed via the lymphatics, and rapidly metabolized by enzyme systems.

Prostaglandins

There are many steps involved in conversion of the fatty acids to prostaglandins. Prostaglandins are not only synthesized when tissues are injured, but are ubiquitous throughout the body. They are not stored but are synthesized upon need. They play a significant role as a local messenger in many normal functions, especially when cells are stimulated. Once produced, prostaglandins do not persist long at their site of formation. They rapidly diffuse to other sites or are rapidly metabolized. Most prostaglandins are so rapidly metabolized, they do not reach the systemic circulation for redistribution.

Migrating cells, especially phagocytes (cells which ingest; engulf), are directly involved with pain response. During phagocytosis (the act of engulfing; ingesting), enzymes designed for the digestion of foreign material, invading agents, and damaged cells may be discharged and act against the host tissues. Release of these enzymes results in production of prostaglandins, with consequent induction of pain.

High concentrations of prostaglandins cause pain by direct action upon nerve endings. More typically, however, at low concentrations, they markedly increase sensitivity to pain. The pain threshold may be so altered that even normally painless stimuli may be painful. This effect of prostaglandins is long-lasting and cumulative, so that continued production of even small amounts can sensitize nerves to other irritants.

Prostaglandins are also incriminated in pain perception within the nervous system. They are produced within the central nervous system and sensitize it to painful substances. Pain is thus induced in two ways (local and central) via direct sensitization of nerve receptors by prostaglandins.

Prostaglandins and Inflammation

There are many contributors to the inflammatory process, and prostaglandins are one of the more significant ones. Prostaglandins are one of the more potent mediators that cause increased blood flow, chemotaxis (chemical signals that summon white blood cells), and subsequent dysfunction of tissues and organs. They are a body's response to noxious agents, and as long as the noxious agents persist, prostaglandins will continue to be produced and add to the inflammatory process.

Prostaglandins and Fever (Pyrexia)

During an inflammatory process, infectious agents, toxins, and tissue fluids enter the circulation and cause fever. The evidence indicates this results from the production of prostaglandins in the central nervous system, specifically the anterior hypothalamus. With fever, depression (malaise) and inappetence may occur. Prostaglandins are also associated with these signs.

The production of fever by prostaglandins is supported by the fact that anti-inflammatory agents which inhibit prostaglandin production may also be antipyretic. It is not, therefore, surprising that both pain and fever are the first signs of inflammation to be relieved by antiprostaglandin therapy. Swelling and redness are alleviated more slowly.

Other Roles of Prostaglandins

Prostaglandins play a very significant role as a local messenger in many normal functions, especially when cells are stimulated. This is important because anti-inflammatory drugs alter prostaglandin function whether they be from normal activities or inflammatory in nature.

These effects of prostaglandins in normal body functions are important because they can be ameliorated by antiprostaglandin drugs. Antiprostaglandins not only affect the "bad" (inflammatory, pain, fever) effects, but also the "good" (blood pressure, air flow to lungs, gastric pH and intestinal mucus, renal function) effects of prostaglandins. It is the loss of activity of the "good" prostaglandins that leads to the side effects observed following use of antiprostaglandins. The most common side effects are gastrointestinal ulcers and renal insufficiency caused by disruption of renal blood flow.

Antiprostaglandins

Antiprostaglandins are a group of compounds of differing chemical structure but similar pharmacological action. They produce an anti-inflammatory effect by inhibiting the formation of prostaglandins. Often they have been referred to as Non-Steroidal Anti-inflammatory Drugs or NSAIDs. Others have called them prostaglandin synthetase inhibitors or cyclooxygenase (COX) inhibitors. Regardless of the particular name applied, they function by reducing the production of mediators of the inflammatory process. Compounds with this activity are not new, dating back to aspirin, that was patented in 1908. Compounds commonly used in veterinary medicine include aspirin, phenylbutazone, ketoprofen, carprofen, flunixin meglumine, tolfenamic acid and, to a lesser extent, human products such as indomethacin, ibuprofen, and naproxen. It wasn't until 1971 that the action of any of these compounds was demonstrated.

Recently researchers have determined that there are two forms of cyclooxygenase: COX-1 and COX-2. In vitro studies suggest that COX-1 is the form that produces the "good" effects of prostaglandins, such as regulation of gastric acidity and intestinal mucus flow as well as regulation of renal blood. In contrast, COX-2 is responsible for production of prostaglandins of inflammation. Therefore, ideally an NSAID that blocked only the prostaglandins of inflammation may be a safer form of medication. Much of this theory is extrapolation of laboratory data, but it has not been demonstrated in man or animals. Researchers are actively screening for compounds that have more or less COX-2 activity or a high ratio of activity of COX-2 to COX-1. Currently available NSAIDs are inhibitors of both COX-1 and COX-2, although the degree of inhibition of each may be variable. The science in this arena is too new to draw broad conclusions.

Flunixin Meglumine

Flunixin meglumine is a potent, non-narcotic, non-steroidal analgesic agent with anti-inflammatory and antipyretic activity. It is a potent inhibitor of the enzyme cyclooxygenase. It has demonstrated biological activity in the following areas:

Bovine Applications

Pyrexia in Cattle

Pyrexia, or fever, in cattle is an abnormal elevation of body temperature. The normal temperature, as taken by rectal thermometer, is 101.5+° F (38.5+° C). This can vary to some degree depending on environmental temperature and humidity, exercise or stress, and some physiological conditions such as parturition and estrus. In most instances veterinarians do not consider an animal febrile until the temperature passes 103+° F. Most infectious diseases will induce a febrile state in cattle. Examples include respiratory diseases, severe mastitis, metritis, and other soft tissue infections where there is an accompanying toxemia. Fever can also occur in non-infectious conditions such as exposure to toxic chemicals, absorption of tissue breakdown products following surgery, or necrotic tissue or immune reactions following vaccination or anaphylaxis. Fever is usually accompanied by decreased appetite, lethargy, increased respiratory rate, rapid weak pulse, thirst, and constipation or diarrhea. Whether these signs are totally due to the fever or are a part of the disease condition may be debatable. Regardless, they are most often found in the same individual. There are no clinical pathology tests or necropsy findings that are particularly characteristic of fever.

Fever is an expected part of an infectious disease and is not a cause for alarm unless the pyrexia is excessively high (e.g., 106+°-107+° F or greater) or of excessive duration (usually several days). Effective treatment of the infectious agent removes the source of the fever-causing agent (toxins), and the fever declines rapidly. When anti-infective therapy is not effective, additional treatment for reduction of fever is indicated. Examples include acute or prolonged viral infections, conditions with extensive tissue damage and absorption of toxins, and endotoxic shock.

Treatment of pyrexia involves use of large doses of steroidal anti-inflammatory agents (e.g., dexamethasone) or NSAIDs. The disadvantage of using large doses of steroids is their effect of decreased immune function. Effective anti-infectives must accompany the use of steroids in these situations. In the case of NSAIDs, the decreased immune function is not a major concern. Other treatment includes nursing care such as providing adequate clean drinking water and shade to protect from direct sun.

Inflammatory Diseases of Cattle

It is beyond the scope of this document to cover all inflammatory diseases of cattle. The major conditions where application of NSAIDs is indicated will be addressed. In younger growing animals, most cases of inflammation are associated with infectious processes. In older animals, infections and musculoskeletal conditions prevail.

One of the most common infections involves the respiratory tract. Commonly referred to as bovine respiratory disease, or BRD, it is a combination of gram negative bacteria (Pasteurella and Hemophilus) and viral agents such as IBR, BVD, PI3, and BRSV. The clinical disease may be mild or a severe pneumonia. BRD occurs in dairy and beef calves from birth to weaning and is probably most commonly seen postweaning. Although less frequently, it can be seen in adult animals as well.

BRD is characterized by sudden onset, fever, depression, lethargy, decreased appetite, and a tendency to be away from herdmates. In most cases, some degree of pneumonia is present. Inflammatory conditions of the lung are characterized by decreased oxygenation of blood. If the pleura (covering of the lungs) are inflamed (pleurisy), there will be pain upon every breath. Infections of the lung often result in permanent scarring or damage to tissues, leaving the animal with lung consolidation and decreased lung capacity. If the inflammation or lung damage is extensive, future growth and production will be affected and result in extensive long-term economic loss.

Endotoxemia is a condition caused by the release of endotoxins from gram negative bacteria. Endotoxins are a component of the cell wall of gram negative bacteria and are released upon death of the bacteria. They are extremely potent toxins and can cause severe shock and even death when given in micrograms per kilogram body weight. Infections where large numbers of gram negative bacteria are present, such as in the intestinal tract, the mammary glands (coliform mastitis), the reproductive tract (metritis), the lungs (pneumonia), and other soft tissues, can lead to endotoxemia.

Endotoxins cause a decrease in blood pressure, pooling of blood in certain organs while decreasing blood flow to other organs, acidosis due to build up of lactic acid, intravascular coagulation (blood clots) and shock which can be fatal. Endotoxemia occurs in animals of all ages and all species. Treatment is aimed at reversing the effects of the endotoxin, with elimination of the infection as secondary target. In many instances, the infection is already at a decline when endotoxemia is on the increase. This is explained by the release of endotoxin from dying bacterial cells.

Non-infectious conditions of the musculoskeletal system in cattle are usually due to physical injury (trauma) or degenerative conditions related to the aging process. Injury can be to tendons, ligaments, joint surfaces and surrounding muscles. Since cattle require four sound limbs to get up and move about adequately, injury to any limb causes severe problems of locomotion. Often these animals are unable to get to feed or water, and rapid weight loss and debilitation occurs. Milk production can fall to near zero, and breeding bulls' ability to mount may be severely jeopardized. Animals will attempt to compensate by placing additional weight on unaffected limbs, but this causes additional stress to those limbs, which can lead to injury of apparently normal areas. The key to treatment of musculoskeletal disorders in cattle is rapid return to mobility. If this cannot be done, an alternate use of the animal or disposal are about the only remaining options. Treatment is aimed at relief of pain, reduction of inflammation, some nursing care (soft, dry bedding and ease of access to food and water), and correction of the cause, if possible.

Flunixin Meglumine in Cattle

Dose Titration Studies

One study utilized an E. coli endotoxin-induced fever model to establish the effective dose of flunixin meglumine (FM) for reduction of fever. Yearling Hereford heifers were the test subjects, and E. coli endotoxin was administered by intravenous injection. The model induced a significant temperature rise that peaked in four hours and then began to decline. Temperatures of each calf were recorded prior to injection of endotoxin and at 1, 2, 3, 4, 5 and 6 hours post injection of endotoxin. Immediately following the 1-hour temperature recording, flunixin meglumine or placebo was administered by intravenous injection. Doses of FM were 0.22, 2.2 and 6.6 mg/kg body weight. Results are presented in Table 1.

Treatment with 0.22 mg/kg of FM resulted in a lower mean temperature than the negative control at one hour post-treatment, but temperatures were higher than the control group thereafter.

Animals receiving the 2.2 mg/kg dose did not show substantial increases in temperature after treatment. The 2-, 3-, and 4-hour temperatures remained within 0.3+°F of the reading at the time of treatment (1 hour). Temperature differences between the negative control group and the 2.2 mg/kg group were statistically significant at 2, 3, 4 and 5 hours.

Animals in the 6.6 mg/kg group behaved much the same as those in the 2.2 mg/kg group; their temperatures remained near the 1-hour value at 2, 3, and 4 hours. Temperatures in the 6.6 mg/kg group declined to lower than pre-endotoxin levels at 5 and 6 hours. Differences between the 2.2 and 6.6 mg/kg groups were significant at only 5 and 6 hours.

Conclusions reached in this trial were: 1) the antipyretic effect of FM was demonstrated against an E. coli endotoxin model, and 2) the dose of 2.2 mg/kg was effective in preventing the rise in temperature generated by the administration of endotoxin.

At early sampling times (1 to 4 hrs), a high level of inhibition of prostaglandin (PGE) and thromboxane (TXB) occurred in the higher dose groups (1.1, 2.2 and 6.6 mg/kg bodyweight). A relationship between the administered dose and percent inhibition of PGE and TXB in exudate and TXB in serum became apparent for the three higher dose rates at sampling times of 10 hours and later. The percent inhibition was generally greater with the 2.2 mg/kg dose than with 1.1 mg/kg, particularly from 12 to 24 hours. The inhibition obtained with the 6.6 mg/kg dose was either similar or slightly greater up to 24 hours post-dosing in comparison to the 2.2 mg/kg dose.

In conclusion, similar efficacy is likely from 0 to 12 hours with the 1.1 and 2.2 mg/kg doses, but a more prolonged action could be expected with the 2.2 mg/kg dose. The dose of 2.2 mg/kg produced greater inhibition of PGE and TXB during the 12 to 24 hour post-dating period. Greater inhibition with the 6.6 mg/kg dose was generally apparent only during the 24 to 36 hour period.

Based on the results of these two trials and an extensive literature review, a dose range of 1.1 to 2.2 mg/kg (0.5 to 1.0 mg/lb) was chosen.

Field Investigations

Beef Cattle Respiratory Disease

Field trials were conducted at 3 locations and involved 363 calves with spontaneously occurring bovine respiratory disease (BRD). Treatments consisted of flunixin meglumine plus antibiotic (oxytetracycline) (n=181) compared to antibiotic (oxytetracycline) alone (n=182). In both instances, antibiotic was administered at 10 mg/kg (4.5 mg/lb) IM for 3 consecutive days. FM was administered IV at 2.2 mg/kg for 1 to 3 days depending on the temperature response after each treatment. FM dosing was repeated when the animals' temperature was above 104+°F. Animals were monitored for 7 additional days following the last antibiotic treatment on day 3.

Parameters included: temperature, character of respiration, depression, illness index score, mortality and treatment failure.

Results:

In conclusion, flunixin meglumine ameliorated some of the clinical signs of bovine respiratory disease and demonstrated efficacy as an antipyretic.

Dairy Calf Respiratory Disease

A field trial with 81 male Holstein calves compared treatment with FM and OTC to OTC alone. FM was dosed once daily at 2.2 mg/kg (1.0 mg/lb) IV for 1 to 3 days and OTC once daily at 10 mg/kg (4.5 mg/lb). Animals with acute signs of pneumonia (rectal temperature greater than 104+°F and respiratory rate greater than 40) were randomly assigned to one of two treatment groups. FM was repeated in calves with temperatures over 104+°F on days 2 and 3.

Results:

In conclusion, flunixin ameliorated some of the clinical signs of bovine respiratory disease and demonstrated efficacy as an antipyretic.

Clinical Efficacy Compared to Other NSAID's

A study was conducted comparing the clinical efficacy of 3 NSAID's used in conjunction with ceftiofur for treatment of bovine respiratory disease. Sixty-six (66) mixed breed beef calves weighing approximately 400 lbs and meeting the criteria of acute BRD (fever, dyspnoea, and moderate clinical illness index score) were randomly divided into 4 treatment groups. All groups received ceftiofur at 0.5 mg/lb daily for 3 days. In addition, three groups received a single dose of either flunixin meglumine (2.2 mg/kg IV), ketoprofen (3 mg/kg) IV or carprofen (1.4 mg/kg) SC. All animals were monitored throughout the trial and for 1 to 2 days post-treatment for clinical signs, fever, mortality and adverse reactions. At the termination of the study, all animals were sacrificed and the lung lesions were described and scored for percent consolidation.

Results showed that treatment with any of the three NSAID's reduced fever statistically significantly more rapidly than the antibiotic alone. All groups showed improvement in clinical illness scores and dyspnoea throughout the study. There were no statistical differences between any of the treatment groups.

At the termination of the trial, all animals were humanely sacrificed and the lung lesions scored. The one animal that died during the trial was similarly scored. The use of flunixin meglumine in combination with ceftiofur resulted in a statistically significant (p+0.0033) reduction of lung consolidation, which was not attained with either carprofen or ketoprofen.

Median Percent Lung Consolidation

Pharmacokinetics

Flunixin meglumine is a weak acid which exhibits a high degree of plasma protein binding (approximately 99%). However, free (unbound) drug appears to readily partition into body tissues. In cattle, elimination occurs primarily through biliary (liver) excretion. Several authors have reported different kinetic norms for cattle. One item for certain is that the half life in cattle (3.0 to 5.0 hours) is considerably longer than in the horse (1.6 hours). Additionally, flunixin tends to be sequestered at the site of inflammation, making dosing decisions based on plasma levels inaccurate. They underestimate both the duration of drug action and the concentration of drug remaining at the site of activity.

Target Animal Safety

Safety was accessed in 24 Hereford calves (12 male and 12 female) 5 to 6 months of age. Doses were 0, 1X, 3X and 5X the recommended 2.2 mg/kg given intravenously once daily for 9 consecutive days. There were 3 male and 3 female animals in each treatment group. Results were:

In conclusion, adverse clinical signs attributed to flunixin intravenous injections were seen in calves administered elevated doses of 6.6 and 11 mg/kg, 3 and 5 times the high end of the recommended dose range, for 3 times the recommended clinical duration. No adverse effects were seen in calves given the high end of the recommended dose range (2.2 mg/kg).

Acute Toxicity

Calves (2 male and 2 female) were administered four intravenous injections of flunixin meglumine in sequential doses of 6.6, 13.2, 26.4 and 52.8 mg/kg (25 times the recommended dose) every other day on a rising dose basis. Results were:

In conclusion, flunixin-related changes included blood in the urine and feces following the 26.4 and 52.8 mg/kg doses and seizures and one mortality after the 52.8 mg/kg dose. In the three remaining animals, all parameters returned to normal during the 14-day post-dose observation period except for one animal positive for fecal occult blood and another positive for urine blood at 14 days.

Reproduction Safety

The first study was a 12-month reproductive study in which six intravenous injections of flunixin at 3X (6.6 mg/kg) the recommended high end of the dose range were administered to pregnant cattle during selected time points of each trimester of pregnancy. Healthy cows were observed for estrus and bred artificially with frozen semen from the same bull. Twenty four pregnant females were divided into groups of 12 each, treated and control. The treated group received two IV injections of flunixin at approximately 90 days, 150 days and 265 days of pregnancy. Offspring were weighed at birth and 30 days of age and observed for any abnormalities.

In conclusion, no adverse effects in the cows or calves were attributed to intravenous injections of flunixin meglumine given at 3X the recommended dose two times during each trimester of pregnancy.

A second study involved treatment of animals prior to breeding, 12/13 days, 36/37 days, 112/113 days, 210/211 days and 265/266 days post breeding. At each time point, animals received 6.6 mg/kg IV on two consecutive days. All animals were allowed to calve naturally and calves were observed at birth and at 30 days.

In conclusion, no adverse effects in the cows or calves were attributed to flunixin intravenous injections administered to the cows at 6.6 mg/kg for 2 days at 6 time points during the reproductive cycle.

Human Food Safety

A significant battery of tests were conducted to demonstrate the safety of flunixin meglumine residues in human food. It was concluded that the liver is the target tissue and an adequate withdrawal time is 4 days following intravenous injections of 2.2 mg/kg for up to 3 days.