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Poisonings from Human Prescription Drugs

By

Safdar A. Khan

, DVM, MS, PhD, DABVT, ASPCA Animal Poison Control Center, Urbana, Illinois

Last full review/revision Oct 2020 | Content last modified Oct 2020

Pets commonly ingest prescription medications from countertops, pill minders, mail-order packages, or other sources. Safety data for human prescription drugs in certain animal species may not be available, because most are not approved for veterinary use. A valid client-patient-veterinarian relationship must exist for veterinarians to recommend extra-label use of human prescription medications to their clients.

Cardiovascular Medications

Cardiovascular medications (drugs used to treat heart disease) fall into several categories, including ACE inhibitors, calcium channel blockers, beta blockers, and diuretics. Some of these medications are used to treat heart diseases in animals, but all can be toxic if a pet accidentally eats a large number of pills.

Angiotensin-converting Enzyme (ACE) Inhibitors

Several ACE inhibitors (for example, enalapril, captopril, lisinopril) are used to treat congestive heart failure in dogs and cats. The primary concern in cases of overdose is abnormally low blood pressure with secondary kidney damage. Onset occurs within a few hours of exposure, or longer for extended-release formulations. Signs of overdose may include vomiting, pale mucous membranes, weakness, and a rapid or slow heartbeat. Activated charcoal can bind the drug from the gastrointestinal tract if given within 1 to 2 hours of ingestion. Blood pressure and kidney function should be monitored, and fluids given as needed.

Calcium Channel Blockers

Calcium channel blockers (for example, diltiazem, amlodipine, verapamil) affect the movement of calcium into the cells of the heart and blood vessels. As a result, they relax blood vessels and increase the supply of blood and oxygen to the heart. They are used in people for high blood pressure, chest pain (angina), and irregular heartbeats. The most common signs of overdose include low blood pressure, slow heart rate, gastrointestinal upset, and irregular heart rhythms. A very rapid heartbeat may develop in response to the drop in blood pressure.

Treatment of an overdose includes correcting the blood pressure and abnormal heart rhythm. In general, vomiting should not be induced unless this can be done within minutes of ingestion. Activated charcoal binds unabsorbed drug in the gastrointestinal tract and is most useful in the first hours after ingestion. If a sustained-release product was ingested, repeat doses of activated charcoal every 4 to 6 hours for a total of 2 to 4 doses can provide additional benefit. Specific medications should be started based on blood pressure, heart rate, electrocardiogram, and blood analysis. Fluids are recommended.

Beta Blockers

Beta blockers (for example, propanolol, atenolol, timolol) affect the response to some nerve impulses in certain parts of the body. As a result, they decrease the heart’s need for blood and oxygen by reducing its workload. They also help the heart to beat more regularly. They are commonly used in people to treat high blood pressure, relieve chest pain (angina), and correct abnormal heart rhythms. The most common signs of overdose in animals are slow heart rate and low blood pressure. Depressed breathing, coma, seizures, a high level of potassium in the blood, and low blood sugar level may develop. Sudden congestive heart failure is also possible. Significant signs may be seen even at recommended dosages—however, no beta blockers are approved for veterinary use.

Because beta blockers are absorbed rapidly, vomiting should be induced only within minutes of ingestion. Administration of activated charcoal should be considered if either multiple tablets or capsules or sustained-release formulation tablets were ingested. Heart rate and the pet’s condition should be monitored for at least 2 to 4 hours. Treatment includes fluids to increase blood pressure and medications to support heart function and decrease blood potassium levels.

Diuretics

Diuretics are used to increase urine output. Common diuretics include chlorothiazide, hydrochlorothiazide, furosemide, spironolactone, and triamterene. The most common signs of diuretic overdose include vomiting, depression, passing large amounts of urine, excessive thirst, and metabolic abnormalities (especially of potassium). Management should include monitoring fluids and electrolytes, with correction as needed.

Tranquilizers, Antidepressants, Sleep Aids, and Anticonvulsants

Tranquilizers, antidepressants, and related drugs are used in both pets and people, but can be very toxic if a pet consumes them by accident.

Benzodiazepines

Benzodiazepines are used to control seizures and to relieve anxiety. Commonly used benzodiazepines include diazepam, alprazolam, chlordiazepoxide, clonazepam, lorazepam, oxazepam, and triazolam. In general, all are rapidly absorbed. Cats may be more sensitive to adverse effects. The most common signs of toxicity in animals are central nervous system depression, depressed breathing, lack of coordination, weakness, disorientation, and vomiting. Some animals, especially at high doses, may initially show central nervous system excitation, followed by central nervous system depression. Other common signs are dangerously low body temperature, low blood pressure, a rapid heartbeat, and decreased muscle tone. Vomiting can be induced if the ingestion is recent and no signs are present. Flushing the stomach, followed by administration of activated charcoal can be performed if the ingested amount is very high. Close monitoring is needed. Additional treatment includes fluids, and medications to support respiratory function and to control central nervous system excitation.

Antidepressants

Antidepressants fall into several classes. One group, called the selective serotonin reuptake inhibitors, includes sertraline, fluoxetine, paroxetine, and fluvoxamine. The tricyclic antidepressants, another group, include amitriptyline, clomipramine, and nortriptyline. Signs of poisoning include agitation, confusion, fever, abnormal heart rhythms, high blood pressure, sudden muscular contractions, involuntary rhythmic movement of the eyes, seizures, metabolic abnormalities, an inability to urinate, dry mouth, enlarged pupils, and constipation. This may be followed by lethargy, lack of coordination, dangerously low body temperature, depressed breathing, a bluish tinge to skin and mucous membranes, low blood pressure, and coma.

Vomiting should be induced in cases of recent exposure if the animal is not showing any signs. This can be followed by activated charcoal (even several hours after ingestion) plus a medication that causes emptying of the bowels. Other medications are given to control seizures and heart rate and rhythm.

An overdose of almost any antidepressant can result in development of the serotonin syndrome. Signs of the serotonin syndrome include altered mental status, agitation, sudden muscular contractions, overactive reflexes, tremors, diarrhea, lack of coordination, and fever. This syndrome is often seen after overdose of substances that result in increased free levels of serotonin, such as antidepressants or profound stimulants (for example, amphetamines, cocaine, pseudoephedrine, and ephedra). Cyproheptadine is often used for treatment.

Barbiturates

Long-acting barbiturates, such as phenobarbital, mephobarbital, and primidone, are commonly used as anticonvulsants or sedatives. Short-acting barbiturates (butabarbital, pentobarbital, secobarbital) and ultra short-acting barbiturates (thiamylal and thiopental) are used mainly to induce anesthesia and to control seizures. The onset of signs after ingestion varies from 15 minutes to several hours, and effects can last up to several days for the long-acting class. The most common signs are sedation, lack of coordination, depressed breathing, coma, loss of reflexes, low blood pressure, and dangerously low body temperature.

Treatment begins with removing unabsorbed drug by inducing vomiting (if the exposure is very recent and no signs are seen) or by flushing the stomach. Additional treatment includes administration of activated charcoal and fluids, along with respiratory support and maintaining body temperature.

Sleep Aids

Zolpidem and zaleplon are sleep aids that act in a similar way as the benzodiazepines. Although sedation would be expected after ingestion, these drugs have been associated with the contradictory state of excitement. In addition to the obvious signs of sedation and lack of coordination, some dogs have developed tremors, vocalizing, and pacing at low dosages.

Vomiting can be induced if the ingestion was recent and no signs are seen. For mild signs, keeping the pet quiet and in a safe place may be enough. If excitement develops, symptomatic treatment should be given and will vary with the signs and their intensity.

Tranquilizers

The most commonly used tranquilizers in veterinary medicine are acepromazine, chlorpromazine, and promazine. They are also used before general anesthesia, to prevent vomiting, and to treat central nervous system agitation after specific drug overdoses (amphetamines, cocaine). The most common signs of an overdose are sedation, weakness, lack of coordination, collapse, behavioral changes, dangerously low body temperature, low blood pressure, and either a rapid or slow heart rate.

Treatment consists of symptomatic and supportive care. Because central nervous system signs begin rapidly, vomiting should be induced only if ingestion was recent, followed by administration of activated charcoal and a medication that causes emptying of the bowels. Body temperature, heart rate, and blood pressure should be monitored and treated symptomatically.

Muscle Relaxants

The most commonly used muscle relaxants include baclofen and cyclobenzaprine. Signs of poisoning may begin as soon as 30 minutes after ingestion. The most common signs are vocalization, drooling, vomiting, lack of coordination, weakness, tremors, shaking, coma, seizures, slow heart rate, dangerously low body temperature, and blood pressure abnormalities. Treatment consists of supportive care, including fluids and respiratory support. Vomiting should be induced if the exposure is recent and no signs are present, followed by administration of activated charcoal.

Topical Agents

Pets ingest many topical preparations, which most often results in only mild inflammation of the stomach and intestines. However, ingestion of certain topical agents, such as 5-fluorouracil and calcipotriene, can be fatal even at low doses.

5-Fluorouracil is available as an ointment or topical solution. It is used in people to treat skin cancers and precancerous skin growths caused by longterm sun exposure. Dogs and cats begin showing signs within a few hours of ingesting 5‑fluorouracil. Initial signs include severe vomiting and diarrhea. Signs often progress to vomiting with blood, tremors, lack of coordination, and seizures. Generally, 5-fluorouracil affects the gastrointestinal tract, liver, kidneys, central nervous system, and bone marrow. The death rate in dogs is high.

Treatment consists primarily of supportive care. Vomiting should be induced after recent ingestion (within an hour) if the animal is not yet showing any signs, followed by activated charcoal and a medication that causes emptying of the bowels. If the animal is spontaneously vomiting or having seizures, medications are administered to protect the gastrointestinal tract and to control seizures and tremors. Fluids should be given and body temperature monitored. Blood and serum values are usually monitored for about 2 weeks. Surviving dogs may show evidence of bone marrow suppression later.

Calcipotriene, is used to treat psoriasis in people. It is available as an ointment and as a cream. Accidental ingestion in dogs is associated with life-threatening increases of calcium in the blood. Signs usually begin within 1 to 3 days of ingestion and include loss of appetite, vomiting, diarrhea, passing large amounts of urine, excessive thirst, depression, and weakness. Blood calcium is usually increased within 12 to 24 hours and may remain high for weeks. This is usually accompanied by an increase in blood phosphorus and soft-tissue mineralization. Kidney failure, coma, and death can occur in severe or untreated cases.

Treatment involves inducing vomiting and administering activated charcoal and a medication that empties the bowels. Fluids, corticosteroids, and diuretics are used to increase urine output and decrease blood calcium (see Disorders of the Parathyroid Glands and of Calcium Metabolism in Dogs : Hypercalcemia (High Blood Calcium Levels)). Blood levels of calcium and phosphorus, and kidney function usually must be monitored for several weeks.

Prescription Nonsteroidal Anti-inflammatory Drugs (NSAIDs)

There are many different prescription nonsteroidal anti-inflammatory drugs (NSAIDs) used to relieve pain and inflammation in both humans and animals. Some commonly prescribed NSAIDs in humans include diclofenac, naproxen, celecoxib, ketoprofen, meloxicam, etodolac, flurbiprofen, and ibuprofen. Accidental ingestion by animals of NSAIDs intended for human use is common. These drugs should never be given to pets unless prescribed by your veterinarian. Most NSAIDs have the potential to adversely affect the gastrointestinal tract, kidneys, and liver, especially if the animal is already sick and possibly dehydrated.

Signs of NSAID poisoning vary based on the particular drug and species of animal involved and the amount ingested. Signs may include vomiting, rapid breathing or heart rate, lack of coordination, and possibly seizures, coma, or death. If you suspect that your pet has ingested a prescription (or over-the-counter) NSAID, you should immediately contact your veterinarian or an animal poison control center.

Treatment of NSAID poisoning consists of removing any drug that has not been absorbed, protecting the gastrointestinal tract and kidneys, and providing supportive care. If the ingestion occurred recently, vomiting may be induced, followed by administration of activated charcoal with a medication that empties the bowels. Fluids may be given to increase urine output. The outlook for recovery depends on the amount ingested and the amount of time between ingestion and treatment.

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