Poisonings from Human Prescription Drugs

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 (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 (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 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.

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 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.

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.

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.

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.