Primaquine

What is primaquine?

Primaquine is a drug used to treat babesiosis in cats, a condition caused by a blood parasite (Babesia felis). Primaquine has also been used to treat blood parasites in owls and raptor birds.

There are no veterinary products available for prescription. Primaquine phosphate oral tablets (generics) may be prescribed for off-label use in cats. This drug is often compounded because the commercially available tablets are typically too strong to be accurately dosed in cats.

Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How do I give my pet primaquine?

• Primaquine is given orally (by mouth).
• Primaquine comes in a tablet format.
• Compounded forms may be in a liquid format. Measure the liquid doses carefully and according to label instructions.
• It is recommended to give primaquine with food.
• If vomiting occurs when dosed on an empty stomach, give future doses with food or a treat.
• The margin of dose safety is low with primaquine, which means it is easier to give an overdose of this medication compared to other drugs. Follow the instructions on the product label, in conjunction with your veterinarian’s directions.

This medication should take effect within 1 to 3 days and an improvement in clinical signs should follow.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects from primaquine?

Primaquine may cause the following side effects:

• Vomiting (especially if not given with food)

Serious adverse reactions associated with this drug may occur without warning and could, in rare cases, lead to death. If any of the following signs develop, stop giving primaquine and contact your veterinarian immediately:

• Lethargy, weakness, susceptibility to infection (signs of bone marrow suppression)
• Weakness, depression, lethargy, seizures (signs of low blood sugar/hypoglycemia)
• Slow heart rate
• Rash and itchiness
• Blue tint to the skin (methemoglobinemia)
• Fatigue, yellowing of the skin, increased breathing effort (signs of red blood cell destruction)

Drug sensitivities can develop over time, with repeated exposure. Your pet may have no reaction after the first few doses but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of the treatment and notify your veterinarian if you have any concerns.

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This medication is short acting and should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

DO NOT USE primaquine in:

• Pets with severe glucose-6-phosphate dehydrogenase (G6PD) deficiency
• Pets that are pregnant
• Pets with diseases associated with a low level of infection-fighting white blood cells (e.g., rheumatoid arthritis or lupus erythematosus)
• Pets with hemolysis (destruction of red blood cells) or low bone marrow function
• Pets that are taking quinacrine
• Dogs (they are highly susceptible to its side effects)

Are there any drug interactions I should be aware of?

The following drugs should NOT BE USED with primaquine:

• Quinacrine

The following drugs should be used WITH CAUTION when given with primaquine:

• Acetohydroxamic acid, quinidine, sulfonamides, sulfonylureas and other hemolysis-inducing drugs
• Amphotericin B, antineoplastic drugs, azathioprine, chloramphenicol and other myelosuppressive drugs
• Cisapride, domperidone, erythromycin, sotalol and other QT-prolonging drugs

In humans, consumption of grapefruit juice may increase primaquine concentrations. Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

• A complete blood count should be performed to assess numbers and health of red cells, white cells, and platelets before starting this medication, and periodically throughout the treatment period.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.
• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.

How do I store primaquine?

• Ensure primaquine is tightly stored in its original container in a cool, dry place and protected from light.
• Store this medication below 104°F (40°C), and preferably between 59°F and 86°F (15°C and 30°C).
• Keep the container out of reach of children and pets.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Be prepared to provide information about the product and your pet’s weight and symptoms.