Antiparasitic combination · For Dogs

Heartgard Plus dosage reference for dogs (Ivermectin / Pyrantel)

This page's standard weight-based reference is 0.006 mg per kg (0.00 mg per lb), with once monthly recorded as the reference frequency. Use the calculator to see the arithmetic for your dog's weight, then confirm the indication, product, and actual dose with a veterinarian.

Onset: N/A (preventive)
Duration: 30 days
Class: Antiparasitic combination

Weight-based calculator estimate from the references listed on this page. This page has not been independently DVM-reviewed — see our methodology .

This information is for educational purposes only. Always consult your veterinarian before giving medication to your pet. Do not use this calculator for emergencies, overdoses, pregnancy, very young animals, very old animals, pets with liver/kidney disease, or pets taking multiple medications.

Each medication page lists the references recorded for its data. The calculator math and editorial presentation are maintained by PetDosageChart; a page is independently DVM-reviewed only when a named reviewer byline appears. See our methodology and limitations.

Ivermectin / Pyrantel (often known by brand names such as Heartgard Plus) is an antiparasitic combination commonly used in veterinary medicine for heartworm prevention, roundworm treatment, and hookworm treatment. Understanding the correct dosage, administration, and potential side effects of Ivermectin / Pyrantel is critical for your dog’s safety and well-being.

A typical Ivermectin / Pyrantel dose for dogs is around 0.006 mg/kg once monthly, within a usual range of 0.006-0.012 mg/kg. Available forms include chewable tablet.

Calculator Warning: Use this only as an educational estimate. Your veterinarian may prescribe a different dose based on your pet’s condition, age, weight, other medications, and medical history.

Ivermectin / Pyrantel Dosage Calculator for Dogs

Enter your dog’s weight below to estimate the Ivermectin / Pyrantel dose from the 0.006 mg/kg guideline. Your veterinarian may adjust it for your dog’s age, condition, and other medications, so treat the result as an educational starting point, not a prescription.

Dosage Calculator · 01

Enter your dog's weight

Quick Dosage Chart

Typical Ivermectin / Pyrantel amounts for common dog weights, for quick reference:

Dosage Chart · 02

Heartgard Plus weight-based reference chart for dogs

Scroll sideways to see full table

Weight	Lower Reference	Standard Reference	Upper Reference	Frequency
5 lbs (2.3 kg)	0.014 mg	0.014 mg	0.028 mg	once monthly
10 lbs (4.5 kg)	0.027 mg	0.027 mg	0.054 mg	once monthly
15 lbs (6.8 kg)	0.041 mg	0.041 mg	0.082 mg	once monthly
20 lbs (9.1 kg)	0.055 mg	0.055 mg	0.11 mg	once monthly
25 lbs (11.3 kg)	0.068 mg	0.068 mg	0.14 mg	once monthly
30 lbs (13.6 kg)	0.082 mg	0.082 mg	0.16 mg	once monthly
40 lbs (18.1 kg)	0.11 mg	0.11 mg	0.22 mg	once monthly
50 lbs (22.7 kg)	0.14 mg	0.14 mg	0.27 mg	once monthly
60 lbs (27.2 kg)	0.16 mg	0.16 mg	0.33 mg	once monthly
70 lbs (31.7 kg)	0.19 mg	0.19 mg	0.38 mg	once monthly
80 lbs (36.3 kg)	0.22 mg	0.22 mg	0.44 mg	once monthly
90 lbs (40.8 kg)	0.24 mg	0.24 mg	0.49 mg	once monthly
100 lbs (45.4 kg)	0.27 mg	0.27 mg	0.54 mg	once monthly
120 lbs (54.4 kg)	0.33 mg	0.33 mg	0.65 mg	once monthly
150 lbs (68 kg)	0.41 mg	0.41 mg	0.82 mg	once monthly

Parenthetical tablet amounts are arithmetic comparisons only. They do not account for scoring, release type, concentration, product labeling, or whether this medication is appropriate for an individual animal.

By Weight

Heartgard Plus reference by dog weight

Choose a common weight to open its optional reference page. Use the main medication calculator for a different exact weight.

Common-weight pages are convenience views of the same educational reference, not separate medical recommendations.

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How to Give Ivermectin / Pyrantel to Your Dog

Give Heartgard Plus on the same day each month, year-round. It is a beef-flavored chewable that most dogs eat willingly. A heartworm test is required before starting. At the very low doses used in Heartgard, ivermectin is generally safe even for most MDR1-positive breeds, but consult your vet.

It is generally recommended to give Ivermectin / Pyrantel with food to help reduce stomach upset. It may interact with spinosad (may increase ivermectin levels) and P-glycoprotein inhibitors.

Side Effects and Safety

Common side effects include vomiting, diarrhea, decreased appetite, and lethargy. More serious side effects can occur, such as allergic reaction, tremors (rare), and seizures (rare, MDR1 breeds at higher doses).

Cautions · 12

When Heartgard Plus should be used with caution or avoided

Some dogs should not take Heartgard Plus, or need a different dose and closer monitoring. Tell your veterinarian about your pet's full health history and every other medication or supplement they take before giving Heartgard Plus.

dogs not tested for heartworm
known ivermectin sensitivity (MDR1 mutation at higher doses)

Interactions · 13

Heartgard Plus drug interactions

Heartgard Plus can interact with other drugs. This list is not complete — always give your veterinarian a full list of your dog's medications and supplements.

spinosad (may increase ivermectin levels)

P-glycoprotein inhibitors

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult dog at a known weight. Do not rely on it in these situations — talk to your veterinarian instead:

In an emergency, or after accidental ingestion or a suspected overdose
For pregnant or nursing pets
For very young or very old dogs
For pets with liver disease, kidney disease, or another chronic illness
For pets taking several medications at once
When you are not sure of your dog's current, accurate weight
For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

If you think your dog had too much Heartgard Plus, or swallowed any medication by accident, act right away. Do not wait for symptoms to appear.

Call your veterinarian or the nearest emergency animal hospital.
ASPCA Animal Poison Control Center: (888) 426-4435
Pet Poison Helpline: (855) 764-7661

A consultation fee may apply to the poison hotlines. Have the medication packaging ready, and note how much your pet may have taken and when. Do not try to make your pet vomit unless a veterinarian tells you to.

When to Call the Vet

If your dog experiences any of the following, contact your veterinarian or an emergency clinic immediately:

Vomiting within 1 hour of dosing
Your dog misses more than one monthly dose
You moved from a non-endemic to an endemic heartworm area
Any neurological signs (tremors, incoordination)
Your dog tests positive for heartworm

Frequently Asked Questions

Frequently Asked · 07

Questions about this medication

Is Heartgard enough for my dog?

Heartgard Plus prevents heartworm and treats roundworms and hookworms, but it does NOT protect against fleas, ticks, or other external parasites. Most dogs need a flea/tick preventive (like NexGard) in addition to Heartgard. Your vet can recommend a complete parasite prevention plan.

What happens if I miss a month of Heartgard?

If you miss one month, give the dose as soon as you remember and resume the monthly schedule. If you miss more than one month, contact your vet — your dog may need to be tested for heartworm before restarting, as the preventive only kills larvae acquired in the previous 30 days.

Can I give Heartgard to Collies?

Yes. At the very low ivermectin doses used in Heartgard (6 mcg/kg), it is considered safe for Collies and other MDR1-positive breeds. The ivermectin toxicity risk in these breeds occurs at much higher doses (300+ mcg/kg), far above what Heartgard contains.

Does my dog need Heartgard year-round?

The American Heartworm Society recommends year-round heartworm prevention in all areas. Even in colder climates, unpredictable warm spells can allow mosquitoes to transmit heartworm. Year-round prevention is the safest approach.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your dog's weight by the lower, standard, and upper mg/kg values recorded for Heartgard Plus. It cannot decide whether this drug, indication, formulation, or schedule is appropriate for an individual animal.

Context in this medication record

Commonly listed uses: heartworm prevention, roundworm treatment, hookworm treatment
Recorded forms: chewable tablet
Reference timing: once monthly; onset N/A (preventive); duration 30 days

Individual checks a calculator cannot perform

Confirm the diagnosis and the reason this medication is being considered.
Match the exact product, concentration, route, and whether a tablet may be split.
Account for age, pregnancy, organ function, genetics, allergies, and prior reactions.
Review every prescription, over-the-counter product, and supplement your pet takes.

Recorded cautions

dogs not tested for heartworm; known ivermectin sensitivity (MDR1 mutation at higher doses).

Recorded interactions

spinosad (may increase ivermectin levels); P-glycoprotein inhibitors.

These lists reproduce the structured record used by this page and may not be exhaustive. Show your veterinarian the product label and your dog's complete medication list before acting on a number.

Related · 08

Related medications for dogs

Sources · 09

Sources & references

The structured medication record behind this page names the references below. The links open the publisher or official resource; they do not turn this page into a prescription for an individual animal.

Plumb's Veterinary Drug Handbook — listed in this medication's source record.
Merck Veterinary Manual — listed in this medication's source record.
DailyMed label search for Ivermectin / Pyrantel — check current product and formulation labels; some veterinary uses may be off-label.

Source names are shown at the record level; passage-level page and label citations are still being added. Read our methodology and limitations.

Transparency · 11

How this page was made

This page's structured medication record includes Plumb's Veterinary Drug Handbook among its source names. PetDosageChart applies the record's mg/kg values to the entered weight and presents the arithmetic result. A source record is not the same as an individualized prescription or an independent clinical review.

Sources cited: Plumb's Veterinary Drug Handbook
Merck Veterinary Manual
Calculator formula: Doses scale linearly from a standard basis of 0.006 mg per kg (0.00 mg per lb) of body weight, given once monthly. The calculator multiplies that basis by your dog's weight and shows an arithmetic comparison with recorded tablet sizes. That comparison does not determine whether a tablet is scored, splittable, or appropriate for your pet.
Editorial owner: Prepared and maintained by the PetDosageChart editorial team, a software-led publisher and not a veterinary practice.
DVM review status: Not independently DVM-reviewed. A named reviewer and review date appear here only after a confirmed review.

More on our methodology and editorial process — how we source, calculate, and review dogs dosage data.

Safety · 10

More resources

Pet Medication Safety Hub — What's safe, what's dangerous, and emergency signs
How we calculate dosages — Our sources, math, and review process
Printable emergency checklist — One-page reference for your fridge or first aid kit