The last time I purchased Heartgard for my dog, it required a prescription from the vet and about $60 for a 6 month supply. This would run me $120 per year. If I had two dogs, $240 per year. In addition, I have to have a prescription from my vet. I knew there had to be a cheaper and easier way. The only active ingredient in Heartgard is Ivermectin, which is sold over the counter for livestock.
After extensive research online, which included hundreds of forum posting, I have waded through the misinformation and worked out the proper dosage, which I describe below. I am amazed with the amount of misinformation posted by people who flat out do not understand how to calculate dosages. When challenged on their incorrect dosage by others, they become highly defensive and usually use the standard “I have raised hundreds of dogs and used this on all of them without harm” or my favorite “this is what my vet told me, so your wrong.” With all due respect to your vet, the calculations (shown below) don’t lie. So take some time, read through he rest of this page and then make an informed discussion on what the correct dosage of Ivermectin should be.
If you simply want to know the proper dilution and dosage then jump to the Quick Start Guide.
The only active ingredient in Heartgard is Ivermectin. It is a common dewormer on all sorts of livestock. In Heartgard, it is used as a preventative measure for heart worms in dogs. Just to be clear, Ivermectin is Ivermectin, whether in the Heartgard chewable or in a 100ml injectable solution for cattle. The only difference is the concentration, and the medium it is contained in.
Ivermectin is highly powerful. Only a very small amount is needed to protect against heartworm. Only a tiny amount is needed to prevent hearworms in dogs. Luckily for dogs currently getting 10X-100X the dose needed from uninformed owners, there is a high overdose tolerance. I have no idea what the long term impact is, perhaps nothing, but why take the risk when it is not needed?
The Heartgard tablets come in three dosages, 68 mcg (micro grams) for dogs up to 25lbs, 136 mcg for dogs 26 to 50lbs and 272 mcg for dogs 51 to 100 lbs. Using the lower and upper bounds of dosages, we determine an acceptable range of 2.72 mcg per lb (272 mcg / 100 lbs) to 5.33 mcb per lb (272 mcg / 51 lbs). For all calculations below, we will use the lower limit of 2.72 mcg per lb, as why would I give my dog more medicine (chemicals) than necessary to prevent heartworm. This also provides some level of safety. Dosages up to 2X off will still be in the acceptable range.
Standard swine and bovine Ivermectin comes in a 1% injectable solution. There are other strengths available, but 1% seems to be the most common. The 1% solution means there are 10,000 mcg of Ivermectin in each 1 mL of solution. ( 1mL = 1 g = 1,000 mg = 1,000,000 mcg and 1,000,000 mcg x 1% = 10,000 mcg per 1 mL of injectable solution)
So for a 100 lbs dog, a dosage of 272 mcg is needed ( 2.72 mcg/lb x 100 lbs = 272 mcg). This equates to 0.0272 mL of 1% solution (272mcg / 10,000 mcg/mL). The average drop of water is 0.05 mL, so half a drop would be needed for a 100 lbs dog. This is not really possible to control half a drop or measure out 0.0272 mL, so the solution needs to be diluted beyond the 1% solution for ease of measurement.
There are two ways to approach this problem, first we can dilute the solution by 10 to 1 or even 100 to 1 and then calculate the dosage. The other method is to determine our desired dosage and then calculate how much we need to dilute the 1% solution to achieve this. I chose the second method, in order to achieve an easy to remember final dosage.
My desired dosage is 0.01 mL per 1 lb of dog. So my 44 lbs dog would require a 0.44 mL dose and a 160 lb great dane would require 1.60 mL. This volume is easy to remember, measure and get the dog to eat.
Now lets determine how much we need to dilute the standard 1% Ivermectin solution. Start with the standard dosage per pound of dog, 2.72 mcg per lb and divide by our desired 0.01mL per 1 lb of dog. The pounds cancel out and we are left with 2.72 mcg per 0.01mL as our desired concentration. To get rid of the decimal on the bottom, multiply top and bottom by 100 to get 272mcg per 1mL. Now I want to create a 100mL vial of the diluted solution so I again multiply top and bottom by 100 to get 27,200mcg per 100mL. As stated above the 1% Ivermectin has 10,000 mcg of Ivermectin per 1mL of solution. We flip the second fraction and multiply to cancel the mcg and we get 2.72 mL of 1% solution per 100 mL of total solution.
This means we need to mix 2.72mL of the 1% Ivermectin with 97.28 mL of an inactive dilutant to achieve the proper concentration for a dose amount of 0.01mL per 1 lb of dog.
100mL diluted solution-2.72mL 1% Ivermectin solution=97.28mL of Dilutant
Based upon the above math, we need to mix 2.72 parts of the 1% Ivermectin to 97.28 parts of the dilutant. In this case we are using propylene glycol as the dilutant as Ivermectin does not mix with water.
Note: Lots of people on web forums mess up the above calculation. Be careful! I personally vouch for the above calculation, which is why I present it for public scrutiny..
Wow this got long fast. If you got past all that math, great, if not, no worries below is the strait forward diluting.
Here's what you will need:
Ivermectin 1% Injectable 50ml $25.95:
Propylene Glycol (inactive dilutant, don't let the name scare you):
1 Gallon $18.95 (note: expensive shipping ~$20):
8oz $4.00 (6$ shipping to CA):
Dosage Syringe (XQ-C7) 1ml $0.13:
Measuring Syringe (XQ-CF) 20ml $0.42:
Needle 20ga x 1-1/2" (XQ-AW) $0.11:
The above supplies are good for thousands of monthly dosages. Best to find someone to group purchase with.
Using the large syringe you purchased, draw out 97 cc’s of the propylene glycol and place into a sealable glass jar. It will take multiple draws using a 20cc syringe. Using the smaller syringe you purchased, draw out 0.28 cc’s of the propylene glycol and place in the jar.
Next using the smaller syringe you purchased draw out 2.7 cc’s of the 1% Ivermectin and place in the jar. The trick to getting the Ivermectin out of the vial is to draw up 2.7cc’s of air before inserting the needle into the sealed vial. Then press the plunger down to inject the air into the vial, turn the vial upside down and draw out the Ivermectin. This prevents a vacuum from forming in the vial. Now seal the jar up and mix. Now label the jar with “0.01cc per 1 lb of dog, monthly” or “0.1cc per 10lbs of dog, monthly”. Both will provide an acceptable dosage.
There you go. Follow the above table and provide to your dog monthly to provide the exact same dosage as Heartgard.
Use the previous information at your own risk. This guide is simply being posted to help combat the misinformation posted all over the web and is intended for information only.
Some collies have a genetic condition which allows the Ivermectin to cross the blood brain barrier and can kill. Please be cautious when using Ivermectin in collie breeds and consult a vet.