Ivermectin

(ivermectin)

Brands

Varies by product type.

Availability

See Dosage Recommendations section for the following:

Ivomec for topical, oral, injection. *Note: because the injectable comes in large concentrated formulations correct dilution and dosing is imperative to prevent over dosing. Follow veterinarian direction.
Ivermectin Horse wormer paste 1.87% : tube of 6.08 grams of paste contains 113.7 mg of ivermectin
Brand names: Zimecterin, Rotectin 1, Equalvan, Equimectrin, Bimectin
Ivermectin Oral Sheep Drench: 0.08% = 0.8mg/mL solution (USA)
Brand name: Ivomec Drench for Sheep
Ivermectin Sheep Drench Oral: 0.8 g/L = 0.8mg/mL solution (Australia)
Brand name: Ausmectin Sheep Drench

Pharmacology

Ivermectin is a macrocyclic lactone anthelmintic belonging to the class of avermectins. It has a potent and broad anti-parasitic spectrum at lower dose levels. It facilitates the release of GABA (gamma amino butyric acid) an inhibitory neurotransmitter. This in turn causes the paralysis and death of immature and mature nematodes, as well as arthropods. However, ivermectin is not effective against liver flukes or tapeworms since they are not users of GABA.

*Note: when using ivermectin to rid mites it does not kill mites eggs but rather the hatchlings when used repeatedly at the appropriate intervals and dosage.

Ivermectin is well absorbed orally, parenterally, and as pour-on formulas. Efficacy is greatest in oral, and in SQ treatment.

Concentration of the drug remains in the body fluids for extended periods with the highest concentration being in the liver and fat tissues. The drug does not easily penetrate cerebral spinal fluid which minimizes toxicity. It is metabolized in the liver and mostly excreted in feces with a lesser amount excreted in urine.

Studies report that ivermectin given to rats during pregnancy showed a 3x higher concentration in maternal milk than maternal plasma first day postpartum that resulted in increased death in perinatal pups. Dosage given in study was 0.2 mg/kg/day.

Reports also indicate that ivermectin is teratogenic in rats, as well as rabbits and mice, at human materno-toxic dose levels. Abnormalities reported are limited to cleft palate. Dosage used in this study was 0.2 mg/kg/day (MSD, 1988. See references below).

There is no reported documentation of studies done at therapeutic doses for rats at this time.

*Note: based on above information it is not recommended that ivermectin be given to pregnant rats, or a doe nursing baby rats under 2 weeks of age.

Indications

Used to rid mites, lice, and internal parasites such as pinworms, and roundworms.

Drug Interactions or Contraindications

It is recommended to avoid concomitant use of ivermectin with barbiturates, benzodiazepines (such as Valium), and valproic acid, in order to avoid increased sedation.
*Note: supported recommendation of Vanessa Pisano DVM ²¹:
“Do not use Ivermectin on sick or malnutritioned rats, or on rats that are under 5 weeks old. For smaller sized rats greater than 5 weeks and under 4 months reduce dosage by half.”*

Adverse Reactions

CNS: lethargy, “drunken gait”, tremors, seizures

Resp: breathing slows, breathing paralysis

GI: anorexia

Dosage Recommendations

*Note: accurate dosing to prevent severe toxicity required! If toxicity results the vet may prescribe a glucocorticoid.

Ivomec: 100 mcg/lb to 200 mcg/lb (0.1 mg/lb to 0.2 mg/lb), PO or SQ, once a week for three weeks. ⁴. May be applied as a topical behind the ear.

or

Horsewormer paste 1.87% : tube of 6.08 grams of paste contains 113.7 mg of ivermectin (see brands above): dose 0.01mL for a rat weighing 1 lb or greater. Reduce dose by half for rat weighing less than 1 lb. Give PO (orally), once weekly for three weeks. ³^, ⁴ *Note: accuracy of safely measuring and dosing with the paste is questionable, carrying a greater risk for over dosing. It is recommended, if choosing to dose with the paste, to use a needless 100 unit insulin syringe for measure where 1 unit=0.01mL. This would be approximately the size of a small, uncooked, grain of rice for a l lb rat or greater, and half that size for a rat weighing less than 1 lb. Once amount is measured correctly it can be placed on a tiny, bite-sized, piece of bread and given to the rat.

or

Ivermectin 200 mcg/kg to 400 mcg/kg (0.2 mg/kg to 0.4 mg/kg), PO, SQ, repeat in 7 to 14 days ³⁵^, ⁴¹^, ⁴⁴. (May be applied as a topical behind the ear.)
*Note: 400 mcg/kg (0.4 mg/kg) q7days has reported to be used for cases of Demodex. ⁴¹^, ⁴⁴

or

Ivermectin 0.2 mg/kg q7 days x 3 weeks; PO, SQ ¹. May be applied as a topical behind the ear.

*NOTE*
The following dosing instruction contributed by C.Himsel-Daly DVM.:

When having to dilute ivermectin: Dilute the 1% solution (which is the injectable used for cattle) with propylene glycol 1:10. Take 1 mL ivermectin and mix with 9mL PG; thus diluting it from a 10 mg/mL solution to a 1 mg/mL solution, and dose at 200-400 mcg/kg (0.2 mg/kg-0.4 mg/kg). This makes it more accurate for the really wee ones.

*Note: in the event propylene glycol is not a diluting medium desired for topical application of the injectable form of ivermectin, mineral oil may be used as an alternative diluting medium.

For dosage using Oral Sheep Drench

Ivermectin Oral Sheep Drench: Ivomec Drench for Sheep: 0.08% = 0.8mg/mL solution (USA)

or

Ivermectin Oral Sheep Drench: Ausmectin Sheep Drench:0.8g/L = 0.8mg/mL solution (Australia)

Oral

0.125 mL once weekly for 3 weeks for rat weighing 500 grams. ²³

*Note: for rats of a different weight: divide the weight of the rat by 500 grams and multiply that answer by 0.125 for the correct dose.

Topical (Spot on) behind the ear or back of neck

0.25 mL once weekly for 3 weeks for rat weighing 500 grams. ²³

*Note: for rats of a different weight: divide the weight of the rat by 500 grams and multiply that answer by 0.25 for the correct dose.

Considerations

Always consult a veterinarian if choosing to use in pregnant and lactating rats. Dose the mother rat at recommended adult rat dose. Baby rats should not be given separate treatment since dosing would be achieved through nursing from mother rat.
Topical application or oral dose may be less stressful to rats than injectable.
Injectable form of ivermectin for cattle or sheep requires dilution.
The following contribution by C.Himsel-Daly DVM.:
When using ivermectin horsewormer paste there is no need to decant paste if in the original tube. Decanting any fluid would concentrate the drug and thus raise the concentration in a volumetric dose, thus potentiating toxicity.
If in opening the original tube of paste it is found to have a drip of fluid at the end of the tube, before the actual paste emerges, all that is required is to express the tube, discard that bit of paste until uniform in consistency, and dose according to the veterinarian’s recommendation. If the paste has been dispensed in another container, then mix thoroughly before dosing. Paste tends to be a less accurate dosing method than using the parenteral, or topical product.
Fortunately the paste has a wide margin of safety.
Store injectable and paste at semi-cool room temperature and protect from light. For drench follow storage directions on container.

References

Gordon, L., Nickell, B., Collevechio, K., Mutchler, M., Clark, R., (1981). Oral-range-finding study (multigeneration) in rats with abamectin (MK 0936). Study No. 82-707-0. Unpublished report prepared by Merck Sharp & Dohme Research Laboratories, West Point PA.
Temple, W., & Smith, N. (1994, May 1). Ivermectin (PIM 292). Retrieved December 20, 2008, from http://www.intox.org/databank/documents/pharm/ivermect/ivermect.htm.