Ivermectin -- summary of Pharmacokinetics paper

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Post   » Wed Aug 20, 2003 5:02 pm

Paisley summarized a paper concerning ivermectin and how the route of administration affects the availability of the drug. Original article:

Ivermectin Pharmacokinetics, pdf version: www.vf.uni-lj.si
Ivermectin Pharmacokinetics, html version: www.vf.uni-lj.si

Summary of Ivermectin Pharmacokinetics Study
* “Pharmacokinetics” is the study of the bodily absorption, distribution, metabolism, and excretion of drugs.
  1. Ivermectin levels in blood plasma and milk of various animal species were studied.
  2. Ivermectin’s effects are influenced by
    • its formulation
    • the route of administration (subcutaneous, oral, topical)
    • the species of animal it's administered to
    • the sex of the animal
    • the physiological status of the animal (lactating, etc.)
  3. Antiparasitic efficacy is reflected by the blood plasma concentration levels of Ivermectin.
  4. Ivermectin blood plasma levels increase with an increase in the dose administered.
  5. Water-free injection formulations of Ivermectin have a longer duration of clinical efficacy.
  6. In oral formulations, bioavailability of Ivermectin is greater when using a micelle* solution compared to an oral paste. * A “micelle” is a colloidal aggregate of surfactant molecules. (Micelle solutions of Ivermectin are given to horses via tubes that go up through the nose and into the stomach.)
  7. There were significant differences in Ivermectin’s bioavailability and biological half-life between oral and subcutaneous administrations.
  8. Ivermectin’s blood plasma concentrations were lower after oral administration so systemic bioavailability and duration of antiparasitic action was decreased.
  9. Blood plasma concentration levels of Ivermectin were measurable for a longer period of time after a subcutaneous injection.
  10. Food fed to animals after they received an oral administration of Ivermectin caused the Ivermectin to adsorb to the food. It is recommended that oral Ivermectin be given on an empty stomach.
  11. Greatest bioavailability of Ivermectin is achieved first using subcutaneous administration, followed by oral then topical administration. However, Ivermectin residues were detected for a longer period of time after topical administration than after oral administration.
  12. Ivermectin in blood plasma was 3x greater after subcutaneous administration at a dose of 0.2 mg/kg body weight than after topical (pour-on) administration at a dose of 0.5 mg/kg body weight. However, because of its slow and continuous absorption, it is thought that Ivermectin would still be effective after topical administration.
  13. Ivermectin was detected in the blood plasma of guinea pigs after a subcutaneous administration of a dose of 0.5 mg/kg body weight. (The maximum blood plasma concentration was 0.7 ng/ml, which was the smallest value of all the animal species investigated.)
  14. Ivermectin is excreted into milk. However, the Ivermectin blood plasma levels of the suckling animals were very small. The indirect, oral ingestion of Ivermectin via the milk was considered negligible.
Additional comments: The effect of food on Ivermectin efficacy was studied in horses, hence the recommendation to dose horses on an empty stomach.

"The effect of food was observed in horses. Feeding immediately after an oral administration of ivermectin resulted in the drug's adsorption onto the food, consequently oral administration on an empty stomach is recommended." (Page 3 of the original study)

Guinea pigs (and rabbits) require a constant supply of food in their digestive systems. Fasting can have negative consequences. Do not deprive your pet of food for any length of time.

Originally posted: http://www.guinealynx.info/forums/viewtopic.php?p=152306#152306

For more information on ivermectin, be sure to read www.guinealynx.info/ivermectin.html
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Post   » Fri Sep 12, 2003 7:39 pm

This is a summary of the article entitled Clinical and pharmacological properties of Ivermectin in rabbits and guinea pigs published in The Veterinary Record, January 25, 1992 by Q.A. McKellar, D.M. Midgley, E.A. Galbraith, E.W. Scott, A. Bradley.
Veterinary Record (1992) 130, 71-73
1. Clinical signs of mange associated with Trixacarus caviae were noticed in 21 guinea pigs - alopecia (hair loss) and pruritis (itching). Skin scrapings and microscopic examination confirmed the presence of T. caviae.
2. The guinea pigs were placed into 3 groups and given the following initial treatments:
  • Group 1 (8 guinea pigs) - Ivermectin administered orally using Oramec drench.
  • Group 2 (6 guinea pigs) - Ivermectin administered subcutaneously using Ivomec Injection for Cattle.
  • Group 3 (7 guinea pigs) - Ivermectin administered topically using Ivomec Pour-on for Cattle.
3. Ivermectin was administered to the guinea pigs at a dose of 0.5mg Ivermectin/kg in all the animals.
4. Blood samples were taken 72 hours after the administration of Ivermectin (2 animals from Group 1; 4 animals from Group 2; 3 animals from Group 3).
5. Seven days after the initial treatments, all the guinea pigs received a subcutaneous dose of Ivermectin at a dose of 0.5mg/kg . (This subsequent subcutaneous administration of Ivermectin to all the guinea pigs proved effective as a cure for T. caviae.)
6. Detectable blood plasma levels of Ivermectin in guinea pigs were achieved only after a subcutaneous injection of Ivermectin. Furthermore, this blood plasma level was lower in guinea pigs than in other animal species given the same or smaller doses of Ivermectin by the same route (orally, subcutaneously or topically).
7. It was noted that Ivermectin appears to be either poorly absorbed or rapidly metabolized and excreted by guinea pigs when it is administered orally, subcutaneously or topically. It is suggested that further studies be done to determine if Ivermectin works differently in guinea pigs and what the controlling factors in this difference may be.

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