Pharmacokinetics of doramectin and ivermectin after oral administration in horses.

The study investigates the comparative effectiveness of two drugs, doramectin and ivermectin, in treating parasitic diseases in horses when orally administered. The findings show that doramectin stays longer in a horse’s system and may thus form an effective alternative to ivermectin.

Study Design

• The research team used ten crossbreed adult horses for the study, which underwent fecal examinations to establish their faecal parasite egg counts. The horses, all clinically healthy and with varying body weights, were then divided into two groups of five, considering factors such as sex, body weight, and faecal egg count.
• Blood samples were collected from these horses at different intervals from the time of drug administration up to 75 days post-treatment. High-performance liquid chromatography was then used to analyze the collected blood for levels of the administered drug. The analysis employed computerized kinetic analysis.

Treatment Groups

• Group I were treated with an oral paste formulation of ivermectin at 0.2 mg/kg body weight.
• Group II received an oral dose of 0.2 mg/kg body weight of doramectin, prepared as a paste from an injectable formulation.

Findings

• Doramectin and ivermectin plasma concentrations after oral administration in horses were detected until 30 and 20 days accordingly. Both drugs showed a similar absorption pattern, with no significant differences in peak concentration, time to peak concentration, or absorptive half-life.
• They found the terminal elimination half-life, which is the time for the drug concentration in the body to decrease by half during the elimination phase, to be statistically significantly longer for doramectin than for ivermectin.
• The difference in the elimination half-life led to doramectin having larger mean residence time and area under the concentration time curve values. These were about 30% higher than those of the ivermectin group.
• Based on these results, the researchers concluded that doramectin could be an alternative to ivermectin for controlling parasitic diseases in horses, given its pharmacokinetics, tolerance, and anthelmintic efficacy.