Enhanced absorption of pour-on ivermectin formulation in rats by co-administration of the multidrug-resistant-reversing agent verapamil

Parasitol Res. 1999 Nov;85(11):920-2. doi: 10.1007/s004360050658.


The effect of verapamil, a multidrug-resistance (Mdr)-reversing agent on the absorption of a pour-on formulation of ivermectin was evaluated in rats. Absorption of ivermectin was effectively enhanced (40%) by the presence of verapamil, suggesting that absorption of ivermectin involves Mdr-P-glycoprotein and that verapamil should act as a competitive inhibitor for the transport and extrusion of ivermectin by P-glycoprotein. This hypothesis is consistent with other studies describing verapamil as a blocking agent of P-glycoprotein involved in the efflux of ivermectin in a resistant strain of Haemonchus contortus.

MeSH terms

  • Absorption
  • Administration, Cutaneous
  • Animals
  • Anthelmintics / administration & dosage*
  • Anthelmintics / pharmacokinetics*
  • Drug Resistance, Multiple
  • Ivermectin / administration & dosage*
  • Ivermectin / pharmacokinetics*
  • Rats
  • Rats, Sprague-Dawley
  • Skin Absorption
  • Verapamil / administration & dosage*


  • Anthelmintics
  • Ivermectin
  • Verapamil