Guinea pigs were used to observe the possible side effects of ivermectin (500 μg/kg b.w.) on the heart by recording their electrocardiograms (ECG) at 24, 48 and 72 hours after its injection (experimental groups). Significant effects of ivermectin on the electrocardiographic parameters belong to limb lead II were compared to those of the control group. These were: the increases in amplitudes of P, S (only at 24 hours) and T waves, and also the lengthening (or “prolongation”) in the durations of P and T waves, QRS complex (only at 24 and 48 hours) and PR and QTc intervals at 24, 48 and 72 hours. As a consequence of the prolonged durations mentioned above, statistically significant decreases of heart beats were found on the electrocardiograms recorded at 24 and 48 hours after ivermectin injection (p<0.05). In conclusion, the weak conductance in the heart of guinea pigs as an indicator of the prolongation in durations and intervals (negatively dromotropic) induced by ivermectin can be interpreted as its inhibitory effect on the sarcoplasmic reticulum Ca2+ -ATPase pump causing a late Ca2+ accumulation after systole due to the reduced amount of Ca2+.

Scandinavian Journal of Laboratory Animal Sciences, Vol 35, No 1 (2008)