Continuous infusion of DL-alpha-difluoromethylornithine and improved efficacy against a rat model of Pneumocystis carinii pneumonia

The rapid depletion of Pneumocystis carinii polyamines caused by in vitro exposure to DL-alpha-difluoromethylornithine (DFMO; also called eflornithine or Ornidyl) and the rapid repletion following removal of this drug suggested that the in vivo efficacy of DFMO against P. carinii pneumonia (PCP) may be limited by troughs in drug concentration resulting from the schedule of administration. This led to the prediction that, compared with the response to the standard animal protocol of administering DFMO in drinking water, the response of a rat model of PCP to DFMO would be lessened by bolus administration and improved by continuous infusion. These predictions were confirmed. Intraperitoneal bolus administration of up to 3 g of DFMO kg of body weight-1 was completely ineffective, although this dose has been shown to be effective when given in the drinking water. Conversely, continuous infusion improved the response against PCP seven- to ninefold over the response to drinking water administration. These findings suggest that, compared with the standard clinical investigational protocol for treatment of PCP with DFMO given in four divided daily doses, continuous infusion combined with monitoring of drug concentrations in plasma may improve efficacy and/or reduce the already low rate of adverse effects.