Efficacy and adverse effects of (R)-9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine in feline immunodeficiency virus-infected cats.

Background: (R)-9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine (PMPDAP) is active against feline immunodeficiency virus (FIV) in vitro, and is less toxic than other acyclic nucleoside phosphonates. Its efficacy in naturally infected cats has not been evaluated in large controlled studies.

Hypothesis/objectives: PMPDAP is effective in naturally FIV-infected cats with minimal adverse effects.

Animals: Forty-five privately owned cats naturally infected with FIV.

Methods: Prospective, randomized, placebo-controlled, double-blinded clinical study. Cats were randomly assigned to be treated with PMPDAP (25 mg/kg) daily, PMPDAP 3 times a week, or placebo for a period of 6 weeks.

Results: Administration of PMPDAP to FIV-infected cats did not lead to detectable improvements in clinical, virological, or immunological variables. Proviral load (FIV copies/10(6) cells) did not change significantly during treatment (placebo group: from 9505 ± 10119 to 8564 ± 8615; PMPDAP 3 times a week: from 4818 ± 4426 to 5041 ± 6197; PMPDAP daily: from 3525 ± 5038 to 3167 ± 5824). There was a significant decrease of red blood cell counts (×10(12) /L) (from 8.91 ± 1.82 to 7.34 ± 1.79 in cats treated 3 times per week (P < .001), and from 8.96 ± 1.13 to 6.01 ± 1.36 in cats treated daily (P < .001)), as well as of packed cell volume, and hemoglobin in both groups receiving PMPDAP.

Conclusions and clinical importance: Administration of PMPDAP was not associated with significant improvements in clinical, immunological, or virological parameters, but treatment was associated with adverse effects, mainly anemia. Thus, PMPDAP, as administered in this study, cannot be recommended for treatment of FIV-infected cats.