ACTIVITY OF (S)-1-(3-HYDROXY-2-PHOSPHONYLMETHOXYPROPYL) CYTOSINE AGAINST HUMAN CYTOMEGALOVIRUS WHEN ADMINISTERED AS SINGLE-BOLUS DOSE AND CONTINUOUS-INFUSION IN IN-VITRO CELL-CULTURE PERFUSION SYSTEM

HPMPC [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl) cytosine] is a potent inhibitor of human cytomegalovirus (HCMV) replication as determined by conventional tissue culture methods in which the drug concentration remains constant over time. Previous studies have shown HPMPC to have a long intracellular half life. Despite its relatively short extracellular half-life, HPMPC might provide significant anti-HCMV activity long after the elimination of the drug by first order kinetics. We addressed this hypothesis by measuring the activity of HPMPC in a novel cell culture perfusion system. This system allows us to compare the activity of HPMPC when given as a continuous infusion with its activity when given as a single-bolus dose followed by elimination that simulates the drug's in vivo pharmacokinetics. We show that continuous infusions maintaining maximum concentrations (C(max)s) of 0.05, 0.10, 0.31, and 1.0 mu g/ml and achieving areas under the drug concentration-time curves (AUCs) of 8.4, 17, 50, and 162 mu g.h/ml, respectively, result in 27, 56, 63, and 88% inhibition of viral DNA accumulation, respectively, compared with an untreated control. Single-bolus doses achieving C(max)s of 0.10, 1.25, 3.0, and 7.7 mu g/ml with an elimination half-life of 20 h achieved AUCs of 2.4, 32, 78, and 138 mu g.h/ml and resulted in 0, 48, 69, and 87% inhibition of HCMV DNA accumulation. Single bolus doses achieving C(max)s of 3.9 and 12 mu g/ml with an elimination half-life of 6.5 h achieved AUCs of 34 and 105 mu g.h/ml, respectively, resulting in 15 and 76% inhibition of viral DNA accumulation. Comparison of C-max-versus-effect curves for these three regimens suggests that maximum concentration is not the only important pharmacokinetic determinant of HPMPC's antiviral activity. Similar comparisons of AUC-versus-effect curves for continuous and bolus dosing suggest that the AUC is an important determinant of antiviral activity for AUCs greater than 100 mu g.h/ml. We conclude that single-bolus doses of HPMPC potently inhibit HCMV DNA accumulation but that this activity is more heavily influenced by the AUC than the C-max at the upper end of the AUC range tested. At lower AUCs, some other parameter may be the primary determinant of antiviral activity. Our cell culture perfusion system provides a novel, efficient, and convenient method for addressing questions relating the effects of constantly changing drug concentrations to antiviral effects.