Liposomal encapsulation of foscarnet protects against hypocalcemia induced by free foscarnet

Hypocalcemia and an increase in creatinine level are the most important serious effects associated with foscarnet (PFA) therapy. In an animal model, we have explored the potential protective role of liposome-encapsulated foscarnet (LE-PFA) on these metabolic abnormalities. PFA administered as one bolus injection (0.5 or 1.0 g/kg) caused significant rapid decreases (approximately 20%) in the levels of calcium and phosphorus in serum within a few minutes and up to 30 min after injection. LE-PFA did not induce any of these changes, while peak levels in serum and the half-life of this formulation were much higher than those of the free drug. PFA administered for 2 weeks (340 or 500 mg/kg/day) resulted in no changes in creatinine or blood urea nitrogen levels in serum at the low-dosage level, but at the higher-dosage level, the creatinine level in serum increased by day 5 posttreatment. Furthermore, there was no increase in the creatinine or blood urea nitrogen level after 2 weeks of treatment with LE-PFA at a dosage of 35 mg/kg/day. When the pharmacokinetics of both free PFA and LE-PFA were compared, the plasma half-life of the encapsulated drug was approximately four times longer than that of the free drug. In addition, the systemic clearance of LE-PFA was approximately one-fifth of that of the free drug. In conclusion, free PFA causes hypocalcemia and hypophosphatemia and increases the creatinine level in serum, whereas the LE form of this drug seems to protect against the abnormal changes in calcium and phosphorus levels caused by the free drug. By preventing hypocalcemia and increasing its half-life, LE-PFA can be used at lower doses and at longer intervals. Clinical investigations of these formulations may be worthwhile.