Systemic lanthanum is excreted in the bile of rats

Lanthanum carbonate is a non-calcium-based oral phosphate binder for the control of hyperphosphataemia in patients with chronic kidney disease Stage 5. As part of its pre-clinical safety evaluation, studies were conducted in rats to determine the extent of absorption and routes of excretion. Following oral gavage of a single 1500 mg/kg dose, the peak plasma lanthanum concentration was 1.04 ± 0.31 ng/mL, 8 h post-dose. Lanthanum was almost completely bound to plasma proteins (>99.7%). Within 24 h of administration of a single oral dose, 97.8 ± 2.84% of the lanthanum was recovered in the faeces of rats. Comparing plasma exposure after oral and intravenous administration of lanthanum yielded an absolute oral bioavailability of 0.0007%. Following intravenous administration of lanthanum chloride (0.3 mg/kg), 74.1 ± 5.82% of the dose (96.9 ± 0.50% of recovered lanthanum) was excreted in faeces in 42 days, and in bile-duct cannulated rats, 10.0 ± 2.46% of the dose (85.6 ± 2.97% of recovered lanthanum) was excreted in bile in 5 days. Renal excretion was negligible, with <2% of the intravenous dose recovered in urine. These studies demonstrate that lanthanum undergoes extremely low intestinal absorption and that absorbed drug is predominantly excreted in the bile.