BIOLOGICAL HALF-LIFE OF CAFFEINE IN PIGS

Abstract

Five experiments were conducted with growing pigs to determine the biological half-life of caffeine after injection or various periods of ingestion. Peak plasma caffeine levels were reached within 5 hr after a single oral dose and 2 hr after intramuscular injection, and then declined with a biological half-life of about 12 hr. The caffeine content of tissues was approximately proportional to their water content and 6% of orally administered caffeine was excreted in the urine. Upon continuous ingestion of caffeine, peak plasma levels were reached within 2 days, indicating that accumulation was quite limited. When 1.5 g of caffeine per kg of feed was fed from weaning to market weight, the withdrawal of caffeine 2 days prior to slaughter was sufficient time to insure that caffeine levels in the liver, muscle, kidney and backfat were below 1 μg/g.