Tiamulin distribution in pigs: A pharmacokinetic study of plasma and oral fluid levels with tissues residues detection following intramuscular administration.

Oral fluid reliably reflects tiamulin plasma levels and residues persist in liver and kidneys beyond 10 days post-administration.

This pharmacokinetic study investigated tiamulin distribution in pigs following intramuscular administration, examining concentrations across plasma, individual oral fluid, pooled oral fluid, and tissue matrices using UHPLC-MS/MS. Tiamulin achieved maximum concentrations (Cmax) of 2205±621 µg/L in individual oral fluid at 2.00 hours and 692±111 µg/L in plasma at 3.50 hours, demonstrating rapid absorption and higher oral fluid bioavailability relative to plasma. A very strong correlation between oral fluid and plasma concentrations was observed at 1, 2, and 4 hours post-administration, supporting oral fluid as a viable non-invasive monitoring matrix. Tiamulin persisted in oral fluids at detectable concentrations for up to 10 days post-treatment, while plasma and muscle concentrations fell below the lower limit of quantification (<1 µg/kg or µg/L) by day 10. Residues were still detectable in liver (mean 5.63±1.67 µg/kg) and kidneys (mean 3.37±1.04 µg/kg) at day 10, indicating these organs as primary sites of drug accumulation and slower elimination. Pooled oral fluid consistently showed higher concentrations than individual oral fluid, plasma, or tissues, likely reflecting salivary gland concentration effects and pooling dynamics. These findings have important implications for withdrawal period determinations, particularly regarding hepatic and renal residues, and validate oral fluid sampling as a practical, welfare-friendly alternative to plasma collection for pharmacokinetic monitoring of tiamulin in swine production settings.

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