Pharmacokinetics of carprofen in lactating dogs after intravenous treatment

Analgesia is an important component of veterinary care with nonsteroidal antiinflammatory drugs, particularly carprofen (Rimadyl®) commonly used for dogs. Pharmacokinetic studies of carprofen in lactating dogs have not been examined fully, questioning the use and safety of carprofen. The extent to which lactation changes the pharmacokinetics is unknown, nor is the extent of transfer into milk of lactating dogs and their neonates or pups. We hypothesized that after a single dose of intravenous (4.4 mg/kg) to dogs, concentrations in milk are low and not high enough to produce harmful exposure in pups. We tested our hypothesis in healthy, adult lactating dogs (n = 4) using pharmacokinetic methods and nonchiral and chiral specific assays measuring total, R-, and S-enantiomer carprofen concentrations with high performance liquid chromatography in maternal plasma, milk, and neonatal plasma samples. The CMAX, elimination half-life, and clearance for maternal plasma were 9.09 and 7.3 µg/ml (R-, S+), 6.82 and 6.22 hours (R-, S+), and a higher clearance rate of 95.81 ml/hr/kg (R-) and 73.87 ml/hr/kg (S+) than reported. None of the neonatal plasma concentrations at any time point were more than 10% of the total maternal plasma concentrations and milk:plasma ratio was < 1. This study confirmed the approved dose is appropriate for perioperative and chronic pain in lactating dogs and is safe with reduced exposure to nursing pups. This study suggested that the pharmacokinetics of carprofen in lactating dogs may be different from their nonlactating counterparts. However, further pharmacokinetic studies with more dogs are needed to confirm these findings.