IN-VIVO NONINVASIVE QUANTIFICATION OF MUSCLE DAMAGE FOLLOWING A SINGLE INTRAMUSCULAR INJECTION OF PHENYLBUTAZONE IN SHEEP

Intramuscular drug administration can lead to more or less extensive m uscle damage. The aim of the present study was to show the possibility of quantitating, in vivo and non-invasively, the equivalence of muscl e destroyed by the administration of a test drug (phenylbutazone) know n for its injurious properties. Creatine kinase (CK) kinetic parameter s (clearance, volume of distribution) were measured in 6 sheep after a n iv administration of muscle CK homogenate. In the same 6 sheep, CK r elease after iv and im 8 mg phenylbutazone/kg was measured. The calcul ated total CK released, based on the CK plasma clearance (0.28 mL/kg/m in) and area under the curve of CK activity after im phenylbutazone ad ministration was 191 +/- 140 U/kg. By relating this quantity to that o f CK gluteal muscle (5114 +/- 891 U/g), it was calculated that im phen ylbutazone administration was able to destroy an equivalence of 2.4 +/ - 2.1 g of muscle. For the 2 main sites of im administration (neck and gluteal muscle), general equations are proposed to calculate the equi valence of muscle destroyed in sheep when only plasma CK activity foll owing a test drug administration is available.