A comparative study on the individual plasma activity profiles of rabbit muscle creatine phosphokinase (CPK), AUC∞ and the amount or ratio of total CPK liberated from the injected muscle site after intramuscular administrations of 1 ml each of normal saline, 0.10, 0.75 and 3.38% (v/v) of acetic acid solutions in male rabbits was carried out. The results indicate that the concentration of acetic acid solutions (0, 0.10 and0.75%) showed a fairly good correlation with the total AUC or total CPK liberated after intramuscular administration, whereas the total AUC and total CPK liberated from 3.38% acetic acid solution experiment failed to demonstrate the corresponding muscular lesions. Both the total AUC and total CPK liberated after intramuscular administration of 1 ml, 3.38% acetic acid solution to biceps femoral muscle in rabbits were anomalously smaller than those of 0.75% acetic acid solution experiment (n = 7,P < O.05). Since the buffer capacity of 3.38% acetic acid solution (0.0074) exceeds that of the plasma (0.0067), a strong acidic condition in the injected muscle site may be responsible for the anomaly. It is probable that parts of the liberated CPK due to the intramuscular injection of potent acidic solution were inactivated by the acid at the lesion site. The results suggest that plasma CPK is a good indicator for the muscular lesions due to acidic parenteral solutions with weak buffer capacity (smaller buffer capacity than that of plasma) but is not an adequate indicator for potent acidic solutions that are unlikely used for intramuscular administration. 醋酸溶液肌注於家兔肌肉後，肌肉損傷的程度和醋酸濃度成比例。本報告就各種濃度所引起的CPK變化加以考察、發現0.75%( V/V)以下之醋酸溶液肌注於家兔後，血漿中CPK活性之AUC∞反推算而得之CPK總釋離量和醋酸濃度呈對數相關。但3. 38%之醋酸溶液肌注後，雖然解剖後所見之肌肉損傷度大於0.75%之醋酸溶液，但AUC及CPK總釋離量反而較小。導至此反常之現象主要是因為3.38%醋酸溶液之緩衝容量已超過血漿之緩衝能力，因此在肌肉損傷部位造成強酸性，使釋離出來的C PK失活。
根據實驗結果，可以推斷，血漿中CPK之變動對緩衝容量小的酸性肌注液可以反映肌肉損傷之程度。因為家兔個體間之差異度相當大，所以必須使用二期性平行或交叉實驗來測定。至於緩衝容量大的強酸性溶液，血漿中CPK之變動不能有效地反映其對於肌肉所造成之損傷。然而事實上，緩衝容量太大的溶液並不適宜供注射使用，所以血漿中C PK之變動性對酸性注射液之肌肉損傷性之偵測，有實際的價值。
