Milrinone

Two Procedures for the Prediction of Acute Toxicity (LD50) from Cytotoxicity Data

Single linear regression analysis was used to characterise the relationship between cytotoxicity in a variety of mammalian cell culture systems and acute oral toxicity (LD50) in experimental animals. The following results were obtained.

Firstly, in a cytotoxicity assay using the calf aortic endothelial cell line BKEz-7, IC50 values determined for 44 chemicals in culture showed significant correlation with the oral LD50 values for rat and mouse (computed correlation coefficient r=0.546). After eliminating three chemicals that were characterised by extreme lethality indices (LI = IC50/LD50), the correlation coefficient of the remaining 41 chemicals increased to a value of r=0.728. By using the linear regression model for these 41 chemicals, the oral LD50 for rat and mouse can be predicted correctly from the IC50 values for 83% of substances from a variety of chemical substance classes within a range of approximately one order of magnitude of dosage unit of LD50 for rat and mouse.

Secondly, the mean IC50 values (IC50x¯) determined as the geometrical mean of two or more IC50 values per substance, which were generated in a wide spectrum of mammalian cell lines and collected in a “Registry of Cytotoxicity” (RC), gave similar results (r=0.644). Likewise, with the aid of this method, the oral LD50 for rat and mouse can be predicted for 74% of non-selected chemicals from structurally-different classes in the same dosage range, e.g., 1–25 millimoles per kg body weight.

The prediction of LD50 values from in vitro cytotoxicity data may permit the calculation of a more precise dose range-finding and offers a new way for reducing the number of animals in acute toxicity testing.

Characterization of coronary arterial lesions in the dog following administration of SK&F 95654, a phosphodiesterase III inhibitor

Drugs that inhibit the low-Km, cGMP-inhibitable form of phosphodiesterase III (PDE III) are associated with arterial lesions in the extramural coronary arteries of dogs following oral and intravenous administration at high doses. Acute coronary arterial lesions have been investigated following administration to the dog of SK&F 95654, a potent PDE III inhibitor, and the progression of the lesion defined. Groups of 3 male beagle dogs received a single 2-hr infusion of SK&F 95654 at 8 mg/kg/hr and the characteristics of the coronary arterial lesions were evaluated at 1, 3, 10, and 34 days postdosing by light, scanning, and transmission electron microscopy. At 24 hr postdosing, the arterial lesion was characterized by segmental or circumferential necrosis of medial smooth muscle cells and hemorrhage; adventitial hemorrhage was also noted, particularly in the right atrial artery. Ultrastructural evaluation showed extensive medial necrosis, characterized by loss of smooth muscle cells and their replacement by cellular debris with ingress of erythrocytes, platelets, and inflammatory cells into the media. Associated with medial changes, significant endothelial effects were observed consisting of widening of intercellular boundaries, loss of normal elongated cellular appearance, and the attachment of numerous leukocytes and platelets. During the 10-34-day postdosing period, substantial repair of the arterial lesions occurred such that by day 34 all sections of extramural coronary artery were normal. The lesions induced in the dog are consistent with a hemodynamic effect induced by the pharmacological action of SK&F 95654.