Interaction of halothane and antibiotics on isometric contractions on rat-heart muscle.

Halothane (H), kanamycin (KM), streptomycin (SM), and chloramphenicol (CM) had direct negative inotropic effects on isometric contractions of isolated rat-heart muscles. Potassium penicillin-G did not show any significant changes in isometric contractions. The depression produced by these antibiotics was characterized by an abrupt onset, rapid progression, and rapid complete recovery, which suggests direct physicochemical rather than metabolic effects. On the other hand, the depression produced by H progressed slowly. When KM, SM, or CM were combined with H, there was a greater depression in isometric contractions than seen in the absence of H, suggesting that the innate characteristics of the antibiotics are augmented when any of them is administered together with halothane.