Induction of methemoglobin formation by nitroso-chloramphenicol in hemolyzed blood

We studied the effects of chloramphenicol (CAP), nitroso-chloramphenicol (NO-CAP) and thiamphenicol (TAP) on methemoglobin (MeHb) formation in vitro in hemolyzed blood. At concentrations of 0.5 to 10 mM CAP and TAP did not have any effect on hemoglobin. On the other hand, NO-CAP at 0.25 to 5 mM caused both time and concentration dependent increase in MeHb formation. The oxidation of hemoglobin was reversible by potassium cyanide. Since MeHb was detected only at NO-CAP concentration 0.25 mM or higher, methemoglobin formation is not a sensitive indication of NO-CAP presence.