Amphotericin B and 5-fluorocytosine penetration into blood and fibrin clots.

The fungicidal effect of amphotericin B and 5-fluorocytosine (5-FC) on fungi incorporated into blood and fibrin clots was investigated. Amphotericin B was ineffective against fungi incorporated into blood clots, but effective in the eradication of fungi in fibrin clots. 5-FC was ineffective both against fungi incorporated in blood clots as well as in fibrin clots. The combination of 5-FC and amphotericin B was likewise ineffective against fungi incorporated into blood clots. The failure of these drugs to penetrate blood clots may explain the treatment failure in fungal endocarditis.