Fig. 3. Influence of phenobarbital pretreatment on methoxyflurane metabolism in vivo . Results are urine methoxyflurane metabolite excretion (mean ± SD; controls n = 4, phenobarbital treated n = 5). Each set of five bars represents the preanesthetic sample and days 1–4 after methoxyflurane anesthesia. No dichloroacetic acid was detected in any urine sample (results not shown). No methoxydifluoroacetic acid (MDFA) was detected in the preanesthetic urine. * Significantly different from premethoxyflurane sample ( P < 0.05). ** Significantly different from methoxyflurane controls ( P < 0.05).