Figure 2. Analgesia in the foot, expressed as percent maximum possible effect (%MPE) from intrathecal neostigmine alone (closed square), epidural clonidine alone (closed circle), or their combination (Del). Dose expressed as micrograms for each drug alone or the numerical addition of these two (combination). Each data point represents the mean+/- SEM of 5–8 observations. Inset: Isobologram at the ED50 level, demonstrating additivity of the interaction.