Youe Doctor is probably looking for alternatives to stimulant laxatives, to provide long term relief/prevention. These may not provide a feeling of total relief or evacuation, but may be effective long term.
That being said, do not take any more of the Lactulose, or change medications, until reporting the rash and consulting with the Doctor. You should contact the Doctor, through his on call service tonight, or asap this morning. Proceed to Emergency if you have difficulty breathing, tightness in your throat, or swelling in your face, lips or mouth.
Your Doctor may approve a switch back to Dulcolax for temp relief in the morning, but it would be best to wait for his direction.
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