Question is that if we need second prescription then we did not give the right similimum in the form of first prescription. Or we can say the first prescription is not the right one.
The homoeopathic physician should knows the importance of the first prescription. After the first correct homoeopathic prescription, the striking features for which that remedy was administered have been removed, a change has come and the guiding symptoms of the case have been taken out on which this similimum is given.
Thats why the definition of Second Prescription is the prescription after the first one that has acted.
When we do a proper case taking we are portraying the picture with present conditions, past conditions and family history. Meaning how many layers patient have and we have to unfold those layers to cure the patient. So we should have the knowledge of Causa Morbi, Causa Occasionalis and causes of diseases (i.e. exciting cause, maintaining cause and fundamental cause).
So we require for a complete cure, a succession of remedies, one remedy following another to good advantage because the process of cure is zigzagging and case does not unfold before us when we first consider it.
The second possible reason for the successful succession of remedies is the first prescription may remove all the symptoms of one miasmatic condition, then after suddenly a condition will arise which shows a basic condition of the other miasm. One miasm may have been underneath another and after the first has been removed by the simillimum, the second shows.
In aphorism 272 to 277 of Organon of Medicine, Dr Hahnemann wrote down the guidelines for the second prescription. Dr James Tyler Kent and Dr Constantine Hering, two stalwarts in Homeopathy further elaborated the observations, the possible changes after the first prescription and interpreted its effects. These observations leads us the prognosis of case and helps us to find the cure.