Organon §236

Administer a remedy after or at the end of a paroxysm to avoid the action of the medicine coinciding with the natural recurrence of symptoms.

In this case, the medicinal dose is most expediently and most helpfully given immediately or, at least, very soon after completion of the attack, as soon as the patient has somewhat recovered from it. Then it has time to produce all its possible alterations of the organism towards health, without storm and without violent attack. On the other hand, if the medicine (no matter how specifically appropriate it may be) is administered just before a paroxysm, its action will coincide with the natural resumption of the disease and it will occasion such a counter-action in the organism, such a violent opposition that, at the very least, such an attack will rob much vitality, if it does not endanger life altogether. 199 If, however, one gives the medicine immediately after the completion of the attack (that is, at the time when the fever-free interim has come on, and far in advance of the preparation for the next paroxysm) then the organism's life force is in the best possible shape to allow itself to be quietly altered by the remedy, and thus transposed into a state of health. 

Comment

199 This can be seen in those (by no means rare) fatal cases in which a moderate dose of opium, given in the midst of the chills of the fever, rapidly takes the patient's life.