Aconite, Belladonna, Ferrum phos: reading the onset of an acute fever

The mistake is prescribing on the fever

A child spikes a temperature. The parents are frightened, and sometimes so are we. The instinct is to match the heat. But three of our best acute-fever remedies — Aconite, Belladonna and Ferrum phosphoricum — can all produce a high fever. What separates them is the manner and speed of onset, and the state of mind that comes with it.

Get that distinction and the prescription almost makes itself.

Aconite — sudden, violent, afraid

Aconite is the remedy of the first few hours of a storm that arrives out of nowhere.

• Onset: sudden and violent, often traceable to a dry, cold wind or a fright.
• Mind: intense anxiety, restlessness, a genuine fear of death — the patient may name the hour they expect to die.
• Physicals: hot, dry, red skin; unquenchable thirst for large quantities of cold water; worse around midnight.

If you are called in that first restless, frightened hour after exposure to cold wind, think Aconite before anything else. Miss the window and the picture usually moves on.

Belladonna — sudden, hot, throbbing

Belladonna shares Aconite's suddenness, but the picture is one of congestion and radiating heat.

• Onset: rapid, but dominated by heat, redness and throbbing rather than fear.
• Head and face: flushed red face, dilated pupils, a hot head with cold extremities, throbbing carotids.
• Modalities: markedly worse from light, noise, touch and jarring; often surprisingly thirstless despite the burning heat.

The face tells you: Aconite is pale and frightened; Belladonna is red and burning, drowsy or even delirious with the heat.

Ferrum phos — the fever with no picture yet

Ferrum phosphoricum is the remedy of the early, undefined stage — the inflammation that hasn't declared itself.

• Onset: gradual and vague; "a fever, but nothing specific."
• Look: pale that flushes easily; a moderate fever without Belladonna's congestion or Aconite's terror.
• Use: the first stage, before the case has organised into a clearer remedy — Boericke placed it precisely between health and the fuller inflammatory pictures.

A working rule

Reach for Ferrum phos when it's early and undefined, Aconite when it's sudden and anxious after cold or shock, and Belladonna when it's sudden, hot and throbbing.

None of this replaces taking the whole case — the modalities, the mind, the concomitants. But in the pressure of an acute, these three onsets are a map worth carrying.

Read the full pictures side by side in the Materia Medica, or practise the differential on an AI patient in the case simulator.