Hydrocyanicum acidum

Hydrocyanic acid is the aqueous solution of hydrogen cyanide (HCN), a volatile, highly toxic compound historically obtained from Prussian blue and bitter almond kernels. Toxicology demonstrates rapid inhibition of cellular respiration leading to sudden loss of consciousness, convulsions, respiratory arrest, and cardiac collapse—central medullary failure with intense vagal phenomena—features that strongly shape the homœopathic picture of spasms, apnoea, and instantaneous prostration [Hughes], [Hering], [Allen]. The mother tincture is prepared from a measured dilute solution of HCN in water (careful standardisation is required), from which triturations and centesimals are made according to pharmacopeial rules [Allen], [Clarke]. In crude medicine small drops of dilute prussic acid were once used as antitussive and gastric sedative; overdosage rapidly proves fatal, a fact mirrored in the remedy’s collapse and suffocation states [Hughes], [Clarke]. [Toxicology]

Nineteenth-century physicians employed highly dilute prussic acid as a cough sedative and for gastric irritability, a practice later abandoned owing to toxicity; physiologists (e.g., Magendie) studied its rapid paralytic action on the respiratory centre and heart [Hughes]. Industrially and historically cyanides were used for fumigation and extraction; these contexts provided numerous poisonings whose observed sequences (sudden coma → gasping → convulsions → collapse) informed the clinical selection in homœopathy [Clarke], [Allen].

The pathogenesis arises chiefly from toxicologic observations, small provings, and abundant clinical confirmations in spasmodic respiratory affections (whooping-cough with cyanosis, laryngismus stridulus), epileptiform seizures, anginal collapse, choleraic prostration, and sudden syncope with gasping [Allen], [Hering], [Clarke]. Hahnemann and his contemporaries recorded effects and dosing cautions; later compilers (Allen, Hering) integrated poisonings and clinical experience into the remedy picture [Hahnemann], [Allen], [Hering], [Clarke]. [Proving] [Toxicology] [Clinical]

• Medulla oblongata and respiratory centre—apnoea, Cheyne–Stokes-like gasping, sudden suspension of breathing; spasm of glottis; laryngismus (see Respiration, Throat). [Hughes], [Hering], [Clarke].
• Vagus and heart—instantaneous cardiac weakness, irregularity, syncope, anginoid constriction “as if grasped,” precordial anxiety with cold sweat (see Heart, Chest). [Clarke], [Boericke].
• Cerebro-spinal axis—epileptiform convulsions, opisthotonos, trismus; sudden loss of consciousness (see Mind, Extremities, Back). [Allen], [Hering].
• Larynx and bronchi—whooping-cough with cyanosis, long silent apnœic pauses, then explosive cough; scanty expectoration (see Chest/Respiration). [Clarke], [Boger].
• Stomach and cardia—violent cardialgia, spasm of œsophagus, incessant hiccough, collapse after gastric pain (see Stomach, Throat). [Allen], [Clarke].
• Peripheral circulation—cyanosis, marble coldness, cold clammy sweat; asphyxia neonatorum (see Skin, Generalities). [Hering], [Boericke].
• Infant and senile states—infantile laryngismus, asphyxia at birth; senile syncope with gasping (see Respiration, Generalities). [Clarke], [Boericke].

• Cold air and fanning in asphyxial states—patient craves air; brief relief during gasps (Respiration/Generalities). [Clarke], [Boericke].
• Head low and body at rest during syncope—movement renews faintness (Generalities). [Allen], [Clarke].
• Warm external applications to precordia and epigastrium in collapse—soothes gripping constriction (Heart/Stomach). [Clinical], [Clarke].
• Small sips of cold water in laryngeal spasm (transient)—may abort a cough paroxysm (Throat/Respiration). [Clarke].
• Pressure over sternum—subjectively eases suffocative sense (Chest). [Clinical].
• Eructations or vomiting, when present—momentary ease in cardialgia (Stomach). [Allen].
• Quiet, darkened room—diminishes reflex excitability in convulsive tendency (Mind/Generalities). [Hering].
• Prolonged exhalation training between paroxysms (clinical measure in pertussis)—lengthens interval (Respiration). [Clinical].

• Sudden exertion, rising, or least motion—renewed syncope, gasping (Generalities). [Clarke], [Allen].
• Warm, close room; lack of moving air—apnoea and faintness increase (Respiration). [Clarke], [Boericke].
• Emotion, fright, or startling noises—provoke convulsion or laryngeal spasm (Mind/Throat). [Hering], [Allen].
• Touch or jar—tetanic start; spasm intensifies (Extremities/Back). [Hering].
• Swallowing—spasm of œsophagus; liquids threaten to suffocate (Throat). [Clarke].
• After eating; gastric irritation—cardialgia, hiccough, collapse (Stomach). [Allen].
• Night and early morning—the silent apnœic pauses lengthen; whoop ends in blue face (Respiration/Sleep). [Clarke], [Boger].
• Cold draught on neck in sensitive subjects—glottic spasm (Throat/Respiration). [Clarke].
• During pregnancy/labour (rare notes)—spasms and syncope (Female/Generalities). [Hering].
• Tobacco, alcohol—deepen respiratory depression (Stomach/Respiration). [Hughes], [Clarke].

Asphyxia / Collapse

• Carbo vegetabilis: collapse with desire for air and fanning; more gastric flatulence and lack of reaction; Hydrocy. ac. is more explosive, with silent arrest and convulsion. [Nash], [Clarke].
• Laurocerasus: cyanosis, coldness, dyspnœa; cough with little expectoration; less convulsive than Hydrocy.; both crave air; Lauro. is slower, more pulmonary. [Clarke], [Boericke].
• Camphora: icy collapse, great coldness; cannot bear external heat; less gasping cycles and less laryngeal spasm than Hydrocy. ac. [Boericke], [Kent].
• Opium: apoplectic coma with stertorous breathing and insensibility; Hydrocy. ac. has silent apnœa, sudden gasps, reflex-provoked spasms. [Hering], [Clarke].

Spasm / Convulsions

• Cuprum metallicum: violent clonic spasms, blue face, thumbs clenched; spasms start in fingers; cough ends in spasm; Hydrocy. ac. more medullary arrest with silent apnœa. [Boger], [Clarke].
• Cicuta virosa: tetanic, opisthotonic convulsions with frightful distortion; less respiratory arrest-gasp cycle than Hydrocy. ac. [Hering], [Farrington].
• Nux vomica: convulsions with extreme spinal irritability and conscious struggle; Hydrocy. ac. shows sudden blankness and cardiac-respiratory standstill. [Kent], [Clarke].

Whooping-cough / Laryngeal spasm

• Corallium rubrum: rapid successive coughs until breath fails; face purple; sound is shrill; Hydrocy. ac. shows longer silent pause and more collapse. [Boger], [Clarke].
• Ipecacuanha: suffocative cough with much nausea and vomiting; Ipec. lacks the long apnœic silence and the convulsive arrest of Hydrocy. ac. [Farrington], [Clarke].
• Antimonium tartaricum: rattling with inability to raise; drowsy and cyanosed; Hydrocy. ac. less rattling, more sudden stop-and-gasp. [Boger], [Boericke].

Angina / Cardialgia

• Glonoinum: bursting head, throbbing carotids, heat; Hydrocy. ac. shows cold sweat, instant collapse, and gasping rather than throbbing congestion. [Clarke], [Kent].
• Cactus grandiflorus: iron-band constriction and cardiac spasm; less apnœic silence; Hydrocy. ac. more medullary arrest with gasp cycles. [Clarke], [Boericke].

Choleraic collapse

• Veratrum album: profuse vomiting and diarrhœa with icy collapse; Hydrocy. ac. has less GI storm and more hiccough/apnœa; both icy and prostrate. [Nash], [Clarke].
• Tabacum: deadly nausea, cold sweat, relief from cool air; Hydrocy. ac. more silent apnœa and convulsive element. [Clarke].

• Complementary: Laurocerasus—shared cyanosis and air-craving; Lauro. for slower pulmonary-cardiac failure, Hydrocy. ac. for abrupt arrest with convulsion. [Clarke], [Boericke].
• Complementary: Carbo vegetabilis—after reviving reaction in deep collapse with air-desire, Hydrocy. ac. cuts the apnœic-convulsive paroxysms. [Nash], [Clarke].
• Complementary: Cuprum metallicum—whooping-cough with spasm; Hydrocy. ac. when apnœic silence predominates, Cupr. when clonic spasm dominates. [Boger], [Clarke].
• Follows well: Aconitum—after stormy onset, if fear subsides but arrest-gasp cycles persist. [Kent].
• Follows well: Antimonium tart.—when rattling stage has lessened, yet long silent pauses remain. [Boger].
• Precedes well: Phosphorus—if later haemorrhagic lung weakness remains after apnœa abates. [Farrington].
• Related (angina): Glonoinum, Cactus—distinguish by collapse and gasp vs throbbing/constrictive patterns. [Clarke].
• Antidotes (toxicologic): Ammonia, chlorine, oxygen, and iron salts chemically; in practice, fresh air and artificial respiration are immediate measures (medical emergency). [Hughes], [Clarke].
• Inimicals not specified; avoid routinism; individualise on the arrest-gasp signature. [Clarke], [Boericke].

Hydrocyanic acid epitomises the medicine of the last breath: the organism halts without warning—breath, heart, consciousness—then seizes a single gasp and fights back to a flicker of life. The themes are abruptness, silence, and reflex excitability. Abruptness: attacks begin and end in an instant, with no prodrome beyond a tremor, a hush, or a child’s fixed stare. Silence: in whooping-cough and laryngismus there is a long, awful pause before any sound; in syncope there is no struggle, only a slack fall or stiffening arc; in angina there is constriction without a cry. Reflex excitability: the slightest noise, touch, or attempt to swallow may throw the medullary switch again, re-arresting breath or launching a convulsion [Hering], [Clarke], [Allen]. Kingdom-wise (inorganic acid), the action is direct, chemical, and central; miasmatically syphilitic, it wreaks arrest and dissolution where other remedies inflame. The modalities frame the essence: worse warm, close rooms; worse least motion, noise, touch; worse swallowing and after eating; better cold air, fanning, head low, quiet, and, paradoxically, gentle warmth to chest/epigastrium as a subjective comfort. These recur in Mind (terror of suffocation), Head (blackness on rising), Throat (glottic and œsophageal spasm), Heart (instant power-failure), Respiration (apnœa → gasp → a few breaths), and Skin (blue, cold, clammy).

Differentially, Hydrocyanic acid must be separated from Carbo-veg. (collapse wants air with gaseous distension and a somewhat steadier rhythm; Carbo-veg. is the chronic asphyxiant, Hydrocy. ac. the explosive one), Laurocerasus (similar cyanosis and need for air but slower, less convulsive, more pulmonary), Camphor (icy, but heat is intolerable and spasm is less), Opium (deep, noisy coma without the prolonged silent pause), and Cuprum (convulsions with more clonic violence and less medullary arrest). In pertussis, Corallium rubrum delivers a torrent of coughs; Hydrocyanic acid delivers a long, terrible pause before a feeble gasp. In angina, Glonoinum throbs and bursts; Hydrocyanic acid grips and stops. The clinical art is to recognise the choreography: the hush, the blue, the gasp, the cold sweat—then to place the patient at a window, cool the room, quiet the surroundings, and give the remedy while supporting with measures that match its modalities [Clarke], [Boericke], [Boger].

In practice, Hydrocyanic acid is invaluable when the respiratory centre forgets its work in paroxysms—infantile laryngismus, asphyxia neonatorum, whooping-cough with long apnœic pauses, epileptiform fits with cyanosis, anginoid collapses, and choleraic sinkings with hiccough—especially in nervous, excitable subjects and in the aged exhausted by chronic catarrh. It is not a fever remedy; it is the medicine of the medulla. Improvement is read not in warmth or appetite first, but in lengthening of intervals, shortening of the silent pause, lessened startle-provoked spasm, and a steadier, quieter breath at night.

Indications: Laryngismus stridulus (infants); asphyxia neonatorum (supportive); whooping-cough with prolonged apnœic pauses, cyanosis, cold sweat; epileptiform or tetanic convulsions triggered by noise/touch; angina pectoris with instantaneous collapse and gasps; violent hiccough with suffocative tendency; choleraic or gastro-cardial collapse with cardialgia and cold sweat [Clarke], [Hering], [Allen], [Boericke], [Boger]. Posology: For violent paroxysms many authors used low to medium potencies (3X–6X–12C) repeated at short intervals during the crisis, then extended; in high-strung nervous persons and in pertussis, 30C–200C may be effective when the arrest-gasp signature is clear—reduce as the silent pause shortens [Clarke], [Dewey], [Kent]. Repetition: During acute attacks dose more frequently, then taper as intervals lengthen; in infants, give sparingly and monitor respiration closely (medical co-management). Adjuncts: immediate cool, moving air; head low; absolute quiet; avoid jarring; gentle chest-pressure/hand warmth for subjective comfort; in suspected poisoning or profound collapse, urgent medical measures (oxygen/airway) are paramount while the remedy may be given as an adjunct [Hughes], [Clarke].
Case pearls:
• “Whooping-cough with long silent apnœa, blue face, cold sweat—Hydrocy. ac. 30C shortened the pause; child slept with open window thereafter.” [Clinical], [Clarke], [Boger].
• “Laryngismus in a restless infant—startles from the least sound; Hydrocy. ac. 6X with strict quiet and fresh air cut paroxysms.” [Hering], [Boericke].
• “Anginoid arrest at night; wakes gasping, pulse gone, forehead cold—Hydrocy. ac. 200C removed the nightly ‘stop and gasp’.” [Clinical], [Clarke].
• “Hiccough with suffocation after gastric spasm; Hydrocy. ac. 6X calmed shocks and steadied breath.” [Allen], [Clarke].

Mind

• Mind—Fear—of suffocation—during attacks; begs for air. Decisive in arrest–gasp states. [Clarke].
• Mind—Unconsciousness—sudden—apoplexy-like. Instantaneous blankness hallmark. [Hering], [Allen].
• Mind—Startled—noise from—convulsions, laryngismus agg. Reflex excitability pointer. [Hering].
• Mind—Anxiety—precordial—with cold sweat. Ties heart and breath. [Clarke], [Boericke].
• Mind—Irritability—after attacks—exhaustion with dread of movement. Post-paroxysmal tone. [Clarke].
• Mind—Desire—air—must be fanned/open window. Air-craving confirmation. [Clarke], [Boericke].

Head

• Head—Vertigo—on rising—blackness before eyes—faints. Motion-agg. syncope. [Clarke], [Allen].
• Head—Heaviness—after suffocative paroxysm. Residual medullary fatigue. [Clarke].
• Eyes—Pupils—dilated—convulsions/ syncope with. Neurologic sign. [Hering].
• Face—Pallor—then cyanosis—apnœa during. Colour swing hallmark. [Clarke].
• Head—Noise—agg.—threat of spasm. Reflex rubric. [Hering].
• Head—Sweat—cold—forehead—attacks during. Collapse marker. [Boericke].

Throat & Larynx

• Throat—Constriction—choking—swallowing agg. Core œsophago-glottic spasm. [Clarke], [Allen].
• Larynx—Spasm—laryngismus stridulus—children. Capital indication. [Boericke], [Clarke].
• Voice—Lost—after suffocative paroxysm. Exhausted register. [Clarke].
• Swallowing—Liquids—suffocate—agg. Pathognomonic spasm. [Clarke].
• Cough—Whooping—long apnœa before whoop—cyanosis. Hydrocy. signature. [Boger], [Clarke].
• Respiration—Wants windows open—fanning amel. Air modality. [Boericke], [Clarke].

Stomach

• Stomach—Pain—cardialgia—collapse with—cold sweat. Gastro-cardiac nexus. [Allen], [Clarke].
• Hiccough—violent—threatens suffocation. Shock-to-apnœa rubric. [Allen].
• Nausea—after eating—sinking at epigastrium—faintness. Post-prandial collapse. [Clarke].
• Eructations—ameliorate—impending faint. Small rescue sign. [Allen].
• Stomach—Spasm—warmth/pressure amel. Palliative pointer. [Clarke].
• Appetite—aversion—after attacks. Exhaustion rubric. [Clarke].

Chest & Respiration

• Respiration—Arrest—sudden—followed by gasps. Core pathognomonic rubric. [Hering], [Clarke].
• Respiration—Apnœa—long silent pause—pertussis. Selection clincher. [Boger].
• Chest—Constriction—across sternum—anxiety with. Anginoid sign. [Clarke].
• Respiration—Cold air—amel.—warm room—agg. Master modality. [Clarke], [Boericke].
• Cough—Paroxysmal—cyanosis—collapse. Severe pertussis rubric. [Clarke].
• Respiration—Cheyne-Stokes-like—periodic gasps. Medullary pattern. [Hughes], [Clarke].

Heart

• Heart—Syncope—sudden—cold sweat. Cardio-vagal collapse. [Clarke], [Boericke].
• Pulse—Irregular—intermittent—weak—attacks during. Rhythm arrest. [Clarke].
• Angina pectoris—apnœa—collapse—air-craving. Differentiates from throbbing angina. [Clarke], [Boger].
• Palpitation—faintness with—motion agg. Motion-triggered failure. [Allen], [Clarke].
• Precordium—Anxiety—grasping sensation. Subjective hallmark. [Clarke].
• Heart—Warmth/pressure—amel.—subjective only. Palliative note. [Clinical], [Clarke].

Extremities / Nervous

• Convulsions—epileptiform—noise/touch agg. Reflex convulsive rubric. [Hering].
• Opisthotonos—attacks with. Severe spasm sign. [Allen].
• Trismus—jaws clenched—froth at mouth. Tetaniform aspect. [Hering].
• Hands—Blue—cold—sweaty—attacks during. Peripheral cyanosis. [Clarke].
• Weakness—sudden—collapse—least motion. Global prostration sign. [Clarke].
• Trembling—post-paroxysmal—exhaustion. Recovery rubric. [Clarke].

Generalities

• Generalities—Asphyxia—tendency to—paroxysmal. Central essence. [Clarke], [Hering].
• Generalities—Collapse—sudden—cold sweat. Crisis marker. [Boericke].
• Generalities—Air—craves—fanning amel. Master modality. [Clarke].
• Generalities—Motion—least—agg.—syncope. Bedside caution. [Allen].
• Generalities—Noise/touch—agg.—spasm. Reflex excitability. [Hering].
• Generalities—Warm room—agg.—open air—amel. Environmental key. [Clarke].

Hahnemann, S. — Materia Medica Pura / Chronic Diseases (1821–1834): early notes on Acidum hydrocyanicum effects and cautions; proving fragments (spasm/collapse).
Hering, C. — The Guiding Symptoms of Our Materia Medica (1879–1891): toxicology and clinical confirmations—apnœa, convulsions, laryngismus, cyanosis.
Allen, T. F. — Encyclopædia of Pure Materia Medica (1874–1879): collated provings/poisonings; gastric spasm, hiccough, syncope, whooping-cough data.
Hughes, R. — A Manual of Pharmacodynamics (late 19th c.): physiological action (medullary and cardiac depression); toxicologic sequence; therapeutic deductions.
Clarke, J. H. — A Dictionary of Practical Materia Medica (1900): clinical picture—laryngismus, pertussis with long apnœa, anginal collapse; modalities; relationships.
Boericke, W. — Pocket Manual of Homœopathic Materia Medica (1901): keynotes—spasms, asphyxia, whooping-cough, collapse, cold sweat; modalities.
Boger, C. M. — Synoptic Key of the Materia Medica (1915): repertorial pointers—long apnœa before whoop, reflex excitability, collapse differentials.
Kent, J. T. — Lectures on Homœopathic Materia Medica (1905): comparative insights—Camph., Carbo-veg., Laurocerasus, Glon., Cupr.—miasmatic framing.
Nash, E. B. — Leaders in Homœopathic Therapeutics (1899): collapse/spasm comparisons (Carbo-veg., Verat., Camph.) applied to Hydrocyanic acid states.
Dewey, W. A. — Practical Homœopathic Therapeutics (early 20th c.): pertussis, laryngismus, hiccough, angina groupings; posology hints.
Farrington, E. A. — Clinical Materia Medica (1890): organ-affinity method; nervous–respiratory axis; differentials in spasmodic diseases.
Tyler, M. L. — Homœopathic Drug Pictures (20th c.): vivid clinical notes on arrest-gasp cycles and bedside management (air, quiet) with Hydrocyanic acid.