The Surprising Link Between Cyanide and Medicine
Cyanide is a rapidly acting and potent poison, but its components are also found in a few specific pharmaceutical and chemical compounds [1.6.3, 1.5.5]. These substances, known as cyanogenic compounds, do not necessarily contain free cyanide but can release it through metabolic processes in the body [1.2.1]. Understanding which drugs contain or produce cyanide is crucial for clinicians to manage potential toxicity and for the public to be aware of the risks associated with certain alternative therapies and natural substances.
Sodium Nitroprusside: A Potent Vasodilator
The most prominent and clinically relevant drug that can lead to iatrogenic (medically induced) cyanide poisoning is sodium nitroprusside [1.2.1, 1.6.4]. This potent vasodilator is administered intravenously in critical care settings to manage severe hypertensive crises and heart failure [1.3.2].
Each molecule of sodium nitroprusside contains five cyanide ions [1.3.1]. When administered, it is metabolized, releasing these cyanide ions [1.6.1]. The body has a natural detoxification pathway, primarily in the liver, where an enzyme called rhodanese converts cyanide to the less toxic thiocyanate, which is then excreted by the kidneys [1.3.1, 1.3.2].
However, at high doses (above 2 mcg/kg/min) or during prolonged infusions, this detoxification process can be overwhelmed, leading to cyanide accumulation and toxicity [1.3.3, 1.3.4]. Patients who are malnourished or have liver impairment are at a higher risk [1.3.1]. Symptoms of cyanide toxicity include headache, dizziness, metabolic acidosis, and in severe cases, seizures and coma [1.3.2]. To mitigate this risk, co-administration of sodium thiosulfate is sometimes recommended, as it provides the necessary sulfur donor for the rhodanese enzyme to function effectively [1.3.5].
Amygdalin (Laetrile or "Vitamin B17")
Amygdalin is a naturally occurring cyanogenic glycoside found in the pits of many fruits, such as apricots and peaches, as well as in raw nuts and other plants [1.4.1, 1.4.5]. A semi-synthetic, purified form of amygdalin is known as Laetrile, which has been controversially promoted as an alternative cancer treatment, sometimes under the name "Vitamin B17" [1.4.2, 1.4.5].
Scientific evidence does not support the claims that Laetrile is an effective cancer treatment [1.4.6, 1.4.2]. The theory behind its use was that cancer cells contained enzymes that would selectively release cyanide from amygdalin, killing the cancer cells while leaving normal cells unharmed. However, clinical trials, including those sponsored by the National Cancer Institute, found no benefit and instead documented cases of cyanide toxicity in patients [1.4.1, 1.4.2].
When ingested orally, amygdalin is broken down by enzymes in the intestine, releasing hydrogen cyanide [1.4.3]. This makes oral consumption particularly dangerous and can lead to severe poisoning with symptoms like nausea, headache, low blood pressure, nerve damage, coma, and even death [1.4.1]. The U.S. Food and Drug Administration (FDA) has banned the sale of Laetrile and amygdalin as a medical product due to these risks [1.4.2, 1.4.4].
Other Cyanogenic Compounds
Beyond sodium nitroprusside and amygdalin, other substances can also be metabolized into cyanide:
- Aliphatic nitriles: These are used as solvents and in the manufacturing of plastics. They can release cyanide when metabolized after skin absorption or ingestion [1.2.3, 1.6.1]. Acetonitrile, a solvent previously found in some artificial nail removers, has been a source of fatal cyanide poisoning in children [1.2.3].
- Cyanogenic Glycosides in Plants: Many plants besides apricot kernels contain these compounds. Cassava root, if improperly processed, is a well-known source of potential cyanide toxicity [1.2.1, 1.6.3].
Comparison of Cyanide-Releasing Compounds
| Compound | Type | Common Use / Source | Risk of Toxicity |
|---|---|---|---|
| Sodium Nitroprusside | Pharmaceutical Drug | Intravenous treatment for severe hypertension and heart failure [1.3.2]. | High risk with prolonged or high-dose infusions (>2 mcg/kg/min), especially in patients with hepatic impairment [1.3.1, 1.3.3]. |
| Amygdalin (Laetrile) | Cyanogenic Glycoside | Found in apricot pits and other plant seeds; promoted as an alternative cancer treatment [1.4.1, 1.4.5]. | Significant risk of cyanide poisoning, especially with oral ingestion. Banned by the FDA as a drug [1.4.2, 1.4.4]. |
| Aliphatic Nitriles | Industrial Chemicals | Solvents, plastic manufacturing, some consumer products like artificial nail remover [1.2.3]. | Can release cyanide through metabolism after absorption or ingestion [1.6.1]. |
Conclusion
While the idea of a drug containing cyanide may sound alarming, the clinical reality is nuanced. Sodium nitroprusside remains a valuable, life-saving medication in critical care, with its risks managed through careful dosing and monitoring [1.3.2]. On the other hand, substances like amygdalin (Laetrile) represent a significant public health concern, as they are promoted with unproven claims of benefit while carrying a very real and potentially fatal risk of cyanide poisoning [1.4.6]. It's essential for both healthcare professionals and consumers to be aware of which drugs contain cyanide precursors, their mechanisms, and the potential for toxicity.
For more information on cyanide poisoning, you can visit the Centers for Disease Control and Prevention (CDC).
