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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Adrenocorticotropic Hormone [EPC]
Carbon Monoxide is a medical gas primarily utilized in diagnostic pulmonary function testing to measure the diffusing capacity of the lungs. It is classified under several regulatory categories, including Adrenocorticotropic Hormone [EPC] and Adrenergic Agonists [MoA].
Name
Carbon Monoxide
Raw Name
CARBON MONOXIDE
Category
Adrenocorticotropic Hormone [EPC]
Drug Count
3
Variant Count
3
Last Verified
February 17, 2026
About Carbon Monoxide
Carbon Monoxide is a medical gas primarily utilized in diagnostic pulmonary function testing to measure the diffusing capacity of the lungs. It is classified under several regulatory categories, including Adrenocorticotropic Hormone [EPC] and Adrenergic Agonists [MoA].
Detailed information about Carbon Monoxide
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Carbon Monoxide.
Carbon Monoxide (CO) is a colorless, odorless, and tasteless gas that, while famously known as a byproduct of incomplete combustion and a potent environmental toxin, serves critical roles in modern clinical medicine. In a pharmaceutical context, Carbon Monoxide is primarily administered as a medical gas for diagnostic purposes, specifically to evaluate the gas-exchange capacity of the pulmonary system. Carbon Monoxide belongs to a class of drugs called medical gases, though it is also categorized under various pharmacological classes such as Adrenocorticotropic Hormone [EPC], alpha-Adrenergic Agonist [EPC], and beta-Adrenergic Agonist [EPC] according to specific regulatory frameworks. These classifications often reflect its complex interaction with heme-containing proteins and its endogenous role as a signaling molecule in the human body.
The FDA has approved Carbon Monoxide for use in the Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) test. This diagnostic procedure is the gold standard for assessing how well the lungs transfer gases from the inspired air into the bloodstream. Beyond its diagnostic utility, Carbon Monoxide is a subject of intense clinical research for its potential anti-inflammatory, anti-apoptotic (preventing cell death), and cytoprotective (cell-protecting) properties. Endogenously, Carbon Monoxide is produced by the enzyme heme oxygenase (HO), which breaks down heme from hemoglobin. This biological pathway suggests that CO acts as a critical homeostatic regulator, influencing vascular tone and inflammatory responses.
At the molecular level, Carbon Monoxide works by binding to heme-containing proteins with an affinity significantly higher than that of oxygen. In the context of the DLCO test, Carbon Monoxide is used because its affinity for hemoglobin is approximately 200 to 250 times greater than that of oxygen. When a patient inhales a trace amount of CO, it rapidly crosses the alveolar-capillary membrane and binds to the hemoglobin within red blood cells. The rate at which this occurs allows clinicians to calculate the efficiency of the lung's surface area and the integrity of the pulmonary vasculature.
Beyond hemoglobin binding, Carbon Monoxide interacts with other hemoproteins, including myoglobin, cytochrome c oxidase, and soluble guanylate cyclase (sGC). By stimulating sGC, Carbon Monoxide increases the production of cyclic guanosine monophosphate (cGMP), which leads to the relaxation of smooth muscle cells and vasodilation (widening of blood vessels). This mechanism is similar to that of nitric oxide (NO). Furthermore, Carbon Monoxide modulates various signaling pathways, such as the mitogen-activated protein kinase (MAPK) pathway, which contributes to its potential therapeutic effects in reducing inflammation and protecting tissues from oxidative stress during conditions like organ transplantation or acute lung injury.
When administered as a medical gas, Carbon Monoxide is absorbed exclusively through the lungs. Its bioavailability is effectively 100% for the amount that reaches the alveoli. The absorption rate is limited by the diffusion capacity of the alveolar-capillary membrane and the pulmonary capillary blood flow. Food interactions do not affect the absorption of inhaled Carbon Monoxide, though the presence of other inhaled substances (like nicotine from cigarette smoke) can significantly alter baseline levels.
Once absorbed, Carbon Monoxide is primarily distributed within the intravascular space. Over 85% of absorbed CO binds to hemoglobin to form carboxyhemoglobin (COHb). A smaller fraction binds to myoglobin in muscle tissue and to various intracellular cytochromes. Carbon Monoxide does cross the blood-brain barrier and the placental barrier, which is of significant clinical concern during pregnancy as fetal hemoglobin has an even higher affinity for CO than adult hemoglobin.
Carbon Monoxide is not metabolized by the liver or through traditional enzymatic pathways like the Cytochrome P450 (CYP) system. It remains chemically stable within the body. The only "metabolic" change is its association and dissociation with heme proteins based on the partial pressure of oxygen in the blood.
The primary route of elimination for Carbon Monoxide is through exhalation via the lungs. The elimination half-life is highly dependent on the concentration of inspired oxygen. On room air (21% oxygen), the half-life of CO is approximately 320 minutes (over 5 hours). If the patient is placed on 100% oxygen, the half-life drops to approximately 74-80 minutes. In a hyperbaric chamber with 100% oxygen at 3 atmospheres of pressure, the half-life can be reduced to as little as 20 minutes.
The primary FDA-approved indication for Carbon Monoxide is for diagnostic use in pulmonary function testing. Specifically, it is used to measure the Diffusing Capacity of the Lung (DLCO), also known as the Transfer Factor (TLCO). This test is essential for:
Off-label research is currently exploring the use of low-dose inhaled Carbon Monoxide for treating sepsis, preventing organ rejection in kidney and lung transplants, and managing chronic inflammatory conditions like Crohn's disease, although these are not yet standard clinical practices.
Carbon Monoxide is available strictly as a component of specialized medical gas mixtures. It is never administered in its pure form. Common preparations include:
> Important: Only your healthcare provider can determine if Carbon Monoxide is right for your specific condition. Diagnostic tests involving Carbon Monoxide must be performed in a controlled clinical environment by trained pulmonary technicians.
For diagnostic pulmonary function testing (DLCO), the standard concentration of Carbon Monoxide used is 0.3% (3000 parts per million). This is administered as a single-breath inhalation. The patient is asked to exhale completely to residual volume, then rapidly inhale the gas mixture to total lung capacity, hold their breath for approximately 10 seconds, and then exhale. This procedure may be repeated 2 to 3 times to ensure accuracy, with a minimum of 4 minutes between tests to allow for the clearance of the gas from the previous maneuver.
In therapeutic research settings, much lower doses are used, typically ranging from 100 to 250 parts per million (ppm) inhaled for 1 to 2 hours daily. However, these dosages are strictly experimental and are not approved for general medical use.
Carbon Monoxide testing is approved for pediatric patients who are old enough to follow the breathing instructions required for the DLCO maneuver, typically children aged 6 years and older. The concentration of the gas (0.3%) remains the same as in adults, as the test measures the rate of diffusion rather than a total volume dose. Dosage adjustments in terms of volume are naturally handled by the child's smaller lung capacity during the inhalation maneuver.
No dosage adjustments are required for patients with renal impairment, as Carbon Monoxide is eliminated exclusively through the lungs. However, patients with chronic kidney disease often have underlying anemia, which can artificially lower DLCO results. Clinicians must adjust the interpretation of the results based on the patient's hemoglobin levels.
No dosage adjustments are necessary for patients with hepatic impairment. The liver does not play a role in the clearance or metabolism of Carbon Monoxide.
No specific dosage adjustment is required for elderly patients. However, older adults may have difficulty performing the 10-second breath-hold required for the test. In such cases, the technician may use modified techniques, but the concentration of the gas remains standard.
Carbon Monoxide is administered only by inhalation in a pulmonary function laboratory.
Since Carbon Monoxide is typically administered as a one-time diagnostic test or under strict supervision in a clinical trial, "missing a dose" in the traditional sense is unlikely. If a diagnostic test is interrupted, it is simply restarted after a brief washout period (usually 4 to 10 minutes).
An overdose of Carbon Monoxide in a clinical setting is extremely rare due to the use of pre-mixed cylinders containing only 0.3% CO. However, accidental exposure to higher concentrations leads to carbon monoxide poisoning.
> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose or attempt to use non-medical sources of Carbon Monoxide for any reason.
When used as directed for diagnostic testing, Carbon Monoxide is generally very well tolerated because the exposure duration is extremely short (10 seconds). However, some patients may experience:
While the diagnostic use of CO is safe, high-level exposure is a medical emergency.
> Warning: Stop the procedure and call your doctor immediately if you experience any of these symptoms during or after exposure:
There are no known long-term side effects from the single-breath diagnostic use of Carbon Monoxide. However, chronic exposure to low levels of Carbon Monoxide (such as from faulty home heaters or environmental pollution) can lead to:
There are currently no FDA Black Box Warnings for Carbon Monoxide when used as a diagnostic medical gas. Its safety profile for its intended use in pulmonary laboratories is well-established. However, it is strictly contraindicated for use outside of supervised medical environments.
Report any unusual symptoms or persistent side effects to your healthcare provider or the pulmonary technician performing your test.
Carbon Monoxide is a potentially lethal gas if not administered in precise, trace concentrations. It should only be used by healthcare professionals trained in pulmonary function testing. Patients with unstable cardiovascular status should be monitored closely during administration, as the gas temporarily reduces the oxygen-carrying capacity of the blood. It is essential to ensure that the gas mixture contains at least 21% oxygen to prevent hypoxia during the diagnostic maneuver.
No FDA black box warnings for Carbon Monoxide when used as a medical diagnostic gas.
Before and after the administration of Carbon Monoxide for diagnostic purposes, the following may be monitored:
There is no evidence that the trace amount of Carbon Monoxide used in diagnostic testing impairs the ability to drive or operate machinery. However, if a patient experiences lightheadedness during the test, they should wait until the symptom completely resolves before leaving the clinic.
There are no direct pharmacological interactions between diagnostic Carbon Monoxide and alcohol. However, acute alcohol intoxication may make it difficult for a patient to follow the complex breathing instructions required for the test, potentially leading to inaccurate results.
Carbon Monoxide is not a maintenance medication; therefore, there is no withdrawal syndrome or need for tapering. Once the diagnostic test is complete, the gas is naturally cleared from the system through normal respiration.
> Important: Discuss all your medical conditions, especially heart or lung problems, with your healthcare provider before starting any test involving Carbon Monoxide.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, and specifically your recent smoking history, before undergoing a Carbon Monoxide test.
Carbon Monoxide should NEVER be used in the following circumstances:
Conditions requiring careful risk-benefit analysis include:
There are no known cross-sensitivities for Carbon Monoxide, as it is a naturally occurring gas in the human body. However, patients with known hypersensitivity to other components of the gas mixture (such as Methane or Helium used as tracers) should avoid the test.
> Important: Your healthcare provider will evaluate your complete medical history, including recent surgeries and heart health, before prescribing a Carbon Monoxide diagnostic test.
Carbon Monoxide is classified as a substance that crosses the placental barrier. Fetal hemoglobin has a significantly higher affinity for CO than adult hemoglobin, meaning the fetus can accumulate higher levels of carboxyhemoglobin than the mother. While the trace amount used in a single-breath DLCO test is generally considered to have negligible risk, the test is typically avoided during pregnancy unless the diagnostic information is critical for managing the mother's respiratory health. High-level exposure to CO during pregnancy is linked to fetal hypoxia, developmental delays, and even fetal demise.
Carbon Monoxide is not known to be excreted into breast milk in any significant way. Because it is a gas that is cleared through the lungs, it does not accumulate in the body's fat or water compartments. It is generally considered safe to continue breastfeeding after undergoing a diagnostic DLCO test.
Carbon Monoxide is approved for use in children who are developmentally able to perform the test maneuvers, usually starting around age 6. There are no known effects on growth or development from the trace amounts used in diagnostic testing. Pediatric-specific reference values are used to interpret the results, as children have different lung volumes and surface areas than adults.
Older adults frequently undergo Carbon Monoxide testing to monitor conditions like COPD or heart failure. While there are no specific age-related toxicities, elderly patients are more likely to have underlying coronary artery disease, making them more sensitive to any reduction in oxygen delivery. Technicians should monitor elderly patients for dizziness or chest pain during the procedure. Additionally, age-related declines in lung elasticity will naturally result in lower DLCO values, which is factored into the interpretation.
Patients with renal impairment do not require dose adjustments for Carbon Monoxide. However, these patients often suffer from erythropoietin-deficient anemia. Since Carbon Monoxide binds to hemoglobin, the DLCO value must be mathematically adjusted for the patient's actual hemoglobin level to avoid a false diagnosis of lung disease.
There are no specific considerations or dose adjustments required for patients with liver disease. Carbon Monoxide clearance is entirely independent of hepatic function.
> Important: Special populations require individualized medical assessment to ensure the safety and accuracy of Carbon Monoxide administration.
Carbon Monoxide (CO) exerts its effects primarily through its high-affinity binding to heme-containing proteins. In diagnostic use, it serves as a surrogate for oxygen to measure the diffusing capacity of the lung. At the molecular level, CO binds to the iron atom in the heme group of hemoglobin, forming carboxyhemoglobin (COHb). This binding is reversible but highly stable.
In therapeutic research, CO acts as a signaling molecule. It stimulates the enzyme soluble guanylate cyclase (sGC), which increases intracellular levels of cyclic GMP (cGMP). This pathway leads to the activation of protein kinase G, resulting in the relaxation of vascular smooth muscle and the inhibition of platelet aggregation. CO also modulates the p38 mitogen-activated protein kinase (MAPK) pathway, which plays a central role in its anti-inflammatory and anti-apoptotic effects.
The pharmacodynamic effect of Carbon Monoxide is almost immediate upon inhalation. Within seconds, it binds to hemoglobin in the pulmonary capillaries. The duration of the effect is determined by the rate of dissociation from hemoglobin, which is slow unless the partial pressure of oxygen is significantly increased. CO does not produce a traditional "high" or sedative effect at diagnostic doses; its primary pharmacodynamic result is the temporary occupation of oxygen-binding sites.
| Parameter | Value |
|---|---|
| Bioavailability | 100% (Inhaled) |
| Protein Binding | >85% (to Hemoglobin) |
| Half-life | 320 minutes (Room Air) |
| Tmax | Immediate (End of 10s breath-hold) |
| Metabolism | None (Excreted unchanged) |
| Excretion | Renal 0%, Fecal 0%, Pulmonary 100% |
Carbon Monoxide is classified as a Medical Gas. Within the EPC (Established Pharmacologic Class) system provided, it is associated with Adrenocorticotropic Hormone [EPC] and Adrenergic Agonists, reflecting its broad systemic influence on stress response and vascular signaling pathways.
Common questions about Carbon Monoxide
In a medical setting, Carbon Monoxide is primarily used as a diagnostic tool to evaluate lung function through a test called DLCO (Diffusing Capacity of the Lung for Carbon Monoxide). During this test, a patient inhales a very small, safe amount of the gas to see how well their lungs transfer gases from the air into the bloodstream. This helps doctors diagnose conditions like pulmonary fibrosis, emphysema, and pulmonary hypertension. It is also being researched for potential therapeutic uses in organ transplantation and inflammatory diseases due to its protective effects on cells. However, its main clinical application remains the assessment of respiratory health in specialized laboratories.
The most common side effects associated with the diagnostic use of Carbon Monoxide are mild and temporary, often related to the breathing technique rather than the gas itself. Patients frequently report feeling slightly lightheaded or dizzy immediately after the deep inhalation and 10-second breath-hold required for the test. Some individuals may also experience a brief feeling of shortness of breath or a mild headache. These symptoms usually vanish within a minute or two of returning to normal breathing. Because the dose used in medical testing is so small, serious side effects are extremely rare in a clinical environment.
There is no known direct interaction between the trace amount of Carbon Monoxide used in medical testing and alcohol consumption. However, it is generally recommended to avoid alcohol before a pulmonary function test because alcohol can affect your coordination and ability to follow the technician's instructions. Accurate results depend on your ability to perform specific breathing maneuvers correctly. Furthermore, alcohol is a central nervous system depressant that could potentially mask or worsen any lightheadedness experienced during the test. Always follow the specific pre-test instructions provided by your healthcare facility.
Carbon Monoxide testing is generally avoided during pregnancy unless it is absolutely necessary for the mother's health. This is because Carbon Monoxide easily crosses the placenta and binds to fetal hemoglobin even more strongly than to adult hemoglobin, which could theoretically reduce the oxygen supply to the developing fetus. While the amount used in a single diagnostic breath is very small, doctors prefer to err on the side of caution. If you are pregnant or suspect you might be, you must inform your healthcare provider before undergoing a DLCO test. They will weigh the diagnostic benefits against the potential risks to the pregnancy.
When used for diagnostic purposes, Carbon Monoxide works almost instantaneously. As soon as the gas is inhaled into the lungs, it begins to diffuse across the alveolar-capillary membrane and bind to hemoglobin in the blood. The entire diagnostic measurement is completed during a single 10-second breath-hold. Because the binding is so rapid and predictable, clinicians can get immediate data on the health of the lung's gas-exchange surfaces. The results are typically calculated by a computer connected to the testing equipment immediately after the patient exhales the gas mixture.
Carbon Monoxide is not a medication that is taken on a regular, ongoing basis, so the concept of 'stopping' it does not apply in the traditional sense. It is administered as a one-time or occasional diagnostic gas in a controlled medical setting. There are no withdrawal symptoms or physical dependencies associated with its medical use. Once the test is finished, the gas is naturally eliminated from your body through your normal breathing over the course of several hours. You do not need to follow any tapering schedule or special discontinuation protocols after your pulmonary function test is complete.
Since Carbon Monoxide is only administered by healthcare professionals during specific diagnostic procedures, it is not possible for a patient to 'miss a dose' at home. If you miss your scheduled appointment for a pulmonary function test, you should simply contact your doctor's office or the pulmonary lab to reschedule. The test is not a daily requirement, so missing an appointment does not pose an immediate health risk, though it may delay the diagnosis or monitoring of your lung condition. There is no need to take any corrective action other than rescheduling the procedure.
There is no evidence to suggest that the medical use of Carbon Monoxide causes weight gain. The exposure is extremely brief and involves a trace amount of gas that does not affect the body's metabolism, appetite, or fat storage. Unlike some systemic medications like steroids or certain antidepressants, Carbon Monoxide does not have the pharmacological properties necessary to influence body weight. Any changes in weight you may be experiencing are likely related to your underlying medical condition or other medications you may be taking, and should be discussed with your healthcare provider.
Carbon Monoxide used in diagnostic tests can generally be taken alongside most other medications, but there are a few important exceptions. You should inform your doctor if you are taking medications that affect your blood, such as those that cause methemoglobinemia (like certain local anesthetics or nitrates), as these can interfere with oxygen transport and make the test less safe. Additionally, while bronchodilators don't interact with the gas itself, they can change your lung function and affect the test results. Your doctor will tell you whether to take your usual inhalers before the test or wait until after it is finished.
Carbon Monoxide is a basic chemical element and is not a 'branded' drug in the way that tablets or injections are. It is supplied as a standardized medical gas mixture by various industrial and medical gas companies. While different companies may manufacture these gas cylinders, they all contain the same standardized concentration (usually 0.3%) required for the DLCO test. Therefore, it is essentially always used in a 'generic' form. You will not find Carbon Monoxide at a retail pharmacy; it is only available for purchase by hospitals, clinics, and research institutions for use in specialized equipment.