According to the FDA-approved labeling, Histamine Phosphate is the gold standard positive control for evaluating the validity of skin prick tests (2024).
A study published in the Journal of Allergy and Clinical Immunology found that Histamine skin reactivity is significantly reduced in patients taking second-generation antihistamines for up to 7 days (2022).
The American Academy of Allergy, Asthma & Immunology (AAAAI) states that a wheal of at least 3mm greater than the negative control is required for a positive histamine response (2023).
Data from PubChem indicates that the plasma half-life of histamine is less than 5 minutes due to rapid metabolism by HNMT and DAO enzymes (2024).
The World Health Organization (WHO) recognizes histamine as a critical diagnostic agent for assessing gastric secretory function, although its use is declining in favor of safer alternatives (2021).
Clinical guidelines from the British Society for Allergy and Clinical Immunology (BSACI) emphasize that epinephrine must be immediately available whenever histamine is administered (2023).
Research in the Annals of Allergy, Asthma & Immunology confirms that skin reactivity to histamine can be lower in infants and elderly patients compared to young adults (2022).
According to DailyMed, Histamine Phosphate solutions must be stored between 2°C and 8°C to maintain diagnostic potency (2024).
This page is for informational purposes only and does not replace medical advice. Before using any prescription or over-the-counter medication for Histamine Positive, you must consult a qualified healthcare professional.
Clinical Information
Detailed information about Histamine Positive
ℹ️Overview
Histamine Phosphate is a diagnostic pharmaceutical agent primarily used as a positive control in skin allergy testing and as a gastric acid stimulant. It belongs to the class of non-standardized allergenic extracts and serves as a physiological marker for various diagnostic procedures.
💊Usage & Dosage
Adult Dosage
The dosage of Histamine Phosphate is highly specialized and depends entirely on the diagnostic procedure being performed.
Skin Prick Testing (Allergy Control): Healthcare providers typically use a single drop of a 1 mg/mL or 10 mg/mL solution. A lancet is used to prick the skin through the drop. The result is read exactly 15 minutes later.
Intradermal Testing: If a skin prick test is inconclusive, a doctor may inject a much more dilute solution (usually 0.01 to 0.1 mg/mL) into the top layer of the skin. The volume is typically very small, around 0.02 mL, to create a tiny bleb.
Gastric Secretion Test: Historically, a dose of 0.01 mg to 0.04 mg per kilogram of body weight was administered subcutaneously. This is rarely done today due to the availability of pentagastrin and other safer alternatives.
Bronchial Challenge: Doses start extremely low (e.g., 0.03 mg/mL) and are doubled at set intervals until a 20% drop in lung function (FEV1) is observed or the maximum dose is reached.
Pediatric Dosage
Histamine Phosphate is used in children for allergy testing, but the procedure requires even greater care.
Allergy Testing (Skin Prick): The procedure is similar to adults, but healthcare providers often limit the number of tests performed at once to minimize discomfort and the risk of systemic absorption.
Intradermal Testing: Generally avoided in very young children unless absolutely necessary, as it is more painful and carries a higher risk of systemic reactions.
Safety Note: Histamine Phosphate has not been extensively studied for therapeutic use in children; its use is strictly limited to diagnostic contexts under the supervision of a pediatric allergist.
Dosage Adjustments
Renal Impairment
Since histamine metabolites are cleared through the kidneys, patients with severe renal failure may experience a slightly prolonged systemic effect if large doses are used. However, for standard skin testing, no specific dosage adjustment is usually required.
Hepatic Impairment
The liver plays a role in the methylation of histamine. While no formal guidelines exist for dosage adjustment in liver disease, healthcare providers should exercise caution in patients with advanced cirrhosis if systemic administration is planned.
Elderly Patients
Elderly patients may be more sensitive to the cardiovascular effects of histamine, such as rapid heart rate (tachycardia) or changes in blood pressure. Lower concentrations may be used initially during provocative testing to ensure safety.
How Histamine is Administered
Histamine Phosphate is never self-administered. It is always given by a trained medical professional.
1Preparation: The skin (usually the forearm or back) is cleaned with alcohol and allowed to dry.
2Application: For skin prick testing, a drop is placed on the skin, and a sterile device is used to gently puncture the epidermis.
3Observation: The patient must remain in the clinic for at least 20 to 30 minutes after administration. The healthcare provider will measure the 'wheal' (the raised bump) and the 'flare' (the surrounding redness) using a millimeter ruler.
4Storage: Vials should be stored in a refrigerator at 2°C to 8°C (36°F to 46°F) and protected from light. If the solution becomes discolored or contains particles, it must be discarded.
Missed Dose
As Histamine Phosphate is used for one-time diagnostic procedures, a 'missed dose' is not applicable in the traditional sense. If a diagnostic test is interrupted or a dose is not administered correctly, the healthcare provider will determine when it is safe to repeat the procedure, usually after the skin has returned to its baseline state (often 24 to 48 hours).
Overdose
An overdose of histamine is a medical emergency and can lead to systemic 'histamine poisoning.'
Signs of Overdose: Intense flushing, severe headache, dizziness, rapid heartbeat (tachycardia), sudden drop in blood pressure (hypotension), abdominal cramps, vomiting, and difficulty breathing (bronchospasm).
Emergency Measures: The immediate treatment for a systemic histamine reaction is the administration of epinephrine (adrenaline). Healthcare providers will also use antihistamines (H1 and H2 blockers) and intravenous fluids to stabilize blood pressure. Oxygen may be administered if the patient is experiencing respiratory distress.
> Important: Follow your healthcare provider's instructions. Do not attempt to use any histamine-containing products without direct medical supervision.
⚠️Side Effects
Common Side Effects (>1 in 10)
Because Histamine Phosphate is designed to cause a reaction, 'side effects' at the site of administration are actually the intended result in most diagnostic cases. However, they can still be uncomfortable.
Local Pruritus (Itching): Almost all patients will experience intense itching at the site of the skin test. This typically peaks at 15 minutes and fades within an hour.
Wheal and Flare: A raised, pale bump (wheal) surrounded by a red area (flare) is expected. This can sometimes be large (20-30mm) and may feel warm to the touch.
Local Tenderness: The area may remain slightly sensitive for several hours after the test.
Less Common Side Effects (1 in 100 to 1 in 10)
These effects occur when a small amount of histamine enters the general circulation or when a patient is particularly sensitive.
🔴Warnings
Important Safety Information
Histamine Phosphate is a potent bioactive substance. Its use is strictly diagnostic and must be confined to clinical environments where patients can be monitored. The primary safety concern is the transition from a localized skin reaction to a systemic reaction. Patients must be informed that the test involves the intentional induction of a localized allergic-type response.
Black Box Warnings
No FDA black box warnings for Histamine Phosphate. However, it is considered a high-alert medication in many clinical settings due to its potential to induce rapid cardiovascular and respiratory changes.
Major Precautions
Anaphylaxis Risk: While rare during skin prick testing, systemic absorption can lead to anaphylaxis. This risk is higher with intradermal testing or gastric function testing. Facilities must have an 'anaphylaxis kit' (including epinephrine, oxygen, and IV fluids) ready at all times.
🔄Interactions
Contraindicated Combinations (Do Not Use Together)
There are few absolute contraindications for drug combinations because histamine is used diagnostically, but certain drugs make the test dangerous or useless:
Non-Selective Beta-Blockers (e.g., Propranolol): These are highly problematic. If a patient on a beta-blocker has a severe reaction to histamine, the beta-blocker may prevent epinephrine (the life-saving treatment) from working effectively. This can make a systemic reaction much more difficult to treat.
MAO Isocarboxazid, Phenelzine): Monoamine oxidase inhibitors interfere with the breakdown of histamine. This can lead to exaggerated and prolonged responses, including dangerous spikes in blood pressure or severe headaches.
Serious Interactions (Monitor Closely)
Tricyclic Antidepressants (TCAs): Drugs like Amitriptyline have potent antihistamine properties. They can completely suppress the skin's reaction to histamine, leading to a 'false negative' control and invalidating the entire allergy test.
🚫Contraindications
Absolute Contraindications
Histamine Phosphate must NEVER be used in the following circumstances:
1Known Hypersensitivity to Histamine: If a patient has previously had a severe systemic reaction to Histamine Phosphate, they must not be re-exposed.
2Severe, Uncontrolled Asthma: Because histamine is a potent trigger for bronchospasm, using it in a patient who is already struggling to breathe or who has a very low FEV1 (lung function) is extremely dangerous.
3Recent Myocardial Infarction (Heart Attack): Within the last 3-6 months. The cardiovascular stress of a potential histamine reaction could trigger another cardiac event.
4
👥Special Populations
Pregnancy
Histamine Phosphate is classified as FDA Pregnancy Category C. This means there are no adequate, well-controlled studies in pregnant women.
Risks: The primary concern during pregnancy is the risk of a systemic reaction (anaphylaxis), which could cause maternal hypotension and subsequent fetal hypoxia (lack of oxygen to the baby).
Clinical Use: Allergy skin testing is generally postponed until after delivery unless the allergy being tested for is life-threatening and requires immediate diagnosis for management during pregnancy.
Breastfeeding
It is not known whether exogenous Histamine Phosphate is excreted in human milk. However, because the half-life of histamine is extremely short (minutes), it is highly unlikely that any significant amount would reach the infant through breastfeeding.
🧬Pharmacology
Mechanism of Action
Histamine Phosphate is a direct-acting H1 and H2 receptor agonist.
H1 Receptor Activation: This is the primary mechanism for diagnostic skin testing. Activation of H1 receptors on vascular endothelial cells triggers the release of nitric oxide and prostacyclin, leading to vasodilation. It also causes the contraction of endothelial cells, creating gaps that allow fluid to leak into the extravascular space, forming a wheal. Furthermore, histamine stimulates sensory nerve endings (C-fibers), causing the 'flare' (redness) through an axonal reflex and producing the sensation of itching.
H2 Receptor Activation: In the stomach, histamine binds to H2 receptors on the basolateral membrane of parietal cells. This activates adenylate cyclase, increasing intracellular cAMP, which in turn activates the proton pump (H+/K+ ATPase) to secrete hydrochloric acid into the stomach lumen.
Pharmacodynamics
Frequently Asked Questions
Common questions about Histamine Positive
What is Histamine used for in a medical setting?
In a clinical setting, Histamine Phosphate is primarily used as a diagnostic tool rather than a treatment. Its most common use is as a 'positive control' during allergy skin testing to ensure that the patient's skin is capable of reacting to allergens. It is also used in specialized tests to measure the stomach's ability to produce acid and to check for bronchial hyperreactivity in the lungs. Because it produces a predictable and immediate inflammatory response, it allows doctors to validate other test results. It is never used by patients at home and is always administered by healthcare professionals in a controlled environment.
What are the most common side effects of a histamine skin test?
The most common side effects of a histamine skin test are localized itching, redness, and swelling at the site of the test. These are actually the intended effects of the drug, as they prove the test is working correctly. Most patients experience an intense 'itchy' sensation that peaks about 15 minutes after the test is applied. A small, raised bump called a wheal will form, surrounded by a larger red area called a flare. These symptoms are temporary and usually disappear completely within 30 to 60 minutes without any treatment. Occasionally, a patient may feel a brief flush of warmth or a mild headache if a small amount of the drug enters the bloodstream.
Can I drink alcohol while taking or after a histamine test?
It is generally recommended to avoid alcohol for at least 24 hours before and after a diagnostic histamine test. Alcohol is a vasodilator, meaning it widens blood vessels, which can mimic or enhance the effects of histamine. Drinking alcohol before a test might lead to an exaggerated skin reaction or increase the risk of a 'histamine headache' and facial flushing. Furthermore, if you experience a rare systemic reaction to the test, alcohol in your system could complicate the medical management of your symptoms. Always follow the specific pre-test instructions provided by your allergist or diagnostic center.
Is Histamine safe during pregnancy?
Histamine Phosphate is classified as Pregnancy Category C, meaning its safety in pregnant women has not been established through rigorous clinical trials. The main concern is not the drug itself, but the potential for a systemic allergic-type reaction (anaphylaxis) which could lower the mother's blood pressure and reduce oxygen flow to the baby. Because of this, most doctors recommend postponing elective allergy skin testing until after the baby is born. If the test is absolutely necessary for managing a life-threatening condition, it may be performed with extreme caution. Always discuss the risks and benefits with your obstetrician and allergist before proceeding.
How long does it take for Histamine to work?
Histamine works remarkably fast when applied to the skin or injected. In a skin prick test, the initial redness and itching usually begin within 3 to 5 minutes of application. The reaction continues to grow and reaches its maximum size (peak effect) at exactly 15 minutes, which is when the healthcare provider will measure the result. If used for a gastric function test, the stimulation of stomach acid begins within minutes of a subcutaneous injection. Because the body has very efficient enzymes to break down histamine, the systemic effects are very short-lived, usually lasting less than 5 to 10 minutes in the blood.
Can I stop taking Histamine suddenly?
The concept of 'stopping' Histamine suddenly does not apply because it is not a chronic medication that you take daily. It is administered as a single dose during a diagnostic procedure by a healthcare professional. There is no risk of withdrawal symptoms or 'rebound' effects after the procedure is finished. The drug is cleared from your system by your body's natural enzymes (DAO and HNMT) within minutes to hours. If you are having a series of tests and decide you do not want to continue, you can stop the procedure at any time, but you should discuss the implications for your diagnosis with your doctor.
What should I do if I miss a dose of Histamine?
Since Histamine is given only by healthcare providers during specific medical tests, you cannot 'miss a dose' in the way you might miss a daily pill. If you miss your appointment for the diagnostic test, you simply need to reschedule it. If a healthcare provider fails to administer the histamine control correctly during an allergy test, they will usually wait until the skin has returned to normal (often 24 hours) before attempting the test again. There are no health consequences to missing a diagnostic dose, other than a delay in receiving your test results.
Does Histamine cause weight gain?
No, Histamine Phosphate used in diagnostic testing does not cause weight gain. Weight gain is typically a side effect of medications taken over a long period, such as certain steroids or chronic antidepressants. Because Histamine Phosphate is administered in a tiny, single dose for diagnostic purposes and is cleared from the body almost immediately, it has no impact on metabolism, appetite, or fat storage. If you are experiencing weight gain, it is unrelated to a diagnostic histamine test and should be discussed with your primary care physician to find the actual cause.
Can Histamine be taken with other medications?
Histamine can interact with many other medications, which is why your doctor needs a full list of what you take. The most important interactions are with antihistamines (like Benadryl, Zyrtec, or Claritin), which will block the test from working and give a false result. Other drugs, like tricyclic antidepressants and certain heartburn medications, can also dampen the response. Most critically, beta-blockers can make it dangerous to receive histamine because they interfere with the medications used to treat a severe reaction. You will typically be asked to stop certain medications for 3 to 7 days before a histamine-based diagnostic test.
Is Histamine available as a generic?
Histamine Phosphate is a long-established chemical entity and is available as a generic diagnostic solution. It is not a 'brand name' drug in the way that many modern prescriptions are. Various manufacturers produce Histamine Phosphate injection and skin test solutions for use in hospitals and clinics. Because it is a specialized diagnostic agent and not a retail prescription drug, patients do not typically 'buy' it at a pharmacy; instead, the cost is usually included as part of the diagnostic procedure performed at the doctor's office or hospital.
Similar Medications
Other drugs with the same active ingredient (Histamine)
Flushing: A sudden feeling of warmth and redness in the face, neck, or upper chest.
Headache: A brief, throbbing headache (often called a 'histamine headache') caused by the dilation of blood vessels in the brain.
Dizziness: A mild feeling of lightheadedness, usually lasting only a few minutes.
Nausea: Some patients may feel a brief upset stomach, especially if the drug was administered for a gastric function test.
Rare Side Effects (less than 1 in 100)
Tachycardia: A noticeable racing or pounding heart.
Hypotension: A temporary drop in blood pressure that may cause the patient to feel faint.
Urticaria (Hives): Hives appearing in areas away from the injection site, indicating a mild systemic allergic-like reaction.
Dyspnea: Mild shortness of breath or a feeling of chest tightness.
Serious Side Effects — Seek Immediate Medical Attention
> Warning: Stop the procedure and alert medical staff immediately if you experience any of the following during or after a histamine test.
Anaphylaxis: This is a severe, life-threatening systemic reaction. Symptoms include a sudden feeling of doom, swelling of the lips/tongue/throat, extreme difficulty breathing, and fainting.
Severe Bronchospasm: Intense wheezing or inability to catch one's breath, particularly in patients with a history of asthma.
Cardiac Arrhythmia: Irregular heartbeats or severe chest pain.
Seizures: Though extremely rare, high systemic levels of histamine can lower the seizure threshold in susceptible individuals.
Profuse Vomiting or Diarrhea: Indicating severe systemic involvement and potential shock.
Long-Term Side Effects
Histamine Phosphate is not used for long-term therapy, so chronic side effects are not well-documented. However, repeated skin testing in the same area can lead to:
Skin Sensitization: Very rarely, the skin may become hyper-reactive to any touch or minor irritation in the area where testing was performed.
Pigmentation Changes: In rare cases, a small area of hyperpigmentation (darkening of the skin) may remain at the site of a very strong wheal and flare reaction for several weeks.
Black Box Warnings
There are currently no formal FDA Black Box Warnings for Histamine Phosphate when used as a diagnostic agent. However, the product labeling carries significant 'Precautions' and 'Warnings' regarding the risk of severe bronchial constriction in asthmatic patients and the necessity of having emergency resuscitation equipment available during use.
Report any unusual symptoms or persistent skin changes to your healthcare provider. If you feel unwell after leaving the clinic, contact your doctor or seek emergency care immediately.
Asthma and Respiratory Disease: Histamine is a potent bronchoconstrictor. In patients with unstable asthma or significantly reduced lung function, even a small amount of histamine can trigger a severe asthma attack. Healthcare providers will often perform a baseline lung function test (spirometry) before using histamine.
Cardiovascular Disease: Histamine causes vasodilation and can increase heart rate. Patients with a recent heart attack (myocardial infarction), unstable angina, or severe high blood pressure (hypertension) are at increased risk for cardiac complications during testing.
Peptic Ulcer Disease: Because histamine stimulates gastric acid secretion, it can exacerbate existing stomach ulcers or cause bleeding in patients with a history of severe acid-related disorders.
Monitoring Requirements
During and after the administration of Histamine Phosphate, the following monitoring is typically required:
Visual Observation: A nurse or doctor must observe the patient for signs of systemic flushing, hives, or respiratory distress for at least 20 minutes.
Vital Signs: In systemic testing (like gastric function), blood pressure and heart rate should be monitored at regular intervals.
Lung Auscultation: If a patient reports chest tightness, the doctor will listen to the lungs for wheezing.
Measurement of Reaction: The diameter of the wheal and flare must be accurately recorded in the medical record to provide a baseline for other tests.
Driving and Operating Machinery
Most patients can drive themselves home after a skin prick test, provided they have stayed for the observation period and feel completely normal. However, if a patient experiences dizziness, a headache, or received systemic treatment for a reaction, they should not drive or operate heavy machinery until all symptoms have completely resolved.
Alcohol Use
Alcohol can act as a vasodilator and may enhance the effects of histamine. Patients are generally advised to avoid alcohol for 24 hours before and after diagnostic histamine testing to ensure the accuracy of the results and minimize the risk of flushing or headaches.
Discontinuation
As this is a single-use diagnostic, 'discontinuation' refers to stopping a procedure in progress. If a patient shows any sign of a systemic reaction, the test is immediately stopped, the site is cleaned, and treatment is administered. There is no withdrawal syndrome associated with Histamine Phosphate.
> Important: Discuss all your medical conditions, especially heart or lung problems, with your healthcare provider before starting Histamine testing.
H1-Antihistamines: Common medications like Cetirizine (Zyrtec), Loratadine (Claritin), and Diphenhydramine (Benadryl) must be stopped several days before testing. If not stopped, they will block the H1 receptors, and the histamine control will not work.
H2-Antihistamines: Drugs like Famotidine (Pepcid) can interfere with gastric function testing and may slightly dampen the skin's flare response.
Moderate Interactions
Corticosteroids: While short-term systemic steroids (like Prednisone) have a minimal effect on the immediate skin prick reaction, long-term use or high-dose topical steroids at the test site can thin the skin and alter the inflammatory response.
Phenothiazines: Some antipsychotic medications have antihistamine effects and can interfere with the diagnostic accuracy of the test.
Food Interactions
High-Histamine Foods: Consuming foods very high in histamine (aged cheeses, fermented meats, red wine, sauerkraut) immediately before a test might theoretically increase the baseline 'histamine load,' though this is rarely clinically significant for skin testing.
Caffeine: May slightly increase heart rate, which could be confused with a systemic reaction to histamine.
Herbal/Supplement Interactions
Quercetin: This supplement is often used as a natural antihistamine and may dampen the response to Histamine Phosphate.
St. John's Wort: May interact with the metabolism of various drugs used during the procedure or the management of reactions.
Lab Test Interactions
Histamine Phosphate administration is intended to create a 'lab result' (the wheal and flare). However, it does not typically interfere with standard blood work (like CBC or metabolic panels) unless a severe systemic reaction occurs, which might cause a temporary rise in white blood cell counts or blood glucose due to stress.
For each major interaction, the mechanism is usually pharmacodynamic (blocking the receptor the drug needs to hit) or metabolic (slowing the breakdown of the drug). The clinical consequence is usually a false negative test result or an increased risk of toxicity.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, especially those for allergies, depression, or blood pressure.
Severe Hypotension (Low Blood Pressure)
: Since histamine causes vasodilation and further lowers blood pressure, it can lead to circulatory collapse in patients who are already hypotensive.
5Pheochromocytoma: In patients with this adrenal tumor, histamine can cause a massive release of catecholamines (adrenaline), leading to a life-threatening hypertensive crisis.
Relative Contraindications
In these cases, the healthcare provider must weigh the diagnostic benefit against the potential risks:
Pregnancy: Use only if the diagnostic information is essential and cannot wait until after delivery.
Active Peptic Ulcer Disease: Risk of stimulating excessive acid and causing a bleed.
Compensated Cardiovascular Disease: Patients with stable angina or controlled hypertension require extra monitoring.
Vasomotor Instability: Patients prone to fainting or significant fluctuations in vascular tone.
Cross-Sensitivity
There is no significant cross-sensitivity between histamine and other common drugs, as histamine is a naturally occurring molecule in the body. However, patients who are highly sensitive to sulfites should be checked, as some older formulations of histamine or related diagnostic agents may have contained sulfite preservatives.
> Important: Your healthcare provider will evaluate your complete medical history, especially your heart and lung health, before prescribing Histamine.
Recommendation: Most healthcare providers suggest that breastfeeding can be resumed shortly after a skin test, once any local or mild systemic symptoms in the mother have resolved.
Pediatric Use
Histamine Phosphate is widely used in children as a positive control for allergy testing.
Approved Use: It is safe for use in infants and children when performed by a specialist.
Special Considerations: Children have thinner skin and may show larger reactions than adults. They are also more likely to be distressed by the itching. Healthcare providers often use more dilute solutions or fewer test sites in very young children.
Growth Effects: There are no known effects on growth or development from diagnostic use.
Geriatric Use
Patients over the age of 65 may have different responses to Histamine Phosphate.
Skin Reactivity: Skin becomes less reactive with age (atrophy of mast cells and reduced vascular response), which may result in smaller wheal and flare sizes. This must be accounted for when interpreting the test.
Cardiovascular Sensitivity: Older adults are at higher risk for tachycardia or lightheadedness if systemic absorption occurs.
Renal Function: Reduced kidney function in the elderly may slightly slow the clearance of histamine metabolites.
Renal Impairment
While the kidneys are the primary route for excreting histamine metabolites, no specific dosage adjustments are required for standard skin testing. In the rare case of systemic diagnostic testing, patients with a GFR < 30 mL/min should be monitored more closely for prolonged flushing or headache.
Hepatic Impairment
In patients with severe liver failure (Child-Pugh Class C), the methylation of histamine may be impaired. These patients should be monitored for signs of increased histamine sensitivity, although diagnostic skin testing is generally considered safe.
> Important: Special populations require individualized medical assessment. Always inform your doctor if you are pregnant, nursing, or have chronic kidney or liver issues.
Onset of Action: For skin testing, the onset is almost immediate. The wheal begins to form within 3-5 minutes.
Peak Effect: The maximum size of the wheal and flare reaction typically occurs at 15 minutes.
Duration of Effect: The local reaction usually subsides within 30 to 60 minutes. Systemic effects, if they occur, are generally very brief (5-10 minutes) due to rapid enzymatic degradation.
Pharmacokinetics
| Parameter | Value |
|---|---|
| Bioavailability | High (local/subcutaneous); Low (oral due to first-pass) |
| Protein Binding | Minimal (<10%) |
| Half-life | < 5 minutes (plasma) |
| Tmax | 15 minutes (local skin reaction) |
| Metabolism | HNMT (primary) and Diamine Oxidase (DAO) |
Solubility: Freely soluble in water; insoluble in ether.
Structure: Consists of an imidazole ring attached to an ethylamine chain, with two phosphate groups in the salt form. It is a clear, colorless, odorless solution.
Drug Class
Histamine Phosphate is classified as an Autacoid and a Diagnostic Biological. In the Electronic Orange Book, it is often grouped under Allergenic Extracts because of its role as a standardized control for those products. It is the 'gold standard' against which the potency of other allergenic extracts and the efficacy of antihistamine medications are measured.