Trisaminomethane (Tris / Tromethamine / THAM): A Comprehensive Reference
1. Identity and Nomenclature
Chemical Names and Synonyms
Tris, or tris(hydroxymethyl)aminomethane, known during medical use as tromethamine or THAM, is an organic compound with the formula (HOCH2)3CNH2. The compound carries numerous synonyms in scientific and commercial use. These include: 2-amino-2-(hydroxymethyl)-1,3-propanediol; aminotrimethylolmethane; aminotris(hydroxymethyl)methane; THAM; tris(hydroxymethyl)methanamine; tris(hydroxymethyl)methylamine; Tris Buffer; Trisamine; and tromethamine (INCI). It is also known as trometamol, its International Nonproprietary Name (INN), and by the brand name Trizma.
Chemical Identity
Tris(hydroxymethyl)aminomethane (CAS 77-86-1) is an organic compound that exhibits buffering properties in aqueous solutions. Its chemical formula is C₄H₁₁NO₃, and its molecular structure consists of a central amino group (NH₂) bonded to three hydroxymethyl groups (CH₂OH). Chemically, it is a primary amine with three alcoholic hydroxyl groups. It appears as a white to light yellow powder to crystal at minimum purity grades.
Natural Origin and Synthesis
Trisaminomethane is not a botanical or directly plant-derived ingredient. It is a synthetically produced organic compound. Synthesis proceeds first by adding three moles of formaldehyde to nitromethane in an aldol reaction to form tris(hydroxymethyl)nitromethane; subsequently, the nitro group is reduced to the amino group. It has no established traditional herbal or botanical source.
Common Forms and Preparations
Tris, also referred to as THAM, is produced and supplied as a white crystalline powder. Multiple formulation forms exist for different applications:
- Tris base (free base): Buffer solutions are prepared by dissolving Tris base in water and adjusting the pH with acid, typically hydrochloric acid or sulfuric acid.
- Tris hydrochloride (Tris·HCl): While Tris base has a pKa of around 8.1, which allows it to function as a buffer within the pH range of 7–9, Tris HCl already contains hydrochloric acid. This lowers the pH, making Tris HCl suitable for buffering within the pH range of 7.0–8.6.
- THAM Solution (0.3 M intravenous solution): When used as a therapeutic agent, tromethamine is administered intravenously as a 0.3 M solution, commonly referred to by the brand name THAM.
- Pharmaceutical excipient forms: In the pharmaceutical industry, Tris buffer is also widely used as an excipient in injection and infusion solutions, eye drops, creams, and gels, helping to stabilize these products.
- Tromethamine salt forms: Some medications are formulated as the "tromethamine salt," including hemabate (carboprost as trometamol salt) and ketorolac trometamol.
2. Historical and Traditional Use
Trisaminomethane has no documented history of traditional botanical or ethnobotanical use. It is an entirely synthetic compound whose use history is pharmaceutical and biochemical in nature, originating in the 20th century.
THAM (trometamol; tris-hydroxymethyl aminomethane) is a biologically inert amino alcohol of low toxicity, which buffers carbon dioxide and acids in vitro and in vivo. Its clinical history as a medical agent emerged in the early 1960s. The use of 2-amino-2-hydroxymethyl-1,3-propanediol in the management of respiratory acidosis was documented in the Annals of the New York Academy of Sciences as early as 1961.
THAM has been used for the correction of acute acidosis during cardiac operations and extracorporeal circulation, cardiac arrest, and massive transfusions with ACD blood. Its use in chronic respiratory acidosis has been restricted to the acute decompensated phase and accompanied by mechanical ventilation. Other historical clinical indications include salicylate and barbiturate intoxication and the metabolic acidosis of diabetes.
It has been considered most effective when administered intravenously as a 0.3 M solution in amounts calculated to titrate excess acid in extracellular fluid. THAM can be given orally as a salt in combination with a weak acid such as citrate; in this form, it functions as a gastric antacid and also produces systemic alkalinization.
3. Key Constituents and Active Compound
Trisaminomethane is itself a single, structurally defined organic molecule rather than a complex mixture of phytochemicals. Its biological and pharmacological activity derives entirely from its molecular structure. The relevant functional properties are as follows:
Buffering Mechanism
At 37°C, the pK (the pH at which the weak conjugate acid or base in the solution is 50% ionized) of THAM is 7.8, making it a more effective buffer than bicarbonate in the physiological range of blood pH. The useful buffer range for Tris (pH 7–9) coincides with the physiological pH typical of most living organisms.
Proton-Acceptor Chemistry
THAM is a proton acceptor with a stoichiometric equivalence of titrating one proton per molecule. In vivo, THAM supplements the buffering capacity of the blood bicarbonate system, accepting a proton, generating bicarbonate, and decreasing the partial pressure of carbon dioxide in arterial blood (PaCO₂).
When administered intravenously as a 0.3 M solution, tromethamine acts as a proton acceptor and prevents or corrects acidosis by actively binding hydrogen ions (H⁺). It binds not only cations of fixed or metabolic acids, but also hydrogen ions of carbonic acid. Tromethamine also acts as an osmotic diuretic, increasing urine flow, urinary pH, and excretion of fixed acids, carbon dioxide, and electrolytes.
Membrane Penetration
THAM is non-ionic and penetrates cell membranes reducing acidosis, unlike bicarbonate, which may exacerbate intracellular acidosis. Non-ionized trometamol penetrates cell membranes and is also effective intracellularly as a buffer; this causes potassium shifts from the intra- to the extracellular space.
Reactivity with Peptides and Proteins
Tris contains a primary amine and thus undergoes reactions associated with typical amines, for example condensations with aldehydes. Tris also complexes with metal ions in solution. Tris has been reported to interfere with the activity of a number of enzymes; it should therefore be used carefully when studying proteins.
Advantage Over Sodium Bicarbonate
Tromethamine's mechanism as a proton acceptor that does not generate carbon dioxide offers a significant therapeutic advantage over sodium bicarbonate in patients with compromised respiratory function. Additionally, THAM is sodium-free and does not cause hypernatremia.
Pharmacokinetics
Trisaminomethane rapidly distributes through the extracellular space and slowly penetrates the intracellular space, except for erythrocytes and hepatocytes; it is excreted by the kidney in its protonated form at a rate that slightly exceeds creatinine clearance. THAM alkalinizes serum with an effect that persists for 16–48 hours, in contrast to shorter-acting bicarbonate. This drug is known to be substantially excreted by the kidney, and the risk of toxic reactions may be greater in patients with impaired renal function.
4. Scientific Evidence by Area of Use
4.1 Metabolic Acidosis (Primary Clinical Indication)
Tromethamine functions as an active pharmaceutical ingredient (API) in the form of an intravenous solution, commercially known as THAM. In this capacity, it is a potent, physiologically optimized alkalizing agent indicated for the prevention and correction of severe metabolic acidosis in specific, acute clinical settings such as cardiac bypass surgery and cardiac arrest.
Tromethamine (THAM or tris[hydroxymethyl]aminomethane acetate) is an FDA-approved buffer in clinical use, used to reverse metabolic acidosis.
In a clinical study examining THAM's metabolic effects, 15 patients undergoing major surgical procedures with metabolic acidosis (defined as pH <7.2 or base excess <−5 mmol/L) with indwelling arterial catheters were studied; after developing metabolic acidosis, patients were given THAM via a central vein in a dose of 1.1 × base excess × weight (kg) mL of 0.3 M solution. In this heterogeneous group of patients, THAM corrected metabolic acidosis in a predictable fashion with a fall in PaCO₂. The authors noted that there were no apparent adverse effects of THAM observed in this series.
When disturbances result in severe hypercapnic or metabolic acidemia that overwhelms the capacity of normal pH homeostatic mechanisms (pH ≤ 7.20), the use of THAM within a defined "therapeutic window" is an effective therapy. It may restore the pH of the internal milieu, thus permitting the homeostatic mechanisms of acid-base regulation to assume their normal function.
A comprehensive 1998 guidelines review published in the journal Drugs stated that in the treatment of respiratory failure, THAM has been used in conjunction with hypothermia and controlled hypercapnia; other indications include diabetic or renal acidosis, salicylate or barbiturate intoxication, and increased intracranial pressure associated with cerebral trauma.
Evidence strength: The use of tromethamine for acute metabolic acidosis is supported by FDA approval and decades of clinical experience. However, published clinical data on THAM usage is somewhat limited, and large randomized controlled trials specifically for metabolic acidosis correction are sparse in the literature.
4.2 Intracranial Pressure (ICP) Reduction and Neurological Injury
Tromethamine (THAM) is a non-CO₂-generating buffer solution that has been utilized for a variety of clinical applications including the control of intracranial pressure (ICP). Cerebral lactic acidosis after injury has been linked to edema formation and is postulated to be a major contributor to elevated intracranial pressures. Attenuation of such acidosis via non-CO₂ buffer compounds, such as THAM, can allow stability in ICP and an overall reduction in pressure. Both human and animal studies exist demonstrating the ICP reduction effects of THAM.
A literature review of the human evidence demonstrated an Oxford 2b, GRADE B level of evidence that THAM reduces ICP in traumatic brain injury (TBI) and stroke populations, with minimal adverse effects.
A systematic review published in Neurocritical Care (2014) aimed to perform a comprehensive review of the literature on the use of tromethamine and its effects on ICP in patients with neurological illness, searching all articles from MEDLINE, BIOSIS, EMBASE, Global Health, HealthStar, Scopus, Cochrane Library, and the International Clinical Trials Registry Platform through February 2014. Two reviewers independently identified all manuscripts pertaining to the administration of THAM in human patients that recorded effects on ICP. Secondary outcomes of effect on cerebral perfusion pressure, mean arterial pressure, patient outcome, and adverse effects were recorded. The review found that one study documented a reduction in cerebral perfusion pressure; no significant renal dysfunction, hepatocellular injury, or hypoglycemia were reported; and three prospective randomized controlled trials displayed trends toward improved outcome in severe neurological injury patients.
In a randomized prospective clinical trial of THAM in severe head injury, THAM was studied to determine if it had beneficial effects in early management of severe head injuries and whether adverse effects of hyperventilation could be prevented. A total of 149 patients with severe head injury (Glasgow Coma Scale scores ≤8) were randomly assigned to either a control or a THAM group. Earlier experimental evidence had shown that tromethamine was effective in treating head injury; the drug acts by entering the cerebrospinal fluid compartment, reducing cerebral acidosis and ICP, and reversing the adverse effects of prophylactic hyperventilation on early recovery.
A case series reported that two patients with aneurysmal subarachnoid hemorrhage and two with traumatic brain injury received early THAM for ICP control; the mean time to initiation of THAM therapy was 1.8 days, with a mean duration of 5.3 days. In all patients, after 6 to 12 hours of THAM administration, ICP stability was achieved, with reduction in requirements for hypertonic saline and hyperosmotic agents.
In a randomized controlled trial examining hyperventilation in TBI, patients were randomized to receive normal ventilation (PaCO₂ 35 mmHg), moderate hyperventilation (PaCO₂ 25 mmHg), or tromethamine (THAM) plus hyperventilation; hyperventilation for 5 days resulted in worse outcomes at 3–6 months. The THAM-plus-hyperventilation arm was examined as a potential mitigation strategy.
Evidence strength: The evidence for THAM in ICP control is graded at Oxford Level 2b / GRADE B, meaning it is supported by individual cohort studies, prospective controlled trials, and case series, but not by large definitive randomized trials. Clinical use is well-established in specialist neurocritical care settings.
4.3 Respiratory Acidosis and Neonatal Respiratory Distress
Tris can also be used for the treatment of metabolic acidosis and urine alkalinization in cases where the patient is intoxicated by weakly acidic substances like barbiturates. Its administration is via intravenous injection, as it has a respiratory depressant effect, making its use contraindicated in patients with respiratory insufficiency.
Regarding neonatal applications, the FDA-approved prescribing information specifies that for correction of metabolic acidosis associated with respiratory distress syndrome (RDS) in neonates and infants, the initial dose of THAM solution should be based on initial pH and birthweight, amounting to approximately 1 mL per kg for each pH unit below 7.4; further doses have been given according to changes in PaO₂, pH, and PCO₂.
In the treatment of respiratory failure, THAM has been used in conjunction with hypothermia and controlled hypercapnia.
Evidence strength: The use of THAM in neonatal acidosis associated with RDS is recognized in FDA labeling; the evidence base for this specific indication is primarily observational and based on physiological rationale rather than large dedicated randomized trials.
4.4 Cystic Fibrosis Airway Disease (Investigational)
A study published in JCI Insight (2016) investigated an inhaled application of tromethamine for cystic fibrosis (CF). Because THAM has a long half-life and prolonged buffering capacity in serum, it was hypothesized that inhaled THAM would increase airway surface liquid (ASL) pH for a longer duration than HCO₃⁻ and would enhance ASL bacterial killing. This hypothesis was tested in both pigs and humans with CF. THAM aerosols were found to increase ASL pH in vivo for at least 2 hours and to enhance airway antibacterial activity. THAM is also used as an excipient for inhaled preparations of prostacyclin and nasal preparations of ketorolac.
Evidence strength: The inhaled THAM application for CF is preliminary. The JCI Insight publication represents early translational evidence from animal models and a small human study; large randomized trials have not been completed as of the available literature.
4.5 Role as a Pharmaceutical Excipient / Salt-Forming Agent
Trisaminomethane's largest modern pharmaceutical use is as an excipient and salt-forming agent rather than as a primary therapeutic agent. One significant area where Tris buffer plays a vital role is in the pharmaceutical industry. It is frequently used as an excipient in the formulation of various medications; its buffering capabilities are particularly valuable in vaccines, where maintaining a precise pH is critical for the stability and efficacy of the biological components.
TRIS is a commonly used excipient in various approved parenteral medicinal products, including the mRNA COVID-19 vaccines produced by Pfizer/BioNTech and Moderna. According to package insert data, each dose of the Pfizer-BioNTech COVID-19 vaccine contains 0.06 mg tromethamine and 0.4 mg tromethamine hydrochloride as buffering agents. Tromethamine and tromethamine hydrochloride are ingredients called buffers, used in many vaccines including the Moderna COVID-19 vaccine. These ingredients help stabilize vaccines so they can be stored for longer at higher temperatures; with these ingredients, the Pfizer vaccines can be stored in commonly available refrigerators for longer periods, making them easier to use in clinics.
5. Body Systems and Health Areas of Association
- Acid-Base Homeostasis / Blood Chemistry: The primary therapeutic body system. In vivo, THAM supplements the buffering capacity of the blood bicarbonate system, accepting a proton, generating bicarbonate, and decreasing the partial pressure of carbon dioxide in arterial blood (PaCO₂).
- Renal System: Tromethamine acts as an osmotic diuretic, increasing urine flow, urinary pH, and excretion of fixed acids, carbon dioxide, and electrolytes.
- Central Nervous System / Intracranial Pressure: Cerebral lactic acidosis after injury has been linked to edema formation and is postulated to be a major contributor to elevated intracranial pressures. Attenuation of such acidosis via non-CO₂ buffer compounds such as THAM can allow stability in ICP and an overall reduction in pressure.
- Pulmonary System: THAM is used for respiratory acidosis correction and has been investigated for modification of airway surface liquid pH in cystic fibrosis. Its respiratory depressant effect is a documented risk in patients with compromised ventilation.
- Cardiovascular System: THAM has been used for the correction of acute acidosis during cardiac operations and extracorporeal circulation, as well as cardiac arrest.
- Electrolyte / Metabolic Balance: Non-ionized trometamol penetrates cell membranes and is also effective intracellularly as a buffer; this causes potassium shifts from the intra- to the extracellular space, and hyperkalemia as well as secondary hypokalemia may occur initially.
6. Dosage Forms and Reported Dosages
Intravenous Therapeutic Use (THAM Solution)
The initial loading dose of THAM acetate 0.3 mol/L in the treatment of acidemia may be estimated as follows: THAM (mL of 0.3 mol/L solution) = lean body weight (kg) × base deficit (mmol/L). The maximum daily dose is 15 mmol/kg for an adult (3.5 L of a 0.3 mol/L solution in a 70 kg patient).
Per the FDA-approved prescribing information, the dosing formula for intravenous use is: tromethamine solution (mL of 0.3 M) required = body weight (kg) × base deficit (mEq/L) × 1.1, given by IV infusion; the dose should be limited to the amount sufficient to increase blood pH to near normal limits (~7.35) and to correct metabolic acidosis.
For neonatal RDS applications, the FDA label states that the initial dose should be based on initial pH and birthweight, amounting to approximately 1 mL per kg for each pH unit below 7.4.
Because clinical experience has been limited generally to short-term use, the drug should not be administered for more than a period of one day except in a life-threatening situation.
Route of Administration
Tromethamine is given by slow intravenous infusion, by addition to pump-oxygenator ACD blood or other priming fluid, or by injection into the ventricular cavity during cardiac arrest. If infused into a peripheral vein, a large needle in the largest antecubital vein or an indwelling catheter placed in a large vein of an elevated limb is used to minimize chemical irritation of the alkaline solution; catheters are recommended.
Oral Antacid Form
THAM can be given orally as a salt in combination with a weak acid such as citrate; in this form it acts as a gastric antacid and will also produce systemic alkalinization.
Excipient Quantities in Vaccines
In the Pfizer-BioNTech COVID-19 vaccine (Comirnaty) pediatric formulation, each 0.2 mL dose contains tromethamine at 0.006 mg and tromethamine hydrochloride at 0.04 mg. In the standard adult 0.3 mL dose, each dose contains tromethamine at 0.06 mg and tromethamine hydrochloride at 0.4 mg.
7. Safety Considerations and Interactions
General Toxicity Profile
THAM is a biologically inert amino alcohol of low toxicity when used at appropriate concentrations and routes. Generally, side effects have been infrequent. Although the incidence of ventilatory depression is low, it is important to keep in mind that such depression may occur. Respiratory depression may be more likely to occur in patients who have chronic hypoventilation or those who have been treated with drugs that depress respiration.
Respiratory Depression
In patients with associated respiratory acidosis, tromethamine should be administered with mechanical assistance to ventilation. THAM solution is contraindicated in uremia and anuria. In neonates, it is also contraindicated in chronic respiratory acidosis and salicylate intoxication.
Hypoglycemia Risk
Overdosage in terms of total drug and/or too rapid administration may cause hypoglycemia of a prolonged duration (several hours); therefore, frequent blood glucose determinations should be made during and after therapy.
Hyperkalemia and Renal Considerations
Extreme care should be exercised in patients with renal disease or reduced urinary output because of potential hyperkalemia and the possibility of a decreased excretion of tromethamine. In such patients, the drug should be used cautiously with electrocardiographic monitoring and frequent serum potassium determinations.
Vascular and Local Tissue Effects
Extreme care should be taken to avoid perivascular infiltration. At high alkaline pH, animal studies have documented serious local effects: intravenous toxicity of tromethamine was minimal at neutral pH; however, at a more alkaline pH range, gangrene at the injection sites, tissue necrosis, inflammatory lesions, visible infarcts in the kidneys, bleached liver, darkened spleen, and lesions on the heart were reported, as well as anorexia, bloody urine, and paralysis. These findings were from animal toxicology studies at alkaline pH conditions not representative of properly buffered clinical use.
Electrolyte Overload
The intravenous administration of tromethamine injection can cause fluid and/or solute overloading resulting in dilution of serum electrolyte concentrations, overhydration, congested states, or pulmonary edema.
Elderly Patients and Renal Impairment
This drug is known to be substantially excreted by the kidney, and the risk of toxic reactions may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function.
Reproductive Toxicology (Animal Data)
There were no adverse effects on reproduction at 100 mg/kg/day to rats. However, there were increased resorptions, post-implantation loss, and decreased litter size starting at 300 mg/kg/day. When tromethamine (2500 mg/kg) was orally administered to rats for 15 days, there were no mortalities or clinical signs observed; upon oral administration (250–4000 mg/kg) to male rats for 31 days, there were no mortalities or clinical signs observed except for moderate diarrhea at the highest dose.
Mutagenicity
Tromethamine was toxic, but not mutagenic, to E. coli in an RK assay.
No-Observed-Adverse-Effect Level (NOAEL)
The NOAEL for local toxicity was 100 mg/kg/d and for systemic toxicity was ≥1000 mg/kg/d for rats administered tromethamine (100, 300, 1000 mg/kg/d adjusted to pH 9) by gavage in a reproduction study. The reported NOAEL for repeated oral intake of Tris is 4000 mg/kg body weight.
Enzyme Interference
Caution is necessary when studying some proteins, as Tris has the potential to interfere with the activity of certain enzymes. In addition, Tris may form Schiff bases with aldehydes and ketones, which is relevant to its compatibility with other pharmaceutical ingredients and assay conditions.
Cosmetic Safety Assessment
The Cosmetic Ingredient Review (CIR) Expert Panel reviewed the safety of tromethamine, aminomethyl propanediol, and aminoethyl propanediol as used in cosmetics. All three ingredients are reported to be safe for use in cosmetic formulations at concentrations used in practice, based on their comprehensive safety review.
References
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