THAM As an Alternative Buffer
Tham Description
Tham Solution (tromeThamine injection) is a sterile, non-pyrogenic 0.3 M solution of tromeThamine, adjusted to a pH of approximately 8.6 with glacial acetic acid. It is administered by intravenous injection, by addition to ACD blood for priming cardiac bypass equipment and by injection into the ventricular cavity during cardiac arrest.
Each 100 mL contains tromeThamine 3.6 g (30 mEq) in water for injection. The solution is hypertonic 389 mOsmol/L (calc.). pH 8.6 (8.4-8.7).
The solution contains no bacteriostat, antimicrobial agent or added buffer (except acetic acid for pH adjustment) and is intended only for use as a single-dose injection. When smaller doses are required the unused portion should be discarded.
Tham solution is a parenteral systemic alkalizer and fluid replenisher.
TromeThamine, USP (sometimes called “tris” or “tris buffer”) is chemically designated 2-amino-2-(hydroxymethyl)-1, 3-propanediol, a solid readily soluble in water, also classified as an organic amine buffer. It has the following structural formula:
Water for Injection, USP is chemically designated H20.
Tham – Clinical Pharmacology
When administered intravenously as a 0.3 M solution, tromeThamine act 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, thus increasing bicarbonate anion (HCO3‾). TromeThamine also acts as an osmotic diuretic, increasing urine flow, urinary pH, and excretion of fixed acids, carbon dioxide and electrolytes. A significant fraction of tromeThamine (30% at pH 7.40) is not ionized and therefore is capable of reaching equilibrium in total body water. This portion may penetrate cells and may neutralize acidic ions of the intracellular fluid.
The drug is rapidly eliminated by the kidney; 75% or more appears in the urine after eight hours. Urinary excretion continues over a period of three days.
Water is an essential constituent of all body tissues and accounts for approximately 70% of total body weight. Average normal adult daily requirement ranges from two to three liters (1.0 to 1.5 liters each for insensible water loss by perspiration and urine production).
Water balance is maintained by various regulatory mechanisms. Water distribution depends primarily on the concentration of electrolytes in the body compartments and sodium (Na+) plays a major role in maintaining physiologic equilibrium.
LITERATURE:
Sodium bicarbonate versus THAM in ICU patients with mild metabolic acidosis.
Background:
Sodium bicarbonate is despite its side effects, considered the standard alkali therapy in metabolic acidosis. THAM is an alternative alkalizing agent; however, there are limited data on the use of THAM in metabolic acidosis. The aim of this study was to compare the efficacy and adverse effects of a single dose of sodium bicarbonate and THAM in intensive care unit (ICU) patients with mild metabolic acidosis.
Methods:
18 adult ICU patients with mild metabolic acidosis (serum bicarbonate < 20 mmol/L) were randomized to a single dose of either sodium bicarbonate or THAM, administered over a 1-hour period, and titrated to buffer the excess of acid load.
Results:
Sodium bicarbonate and THAM had equivalent alkalinizing effect during the infusion period. This was still present 4 hours after start of infusion of sodium bicarbonate, and until 3 hours after start of infusion of THAM. Serum potassium levels decreased after sodium bicarbonate infusion, and remained unchanged after THAM. After sodium bicarbonate, sodium increased, and after THAM, serum sodium decreased.
Conclusions:
Sodium bicarbonate and THAM had a similar alkalinizing effect in patients with mild metabolic acidosis; however, the effect of sodium bicarbonate was longer lasting. Sodium bicarbonate did decrease serum potassium, and THAM did not; THAM is therefore not recommended in patient with hyperkalemia. As sodium bicarbonate leads to an increase of serum sodium and THAM to a decrease, THAM may be the alkalinizing agent of choice in patients with hypernatremia. Similarly, because sodium bicarbonate increases PaCO2 and THAM may even decrease PaCO2, sodium bicarbonate is contraindicated and THAM preferred in patients with mixed acidosis with high PaCO2 levels.
- PMID:
- 16013019
- [PubMed – indexed for MEDLINE]
Pharmacology & Dosing
Source Article:
More on Acid–Base Disorders
N Engl J Med 1998; 339:1005-1006, October 1, 1998
- THAM is a biologically inert amino alcohol of low toxicity that buffers carbon dioxide and acids in vitro and in vivo. At 37°C, the pKa (the negative logarithm of the acid ionization constant) of THAM is 7.8, making it a more effective buffer than sodium bicarbonate in the physiologic range of blood pH. THAM is a proton acceptor with a stoichiometric equivalence of one proton per molecule. In vivo, THAM supplements the buffering capacity of the blood bicarbonate system by accepting a proton, generating sodium bicarbonate, and decreasing the partial pressure of carbon dioxide. It rapidly distributes to the extracellular space and slowly penetrates the intracellular space, except in the case of erythrocytes and hepatocytes, and it is excreted by the kidney in its protonated form at a rate that slightly exceeds creatinine clearance. Unlike sodium bicarbonate, which requires an open system to eliminate carbon dioxide in order to exert its buffering effect, THAM is effective in a closed or semiclosed system, and it maintains its buffering ability during hypothermia.
- The initial loading dose of THAM acetate (0.3 M) for the treatment of acidemia may be estimated as follows: THAM (in milliliters of 0.3 M solution) = lean body weight (in kilograms) × the base deficit (in millimoles per liter). The maximal daily dose is 15 mmol per kilogram per day for an adult (3.5 liters of a 0.3 M solution in a patient weighing 70 kg).
