A 53-year-old male patient, with a background marked by complete gastrectomy, is thought to have fostered Wernicke's encephalopathy. The specialist has endorsed an intravenous (IV) mixture of 100 mg vitamin B1 infusion in 100 mL of ordinary saline, to be regulated every 8 hours. However, the IV compounding center has refused to prepare the solution, as the product instructions clearly state that Vitamin B1 Thiamine HCl Powder injection should be administered by intramuscular (IM) injection.
Why can't vitamin B1 injection be given intravenously?
Vitamin B1 is handily decomposed and annihilated in alkaline solutions, particularly when warmed. It can likewise deteriorate when joined with alkaline medications (like sodium phenobarbital, sodium bicarbonate, and potassium citrate). Vitamin B1 is more stable in acidic solutions, and can withstand 100°C sterilization at a pH of 3.5, but gradually loses its efficacy at pH values above 5.
Reviewing the product instructions of various domestic manufacturers, the route of administration is only mentioned as IM injection. The adverse reactions section notes that with high-dose IM injections, attention should be paid to the risk of hypersensitivity reactions, such as difficulty swallowing, skin itching, facial/lip/eyelid edema, and wheezing. The precautions also mention the possibility of hypersensitivity reactions during injection, and caution is advised for those with allergic constitutions.
The "New Pharmacology" textbook also only mentions IM injection and advises against IV administration. Similarly, the "Clinical Drug Use Guide for Chinese Physicians and Pharmacists" only recommends IM injection for severe beriberi, with a switch to oral administration after symptom improvement.
Stability:
Based on the chemical properties of thiamine hydrochloride, manufacturers need to control the pH of the intermediate products for vitamin B1 injection between 2.5-4.0, and then perform 100°C sterilization. The 2015 version of the Chinese Pharmacopeia likewise indicates that the pH of vitamin B1 infusion ought to be between 2.5-4.0. The European Pharmacopoeia 6.8 and the US Pharmacopeia 33 also have similar pH requirements for thiamine hydrochloride solutions.
Therefore, from the perspective of stability, if vitamin B1 injection is administered intravenously, the change in solvent pH may cause decomposition of the thiamine hydrochloride.
Safety:
Both the product instructions and major reference materials mention that vitamin B1 injection may cause allergic reactions, and in some cases, even anaphylactic shock. Although the incidence rate of allergic reactions with intravenous administration of vitamin B1 is not clear, a search of PubMed reveals few reported cases.
The Martindale Drug Reference mentions that Vitamin B1 Thiamine HCl Powder can cause hypersensitivity reactions, mainly occurring after parenteral administration. Between 1970 and July 1988, the UK CSM received 90 reports of adverse reactions after injection of high-dose B-complex vitamins and vitamin C, the most common being allergic reactions (41 cases, including 2 fatalities), respiratory distress or bronchospasm (13 cases), and rash and flushing (22 cases). 78 of these reactions occurred during or immediately after IV injection, while the other 12 occurred after IM injection.
They recommend that parenteral therapy should only be used when absolutely necessary, and in the presence of equipment to treat allergic reactions. Juel J. et al. believe that vitamin B1 injection has a high safety profile, but may still cause allergic or hypersensitivity reactions, which are more likely to occur with IV administration.
Therefore, IM injection may be safer than IV injection, but the clinical observation of Wrenn KD. et al. suggests that for malnourished patients, IV administration of vitamin B1 appears to be as safe as IM injection.
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