In this episode, I will discuss how I would treat Wernicke’s Encephalopathy if I were completely out of IV thiamine.
Wernicke’s encephalopathy is an acute disorder that has significant mortality and neurologic morbidity associated with it. For a detailed episode of how to treat and prevent Wernicke’s go to pharmacyjoe.com/episode292.
At the time of this recording, there is an ongoing shortage of IV thiamine products in the US.
Of the two manufacturers of IV thiamine, Fresenius Kabi has product on backorder due to a manufacturing delay, and Mylan is presumably on back order due to increased demand.
Alternative products that contain thiamine and additional vitamins may be available, such as injectable vitamin B complex that contains 100 mg/mL of thiamine in addition to other B vitamins.
Previous to the shortage, IV thiamine has been liberally recommended for the prophylaxis of Wernicke’s Encephalopathy at a dose of 250 mg per day, while the treatment dose has been recommended to be as much as 1500 mg IV thiamine daily.
These high doses were recommended under the premise that IV thiamine is cheap, safe, and widely available.
In this time of shortage, I would favor conserving IV thiamine for those patients most likely to have Wernicke’s, and obtaining alternative sources of IV thiamine whenever possible.
However, it is likely that clinicians may be faced with the dilemma of having a patient with suspected Wernicke’s Encephalopathy and no IV thiamine available to provide treatment.
In this scenario, the only alternative source of thiamine would be enteral thiamine tablets.
I have always been under the impression that oral thiamine is poorly bioavailable with a saturable active absorption process.
However, a study published in 2012 in BMC Clinical Pharmacology challenges that concept and seems to show that at very high doses there must be some form of passive, non-saturable absorption of thiamine.
Healthy subjects were given oral thiamine at doses of 100 mg, 500 mg, and 1500 mg.
The 500 mg dose achieved plasma thiamine levels approximately equivalent to those achieved by 100 to 200 mg IV doses. The peak concentration for the oral 500 mg dose of thiamine occurred at 3 hours.
The 1500 mg dose achieved plasma levels 3.5 times that of the 500 mg dose. The peak concentration for the oral 1500 mg dose of thiamine occurred at 4 hours.
The results of the study suggest that there is both an active and passive mechanism of thiamine absorption. In the study, high blood levels comparable with some doses of IV thiamine were achieved rapidly, in 4 hours or less.
It should be noted that the study was performed in healthy patients, not critically ill patients with suspected Wernicke’s Encephalopathy.
However, this study appears to be the only information available on the pharmacokinetics of high doses of oral thiamine. If I were faced with a situation of treating Wernicke’s without any IV thiamine I would use the evidence in this study to guide my thiamine dose decision-making.
I have updated my free visual critical care antibiotic guide for 2019. To download this guide and easily remember spectrum of activity, go to pharmacyjoe.com/abx.
If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.
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