Doctors usually think vitamin B1 (thiamine) is very safe, but this case report describes something unusual. A 63-year-old woman with adrenal problems received vitamin B1 through an IV and developed dangerously low blood platelet counts shortly after. Her platelet numbers dropped quickly while she was getting the vitamin, but returned to normal once doctors stopped the treatment. This is the first well-documented case of this rare reaction, reminding doctors that even “safe” vitamins can sometimes cause serious side effects in certain patients.

The Quick Take

  • What they studied: Whether intravenous vitamin B1 (thiamine) can cause a dangerous drop in blood platelets, which are cells that help blood clot
  • Who participated: One 63-year-old woman with adrenal insufficiency (a condition where the body doesn’t make enough of certain hormones) and malnutrition who received IV vitamin B1
  • Key finding: The patient’s platelet count dropped significantly after starting IV thiamine and returned to normal after stopping the treatment, suggesting the vitamin caused the problem
  • What it means for you: While vitamin B1 is generally very safe, doctors should monitor blood platelet counts in patients receiving IV thiamine, especially those who are critically ill or have other health conditions. This is an extremely rare side effect, so most people receiving this vitamin will not experience it

The Research Details

This is a case report, which means doctors documented what happened to one specific patient. The patient had adrenal insufficiency (her body doesn’t produce enough stress hormones) and was malnourished. She received intravenous thiamine (vitamin B1) as nutritional support. Shortly after starting the treatment, her blood platelet count dropped dangerously low. Doctors ran many tests to find other possible causes but found none. The timing and pattern of the platelet drop strongly suggested the vitamin B1 caused the problem.

Doctors used a scoring system called the Naranjo scale to evaluate how likely it was that the thiamine caused the problem. The patient scored a 6, which indicates a “probable” drug reaction. This scoring system considers factors like the timing of the reaction, whether the problem went away when the drug was stopped, and whether other causes were ruled out.

After doctors stopped giving the thiamine, the patient’s platelet count recovered completely with no other treatment needed, which further supported that the vitamin was the cause.

Case reports are important for identifying rare side effects that might not show up in larger studies. This report is valuable because it documents something that hasn’t been clearly described before—a serious blood problem caused by a vitamin that’s usually considered very safe. This helps doctors recognize similar cases in the future and take appropriate precautions.

This is a single case report, which is the lowest level of scientific evidence. However, the documentation is thorough, with systematic testing to rule out other causes. The strong temporal relationship (the problem started when the vitamin was given and stopped when it was removed) supports the connection. The main limitation is that one case cannot prove this happens to everyone—it only shows it can happen in rare circumstances.

What the Results Show

The patient’s platelet count dropped from normal levels to dangerously low levels (severe thrombocytopenia) shortly after intravenous thiamine was started. The decline happened quickly over the course of treatment. When doctors stopped giving the thiamine, the platelet count recovered completely without any other medical intervention needed.

Doctors performed extensive testing to rule out other causes of low platelets, including infections, other medications, and bone marrow problems. All tests came back normal or negative, meaning no other explanation could be found for the platelet drop.

The timing and pattern of events strongly suggested the thiamine caused an immune reaction against the body’s own platelets. This type of reaction is called drug-induced immune thrombocytopenia, where the body’s immune system mistakenly attacks platelets after exposure to a medication.

The patient had additional health complications (adrenal insufficiency and malnutrition) that may have made her more vulnerable to this rare side effect. This suggests that patients with multiple health problems or those who are critically ill might need extra monitoring when receiving IV thiamine. The complete recovery after stopping the vitamin indicates that this reaction, while serious, appears to be reversible.

Thiamine deficiency is known to cause low platelet counts, and giving thiamine to treat this deficiency usually improves the problem. However, this case is unusual because it describes the opposite—low platelet counts developing after thiamine was given, not before. This appears to be the first well-documented case of this specific reaction, making it a new finding in medical literature.

This is only one patient’s case, so we cannot say how common this reaction is or who is most at risk. We don’t know if this would happen to other people receiving IV thiamine. The patient had other health conditions that might have contributed to the reaction. Without more cases or research, doctors cannot determine the exact mechanism of how thiamine caused the problem or predict who might be at higher risk.

The Bottom Line

Healthcare providers should consider monitoring blood platelet counts in patients receiving intravenous thiamine, particularly those who are critically ill, malnourished, or have multiple health conditions. If a patient develops unusual bruising, bleeding, or a sudden drop in platelet count after starting IV thiamine, doctors should consider stopping the treatment and investigating further. This recommendation is based on one case, so the confidence level is low, but the potential seriousness of low platelets warrants caution.

This finding is most relevant to doctors and hospitals administering intravenous thiamine, especially to critically ill patients or those with complex medical conditions. Patients receiving IV thiamine should be aware of this rare possibility and report any unusual symptoms. People taking oral vitamin B1 supplements at home should not be concerned, as this reaction appears specific to intravenous administration and is extremely rare.

In this case, the platelet drop occurred shortly after starting IV thiamine and recovered completely within days of stopping the treatment. If this reaction were to occur in another patient, symptoms might develop similarly quickly, and recovery would likely follow a similar timeline once the vitamin is discontinued.

Want to Apply This Research?

  • For patients receiving IV thiamine in a hospital or clinical setting, track platelet count values before starting treatment and at regular intervals during treatment (daily or as ordered by the doctor). Note any symptoms like unusual bruising, bleeding gums, or nosebleeds.
  • If using a health tracking app, patients should report any unusual bleeding or bruising symptoms immediately to their healthcare provider, especially if they’re receiving IV vitamin treatments. Healthcare providers should document thiamine administration and any subsequent blood work results.
  • Maintain a log of blood test results (specifically platelet counts) before, during, and after IV thiamine therapy. Track any physical symptoms that might indicate low platelets. Share this information with all healthcare providers involved in care to ensure continuity and early detection of any problems.

This case report describes a single patient’s experience and does not represent what will happen to most people receiving thiamine. While vitamin B1 is generally considered safe, this report highlights that any medication can rarely cause serious side effects. This information is for educational purposes only and should not replace professional medical advice. If you are receiving or considering intravenous thiamine, discuss potential risks and benefits with your healthcare provider. If you experience unusual bruising, bleeding, or other concerning symptoms during or after thiamine treatment, contact your doctor immediately. Do not stop prescribed medications without medical guidance.