1/ Follow up for our #IDFellows and #IDTwitter on an #IDCase - 25 year old female with behcet's disease and chronic pain who presents for positive T Spot done for screening. Started on Rifampin for latent TB Infection. She calls 3 days later with diffuse pain.
2/ Great job, #IDTwitter, honing in on the issue! This was intentionally vague to stimulate discussion. As you alluded to, the key lies in what else she was taking. But first, what might we worry about as adverse effects Rifampin?
3/ Allergic reactions to rifampin are relatively rare though they have been described. However, patients may experience flushing, rash and itching that is unrelated to hypersensitivity. Rifampin can often be continued in these patients. PMID: 10575418
4/ A flu-like syndrome associated with Rifampin use has been described, which is manifested as fever, chills, myalgias and headache. The risk of developing this syndrome increases with increasing dose and is associated with intermittent rather than daily dosing. 
5/ Interestingly this flu-like reaction is seemingly associated with antibody production. The above study, from 1971, documented the development of Rifampicin related antibodies in 1/3 of patients; mostly those who received intermittent dosing.
6/ Very rarely, Rifampin can cause liver dysfunction. This occurs more often when patients have underlying liver disease or in those receiving hepatotoxic agents. Other rare side effects include renal failure, hemolytic anemia, thrombocytopenia and possible DIC, and leukopenia.
7/ But Rifampin is most known for is its drug-drug interactions! It up-regulates the Cytochrome P450 CYP3A and P-gp multidrug efflux transporters which can impact the metabolism of many drugs. Though it is a bit dated, I still like this reference (doi:10.1001/archinte.162.9.985)
8/ In this #IDCase, the patient had been taking opioids for autoimmune associated joint pain. The addition of Rifampin resulted in increased metabolism of her prescribed opioid analgesics and re-emergence of her pain.
9/ Though it is common to think drug-drug interaction with Rifampin, it is important to assess for other adverse effects. When prescribing a new medication it is important to counsel on possible adverse effects and review med lists for possible #DDIs!
10/ Thanks for tuning in #IDTwitter! What Rifampin related stories do you have? Have you had Rifampin patients develop myalgias and flu-like illness? What surprising drug-drug interactions have you see?
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