Benadryl abuse

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Benadryl abuse

Post by bcop » Thu Jun 06, 2019 10:17 pm

I have an employee at our hospital who was drug tested for cause and was found to have vials of Benadryl (diphenhydramine) as well as syringes and needles in his lunchbox. He has a previous history of propofol and fentanyl abuse. His drug screens have come back negative so far, the propofol test is still pending but his diphenhyhdramine concentration came back at 11,401 ng/ml.

When I spoke to the employee he said he had a sunburn the weekend before so he took Benadryl and ibuprofen on Monday. When asked how he took the Benadryl he said orally. His urine drug test was done two days later on Wednesday. Is it possible to have that high a level of diphenhydramine, which is short-acting and clears fairly rapidly, from oral doses alone? The question is can we call it a positive test? Obviously, since he had vials of Benadryl and needles and syringes with him with lot numbers corresponding to those from both our hospital and the other hospital he works at, with no prescription that I am aware of, HR should not be relying on his UDS screen to decide what to do with him. He is in contact with IPN already but I will need to let his case manager know if this is a positive drug screen.

Robert Swotinsky MD
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Re: Benadryl abuse

Post by Robert Swotinsky MD » Fri Jun 07, 2019 6:11 am

A short-acting, quickly metabolized drug can be present in urine 2 days after its use. The urine that has collected in the bladder includes urine that was produced by the kidneys over a day or so. Thus, it represents a filtrate of the blood over a day or so.

- A tablet of Benadryl contains 25 mg diphenhydramine.

- Abuse of diphenhydramine has been reported in the medical literature, e.g.,

- In this particular case, the donor's urine concentration is higher than expected. The data about therapeutic use of diphenhydramine and urine concentrations is limited. For example, there is a 1966 study reports urine concentrations of diphenhydramine of 100 - 3,500 ng/mL during the first 24 hours after ingestion of 100 mg of the drug by 4 volunteers. [J.E. Wallace, J.D. Biggs, and E.V. Dahl. Determination of diphenhydramine and certain related compounds by ultraviolet spectrophotometry. Anal Chem. 38:831-834, 1996] In the case presented, the urine concentration is 11,401 ng/mL which comes closer to values found in post-accident and post-mortem tests, where diphenhydramine abuse was suspected.

- The usual method of MRO review seems inadequate in this particular situation. The target drug is widely available without a prescription. So, the MRO can't determine that the drug was, or was not, taken as prescribed. And, there are no guidelines about concentrations to rule out, or rule in, therapeutic v. illicit use.

Limiting the reporting options to positive or negative would seem inadequate. An accurate and informative report in this case would be, "The test identified diphenhydramine at a concentration consistent with abuse."

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