Dilantin (phenytoin) Can Cause Vitamin D Deficiency

Dilantin (phenytoin) is probably one of the dirtiest drugs, but is necessary as it treats an obviously serious condition (seizures). It has many clinical quirks that you need to be aware of. 72 year old female with a long history of seizures was on a maintainence dose of 200 mg twice daily. Seizures were well managed and patient displayed no symptoms of Dilantin toxicity with a Total Dilantin level of 12. (Remember the clinical quirks about Dilantin levels especially if your patient is displaying symptoms of toxicity!) This particular patient was just recently admitted to the hospital for a wrist fracture, and it was discovered that she had osteoporosis. Upon this discovery, the provider ordered a vitamin D level to assess if/how much supplementation they felt was necessary. The level came back at 6. (normal is 30-100 in most labs) Why was this level so low? – Long term Dilantin can cause/worsen vitamin D deficiency. The patient was started on a Vitamin D supplement.

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  1. thelma sudack

    I was taking Dilantin for almost 38 years when one day I took my meds as usual, then boom! I started this reaction! I tried to tell my doctor. He kept saying I could not just START suddenly having a reaction to it. Well, the next morning I went to the E.R> and sat there while taking my meds. Sure enough I had an even worse reaction! So bad they had to admit me and give me meds to open my airways! I took Dilantin while pregnant with my foour beautiful children. However years later one had to have heart/valve replacement ( said to be caused by Dilantin) . So anyone out there having any reaction what so ever that is unusual, get help!

    • Trevor Smith

      my doctor just asked me to start 1000 mgs vitamin d daily also on Dilantin 600 mgs daily

  2. Islam abou el majd

    Just an exciting medical article drug drug interaction s very important field to disscus thank u for this….

  3. Andalu Gunda MS,R.Ph.

    Very useful information.I recently read in an article that adverse drug reactions are the fourth leading cause of death. Clinical Pharmacists play very important role in health care system. Now that with pharmacogenetic testing we can further reduce ADRs.With CYP2C9 testing it is quite possible to avoid toxicity of Dilantin and can get the right dosage for the first time.

  4. greg renstrom

    clearly, taking dilantin has positive results and negative risks. i had a seizure in 1960 and another in 1973. as far as i can tell, that’s it. i have been on the standard dilantin-phenobarbital combination all these fifty-seven years. and it’s worked. but in addition to common expected dental complications, i have dramatically diminished balance and mobility, both determined by my neurologist to be side-effects of the drug. recovery from even relatively minor surgery is at least two or three-times longer because of the drug. it something i have simply had to consider when looking at and planning for overall health.

    • Lonna

      Hi Greg. That’s great if you haven’t had more seizures. I have petit Mal seizures. I have most in the night while sleeping. An arm or leg will jerk. Sometimes causing me to wake. Other times I don’t know until my husband to tell me to stop hitting/kicking him. Haha.
      I had a neurologist tell me I shouldn’t be on Dilantin for as long as I have been. It wasn’t meant for long term use.

  5. Lonna

    I’ve been on Dilantin 47 years now. Started staking it in middle school for epilepsy. Once my gums were swollen and I took a sterile needle to pop my gums. When that did nothing I showed my mom. Off to the doctor I went. The doctor adjusted my Dilantin and my gums went back to normal. True story, I was a kid and didn’t know.
    Now in my 50s my issues related to Dilantin are bone fractures and the vitamin d deficiency. I also found out nobody should be on Dilantin long term. At the same time I don’t think there are many options since the neurologists still have me on it. Tegretol made my eyes flutter.

  6. Trevor Smith

    I had endo carditis as a result of not going to the dentisr on a regular basis as a kid ,later at 47 had a seisure on Dikantin now 300 morning ,300 at nigth will lesson my dose in time ,was used to be 200 at nigth 300mgs in Mornign

  7. Mike Perkins

    Been on 500mg Dilantin since 1976 (46 yrs). 1st seizure was 1964 at age 20. Didn’t go to Dr so no meds until 1974 after a 2nd seizure. Dr started me on 200mg daily and gradually increased to 500mg in 1976 at which point seizures stopped. They were becoming more frequent and severe. I take a high dose of 4000ic of vitamin D-3 daily. Dr must run a test as vitamin D deficiency resulting from Phenytoin (Dilantin) impact is unique to each patient. Drs don’t recommend phenytoin as a 1st choice now, but will not switch patients who are successfully on it as they may have seizures on the new one.


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Written By Eric Christianson

June 11, 2014

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