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Precautions and Warnings With Phenytoin

There are many phenytoin precautions and warnings to be aware of before starting treatment with the drug, such as the safety of taking phenytoin while pregnant or nursing and people who should not take the drug at all. It is important to know that phenytoin may increase blood sugar levels, cause very serious skin rashes, or weaken bones in some people. Among the people who should not take phenytoin are those who are allergic to any active or inactive components used to make the medicine.

Phenytoin: What Should I Tell My Healthcare Provider?

You should talk with your healthcare provider prior to taking phenytoin (Dilantin®) if you have:
  • Porphyria
  • Swollen lymph nodes
  • Diabetes
  • Liver disease, such as liver failure or cirrhosis
  • Any allergies, including allergies to food, dyes, or preservatives.
Also let your healthcare provider know if you are:
  • Pregnant or thinking of becoming pregnant
  • Breastfeeding.
You should also make sure to tell your healthcare provider about all other medicines you are taking, including prescription and non-prescription medicines, vitamins, and herbal supplements.

Specific Warnings and Precautions With Phenytoin

Some warnings and precautions to be aware of prior to taking phenytoin include:
  • Seizure medications, including phenytoin, may increase the risk of suicidal thoughts or behavior. If you feel depressed or have any suicidal thoughts, let your healthcare provider know right away (see Seizure Medications and Suicide for more information).


  • There have been reports of lymph node problems in people taking phenytoin. It is not known if phenytoin is the cause of these problems. These problems, which may include swollen and tender lymph nodes, can be a sign of serious problems (such as certain cancers).
  • Alcohol can affect the way your body handles phenytoin. Talk with your healthcare provider about your alcohol consumption. It is important to keep your alcohol intake consistent (see Dilantin and Alcohol).
  • Phenytoin may make porphyria worse. Porphyria is a group of conditions involving problems with certain enzymes in the body.
  • The liver helps remove phenytoin from the body. If you have liver disease, you may need a lower phenytoin dosage.
  • Because phenytoin can cause very serious skin rashes (which are sometimes life-threatening), tell your healthcare provider right away if you notice a rash during treatment with phenytoin. Most likely, you will need to stop phenytoin either temporarily or permanently.
  • Phenytoin may increase your blood sugar. This is especially important for people with diabetes.
  • Phenytoin may cause bone weakness, because it affects the way your body deals with vitamin D (which is important for strong bones).
  • As with all seizure medications, phenytoin should not be stopped suddenly (see Dilantin Withdrawal).
  • Strange behavior or thinking may be a sign of too much phenytoin in your blood. Let your healthcare provider know if you notice any unusual behavior or thinking.
  • Because phenytoin can cause gum problems, good dental care is very important while you are taking phenytoin.
  • Phenytoin can potentially interact with certain other medications (see Drug Interactions With Phenytoin).
  • Phenytoin is considered a pregnancy Category D medication. This means that it is probably not safe for pregnant women. Talk with your healthcare provider about the risks and benefits of taking the drug during pregnancy (see Dilantin and Pregnancy).
  • Phenytoin passes through breast milk. Therefore, if you are breastfeeding or plan to start breastfeeding, discuss this with your healthcare provider prior to taking the drug (see Dilantin and Breastfeeding).
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