Fentanyl (injection route)

It is very important that your doctor check you closely while you or your child are receiving this medicine. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to receive it.

This medicine may cause a serious allergic reaction called anaphylaxis, which can be life-threatening and require immediate medical attention. Call your doctor right away if you or your child have a rash, itching, hoarseness, trouble breathing, trouble swallowing, or any swelling of your hands, face, or mouth while you are using this medicine.

Do not use too much of this medicine or use it more often than your doctor tells you to. This can be life-threatening. Signs of an overdose include: change or loss of consciousness, cold, clammy skin, coughing that sometimes produces a pink frothy sputum, decreased awareness or responsiveness, extreme dizziness or weakness, increased sweating, irregular, fast, or slow, or shallow breathing, pale or blue lips, fingernails, or skin, sleepiness or unusual drowsiness, slow heartbeat, seizures, swelling in legs and ankles, or trouble breathing. Call your doctor right away if you notice these symptoms.

Dizziness, lightheadedness, or fainting may occur with this medicine, especially when you get up suddenly from a lying or sitting position. Getting up slowly may help lessen this problem. Also, lying down for a while may relieve the dizziness or lightheadedness.

This medicine will add to the effects of alcohol and other central nervous system (CNS) depressants. CNS depressants are medicines that slow down the nervous system, which may cause drowsiness or make you less alert. Some examples of CNS depressants are antihistamines or medicine for hay fever, allergies, or colds, sedatives, tranquilizers, or sleeping pills, prescription pain medicine or opioids, barbiturates or seizure medicines, muscle relaxants, or anesthetics (numbing medicines), including some dental anesthetics. This effect may last for a few days after you stop using this medicine. Check with your medical doctor or dentist before taking any of the above while you or your child are receiving this medicine.

This medicine may cause sleep-related breathing problems (eg, sleep apnea, sleep-related hypoxemia). Your doctor may decrease your dose if you have sleep apnea (stop breathing for short periods during sleep) while using this medicine.

This medicine may make you dizzy, drowsy, confused, or disoriented. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or not alert.

This medicine may be habit-forming. If you feel that the medicine is not working as well, do not use more than your prescribed dose. Call your doctor for instructions.

Using opioids for a long time can cause severe constipation. To prevent this, your doctor may direct you to take laxatives, drink a lot of fluids, or increase the amount of fiber in your diet. Be sure to follow the directions carefully, because continuing constipation can lead to more serious problems.

If you have been using this medicine regularly for several weeks or more, do not change your dose or suddenly stop using it without checking with your doctor. Your doctor may want you to gradually reduce the amount you are using before stopping it completely. This may help prevent worsening of your condition and reduce the possibility of withdrawal symptoms, such as abdominal or stomach cramps, anxiety, fever, nausea, runny nose, sweating, tremors, or trouble sleeping.

If you think you have, or someone else has, taken an overdose of this medicine, get emergency help at once. Your healthcare provider may prescribe naloxone to treat an overdose. Naloxone is a medicine that can temporarily reverse the effects of an overdose. If you have been prescribed naloxone, or purchased it over-the-counter, make sure your household members know how to use it in the event of an overdose. Emergency help is still needed after naloxone is used because the reversal effects are only temporary. Signs of an overdose include: change or loss of consciousness, cold, clammy skin, coughing that sometimes produces a pink frothy sputum, decreased awareness or responsiveness, extreme dizziness or weakness, increased sweating, irregular, fast, or slow, or shallow breathing, pale or blue lips, fingernails, or skin, sleepiness or unusual drowsiness, slow heartbeat, seizures, swelling in legs and ankles, or trouble breathing. Call your doctor right away if you notice these symptoms.

This medicine may increase risk for muscle rigidity and movement. Tell your doctor if you or your child have stiff or rigid muscles after using this medicine.

Call your doctor right away if you have worsening of pain, increased sensitivity to pain, or new pain after taking this medicine. These may be symptoms of opioid-induced hyperalgesia and allodynia.

Check with your doctor right away if you have anxiety, restlessness, a fast heartbeat, fever, sweating, muscle spasms, twitching, nausea, vomiting, diarrhea, or see or hear things that are not there. These may be symptoms of a serious condition called serotonin syndrome. Your risk may be higher if you also take certain other medicines that affect serotonin levels in your body.

This medicine may cause adrenal gland problems. Check with your doctor right away if you have darkening of the skin, diarrhea, dizziness, fainting, loss of appetite, mental depression, nausea, skin rash, unusual tiredness or weakness, or vomiting.

Using this medicine while you are pregnant may cause neonatal withdrawal syndrome in your newborn babies. Tell your doctor right away if your baby has an abnormal sleep pattern, diarrhea, a high-pitched cry, irritability, shakiness or tremors, weight loss, vomiting, or fails to gain weight.

Using too much of this medicine may cause infertility (unable to have children). Talk with your doctor before using this medicine if you plan to have children.

Do not eat grapefruit or drink grapefruit juice while you are using this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.