The most common signs and symptoms of overdose with Carbymal are dizziness, diplopia, drowsiness, headache, ataxia, and slurred speech. Some tolerance to the neurotoxic effects is observed and effects can be minimized by initially prescribing low doses then gradually increasing dosage to reach the necessary maintenance dosage. Convulsions may be precipitated by acute intoxication with Carbymal, and it can exacerbate absence and myoclonic seizures. Various types of involuntary motor activity in elderly patients have been reported, and hallucinations have occurred. Skin rashes have been reported. Certain Asian populations seem to have an increased risk for Stevens-Johnson syndrome. If leukopenia occurs, it is usually mild. Other hematologic reactions to Carbymal are rare but sometimes life-threatening. Aplastic anemia is of particular concern, and agranulocytosis has also occurred.
Tegretol, Carbymal USP, is an anticonvulsant and specific analgesic for trigeminal neuralgia, available for oral administration as chewable tablets of 100 mg, tablets of 200 mg, XR tablets of 100, 200, and 400 mg, and as a suspension of 100 mg/5 mL (teaspoon). Its chemical name is 5H-dibenzazepine-5-carboxamide, and its structural formula is:
Carbymal USP is a white to off-white powder, practically insoluble in water and soluble in alcohol and in acetone. Its molecular weight is 236.27.
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to Carbymal.
8. Cautions with other medicines
There are some medicines that may interfere with the effects of Carbymal.
Tell your doctor if you are taking any of these medicines:
- medicines for your heart such as warfarin, apixaban, rivaroxaban or diltiazem
- antibiotics or antifungals such as clarithromycin, erythromycin or fluconazole
- medicines used for depression or anxiety such as amitriptyline, citalopram or mirtazapine
- ciclosporin, tacrolimus or sirolimus - immunosuppressants used after transplant operations, but also sometimes to treat arthritis or psoriasis
- medicines used to treat HIV or AIDS such as dasubavir or ritonavir
- have taken medicines called monoamine oxidase inhibitors (MAOIs), used to treat depression - these can affect Carbymal even if they've been stopped for a few weeks
Before taking Carbymal, tell your doctor or pharmacist if you are allergic to it; or to other anti-seizure medications (such as fosphenytoin, oxcarbazepine, phenobarbital, phenytoin, primidone) or tricyclic antidepressants (such as amitriptyline, desipramine); or if you have any other allergies. This product may contain inactive ingredients (such as sorbitol in the suspension), which can cause allergic reactions or other problems. Talk to your pharmacist for more details.
Before using this medication, tell your doctor or pharmacist your medical history, especially of: decreased bone marrow function (bone marrow depression), blood disorders (such as porphyria, anemia), glaucoma, heart disease (such as coronary artery disease, heart failure, irregular heartbeat), kidney disease, liver disease, mental/mood disorders (such as depression), mineral imbalances (such as low levels of sodium or calcium in the blood ).
This drug may make you dizzy or drowsy. Alcohol or marijuana (cannabis) can make you more dizzy or drowsy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Avoid alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).
This medication may make you more sensitive to the sun. Limit your time in the sun. Avoid tanning booths and sunlamps. Use sunscreen and wear protective clothing when outdoors. Get medical help right away if you get sunburned or have skin blisters/redness.
The chewable tablets or suspension may contain sugar. Caution is advised if you have diabetes or any other condition that requires you to limit/avoid sugar in your diet. Ask your doctor or pharmacist about using this product safely.
Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).
Older adults may be more sensitive to the side effects of this drug, especially, confusion, unsteadiness, or irregular heartbeat. Confusion and unsteadiness can increase the risk of falling. Older adults may also be at greater risk of developing a type of mineral imbalance (low levels of sodium in the blood), especially if they are also taking "water pills" (diuretics).
During pregnancy, this medication should be used only when clearly needed. It may harm an unborn baby. However, since untreated seizures are a serious condition that can harm both a pregnant woman and her unborn baby, do not stop taking this medication unless directed by your doctor. If you are planning pregnancy, become pregnant, or think you may be pregnant, discuss with your doctor right away the benefits and risks of using this medication during pregnancy. If you are pregnant, prenatal care that includes tests for birth defects is recommended. Since birth control pills, patches, implants, and injections may not work if used with this medication (see also Drug Interactions section), discuss reliable forms of birth control with your doctor.
This medication passes into breast milk. Consult your doctor before breast-feeding.
Drug–drug interactions are common with Carbymal due to relatively high protein binding (65–80%) and involvement of drug-metabolizing enzymes, including CYP2C19 and CYP3A4. Carbymal is eliminated primarily via the kidneys; thus, renal failure or insufficiency can lead to elevated results and increase the risk for toxicity.
What if I forget to take it?
If you take Carbymal and miss a dose:
- once a day - take the missed dose as soon as you remember. If it's less than 12 hours before the next dose is due, it's better to leave out the missed dose and take your next dose as normal.
- twice a day - take the missed dose as soon as you remember. If it's less than 8 hours before the next dose is due, it's better to leave out the missed dose and take your next dose as normal.
Do not take 2 doses at the same time to make up for a forgotten dose.
If you have epilepsy, it's important to take this medicine regularly. Missing doses may trigger a seizure.
If you forget doses often, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.
What should I avoid while taking Carbymal?
Drinking alcohol with this medicine can cause side effects.
Grapefruit may interact with Carbymal and lead to unwanted side effects. Avoid the use of grapefruit products.
Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.
Drinking alcohol can increase some of the side effects, and can also increase your risk of seizures.
Carbymal could make you sunburn more easily. Avoid sunlight or tanning beds. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.
Case 1. Immunoallergic hepatitis caused by Carbymal.
A 50 year old man with epilepsy was switched from valproate to Carbymal and one month later presented with high fevers and fatigue. He was treated with amoxicillin and developed a diffuse maculopapular rash, adenopathy and jaundice within a few days. Laboratory testing showed eosinophilia (8%) and elevations in serum enzymes with mild jaundice (Table). Tests for viral hepatitis, autoimmune liver disease and liver imaging were negative or nonrevealing. Carbymal was continued for another 5 days when a liver biopsy showed evidence of drug induced liver disease. Because of worsening rash and hemorrhagic bullae, a single intravenous injection of prednisolone (250 mg) was given. He improved rapidly and was discharged after 12 days in the hospital, but returned a few days later with relapse in fever, rash and fatigue. Serum enzymes had risen as well. He was started on oral prednisone (
40 mg/day) and improved. The dose of prednisone was gradually decreased and was stopped 12 weeks later. In follow up, he was asymptomatic and had normal liver tests on chronic valproate therapy.
How it works
It’s not completely known how this drug treats epilepsy or trigeminal nerve pain. It is known to block sodium currents in your brain and body. This helps to reduce abnormal electrical activity between your nerve cells.
Carbymal oral tablet may cause drowsiness. It can also cause other side effects.
Other uses for this medicine
Carbymal is also sometimes used to treat mental illnesses, depression, posttraumatic stress disorder, drug and alcohol withdrawal, restless legs syndrome, diabetes insipidus, certain pain syndromes, and a disease in children called chorea. Talk to your doctor about the possible risks of using this medication for your condition.
This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.
What other information should I know?
Before having any laboratory test, tell your doctor and the laboratory personnel that you are taking Carbymal.
Carbymal can interfere with the results of home pregnancy tests. Talk to your doctor if you think you might be pregnant while you are taking Carbymal. Do not try to test for pregnancy at home.
The extended-release tablet does not dissolve in the stomach after swallowing. It slowly releases the medicine as it passes through your digestive system. You may notice the tablet coating in your stool.
Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
CYP3A4 inducers can increase the rate of Tegretol metabolism. Drugs that have been shown, or that would be expected, to decrease plasma Carbymal levels include cisplatin, doxorubicin HCl, felbamate, fosphenytoin, rifampin, phenobarbital, phenytoin, primidone, methsuximide, theophylline, aminophylline.
Taking aprepitant with Carbymal will increase the level of Carbymal in your body. This can cause side effects. Your doctor may monitor your blood levels of Carbymal if you’re taking it with this drug.
Interferences in Carbymal measurement
Carbymal (Tegretol, Carbatrol) is a tricyclic anticonvulsant drug used for the treatment of partial and tonic-clonic seizures, trigeminal neuralgia, and manic-depression. The therapeutic range for Carbymal is 4–12 μg/mL, and signs of toxicity, such as stupor, seizures, and respiratory depression may occur at concentrations exceeding 15 μg/mL. Carbymal is metabolized primarily by cytochrome P450 isozyme (CYP) 3A4, to the active metabolite, Carbymal-10,11-epoxide. The 10,11-epoxide metabolite has similar activity as the parent drug, and may contribute significantly to efficacy of the drug in populations such as children, that accumulate the metabolite. The concentration of the metabolite may be higher than the parent drug concentrations in situations of Carbymal overdose and in patients with renal failure (uremia); therefore, monitoring drug ratios of parent and metabolite may be useful for evaluating compliance and drug-drug interactions.
What is the dosage for Carbymal?
Carbymal may be taken with or without food. Carbymal is excreted by the kidney and eliminated by the liver, and dosages may need to be lowered in patients with liver or kidney dysfunction. Blood levels of Carbymal are used for adjusting dosing. The dose for seizures is 800 to 1600 mg daily in divided doses. Trigeminal neuralgia is treated with 400-1200 mg daily in divided doses. The dose for treating bipolar disorder using Equetro is begun at 200 mg every 12 hours initially, and then increased by 200 mg a day up to a maximum dose of 1600 mg per day.
Drug-drug interactions are common with Carbymal , due to relatively high protein binding (65–80%), and involvement of drug metabolizing enzymes, including CYP2C19 and CYP3A4. Carbymal is primarily eliminate via the kidneys, thus renal failure or insufficiency can lead to elevated results and increase the risk for toxicity.