The use of carbamazepine in combination with monoamine-oxidase inhibitors (MAO Inhibitors) is not recommended. Therefore, treatment with MAO inhibitors must be stopped at least 2 weeks before starting treatment with carbamazepine.
Influence of carbamazepine on the plasma concentration of other drugs:
Carbamazepine induces the cytochrome P450 system (predominantly the isoenzyme CYP3A4) and other phase I and phase II enzyme systems in the liver, so that the plasma concentrations of substances that are primarily metabolized by CYP3A4 are reduced and these may become ineffective under certain circumstances. Your dose may need to be adjusted according to clinical needs.
This applies, for example, to:
Analgesics, anti-inflammatory substances: buprenorphine, fentanyl, methadone, paracetamol (long term use of carbamazepine and paracetamol (acetaminophen) may result in hepatotoxicity), phenazone, tramadol.
Antihelmintics: praziquantel, albendazole.
Anticoagulants: warfarin, phenprocoumon, dicoumarol, acenocoumarol, rivaroxaban, dabigatran, apixaban and edoxaban.
Antidepressants: bupropion, citalopram, mianserin, nefazodone, sertraline, trazodone (however, it appears that the antidepressant effect of trazodone is increased).
Tricyclic antidepressants: imipramine, amitriptyline, nortriptyline, clomipramine.
Antiemetics: aprepitant.
Other Anticonvulsantss: clonazepam, ethosuximide, felbamate, lamotrigine, eslicarbazepine, oxcarbazepine, primidone, tiagabine, topiramate, valproic acid, zonisamide. In order to avoid phenytoin intoxication and sub-therapeutic concentrations of carbamazepine, it is recommended to adjust the plasma concentration of phenytoin to 13 microgram/ml before starting the additional treatment with carbamazepine.
Antifungals: caspofungin, azole-type antifungals: e.g. itraconazole, voriconazole. Alternative anti-convulsants may be recommended in patients treated with voriconazole or itraconazole.
Antivirals: protease inhibitors for HIV treatment (e.g. indinavir, ritonavir, saquinavir).
Anxiolytics: alprazolam, midazolam, clobazam.
Bronchodilators or Anti-asthmatics: theophylline.
Immunosuppressants: ciclosporin, tacrolimus, sirolimus, everolimus.
Cardiovascular Drugs: calcium antagonists (dihydropyridine group e.g. felodipine), digoxin, simvastatin, atorvastatin, lovastatin, cerivastatin, ivabradine.
Hormonal contraceptives (alternative contraceptive methods should be considered).
Corticosteroids: e.g. prednisolone, dexamethasone.
Typical Neuroleptics: haloperidol and bromperidol,
Atypical Neuroleptics: clozapine, olanzapine, quetiapine, risperidone, ziprasidone, aripiprazole, paliperidone.
Thyroid Hormones: levothyroxine.
Tetracyclines: e.g. doxycycline.
Cytostatics: imatinib, cyclophosphamide, lapatinib, temsirolimus.
Other: quinidine, oestrogens, methylphenidate, progesterone derivatives, propranolol, flunarizine, rifabutin.
Drugs used to treat erectile dysfunction: tadalafil.
When taking the "tablet", sudden bleeding between periods can occur, in addition to the reduced effectiveness of the hormonal contraceptives. Therefore, other, non-hormonal contraceptive methods should be recommended.
The plasma concentration of phenytoin can be both increased and decreased by carbamazepine, which in exceptional cases can lead to confusional states and even coma.
Carbamazepine may decrease plasma levels of bupropion and increase that of the metabolite hydroxybupropion, thereby reducing the clinical efficacy and safety of bupropion.
Carbamazepine may decrease plasma levels of trazodone, but appears to increase the antidepressant effect of trazodone.
Carbamazepine may accelerate the metabolism of zotepine.
Decreased plasma concentration of carbamazepine
Carbamazepine is metabolised by the cytochrome P450 system (mainly by the isoenzyme CYP3A4). Inducers of CYP3A4 could therefore increase carbamazepine metabolism and thereby possibly lead to a decrease in carbamazepine plasma concentrations and therapeutic effect. Conversely, after stopping a CYP3A4 inducer, there could be a reduced metabolism of carbamazepine and consequently an increase in carbamazepine plasma concentrations. A reduction in the carbamazepine plasma concentration is possible, e.g. with the following substances (arranged according to substance class):
Other Anticonvulsants: felbamate, methosuximide, oxcarbazepine, phenobarbital, phensuximide, phenytoin (to avoid phenytoin intoxication and sub-therapeutic concentrations of carbamazepine, it is recommended to adjust the plasma concentration of phenytoin to 13 micrograms/ml before starting the additional treatment with carbamazepine), fosphenytoin, primidone, progabide and possibly (here the data are partially contradictory) clonazepam, valproic acid, valpromide.
Tuberculosis drug: rifampicin.
Bronchodilators or Anti-Asthmatics: theophylline, aminophylline.
Dermatics: isotretinoin.
Cytostatics: cisplatin, doxorubicin.
Other: St John's wort (Hypericum perforatum).
On the other hand, the plasma levels of the pharmacologically active metabolite carbamazepine-10, 11-epoxide can be increased by valproic acid and primidone.
Administration of felbamate can reduce the plasma level of carbamazepine and increase that of carbamazepine-10, 11-epoxide, while at the same time the felbamate level can be reduced.
Due to the mutual influence, especially when several antiepileptic drugs are administered at the same time, it is recommended to monitor the plasma levels and, if required, to adjust the dosage of carbamazepine.
Increased plasma concentration of carbamazepine and/or carbamazepine-10, 11-epoxide
Carbamazepine is primarily metabolized by cytochrome P-450 3A4 (CYP3A4) to the active metabolite, carbamazepine-10, 11-epoxide. The concomitant use of inhibitors of CYP3A4 can therefore lead to an increase in carbamazepine plasma concentrations, which can result in side effects.
Elevated plasma levels of carbamazepine can lead to the symptoms mentioned in section 4.8 (e.g. dizziness, drowsiness, unsteady gait, double vision). Therefore, if such symptoms occur, the carbamazepine plasma concentration should be monitored and the dose should be reduced if required.
The plasma concentration of carbamazepine can be increased, e.g. by the following substances (arranged according to substance class):
Analgesics, anti-inflammatory substances: dextropropoxyphene/propoxyphene, ibuprofen.
Androgens: danazol.
Antibiotics: macrolide antibiotics (e.g. erythromycin, troleandomycin, josamycin, clarithromycin, ciprofloxacin).
Antidepressants: fluoxetine, fluvoxamine, nefazodone, paroxetine, trazodone, viloxazine, possibly desipramine.
Other anticonvulsants: stiripentol, vigabatrin.
Antifungals: azoles (e.g. itraconazole, ketoconazole, fluconazole, voriconazole). Alternative anti-convulsants may be recommended in patients treated with voriconazole or itraconazole.
Antihistamines: loratadine, terfenadine.
Tuberculosis medicine: isoniazid.
Antivirals: protease inhibitors for HIV treatment (e.g. ritonavir).
Carbonic anhydrase inhibitors (diuretics): acetazolamide.
Calcium antagonists: diltiazem, verapamil.
Muscle relaxants: oxybutynin, dantrolene.
Neuroleptics: loxapine, olanzapine, quetiapine.
Platelet aggregation inhibitor: ticlopidine.
Ulcer therapeutics: omeprazole, possibly cimetidine.
Other: grapefruit juice, nicotinamide (in high doses).
Increased plasma concentration of the active metabolite carbamazepine-10,11-epoxide:
Human microsomal epoxide hydrolase has been identified as the enzyme involved in the formation of the 10, 11-trans diol from carbamazepine-10, 11-epoxide. Concomitant administration of human microsomal epoxide hydrolase inhibitors may therefore lead to increased plasma concentrations of carbamazepine-10, 11-epoxide.
Increased plasma levels of carbamazepine-10, 11-epoxide can lead to the symptoms mentioned in section 4.8 (e.g. dizziness, drowsiness, unsteady gait, double vision). Therefore, if such symptoms occur, the plasma concentration should be monitored and the dose should be adjusted if necessary when the following substances are co-administered:
Loxapine, quetiapine, primidone, progabide, valproic acid, valnoctamide, valpromide and brivaracetam.
Other interactions that require special attention:
Concomitant use of carbamazepine and levetiracetam may increase carbamazepine-induced toxicity.
The liver toxicity of isoniazid can be increased by carbamazepine.
The simultaneous use of carbamazepine and lithium or metoclopramide on the one hand and neuroleptics (Haloperidol, Thioridazine) on the other hand can promote the occurrence of neurological side effects. In patients treated with neuroleptics, it should be noted that carbamazepine can reduce the plasma level of these drugs and thereby cause a worsening of the clinical picture. A dose adjustment of the respective neuroleptic may be required.
It should be noted that the simultaneous use of lithium and carbamazepine in particular can increase the neurotoxic effects of both active substances, even in the presence of therapeutic lithium levels. Therefore, careful monitoring of blood levels of both is required. A previous treatment with neuroleptics should be more than 8 weeks ago and not take place at the same time. The following signs of neurotoxic symptoms should be observed: Unsteady gait, ataxia, horizontal nystagmus, increased muscle reflexes, muscle twitching (muscle fasciculations).
The combined administration of carbamazepine and some diuretics (hydrochlorothiazide, furosemide) can lead to symptomatic hyponatraemia.
The effectiveness of non-depolarising muscle relaxants such as pancuronium can be impaired by carbamazepine. As a result, the neuromuscular blockade can be removed more quickly. Patients treated with muscle relaxants should be monitored for this and the dose of these drugs should be increased if required.
Like other psychoactive substances, carbamazepine can reduce the pateint's alcohol tolerance. Therefore, patients should not drink alcohol during treatment.
Concomitant administration of carbamazepine and direct-acting oral anti-coagulants (rivaroxaban, dabigatran, apixaban and edoxaban) may lead to reduced plasma levels of the direct-acting oral anti-coagulants. Please refer to the following table for more details:
| Direct-acting oral anticoagulants (DOAC) | Recommendations for concomitant use of DOAC and carbamazepine |
| Apixaban | In the prophylaxis of venous thromboembolism (VTE) after elective hip or knee replacement surgery, in the prophylaxis of stroke and systemic embolism in patients with non-valvular atrial fibrillation (NVAF) as well as in the prophylaxis of recurrent deep vein thrombosis (DVT) and pulmonary embolism (PE), concomitant use should only be done with caution. Concomitant use should be avoided when treating DVT and PE. |
| Rivaroxaban | Concomitant use should be avoided unless the patient is closely monitored for signs and symptoms of thrombosis. |
| Dabigatran | Concomitant use should be avoided. |
| Edoxaban | Concomitant administration should only be done with caution. |
There are indications in the literature that the additional intake of carbamazepine in the case of pre-existing neuroleptic therapy increases the risk of the occurrence of a neuroleptic malignant syndrome or Stevens-Johnson syndrome.
If isotretinoin (active ingredient for acne treatment) and carbamazepine are administered at the same time, the carbamazepine plasma level should be monitored.
Concomitant administration of carbamazepine with paracetamol can reduce the bioavailability of paracetamol.
Carbamazepine appears to increase the elimination of thyroid hormones and increase the need for them in patients with hypothyroidism. For this reason, the thyroid parameters should be determined at the start and end of treatment with carbamazepine in patients who are receiving substitution therapy. If necessary, a dose adjustment of the thyroid hormone preparations should be made. In particular, concomitant treatment with carbamazepine and other anticonvulsants (e.g. phenobarbital) may change thyroid function.
The concomitant administration of antidepressants of the serotonin reuptake inhibitor type (e.g. fluoxetine) can lead to toxic serotonin syndrome.
It is recommended not to use carbamazepine in combination with nefazodone (an antidepressant), as carbamazepine can lead to a significant reduction in the nefazodone plasma level up to a loss of efficacy. In addition, when nefazodone and carbamazepine are taken at the same time, the carbamazepine plasma level increases and that of its active degradation product, carbamazepine-10, 11-epoxide, decreases.
Concomitant use of carbamazepine and anti-arrhythmics, cyclic antidepressants, or erythromycin increases the risk of cardiac conduction disorders.
Impairment of serological examinations
By interfering with the HPLC analysis, carbamazepine can lead to false positive perphenazine concentrations.
Carbamazepine and its 10, 11-epoxide metabolite can cause false positive concentrations of tricyclic antidepressants in fluorescence polarisation immunoassays.