Carbamazepine serum level

When carbamazepine is administered with primidone, decreased primidone levels and higher carbamazepine serum levels may result. Cimetidine administered with carbamazepine may result in an increase in plasma levels of carbamazepine that can lead to toxicity. Blood levels of lamotrigine increase when the agent is administered with valproic acid, requiring a lower dosage of lamotrigine... 

Carbamazepine serum levels are usually obtained every 1 or 2 weeks during the first 2 months, and then every 3 to 6 months during maintenance therapy. Serum samples are drawn 10 to 12 hours after the dose and at least 4 to 7 days after dosage initiation or change. Most clinicians attempt to maintain levels between 6 and 10 mcg/mL, but some patients may require up to 14 mcg/mL. 

Drugs that can increase carbamazepine serum levels include cimetidine, danazol, diltiazem, erythromycin, felbamate, clarithromycin, fluoxetine, isoniazid, niacinamide, propoxyphene, ketaconazole, itraconazole, verapamil, valproate, troleandomycin, loratadine, nicotinamide, tricyclic antidepressants, SSRIs, nefazodone, protease inhibitors. 

Drugs that can decrease carbamazepine serum levels include charcoal, cisplatin, doxorubicin, felbamate, hydantoins, rifampin, phenobarbital, primidone, theophylline. The serum levels of oral contraceptives, haloperidol, bupropion, anticoagulants, felbamate, valproic acid, felodipine, tricyclic antidepressants, acetaminophen, ziprasidone, voriconazole, topiramate, tiagabine, olanzapine, and lamotrigine can be lowered by carbamazepine. 

Carbamazepine Some, but not all, reports indicate that carbamazepine serum levels can be increased by fluoxetine and fluvoxamine. Toxicity may develop. Sertraline normally appears not to affect carbamazepine, but sertraline levels may be reduced by carbamazepine. Isolated cases of Par-kinson-like and serotonin syndrome have occurred with fluoxetine and carbamazepine, while an isolated case of pancytopenia has been reported with sertraline and carbamazepine. The metabolism of citalopram may be increased. 

Carbamazepine serum levels are usually obtained every 1 to... 

Co-administration with fluvoxamine may result in increases in carbamazepine serum levels by up to 60%. The mechanism is not totally understood, since carbamazepine is metabolized mainly by the cytochrome P450 enzyme CYP3A4 while fluvoxamine is metabolized by CYP1A2. CYP3A4 is not significantly affected by fluvoxamine. 

Anti-infective drugs Ciprofloxacin can greatly increase the risk of seizure induction in patients taking anticonvulsants. Erythromycin produces a rapid 100-200% rise in carbamazepine levels. There is a possibility of reduced plasma levels of the protease inhibitors indinavir and saquinavir with carbamazepine. Isoniazid increases carbamazepine serum levels, and leads to the possible emergence of toxicity (disorientation and aggression). Mefloquine may antagonize the anticonvulsant effect of carbamazepine. Ritonavir, a protease inhibitor, may cause toxicity by raising carbamazepine plasma levels. 

This inhibits the hepatic microsomal enzymes thus, carbamazepine serum levels can increase by up to 2-fold. 

Isolated data suggest that theophylline might decrease carbamazepine serum levels. 

No changes in carbamazepine serum levels were seen in 10 patients who took aspirin 1.5 g daily for 3 days. It would appear that no precautions are necessary if aspirin is used in patients on carbamazepine. 

An established and clinically important interaction. If concurrent use is necessary carbamazepine serum levels should be monitored and the dosage reduced as necessary. 

Carbamazepine serum levels can be raised by dextropropoxyphene. Toxicity may develop unless suitable dosage reductions are made. Oxcarbazepine appears not to interact with dextropro-pox3q hene. 

Two patients had a modest rise in their carbamazepine serum levels after they took gemfibrozil... 

Carbamazepine serum levels are markedly and very rapidly increased by isoniazid and toxicity can occur. Rifampicin has been reported both to augment and negate this interaction. There is evidence to surest that carbamazepine may potentiate isoniazid hepatotoxicity. 

Carbamazepine serum levels are markedly and rapidly increased by eiythromycin or troleandomycin, and toxicity can often develop within 1 to 3 days. Telithromycin is predicted to interact similarly. Clarithromycin also raises carbamazepine levels, but to a lesser extent. Studies suggest that azithromycin, flurithromycin, josamycin, midecamycin, and roxithromycin have no interaction, or no clinically significant interaction, with carbamazepine, but note that a case of carbamazepine toxicity has been reported in a patient given roxithromycin. 

Carbamazepine serum levels are reduced to some extent by phenobarbital, and carbamazepine-10,11-epoxide levels are raised. In children, phenobarbital clearance is decreased by carbamazepine. 

A comparative study found that on average patients taking both carbamazepine and phenobarbital (44 patients) had carbamazepine serum levels that were 18% lower than those taking carbamazepine alone (43 patients). Similar results were found in other studies in both adult and paediatric patients taking both drugs. Levels of the active metabolite, carbamazepine-10,11-epoxide, were increased. " However, one study... 

Omeprazole markedly raised the levels of a single dose of carbamazepine, but had no significant effect on carbamazepine taken long-term. Some anecdotal reports surest that carbamazepine serum levels may possibly be reduced by lansoprazole. Pantoprazole did not affect the pharmacokinetics of carbamazepine in one study. 

The ofter4 cases are consistent, in that carbamazepine levels fell shortly after lansoprazole was added, and/or the control of seizures suddenly worsened. One patient had a fall in carbamazepine serum levels from 11.5 to 7.7 mg/L. The carbamazepine levels of another patient returned to normal when the lansoprazole was stopped. ... 

Omeprazole 20 mg daily for 14 days was found to increase the AUC of a single 400-mg dose of carbamazepine in 7 patients by 75%. The clearance was reduced by 40% and the elimination half-life was more than doubled (from 17.2 to 37.3 hours). However, a retrospective study of the records of 10 patients who had been taking omeprazole 20 mg daily with longterm carbamazepine (rather than a single dose) found a non-significant reduction in carbamazepine serum levels. ... 

Some reports describe rises in serum phen 4oin levels, with toxicity, whereas others describe falls in phen i oin levels. Genetic differences in the metabolism of these drugs may be an explanation for the differences. Falls in carbamazepine serum levels, sometimes with rises in carbamazepine-10,ll-epoxide levels, have been described. 

Information about antiepilepties other than phenytoin is limited, but progabide is reported to minimally reduee, - minimally increase or not to change carbamazepine - " serum levels. An increase of up to 24% in the levels of earbamazepine-10,11-epoxide (the active metabolite of carbamazepine) has also been reported. - Vaiproate, - " and clonazepam" serum levels were not significantly affected by progabide. Progabide appears to eause a small inerease in serum phenobarbital levels, which is of little elinieal importanee. - " ... 

Phenobarbital, phenytoin and carbamazepine can cause a small to moderate reduction in the serum levels of zonisamide, while lamotrigine may increase zonisamide levels. Clonazepam and valproate have little or no effect. Zonisamide shows variable effects (a modest decrease, an increase, or no effect) on carbamazepine serum levels, but has no important effect on lamotrigine, phenobarbital, primidone or valproate levels. Most studies also suggest that zonisamide has no effect on phenytoin levels, but two showed a modest increase. 

Haloperidol. A study in 9 schizophrenics taking haloperidol (average dose 30 mg daily) found a 55% reduction in plasma haloperidol levels (a mean fall from 45.5 to 21.2 nanograms/mL) when they were given carbamazepine for 5 weeks (precise dose not stated). They also took trihexyphenidyl 10 mg daily and oxazepam 30 mg at night as necessary. Carbamazepine serum levels and the control of the disease remained unchanged. 

Clonazepam, in slowly increasing doses up to a maximum of 4 to 6 mg/day given over a 6-week period, had no effect on carbamazepine serum levels. Some patients were also taking phenobarbital. A study in 7 healthy subjects found that carbamazepine 200 mg daily given over a 3-week period reduced the plasma levels of clonazepam 1 mg daily from a range of 4 to 7 nanograms/mL down to 2.5 to 4 nanograms/mL, and reduced the half-life by about one-third. A retrospective analysis of the this interaction in 183 patients found that clonazepam clearance was increased by 22% and carbamazepine clearance was decreased by 20.5% by concurrent use. ... 

Carbamazepine Serum Levels Comparison of Gas Chromatographic, Spectro-metric and Liquid Chromatographic Methods... 

Staniszewska A, Burda P, Waldman W, Anand JS. Correlation between carbamazepine serum level and clinical condition of acute poisoned patient. Przegl Lek 2009 66(6) 279-81. 

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