Arton Baftiu

Experience from therapeutic drug monitoring and gender aspects of gabapentin and pregabalin in clinical practice

PURPOSE Gabapentin and pregabalin are antiepileptic drugs (AEDs) with epilepsy and neuropathic pain indications. The purpose of this study was to investigate pharmacokinetic variability of gabapentin and pregabalin and indications for therapeutic drug monitoring (TDM) in clinical practice with focus on gender aspects. METHOD Anonymous data from routine TDM-service at the National Center for Epilepsy regarding serum concentration measurements of gabapentin and pregabalin, 2009-2013, were utilised. All included samples were drug-fasting in the morning at steady-state. RESULTS In total, 356 patients were included; gabapentin 189 (66% women), average age 53 years and pregabalin 167 (56% women), average age 50 years. For gabapentin, mean serum concentration/dose(C/D)-ratio was similar across genders. Only 13% of the patients had concentrations above the lower limit of the reference range (70-120 μmol/L), which indicates a need for reevaluation of the reference range. For pregabalin, the C/D-ratio in women (0.08±0.06) was 42% higher than in men (0.056±0.05; p<0.05). The pharmacokinetic variability (C/D-ratio) was >100-fold for both gabapentin and pregabalin. An indication of use (epilepsy/pain/other) was stated in only 26% of the cases (n=94). Epilepsy was assumed as indication when other AEDs were also measured (50% of patients). This was similar for both genders and for both AEDs. Indications for TDM were stated in 155 cases (44%) and were similar for gabapentin and pregabalin. CONCLUSION Gabapentin and pregabalin are more used in women than in men, and routine use of TDM is most common in patients with epilepsy. Pharmacokinetic variability is extensive, highlighting a need for individualisation of therapy regardless of indication.

Withdrawal of antiepileptic drugs during presurgical video-EEG monitoring: an observational study for evaluation of current practice at a referral center for epilepsy

Withdrawal of antiepileptic drugs (AEDs) before and during video‐EEG‐monitoring is commonly implemented to reduce time needed to register a sufficient number of seizures during presurgical evaluation. There are, however, few guidelines regarding withdrawal rate and observation time.

The Impact of Pharmacokinetic Interactions with Eslicarbazepine Acetate Versus Oxcarbazepine and Carbamazepine in Clinical Practice

Background: Eslicarbazepine acetate (ESL) is a new anti-epileptic drug (AED) chemically related to oxcarbazepine (OXC) and carbamazepine (CBZ) and is increasingly used in clinical practice. The purpose of the study was to investigate 2-way pharmacokinetic interactions between ESL and other AEDs as compared to OXC and CBZ. Methods: Anonymous data regarding age, gender, use of AEDs, daily doses and serum concentration measurements of ESL, OXC, CBZ and lamotrigine (LTG) and other AEDs were retrieved from 2 therapeutic drug monitoring (TDM) databases in Norway. Drugs were categorized according to their known potential for interactions. Concentration/dose (C/D) ratios were calculated. Results: Data from 1100 patients were available. The C/D ratios of ESL and OXC were unchanged in combination with enzyme-inducing AEDs or valproate (VPA). The C/D ratio of CBZ decreased by 40% and 22% in combination with other enzyme-inducing AEDs or VPA, respectively, pointing to an increased clearance. ESL demonstrated no significant enzyme-inducing effect on LTG metabolism although there was a 20% and 34% decrease in the C/D ratio of LTG in combination with OXC and CBZ, respectively. Conclusions: Possible pharmacokinetic interactions have been studied for ESL as compared to OXC and CBZ. The pharmacokinetics of ESL is not affected by enzyme-inducing AEDs or VPA and does not affect the metabolism of LTG in contrast to OXC and CBZ. The study demonstrates the value of using TDM databases to explore the potential for pharmacokinetic interactions of new AEDs.

Therapeutic Drug Monitoring of Clobazam and Its Metabolite-Impact of Age and Comedication on Pharmacokinetic Variability.

Background: Clobazam (CLB) has been used as an antiepileptic drug for several decades. There is still insufficient data regarding its pharmacokinetic variability in clinical practice. The purpose of this study was to investigate pharmacokinetic variability of CLB with emphasis on the impact of age and comedication in patients with epilepsy. Methods: Serum concentration measurements of CLB and its metabolite N-desmethylclobazam (NCLB), as well as demographic and clinical data were retrieved from the routine therapeutic drug monitoring service at the National Center for Epilepsy, Norway, 2009–2013. NCLB/CLB and total (CLB + NCLB), CLB and NCLB concentration/dose (C/D) ratios were calculated. Results: 550 patients (296 women/254 men), average age 27 years (range 1–86), were included. The interindividual pharmacokinetic variability was extensive, as illustrated by a 100-fold variability in serum concentration compared with dose (total C/D ratio 0.03–3.29 µmol·L−1·mg−1). The CLB C/D ratio was 36% lower in young children (2–9 years) than in adults (18–64 years), reflecting a higher clearance. In patients receiving phenytoin, felbamate, stiripentol, oxcarbazepine or eslicarbazepine acetate, valproate, phenobarbital, zonisamide or carbamazepine one or more of the calculated ratios were significantly different from that in patients receiving no or neutral comedications. The mean values for the different groups were in the order of 20%–230% of C/D ratios in the neutral group and 200%–950% of the NCLB/CLB ratio. Conclusions: The pharmacokinetic variability of CLB and its metabolite NCLB in clinical practice is extensive, and is influenced by drug–drug interactions, age, and pharmacogenetics. Therapeutic drug monitoring of CLB and NCLB is therefore valuable in patient management.

Pharmacokinetic variability of valproate in women of childbearing age

The purpose was to investigate pharmacokinetic variability of valproic acid (VPA) in women of childbearing age by therapeutic drug monitoring (TDM) data to elucidate the variable relationship between dose and serum concentrations with the ultimate aim of facilitating safer use of VPA. Anonymized retrospective data from the TDM database (2006–2015) at the National Center for Epilepsy in Norway were used. Trough total concentrations of VPA at assumed steady state in women aged 14–46 years were analyzed. Data from 643 nonpregnant women of childbearing age (mean age = 27 years) were included. Mean dose and serum concentration of VPA were 968 (standard deviation [SD] = 453) mg/day and 411 (SD = 138) μmol/L, respectively, and 59% used polytherapy. The pharmacokinetic variability in serum concentration/dose (C/D) ratios between women was extensive. For doses <700 mg/day (n = 202; 32%; 150–625 mg/day), mean serum concentration was 336 μmol/L and variability in C/D ratio was 10‐fold. The variability decreased with increasing dose to eightfold (≥700 to <1,500 mg/day, n = 358) and fourfold (≥1,500 mg/day, n = 96). This study demonstrates the extensive pharmacokinetic variability of VPA among women of childbearing age, which is most pronounced at low doses. In future studies, serum concentrations of VPA, rather than dosage, should be used as a guide for exposure of VPA and possible risks of teratogenicity to evaluate safety aspects of VPA in women.

Availability of antiepileptic drugs across Europe.

Europe consists of 53 countries with widely different economic conditions and different political, educational, and health care systems. This study was aimed at determining the availability of antiepileptic drugs (AEDs) across Europe. An electronic questionnaire was submitted to all 43 European chapters of the International League Against Epilepsy (ILAE). Outcome measures were availability of older, newer, and newest AEDs, generic products, indications, reimbursement rules, and reasons for lack of availability of AEDs. Countries were divided according to economic status as defined by the World Bank. Thirty‐four chapters (79%) provided data. There were large differences in AED availability across countries, especially between high‐income countries and the other countries. The newest AEDs were not available in any of the 12 non–high‐income countries. Availability was higher in countries with public reimbursement systems. Reimbursement policies ranged from full reimbursement for all AEDs to complete lack of reimbursement. Main hurdles for poor access to AEDs included lack of regulatory approval, high prices and reimbursement restrictions. The availability of AEDs differs across European countries, with many hurdles hampering access to epilepsy medicines, particularly to new medications. These findings raise major concerns on the quality of epilepsy care in many countries.

Utilisation and polypharmacy aspects of antiepileptic drugs in elderly versus younger patients with epilepsy: A pharmacoepidemiological study of CNS-active drugs in Norway, 2004-2015

BACKGROUND AND PURPOSE Many patients with epilepsy use antiepileptic drugs (AEDs) in combination. The elderly is a vulnerable group regarding polypharmacy. The purpose of this study was to investigate changes in utilisation of AEDs, and the extent of polypharmacy with other CNS-active drugs in elderly versus younger patients in Norway. METHODS This pharmacoepidemiological study included all prescriptions of antiepileptic, antidepressant and antipsychotic drugs from Norwegian pharmacies in the Norwegian Prescription Database (NorPD) (2004-2015). Variables included number of patients, utilisation in defined daily doses, age, gender, and diagnosis specific reimbursement codes for AEDs. RESULTS The use of AEDs has increased in all age groups in this population-based study in Norway. In the elderly, AEDs used in neuropathic pain (mainly gabapentin and pregabalin) have increased more than 10-fold (from 0.7 to 9.6 DDDs/1000 elderly/day, 2004-2015), while the prevalence of users is four times more than in younger patients. Polypharmacy between antiepileptic, antidepressant and antipsychotic drugs occurred in 35% of elderly and 38% of younger patients with epilepsy. The use of enzyme-inducers was common, and occurred more often in elderly patients. A total of 42 different interactions that may have clinical implications were identified among these drugs. CONCLUSION The use of AEDs in elderly compared to younger patients is increasing, especially in neuropathic pain. Polypharmacy with antiepileptic, antidepressant and/or antipsychotic drugs was documented in more than one third of the patients. Awareness of increased drug utilisation, polypharmacy with potential drug interactions, and focus on elderly patients are important for increased patient safety.