Pharmacokinetic-Pharmacodynamic Modeling of Intravenous and Oral Topiramate and Its Effect on the Symbol-Digit Modalities Test in Adult Healthy Volunteers

The potential of intravenous topiramate for the treatment of status epilepticus

There is considerable clinical evidence that topiramate (TPM) has a high potential in the treatment of refractory and super-refractory status epilepticus (RSE, SRSE). Because TPM is only approved for oral administration, it is applied as suspension via a nasogastric tube for SE treatment. However, this route of administration is impractical in an emergency setting and leads to variable absorption with unpredictable plasma levels and time to peak concentration. Thus, the development of an intravenous (i.v.) solution for TPM is highly desirable. Here we present data on two parenteral formulations of TPM that are currently being developed. One of these solutions is using sulfobutylether-β-cyclodextrin (SBE-β-CD; Captisol®) as an excipient. A 1% solution of TPM in 10% Captisol® has been reported to be well tolerated in safety studies in healthy volunteers and patients with epilepsy or migraine, but efficacy data are not available. The other solution uses the FDA- and EMA-approved excipient amino sugar meglumine. Meglumine is much more effective to dissolve TPM in water than Captisol®. A 1% solution of TPM can be achieved with 0.5-1% of meglumine. While the use of Captisol®-containing solutions is restricted in children and patients with renal impairment, such restrictions do not apply to meglumine. Recently, first-in-human data were reported for a meglumine-based solution of TPM, indicating safety and efficacy when used as a replacement for oral administration in a woman with epilepsy. Based on the multiple mechanisms of action of TPM that directly target the molecular neuronal alterations that are thought to underlie the loss of efficacy of benzodiazepines and other anti-seizure medications during prolonged SE and its rapid brain penetration after i.v. administration, we suggest that parenteral (i.v.) TPM is ideally suited for the treatment of RSE and SRSE. This paper was presented at the 8th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures held in September 2022.

Severity of Topiramate-Related Working Memory Impairment Is Modulated by Plasma Concentration and Working Memory Capacity

Drug side effects that impair cognition can lead to diminished quality of life and discontinuation of therapy. Topiramate is an antiepileptic drug that elicits cognitive deficits more frequently than other antiepileptic drugs, impairing multiple cognitive domains including language, attention, and memory. Although up to 40% of individuals taking topiramate may experience cognitive deficits, we are currently unable to predict which individuals will be most severely affected before administration. The objective of this study was to show the contributions of plasma concentration and working memory capacity in determining the severity of an individual's topiramate-related cognitive impairment. Subjects were enrolled in a double-blind, placebo-controlled crossover study during which they received a single dose of either 100, 150, or 200 mg topiramate. Working memory function was assessed using a modified Sternberg working memory task with 3 memory loads administered 4 hours after dosing. After adjustment for differences in working memory capacity, each 1 μg/mL of topiramate plasma concentration was associated with a 3.6% decrease in accuracy for all memory loads. Placebo effects occurred as a function of working memory capacity, with individuals with high working memory capacity experiencing less severe placebo-related impairment compared with those with low working memory capacity. Our results demonstrate that severity of topiramate-related cognitive deficits occurs as a function of both drug exposure and baseline cognitive function. By identifying patient- and exposure-related characteristics that modulate the severity of cognitive side effects, topiramate dosing strategies may be individually tailored in the future to prevent unwanted cognitive impairment.

Real-world assessment of treatment with extended-release topiramate (Trokendi XR®) and comparison with previous immediate-release topiramate treatment

AIM

Examine clinical profile of extended-release topiramate (Trokendi XR^®) and compare treatment-emergent adverse events (TEAEs) associated with Trokendi XR versus previous immediate-release topiramate (TPM-IR) treatment.

PATIENTS & METHODS

Pilot retrospective study analyzing data extracted from medical charts of patients ≥6 years of age prescribed Trokendi XR.

RESULTS

Trokendi XR was the most commonly used to prevent migraine. The most common TEAEs recorded during topiramate treatment were cognitive symptoms (word-finding difficulty, attention/concentration difficulty, slowed thinking), paresthesia, gastrointestinal problems and decreased appetite/weight loss. TEAE incidence was significantly (p < 0.001) lower during Trokendi XR versus previous TPM-IR treatment.

CONCLUSION

Trokendi XR use and outcomes in clinical practice were consistent with established profile of topiramate. Results supported the potential for better tolerability of Trokendi XR versus TPM-IR.

Topiramate in Migraine Prevention: A 2016 Perspective

BACKGROUND

In evidence-based guidelines published in 2000, topiramate was a third-tier migraine preventive with no scientific evidence of efficacy; recommendation for its use reflected consensus opinion and clinical experience. Its neurostabilizing activity, coupled with its favorable weight profile, made topiramate an attractive alternative to other migraine preventives that caused weight gain. When guidelines for migraine prevention in episodic migraine were published in 2012, topiramate was included as a first-line option based on double-blind, randomized controlled trials involving nearly 3000 patients. The scientific and clinical interest in topiramate has generated a large body of data from randomized controlled trials, meta-analyses, patient registries, cohort studies, and claims data analyses that have more fully characterized its role as a migraine preventive.

AIM

This article will review the profile of topiramate that has emerged out of the past decade of research and clinical use in migraine prophylaxis. It will also address the rationale for extended-release (XR) formulations in optimizing topiramate therapy in migraine.

SUMMARY

Topiramate has activity at multiple molecular targets, which may account for why it is effective in migraine and most other, more specific, anticonvulsants are not. Based on randomized controlled trials, topiramate reduces migraine frequency and acute medication use, improves quality of life, and reduces disability in patients with episodic migraine and in those with chronic migraine with or without medication overuse headache. Its efficacy in chronic migraine is not improved by the addition of propranolol. Topiramate's ability to prevent progression from high-frequency episodic migraine to chronic migraine remains unclear. Consistent with clinicians' perceptions, migraineurs are more sensitive to topiramate-associated side effects than patients with epilepsy. Paresthesia is a common occurrence early in treatment but is rarely cause for terminating topiramate treatment. Cognitive problems occur much less frequently than paresthesia but are more troublesome in terms of treatment discontinuation. Cognitive complaints can often be managed by slowly increasing the topiramate dose in small increments to allow habituation. As with other carbonic anhydrase inhibitors, topiramate has metabolic effects that favor the development of metabolic acidosis and possibly renal stones. Because migraineurs have an increased risk of renal stones independent of topiramate exposure, clinicians should counsel all migraine patients to maintain hydration. Abrupt onset of blurring, other visual disturbances, and/or ocular pain following topiramate's initiation should be evaluated promptly since this may indicate rare but potentially sight-threatening idiosyncratic events. Postmarketing evidence has shown that first-trimester exposure to topiramate monotherapy is associated with increased occurrence of cleft lip with or without cleft palate (Pregnancy Category D). Even though topiramate's long half-life would seemingly support q.d. dosing, randomized controlled migraine trials used b.i.d. administration of immediate-release (IR) topiramate, which has more favorable plasma concentration-time profile (ie, lower peak concentrations and higher trough concentrations) than q.d. IR dosing. Given the sensitivity of migraineurs to topiramate-related adverse events, particularly cognitive effects, pharmacokinetic profiles should be considered when optimizing migraine outcomes. The extended-release (XR) formulations Qudexy^® XR (Upsher-Smith Laboratories) and Trokendi XR^® (Supernus Pharmaceuticals) were specifically designed to achieve the adherence benefits of q.d. dosing but with more favorable (ie, more constant) steady-state plasma concentrations over the 24-hour dosing interval vs IR topiramate b.i.d. Intriguing results from a study in healthy volunteers showed consistently less impairment in neuropsychometric tests of verbal fluency and mental processing speed with an XR topiramate formulation (Trokendi XR) vs IR topiramate b.i.d. These findings suggest a pharmacodynamic effect associated with significantly reducing plasma concentration fluctuation when topiramate absorption is slowed. Results of retrospective studies in migraineurs treated with XR topiramate appear to support a clinically meaningful benefit of XR topiramate vs IR topiramate in terms of significantly fewer cognitive effects, improved adherence, and overall better outcomes of migraine prophylaxis with topiramate.