Dichloroacetate: population pharmacokinetics with a pharmacodynamic sequential link model.

Dichloroacetate (DCA) is a small molecule that reduces ambient concentrations of lactate in man. It was the purpose of this study to develop pharmacokinetic and pharmacodynamic models for determination of a dose for a pivotal Phase III clinical trial of DCA in patients with traumatic brain injury (TBI). Population pharmacokinetic and pharmacodynamic models were developed for DCA using NONMEM software. The pharmacokinetic data were fit to a physiologic two-compartment model, and the pharmacodynamic data were fit to an indirect physiologic response model. Simulations were employed to evaluate various dosing strategies for consideration in a pivotal Phase III clinical trial of DCA. For the pharmacokinetic model, it was discovered that the clearance of DCA decreased on multiple dosing from 4.82 L/h to 1.07 L/h and that the pharmacokinetics and pharmacodynamics in TBI patients could not be predicted from normal volunteers. Population pharmacokinetic modeling and simulation of the expected effects of several dosing strategies were useful procedures for designing a Phase III trial.

Differentiating the efficacy of 5-HT(1B/1D) agonists.

OBJECTIVE: To examine, for a set of published clinical trials of serotonin (5-HT(1B/1D)) agonists as acute treatments for migraine, whether transformation of efficacy data into therapeutic gain (TG) or number needed to treat (NNT) is useful. BACKGROUND: Pivotal clinical trials of 5-HT(1B/1D) agonists in migraine use a primary end point of change in pain score from 3 or 2 to 1 or 0. Placebo response rates among such studies are variable. Meta-analytic comparisons of 5-HT(1B/1D) agonists often employ TG and NNT as efficacy measures. METHODS: Data from US product labeling or published sources were converted into TG (TG = active response rate [%] - placebo response rate [%]) and NNT (NNT = 1/TG). Pivotal clinical trial data were compared before and after transformation. RESULTS: Therapeutic gain ranged from 17.5% to 51%. The transformation of TG into NNT yielded no clinically significant difference in efficacy estimate for the range of 17.5% to 47% (N = 29 clinical trials). However, NNT and TG had a nonlinear relationship for some secondary end points. When the relationship between the standard primary and secondary end points was compared, the correlation of TG with clinical disability (Pearson coefficient R = 0.93) was stronger than for NNT. Placebo response rates correlated more strongly with NNT (R = 0.66) than active response rates (R = 0.42; N = 29 clinical trials), although both TG and NNT were sensitive to placebo response rate. CONCLUSIONS: Transforming efficacy rates into TG or NNT adds no new information to placebo-controlled trials. The variables, TG and NNT, should not be used to compare members of this class of drugs. Migraine therapies can only be compared using well-designed head-to-head studies and not by meta-analysis. Broader measures of efficacy should be used to describe and compare 5-HT(1B/1D) efficacy.

Comparative tolerability of oral 5-HT1B/1D agonists.

OBJECTIVES: To compare the relative tolerability of 5-HT1B/1D agonists and to investigate the relationships (if any) among systemic exposure, lipophilicity, and clinical tolerability for 5-HT1B/1D agonists. METHODS: Post hoc correlations were sought among the following variables: absolute dose (= administered dose x oral bioavailability), Cmax, LogDpH7.4 (LogD), frequencies of all, neurological and dizziness/somnolence/drowsiness adverse events, adjusted for corresponding placebo-associated frequencies. RESULTS: For effective doses of all drugs with available data, absolute dose-response relationships exist for adverse event frequencies. The overall rank order of the frequency of adverse events was as follows: naratriptan < sumatriptan = rizatriptan < zolmitriptan. With the exception of eletriptan, 5-HT1B/1D agonists exhibit correlations between absolute dose, Cmax (R = 0.97), and LogD (R = 0. 71). For neurological and dizziness/somnolence/drowsiness adverse event frequencies, the overall rank order was sumatriptan < naratriptan < rizatriptan < zolmitriptan. Neither LogD nor absolute dose size predicted adverse event frequencies. CONCLUSIONS: Triptans may be distinguished in terms of their tolerability. Effectiveness, absolute dose size, and lipophilicity are related for the 5-HT1B/1D agonists considered here, except eletriptan. Adverse event frequencies cannot be predicted from in vitro measures of lipophilicity, in vivo estimates of absolute bioavailability, dose size, or any combination of these variables. Since these drugs are all agonists at 5-HT1B/1D receptors in the low nanomolar range, but differ in their tolerability profiles, adverse effects are not likely to be mediated through 5-HT1B/1D receptors. Drugs of this class must be studied individually and on a reasonably large scale in clinical development programs.

Acute migraine treatment outcome measures: a clinician's view.

The efficacy of acute therapies for migraine can be measured in many ways. Traditional endpoints (such as reduction in pain from moderate or severe to mild or absent) are used for regulatory purposes, but do not reflect all components of the migraine syndrome, nor, necessarily, what is most valued by patients and clinicians. There is also a pharmacokinetic-pharmacodynamic disconnection for these traditional types of endpoint, suggesting that they teach us little about how these drugs work. More rigorous, but nonetheless pain-score based, endpoints are reviewed. The biases that can attach to measures such as therapeutic gain and number needed to treat, in the context of migraine therapy, and the limitations of these measures for use in meta-analysis, are discussed. The clinical subtleties of these endpoints are numerous: understanding patients' ability to distinguish between multiple headache types, the best timing of treatment relative to the start of an attack, and measuring clinical outcome may be statistically difficult, but yet may also provide more clinical utility than pain-score analyses. The three therapeutic strategies (Step, Stepped-within-attack, and Stratified care) are reviewed and the place of 5HT(1B/1D) agonists within them, based on the currently best available evidence, is identified. Consideration should be given to more real-life studies, to measuring drug efficacy after early administration during onset of headache, and to greater sophistication in our approach to the necessarily gestalt measures of patient satisfaction and treatment preference.

Migraine polypharmacy and the tolerability of sumatriptan: a large-scale, prospective study.

Polypharmacy (the prescription of more than one therapy for a single patient) and subcutaneous (s.c.) sumatriptan tolerability were prospectively studied in 12,339 migraineurs, each followed for up to 1 year. Inclusion/exclusion criteria were minimal and mirrored United States Imitrex labeling. Drug usage and compliance monitoring were automatically interfaced with prescription refill. Concomitant drugs were used by 79% of patients, with analgesics, antidepressants, and sedatives used most commonly. No adverse interactions between sumatriptan and neurological drugs were found, possibly reflecting relative inability of the former to cross the blood-brain barrier. No difference in cardiovascular adverse events was associated with oral contraceptive use, which was more common than expected. No other drug class influenced adverse event probability, although sample sizes for these comparisons was sometimes <400 patients. This study confirms the prevalence of polypharmacy in migraine, identifies the drugs used, and concludes that, on a population basis, the tolerability of s.c. sumatriptan, when used according to labeled instructions, is unaffected by these concomitant drugs.

Prospective large-scale study of the tolerability of subcutaneous sumatriptan injection for acute treatment of migraine.

To investigate prospectively serious adverse events associated with sumatriptan injection, we studied 12,339 typical migraineurs for up to 12 months each. This study imitated the ordinary clinical use of sumatriptan injection except that: (a) a short, written informed consent was required, (b) there was a centralized, automated dispensing service that audited each patient's product use, (c) patients were sometimes reviewed by telephone, and (d) drug supply and medical consultation were without charge. All adverse events were recorded regardless of etiology. There were 25 fatalities during the study, none being attributable to sumatriptan injection. Of six strokes in the study, two occurred soon after treatment of a migraine attack with sumatriptan injection; whether these were migraine-related or drug-related is discussed. None of the three myocardial infarctions was due to sumatriptan injection use. We conclude that sumatriptan injection is well tolerated when used in accordance with labeling.

Pregnancy and perinatal outcomes in migraineurs using sumatriptan: a prospective study.

BACKGROUND: Sumatriptan is an acute treatment for migraine which is often used by women in their child-bearing years, and who become unexpectedly pregnant. Within the context of the post-marketing use of sumatriptan injection for the acute treatment of migraine, and in compliance with approved labeling, we wished to compare perinatal pregnancy outcomes in women who did and did not use the drug after conception. METHODS: Open-label, prospective study conducted in 12,339 migraineurs (including 9,861 women) whose demography and consumption pattern of sumatriptan injections were typical, and were predicted to include 150 pregnancies. Outcome of pregnancy was the end-point. RESULTS: There were 168 of 173 pregnancies that were well-documented. Sumatriptan was only used prior to conception in 92 cases. There were 76 first trimester exposures to sumatriptan. There were no differences in pregnancy outcome between the two groups. CONCLUSIONS: Perinatal and pregnancy outcome did not differ between patients who had and had not used sumatriptan after conception, at the resolution of these sample sizes. This study design complements the ongoing pregnancy registry, which is now widened to patients exposed to all formulations of sumatriptan.

Dichloroacetate and cerebral ischaemia therapeutics.

Brain ischaemia is a major medical problem which totally lacks meaningful therapeutic options. A drug that reduces morbidity and mortality associated with head injury and stroke would constitute a major medical breakthrough. Although many mechanistic approaches have been evaluated clinically for both stroke and head injury, none have yet to be proven successful. Dichloroacetate (DCA, Ceresine) is a small molecule that activates pyruvate dehydrogenase (PDH) and crosses the blood-brain barrier. PDH activation reduces neurotoxic lactic acidosis which always accompanies brain ischaemia. DCA shows substantial efficacy in a variety of models of stroke, pre-stroke, head or spinal cord injury. Agents that lower cerebral lactic acidosis have not yet been clinically evaluated in head injury and stroke, although DCA has been shown clinically to reduce ambient lactate concentrations in patients with such conditions. DCA has also been shown to be well-tolerated in these patients, and unlike many halogenated molecules, is not mutagenic. Since elevated brain lactate is correlated with poor outcome in both preclinical and clinical studies, an agent such as DCA may prove to reduce the brain injury associated with these disorders. Potential clinical applications of DCA include stroke, head injury, spinal cord injury, and chronic disorders such as congenital lactic acidosis (CLA) and mitochondrial lactic acidosis and stroke-like syndrome (MELAS).

Migraine chronobiology.

This study was undertaken to determine whether migraine attacks exhibits circadian, menstrual, or seasonal variations in frequency and, thus, to characterize more precisely this relapsing, remittent, pleomorphic disease. An analysis of 3582 well-documented migraine attacks in 1698 adults was undertaken. The demographics of the study population accurately represented the known epidemiology of the disease. Migraine attacks started more frequently between 4 AM and 9 AM and within the first few days after onset of menses; this migraine periodicity is strongest amongst women not using oral contraceptives. Seasonal periodicity, if any, is clearly weaker than circadian or menstrual. These chronobiological features may assist in the differential diagnosis of migraine from premenstrual headache and fibromyalgia.

Potential therapeutic applications of fructose-1,6-diphosphate.

Ischaemia-related tissue injury is the leading cause of death in developed countries. Drugs that can reduce ischaemic injury would be beneficial in treatment of myocardial infarction (MI), surgical trauma and stroke. Fructose-1,6-diphosphate (FDP) is a key intermediate in anaerobic glycolysis and is the product of the major regulatory enzyme in the pathway (phosphofructokinase). Preclinical and clinical data suggest that FDP has substantial cytoprotective effects in a variety of ischaemia-reperfusion injury scenarios. Evidence indicates that FDP has a direct effect on ATP pools, reduces ischaemia-induced tissue damage and has positive inotropic effects on heart function. The clinical data suggest that FDP may be a useful drug in a variety of ischaemic and inflammatory clinical settings where acute management of tissue injury is desired. Potential uses include: iv. administration for the reduction of ischaemic injury in sickle cell anaemia, bypass surgery, congestive heart failure, myocardial infarction, as well as organ preservation in transplants.

Reduction of serum lactate by sodium dichloroacetate, and human pharmacokinetic-pharmacodynamic relationships.

Sodium dichloroacetate (DCA) or placebo, two infusions 30 min in duration and 8 h apart, was administered to healthy subjects under double-blind conditions. The objectives were to characterize accurately the tolerability of DCA, its pharmacokinetics, and the reduction of resting serum lactate concentration by DCA. A hybrid, one-compartment pharmacokinetic model fitted best, with zero-order elimination mean of 27.9 micrograms/ml/h at concentrations above about 80 to 120 micrograms/ml, and with first-order elimination (mean kelim = 0.54) at lower serum concentrations of DCA. Resting serum lactate was dose-independently, maximally reduced within 15 min of the end of all active infusions. The duration of suppression of resting serum lactate was dose-dependent, from 4.5 h (30 mg/kg) to > 8 h (100 mg/kg). Second infusions (15-50 mg/kg) again promptly and maximally reduced resting serum lactate. Hysteresis loops were asymmetrical for all doses but exhibited change in shape that was dose-dependent; no good pharmacokinetic-pharmacodynamic model could be fitted that was consistent between doses. Infusions were well tolerated, 100 mg/kg + 50 mg/kg being the highest doses. Somnolence, the only dose-related adverse event, was reported by 3 of 37 subjects at times corresponding to the highest serum DCA concentrations. This study demonstrates the tolerability of i.v. DCA, proposes a simple pharmacokinetic model for its elimination, characterizes the dose-response relationship in terms of time course of effect, shows the dissociation between elimination of DCA and offset of response and will guide further studies of DCA in patients with head injury or stroke.