Anticonvulsant action of tiagabine, a new GABA-uptake inhibitor

Synthesis and Molecular Docking of New Thiophene Derivatives as Lactate Dehydrogenase-A Inhibitors

BACKGROUND & OBJECTIVE

A series of novel derivatives possessing the thiophene moiety were synthesized using ethyl 5'-amino-2,3'-bithiophene-4'-carboxylate as the starting material.

METHODS

The new synthesized derivatives were screened as lactate dehydrogenase (LDH) inhibitors. LDH plays an important role in glucose metabolism in cancer cells and can affect tumor genesis and metastasis.

RESULTS

3-Substituted p-tolylthieno[2,3-d]pyrimidin-4(3H)-ones 4 were the most potent inhibitors in this study compared to Galloflavin reference drug.

CONCLUSION

Molecular docking studies on the Human Lactate Dehydrogenase active site were carried out on the synthesized compounds and the MolDock scores ranged between -127 to -171.

Tiagabine: efficacy and safety in adjunctive treatment of partial seizures

PURPOSE

To assess the efficacy and safety of tiagabine (TGB), a new antiepileptic drug (AED), as add-on therapy in patients with refractory partial seizures.

METHODS

This response-dependent study used an open-label screening phase (in which patients were titrated to their optimal TGB dose, < or =64 mg/day) followed by a double-blind, placebo-controlled, crossover phase. Initial eligibility criteria included (a) seizures inadequately controlled by existing AEDs, and (b) six or more partial seizures during an 8-week baseline period. Patients showing benefit from TGB (> or =25% reduction in total seizure rate relative to baseline) were eligible for randomization into the double-blind phase, which comprised two 7-week assessment periods separated by a 3-week crossover period.

RESULTS

Forty-four (50%) of the 88 enrolled patients entered the double-blind phase of the study during which there were significant reductions compared with placebo in all partial (p < 0.01), complex partial (p < 0.001), and secondarily generalized tonic-clonic seizure rates (p < 0.05). Thirty-three percent of patients experienced a reduction of > or =50% in the all partial seizure rate. Eight (22%) patients receiving TGB during the double-blind phase reported adverse events, of which dizziness and incoordination were the most frequent. Three patients withdrew from treatment during the double-blind phase because of adverse events; two during treatment with TGB and one during treatment with placebo. TGB did not affect plasma concentrations of other coadministered AEDs.

CONCLUSIONS

TGB was significantly better than placebo in terms of seizure rate reduction and was generally well-tolerated in patients with difficult to control seizures.

Pharmacology and clinical experience with tiagabine

Tiagabine (TGB), a recently approved anti-epileptic drug (AED), has a specific and unique mechanism of action involving the inhibition of gamma-aminobutyric acid (GABA) re-uptake into neurones and glia. TGB is potent and has linear and predictable pharmacokinetics. It does not induce or inhibit hepatic metabolism and has no clinically significant effects on the serum concentrations of other AEDs or commonly used non-AEDs. Double-blind, placebo-controlled studies in primarily hepatic enzyme-induced patients showed that TGB 30 - 56 mg/day is an effective add-on treatment for all subtypes of partial seizures. The most common adverse effects in the trials were dizziness, asthenia (weakness), somnolence, accidental injury, infection, headache, nausea and nervousness. These side effects were usually mild to moderate in severity and generally did not require medical intervention. Long-term safety studies show continued efficacy of TGB over time and no evidence of tolerance for efficacy. Open studies confirm that patients with medically refractory partial epilepsy can be successfully converted to TGB monotherapy and that TGB may be effective for other seizure types, such as infantile spasms.

Tiagabine

Tiagabine (TGB) is a recently approved antiepileptic drug (AED) that inhibits y-aminobutyric acid (GABA) reuptake into neurons and glia, a mechanism of action that is specific and unique among the AEDs. TGB is potent and has linear and predictable pharmacokinetics. It has no clinically relevant effects on hepatic metabolism or serum concentrations of other AEDs, effects on laboratory values, or interactions with common non-AEDs. TGB is effective as add-on therapy for partial seizures in patients with medically refractory epilepsy in doses ranging from 30 to 56 mg daily. Conversion to TGB monotherapy can be achieved in patients with medically refractory epilepsy, although additional controlled studies are needed to confirm the efficacy of TGB as monotherapy and to establish the effective dosage range. In controlled studies, the most common adverse events of TGB are dizziness, asthenia, somnolence, accidental injury, infection, headache, nausea, and nervousness. These are usually mild to moderate in severity and almost always resolve without medical intervention.

Tiagabine antinociception in rodents depends on GABA(B) receptor activation: parallel antinociception testing and medial thalamus GABA microdialysis

The effects of a new antiepileptic drug, tiagabine, (R)-N-[4,4-di-(3-methylthien-2-yl)but-3-enyl] nipecotic acid hydrochloride, were studied in mice and rats in antinociceptive tests, using three kinds of noxious stimuli: mechanical (paw pressure), chemical (abdominal constriction) and thermal (hot plate). In vivo microdialysis was performed in parallel in awake, freely moving rats in order to evaluate possible alterations in extracellular gamma-aminobutyric acid (GABA) levels in a pain-modulating region, the medial thalamus. Systemic administration of tiagabine, 30 mg kg(-1) i.p., increased nearly twofold the extracellular GABA levels in rats and increased significantly the rat paw pressure nociceptive threshold in a time-correlated manner. Dose-related significant tiagabine-induced antinociception was also observed at the doses of 1 and 3 mg kg(-1) i.p. in the mouse hot plate and abdominal constriction tests. The tiagabine antinociception was completely antagonised by pretreatment with the selective GABA(B) receptor antagonist, CGP 35348, (3-aminopropyl-diethoxy-methyl-phosphinic acid) (2.5 microg/mouse or 25 microg/rat i.c.v.), but not by naloxone (1 mg kg(-1) s.c.), both administered 15 min before tiagabine. Thus, it is suggested that tiagabine causes antinociception due to raised endogenous GABA levels which in turn activate GABA(B) receptors.

Development of a limited sampling approach in pharmacokinetic studies: experience with the antiepilepsy drug tiagabine

A sparse sampling method is proposed to assess pharmacokinetic parameters after a single dose of the antiepilepsy drug tiagabine. Pharmacokinetic parameters obtained from two different pharmacokinetic studies were compared using sparse sampling (7 blood samples) with extensive sampling (15 to 16 blood samples). The results indicated that sparse blood samples taken at appropriate times can be used to estimate pharmacokinetic parameters as accurately as extensive blood samples. In addition, a limited sampling model (LSM) was developed using samples from 10 subjects at two time points (6 and 8 hours). The model was validated in 40 subjects and provided good population mean estimates of area under the concentration-time curve (AUC) and maximum concentration (Cmax). The sparse sampling method described here can be used to assess pharmacokinetic parameters in drug development provided a prior knowledge of the pharmacokinetics of a drug has been obtained from extensive sampling. Further, the LSM described here may be useful in estimating AUC and Cmax of tiagabine using two samples in clinical settings. The LSM approach described here can also be used to estimate AUC and Cmax of a drug in preclinical toxicokinetic studies without detailed pharmacokinetic studies.

Tiagabine

Tiagabine is a novel antiepileptic drug that was designed to block gamma-aminobutyric acid uptake by presynaptic neurons and glial cells. It has been shown to be effective against partial seizures in adults and adolescents. Preliminary pediatric data are also encouraging. This article reviews the available animal and human data on the pharmacokinetics, efficacy, and safety of tiagabine.

International experience with tiagabine add-on therapy

Tiagabine (TGB) hydrochloride is a novel antiepileptic drug (AED) that is a potent and specific inhibitor of gamma-aminobutyric acid (GABA) uptake into glial and neuronal elements. In accordance with medical and regulatory standards, the clinical development program for TGB as an AED has assessed the value of TGB in add-on treatment, focusing mainly on partial seizures, including secondarily generalized seizures. Five add-on, placebo-controlled trials and six noncomparative, open-label, long-term multicenter trials have been or are being conducted in Australia, Europe, and the U.S.A. The results of these trials, involving 2,261 patients, indicate that TGB has efficacy as add-on therapy in patients with epilepsy difficult to control with existing AEDs. Efficacy of TGB is also sustained with long-term treatment. A clear dose-response has been demonstrated, and the minimal effective dose level is 30 mg. TGB is also tolerated, and with long-term therapy no new or more severe types of adverse events develop. These studies have included a wide age range of patients, including adolescents and the elderly.

Tiagabine: the safety landscape

Tiagabine (TGB) hydrochloride is a potential new antiepileptic drug (AED) undergoing clinical development. Experience in humans amounts to 1,810 patient-years of exposure. TGB was found to be tolerated in an integrated safety analysis of five double-blind, add-on therapy trials involving approximately 1,000 patients with epilepsy with difficult-to-control seizures with existing AEDs. Discontinuation resulting from adverse events were infrequent, occurring in 15% of patients receiving TGB compared to 5% receiving placebo. The most frequently reported adverse event was dizziness, which was usually transient and did not require medical intervention. Adverse events that were statistically significantly more common with TGB than placebo were dizziness, asthenia, nervousness, tremor, diarrhea, and depression (not major depression). Adverse events were usually mild to moderate in severity and transient, and most were associated with dose titration. The incidence, type, and severity of adverse events in long-term studies were comparable with those in short-term studies. Serious adverse events were uncommon and no idiosyncratic events were reported.

Tiagabine pharmacology in profile

Tiagabine (TGB) hydrochloride, a nipecotic acid derivative linked to a lipophilic anchor, potently and specifically inhibits uptake of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) into astrocytes and neurons. With microdialysis, TGB has been shown to increase extracellular overflow of GABA in the midbrain of awake rats. TGB administration prolongs neuronal depolarization induced by iontophoretically applied GABA in hippocampal slices. TGB is effective in a wide range of seizure models, including pentylenetetrazol-induced, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM)-induced tonic, amygdala-kindled and picrotoxin-induced convulsions, and maximal electroshock seizures in rodents. In humans, TGB absorption is rapid and complete. It is metabolized in the liver, largely by isoform 3A of the cytochrome P450 family of enzymes. The process of elimination is linear, with a half-life of 5-8 h. TGB does not induce or inhibit metabolic processes, although it provides a target for enzyme inducers that can lower its elimination half-life to 2-3 h. Accordingly, TGB does not alter the concentrations of other antiepileptic drugs (AEDs), with the possible exception of a small decrease in valproate levels. A controlled-release formulation of TGB would offset any potential clinical disadvantage of the short elimination half-life, particularly in patients receiving concurrent treatment with enzyme-induced AEDs.