Product Details

PIRACETAM

Piracetam is a nootropic drug in the racetams group, with chemical name 2-oxo-1-pyrrolidine acetamide. It shares the same 2-oxo-pyrrolidone base structure with pyroglutamic acid and is a cyclic derivative of the neurotransmitter γ-aminobutyric acid (GABA). However its mechanism of action differ from that of endogenous GABA.Piracetam has neuroprotective and anticonvulsant properties and is reported to improve neural plasticity [1]. Its efficacy is documented in cognitive disorders and dementia, vertigo, cortical myoclonus, dyslexia, and sickle cell anemia although the clinical application in these conditions is not yet established. Piracetam has effects on the vascular system by reduce erythrocyte adhesion to vascular endothelium, hinder vasospasm and facilitate microcirculation [1].

Originally marketed by UCB Pharma in 1971, piracetam was the first nootropic drug to modulate cognitive function without causing sedation or stimulation [1]. In the United States, it is not approved by the US Food and Drug Administration for any medical use and it is not permitted to be sold as a dietary supplement. In the UK, piracetam is prescribed mainly for myoclonus, but is used off-label for other conditions such as learning difficulties in children, memory loss or other cognitive defects in the elderly, and sickle-cell vaso-occlusive crises [4]. Evidence to support its use for many conditions is unclear.

Indication

Indicated in adult patients suffering from myoclonus of cortical origin, irrespective of aetiology, and should be used in combination with other anti-myoclonic therapies [5].

Pharmacodynamics

Piracetam is known to mediate various pharmacodynamic actions:

Neuronal effects:

Piracetam modulates the cholinergic, serotonergic, noradrenergic, and glutamatergic neurotransmission although the drug does not display high affinity to any of the associated receptors (Ki >10μM). Instead, piracetam increases the density of postsynaptic receptors and/or restore the function of these receptors through stabilizing the membrane fluidity [1]. In the forebrain of aging mice, the density of NMDA receptors was increased by approximately 20% following 14 days of piracetam treatment. Based on the findings of various animal and human studies, the cognitive processses including learning, memory, attention and consciousness were enhanced from piracetam therapy without inducing sedation and psychostimulant effects [5]. Piracetam mediate neuroprotective effects against hypoxia-induced damage, intoxication, and electroconvulsive therapy [5].

In two studies involving alcohol-treated rats with evidences of withdrawal-related neuronal loss, piracetam was shown to reduce the extent of neuronal loss and increase the numbers of synapses in the hippocampus by up to 20% relative to alcohol-treated or alcohol-withdrawn rats [1]. This suggests that piracetam is capable in promoting neuroplasticity when recoverable neural circuits are present [1]. Although the mechanism of action is not fully understood, administration of piracetam prior to a convulsant stimulus reduces the seizure severity and enhances the anticonvulsant effectiveness of conventional antiepileptics such as carbamazepine and diazepam [3].

Vascular effects:

Piracetam is shown to increase the deformability of erythrocytes, reduce platelet aggregation in a dose-dependent manner, reduce the adhesion of erythrocytes to vascular endothelium and capillary vasospasm. In healthy volunteers, piracetam mediated a direct stimulant effect on prostacycline synthesis and reduced the plasma levels of fibrinogen and von Willebrand’s factors (VIII: C; VIII R: AG; VIII R: vW) by 30 to 40% [5]. Potentiated microcirculation is thought to arise from a combination of effects on erythrocytes, blood vessels and blood coagulation [1].

Mechanism of action

Piracetam interacts with the polar heads in the phospholipids membrane and the resulting mobile drug-lipid complexes are thought to reorganize the lipids and influence membrane function and fluidity [1]. Such interaction has been reported in a study that investigated the effects of neuronal outgrowth induced by beta amyloid peptides; while amyloid peptides cause lipid disorganization within the cell membranes leading to neuronal death, piracetam demonstrated to decrease the destabilizing effects of amyloid peptide [2]. The authors suggest that piracetam induces a positive curvature of the membrane by occupying the polar groups in the phospholipids to counteract the negative curvature induced by amyloid peptides , which in turn would decrease the likelihood of membrane fusion [1]. This mechanism of action is thought to improve membrane stability, allowing the membrane and transmembrane proteins to maintain and recover the three-dimensional structure or folding for normal function [4] such as membrane transport, chemical secretion, and receptor binding and stimulation [1].

Through restored membrane fluidity, piracetam promotes restored neurotransmission such as glutamatergic and cholinergic systems, enhances neuroplasticity and mediates neuroprotective and anticonvulsant effects at the neuronal level [1]. It is also demonstrated that piracetam also improves the fluidity of platelet membranes. At the vascular level, piracetam decreases adhesion of erythrocytes to cell wall and reduces vasospasm which in turn improves microcirculation including cerebral and renal blood flow [1].

Absorption

Piracetam displays a linear and time-dependent pharmacokinetic properties with low intersubject variability over a large range of doses. Piracetam is rapidly and extensively absorbed following oral administration with the peak plasma concentration is reached within 1 hour after dosing in fasted subjects. Following a single oral dose of 3.2 g piracetam, the peak plasma concentration (Cmax) was 84 µg/mL. Intake of food may decrease the Cmax by 17% and increase the time to reach Cmax (Tmax) from 1 to 1.5 hours. Tmax in the cerebrospinal fluid is achieved approximately 5 hours post-administration [4].

The absolute bioavailability of piracetam oral formulations is close to 100% and the steady state plasma concentrations are achieved within 3 days of dosing [4].

Volume of distribution

Vd is approximately 0.6L/kg. Piracetam may cross the blood-brain barrier as it was measured in the cerebrospinal fluid following intravenous administration [4]. Piracetam diffuses to all tissues except adipose tissues, crosses placental barrier and penetrates the membranes of isolated red blood cells [4].

Protein binding

Piracetam is not reported to be bound to plasma proteins [4].

Metabolism

As large proportion of total piracetam administered is excreted as unchanged drug, there is no known major metabolism of piracetam [4].

Route of elimination

Piracetam is predominantly excreted via renal elimination, where about 80-100% of the total dose is recovered in the urine. Approximately 90% of the dose of piracetam is excreted in the urine as unchanged drug [4].

Half life

The plasma half life of piracetam is approximately 5 hours following oral or intravenous administration. The half life in the cerebrospinal fluid was 8.5 hours [4].

Clearance

The apparent total body clearance is 80-90 mL/min [4].

Toxicity

The cases of overdose with piracetam is rare. The highest reported overdose with piracetam was oral intake of 75g which was associated with diarrhea and abdominal pain; the signs were most likely related to the extreme high dose of sorbitol contained in the used formulation. In cases of acute, significant overdosage, stomach emptying by gastric lavage or induced emesis is recommended as there are no known antidotes for piracetam [4]. Management for an overdose will most likely be symptomatic treatment and may include hemodialysis, where the extraction efficacy of the dialyser is 50 to 60% for the drug [4].

Oral LD50 in a mouse acute toxicity study was 2000 mg/kg

SOURCE:DRUGBANK