Napilex Cr

Uses

Soduim Valproate & Valproic Acid is used for the treatment of all types of epilepsy, e.g. Partial seizures, Absence seizures (petit mal), Generalized tonic-clonic seizures (grand mal), Myoclonic seizures, Atonic seizures, Mixed seizures that include absence attack, Prophylaxis of febrile convulsion, Prophylaxis of post-traumatic epilepsy. It is also used for the treatment of bipolar disorder & prophylaxis of migraine.

Napilex Cr is also used to associated treatment for these conditions: Acute Depressive Episode, Bipolar Disorder (BD), Complex Partial Seizures, Migraine, Seizure, Absence, Seizure, multiple types, Acute Manic episode

How Napilex Cr works

The exact mechanisms by which valproate exerts it's effects on epilepsy, migraine headaches, and bipolar disorder are unknown however several pathways exist which may contribute to the drug's action.

Valproate is known to inhibit succinic semialdehyde dehydrogenase. This inhibition results in an increase in succinic semialdehyde which acts as an inhibitor of GABA transaminase ultimately reducing GABA metabolism and increasing GABAergic neurotransmission. As GABA is an inhibitory neurotransmitter, this increase results in increased inhibitory activity. A possible secondary contributor to cortical inhibition is a direct suppression of voltage gated sodium channel activity and indirect suppression through effects on GABA.

It has also been suggested that valproate impacts the extracellular signal-related kinase pathway (ERK). These effects appear to be dependent on mitogen-activated protein kinase (MEK) and result in the phosphorylation of ERK1/2. This activation increases expression of several downstream targets including ELK-1 with subsequent increases in c-fos, growth cone-associated protein-43 which contributes to neural plasticity, B-cell lymphoma/leukaemia-2 which is an anti-apoptotic protein, and brain-derived neurotrophic factor (BDNF) which is also involved in neural plasticity and growth. Increased neurogenesis and neurite growth due to valproate are attributed to the effects of this pathway. An additional downstream effect of increased BDNF expression appears to be an increase in GABA_A receptors which contribute further to increased GABAergic activity.

Valproate exerts a non-competitive indirect inhibitory effect on myo-inosital-1-phophate synthetase. This results in reduced de novo synthesis of inositol monophosphatase and subsequent inositol depletion. It is unknown how this contributed to valproate's effects on bipolar disorder but [lithium] is known to exert a similar inositol-depleting effect. Valproate exposure also appears to produce down-regulation of protein kinase C proteins (PKC)-α and -ε which are potentially related to bipolar disorder as PKC is unregulated in the frontal cortex of bipolar patients. This is further supported by a similar reduction in PKC with lithium. The inhibition of the PKC pathway may also be a contributor to migraine prophylaxis. Myristoylated alanine-rich C kinase substrate, a PKC substrate, is also downregulated by valproate and may contribute to changes in synaptic remodeling through effects on the cytoskeleton.

Valproate also appears to impact fatty acid metabolism. Less incorporation of fatty acid substrates in sterols and glycerolipids is thought to impact membrane fluidity and result in increased action potential threshold potentially contributing to valproate's antiepileptic action. Valproate has been found to be a non-competitive direct inhibitor of brain microsomal long-chain fatty acyl-CoA synthetase. Inhibition of this enzyme decreases available arichidonyl-CoA, a substrate in the production of inflammatory prostaglandins. It is thought that this may be a mechanism behind valproate's efficacy in migraine prophylaxis as migraines are routinely treated with non-steroidal anti-inflammatory drugs which also inhibit prostaglandin production.

Finally, valproate acts as a direct histone deactylase (HDAC) inhibitor. Hyperacetylation of lysine residues on histones promoted DNA relaxation and allows for increased gene transcription. The scope of valproate's genomic effects is wide with 461 genes being up or down-regulated. The relation of these genomic effects to therapeutic value is not fully characterized however H3 and H4 hyperacetylation correlates with improvement of symptoms in bipolar patients. Histone hyperacetylation at the BDNF gene, increasing BDNF expression, post-seizure is known to occur and is thought to be a neuroprotective mechanism which valproate may strengthen or prolong. H3 hyperacetylation is associated with a reduction in glyceraldehyde-3-phosphate dehydrogenase, a pro-apoptotic enzyme, contributing further to valproate's neuroprotective effects.

Dosage

Napilex Cr dosage

Soduim Valproate & Valproic Acid is a prolong release formulation of sodium Valproate, thus Soduim Valproate & Valproic Acid may be given once or twice daily.

Epilepsy:

• AdultsInitially 600 mg daily given in 2 divided doses, preferably after food, increasing by 200 mg/day at 3-day intervals to a maximum of 2.5 g daily in divided doses until control of seizure is achieved. Usual maintenance dose is 1-2 g daily (20-30 mg/kg daily).
• Children Initially 20 mg/kg daily in divided doses, may be increased (up to 20 kg) provided plasma concentrations monitored (above 40 mg/kg daily also monitor clinical chemistry and hematological parameters).
• Children Initially 400 mg daily in divided doses increased until control (0ver 20 kg) (usually in the range of 20-30 mg/kg daily); Maximum 35 mg/kg daily. Febrile convulsion 20-30 mg/kg/day in 3 divided doses.

Bipolar disorder initially 20-30 mg/kg/day in 2-3 divided doses; adjust dosage in 3-5 days. Maintenance dosage is 1000-2000 mg/day.Prophylaxis of migraine 300 mg twice daily, although some may require 1000 mg daily.

Side Effects

The most common side effects are anorexia, nausea and vomiting. However, these side effects are minimized with the use of enteric coated tablets. Effects on the CNS include sedation, ataxia and tremor. These symptoms occur infrequently and usually respond to a decrease in doses. Rash, alopecia and stimulation of appetite have been observed occasionally. Sodium Valproate has several effects on hepatic function of which elevation of liver enzymes in plasma is observed in up to 40% of patients and often occurs asymptomatically during the first few months of therapy. Rarely a fulminate hepatitis that may be fatal may develop. Children below 2 years of age with other medical conditions and those being treated with multiple antiepileptic agents are specially prone to suffer from hepatic injury, acute pancreatitis and hyperammonemia have also been frequently associated with the use of Sodium Valproate.

Toxicity

LD₅₀ Values

Oral, mouse: 1098 mg/kg

Oral, rat: 670 mg/kg

Overdose

Symptoms of overdose include somnolence, heart block, deep coma, and hypernatremia. Fatalities have been reported, however patients have recovered from valproate serum concentrations as high as 2120 mcg/mL. The unbound fraction may be removed by hemodialysis. Naloxone has been demonstrated to reverse the CNS depressant effects of overdose but may also reverse the anti-epileptic effects.

Reproductive Toxicity

Valproate use in pregnancy is known to increase the risk of neural tube defects and other structural abnormalities. The risk of spina bifida increases from 0.06-0.07% in the normal population to 1-2% in valproate users. The North American Antiepileptic Drug (NAAED) Pregnancy Registry reports a major malformation rate of 9-11%, 5 times the baseline rate. These malformations include neural tube defects, cardiovascular malformations, craniofacial defects (e.g., oral clefts, craniosynostosis), hypospadias, limb malformations (e.g., clubfoot, polydactyly), and other malformations of varying severity involving other body systems. Other antiepileptic drugs, lamotrigine, carbemazepine, and phenytoin, have been found to reduce IQ in children exposed in utero. Valproate was also studied however the results did not achieve statistical significance (97 IQ (CI: 94-101)). Observational studies report an absolute risk increase of 2.9% (relative risk 2.9 times baseline) of autism spectrum disorder in children exposed to valproate in utero. There have been case reports of fatal hepatic failure in children of mothers who used valproate during pregnancy.

There have been reports of male infertility when taking valproate.

Lactation

Valproate is excreted in human milk. Data in the published literature describe the presence of valproate in human milk (range: 0.4 mcg/mL to 3.9 mcg/mL), corresponding to 1% to 10% of maternal serum levels. Valproate serum concentrations collected from breastfed infants aged 3 days postnatal to 12 weeks following delivery ranged from 0.7 mcg/mL to 4 mcg/mL, which were 1% to 6% of maternal serum valproate levels. A published study in children up to six years of age did not report adverse developmental or cognitive effects following exposure to valproate via breast milk.

Other Toxicity Considerations

Use in pediatrics under 2 years of age increases the risk of fatal hepatotoxicity.

Precaution

Liver functions should be monitored before therapy and during first 6 months especially in patients most at risk, No undue potential for bleeding before starting and before major surgery must be ensured, Care should be taken in renal impairment, pregnancy, breast-feeding and systemic lupus erythematosus. Sodium Valproate is partially eliminated in the urine as a ketone metabolite, which may lead to a false interpretation of the urine ketone test. Sudden withdrawal of therapy should be avoided.

Interaction

Sodium Valproate appears to act as a non specific inhibitor of drug metabolism. Drugs to which it interacts most significantly are Phenobarbital, Phenytoin, Warfarin, Aspirin etc.

Volume of Distribution

11 L/1.73m².

Elimination Route

The intravenous and oral forms of valproic acid are expected to produce the same AUC, Cmax, and Cmin at steady-state. The oral delayed-release tablet formulation has a Tmax of 4 hours. Differences in absorption rate are expected from other formulations but are not considered to be clinically important in the context of chronic therapy beyond impacting frequency of dosing. Differences in absorption may create earlier Tmax or higher Cmax values on initiation of therapy and may be affected differently by meals. The extended release tablet formulation had Tmax increase from 4 hours to 8 hours when taken with food. In comparison, the sprinkle capsule formulation had Tmax increase from 3.3 hours to 4.8 hours. Bioavailability is reported to be approximately 90% with all oral formulations with enteric-coated forms possibly reaching 100%.

Half Life

13-19 hours.

The half-life in neonates ranges from 10-67 hours while the half-life in pediatric patients under 2 months of age ranges from 7-13 hours.

Clearance

0.56 L/hr/m²

Pediatric patients between 3 months and 10 years of age have 50% higher clearances by weight. Pediatric patients 10 years of age or older approximate adult values.

Elimination Route

Most drug is eliminated through hepatic metabolism, about 30-50%. The other major contributing pathway is mitochondrial β-oxidation, about 40%. Other oxidative pathways make up an additional 15-20%. Less than 3% is excreted unchanged in the urine.

Pregnancy & Breastfeeding use

Sodium Valproate crosses the placenta and in humans, exposure to valproate in the first trimester has been associated with neural tube defects such as anencephaly and spina bifida in newborn. Pregnant women treated with Soduim Valproate & Valproic Acid should be offered to estimate serum a-fetoprotein. This is excreted in breast milk. However, breast-feeding by a mother taking Soduim Valproate & Valproic Acid probably causes no risk to the child.

Contraindication

Sodium Valproate is contraindicated to patients who have known hypersensitivity to the drug and liver dysfunction. Care should be exercised when prescribing Sodium Valproate in women of child bearing age.

Storage Condition

Store in a cool and dry place, below 30° C and keep away from light.

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