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====== Valproate ====== | ====== Valproate ====== | ||
- | Valproic acid (2-propyl pentanoic acid, 2-propyl valeric acid) is a short-chain branched fatty acid. Prior to the serendipitous discovery of its anti-epileptic activity in 1963, valproic acid was used as an organic solvent. | + | Valproic acid (2-propyl pentanoic acid, 2-propyl valeric acid) is a short-chain branched fatty acid. Prior to the serendipitous discovery of its anti-epileptic activity in 1963, valproic acid was used as an organic solvent[(: |
===== Authorised indications ===== | ===== Authorised indications ===== | ||
UK-SmPC: In the treatment of generalized, | UK-SmPC: In the treatment of generalized, | ||
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Valproate sodium injection is indicated as an intravenous alternative in patients for whom oral administration of valproate products is temporarily not feasible. | Valproate sodium injection is indicated as an intravenous alternative in patients for whom oral administration of valproate products is temporarily not feasible. | ||
===== Clinical applications ===== | ===== Clinical applications ===== | ||
- | Valproate is one of the most effective broad-spectrum AEDs for all types of seizures and epilepsies. It has superior efficacy in all types of generalised seizures (idiopathic and symptomatic), | + | * Valproate is one of the most effective broad-spectrum AEDs for all types of seizures and epilepsies |
- | + | * It has superior efficacy in all types of generalised seizures (idiopathic and symptomatic), | |
- | However, valproate is (1) far inferior to carbamazepine and some newer AEDs in the treatment of focal epilepsies | + | |
- | + | * valproate | |
- | Unlike many other AEDs, valproate appears to have a very low potential to aggravate seizures[(: | + | |
==== Dosage and titration ==== | ==== Dosage and titration ==== | ||
**Adults:** start treatment with 200 mg/day in two equally divided doses for 3 days. Titrate in increments of 200 mg/day every 3 days to a maintenance dose of usually 1000–1500 mg/day (maximum 3000 mg/day) given in two equally divided doses. Higher initial dosage and faster titration rates are usually well tolerated. | **Adults:** start treatment with 200 mg/day in two equally divided doses for 3 days. Titrate in increments of 200 mg/day every 3 days to a maintenance dose of usually 1000–1500 mg/day (maximum 3000 mg/day) given in two equally divided doses. Higher initial dosage and faster titration rates are usually well tolerated. | ||
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Reference range (measures valproic acid): 50–100 mg/l (300–700 μmol/l). | Reference range (measures valproic acid): 50–100 mg/l (300–700 μmol/l). | ||
+ | Also see: [[https:// | ||
==== Main ADRs ==== | ==== Main ADRs ==== | ||
- | Valproate is associated with serious ADRs, particularly in children and women. Acute liver necrosis and acute pancreatitis, | + | * Valproate is associated with serious ADRs, particularly in children and women. Acute liver necrosis and acute pancreatitis, |
+ | * An estimated 1–2% risk of neural tube defects, predominantly spina bifida aperta, in babies of women on valproate is well established | ||
+ | * overall risk of major teratogenic effects with valproate is two to three-times higher than the background prevalence of major non-syndromic congenital anomalies. This together with polycystic ovary syndrome | ||
- | **CNS-related ADRs:** in contrast with other older AEDs, valproate is not usually associated with drowsiness and fatigability or significant dose-related effects on cognition or behaviour. Valproate encephalopathy is exceptional. | + | **CNS-related ADRs:** |
+ | | ||
+ | * Valproate encephalopathy is exceptional. | ||
+ | * Tremor is the more troublesome CNS adverse effect of valproate. There is great individual susceptibility to the development of tremor, which is usually mild, but may become very intense, socially embarrassing and disabling. It is reversible and declines when the dose is lowered. | ||
- | Tremor is the more troublesome CNS adverse effect of valproate. There is great individual susceptibility to the development of tremor, which is usually mild, but may become very intense, socially embarrassing and disabling. It is reversible and declines when the dose is lowered. | + | **Systemic:** |
- | + | * the most serious are **fatal hepatotoxicity** and **acute haemorrhagic pancreatitis**. | |
- | Systemic: the most serious are fatal hepatotoxicity and acute haemorrhagic pancreatitis. | + | * **fatal hepatotoxicity** |
- | + | | |
- | Hepatic failure resulting in fatalities is primarily age-dependent and occurs mainly in children receiving polypharmacy and with organic brain disease. The risk is 1/600 before the age of 3 years. | + | * the risk is 1/600 before the age of 3 years. |
- | However, this may not be helpful because: | + | * incidence decreases considerably in progressively older patient groups (range 1/ |
- | * benign elevation of liver enzymes is common during valproate treatment | + | * usually occurred during the first 6 months of treatment. The diagnosis is based on clinical criteria with non-specific symptoms, such as malaise, weakness, lethargy, facial oedema, anorexia, vomiting and loss of seizure control. |
- | * severe hepatotoxicity is not preceded by progressive elevation of liver enzymes. | + | * Liver function tests should be performed prior to therapy and at frequent intervals thereafter, especially during the first 6 months. However |
- | Raised liver enzymes are common during treatment with valproate, particularly if used in conjunction with other AEDs. These are usually transient or respond to dose reduction. | + | * benign elevation of liver enzymes is common during valproate treatment, particularly if used in conjunction with other AEDs. These are usually transient or respond to dose reduction |
- | + | * severe hepatotoxicity is not preceded by progressive elevation of liver enzymes. | |
- | Acute haemorrhagic pancreatitis with markedly increased amylase and lipase levels is another rare, but serious, adverse effect of valproate treatment. It develops within the first 3 months of treatment, is more prevalent in children and with polytherapy. | + | * patients |
- | + | * an abnormally low prothrombin level, particularly in association with other relevant abnormalities, | |
- | Hyperammonaemic | + | * any concomitant use of salicylates should be stopped, since they employ the same metabolic pathway. |
- | + | * **acute | |
- | Thrombocytopenia and other haematological abnormalities: | + | * hyperammonaemic |
- | + | | |
- | Weight gain occurs in 20% of patients and is some-times marked; women are more vulnerable. This is usually reversible if valproate is withdrawn early. | + | * Evidence of haemorrhage, |
- | + | | |
- | Hair loss and changes in hair texture or colour are relatively rare; they usually occur in the early months of valproate treatment and may resolve spontaneously despite continuation of the drug. | + | |
- | + | | |
- | Other ADRs concern the gastrointestinal system (e.g. anorexia, constipation, | + | |
FDA warning: All patients who are currently taking or starting on valproate for any indication should be monitored for notable changes in behaviour that could indicate the emergence or worsening of suicidal thoughts or behaviour or depression. | FDA warning: All patients who are currently taking or starting on valproate for any indication should be monitored for notable changes in behaviour that could indicate the emergence or worsening of suicidal thoughts or behaviour or depression. | ||
=== Considerations in women === | === Considerations in women === | ||
- | Valproate treatment in women raises many issues. | ||
**Pregnancy: | **Pregnancy: | ||
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**Interaction with hormonal contraception: | **Interaction with hormonal contraception: | ||
- | |||
- | Other issues: see endocrine abnormalities. | ||
==== Main mechanisms of action ==== | ==== Main mechanisms of action ==== | ||
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* increasing GABA release | * increasing GABA release | ||
* inhibiting GABA uptake. | * inhibiting GABA uptake. | ||
- | However, this GABAergic action is observed only at high valproate levels and may explain its efficacy in other, but not absence, seizures. GABAergic drugs that affect GABAB receptors have a pro-absence action because they potentiate absences. Another explanation for the effect of valproate on absence seizures is that this drug, like ethosuximide, | + | * However, this GABAergic action is observed only at high valproate levels and may explain its efficacy in other, but not absence, seizures. |
+ | * GABAergic drugs that affect GABAB receptors have a pro-absence action because they potentiate absences. Another explanation for the effect of valproate on absence seizures is that this drug, like ethosuximide, | ||
==== Pharmacokinetics ==== | ==== Pharmacokinetics ==== | ||
**Oral bioavailability: | **Oral bioavailability: | ||
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The major elimination pathway is via glucuronidation (40–60%). The remainder is largely metabolised via oxidation pathways, β-oxidation accounting for 30–40% and ω-oxidation, | The major elimination pathway is via glucuronidation (40–60%). The remainder is largely metabolised via oxidation pathways, β-oxidation accounting for 30–40% and ω-oxidation, | ||
- | Elimination half-life: this is variable, but generally appears to be 8–12 hours (range 4–16 hours). It is shorter in patients receiving enzyme-modifying AEDs or in long-term valproate treatment of children and adults. Many antipsychotic and antidepres sant drugs result in competitive metabolism or enzyme inhibition when given as a co-medication with valproate. | + | **Elimination half-life:** this is variable, but generally appears to be 8–12 hours (range 4–16 hours). It is shorter in patients receiving enzyme-modifying AEDs or in long-term valproate treatment of children and adults. Many antipsychotic and antidepres sant drugs result in competitive metabolism or enzyme inhibition when given as a co-medication with valproate. |
**Drug interactions** | **Drug interactions** | ||
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**Effect of other AEDs on valproate: | **Effect of other AEDs on valproate: | ||
* The addition of ethosuximide may reduce the plasma concentration of valproate. | * The addition of ethosuximide may reduce the plasma concentration of valproate. | ||
- | **Effects of valproate on other AEDs:** valproate does not interact with most of the newer AEDs. A notable exception is lamotrigine.Valproate is a potent inhibitor of UGT-dependent metabolism of lamotrigine, | + | **Effects of valproate on other AEDs:** |
+ | | ||
+ | * The addition of valproate to ethosuximide or phenobarbital may double the plasma concentration of these AEDs with concomitant toxicity. | ||
+ | * There is evidence of severe CNS depression, with or without significant elevations of barbiturate or valproate plasma concentrations. | ||
+ | * All patients receiving concomitant barbiturate therapy should be closely monitored for neurological toxicity. | ||
+ | * Plasma barbiturate concentrations should be measured, if possible, and the barbiturate dosage decreased, if appropriate. | ||
+ | * Plasma levels of carbamazepine decrease to around 17%, while those of carbamazepine-10, | ||
+ | * Valproate displaces phenytoin from its plasma albumin-binding sites and inhibits its hepatic metabolism. Valproate significantly increases the free fraction of phenytoin and reduces its total plasma concentration. | ||
+ | * Valproate does not interact with hormonal contraception. | ||
- | The addition | + | ==== Disadvantages ==== |
+ | Particularly unsuitable for: | ||
+ | * women, because | ||
+ | * for focal epilepsis in young children since the doses of valproate required to be effective are much higher in focal than generalised epilepsies. Besides there are other, more effective and safer drugs for focal seizures | ||
- | There is evidence of severe CNS depression, with or without significant elevations | + | ==== History ==== |
+ | Valproic acid (VPA; valproate; di-n-propylacetic acid, DPA; 2-propylpentanoic acid, or 2-propylvaleric acid) was first synthesized in 1882, by Burton[(: | ||
- | Plasma levels of carbamazepine decrease to around 17%, while those of carbamazepine-10,11-epoxide increase | + | Two colleagues, H. Meunier and Y. Meunier, working for a small company, Berthier Laboratories, |
- | Valproate displaces phenytoin from its plasma albumin-binding sites and inhibits its hepatic metabolism. Valproate significantly increases | + | It was first released as antiepileptic drug in France in 1967 after the publication of preclinical studies by Carraz et al. in 1964[(: |
- | + | ==== References | |
- | Valproate does not interact with hormonal contraception. | + | ~~REFNOTES~~ |
- | + | ||
- | ==== Main disadvantages | + | |
- | The superior efficacy of valproate in generalised seizures is hindered by serious acute and chronic ADRs. It is particularly unsuitable for: | + | |
- | * women, because of hormonal changes, weight gain and teratogenicity | + | |
- | * young children, particularly those Valproate is the superior AED for generalised epilepsies, but its use in focal epilepsies is of very limited value, because: the doses of valproate required to be effective are much higher in focal than generalised epilepsies | + | |
- | there are other, more effective and safer drugs for focal seizures | + |