Liver valproate sodium

I Pharmacokinetics. Valproate sodium is rapidly converted to valproic acid in the stomach, whereas divalproex sodium delayed-release and extended-release tablets must pass into the small intestine to be converted to valproic acid. Valproic acid is highly bound to albumin and other plasma proteins, and it is extensively metabolized in the liver. A summary of the absorption, distribution, metabolism, and elimination data for valproate is found in Table 68-11. ... 

Most benzodiazepines undergo oxidative metabolism in the liver that may be enhanced by enzyme inducers (e.g. carbamazepine, phenytoin) or slowed by inhibitors (sodium valproate, fluoxetine, fluvoxamine). Oxazepam, lorazepam and temazepam are directly conjugated and are not subject to these interactions. 

Pre-existing liver disease In general patients with pre-existing liver disease are not at increased risk of drug-induced hepatotoxicity exceptions to this include methotrexate and sodium valproate... 

Sodium valproate is extensively metabolised in the liver and has a t / of 13 h. It is 90% bound to plasma albumin. Sodium valproate is a nonspecific inhibitor of metabolism, and indeed inhibits its own metabolism, and that of lamotrigine, phenobarbitone, phenytoin and carbamazepine. Sodium valproate does not induce drug metabolising enzymes but its metabolism is enhanced by induction due to other drugs, including antiepileptics. 

Acute hepatocellular necrosis. This reaction varies from a transient disturbance of liver function tests to acute hepatitis. It can be induced by several drugs including general anaesthetics (halothane), antiepileptics (carbamazepine, phenytoin, sodium valproate, phenobarbital), antidepressants (MAO inhibitors), antiinflammatory drugs (indomethacin, ibuprofen), antimicrobials (isoniazid, sulphonamides, nitrofurantoin) and cardiovascular drugs (methyldopa, hydralazine). 

The most commonly observed side effects for valproate are gastrointestinal (anorexia, nausea, and Indigestion). These effects can be minimized by selecting divalproex sodium, which is enterically coated, and by Initiating therapy at a low dose. More Importantly, however, valproate is associated with the development of fatal hepatotoxicity, especially in children or when coadministered with other AEDs. Frequent monitoring of liver function tests is mandatory for determining the onset of toxicity. 

Clinical Effectiveness Unit guidelines on the management of hormonal contraceptives and drug interactions state that valproate does not induce liver enzymes and causes no reduction in ethinylestradiol or progestagens. The manufacturers of sodium valproate and valproate semi sodium state that valproate does not affect the efficacy of hormonal... 

None of these interactions is extensively documented but all appear to be established and of clinical importance. Serum ciclosporin levels should be well monitored if carbamazepine, phenobarbital or phenytoin are added and the ciclosporin dosage increased appropriately. Primidone is metabolised to phenobarbital by the liver, and therefore would be expected to reduce ciclosporin levels. Information about oxcarbazepine is very limited but small reductions in its dose, together with an increase in ciclosporin dose, may be adequate to control any interaction. However, more study is required before oxcarbazepine can be recommended as a suitable alternative. The effects of the interaction may persist for a week or more after the anticonvulsant is withdrawn. Sodium valproate seems not to alter ciclosporin levels, but the case reports of nephritis and hepatotoxicity suggest some caution is warranted. 

Skin A child who was given sodium valproate for epilepsy developed a febrile rash 4 weeks after receiving phenobarbital as well [231" ]. Laboratory testing showed a leukocytosis with eosinophilia and raised C-reactive protein and liver enzymes. Anticonvulsant hypersensitivity syndrome due to phenobarbital was suspected and phenobarbital was withdrawn, with slow full recovery. 

Stewart JD, Horvath R, Baruffini E, Ferrero I, Bulst S, Watkins PB, Fontana RJ, Day CP, Chinnery PF. Polymerase Y gene POLG determines the risk of sodium valproate-induced liver toxicity. Hepatology 2010 52(5) 1791-6. 

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