Valproate

Epilepsy

Valproate Sodium Injection, USP is indicated as an intravenous alternative in patients for whom oral administration of Valproate products is temporarily not feasible in the following conditions:

Valproate Sodium Injection, USP is indicated as monotherapy and adjunctive therapy in the treatment of patients with complex partial seizures that occur either in isolation or in association with other types of seizures. Valproate Sodium Injection, USP is also indicated for use as sole and adjunctive therapy in the treatment of patients with simple and complex absence seizures, and adjunctively in patients with multiple seizure types that include absence seizures.

Simple absence is defined as very brief clouding of the sensorium or loss of consciousness accompanied by certain generalized epileptic discharges without other detectable clinical signs. Complex absence is the term used when other signs are also present.

See WARNINGS AND PRECAUTIONS (5.1) for statement regarding fatal hepatic dysfunction.

Important Limitations

Because of the risk to the fetus of decreased IQ, neural tube defects, and other major congenital malformations, which may occur very early in pregnancy, Valproate should not be administered to a woman of childbearing potential unless the drug is essential to the management of her medical condition [see WARNINGS AND PRECAUTIONS (5.2, 5.3, 5.4), USE IN SPECIFIC POPULATIONS (8.1), and PATIENT COUNSELING INFORMATION (17)].

Epilepsy

Valproate sodium injection is for intravenous use only.

Use of Valproate sodium injection for periods of more than 14 days has not been studied. Patients should be switched to oral Valproate products as soon as it is clinically feasible.

Valproate sodium injection should be administered as a 60 minute infusion (but not more than 20 mg/min) with the same frequency as the oral products, although plasma concentration monitoring and dosage adjustments may be necessary.

In one clinical safety study, approximately 90 patients with epilepsy and with no measurable plasma levels of Valproate were given single infusions of Valproate sodium injection (up to 15 mg/kg and mean dose of 1184 mg) over 5-10 minutes (1.5-3.0 mg/kg/min). Patients generally tolerated the more rapid infusions well [see ADVERSE REACTIONS (6.1)]. This study was not designed to assess the effectiveness of these regimens. For pharmacokinetics with rapid infusions, see CLINICAL PHARMACOLOGY (12.3).

Initial Exposure to Valproate
The following dosage recommendations were obtained from studies utilizing oral divalproex sodium products.

Complex Partial Seizures
For adults and children 10 years of age or older.

Monotherapy (Initial Therapy)
Valproate sodium injection has not been systematically studied as initial therapy. Patients should initiate therapy at 10 to 15 mg/kg/day. The dosage should be increased by 5 to 10 mg/kg/week to achieve optimal clinical response. Ordinarily, optimal clinical response is achieved at daily doses below 60 mg/kg/day. If satisfactory clinical response has not been achieved, plasma levels should be measured to determine whether or not they are in the usually accepted therapeutic range (50 to 100 mcg/mL). No recommendation regarding the safety of Valproate for use at doses above 60 mg/kg/day can be made.
The probability of thrombocytopenia increases significantly at total trough Valproate plasma concentrations above 110 mcg/mL in females and 135 mcg/mL in males. The benefit of improved seizure control with higher doses should be weighed against the possibility of a greater incidence of adverse reactions.

Conversion to Monotherapy
Patients should initiate therapy at 10 to 15 mg/kg/day. The dosage should be increased by 5 to 10 mg/kg/week to achieve optimal clinical response. Ordinarily, optimal clinical response is achieved at daily doses below 60 mg/kg/day. If satisfactory clinical response has not been achieved, plasma levels should be measured to determine whether or not they are in the usually accepted therapeutic range (50-100 mcg/mL). No recommendation regarding the safety of Valproate for use at doses above 60 mg/kg/day can be made. Concomitant antiepilepsy drug (AED) dosage can ordinarily be reduced by approximately 25% every 2 weeks. This reduction may be started at initiation of Valproate sodium injection therapy, or delayed by 1 to 2 weeks if there is a concern that seizures are likely to occur with a reduction. The speed and duration of withdrawal of the concomitant AED can be highly variable, and patients should be monitored closely during this period for increased seizure frequency.

Adjunctive Therapy
Valproate sodium injection may be added to the patient’s regimen at a dosage of 10 to 15 mg/kg/day. The dosage may be increased by 5 to 10 mg/kg/week to achieve optimal clinical response. Ordinarily, optimal clinical response is achieved at daily doses below 60 mg/kg/day. If satisfactory clinical response has not been achieved, plasma levels should be measured to determine whether or not they are in the usually accepted therapeutic range (50 to 100 mcg/mL). No recommendation regarding the safety of Valproate for use at doses above 60 mg/kg/day can be made. If the total daily dose exceeds 250 mg, it should be given in divided doses.
In a study of adjunctive therapy for complex partial seizures in which patients were receiving either carbamazepine or phenytoin in addition to Valproate, no adjustment of carbamazepine or phenytoin dosage was needed [see CLINICAL STUDIES (14)]. However, since Valproate may interact with these or other concurrently administered AEDs as well as other drugs, periodic plasma concentration determinations of concomitant AEDs are recommended during the early course of therapy [see DRUG INTERACTIONS (7)].

Simple and Complex Absence Seizures
The recommended initial dose is 15 mg/kg/day, increasing at one week intervals by 5 to 10 mg/kg/day until seizures are controlled or side effects preclude further increases. The maximum recommended dosage is 60 mg/kg/day. If the total daily dose exceeds 250 mg, it should be given in divided doses.
A good correlation has not been established between daily dose, serum concentrations, and therapeutic effect. However, therapeutic Valproate serum concentration for most patients with absence seizures is considered to range from 50 to 100 mcg/mL. Some patients may be controlled with lower or higher serum concentrations [see CLINICAL PHARMACOLOGY (12.3)].
As the Valproate sodium injection dosage is titrated upward, blood concentrations of phenobarbital and/or phenytoin may be affected [see DRUG INTERACTIONS (7.2)].
Antiepilepsy drugs should not be abruptly discontinued in patients in whom the drug is administered to prevent major seizures because of the strong possibility of precipitating status epilepticus with attendant hypoxia and threat to life.

Replacement Therapy
When switching from oral Valproate products, the total daily dose of Valproate sodium injection should be equivalent to the total daily dose of the oral Valproate product [see CLINICAL PHARMACOLOGY (12)], and should be administered as a 60 minute infusion (but not more than 20 mg/min) with the same frequency as the oral products, although plasma concentration monitoring and dosage adjustments may be necessary. Patients receiving doses near the maximum recommended daily dose of 60 mg/kg/day, particularly those not receiving enzyme-inducing drugs, should be monitored more closely. If the total daily dose exceeds 250 mg, it should be given in a divided regimen. There is no experience with more rapid infusions in patients receiving Valproate sodium injection as replacement therapy. However, the equivalence shown between Valproate sodium injection and oral Valproate products (divalproex sodium) at steady state was only evaluated in an every 6 hour regimen. Whether, when Valproate sodium injection is given less frequently (i.e., twice or three times a day), trough levels fall below those that result from an oral dosage form given via the same regimen, is unknown. For this reason, when Valproate sodium injection is given twice or three times a day, close monitoring of trough plasma levels may be needed.

General Dosing Advice

Dosing in Elderly Patients
Due to a decrease in unbound clearance of Valproate and possibly a greater sensitivity to somnolence in the elderly, the starting dose should be reduced in these patients. Dosage should be increased more slowly and with regular monitoring for fluid and nutritional intake, dehydration, somnolence, and other adverse reactions. Dose reductions or discontinuation of Valproate should be considered in patients with decreased food or fluid intake and in patients with excessive somnolence. The ultimate therapeutic dose should be achieved on the basis of both tolerability and clinical response [see WARNINGS AND PRECAUTIONS (5.13), USE IN SPECIFIC POPULATIONS (8.5) and CLINICAL PHARMACOLOGY (12.3)].

Dose-Related Adverse Reactions
The frequency of adverse effects (particularly elevated liver enzymes and thrombocytopenia) may be dose-related. The probability of thrombocytopenia appears to increase significantly at total Valproate concentrations of ≥ 110 mcg/mL (females) or ≥ 135 mcg/mL (males) [see WARNINGS AND PRECAUTIONS (5.7)]. The benefit of improved therapeutic effect with higher doses should be weighed against the possibility of a greater incidence of adverse reactions.

Administration
Rapid infusion of Valproate sodium injection has been associated with an increase in adverse reactions. There is limited experience with infusion times of less than 60 minutes or rates of infusion > 20 mg/min in patients with epilepsy [see ADVERSE REACTIONS (6)].
Valproate sodium injection should be administered intravenously as a 60 minute infusion, as noted above. It should be diluted with at least 50 mL of a compatible diluent. Any unused portion of the vial contents should be discarded.
Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration whenever solution and container permit.

Compatibility and Stability
Valproate sodium injection was found to be physically compatible and chemically stable in the following parenteral solutions for at least 24 hours when stored in glass or polyvinyl chloride (PVC) bags at controlled room temperature 15º to 30°C (59º to 86°F).

• dextrose (5%) injection, USP
• sodium chloride (0.9%) injection, USP
• lactated ringer’s injection, USP

Dosing in Patients Taking Rufinamide

Patients stabilized on rufinamide before being prescribed Valproate should begin Valproate therapy at a low dose, and titrate to a clinically effective dose [see Drug Interactions (7.2)].

Hepatotoxicity

General Information on Hepatotoxicity

Hepatic failure resulting in fatalities has occurred in patients receiving Valproate. These incidents usually have occurred during the first six months of treatment. Serious or fatal hepatotoxicity may be preceded by non-specific symptoms such as malaise, weakness, lethargy, facial edema, anorexia, and vomiting. In patients with epilepsy, a loss of seizure control may also occur. Patients should be monitored closely for appearance of these symptoms. Serum liver tests should be performed prior to therapy and at frequent intervals thereafter, especially during the first six months of Valproate therapy. However, physicians should not rely totally on serum biochemistry since these tests may not be abnormal in all instances, but should also consider the results of careful interim medical history and physical examination.

Caution should be observed when administering Valproate products to patients with a prior history of hepatic disease. Patients on multiple anticonvulsants, children, those with congenital metabolic disorders, those with severe seizure disorders accompanied by mental retardation, and those with organic brain disease may be at particular risk. See below, “Patients with Known or Suspected Mitochondrial Disease.”

Experience has indicated that children under the age of two years are at a considerably increased risk of developing fatal hepatotoxicity, especially those with the aforementioned conditions. When Valproate sodium injection is used in this patient group, it should be used with extreme caution and as a sole agent. The benefits of therapy should be weighed against the risks. Use of Valproate sodium injection has not been studied in children below the age of 2 years.

In progressively older patient groups experience in epilepsy has indicated that the incidence of fatal hepatotoxicity decreases considerably.

Patients with Known or Suspected Mitochondrial Disease

Valproate is contraindicated in patients known to have mitochondrial disorders caused by POLG mutations and children under two years of age who are clinically suspected of having a mitochondrial disorder [see CONTRAINDICATIONS (4)]. Valproate-induced acute liver failure and liver-related deaths have been reported in patients with hereditary neurometabolic syndromes caused by mutations in the gene for mitochondrial DNA polymerase γ (POLG) (e.g., Alpers- Huttenlocher Syndrome) at a higher rate than those without these syndromes. Most of the reported cases of liver failure in patients with these syndromes have been identified in children and adolescents.

POLG-related disorders should be suspected in patients with a family history or suggestive symptoms of a POLG-related disorder, including but not limited to unexplained encephalopathy, refractory epilepsy (focal, myoclonic), status epilepticus at presentation, developmental delays, psychomotor regression, axonal sensorimotor neuropathy, myopathy cerebellar ataxia, opthalmoplegia, or complicated migraine with occipital aura. POLG mutation testing should be performed in accordance with current clinical practice for the diagnostic evaluation of such disorders. The A467T and W748S mutations are present in approximately 2/3 of patients with autosomal recessive POLG-related disorders.

In patients over two years of age who are clinically suspected of having a hereditary mitochondrial disease, Valproate should only be used after other anticonvulsants have failed. This older group of patients should be closely monitored during treatment with Valproate for the development of acute liver injury with regular clinical assessments and serum liver test monitoring.

The drug should be discontinued immediately in the presence of significant hepatic dysfunction, suspected or apparent. In some cases, hepatic dysfunction has progressed in spite of discontinuation of drug [see BOXED WARNING and CONTRAINDICATIONS (4)].

Birth Defects

Valproate can cause fetal harm when administered to a pregnant woman. Pregnancy registry data show that maternal Valproate use can cause neural tube defects and other structural abnormalities (e.g., craniofacial defects, cardiovascular malformations, hypospadias, limb malformations). The rate of congenital malformations among babies born to mothers using Valproate is about four times higher than the rate among babies born to epileptic mothers using other anti-seizure monotherapies. Evidence suggests that folic acid supplementation prior to conception and during the first trimester of pregnancy decreases the risk for congenital neural tube defects in the general population.

Decreased IQ Following in utero Exposure

Valproate can cause decreased IQ scores following in utero exposure. Published epidemiological studies have indicated that children exposed to Valproate in utero have lower cognitive test scores than children exposed in utero to either another antiepileptic drug or to no antiepileptic drugs. The largest of these studies1 is a prospective cohort study conducted in the United States and United Kingdom that found that children with prenatal exposure to Valproate (n = 62) had lower IQ scores at age 6 (97 [95% C.I. 94-101]) than children with prenatal exposure to the other antiepileptic drug monotherapy treatments evaluated: lamotrigine (108 [95% C.I. 105–110]), carbamazepine (105 [95% C.I. 102–108]), and phenytoin (108 [95% C.I. 104–112]). It is not known when during pregnancy cognitive effects in Valproate-exposed children occur. Because the women in this study were exposed to antiepileptic drugs throughout pregnancy, whether the risk for decreased IQ was related to a particular time period during pregnancy could not be assessed.

Although all of the available studies have methodological limitations, the weight of the evidence supports the conclusion that Valproate exposure in utero can cause decreased IQ in children.

In animal studies, offspring with prenatal exposure to Valproate had malformations similar to those seen in humans and demonstrated neurobehavioral deficits [see USE IN SPECIFIC POPULATIONS (8.1)].

Women with epilepsy who are pregnant or who plan to become pregnant should not be treated with Valproate unless other treatments have failed to provide adequate symptom control or are otherwise unacceptable. In such women, the benefits of treatment with Valproate during pregnancy may still outweigh the risks.

Use in Women of Childbearing Potential

Because of the risk to the fetus of decreased IQ and major congenital malformations (including neural tube defects), which may occur very early in pregnancy, Valproate should not be administered to a woman of childbearing potential unless the drug is essential to the management of her medical condition. This is especially important when Valproate use is considered for a condition not usually associated with permanent injury or death (e.g., migraine). Women should use effective contraception while using Valproate. Women who are planning a pregnancy should be counseled regarding the relative risks and benefits of Valproate use during pregnancy, and alternative therapeutic options should be considered for these patients [see BOXED WARNING and USE IN SPECIFIC POPULATIONS (8.1)].

To prevent major seizures, Valproate should not be discontinued abruptly, as this can precipitate status epilepticus with resulting maternal and fetal hypoxia and threat to life.

Evidence suggests that folic acid supplementation prior to conception and during the first trimester of pregnancy decreases the risk for congenital neural tube defects in the general population. It is not known whether the risk of neural tube defects or decreased IQ in the offspring of women receiving Valproate is reduced by folic acid supplementation. Dietary folic acid supplementation both prior to conception and during pregnancy should be routinely recommended for patients using Valproate.

Pancreatitis

Cases of life-threatening pancreatitis have been reported in both children and adults receiving Valproate. Some of the cases have been described as hemorrhagic with rapid progression from initial symptoms to death. Some cases have occurred shortly after initial use as well as after several years of use. The rate based upon the reported cases exceeds that expected in the general population and there have been cases in which pancreatitis recurred after rechallenge with Valproate. In clinical trials, there were 2 cases of pancreatitis without alternative etiology in 2416 patients, representing 1044 patient-years experience. Patients and guardians should be warned that abdominal pain, nausea, vomiting, and/or anorexia can be symptoms of pancreatitis that require prompt medical evaluation. If pancreatitis is diagnosed, Valproate should ordinarily be discontinued. Alternative treatment for the underlying medical condition should be initiated as clinically indicated [see BOXED WARNING].

Urea Cycle Disorders

Valproate sodium is contraindicated in patients with known urea cycle disorders (UCD).

Hyperammonemic encephalopathy, sometimes fatal, has been reported following initiation of Valproate therapy in patients with urea cycle disorders, a group of uncommon genetic abnormalities, particularly ornithine transcarbamylase deficiency. Prior to the initiation of Valproate therapy, evaluation for UCD should be considered in the following patients: 1) those with a history of unexplained encephalopathy or coma, encephalopathy associated with a protein load, pregnancy-related or postpartum encephalopathy, unexplained mental retardation, or history of elevated plasma ammonia or glutamine; 2) those with cyclical vomiting and lethargy, episodic extreme irritability, ataxia, low BUN, or protein avoidance; 3) those with a family history of UCD or a family history of unexplained infant deaths (particularly males); 4) those with other signs or symptoms of UCD. Patients who develop symptoms of unexplained hyperammonemic encephalopathy while receiving Valproate therapy should receive prompt treatment (including discontinuation of Valproate therapy) and be evaluated for underlying urea cycle disorders [see CONTRAINDICATIONS (4) and WARNINGS AND PRECAUTIONS (5.9)].

Bleeding and Other Hematopoietic Disorders

Valproate is associated with dose-related thrombocytopenia. In a clinical trial of Valproate as monotherapy in patients with epilepsy, 34/126 patients (27%) receiving approximately 50 mg/kg/day on average, had at least one value of platelets ≤ 75 x 109/L. Approximately half of these patients had treatment discontinued, with return of platelet counts to normal. In the remaining patients, platelet counts normalized with continued treatment. In this study, the probability of thrombocytopenia appeared to increase significantly at total Valproate concentrations of ≥ 110 mcg/mL (females) or ≥ 135 mcg/mL (males). The therapeutic benefit which may accompany the higher doses should therefore be weighed against the possibility of a greater incidence of adverse effects. Valproate use has also been associated with decreases in other cell lines and myelodysplasia.

Because of reports of cytopenias, inhibition of the secondary phase of platelet aggregation, and abnormal coagulation parameters (e.g., low fibrinogen, coagulation factor deficiencies, acquired von Willebrand's disease), measurements of complete blood counts and coagulation tests are recommended before initiating therapy and at periodic intervals. It is recommended that patients receiving Valproate sodium injection be monitored for blood counts and coagulation parameters prior to planned surgery and during pregnancy [see Use in Specific Populations (8.1)]. Evidence of hemorrhage, bruising, or a disorder of hemostasis/coagulation is an indication for reduction of the dosage or withdrawal of therapy.

Hyperammonemia

Hyperammonemia has been reported in association with Valproate therapy and may be present despite normal liver function tests. In patients who develop unexplained lethargy and vomiting or changes in mental status, hyperammonemic encephalopathy should be considered and an ammonia level should be measured. Hyperammonemia should also be considered in patients who present with hypothermia [see WARNINGS AND PRECAUTIONS (5.10)]. If ammonia is increased, Valproate therapy should be discontinued. Appropriate interventions for treatment of hyperammonemia should be initiated, and such patients should undergo investigation for underlying urea cycle disorders [see CONTRAINDICATIONS (4) and WARNINGS AND PRECAUTIONS (5.6, 5.9)].

Asymptomatic elevations of ammonia are more common and when present, require close monitoring of plasma ammonia levels. If the elevation persists, discontinuation of Valproate therapy should be considered.

Hyperammonemia and Encephalopathy associated with Concomitant Topiramate Use

Concomitant administration of topiramate and Valproate has been associated with hyperammonemia with or without encephalopathy in patients who have tolerated either drug alone. Clinical symptoms of hyperammonemic encephalopathy often include acute alterations in level of consciousness and/or cognitive function with lethargy or vomiting. Hypothermia can also be a manifestation of hyperammonemia [see WARNINGS AND PRECAUTIONS (5.10)]. In most cases, symptoms and signs abated with discontinuation of either drug. This adverse reaction is not due to a pharmacokinetic interaction. Patients with inborn errors of metabolism or reduced hepatic mitochondrial activity may be at an increased risk for hyperammonemia with or without encephalopathy. Although not studied, an interaction of topiramate and Valproate may exacerbate existing defects or unmask deficiencies in susceptible persons. In patients who develop unexplained lethargy, vomiting, or changes in mental status, hyperammonemic encephalopathy should be considered and an ammonia level should be measured [see CONTRAINDICATIONS (4) and WARNINGS AND PRECAUTIONS (5.8)].

Hypothermia

Hypothermia, defined as an unintentional drop in body core temperature to < 35°C (95°F), has been reported in association with Valproate therapy both in conjunction with and in the absence of hyperammonemia. This adverse reaction can also occur in patients using concomitant topiramate with Valproate after starting topiramate treatment or after increasing the daily dose of topiramate [see DRUG INTERACTIONS (7.3)]. Consideration should be given to stopping Valproate in patients who develop hypothermia, which may be manifested by a variety of clinical abnormalities including lethargy, confusion, coma, and significant alterations in other major organ systems such as the cardiovascular and respiratory systems. Clinical management and assessment should include examination of blood ammonia levels.

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multi-organ Hypersensitivity Reactions

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as Multi-organ Hypersensitivity, has been reported in patients taking Valproate. DRESS may be fatal or life-threatening. DRESS typically, although not exclusively, presents with fever, rash, and/or lymphadenopathy, in association with other organ system involvement, such as hepatitis, nephritis, hematological abnormalities, myocarditis, or myositis sometimes resembling an acute viral infection. Eosinophilia is often present. Because this disorder is variable in its expression, other organ systems not noted here may be involved. It is important to note that early manifestations of hypersensitivity, such as fever or lymphadenopathy, may be present even though rash is not evident. If such signs or symptoms are present, the patient should be evaluated immediately. Valproate should be discontinued and not be resumed if an alternative etiology for the signs or symptoms cannot be established.

Interaction with Carbapenem Antibiotics

Carbapenem antibiotics (for example, ertapenem, imipenem, meropenem; this is not a complete list) may reduce serum Valproate concentrations to subtherapeutic levels, resulting in loss of seizure control. Serum Valproate concentrations should be monitored frequently after initiating carbapenem therapy. Alternative antibacterial or anticonvulsant therapy should be considered if serum Valproate concentrations drop significantly or seizure control deteriorates [see DRUG INTERACTIONS (7.1)].

Somnolence in the Elderly

In a double-blind, multicenter trial of Valproate in elderly patients with dementia (mean age = 83 years), doses were increased by 125 mg/day to a target dose of 20 mg/kg/day. A significantly higher proportion of Valproate patients had somnolence compared to placebo, and although not statistically significant, there was a higher proportion of patients with dehydration. Discontinuations for somnolence were also significantly higher than with placebo. In some patients with somnolence (approximately one-half), there was associated reduced nutritional intake and weight loss. There was a trend for the patients who experienced these events to have a lower baseline albumin concentration, lower Valproate clearance, and a higher BUN. In elderly patients, dosage should be increased more slowly and with regular monitoring for fluid and nutritional intake, dehydration, somnolence, and other adverse reactions. Dose reductions or discontinuation of Valproate should be considered in patients with decreased food or fluid intake and in patients with excessive somnolence [see DOSAGE AND ADMINISTRATION (2.2)].

Post-traumatic Seizures

A study was conducted to evaluate the effect of IV Valproate in the prevention of post-traumatic seizures in patients with acute head injuries. Patients were randomly assigned to receive either IV Valproate given for one week (followed by oral Valproate products for either one or six months per random treatment assignment) or IV phenytoin given for one week (followed by placebo). In this study, the incidence of death was found to be higher in the two groups assigned to Valproate treatment compared to the rate in those assigned to the IV phenytoin treatment group (13% vs. 8.5%, respectively). Many of these patients were critically ill with multiple and/or severe injuries, and evaluation of the causes of death did not suggest any specific drug-related causation. Further, in the absence of a concurrent placebo control during the initial week of intravenous therapy, it is impossible to determine if the mortality rate in the patients treated with Valproate was greater or less than that expected in a similar group not treated with Valproate, or whether the rate seen in the IV phenytoin treated patients was lower than would be expected. Nonetheless, until further information is available, it seems prudent not to use Valproate sodium injection in patients with acute head trauma for the prophylaxis of post-traumatic seizures.

Monitoring: Drug Plasma Concentration

Since Valproate may interact with concurrently administered drugs which are capable of enzyme induction, periodic plasma concentration determinations of Valproate and concomitant drugs are recommended during the early course of therapy [see DRUG INTERACTIONS (7)].

Effect on Ketone and Thyroid Function Tests

Valproate is partially eliminated in the urine as a keto-metabolite which may lead to a false interpretation of the urine ketone test.

There have been reports of altered thyroid function tests associated with Valproate. The clinical significance of these is unknown.

Effect on HIV and CMV Viruses Replication

There are in vitro studies that suggest Valproate stimulates the replication of the HIV and CMV viruses under certain experimental conditions. The clinical consequence, if any, is not known. Additionally, the relevance of these in vitro findings is uncertain for patients receiving maximally suppressive antiretroviral therapy. Nevertheless, these data should be borne in mind when interpreting the results from regular monitoring of the viral load in HIV infected patients receiving Valproate or when following CMV infected patients clinically.

Carcinogenesis, Mutagenesis, and Impairment of Fertility

Carcinogenesis
Valproate was administered orally to rats and mice at doses of 80 and 170 mg/kg/day (less than the maximum recommended human dose on a mg/m2 basis) for two years. The primary findings were an increase in the incidence of subcutaneous fibrosarcomas in high-dose male rats receiving Valproate and a dose-related trend for benign pulmonary adenomas in male mice receiving Valproate. The significance of these findings for humans is unknown.

Mutagenesis
Valproate was not mutagenic in an in vitro bacterial assay (Ames test), did not produce dominant lethal effects in mice, and did not increase chromosome aberration frequency in an in vivo cytogenetic study in rats. Increased frequencies of sister chromatid exchange (SCE) have been reported in a study of epileptic children taking Valproate, but this association was not observed in another study conducted in adults. There is some evidence that increased SCE frequencies may be associated with epilepsy. The biological significance of an increase in SCE frequency is not known.

Impairment of Fertility
Chronic toxicity studies of Valproate in juvenile and adult rats and dogs demonstrated reduced spermatogenesis and testicular atrophy at oral doses of 400 mg/kg/day or greater in rats (approximately equivalent to or greater than the maximum recommended human dose (MRHD) on a mg/m2 basis) and 150 mg/kg/day or greater in dogs (approximately 1.4 times the MRHD or greater on a mg/m2 basis). Fertility studies in rats have shown no effect on fertility at oral doses of Valproate up to 350 mg/kg/day (approximately equal to the MRHD dose on a mg/m2 basis) for 60 days. The effect of Valproate on testicular development and on sperm parameters and fertility in humans is unknown.

The studies described in the following section were conducted with oral divalproex sodium products.

Epilepsy

The efficacy of Valproate in reducing the incidence of complex partial seizures (CPS) that occur in isolation or in association with other seizure types was established in two controlled trials.

In one, multiclinic, placebo controlled study employing an add-on design (adjunctive therapy), 144 patients who continued to suffer eight or more CPS per 8 weeks during an 8 week period of monotherapy with doses of either carbamazepine or phenytoin sufficient to assure plasma concentrations within the “therapeutic range” were randomized to receive, in addition to their original antiepilepsy drug (AED), either divalproex sodium or placebo. Randomized patients were to be followed for a total of 16 weeks. The following Table presents the findings.

Figure 1 presents the proportion of patients (X axis) whose percentage reduction from baseline in complex partial seizure rates was at least as great as that indicated on the Y axis in the adjunctive therapy study. A positive percent reduction indicates an improvement (i.e., a decrease in seizure frequency), while a negative percent reduction indicates worsening. Thus, in a display of this type, the curve for an effective treatment is shifted to the left of the curve for placebo. This Figure shows that the proportion of patients achieving any particular level of improvement was consistently higher for Valproate than for placebo. For example, 45% of patients treated with Valproate had a ≥ 50% reduction in complex partial seizure rate compared to 23% of patients treated with placebo.

The second study assessed the capacity of Valproate to reduce the incidence of CPS when administered as the sole AED. The study compared the incidence of CPS among patients randomized to either a high or low dose treatment arm. Patients qualified for entry into the randomized comparison phase of this study only if 1) they continued to experience 2 or more CPS per 4 weeks during an 8 to 12 week long period of monotherapy with adequate doses of an AED (i.e., phenytoin, carbamazepine, phenobarbital, or primidone) and 2) they made a successful transition over a two week interval to Valproate. Patients entering the randomized phase were then brought to their assigned target dose, gradually tapered off their concomitant AED and followed for an interval as long as 22 weeks. Less than 50% of the patients randomized, however, completed the study. In patients converted to divalproex sodium monotherapy, the mean total Valproate concentrations during monotherapy were 71 and 123 mcg/mL in the low dose and high dose groups, respectively.

The following Table presents the findings for all patients randomized who had at least one post‑randomization assessment.

Figure 2 presents the proportion of patients (X axis) whose percentage reduction from baseline in complex partial seizure rates was at least as great as that indicated on the Y axis in the monotherapy study. A positive percent reduction indicates an improvement (i.e., a decrease in seizure frequency), while a negative percent reduction indicates worsening. Thus, in a display of this type, the curve for a more effective treatment is shifted to the left of the curve for a less effective treatment. This Figure shows that the proportion of patients achieving any particular level of reduction was consistently higher for high dose Valproate than for low dose Valproate. For example, when switching from carbamazepine, phenytoin, phenobarbital or primidone monotherapy to high dose Valproate monotherapy, 63% of patients experienced no change or a reduction in complex partial seizure rates compared to 54% of patients receiving low dose Valproate.

1. Meador KJ, Baker GA, Browning N, et al. Fetal antiepileptic drug exposure and cognitive outcomes at age 6 years (NEAD study): a prospective observational study. Lancet Neurology 2013; 12 (3):244-252.