Stavzor
- Generic Name: valproic acid
- Brand Name: Stavzor
Stavzor (Valproic Acid) side effects drug center
Stavzor Side Effects Center
What Is Stavzor?
Stavzor (valproic acid) Delayed Release Capsules is an anticonvulsant used to treat various types of seizure disorders, manic episodes associated with bipolar disorder, and to prevent migraine headaches.
What Are Side Effects of Stavzor?
Common side effects of Stavzor include: < br/>
- drowsiness
- weakness
- diarrhea
- constipation
- upset stomach
- abdominal pain
- nausea
- vomiting
- indigestion
- changes in menstrual periods
- enlarged breasts
- tremor (shaking)
- dizziness
- hair loss
- weight changes
- rash
- vision changes, or
- unusual or unpleasant taste in your mouth
Dosage for Stavzor
Dosage of Stavzor depends on the condition being treated.
What Drugs, Substances, or Supplements Interact with Stavzor?
Stavzor may interact with topiramate, tolbutamide, blood thinners, aspirin or acetaminophen (Tylenol), zidovudine, clozapine, diazepam, meropenem or imipenem and cilastatin, rifampin, ethosuximide, cold or allergy medicine, narcotics, sleeping pills, muscle relaxers, and medicine for depression or anxiety. Tell your doctor all medications and supplements you use.
Stavzor During Pregnancy and Breastfeeding
Stavzor can cause birth defects. Do not start taking Stavzor without telling your doctor if you are pregnant or planning to become pregnant. Use birth control while taking Stavzor. Having a seizure during pregnancy could harm both mother and baby. If you become pregnant while taking Stavzor, do not stop taking the medicine without your doctor's advice. This drug passes into breast milk and may harm a nursing baby. Do not breastfeed while taking Stavzor.
Additional Information
Our Stavzor (valproic acid) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.
Stavzor Consumer Information
Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).
Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include: skin rash, fever, swollen glands, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes.
Call your doctor at once if the person taking this medicine has signs of liver or pancreas problems, such as: loss of appetite, upper stomach pain (that may spread to your back), ongoing nausea or vomiting, dark urine, swelling in the face, or jaundice (yellowing of the skin or eyes).
Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, depression, anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.
Call your doctor at once if you have any of these other side effects:
- confusion, tiredness, cold feeling, vomiting, change in your mental state;
- easy bruising, unusual bleeding (nose, mouth, or gums), purple or red pinpoint spots under your skin;
- severe drowsiness; or
- worsening seizures.
Severe drowsiness may be more likely in older adults.
Common side effects may include:
- nausea, vomiting, stomach pain, diarrhea;
- dizziness, drowsiness, weakness;
- headache;
- tremors, problems with walking or coordination;
- blurred vision, double vision;
- hair loss; or
- changes in appetite, weight gain.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
Read the entire detailed patient monograph for Stavzor (Valproic Acid)
Stavzor Professional Information
SIDE EFFECTS
The following serious adverse reactions are described below and elsewhere in the labeling:
- Hepatic failure [see WARNINGS AND PRECAUTIONS]
- Birth defects [see WARNINGS AND PRECAUTIONS]
- Decreased IQ following in utero exposure [see WARNINGS AND PRECAUTIONS]
- Pancreatitis [see WARNINGS AND PRECAUTIONS
- Hyperammonemic encephalopathy [see WARNINGS AND PRECAUTIONS]
- Suicidal behavior and ideation [see WARNINGS AND PRECAUTIONS]
- Bleeding and other hematopoietic disorders [see WARNINGS AND PRECAUTIONS]
- Hypothermia [see WARNINGS AND PRECAUTIONS]
- Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan hypersensitivity reactions [see WARNINGS AND PRECAUTIONS]
- Somnolence in the elderly [see WARNINGS AND PRECAUTIONS]
Because clinical studies are conducted under widely varying conditions, adverse reaction rates observed in the clinical studies of a drug cannot be directly compared to rates in the clinical studies of another drug and may not reflect the rates observed in practice.
Mania
The incidence of adverse reactions has been ascertained based on combined data from 2 placebo-controlled clinical trials of valproate in the treatment of manic episodes associated with bipolar disorder. The adverse reactions were usually mild or moderate in intensity, but sometimes were serious enough to interrupt treatment. In clinical trials, the rates of premature termination due to intolerance were not statistically different between placebo, valproate, and lithium carbonate. A total of 4%, 8% and 11% of patients discontinued therapy due to intolerance in the placebo, valproate, and lithium carbonate groups, respectively.
Table 2 summarizes those adverse reactions reported for patients in these trials where the incidence rate in the valproate-treated group was greater than 5% and greater than the placebo incidence, or where the incidence in the valproate-treated group was statistically significantly greater than the placebo group. Vomiting was the only event that was reported by significantly (p ≤ 0.05) more patients receiving valproate compared to placebo.
Table 2: Adverse Reactions Reported by >5% of Valproate-Treated Patients During Placebo-Controlled Trials of Acute Maniaa
| Adverse Reaction | Valproate (n=89) % |
Placebo (n=97) % |
| Nausea | 22 | 15 |
| Somnolence | 19 | 12 |
| Dizziness | 12 | 4 |
| Vomiting | 12 | 3 |
| Accidental Injury | 11 | 5 |
| Asthenia | 10 | 7 |
| Abdominal Pain | 9 | 8 |
| Dyspepsia | 9 | 8 |
| Rash | 6 | 3 |
| a The following adverse reactions occurred at an equal or greater incidence for placebo than for valproate: back pain, headache, constipation, diarrhea, tremor, and pharyngitis. | ||
The following additional adverse reactions were reported by greater than 1% but not more than 5% of the 89 valproate-treated patients in controlled clinical trials:
Body as a Whole: Chest pain, chills, chills and fever, fever, neck pain, neck rigidity.
Cardiovascular System: Hypertension, hypotension, palpitations, postural hypotension, tachycardia, vasodilation.
Digestive System: Anorexia, fecal incontinence, flatulence, gastroenteritis, glossitis, periodontal abscess.
Hemic and Lymphatic System: Ecchymosis.
Metabolic and Nutritional Disorders: Edema, peripheral edema.
Musculoskeletal System: Arthralgia, arthrosis, leg cramps, twitching.
Nervous System: Abnormal dreams, abnormal gait, agitation, ataxia, catatonic reaction, confusion, depression, diplopia, dysarthria, hallucinations, hypertonia, hypokinesia, insomnia, paresthesia, reflexes increased, tardive dyskinesia, thinking abnormalities, vertigo.
Respiratory System: Dyspnea, rhinitis.
Skin and Appendages: Alopecia, discoid lupus erythematosus, dry skin, furunculosis, maculopapular rash, seborrhea.
Special Senses: Amblyopia, conjunctivitis, deafness, dry eyes, ear pain, eye pain, tinnitus.
Urogenital System: Dysmenorrhea, dysuria, urinary incontinence.
Epilepsy
Based on a placebo-controlled trial of adjunctive therapy for treatment of complex partial seizures, valproate was generally well tolerated with most adverse reactions rated as mild to moderate in severity. Intolerance was the primary reason for discontinuation in the valproate-treated patients (6%), compared to 1% of placebo-treated patients.
Table 3 lists treatment-emergent adverse reactions which were reported by ≥ 5% of valproate-treated patients and for which the incidence was greater than in the placebo group, in the placebo-controlled trial of adjunctive therapy for treatment of complex partial seizures. Since patients were also treated with other antiepilepsy drugs, it is not possible, in most cases, to determine whether the following adverse reactions can be ascribed to valproate alone, or the combination of valproate and other antiepilepsy drugs.
Table 3: Adverse Reactions Reported by ≥ 5% of Patients Treated with Valproate During Placebo-Controlled Trial of Adjunctive Therapy for Complex Partial Seizures
| Body System/Event | Valproate (n = 77) % |
Placebo (n = 70) % |
| Body as a Whole | ||
| Headache | 31 | 21 |
| Asthenia | 27 | 7 |
| Fever | 6 | 4 |
| Gastrointestinal System | ||
| Nausea | 48 | 14 |
| Vomiting | 27 | 7 |
| Abdominal pain | 23 | 6 |
| Diarrhea | 13 | 6 |
| Anorexia | 12 | 0 |
| Dyspepsia | 8 | 4 |
| Constipation | 5 | 1 |
| Nervous System | ||
| Somnolence | 27 | 11 |
| Tremor | 25 | 6 |
| Dizziness | 25 | 13 |
| Diplopia | 16 | 9 |
| Amblyopia/Blurred Vision | 12 | 9 |
| Ataxia | 8 | 1 |
| Nystagmus | 8 | 1 |
| Emotional Lability | 6 | 4 |
| Thinking Abnormal | 6 | 0 |
| Amnesia | 5 | 1 |
| Respiratory System | ||
| Flu Syndrome | 12 | 9 |
| Infection | 12 | 6 |
| Bronchitis | 5 | 1 |
| Rhinitis | 5 | 4 |
| Other | ||
| Alopecia | 6 | 1 |
| Weight Loss | 6 | 0 |
Table 4 lists treatment-emergent adverse reactions which were reported by ≥ 5% of patients in the high dose valproate group, and for which the incidence was greater than in the low dose group, in a controlled trial of valproate monotherapy treatment of complex partial seizures. Since patients were being titrated off another antiepilepsy drug during the first portion of the trial, it is not possible, in many cases, to determine whether the following adverse reactions can be ascribed to valproate alone, or the combination of valproate and other antiepilepsy drugs.
Table 4: Adverse Reactions Reported by ≥5% of Patients in the High-Dose Group in the Controlled Trial of Valproate Monotherapy for Complex Partial Seizuresa
| Body System/Event | High Dose (n = 131) % |
Low Dose (n = 134) % |
| Body as a Whole | ||
| Asthenia | 21 | 10 |
| Digestive System | ||
| Nausea | 34 | 26 |
| Diarrhea | 23 | 19 |
| Vomiting | 23 | 15 |
| Abdominal pain | 12 | 9 |
| Anorexia | 11 | 4 |
| Dyspepsia | 11 | 10 |
| Hemic/Lymphatic System | ||
| Thrombocytopeni a | 24 | 1 |
| Ecchymosis | 5 | 4 |
| Metabolic/N utritional | ||
| Weight Gain | 9 | 4 |
| Peripheral Edema | 8 | 3 |
| Nervous System | ||
| Tremor | 57 | 19 |
| Somnolence | 30 | 18 |
| Dizziness | 18 | 13 |
| Insomnia | 15 | 9 |
| Nervousness | 11 | 7 |
| Amnesia | 7 | 4 |
| Nystagmus | 7 | 1 |
| Depression | 5 | 4 |
| Respiratory System | ||
| Infection | 20 | 13 |
| Pharyngitis | 8 | 2 |
| Dyspnea | 5 | 1 |
| Skin and Appendages | ||
| Alopecia | 24 | 13 |
| Special Senses | ||
| Amblyopia/Blurred Vision | 8 | 4 |
| Tinnitus | 7 | 1 |
| a Headache was the only adverse event that occurred in ≥ 5% of patients in the high-dose group and at an equal or greater incidence in the low-dose group. | ||
The following additional adverse reactions were reported by greater than 1% but less than 5% of the 358 patients treated with valproate in the controlled trials of complex partial seizures:
Body as a Whole: Back pain, chest pain, malaise.
Cardiovascular System: Tachycardia, hypertension, palpitation.
Digestive System: Increased appetite, flatulence, hematemesis, eructation, pancreatitis, periodontal abscess.
Hemic and Lymphatic System: Petechia.
Metabolic and Nutritional Disorders: SGOT increased, SGPT increased.
Musculoskeletal System: Myalgia, twitching, arthralgia, leg cramps, myasthenia.
Nervous System: Anxiety, confusion, abnormal gait, paresthesia, hypertonia, incoordination, abnormal dreams, personality disorder.
Respiratory System: Sinusitis, cough increased, pneumonia, epistaxis.
Skin and Appendages: Rash, pruritus, dry skin.
Special Senses: Taste perversion, abnormal vision, deafness, otitis media.
Urogenital System: Urinary incontinence, vaginitis, dysmenorrhea, amenorrhea, urinary frequency.
Migraine
Based on 2 placebo-controlled clinical trials and their long-term extension, valproate was generally well tolerated with most adverse reactions rated as mild to moderate in severity. Of the 202 patients exposed to valproate in the placebo-controlled trials, 17% discontinued for intolerance. This is compared to a rate of 5% for the 81 placebo patients. Including the long-term extension study, the adverse reactions reported as the primary reason for discontinuation by ≥1% of 248 valproate-treated patients were alopecia (6%), nausea and/or vomiting (5%), weight gain (2%), tremor (2%), somnolence (1%), elevated SGOT and/or SGPT (1%), and depression (1%).
Table 5 includes those adverse reactions reported for patients in the placebo-controlled trials where the incidence rate in the valproate-treated group was greater than 5% and was greater than that for placebo patients.
Table 5: Adverse Reactions Reported by >5% of Valproate-Treated Patients During Migraine Placebo-Controlled Trials with a Greater Incidence Than Patients Taking Placebo
| Body System Event | Valproate (n = 202) % |
Placebo (n = 81) % |
| Gastrointestinal System | ||
| Nausea | 31 | 10 |
| Dyspepsia | 13 | 9 |
| Diarrhea | 12 | 7 |
| Vomiting | 11 | 1 |
| Abdominal pain | 9 | 4 |
| Increased appetite | 6 | 4 |
| Nervous System | ||
| Asthenia | 20 | 9 |
| Somnolence | 17 | 5 |
| Dizziness | 12 | 6 |
| Tremor | 9 | 0 |
| Other | ||
| Weight gain | 8 | 2 |
| Back pain | 8 | 6 |
| Alopecia | 7 | 1 |
The following additional adverse reactions were reported by greater than 1% but not more than 5% of the 202 valproate-treated patients in the controlled clinical trials:
Body as a Whole: Chest pain, chills, face edema, fever and malaise.
Cardiovascular System: Vasodilatation.
Digestive System: Anorexia, constipation, dry mouth, flatulence, gastrointestinal disorder (unspecified), and stomatitis.
Hemic and Lymphatic System: Ecchymosis.
Metabolic and Nutritional Disorders: Peripheral edema, SGOT increase, and SGPT increase.
Musculoskeletal System: Leg cramps and myalgia.
Nervous System: Abnormal dreams, amnesia, confusion, depression, emotional lability, insomnia, nervousness, paresthesia, speech disorder, thinking abnormalities, and vertigo.
Respiratory System: Cough increased, dyspnea, rhinitis, and sinusitis.
Skin and Appendages: Pruritus and rash.
Special Senses: Conjunctivitis, ear disorder, taste perversion, and tinnitus.
Urogenital System: Cystitis, metrorrhagia, and vaginal hemorrhage.
Postmarketing Experience
The following adverse reactions have been identified during post approval use of STAVZOR (valproic acid) or divalproex sodium. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
Dermatologic: Hair texture changes, hair color changes, photosensitivity, erythema multiforme, toxic epidermal necrolysis, nail and nail bed disorders, and Stevens-Johnson syndrome.
Psychiatric: Emotional upset, psychosis, aggression, psychomotor hyperactivity, hostility, disturbance in attention, learning disorder, and behavioral deterioration.
Neurologic: Paradoxical convulsion, parkinsonism
There have been several reports of acute or subacute cognitive decline and behavioral changes (apathy or irritability) with cerebral pseudoatrophy on imaging associated with valproate therapy; both the cognitive/behavioral changes and cerebral pseudoatrophy reversed partially or fully after valproate discontinuation.
There have been reports of acute or subacute encephalopathy in the absence of elevated ammonia levels, elevated valproate levels, or neuroimaging changes. The encephalopathy reversed partially or fully after valproate discontinuation.
Musculoskeletal: Fractures, decreased bone mineral density, osteopenia, osteoporosis, and weakness.
Hematologic: Relative lymphocytosis, macrocytosis, hypofibrinogenemia, leukopenia, eosinophilia, anemia including macrocytic with or without folate deficiency, bone marrow suppression, pancytopenia, aplastic anemia, agranulocytosis, and acute intermittent porphyria.
Endocrine: Irregular menses, secondary amenorrhea, hyperandrogenism, hirsutism, elevated testosterone level, breast enlargement, galactorrhea, polycystic ovary disease, parotid gland swelling, decreased carnitine concentrations, hyponatremia, hyperglycinemia, and inappropriate ADH secretion.
There have been rare reports of Fanconi's syndrome occurring chiefly in children.
Metabolism and Nutrition: Weight gain.
Reproductive: Aspermia, azoospermia, decreased sperm count, decreased spermatozoa motility, male infertility, and abnormal spermatozoa morphology.
Genitourinary: Enuresis, tubulointerstitial nephritis, and urinary tract infection.
Special Senses: Hearing loss.
Other: Allergic reaction, anaphylaxis, developmental delay, bone pain, bradycardia, and cutaneous vasculitis.
DRUG INTERACTIONS
Effects Of Co-Administered Drugs On Valproate Clearance
Drugs that affect the level of expression of hepatic enzymes, particularly those that elevate levels of glucuronosyltransferases (such as ritonavir), may increase the clearance of valproate. For example, phenytoin, carbamazepine, and phenobarbital (or primidone) can double the clearance of valproate. Thus, patients on monotherapy will generally have longer half-lives and higher concentrations than patients receiving polytherapy with antiepilepsy drugs.
In contrast, drugs that are inhibitors of cytochrome P450 isozymes, e.g., antidepressants, may be expected to have little effect on valproate clearance because cytochrome P450 microsomal mediated oxidation is a relatively minor secondary metabolic pathway compared to glucuronidation and beta-oxidation.
Because of these changes in valproate clearance, monitoring of valproate and concomitant drug concentrations should be increased whenever enzyme inducing drugs are introduced or withdrawn.
The following list provides information about the potential for an influence of several commonly prescribed medications on valproate pharmacokinetics. The list is not exhaustive nor could it be, since new interactions are continuously being reported.
Drugs For Which A Potentially Important Interaction Has Been Observed
Aspirin
A study involving the co-administration of aspirin at antipyretic doses (11 to 16 mg/kg) with valproate to pediatric patients (n=6) revealed a decrease in protein binding and an inhibition of metabolism of valproate. Valproate-free fraction was increased 4-fold in the presence of aspirin compared to valproate alone. The β-oxidation pathway consisting of 2-E-valproic acid, 3-OHvalproic acid, and 3-keto valproic acid was decreased from 25% of total metabolites excreted on valproate alone to 8.3% in the presence of aspirin. Caution should be observed if valproate and aspirin are to be co-administered.
Carbapenem Antibiotics
A clinically significant reduction in serum valproic acid concentration has been reported in patients receiving carbapenem antibiotics (for example, ertapenem, imipenem, meropenem; this is not a complete list) and may result in loss of seizure control. The mechanism of this interaction is not well understood. Serum valproic acid concentrations should be monitored frequently after initiating carbapenem therapy. Alternative antibacterial or anticonvulsant therapy should be considered if serum valproic acid concentrations drop significantly or seizure control deteriorates [see WARNINGS AND PRECAUTIONS].
Estrogen-Containing Hormonal Contraceptives
Estrogen-containing hormonal contraceptives may increase the clearance of valproate, which may result in decreased concentration of valproate and potentially increased seizure frequency. Prescribers should monitor serum valproate concentrations and clinical response when adding or discontinuing estrogen containing products.
Felbamate
A study involving the co-administration of 1,200 mg/day of felbamate with valproate to patients with epilepsy (n=10) revealed an increase in mean valproate peak concentration by 35% (from 86 to 115 mcg/mL) compared to valproate alone. Increasing the felbamate dose to 2,400 mg/day increased the mean valproate peak concentration to 133 mcg/mL (another 16% increase). A decrease in valproate dosage may be necessary when felbamate therapy is initiated.
Rifampin
A study involving the administration of a single dose of valproate (7 mg/kg) 36 hours after 5 nights of daily dosing with rifampin (600 mg) revealed a 40% increase in the oral clearance of valproate. Valproate dosage adjustment may be necessary when it is co-administered with rifampin.
Alcohol
An in vitro study evaluating dissolution of valproic acid showed earlier dissolution in the presence of ethanol than in the absence of ethanol. This has not been studied in humans. However, there is a potential for an earlier Tmax and therefore a higher Cmax when valproic acid is given with alcohol. Caution is advised if valproic acid is taken with alcohol.
Drugs For Which Either No Interaction Or A Likely Clinically Unimportant Interaction Has Been Observed
Antacids
A study involving the co-administration of valproate 500 mg with commonly administered antacids (Maalox, Trisogel, and Titralac -160 mEq doses) did not reveal any effect on the extent of absorption of valproate.
Chlorpromazine
A study involving the administration of 100 to 300 mg/day of chlorpromazine to schizophrenic patients already receiving valproate (200 mg BID) revealed a 15% increase in trough plasma levels of valproate.
Haloperidol
A study involving the administration of 6 to 10 mg/day of haloperidol to schizophrenic patients already receiving valproate (200 mg BID) revealed no significant changes in valproate trough plasma levels.
Cimetidine And Ranitidine
Cimetidine and ranitidine do not affect the clearance of valproate.
Effects Of Valproate On Other Drugs
Valproate has been found to be a weak inhibitor of some P450 isozymes, epoxide hydrase, and glucuronosyltransferases.
The following list provides information about the potential for an influence of valproate co-administration on the pharmacokinetics or pharmacodynamics of several commonly prescribed medications. The list is not exhaustive, since new interactions are continuously being reported.
Drugs For Which A Potentially Important Valproate Interaction Has Been Observed
Amitriptyline/Nortriptyline
Administration of a single oral 50 mg dose of amitriptyline to 15 normal volunteers (10 males and 5 females) who received valproate (500 mg BID) resulted in a 21% decrease in plasma clearance of amitriptyline and a 34% decrease in the net clearance of nortriptyline. Rare postmarketing reports of concurrent use of valproate and amitriptyline resulting in an increased amitriptyline level have been received. Concurrent use of valproate and amitriptyline has rarely been associated with toxicity. Monitoring of amitriptyline levels should be considered for patients taking valproate concomitantly with amitriptyline. Consideration should be given to lowering the dose of amitriptyline/nortriptyline in the presence of valproate.
Carbamazepine/Carbamazepine-10,11-Epoxide
Serum levels of carbamazepine (CBZ) decreased 17% while that of carbamazepine-10,11-epoxide (CBZ-E) increased by 45% upon co-administration of valproate and CBZ to epileptic patients.
Clonazepam
The concomitant use of valproic acid and clonazepam may induce absence status in patients with a history of absence type seizures.
Diazepam
Valproate displaces diazepam from its plasma albumin binding sites and inhibits its metabolism. Co-administration of valproate (1,500 mg daily) increased the free fraction of diazepam (10 mg) by 90% in healthy volunteers (n=6). Plasma clearance and volume of distribution for free diazepam were reduced by 25% and 20%, respectively, in the presence of valproate. The elimination half-life of diazepam remained unchanged upon addition of valproate.
Ethosuximide
Valproate inhibits the metabolism of ethosuximide. Administration of a single ethosuximide dose of 500 mg with valproate (800 to 1,600 mg/day) to healthy volunteers (n=6) was accompanied by a 25% increase in elimination half-life of ethosuximide and a 15% decrease in its total clearance as compared to ethosuximide alone. Patients receiving valproate and ethosuximide, especially along with other anticonvulsants, should be monitored for alterations in serum concentrations of both drugs.
Lamotrigine
In a steady-state study involving 10 healthy volunteers, the elimination half-life of lamotrigine increased from 26 to 70 hours with valproate co-administration (a 165% increase). The dose of lamotrigine should be reduced when co-administered with valproate. Serious skin reactions (such as Stevens-Johnson Syndrome and toxic epidermal necrolysis) have been reported with concomitant lamotrigine and valproate administration. See lamotrigine package insert for details on lamotrigine dosing with concomitant valproate administration.
Phenobarbital
Valproate was found to inhibit the metabolism of phenobarbital. Co-administration of valproate (250 mg BID for 14 days) with phenobarbital to normal subjects (n=6) resulted in a 50% increase in half-life and a 30% decrease in plasma clearance of phenobarbital (60 mg single-dose). The fraction of phenobarbital dose excreted unchanged increased by 50% in presence of valproate.
There is evidence for severe CNS depression, with or without significant elevations of barbiturate or valproate serum concentrations. All patients receiving concomitant barbiturate therapy should be closely monitored for neurological toxicity. Serum barbiturate concentrations should be obtained, if possible, and the barbiturate dosage decreased, if appropriate.
Primidone, which is metabolized to a barbiturate, may be involved in a similar interaction with valproate.
Phenytoin
Valproate displaces phenytoin from its plasma albumin binding sites and inhibits its hepatic metabolism. Co-administration of valproate (400 mg TID) with phenytoin (250 mg) in normal volunteers (n=7) was associated with a 60% increase in the free fraction of phenytoin. Total plasma clearance and apparent volume of distribution of phenytoin increased 30% in the presence of valproate. Both the clearance and apparent volume of distribution of free phenytoin were reduced by 25%.
In patients with epilepsy, there have been reports of breakthrough seizures occurring with the combination of valproate and phenytoin. The dosage of phenytoin should be adjusted as required by the clinical situation.
Propofol
The concomitant use of valproate and propofol may lead to increased blood levels of propofol. Reduce the dose of propofol when co-administering with valproate. Monitor patients closely for signs of increased sedation or cardiovascular depression.
Rufinamide
Based on a population pharmacokinetic analysis, rufinamide clearance was decreased by valproate. Rufinamide concentrations were increased by <16% to 70%, dependent on concentration of valproate (with the larger increases being seen in pediatric patients at high doses or concentrations of valproate). Patients stabilized on rufinamide before being prescribed valproate should begin valproate therapy at a low dose and titrate to a clinically effective dose [see DOSAGE AND ADMINISTRATION]. Similarly, patients on valproate should begin at a rufinamide dose lower than 10 mg/kg per day (pediatric patients) or 400 mg per day (adults).
Tolbutamide
From in vitro experiments, the unbound fraction of tolbutamide was increased from 20% to 50% when added to plasma samples taken from patients treated with valproate. The clinical relevance of this displacement is unknown.
Warfarin
In an in vitro study, valproate increased the unbound fraction of warfarin by up to 32.6%. The therapeutic relevance of this is unknown; however, coagulation tests should be monitored if valproic acid therapy is instituted in patients taking anticoagulants.
Zidovudine
In 6 patients who were seropositive for HIV, the clearance of zidovudine (100 mg q8h) was decreased by 38% after administration of valproate (250 or 500 mg q8h); the half-life of zidovudine was unaffected.
Drugs For Which Either No Interaction Or A Likely Clinically Unimportant Interaction Has Been Observed
Acetaminophen
Valproate had no effect on any of the pharmacokinetic parameters of acetaminophen when it was concurrently administered to 3 epileptic patients.
Clozapine
In psychotic patients (n=11), no interaction was observed when valproate was co-administered with clozapine.
Lithium
Co-administration of valproate (500 mg BID) and lithium carbonate (300 mg TID) to normal male volunteers (n=16) had no effect on the steady-state kinetics of lithium.
Lorazepam
Concomitant administration of valproate (500 mg BID) and lorazepam (1 mg BID) in normal male volunteers (n=9) was accompanied by a 17% decrease in the plasma clearance of lorazepam.
Olanzapine
No dose adjustment for olanzapine is necessary when olanzapine is administered concomitantly with valproate. Co-administration of valproate (500 mg BID) and olanzapine (5 mg) to healthy adults (n=10) caused 15% reduction in Cmax and 35% reduction in AUC of olanzapine.
Oral Contraceptive Steroids
Administration of a single-dose of ethinyloestradiol (50 mcg)/levonorgestrel (250 mcg) to 6 women on valproate (200 mg BID) therapy for 2 months did not reveal any pharmacokinetic interaction.
Topiramate
Concomitant administration of valproic acid and topiramate has been associated with hyperammonemia with and without encephalopathy [see CONTRAINDICATIONS and WARNINGS AND PRECAUTIONS]. Concomitant administration of topiramate with valproic acid has also been associated with hypothermia in patients who have tolerated either drug alone. It may be prudent to examine blood ammonia levels in patients in whom the onset of hypothermia has been reported [see WARNINGS AND PRECAUTIONS].
Read the entire FDA prescribing information for Stavzor (Valproic Acid)
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