pms-Topiramate

pms-Topiramate Special Precautions

topiramate

Manufacturer:

Pharmascience

Distributor:

T-BOMA
Full Prescribing Info
Special Precautions
General: Antiepileptic drugs (AEDs), including pms-TOPIRAMATE, should be withdrawn gradually to minimize the potential for seizures or increased seizure frequency. In clinical trials in adult patients with epilepsy, dosages were decreased by 50 - 100 mg/day at weekly intervals. In clinical trials of children, topiramate was gradually withdrawn over a two- to eight-week period (see General; and Recommended Dose and Dosage Adjustment: Epilepsy: Drug Discontinuation under Dosage & Administration).
In patients without a history of seizures or epilepsy, pms-TOPIRAMATE should be gradually withdrawn to minimize the potential for seizures or increased seizure frequency. In clinical trials in adult patients receiving topiramate for migraine prophylaxis dosages were decreased by 25 - 50 mg/day at weekly intervals (see General; and Recommended Dose and Dosage Adjustment: Migraine Prophylaxis: Drug Discontinuation under Dosage & Administration).
In situations where rapid withdrawal of pms-TOPIRAMATE is medically required, appropriate monitoring is recommended (see General under Dosage & Administration).
Carcinogenesis and Mutagenesis: See Pharmacology: Toxicology: Carcinogenicity and Mutagenicity under Actions for discussion on animal data.
Endocrine and Metabolism: Hyperammonemia and Encephalopathy: Topiramate alone or in concomitant treatment with valproic acid (VPA) or other antiepileptic medications can cause hyperammonemia with or without encephalopathy. Although hyperammonemia may be asymptomatic, 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. In patients using concomitant topiramate and valproate this adverse event can occur after starting topiramate treatment or after increasing the daily dose of topiramate. Treatment-induced encephalopathy has also been reported without hyperammonemia (see Hypothermia with Concomitant Valproic Acid (VPA) Use as follows; Drug-Drug Interactions: Antiepileptic Drugs (AEDs): Effects of Other AEDs on pms-TOPIRAMATE: Valproic Acid under Interactions).
If hyperammonemia is suspected serum ammonia levels should be monitored (see Monitoring for Hyperammonemia/Encephalopathy as follows). If elevated serum ammonia concentrations persist, consider discontinuing topiramate and/or VPA. The symptoms and signs of hyperammonemic encephalopathy may abate with discontinuation of either drug.
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, topiramate treatment or an interaction of concomitant topiramate and valproic acid treatment may exacerbate existing defects or unmask deficiencies in susceptible persons.
Hyperammonemia/Encephalopathy with Topiramate Monotherapy: Post-Market: Hyperammonemia with and without encephalopathy has been reported in adult patients who were taking topiramate alone (see Post-Market Adverse Drug Reactions under Adverse Reactions).
Clinical Trials: Topiramate treatment has produced hyperammonemia (in some instances, dose-related) in clinical investigational programs of adolescents (12 - 16 years) who were treated with topiramate monotherapy for migraine prophylaxis (incidence above the upper limit of normal, placebo: 22%; 50 mg/day: 26%; 100 mg/day: 41%). Pediatric patients under two years of age who were treated with adjunctive topiramate for partial onset epilepsy, also experienced hyperammonemia (placebo: 8%; 5 mg/kg/day: 10%; 15 mg/kg/day: 0%; 25 mg/kg/day: 9%). pms-TOPIRAMATE is not indicated for migraine prophylaxis in patients under 18 years of age. pms-TOPIRAMATE is also not indicated for any use in patients under two years of age (see Pediatrics (< 2 years of age) under Indications/Uses).
In some patients, ammonia was markedly increased (> 50% above upper limit of normal). In adolescent patients, the incidence of markedly increased hyperammonemia was 6% for placebo, 6% for 50 mg, and 12% for 100 mg topiramate daily. The hyperammonemia associated with topiramate treatment occurred with and without encephalopathy in placebo-controlled trials and in an open-label, extension trial. Dose-related hyperammonemia was also observed in the extension trial in pediatric patients up to two years old.
Hyperammonemia/Encephalopathy with Concomitant Valproic Acid (VPA): Post-market: In post-marketing reports, concomitant administration of topiramate and valproic acid (VPA) has been associated with hyperammonemia with or without encephalopathy in patients who have tolerated either drug alone. The risk of encephalopathy is greater for concomitant topiramate-VPA therapy than for VPA monotherapy. This adverse reaction is not due to a pharmacokinetic interaction (see Drug-Drug Interactions: Antiepileptic Drugs (AEDs): Effects of Other AEDs on pms-TOPIRAMATE: Valproic Acid under Interactions).
Clinical Trials: Although topiramate is not indicated for use in patients under two years of age, in an investigational trial in this population, VPA clearly produced a dose-related increase in the incidence of treatment-emergent hyperammonemia (above the upper limit of normal, placebo: 0%, 5 mg/kg/day: 12%, 15 mg/kg/day: 7%, 25 mg/kg/day: 17%). Markedly increased, dose-related hyperammonemia also occurred in these patients (placebo: 0%; 5 mg/kg/day: 0%, 15 mg/kg/day: 7%, 25 mg/kg/day: 8%). Dose-related hyperammonemia was similarly observed in a long-term extension trial in these very young, pediatric patients.
Monitoring for Hyperammonemia/Encephalopathy: Asymptomatic elevations of serum ammonia levels may occur with topiramate treatment and require close monitoring. In patients who develop unexplained vomiting, lethargy, confusion, other changes in mental status or hypothermia, associated with any topiramate treatment, hyperammonemic encephalopathy should be considered a possible cause of these symptoms and serum ammonia levels measured. Hyperammonemia may be present despite normal liver function tests (see Hypothermia with Concomitant Valproic Acid (VPA) Use as follows; Post-Market Adverse Drug Reactions under Adverse Reactions; Drug-Drug Interactions: Antiepileptic Drugs (AEDs): Effects of Other AEDs on pms-TOPIRAMATE: Valproic Acid under Interactions).
Treatment-induced encephalopathy may occur with or without hyperammonemia; normal serum ammonia levels cannot be used to rule out treatment-induced encephalopathy.
Hypothermia with Concomitant Valproic Acid (VPA) Use: Hypothermia, defined as an unintentional drop in body core temperature to < 35°C (95°F), has been reported in association with topiramate use with concomitant valproic acid (VPA) both in conjunction with hyperammonemia and in the absence of hyperammonemia. This adverse reaction in patients using concomitant topiramate and valproate can occur after starting topiramate treatment or after increasing the daily dose of topiramate (see Drug-Drug Interactions: Antiepileptic Drugs (AEDs): Effects of Other AEDs on pms-TOPIRAMATE: Valproic Acid under Interactions). Consideration should be given to stopping topiramate or 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 (see Hyperammonemia and Encephalopathy as previously mentioned).
Oligohidrosis and Hyperthermia: Oligohidrosis (decreased sweating), anhidrosis and hyperthermia (elevation of body temperature above normal), infrequently resulting in hospitalization, including fatalities, have been reported in patients treated with topiramate. Some of the cases were reported after exposure to elevated environmental temperatures. Oligohidrosis and hyperthermia may have potentially serious sequelae, and may be preventable by prompt recognition of symptoms and appropriate treatment.
These reports have primarily involved children. Patients treated with pms-TOPIRAMATE, especially pediatric patients, should be monitored closely for evidence of decreased sweating and increased body temperature, particularly in hot weather. Proper hydration before and during activities such as exercise or exposure to warm temperatures is recommended.
Caution should be used when pms-TOPIRAMATE is prescribed with other drugs that predispose patients to heat-related disorders; these drugs include, but are not limited to, other carbonic anhydrase inhibitors and drugs with anticholinergic activity (see Post-Market Adverse Drug Reactions under Adverse Reactions).
Metabolic Acidosis: Hyperchloremic, non-anion gap, metabolic acidosis (i.e., decreased serum bicarbonate below the normal reference range in the absence of respiratory alkalosis) is associated with topiramate treatment. This decrease in serum bicarbonate is due to the inhibitory effect of topiramate on renal carbonic anhydrase. Generally, the decrease in bicarbonate occurs early in treatment although it can occur at any time during treatment. These decreases are usually mild to moderate (average decrease of 4 mmol/L at doses of 100 mg/day or above in adults and at approximately 6 mg/kg/day in pediatric patients). Rarely, patients have experienced decreases to values below 10 mmol/L. Conditions or therapies that predispose to acidosis (such as renal disease, severe respiratory disorders, status epilepticus, diarrhea, surgery, ketogenic diet, or certain drugs) may be additive to the bicarbonate-lowering effects of topiramate.
In patients > 16 years of age, the incidence of persistent treatment-emergent decreases in serum bicarbonate (levels of < 20 mmol/L at two consecutive visits or at the final visit) in controlled clinical trials for adjunctive treatment of epilepsy was 32% for 400 mg/day, and 1% for placebo. Metabolic acidosis has been observed at doses as low as 50 mg/day. The incidence of a markedly abnormally low serum bicarbonate (i.e., absolute value < 17 mmol/L and > 5 mmol/L decrease from pre-treatment) in these trials was 3% for 400 mg/day, and 0% for placebo. In the monotherapy trial, the incidence was 1% for 50 mg/day and 7% for 400 mg/day. Serum bicarbonate levels have not been systematically evaluated at daily doses greater than 400 mg/day.
In pediatric patients two to 16 years of age, the incidence of persistent treatment-emergent decreases in serum bicarbonate in placebo-controlled trials for adjunctive treatment of Lennox-Gastaut Syndrome or refractory partial onset seizures was 67% for topiramate (at approximately 6 mg/kg/day), and 10% for placebo. The incidence of a markedly abnormally low serum bicarbonate (i.e., absolute value < 17 mmol/L and > 5 mmol/L decrease from pre-treatment) in these trials was 11% for topiramate and 0% for placebo.
The incidence of persistent treatment-emergent decreases in serum bicarbonate in placebo-controlled trials for adults for prophylaxis of migraine was 44% for 200 mg/day, 39% for 100 mg/day, 23% for 50 mg/day, and 7% for placebo. The incidence of a markedly abnormally low serum bicarbonate (i.e., absolute value < 17 mmol/L and > 5 mmol/L decrease from pre-treatment) in these trials was 11% for 200 mg/day, 9% for 100 mg/day, 2% for 50 mg/day, and < 1% for placebo.
Although not approved for use in patients under two years of age for any indication (see Pediatrics (< 2 years of age) under Indications/Uses), a controlled trial that examined this population revealed that topiramate produced a metabolic acidosis that was notably greater in magnitude than that observed in controlled trials in older children and adults. The mean treatment difference (25 mg/kg/day topiramate-placebo) was -5.9 mEq/L for bicarbonate. The incidence of metabolic acidosis (defined by a serum bicarbonate < 20 mEq/L) was 0% for placebo, 30% for 5 mg/kg/day, 50% for 15 mg/kg/day, and 45% for 25 mg/kg/day. The incidence of markedly abnormal changes (i.e., < 17 mEq/L and > 5 mEq/L decrease from baseline of > 20 mEq/L) was 0% for placebo, 4% for 5 mg/kg/day, 5% for 15 mg/kg/day, and 5% for 25 mg/kg/day.
Cases of moderately severe metabolic acidosis have been reported in patients as young as five months old, especially at daily doses above 5 mg/kg/day.
In pediatric patients, six to 15 years of age, the incidence of persistent treatment-emergent decreases in serum bicarbonate in the epilepsy controlled clinical trial for monotherapy was 9% for 50 mg/day and 25% for 400 mg/day. The incidence of a markedly abnormally low serum bicarbonate (i.e., absolute value < 17 mEq/L and > 5 mEq/L decrease from pretreatment) in this trial was 1% for 50 mg/day and 6% for 400 mg/day.
In patients ≥ 16 years of age, the incidence of persistent treatment-emergent decreases in serum bicarbonate in the epilepsy controlled clinical trial for monotherapy was 14% for 50 mg/day and 25% for 400 mg/day. The incidence of a markedly abnormally low serum bicarbonate (i.e., absolute value < 17 mEq/L and > 5 mEq/L decrease from pretreatment) in this trial for adults was 1% for 50 mg/day and 6% for 400 mg/day.
Some manifestations of acute or chronic metabolic acidosis may include hyperventilation, nonspecific symptoms such as fatigue and anorexia, or more severe sequelae including cardiac arrhythmias or stupor. Chronic, untreated metabolic acidosis may increase the risk for nephrolithiasis or nephrocalcinosis (see Renal: Kidney Stones as follows), and may also result in osteomalacia (referred to as rickets in pediatric patients) and/or osteoporosis with an increased risk for fractures. Chronic metabolic acidosis in pediatric patients may also reduce growth rates. A reduction in growth rate may eventually decrease the maximal height achieved. The effect of topiramate on growth and bone-related sequelae has not been systematically investigated in long-term, placebo-controlled trials. Long-term, open-label treatment of infants/toddlers, with intractable partial epilepsy, for up to one year, showed reductions from baseline in Z SCORES for length, weight, and head circumference compared to age and sex-matched normative data, although these patients with epilepsy are likely to have different growth rates than normal infants. Reductions in Z SCORES for length and weight were correlated to the degree of acidosis. Topiramate treatment that causes metabolic acidosis during pregnancy can possibly produce adverse effects on the fetus and might also cause metabolic acidosis in the neonate from possible transfer of topiramate to the fetus.
Measurement of baseline and periodic serum bicarbonate during topiramate treatment is recommended. If metabolic acidosis develops and persists, consideration should be given to reducing the dose or discontinuing topiramate (using dose tapering). If the decision is made to continue patients on topiramate in the face of persistent acidosis, alkali treatment should be considered.
Decreases in Serum Potassium with Concomitant Treatment with Hydrochlorothiazide (HCTZ): In a drug interaction study, a greater decrease from baseline in serum potassium values was seen with concomitant treatment than for either drug alone. At the end of each treatment period, 27% (3/11) of subjects on topiramate treatment alone and 25% (3/12) of subjects on HCTZ treatment alone showed a serum potassium value of < 3.6 mEq/L, compared to 61% (14/23) of subjects on concomitant drug treatment. One of the subjects who had hypokalemia with concomitant treatment also had an abnormal ECG (non-specific ST-T wave changes), which may have been related to the decrease in plasma potassium levels. Caution should be used when treating patients who are receiving pms-TOPIRAMATE and hydrochlorothiazide concomitantly (see Drug-Drug Interactions: Other Drug Interactions: Hydrochlorothiazide (HCTZ) under Interactions).
Nutritional Supplementation: A dietary supplement or increased food intake may be considered if the patient is losing weight while on this medication.
Hepatic/Biliary/Pancreatic: Decreased Hepatic Function: In hepatically impaired patients, pms-TOPIRAMATE should be administered with caution as the clearance of topiramate was decreased compared with normal subjects.
Neurologic: Central Nervous System (CNS) Effects: Adverse events most often associated with the use of topiramate were CNS-related and were observed in both the epilepsy and migraine populations. In adults, the most significant of these can be classified into three general categories: i) psychomotor slowing, difficulty with concentration and speech or language problems, in particular, word-finding difficulties; ii) somnolence or fatigue; and iii) mood disturbances including irritability and depression.
In the controlled epilepsy adjunctive therapy trials, these events were generally mild to moderate and generally occurred early in therapy. While the incidence of psychomotor slowing does not appear to be dose related, both language problems and difficulty with concentration or attention increased in frequency with increasing dosage in the six double-blind trials, suggesting that these events are dose-related (see Post-Market Adverse Drug Reactions under Adverse Reactions).
Central nervous system and psychiatric-related events were also more frequently reported in topiramate-treated subjects in the migraine prophylaxis trials. These included: anorexia, dizziness, difficulty with memory, somnolence, language problems, and difficulty with concentration and attention. Most of the events were mild or moderate in severity, some of which led to withdrawal from treatment (see Migraine Prophylaxis: Adverse Drug Reaction Overview under Adverse Reactions).
Additional non-specific CNS effects occasionally observed with topiramate as add-on epilepsy therapy include dizziness or imbalance, confusion and memory problems. Although the duration of the epilepsy monotherapy studies was considerably longer than the epilepsy adjunctive therapy studies, these adverse events were reported at lower incidences in the monotherapy trials.
Paresthesia: Paresthesia, an effect associated with the use of other carbonic anhydrase inhibitors, appears to be a common effect of topiramate. Paresthesia was more frequently reported in the migraine prophylaxis and epilepsy monotherapy trials vs. the adjunctive therapy trials in epilepsy. The higher incidence in the epilepsy monotherapy studies may have been related to the higher topiramate plasma concentrations achieved in the monotherapy studies. In the majority of instances, paresthesia did not lead to treatment discontinuation.
Ophthalmologic: Acute Myopia and Secondary Angle Closure Glaucoma: A syndrome consisting of acute myopia associated with secondary angle closure glaucoma has been reported in patients receiving topiramate. Symptoms include acute onset of decreased visual acuity and/or ocular pain. Ophthalmologic findings can include myopia, anterior chamber shallowing, ocular hyperemia (redness) and increased intraocular pressure. Mydriasis may or may not be present. This syndrome may be associated with supraciliary effusion resulting in anterior displacement of the lens and iris, with secondary angle closure glaucoma. Symptoms typically occur within a few days to one month of initiating pms-TOPIRAMATE therapy. In contrast to primary narrow angle glaucoma, which is rare under 40 years of age, secondary angle closure glaucoma associated with topiramate has been reported in pediatric patients as well as adults. The primary treatment to reverse symptoms is discontinuation of pms-TOPIRAMATE as rapidly as possible, according to the judgment of the treating physician. Other measures, in conjunction with discontinuation of pms-TOPIRAMATE, may be helpful (see Post-Market Adverse Drug Reactions under Adverse Reactions).
In all cases of acute visual blurring and/or painful/red eye(s), immediate consultation with an ophthalmologist/emergency room is recommended.
Elevated intraocular pressure of any etiology, if left untreated, can lead to serious sequelae including permanent vision loss.
Maculopathy, including visual field defect, has been observed very rarely in post-marketing reports (see Post-Market Adverse Drug Reactions under Adverse Reactions).
Visual Field Defects: Visual field defects have been reported in patients receiving topiramate independent of elevated intraocular pressure. In clinical trials, although most events did resolve, some of these events were not reversible after topiramate discontinuation. If visual problems occur at any time during topiramate treatment, consideration should be given to discontinuing the drug.
Psychiatric: Suicidal Ideation and Behaviour: Suicidal ideation and behaviour have been reported in patients treated with antiepileptic agents in several indications.
All patients treated with AEDs, irrespective of indication, should be monitored for signs of suicidal ideation and behaviour and appropriate treatment should be considered. Patients (and caregivers of patients) should be advised to seek medical advice should signs of suicidal ideation or behaviour emerge.
An FDA meta-analysis of randomized placebo-controlled trials, in which AEDs were used for various indications, has shown a small increased risk of suicidal ideation and behaviour in patients treated with these drugs. The mechanism of this risk is not known.
There were 43,892 patients treated in the placebo-controlled clinical trials that were included in the meta-analysis. Approximately 75% of patients in these clinical trials were treated for indications other than epilepsy and, for the majority of non-epilepsy indications the treatment (AED or placebo) was administered as monotherapy. Patients with epilepsy represented approximately 25% of the total number of patients treated in the placebo-controlled clinical trials and, for the majority of epilepsy patients, treatment (AED or placebo) was administered as adjunct to other antiepileptic agents (i.e., patients in both treatment arms were being treated with one or more AED). Therefore, the small increased risk of suicidal ideation and behaviour reported from the meta-analysis (0.43% for patients on AEDs compared to 0.24% for patients on placebo) is based largely on patients that received monotherapy treatment (AED or placebo) for non-epilepsy indications. The study design does not allow an estimation of the risk of suicidal ideation and behaviour for patients with epilepsy that are taking AEDs, due both to this population being the minority in the study, and the drug-placebo comparison in this population being confounded by the presence of adjunct AED treatment in both arms.
Serious Skin Reactions: Serious skin reactions (Stevens-Johnson Syndrome [SJS] and Toxic Epidermal Necrolysis [TEN]) have been reported in patients receiving topiramate (see Post-Market Adverse Drug Reactions under Adverse Reactions). The majority of cases have occurred in patients concurrently taking other medications that are known to be associated with SJS and TEN. There have also been several cases in patients receiving monotherapy. The most frequently reported latency (half of cases where latency was assessable) was 3 weeks to 4 months after initiating topiramate therapy. It is recommended that patients be informed about the signs of serious skin reactions. If SJS or TEN are suspected, use of pms-TOPIRAMATE should be discontinued.
Fetal Toxicity: When multiple species of pregnant animals received topiramate at clinically relevant doses, structural malformations, including craniofacial defects, and reduced fetal weights occurred in offspring. In humans, topiramate crosses the placenta and similar concentrations have been reported in the umbilical cord and maternal blood.
pms-TOPIRAMATE can cause fetal harm when administered to a pregnant woman. Data from pregnancy registries indicate that infants exposed to topiramate in utero have an increased risk for cleft lip and/or cleft palate (oral clefts) and other congenital malformations (e.g., hypospadias and anomalies involving various body systems including limbs and heart). This has been reported with topiramate monotherapy and topiramate as part of a polytherapy regimen (see Pregnant Women: Epilepsy; and Pregnancy Registry Data under Use in Pregnancy & Lactation).
In addition, data from these registries and other studies indicate that, compared with monotherapy, there may be an increased risk of teratogenic effects associated with the use of AEDs in combination therapy. The risk has been observed in all doses and effects were reported to be dose-dependent. In women treated with topiramate who have had a child with a congenital malformation, there appears to be an increased risk of malformations in subsequent pregnancies when exposed to topiramate. There is an increased risk of pre-term labor and premature delivery associated with the use of AEDs, including topiramate.
Compared with a reference group not taking AEDs, registry data for topiramate monotherapy showed a higher prevalence of low birth weight (< 2,500 grams). One pregnancy registry reported an increased frequency of infants who were small for gestational age (SGA; defined as birth weight below the 10th percentile corrected for their gestational age, stratified by sex) among those exposed to topiramate monotherapy in utero. SGA has been observed in all doses and is dose-dependent. The prevalence of SGA is greater in women who received higher doses of topiramate during pregnancy. In addition, the prevalence of SGA for women who continued topiramate use later in pregnancy is higher compared to women who stopped its use before the third trimester. These data indicated that the overall occurrence of SGA in neonates exposed to topiramate in utero was 18% compared to 7% in the reference group. The long-term consequences of the SGA findings could not be determined. A causal relationship for low birth weight and SGA has not been established.
Consider the benefits and the risks of pms-TOPIRAMATE when administering this drug in women of childbearing potential (see Information for Patients: Fetal Toxicity as follows; Women of Childbearing Potential under Use in Pregnancy & Lactation). pms-TOPIRAMATE should be used during pregnancy only if the potential benefit outweighs the potential risk. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to a fetus (see Pregnant Women: Epilepsy under Use in Pregnancy & Lactation).
Renal: Kidney Stones: A total of 32/1,715 (1.9%) of patients exposed to topiramate during its epilepsy adjunctive therapy development reported the occurrence of kidney stones, an incidence about 10 times that expected in a similar, untreated population (M/F ratio: 27/1,092 male; 5/623 female). In double-blind epilepsy monotherapy studies, a total of 8/886 (0.9%) of adults reported the occurrence of kidney stones. In the general population, risk factors for kidney stone formation include gender (male), ages between 20 - 50 years, prior stone formation, family history of nephrolithiasis, and hypercalciuria (see Endocrine and Metabolism: Metabolic Acidosis as previously mentioned). Based on logistic regression analysis of the clinical trial data, no correlation between mean topiramate dosage, duration of topiramate therapy, or age and the occurrence of kidney stones was established; of the risk factors evaluated, only gender (male) showed a correlation with the occurrence of kidney stones. In the pediatric patients studied, there were no kidney stones observed.
Carbonic anhydrase inhibitors, e.g., acetazolamide, promote stone formation by reducing urinary citrate excretion and by increasing urinary pH. Concomitant use of pms-TOPIRAMATE, a weak carbonic anhydrase inhibitor, with other carbonic anhydrase inhibitors may create a physiological environment that increases the risk of kidney stone formation, and should therefore be avoided (see Drug-Drug Interactions: Other Drug Interactions: Agents Predisposing to Nephrolithiasis under Interactions).
Patients, especially those with a predisposition to nephrolithiasis, may have an increased risk of renal stone formation and associated signs and symptoms such as renal colic, renal pain or flank pain. Increased fluid intake increases the urinary output, lowering the concentration of substances involved in stone formation. Therefore, adequate hydration is recommended to reduce this risk. None of the risk factors for nephrolithiasis can reliably predict stone formation during topiramate treatment.
Adjustment of Dose in Renal Failure: The major route of elimination of unchanged topiramate and its metabolites is via the kidney. Renal elimination is dependent on renal function and is independent of age. Patients with impaired renal function (CLCR < 70 mL/min/1.73 m2) or with end-stage renal disease receiving hemodialysis treatments may take 10 to 15 days to reach steady-state plasma concentrations as compared to four to eight days in patients with normal renal function. As with all patients, the titration schedule should be guided by clinical outcome (i.e., seizure control, avoidance of side effects) with the knowledge that patients with known renal impairment may require a longer time to reach steady state at each dose (see Dosing Considerations and Patients with Renal Impairment under Dosage & Administration).
Information for Patients: Patients receiving pms-TOPIRAMATE should be given the following instructions by the physician: 1. Eye Disorders: Patients taking pms-TOPIRAMATE should be told to seek immediate medical attention if they experience blurred vision, visual disturbances, or periorbital pain.
2. Oligohydrosis and Hyperthermia: Patients, especially pediatric patients, treated with pms-TOPIRAMATE should be monitored closely for evidence of decreased sweating and increased body temperature, especially in hot weather. Patients should be counselled to contact their healthcare professionals immediately if they develop these symptoms.
3. Metabolic Acidosis: Patients should be warned about the potential significant risk for metabolic acidosis that may be asymptomatic and if left untreated may be associated with adverse effects on kidneys (e.g., kidney stones, nephrocalcinosis), bones (e.g., osteoporosis, osteomalacia, and/or rickets in children), and growth (e.g., growth delay/retardation) in pediatric patients, and on the fetus.
Patients should be advised that in many cases metabolic acidosis is asymptomatic, but some patients could experience symptoms such as rapid breathing, persistent lack of energy, loss of appetite, heart problems, confused thinking or reduced consciousness. Patients should be counselled to contact their healthcare professionals immediately if they develop these symptoms.
4. Suicidal Behaviour and Ideation: Patients, their caregivers, and families should be counselled that AEDs, including pms-TOPIRAMATE, may increase the risk of suicidal thoughts and behaviour and should be advised of the need to be alert for the emergence or worsening of the signs and symptoms of depression, any unusual changes in mood or behaviour or the emergence of suicidal thoughts, or behaviour or thoughts about self-harm. Behaviours of concern should be reported immediately to healthcare providers.
5. Interference with Cognitive and Motor Performance: Patients should be warned about the potential for somnolence, dizziness, confusion, difficulty concentrating, or visual effects and should be advised not to drive or operate machinery until they have gained sufficient experience on pms-TOPIRAMATE to gauge whether it adversely affects their mental performance, motor performance, and/or vision.
Even when taking pms-TOPIRAMATE or other anticonvulsants, some patients with epilepsy will continue to have unpredictable seizures. Therefore, all patients taking pms-TOPIRAMATE for epilepsy should be told to exercise appropriate caution when engaging in any activities where loss of consciousness could result in serious danger to themselves or those around them (including swimming, driving a car, climbing in high places, etc.). Some patients with refractory epilepsy will need to avoid such activities altogether. Physicians should discuss the appropriate level of caution with their patients, before patients with epilepsy engage in such activities.
6. Hyperammonemia and Encephalopathy: Patients should be warned about the possible development of hyperammonemia with or without encephalopathy. Although hyperammonemia may be asymptomatic, clinical symptoms of hyperammonemic encephalopathy often include acute alterations in level of consciousness and/or cognitive function with lethargy or vomiting. This hyperammonemia and encephalopathy can develop with pms-TOPIRAMATE treatment alone or with pms-TOPIRAMATE treatment with concomitant valproic acid (VPA).
Patients should be instructed to contact their physician if they develop unexplained lethargy, vomiting, changes in mental status, or hypothermia (body core temperature < 35°C [95°F]).
7. Kidney Stones: Patients, particularly those with predisposing factors, should be instructed to maintain an adequate fluid intake in order to minimize the risk of kidney stone formation.
8. Serious Skin Reactions: Patients should be advised of the early signs and symptoms of potential serious skin reactions, including but not limited to rash, sore throat, fever, and mouth ulcers. Patients should be advised that because these signs and symptoms may signal a serious reaction, that they must report any occurrence immediately to a physician. In addition, the patient should be advised that these signs and symptoms should be reported even if mild or when occurring after extended use (see Serious Skin Reactions as previously mentioned).
9. Fetal Toxicity: Inform pregnant women and women of childbearing potential that use of pms-TOPIRAMATE during pregnancy can cause fetal harm, including an increased risk for cleft lip and/or cleft palate (oral clefts), which occur early in pregnancy before many women know they are pregnant. There may also be risks to the fetus from chronic metabolic acidosis with use of pms-TOPIRAMATE during pregnancy. When appropriate, prescribers should counsel pregnant women and women of childbearing potential about alternative therapeutic options.
Prescribers should advise women of childbearing potential who are not planning a pregnancy to use effective contraception while using pms-TOPIRAMATE, keeping in mind that there is a potential for decreased contraceptive efficacy when using estrogen-containing birth control with topiramate (see Drug-Drug Interactions: Other Drug Interactions: Oral Contraceptives under Interactions).
Prophylactic treatment of migraine: Taking pms-TOPIRAMATE to prevent migraine attacks does not outweigh the risk of malformations to the fetus. Consequently, pms-TOPIRAMATE is contraindicated in pregnancy and in women of childbearing potential who are not using an effective method of contraception (see Dosing Considerations under Dosage & Administration; Contraindications; Pregnant Women: Epilepsy and Migraine Prophylaxis under Use in Pregnancy & Lactation).
Monitoring and Laboratory Tests: It has been observed in clinical trials that topiramate-treated subjects experienced an average decrease in serum bicarbonate level of 4 mmol/L and an average increase in serum chloride level of 4 mmol/L (see Endocrine and Metabolism: Metabolic Acidosis as previously mentioned).
Topiramate treatment with or without concomitant valproic acid (VPA) can cause hyperammonemia with or without encephalopathy (see Endocrine and Metabolism: Hyperammonemia and Encephalopathy as previously mentioned).
Hypokalemia Observed During Concomitant Treatment with Hydrochlorothiazide: In a drug interaction study with the diuretic hydrochlorothiazide (HCTZ), the percentage of patients with a serum potassium measurement of < 3.6 mEq/L was greater at the end of concomitant treatment than at the end of treatment for either drug alone: 27% (3/11) of subjects on topiramate treatment alone and 25% (3/12) of subjects on HCTZ alone vs. 61% (14/22) of subjects on concomitant drug treatment (see Endocrine and Metabolism: Decreases in Serum Potassium with Concomitant Treatment with Hydrochlorothiazide (HCTZ) as previously mentioned; Drug-Drug Interactions: Other Drug Interactions: Hydrochlorothiazide (HCTZ) under Interactions).
Use in Children: Safety and effectiveness in patients below the age of two years have not been established for the adjunctive therapy treatment of partial onset seizures, primary generalized tonic-clonic seizures, or seizures associated with Lennox-Gastaut syndrome. In a single randomized, double-blind, placebo-controlled investigational trial, the efficacy, safety, and tolerability of topiramate oral liquid and sprinkle formulations as an adjunct to concurrent AED therapy in infants one to 24 months of age with refractory partial onset seizures were assessed. After 20 days of double-blind treatment, topiramate (at fixed doses of 5, 15, and 25 mg/kg/day) did not demonstrate efficacy compared with placebo in controlling seizures.
Results from the previously mentioned controlled epilepsy trial and an open-label, long-term extension study in patients under two years of age indicated that some adverse reactions/toxicities occurred in patients under two years of age that had not been previously observed in older pediatric patients and adults for various indications. These events included growth/length retardation, certain clinical laboratory abnormalities, and other adverse reactions/toxicities that occurred with a greater frequency and/or greater severity.
Infection: These very young pediatric patients (< 2 years) appeared to experience an increased risk for infections (any topiramate dose: 12% vs. placebo: 0%) and of respiratory disorders (any topiramate dose: 40% vs. placebo: 16%). The following adverse reactions were observed in at least 3% of patients on topiramate and were 3% to 7% more frequent than in patients on placebo: viral infection, bronchitis, pharyngitis, rhinitis, otitis media, upper respiratory infection, cough, and bronchospasm. A generally similar profile was observed in older children.
Creatinine and BUN: Topiramate resulted in an increased incidence of patients with increased creatinine (any topiramate dose: 5% vs. placebo: 0%), BUN (any topiramate dose: 3% vs. placebo: 0%), protein (any topiramate dose: 34% vs. placebo: 6%), and an increased incidence of decreased potassium (any topiramate dose: 7% vs. placebo: 0%). This increased frequency of abnormal values was not dose-related. The clinical significance of these findings is uncertain.
Other Events: Topiramate treatment also produced a dose-related increase in the percentage of patients who had a shift from normal at baseline to high/increased (above the normal reference range) in total eosinophil count at the end of treatment (placebo: 6%; 5 mg/kg/day: 10%; 15 mg/kg/day: 9%; 25 mg/kg/day: 14%; any topiramate dose: 11%.
There was a mean dose-related increase in alkaline phosphatase. The clinical significance of these findings is uncertain.
Topiramate produced a dose-related increased incidence of treatment-emergent hyperammonemia (see Endocrine and Metabolism: Hyperammonemia and Encephalopathy as previously mentioned).
Treatment with topiramate for up to one year was associated with reductions in Z SCORES for length, weight, and head circumference (see Endocrine and Metabolism: Metabolic Acidosis as previously mentioned; Adverse Reactions).
Open-Label Epilepsy Trial: In an open-label, adjunctive therapy, epilepsy trial, increasing impairment of adaptive behaviour was documented in behavioural testing over time in children under two years of age. There was a suggestion that this effect was dose-related. However, because of the absence of an appropriate control group, it is not known if this decrement in function was treatment-related or reflects the patient's underlying disease. For example, patients who received higher doses may have more severe underlying disease.
In this open-label, uncontrolled study, the mortality was 37 deaths/1,000 patient years. It is not possible to know whether this mortality rate is related to topiramate treatment, because the background mortality rate for a similar, significantly refractory, young pediatric population under two years with partial epilepsy is not known.
Safety and efficacy of topiramate for the monotherapy treatment of partial onset seizures or any other type of epilepsy in patients under two years of age have not been established.
Migraine Prophylaxis: Although not indicated for migraine prophylaxis in patients under 18 years of age (see Migraine Prophylaxis under Indications/Uses), in a double-blind, placebo-controlled trial of migraine prophylaxis in patients 12 to 16 years, topiramate treatment produced a dose-related increased shift in serum creatinine from normal at baseline to an increased value at the end of 4 months. The incidence of these abnormal shifts was 4% for placebo, 4% for 50 mg, and 18% for 100 mg.
Weight Loss in Pediatrics (> 2 years of age): Topiramate administration is associated with weight loss in some children that generally occurs early in therapy. Of those pediatric subjects treated in clinical trials for at least a year who experienced weight loss, 96% showed a resumption of weight gain within the period tested. In two- to four-year-olds, the mean change in weight from baseline at 12 months (n = 25) was +0.7 kg (range -1.1 to 3.2); at 24 months (n = 14), the mean change was +2.2 kg (range -1.1 to 6.1). In 5- to 10-year-olds, the mean change in weight from baseline at 12 months (n = 88) was +0.7 kg (range -6.7 to 11.8); at 24 months (n = 67), the mean change was +3.3 kg (range -8.6 to 20.0). Weight decreases, usually associated with anorexia or appetite changes, were reported as adverse events for 9% of patients treated with topiramate. The long-term effects of reduced weight gain in pediatric patients are not known.
Use in the Elderly: There is limited information in patients over 65 years of age. The possibility of age-associated renal function abnormalities should be considered when using pms-TOPIRAMATE. (See Pharmacology: Pharmacokinetics: Special Populations and Conditions: Geriatrics under Actions.)
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