Galantamine

5 WARNINGS AND PRECAUTIONS Serious skin reactions: discontinue at first appearance of skin rash (5.1) All patients should be considered at risk for adverse effects on cardiac conduction, including bradycardia and AV block, due to vagotonic effects on sinoatrial and atrioventricular nodes (5.3) Active or occult gastrointestinal bleeding: monitor, especially those with an increased risk for developing ulcers (5.4) Cholinomimetics may cause bladder outflow obstruction (5.5) Monitor for respiratory adverse events in patients with a history of severe asthma or obstructive pulmonary disease (5.7)

5.1 Serious Skin Reactions Serious skin reactions (Stevens-Johnson syndrome and acute generalized exanthematous pustulosis) have been reported in patients receiving galantamine extended-release capsules and galantamine tablets. Inform patients and caregivers that the use of galantamine extended-release capsules should be discontinued at the first appearance of a skin rash, unless the rash is clearly not drug-related. If signs or symptoms suggest a serious skin reaction, use of this drug should not be resumed and alternative therapy should be considered.

5.2 Anesthesia Galantamine, as a cholinesterase inhibitor, is likely to exaggerate the neuromuscular blocking effects of succinylcholine-type and similar neuromuscular blocking agents during anesthesia.

5.3 Cardiovascular Conditions Because of their pharmacological action, cholinesterase inhibitors have vagotonic effects on the sinoatrial and atrioventricular nodes, leading to bradycardia and AV block. Bradycardia and all types of heart block have been reported in patients both with and without known underlying cardiac conduction abnormalities [see Adverse Reactions (6.1 , 6.2) ] . Therefore, all patients should be considered at risk for adverse effects on cardiac conduction. Patients treated with galantamine up to 24 mg/day using the recommended dosing schedule showed a dose-related increase in risk of syncope (placebo 0.7% [2/286]; 4 mg twice daily 0.4% [3/692]; 8 mg twice daily 1.3% [7/552]; 12 mg twice daily 2.2% [6/273]).

5.4 Gastrointestinal Conditions Through their primary action, cholinomimetics may be expected to increase gastric acid secretion due to increased cholinergic activity. Therefore, patients should be monitored closely for symptoms of active or occult gastrointestinal bleeding, especially those with an increased risk for developing ulcers, e.g., those with a history of ulcer disease or patients using concurrent nonsteroidal anti-inflammatory drugs (NSAIDs). Clinical studies of galantamine have shown no increase, relative to placebo, in the incidence of either peptic ulcer disease or gastrointestinal bleeding. Galantamine, as a predictable consequence of its pharmacological properties, has been shown to produce nausea, vomiting, diarrhea, anorexia, and weight loss. During therapy with galantamine extended-release capsules, the patient’s weight should be monitored.

5.5 Genitourinary Conditions Although this was not observed in clinical trials with galantamine, cholinomimetics may cause bladder outflow obstruction.

5.6 Neurological Conditions Cholinesterase inhibitors are believed to have some potential to cause generalized convulsions [see Adverse Reactions (6.2) ] . Seizure activity may also be a manifestation of Alzheimer’s disease. Patients with Alzheimer’s disease should be monitored closely for seizures while taking galantamine extended-release capsules. An increase in cholinergic tone may worsen symptoms related to extrapyramidal disorders [see Adverse Reactions (6.2) ] .

5.7 Pulmonary Conditions Because of its cholinomimetic action, galantamine extended-release capsules should be prescribed with care to patients with a history of severe asthma or obstructive pulmonary disease. Respiratory function should be monitored closely for the occurrence of respiratory adverse effects.

5.8 Deaths in Patients with Mild Cognitive Impairment (MCI) In two randomized placebo-controlled trials of 2 years duration in patients with mild cognitive impairment (MCI), a total of 13 patients on galantamine (n=1026) and 1 patient on placebo (n=1022) died. The deaths were due to various causes which could be expected in an elderly population; about half of the galantamine deaths appeared to result from various vascular causes (myocardial infarction, stroke, and sudden death). Although the difference in mortality between galantamine- and placebo-treated groups in these two studies was significant, the results are highly discrepant with other studies of galantamine. Specifically, in these two MCI studies, the mortality rate in the placebo-treated patients was markedly lower than the rate in placebo-treated patients in trials of galantamine in Alzheimer’s disease or other dementias (0.7 per 1000 person years compared to 22 to 61 per 1000 person years, respectively). Although the mortality rate in the galantamine-treated MCI patients was also lower than that observed in galantamine-treated patients in Alzheimer’s disease and other dementia trials (10.2 per 1000 person years compared to 23 to 31 per 1000 person years, respectively), the relative difference was much less. When the Alzheimer’s disease and other dementia studies were pooled (n=6000), the mortality rate in the placebo group numerically exceeded that in the galantamine group. Furthermore, in the MCI studies, no patients in the placebo group died after 6 months, a highly unexpected finding in this population. Individuals with mild cognitive impairment demonstrate isolated memory impairment greater than expected for their age and education, but do not meet current diagnostic criteria for Alzheimer’s disease.

Serious adverse reactions are discussed in more detail in the following sections of the labeling: Serious Skin Reactions [see Warnings and Precautions (5.1) ] Cardiovascular Conditions [see Warnings and Precautions (5.3) ] Gastrointestinal Conditions [see Warnings and Precautions (5.4) ] Genitourinary Conditions [see Warnings and Precautions (5.5) ] Neurological Conditions [see Warnings and Precautions (5.6) ] Pulmonary Conditions [see Warnings and Precautions (5.7) ] Deaths in Patients with Mild Cognitive Impairment (MCI) [see Warnings and Precautions (5.8) ] The most common adverse reactions (≥5%) were nausea, vomiting, diarrhea, dizziness, headache, and decreased appetite (6.1) To report SUSPECTED ADVERSE REACTIONS, contact Aurobindo Pharma USA, Inc. at 1-866-850-2876 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch .

6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The most common adverse reactions in galantamine-treated patients from double-blind clinical trials (≥5%) were nausea, vomiting, diarrhea, dizziness, headache, and decreased appetite. The most common adverse reactions associated with discontinuation (≥1%) in galantamine-treated patients from double-blind clinical trials were nausea (6.2%), vomiting (3.3%), decreased appetite (1.5%), and dizziness (1.3%). The safety of the extended-release capsule and immediate-release tablet formulations of galantamine was evaluated in 3956 galantamine-treated patients who participated in 8 placebo-controlled clinical studies and 1454 patients in 5 open-label clinical studies with mild to moderate dementia of the Alzheimer’s type. In clinical studies, the safety profile of once-daily treatment with extended-release galantamine was similar in frequency and nature to that seen with tablets. The information presented in this section was derived from pooled double-blind studies and from pooled open-label data. Commonly-Observed Adverse Reactions in Double-Blind, Placebo-Controlled Clinical Trials Table 1 lists the adverse reactions reported in ≥1% of galantamine-treated patients in 8 placebo-controlled, double-blind clinical trials. Table 1. Adverse Reactions Reported by ≥1% of Galantamine-Treated Patients in Pooled Placebo-Controlled, Double-Blind Clinical Trials System/Organ Class Adverse Reaction Galantamine (n=3956) % Placebo (n=2546) % Metabolism and Nutrition Disorders Decreased appetite 7.4 2.1 Psychiatric Disorders Depression 3.6 2.3 Nervous System Disorders Dizziness 7.5 3.4 Headache 7.1 5.5 Tremor 1.6 0.7 Somnolence 1.5 0.8 Syncope 1.4 0.6 Lethargy 1.3 0.4 Cardiac Disorders Bradycardia 1 0.3 Gastrointestinal Disorders Nausea 20.7 5.5 Vomiting 10.5 2.3 Diarrhea 7.4 4.9 Abdominal pain 3.8 2 Abdominal discomfort 2.1 0.7 Dyspepsia 1.5 1 Musculoskeletal and Connective Tissue Disorders Muscle spasms 1.2 0.5 General Disorders and Administration Site Conditions Fatigue 3.5 1.8 Asthenia 2 1.5 Malaise 1.1 0.5 Investigations Decreased weight 4.7 1.5 Injury, Poisoning and Procedural Complications Fall 3.9 3 Laceration 1.1 0.5 The majority of these adverse reactions occurred during the dose-escalation period. In those patients who experienced the most frequent adverse reaction, nausea, the median duration of the nausea was 5 to 7 days. Other Adverse Reactions Observed in Clinical Trials of Galantamine The following adverse reactions occurred in <1% of all galantamine-treated patients (N=3956) in the above double-blind, placebo-controlled clinical trial data sets. In addition, the following also includes all adverse reactions reported at any frequency rate in patients (N=1454) who participated in open-label studies. Adverse reactions listed in Table 1 above were not included below: Metabolism and Nutrition Disorders: Dehydration Nervous System Disorders: Dysgeusia, Hypersomnia, Paresthesia Eye Disorders: Blurred vision Cardiac Disorders: First degree atrioventricular block, Palpitations, Sinus bradycardia, Supraventricular extrasystoles Vascular Disorders: Flushing, Hypotension Gastrointestinal Disorders: Retching Skin and Subcutaneous Tissue Disorders: Hyperhidrosis Musculoskeletal and Connective Tissue Disorders: Muscular weakness Discontinuations Due to Adverse Reactions In the 8 placebo-controlled studies of adults, 418 (10.6%) galantamine-treated patients (N=3956) and 56 (2.2%) placebo patients (N=2546) discontinued due to an adverse reaction. Those events with an incidence of ≥0.5% in the galantamine-treated patients included nausea (245, 6.2%), vomiting (129, 3.3%), decreased appetite (60, 1.5%), dizziness (50, 1.3%), diarrhea (31, 0.8%), headache (29, 0.7%), and decreased weight (26, 0.7%). The only event with an incidence of ≥0.5% in placebo patients was nausea (17, 0.7%). In the 5 open-label studies, 103 (7.1%) patients (N=1454) discontinued due to an adverse reaction. Those events with an incidence of ≥0.5% included nausea (43, 3%), vomiting (23, 1.6%), decreased appetite (13, 0.9%), headache (12, 0.8%), decreased weight (9, 0.6%), dizziness (8, 0.6%), and diarrhea (7, 0.5%).

6.2 Postmarketing Experience The following additional adverse reactions have been identified during post-approval use of galantamine extended-release capsules or galantamine tablets. 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: Immune System Disorders: Hypersensitivity Psychiatric Disorders: Hallucinations Nervous System Disorders: Seizures, extrapyramidal disorder [see Warnings and Precautions (5.6) ] Ear and Labyrinth Disorders: Tinnitus Cardiac Disorders: Complete atrioventricular block Vascular Disorders: Hypertension Hepatobiliary Disorders: Hepatitis, increased hepatic enzyme Skin and Subcutaneous Tissue Disorders: Stevens-Johnson syndrome, acute generalized exanthematous pustulosis, erythema multiforme

12.1 Mechanism of Action Although the etiology of cognitive impairment in Alzheimer’s disease (AD) is not fully understood, it has been reported that acetylcholine-producing neurons degenerate in the brains of patients with Alzheimer’s disease. The degree of this cholinergic loss has been correlated with degree of cognitive impairment and density of amyloid plaques (a neuropathological hallmark of Alzheimer’s disease). Galantamine, a tertiary alkaloid, is a competitive and reversible inhibitor of acetylcholinesterase. While the precise mechanism of galantamine’s action is unknown, it is postulated to exert its therapeutic effect by enhancing cholinergic function. This is accomplished by increasing the concentration of acetylcholine through reversible inhibition of its hydrolysis by cholinesterase. If this mechanism is correct, galantamine’s effect may lessen as the disease process advances and fewer cholinergic neurons remain functionally intact. There is no evidence that galantamine alters the course of the underlying dementing process.

12.3 Pharmacokinetics The pharmacokinetics of galantamine are linear over a dose range of 8 to 32 mg/day. Absorption and Distribution Galantamine is absorbed with time to peak concentration of about 1 hour. The absolute bioavailability of galantamine is about 90%. Food did not affect the AUC of galantamine, but C max was decreased by 25% and T max was delayed by 1.5 hours, when galantamine was administered with food. The mean volume of distribution of galantamine is 175 L. The plasma protein binding of galantamine is 18% at therapeutically relevant concentrations. In whole blood, galantamine is mainly distributed to blood cells (52.7%). The blood to plasma concentration ratio of galantamine is 1.2. Metabolism and Elimination Galantamine is metabolized by hepatic cytochrome P450 enzymes, glucuronidated, and excreted unchanged in the urine. In vitro studies indicate that cytochrome CYP2D6 and CYP3A4 were the major cytochrome P450 isoenzymes involved in the metabolism of galantamine, and inhibitors of both pathways increase oral bioavailability of galantamine modestly. O-demethylation, mediated by CYP2D6 was greater in extensive metabolizers of CYP2D6 than in poor metabolizers. In plasma from both poor and extensive metabolizers, however, unchanged galantamine and its glucuronide accounted for most of the sample radioactivity. In studies of oral 3 H-galantamine, unchanged galantamine and its glucuronide, accounted for most plasma radioactivity in poor and extensive CYP2D6 metabolizers. Up to 8 hours post-dose, unchanged galantamine accounted for 39 to 77% of the total radioactivity in the plasma, and galantamine glucuronide for 14 to 24%. By 7 days, 93 to 99% of the radioactivity had been recovered, with about 95% in urine and about 5% in the feces. Total urinary recovery of unchanged galantamine accounted for, on average, 32% of the dose and that of galantamine glucuronide for another 12% on average. After intravenous or oral administration, about 20% of the dose was excreted as unchanged galantamine in the urine in 24 hours, representing a renal clearance of about 65 mL/min, about 20 to 25% of the total plasma clearance of about 300 mL/min. Galantamine has a terminal half-life of about 7 hours. Galantamine extended-release capsules 24 mg administered once daily under fasting conditions are bioequivalent to galantamine tablets 12 mg twice daily with respect to AUC 24h and C min . The C max and T max of the extended-release capsules were lower and occurred later, respectively, compared with the immediate-release tablets, with C max about 25% lower and median T max occurring about 4.5 to 5 hours after dosing. Dose-proportionality is observed for galantamine extended-release capsules over the dose range of 8 to 24 mg daily and steady state is achieved within a week. There was no effect of age on the pharmacokinetics of galantamine extended-release capsules. CYP2D6 poor metabolizers had drug exposures that were approximately 50% higher than for extensive metabolizers. There are no appreciable differences in pharmacokinetic parameters when galantamine extended-release capsules are given with food compared to when they are given in the fasted state. Specific Populations Elderly Data from clinical trials in patients with Alzheimer’s disease indicate that galantamine concentrations are 30 to 40% higher in those patients than in healthy young subjects. Gender and Race A population pharmacokinetic analysis (on 539 men and 550 women) indicates that galantamine clearance is about 20% lower in women than in men (which is explained by a lower body weight in women) and that race (n=1029 White, 24 Black, 13 Asian and 23 other) did not affect the clearance of galantamine. Hepatic Impairment Following a single 4 mg dose of galantamine tablets, the pharmacokinetics of galantamine in subjects with mild hepatic impairment (n=8; Child-Pugh score of 5 to 6) were similar to the pharmacokinetics of galantamine in healthy subjects. In patients with moderate hepatic impairment (n=8; Child Pugh score of 7 to 9), galantamine clearance was decreased by about 25% compared to galantamine clearance in normal volunteers. Exposure to galantamine would be expected to increase further with increasing degree of hepatic impairment [see Dosage and Administration (2.2) and Use in Specific Populations (8.6) ] . Renal Impairment Following a single 8 mg dose of galantamine tablets, AUC increased by 37% and 67% in patients with moderate and severe renal impairment, respectively, compared with normal volunteers [see Dosage and Administration (2.3) and Use in Specific Populations (8.7) ] . Drug-Drug Interactions Multiple metabolic pathways and renal excretion are involved in the elimination of galantamine so no single pathway appears predominant. Based on in vitro studies, CYP2D6 and CYP3A4 were the major enzymes involved in the metabolism of galantamine. CYP2D6 was involved in the formation of O-desmethyl-galantamine, whereas CYP3A4 mediated the formation of galantamine-N-oxide. Galantamine is also glucuronidated and excreted unchanged in urine. Effect of Other Drugs on Galantamine CYP3A4 Inhibitors : Ketoconazole Ketoconazole, a strong inhibitor of CYP3A4 and an inhibitor of CYP2D6, when administered at a dose of 200 mg two times a day for 4 days, increased the AUC of galantamine by 30%. Erythromycin Erythromycin, a moderate inhibitor of CYP3A4, when administered at a dose of 500 mg four times a day for 4 days, affected the AUC of galantamine minimally (10% increase). CYP2D6 Inhibitors: A population pharmacokinetics analysis on a database of 852 patients with Alzheimer’s disease showed that the clearance of galantamine was reduced about 25 to 33% by the concurrent administration of amitriptyline (n=17), fluoxetine (n=48), fluvoxamine (n=14), and quinidine (n=7), all of which are known inhibitors of CYP2D6. Paroxetine Paroxetine, a strong inhibitor of CYP2D6, when administered at a dose of 20 mg/day for 16 days, increased the oral bioavailability of galantamine by about 40%. H2 Antagonists Galantamine was administered as a single dose of 4 mg on Day 2 of a 3-day treatment with either cimetidine (800 mg daily) or ranitidine (300 mg daily). Cimetidine increased the bioavailability of galantamine by approximately 16%. Ranitidine had no effect on the pharmacokinetics of galantamine. Memantine Memantine, an N-methyl-D-aspartate receptor antagonist, when administered at a dose of 10 mg two times a day, had no effect on the pharmacokinetics of galantamine (16 mg/day) at steady state. Effect of Galantamine on Other Drugs In Vitro Studies In vitro studies show that galantamine did not inhibit the metabolic pathways catalyzed by CYP1A2, CYP2A6, CYP3A4, CYP4A, CYP2C, CYP2D6 or CYP2E1. This indicates that the inhibitory potential of galantamine towards the major forms of cytochrome P450 is very low. In Vivo Studies Warfarin Multiple doses of galantamine at 24 mg/day had no effect on the pharmacokinetics of R- and S-warfarin (administered in a single dose of 25 mg) or on the increased prothrombin time induced by warfarin. The protein binding of warfarin was unaffected by galantamine. Digoxin Multiple doses of galantamine at 24 mg/day had no effect on the steady-state pharmacokinetics of digoxin (at a dose of 0.375 mg once daily) when those two drugs were co-administered. In that study, however, one healthy subject was hospitalized on account of 2nd and 3rd degree heart block and bradycardia.

12.5 Pharmacogenomics CYP2D6 Poor Metabolizers Approximately 7% of the normal population has a genetic variation that leads to reduced levels of activity of CYP2D6 isozyme. Such individuals have been referred to as poor metabolizers. After a single oral dose of 4 mg or 8 mg galantamine, CYP2D6 poor metabolizers demonstrated a similar C max and about 35% AUC ∞ increase of unchanged galantamine compared to extensive metabolizers. A total of 356 patients with Alzheimer’s disease enrolled in two Phase 3 studies were genotyped with respect to CYP2D6 (n=210 hetero-extensive metabolizers, 126 homo-extensive metabolizers, and 20 poor metabolizers). Population pharmacokinetic analysis indicated that there was a 25% decrease in median clearance in poor metabolizers compared to extensive metabolizers. Dosage adjustment is not necessary in patients identified as poor metabolizers as the dose of drug is individually titrated to tolerability.

The pharmacokinetics of galantamine are linear over a dose range of 8 to 32 mg/day. Absorption and Distribution Galantamine is absorbed with time to peak concentration of about 1 hour. The absolute bioavailability of galantamine is about 90%. Food did not affect the AUC of galantamine, but C max was decreased by 25% and T max was delayed by 1.5 hours, when galantamine was administered with food. The mean volume of distribution of galantamine is 175 L. The plasma protein binding of galantamine is 18% at therapeutically relevant concentrations. In whole blood, galantamine is mainly distributed to blood cells (52.7%). The blood to plasma concentration ratio of galantamine is 1.2. Metabolism and Elimination Galantamine is metabolized by hepatic cytochrome P450 enzymes, glucuronidated, and excreted unchanged in the urine. In vitro studies indicate that cytochrome CYP2D6 and CYP3A4 were the major cytochrome P450 isoenzymes involved in the metabolism of galantamine, and inhibitors of both pathways increase oral bioavailability of galantamine modestly. O-demethylation, mediated by CYP2D6 was greater in extensive metabolizers of CYP2D6 than in poor metabolizers. In plasma from both poor and extensive metabolizers, however, unchanged galantamine and its glucuronide accounted for most of the sample radioactivity. In studies of oral 3 H-galantamine, unchanged galantamine and its glucuronide, accounted for most plasma radioactivity in poor and extensive CYP2D6 metabolizers. Up to 8 hours post-dose, unchanged galantamine accounted for 39 to 77% of the total radioactivity in the plasma, and galantamine glucuronide for 14 to 24%. By 7 days, 93 to 99% of the radioactivity had been recovered, with about 95% in urine and about 5% in the feces. Total urinary recovery of unchanged galantamine accounted for, on average, 32% of the dose and that of galantamine glucuronide for another 12% on average. After intravenous or oral administration, about 20% of the dose was excreted as unchanged galantamine in the urine in 24 hours, representing a renal clearance of about 65 mL/min, about 20 to 25% of the total plasma clearance of about 300 mL/min. Galantamine has a terminal half-life of about 7 hours. Galantamine extended-release capsules 24 mg administered once daily under fasting conditions are bioequivalent to galantamine tablets 12 mg twice daily with respect to AUC 24h and C min . The C max and T max of the extended-release capsules were lower and occurred later, respectively, compared with the immediate-release tablets, with C max about 25% lower and median T max occurring about 4.5 to 5 hours after dosing. Dose-proportionality is observed for galantamine extended-release capsules over the dose range of 8 to 24 mg daily and steady state is achieved within a week. There was no effect of age on the pharmacokinetics of galantamine extended-release capsules. CYP2D6 poor metabolizers had drug exposures that were approximately 50% higher than for extensive metabolizers. There are no appreciable differences in pharmacokinetic parameters when galantamine extended-release capsules are given with food compared to when they are given in the fasted state. Specific Populations Elderly Data from clinical trials in patients with Alzheimer’s disease indicate that galantamine concentrations are 30 to 40% higher in those patients than in healthy young subjects. Gender and Race A population pharmacokinetic analysis (on 539 men and 550 women) indicates that galantamine clearance is about 20% lower in women than in men (which is explained by a lower body weight in women) and that race (n=1029 White, 24 Black, 13 Asian and 23 other) did not affect the clearance of galantamine. Hepatic Impairment Following a single 4 mg dose of galantamine tablets, the pharmacokinetics of galantamine in subjects with mild hepatic impairment (n=8; Child-Pugh score of 5 to 6) were similar to the pharmacokinetics of galantamine in healthy subjects. In patients with moderate hepatic impairment (n=8; Child Pugh score of 7 to 9), galantamine clearance was decreased by about 25% compared to galantamine clearance in normal volunteers. Exposure to galantamine would be expected to increase further with increasing degree of hepatic impairment [see Dosage and Administration (2.2) and Use in Specific Populations (8.6) ] . Renal Impairment Following a single 8 mg dose of galantamine tablets, AUC increased by 37% and 67% in patients with moderate and severe renal impairment, respectively, compared with normal volunteers [see Dosage and Administration (2.3) and Use in Specific Populations (8.7) ] . Drug-Drug Interactions Multiple metabolic pathways and renal excretion are involved in the elimination of galantamine so no single pathway appears predominant. Based on in vitro studies, CYP2D6 and CYP3A4 were the major enzymes involved in the metabolism of galantamine. CYP2D6 was involved in the formation of O-desmethyl-galantamine, whereas CYP3A4 mediated the formation of galantamine-N-oxide. Galantamine is also glucuronidated and excreted unchanged in urine. Effect of Other Drugs on Galantamine CYP3A4 Inhibitors : Ketoconazole Ketoconazole, a strong inhibitor of CYP3A4 and an inhibitor of CYP2D6, when administered at a dose of 200 mg two times a day for 4 days, increased the AUC of galantamine by 30%. Erythromycin Erythromycin, a moderate inhibitor of CYP3A4, when administered at a dose of 500 mg four times a day for 4 days, affected the AUC of galantamine minimally (10% increase). CYP2D6 Inhibitors: A population pharmacokinetics analysis on a database of 852 patients with Alzheimer’s disease showed that the clearance of galantamine was reduced about 25 to 33% by the concurrent administration of amitriptyline (n=17), fluoxetine (n=48), fluvoxamine (n=14), and quinidine (n=7), all of which are known inhibitors of CYP2D6. Paroxetine Paroxetine, a strong inhibitor of CYP2D6, when administered at a dose of 20 mg/day for 16 days, increased the oral bioavailability of galantamine by about 40%. H2 Antagonists Galantamine was administered as a single dose of 4 mg on Day 2 of a 3-day treatment with either cimetidine (800 mg daily) or ranitidine (300 mg daily). Cimetidine increased the bioavailability of galantamine by approximately 16%. Ranitidine had no effect on the pharmacokinetics of galantamine. Memantine Memantine, an N-methyl-D-aspartate receptor antagonist, when administered at a dose of 10 mg two times a day, had no effect on the pharmacokinetics of galantamine (16 mg/day) at steady state. Effect of Galantamine on Other Drugs In Vitro Studies In vitro studies show that galantamine did not inhibit the metabolic pathways catalyzed by CYP1A2, CYP2A6, CYP3A4, CYP4A, CYP2C, CYP2D6 or CYP2E1. This indicates that the inhibitory potential of galantamine towards the major forms of cytochrome P450 is very low. In Vivo Studies Warfarin Multiple doses of galantamine at 24 mg/day had no effect on the pharmacokinetics of R- and S-warfarin (administered in a single dose of 25 mg) or on the increased prothrombin time induced by warfarin. The protein binding of warfarin was unaffected by galantamine. Digoxin Multiple doses of galantamine at 24 mg/day had no effect on the steady-state pharmacokinetics of digoxin (at a dose of 0.375 mg once daily) when those two drugs were co-administered. In that study, however, one healthy subject was hospitalized on account of 2nd and 3rd degree heart block and bradycardia.