Metyrosine

Metyrosine
Adult Indications & Dosage
Pediatric Indications & Dosage
Contraindications
Warnings & Precautions
Adverse Reactions
Drug Interactions
Use in Specific Populations
Administration & Monitoring
Overdosage
Pharmacology
Clinical Studies
How Supplied
Images
Patient Counseling Information
Precautions with Alcohol
Brand Names
Look-Alike Names

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Adeel Jamil, M.D. [2]

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Overview

Metyrosine is an antihypertensive and tyrosine hydroxylase inhibitor that is FDA approved for the treatment of pheochromocytoma. Common adverse reactions include diarrhea, sedation and fatigue.

Adult Indications and Dosage

FDA-Labeled Indications and Dosage (Adult)

• Metyrosine is indicated in the treatment of patients with pheochromocytoma for:

• Preoperative preparation of patients for surgery
• Management of patients when surgery is contraindicated
• Chronic treatment of patients with malignant pheochromocytoma.

• Metyrosine is not recommended for the control of essential hypertension.

Dosing Information

• The recommended initial dosage of Metyrosine for adults and children 12 years of age and older is 250 mg orally four times daily. This may be increased by 250 mg to 500 mg every day to a maximum of 4.0 g/day in divided doses. When used for preoperative preparation, the optimally effective dosage of Metyrosine should be given for at least five to seven days.

• Optimally effective dosages of Metyrosine usually are between 2.0 and 3.0 g/day, and the dose should be titrated by monitoring clinical symptoms and catecholamine excretion. In patients who are hypertensive, dosage should be titrated to achieve normalization of blood pressure and control of clinical symptoms. In patients who are usually normotensive, dosage should be titrated to the amount that will reduce urinary metanephrines and/or vanillylmandelic acid by 50 percent or more.

• If patients are not adequately controlled by the use of Metyrosine, an alpha-adrenergic blocking agent (phenoxybenzamine) should be added.

• Use of Metyrosine in children under 12 years of age has been limited and a dosage schedule for this age group cannot be given.

Off-Label Use and Dosage (Adult)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Metyrosine in adult patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Metyrosine in adult patients.

Pediatric Indications and Dosage

FDA-Labeled Indications and Dosage (Pediatric)

There is limited information regarding Metyrosine FDA-Labeled Indications and Dosage (Pediatric) in the drug label.

Off-Label Use and Dosage (Pediatric)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Metyrosine in pediatric patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Metyrosine in pediatric patients.

Contraindications

• Metyrosine is contraindicated in persons known to be hypersensitive to this compound.

Warnings

Maintain Fluid Volume During and After Surgery

• When Metyrosine is used preoperatively, alone or especially in combination with alpha-adrenergic blocking drugs, adequate intravascular volume must be maintained intraoperatively (especially after tumor removal) and postoperatively to avoid hypotension and decreased perfusion of vital organs resulting from vasodilatation and expanded volume capacity. Following tumor removal, large volumes of plasma may be needed to maintain blood pressure and central venous pressure within the normal range.

• In addition, life-threatening arrhythmias may occur during anesthesia and surgery, and may require treatment with a beta-blocker or lidocaine. During surgery, patients should have continuous monitoring of blood pressure and electrocardiogram.

Intraoperative Effects

• While the preoperative use of Metyrosine in patients with pheochromocytoma is thought to decrease intraoperative problems with blood pressure control, Metyrosine does not eliminate the danger of hypertensive crises or arrhythmias during manipulation of the tumor, and the alpha-adrenergic blocking drug, phentolamine, may be needed.

Interaction with Alcohol

• Metyrosine may add to the sedative effects of alcohol and other CNS depressants, e.g., hypnotics, sedatives, and tranquilizers.

PRECAUTIONS

General

Metyrosine Crystalluria

• Crystalluria and urolithiasis have been found in dogs treated with Metyrosine at doses similar to those used in humans, and crystalluria has also been observed in a few patients. To minimize the risk of crystalluria, patients should be urged to maintain water intake sufficient to achieve a daily urine volume of 2000 mL or more, particularly when doses greater than 2 g per day are given. Routine examination of the urine should be carried out. Metyrosine will crystallize as needles or rods. If metyrosine crystalluria occurs, fluid intake should be increased further. If crystalluria persists, the dosage should be reduced or the drug discontinued.

Relatively Little Data Regarding Long-term Use

• The total human experience with the drug is quite limited and few patients have been studied long-term. Chronic animal studies have not been carried out. Therefore, suitable laboratory tests should be carried out periodically in patients requiring prolonged use of Metyrosine and caution should be observed in patients with impaired hepatic or renal function.

Adverse Reactions

Clinical Trials Experience

Sedation:

• The most common adverse reaction to Metyrosine is moderate to severe sedation, which has been observed in almost all patients. It occurs at both low and high dosages. Sedative effects begin within the first 24 hours of therapy, are maximal after two to three days, and tend to wane during the next few days. Sedation usually is not obvious after one week unless the dosage is increased, but at dosages greater than 2000 mg/day some degree of sedation or fatigue may persist.

• In most patients who experience sedation, temporary changes in sleep pattern occur following withdrawal of the drug. Changes consist of insomnia that may last for two or three days and feelings of increased alertness and ambition. Even patients who do not experience sedation while on Metyrosine may report symptoms of psychic stimulation when the drug is discontinued.

Extrapyramidal Signs:

• Extrapyramidal signs such as drooling, speech difficulty, and tremor have been reported in approximately 10 percent of patients. These occasionally have been accompanied by trismus and frank parkinsonism.

Anxiety and Psychic Disturbances:

• Anxiety and psychic disturbances such as depression, hallucinations, disorientation, and confusion may occur. These effects seem to be dose-dependent and may disappear with reduction of dosage.

Diarrhea

• Diarrhea occurs in about 10 percent of patients and may be severe. Anti-diarrheal agents may be required if continuation of Metyrosine is necessary.

Miscellaneous

• Infrequently, slight swelling of the breast, galactorrhea, nasal stuffiness, decreased salivation, dry mouth, headache, nausea, vomiting, abdominal pain, and impotence or failure of ejaculation may occur. Crystalluria and transient dysuria and hematuria have been observed in a few patients. Hematologic disorders (including eosinophilia, anemia, thrombocytopenia, and thrombocytosis), increased SGOT levels, peripheral edema, and hypersensitivity reactions such as urticaria and pharyngeal edema have been reported rarely.

Postmarketing Experience

There is limited information regarding Metyrosine Postmarketing Experience in the drug label.

Drug Interactions

• Caution should be observed in administering Metyrosine to patients receiving phenothiazines or haloperidol because the extrapyramidal effects of these drugs can be expected to be potentiated by inhibition of catecholamine synthesis.

• Concurrent use of Metyrosine with alcohol or other CNS depressants can increase their sedative effects.

Laboratory Test Interference

• Spurious increases in urinary catecholamines may be observed in patients receiving Metyrosine due to the presence of metabolites of the drug.

Use in Specific Populations

Pregnancy

Pregnancy Category (FDA): C

• Animal reproduction studies have not been conducted with Metyrosine. It is also not known whether Metyrosine can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Metyrosine should be given to a pregnant woman only if clearly needed.

Pregnancy Category (AUS): There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Metyrosine in women who are pregnant.

Labor and Delivery

There is no FDA guidance on use of Metyrosine during labor and delivery.

Nursing Mothers

• It is not known whether Metyrosine is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Metyrosine is administered to a nursing woman.

Pediatric Use

• Safety and effectiveness in pediatric patients below the age of 12 years have not been established.

Geriatic Use

• Clinical studies of Metyrosine did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Gender

There is no FDA guidance on the use of Metyrosine with respect to specific gender populations.

Race

There is no FDA guidance on the use of Metyrosine with respect to specific racial populations.

Renal Impairment

There is no FDA guidance on the use of Metyrosine in patients with renal impairment.

Hepatic Impairment

There is no FDA guidance on the use of Metyrosine in patients with hepatic impairment.

Females of Reproductive Potential and Males

There is no FDA guidance on the use of Metyrosine in women of reproductive potentials and males.

Immunocompromised Patients

There is no FDA guidance one the use of Metyrosine in patients who are immunocompromised.

Administration and Monitoring

Administration

There is limited information regarding Metyrosine Administration in the drug label.

Monitoring

There is limited information regarding Metyrosine Monitoring in the drug label.

IV Compatibility

There is limited information regarding the compatibility of Metyrosine and IV administrations.

Overdosage

• Signs of metyrosine overdosage include those central nervous system effects observed in some patients even at low dosages.

• At doses exceeding 2000 mg/day, some degree of sedation or feeling of fatigue may persist. Doses of 2000-4000 mg/day can result in anxiety or agitated depression, neuromuscular effects (including fine tremor of the hands, gross tremor of the trunk, tightening of the jaw with trismus), diarrhea, and decreased salivation with dry mouth.

• Reduction of drug dose or cessation of treatment results in the disappearance of these symptoms.

• The acute toxicity of metyrosine was 442 mg/kg and 752 mg/kg in the female mouse and rat respectively.

Pharmacology

Mechanism of Action

• Metyrosine inhibits tyrosine hydroxylase, which catalyzes the first transformation in catecholamine biosynthesis, i.e., the conversion of tyrosine to dihydroxyphenylalanine (DOPA). Because the first step is also the rate-limiting step, blockade of tyrosine hydroxylase activity results in decreased endogenous levels of catecholamines, usually measured as decreased urinary excretion of catecholamines and their metabolites.

Structure

Metyrosine1 (Metyrosine) is (–)-α-methyl-L-tyrosine or (α-MPT). It has the following structural formula:

This image is provided by the National Library of Medicine.

• Metyrosine is a white, crystalline compound of molecular weight 195. It is very slightly soluble in water, acetone, and methanol, and insoluble in chloroform and benzene. It is soluble in acidic aqueous solutions. It is also soluble in alkaline aqueous solutions, but is subject to oxidative degradation under these conditions.

• Metyrosine is supplied as capsules, for oral administration. Each capsule contains 250 mg metyrosine. Inactive ingredients are colloidal silicon dioxide, gelatin, hydroxypropyl cellulose, magnesium stearate, titanium dioxide, and FD&C Blue 2.

Pharmacodynamics

There is limited information regarding Metyrosine Pharmacodynamics in the drug label.

Pharmacokinetics

• In patients with pheochromocytoma, who produce excessive amounts of norepinephrine and epinephrine, administration of one to four grams of Metyrosine per day has reduced catecholamine biosynthesis from about 35 to 80 percent as measured by the total excretion of catecholamines and their metabolites (metanephrine and vanillylmandelic acid). The maximum biochemical effect usually occurs within two to three days, and the urinary concentration of catecholamines and their metabolites usually returns to pretreatment levels within three to four days after Metyrosine is discontinued. In some patients the total excretion of catecholamines and catecholamine metabolites may be lowered to normal or near normal levels (less than 10 mg/24 hours). In most patients the duration of treatment has been two to eight weeks, but several patients have received Metyrosine for periods of one to 10 years. Most patients with pheochromocytoma treated with Metyrosine experience decreased frequency and severity of hypertensive attacks with their associated headache, nausea, sweating, and tachycardia. In patients who respond, blood pressure decreases progressively during the first two days of therapy with Metyrosine; after withdrawal, blood pressure usually increases gradually to pretreatment values within two to three days.

• Metyrosine is well absorbed from the gastrointestinal tract. From 53 to 88 percent (mean 69 percent) was recovered in the urine as unchanged drug following maintenance oral doses of 600 to 4000 mg/24 hours in patients with pheochromocytoma or essential hypertension. Less than 1% of the dose was recovered as catechol metabolites. These metabolites are probably not present in sufficient amounts to contribute to the biochemical effects of metyrosine. The quantities excreted, however, are sufficient to interfere with accurate determination of urinary catecholamines determined by routine techniques.

• Plasma half-life of metyrosine determined over an 8-hour period after single oral doses was 3-3.7 hours in three patients.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment of Fertility

• Long-term carcinogenic studies in animals and studies on mutagenesis and impairment of fertility have not been performed with metyrosine.

Clinical Studies

There is limited information regarding Metyrosine Clinical Studies in the drug label.

How Supplied

Capsules Metyrosine, 250 mg, are opaque, two-toned blue capsules coded Aton 305 on one side and Metyrosine on the other. They are supplied as follows:

NDC 25010-305-15 bottles of 100.

Storage

There is limited information regarding Metyrosine Storage in the drug label.

Images

Drug Images

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Package and Label Display Panel

PRINCIPAL DISPLAY PANEL - 250 MG CAPSULE LABEL

Metyrosine® 250 mg (Metyrosine)

NDC 25010-305-15

Distributed by: ATON PHARMA, INC. LAWRENCEVILLE, NJ 08648, USA

Rx only

USUAL ADULT DOSAGE: See accompanying circular.

This is a bulk package and not intended for dispensing.

Package not child resistant.

Dispense in a well-closed container.

100 Capsules

This image is provided by the National Library of Medicine.

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Patient Counseling Information

• When receiving Metyrosine, patients should be warned about engaging in activities requiring mental alertness and motor coordination, such as driving a motor vehicle or operating machinery. Metyrosine may have additive sedative effects with alcohol and other CNS depressants, e.g., hypnotics, sedatives, and tranquilizers.

• Patients should be advised to maintain a liberal fluid intake.

Precautions with Alcohol

Alcohol-Metyrosine interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.

Brand Names

• Demser®

Look-Alike Drug Names

There is limited information regarding Metyrosine Look-Alike Drug Names in the drug label.

Drug Shortage Status

Price

References

The contents of this FDA label are provided by the National Library of Medicine.