Penicillamine

PENICILLAMINE — penicillamine capsule
Navinta LLC

Physicians planning to use penicillamine should thoroughly familiarize themselves with its toxicity, special dosage considerations, and therapeutic benefits. Penicillamine should never be used casually. Each patient should remain constantly under the close supervision of the physician. Patients should be warned to report promptly any symptoms suggesting toxicity.

DESCRIPTION

Penicillamine is a chelating agent used in the treatment of Wilson’s disease. It is also used to reduce cystine excretion in cystinuria and to treat patients with severe, active rheumatoid arthritis unresponsive to conventional therapy (see INDICATIONS). It is 3-mercapto-D-valine. It is a white, or practically white, crystalline powder, freely soluble in water, slightly soluble alcohol, insoluble in chloroform and in ether. Although its configuration is D, it is levorotatory as usually measured:

[α] 25°= -62.5° ± 2° (c = 1, 1N NaOH),

D

calculated on a dried basis.

The empirical formula is C5 H11 NO2 S, giving it a molecular weight of 149.21. The structural formula is:

Image

It reacts readily with formaldehyde or acetone to form a thiazolidine-carboxylic acid. Penicillamine Capsules, USP for oral administration contain 250 mg of penicillamine. Each capsule contains the following inactive ingredients: lactose monohydrate, magnesium stearate, D&C yellow no. 10, gelatin and titanium dioxide. The imprinting ink contains shellac, dehydrated alcohol, isopropyl alcohol, butyl alcohol, propylene glycol, strong ammonia solution, black iron oxide, potassium hydroxide and purified water.

CLINICAL PHARMACOLOGY

Penicillamine is a chelating agent recommended for the removal of excess copper in patients with Wilson’s disease. From in vitro studies which indicate that one atom of copper combines with two molecules of penicillamine, it would appear that 1 g of penicillamine should be followed by the excretion of about 200 mg of copper; however, the actual amount excreted is about 1% of this.

Penicillamine also reduces excess cystine excretion in cystinuria. This is done, at least in part, by disulfide interchange between penicillamine and cystine, resulting in formation of penicillamine-cysteine disulfide, a substance that is much more soluble than cystine and is excreted readily.

Penicillamine interferes with the formation of cross-links between tropocollagen molecules and cleaves them when newly formed.

The mechanism of action of penicillamine in rheumatoid arthritis is unknown although it appears to suppress disease activity. Unlike cytotoxic immunosuppressants, penicillamine markedly lowers IgM rheumatoid factor but produces no significant depression in absolute levels of serum immunoglobulins. Also unlike cytotoxic immunosuppressants which act on both, penicillamine in vitro depresses T-cell activity but not B-cell activity.

In vitro , penicillamine dissociates macroglobulins (rheumatoid factor) although the relationship of the activity to its effect in rheumatoid arthritis is not known.

In rheumatoid arthritis, the onset of therapeutic response to penicillamine may not be seen for 2 or 3 months. In those patients who respond, however, the first evidence of suppression of symptoms such as pain, tenderness, and swelling is generally apparent within 3 months. The optimum duration of therapy has not been determined. If remissions occur, they may last from months to years, but usually require continued treatment (see DOSAGE AND ADMINISTRATION).

In all patients receiving penicillamine, it is important that penicillamine capsules be given on an empty stomach, at least 1 hour before meals or 2 hours after meals, and at least 1 hour apart from any other drug, food, milk, antacid, zinc, or iron-containing preparation. This permits maximum absorption and reduces the likelihood of inactivation by metal binding in the gastrointestinal tract.

Pharmacokinetics

Penicillamine is absorbed rapidly but incompletely (40-70%) from the gastrointestinal tract, with wide inter-individual variations. Food, antacids, and iron reduce absorption of the drug. The peak plasma concentration of penicillamine occurs 1 to 3 hours after ingestion; it is approximately 1 to 2 mg/L after an oral dose of 250 mg. The drug appears in the plasma as free penicillamine, penicillamine disulfide, and penicillamine-cysteine disulfide. When prolonged treatment is stopped, there is a slow elimination phase lasting 4 to 6 days.

More than 80% of plasma penicillamine is bound to proteins, especially albumin and ceruloplasmin. The drug also binds to erythrocytes and macrophages. A small fraction of the dose is metabolized in the liver to S-methyl-D-penicillamine. Excretion is mainly renal, mainly as disulfides.

INDICATIONS

Penicillamine capsules are indicated in the treatment of Wilson’s disease, cystinuria, and in patients with severe, active rheumatoid arthritis who have failed to respond to an adequate trial of conventional therapy. Available evidence suggests that penicillamine capsules are not of value in ankylosing spondylitis.

Wilson’s Disease

Wilson’s disease (hepatolenticular degeneration) occurs in individuals who have inherited an autosomal-recessive defect that leads to an accumulation of copper far in excess of metabolic requirements. The excess copper is deposited in several organs and tissues, and eventually produces pathological effects primarily in the liver, where damage progresses to postnecrotic cirrhosis, and in the brain, where degeneration is widespread. Copper is also deposited as characteristic, asymptomatic, golden-brown Kayser-Fleischer rings in the corneas of all patients with cerebral symptomatology and some patients who are either asymptomatic or manifest only hepatic symptomatology.

Two types of patients require treatment for Wilson’s disease: (1) the symptomatic, and (2) the asymptomatic in whom it can be assumed the disease will develop in the future if the patient is not treated.

The diagnosis, if suspected on the basis of family or individual history or physical examination, can be confirmed if the plasma copper-protein ceruloplasmin** is less than 20 mg/dL and either a quantitative determination in a liver biopsy specimen shows an abnormally high concentration of copper (greater than 250 mcg/g dry weight) or Kayser-Fleischer rings are present.

Treatment has two objectives:

(1) to minimize dietary intake of copper;

(2) to promote excretion and complex formation (i.e., detoxification) of excess tissue copper.

The first objective is attained by a daily diet that contains no more than 1 or 2 mg of copper. Such a diet should exclude, most importantly, chocolate, nuts, shellfish, mushrooms, liver, molasses, broccoli, and cereals and dietary supplements enriched with copper, and be composed to as great an extent as possible of foods with a low copper content. Distilled or demineralized water should be used if the patient’s drinking water contains more than 0.1 mg/L of copper.

For the second objective, a copper chelating agent is used.

In symptomatic patients, this treatment usually produces marked neurologic improvement, fading of Kayser-Fleischer rings, and gradual amelioration of hepatic dysfunction and psychic disturbances.

Clinical experience to date suggests that life is prolonged with the above regimen.

Noticeable improvement may not occur for 1 to 3 months. Occasionally, neurologic symptoms become worse during initiation of therapy with penicillamine capsules. Despite this, the drug should not be withdrawn. Temporary interruption carries an increased risk of developing a sensitivity reaction upon resumption of therapy, although it may result in clinical improvement of neurological symptoms (see WARNINGS). If the neurological symptoms and signs continue to worsen for a month after the initiation of penicillamine capsules therapy, several short courses of treatment with 2,3-dimercaprol (BAL) while continuing penicillamine capsules may be considered.

Treatment of asymptomatic patients has been carried out for over 30 years. Symptoms and signs of the disease appear to be prevented indefinitely if daily treatment with penicillamine capsules are continued.

Cystinuria

Cystinuria is characterized by excessive urinary excretion of the dibasic amino acids, arginine, lysine, ornithine, and cystine, and the mixed disulfide of cysteine and homocysteine. The metabolic defect that leads to cystinuria is inherited as an autosomal-recessive trait. Metabolism of the affected amino acids is influenced by at least two abnormal factors: (1) defective gastrointestinal absorption and (2) renal tubular dysfunction.

Arginine, lysine, ornithine, and cysteine are soluble substances, readily excreted. There is no apparent pathology connected with their excretion in excessive quantities.

Cystine, however, is so slightly soluble at the usual range of urinary pH that it is not excreted readily, and so crystallizes and forms stones in the urinary tract. Stone formation is the only known pathology in cystinuria.

Normal daily output of cystine is 40 to 80 mg. In cystinuria, output is greatly increased and may exceed 1 g/day. At 500 to 600 mg/day, stone formation is almost certain. When it is more than 300 mg/day, treatment is indicated.

Conventional treatment is directed at keeping urinary cystine diluted enough to prevent stone formation, keeping the urine alkaline enough to dissolve as much cystine as possible, and minimizing cystine production by a diet low in methionine (the major dietary precursor of cystine). Patients must drink enough fluid to keep urine-specific gravity below 1.010, take enough alkali to keep urinary pH at 7.5 to 8, and maintain a diet low in methionine. This diet is not recommended in growing children and probably is contraindicated in pregnancy because of its low protein content (see PRECAUTIONS).

When these measures are inadequate to control recurrent stone formation, penicillamine capsules may be used as additional therapy, and when patients refuse to adhere to conventional treatment, penicillamine capsules may be a useful substitute. It is capable of keeping cystine excretion to near normal values, thereby hindering stone formation and the serious consequences of pyelonephritis and impaired renal function that develop in some patients. Bartter and colleagues depict the process by which penicillamine interacts with cystine to form penicillamine-cysteine mixed disulfide as:

CSSC + PS’ Image CS’ + CSSP

PSSP + CS’ Image PS’ + CSSP

CSSC + PSSP’ Image 2CSSP

CSSC = cystine

CS’ = deprotonated cysteine

PSSP = penicillamine disulfide

PS’ = deprotonated penicillamine sulfhydryl

CSSP = penicillamine-cysteine mixed disulfide

In this process, it is assumed that the deprotonated form of penicillamine, PS’, is the active factor in bringing about the disulfide interchange.

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