Penicillamine

PENICILLAMINE- penicillamine capsule
Actavis Pharma, Inc.

DESCRIPTION

Penicillamine, USP 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 in alcohol, and insoluble in ether, acetone, benzene, and carbon tetrachloride. 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 structural formula is:

C₅ H₁₁ NO₂ S M.W. 149.21

It reacts readily with formaldehyde or acetone to form a thiazolidine-carboxylic acid.

Penicillamine capsules USP for oral administration contain 250 mg of penicillamine, USP. Each capsule contains the following inactive ingredients: magnesium stearate and mannitol. Each capsule shell contains: gelatin, sodium lauryl sulfate and titanium dioxide. The imprinting ink contains: black iron oxide, potassium hydroxide, propylene glycol and shellac.

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 one gram of penicillamine should be followed by the excretion of about 200 milligrams of copper; however, the actual amount excreted is about one percent 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 capsules may not be seen for two or three months. In those patients who respond, however, the first evidence of suppression of symptoms such as pain, tenderness, and swelling is generally apparent within three 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 one hour before meals or two hours after meals, and at least one 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% to 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 cysteine-penicillamine 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 1 is <20 mg/dL and either a quantitative determination in a liver biopsy specimen shows an abnormally high concentration of copper (>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 one or two milligrams 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 of copper per liter.

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 one to three 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 thirty years. Symptoms and signs of the disease appear to be prevented indefinitely if daily treatment with penicillamine capsules are continued.

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1

For quantitative test for serum ceruloplasmin see: Morell, A.G.; Windsor, J.; Sternlieb, I. ; Scheinberg, I.H.: Measurement of the concentration of ceruloplasmin in serum by determination of its oxidase activity, in “Laboratory Diagnosis of Liver Disease”, F.W. Sunderman; F.W. Sunderman, Jr. (eds.), St. Louis, Warren H. Green, Inc., 1968, pp. 193-195.