INDICATIONS
Penicillamine tablets 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 tablets are not of value in ankylosing spondylitis.
Wilsons Disease
Wilson's disease (hepatolenticular degeneration) results from the interaction of an inherited defect and an abnormality in copper metabolism. The metabolic defect, which is the consequence of the autosomal inheritance of one abnormal gene from each parent, manifests itself in a greater positive copper balance than normal. As a result, copper is deposited in several organs and appears eventually to produce pathologic effects most prominently seen in the brain, where degeneration is widespread; in the liver, where fatty infiltration, inflammation, and hepatocellular damage progress to postnecrotic cirrhosis; in the kidney, where tubular and glomerular dysfunction results; and in the eye, where characteristic corneal copper deposits are known as Kayser-Fleischer rings.
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.
Diagnosis, suspected on the basis of family or individual history, physical examination, or a low serum concentration of ceruloplasmin*, is confirmed by the demonstration of Kayser-Fleischer rings or, particularly in the asymptomatic patient, by the quantitative demonstration in a liver biopsy specimen of a concentration of copper in excess of 250 mcg/g dry weight.
Treatment has two objectives:
(1) to minimize dietary intake and absorption of copper.
(2)
to promote excretion of copper deposited in tissues.
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 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 tablets. Despite this, the drug should not be discontinued permanently. Although temporary interruption may result in clinical improvement of the neurological symptoms, it carries an increased risk of developing a sensitivity reaction upon resumption of therapy (See WARNINGS).
*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 to 195.
Treatment of asymptomatic patients has been carried out for over ten years. Symptoms and signs of the disease appear to be prevented indefinitely if daily treatment with penicillamine tablets can be 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 tablets may be used as additional therapy. When patients refuse to adhere to conventional treatment, Penicillamine tablets 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= Cystine
CS'= deprotonated Cysteine
PSSP=Penicillamine
PS'=deprotonated Penicillamine Sulfhydryl
CSSP= Penicillamine-Cysteine Mixed Disulphide
In this process, it is assumed that the deprotonated form of penicillamine, PS', is the active factor in bringing about the disulfide interchange.
Rheumatoid Arthritis
Because penicillamine tablets, can cause severe adverse reactions, its use in rheumatoid arthritis should be restricted to patients who have severe, active disease and who have failed to respond to an adequate trial of conventional therapy. Even then, benefit-to-risk ratio should be carefully considered. Other measures, such as rest, physiotherapy, salicylates, and corticosteroids should be used, when indicated, in conjunction with penicillamine tablets (see PRECAUTIONS).
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