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Introduction

  1. Pharmacology. Penicillamine is a derivative of penicillin that has no antimicrobial activity but effectively chelates some heavy metals, such as lead, mercury, and copper. Because of its poor safety profile, it has largely been replaced by succimer (DMSA) and unithiol (DMPS). Penicillamine is well absorbed orally, and the penicillamine-metal complex is eliminated in the urine. No parenteral form is available. Note: Although the chemical derivative N-acetylpenicillamine may demonstrate better CNS and peripheral nerve penetration, it is not currently available in the United States.
  2. Indications
    1. Heavy metal poisoning caused by lead or mercury.
    2. Copper poisoning and treatment of Wilson disease to remove copper deposits in tissues.
    3. Penicillamine has also been used for arsenic, bismuth, and nickel poisoning, but it is not the agent of choice owing to its toxicity.
  3. Contraindications
    1. Penicillin allergy is a contraindication (penicillamine products may be contaminated with penicillin).
    2. Renal insufficiency is a relative contraindication because the complex is eliminated only through the urine.
    3. Concomitant administration with other hematopoiesis-depressant drugs (eg, gold salts, immunosuppressants, antimalarial agents, and phenylbutazone) is not recommended.
    4. Cadmium poisoning. Penicillamine may increase renal levels of cadmium and the potential for nephrotoxicity.
  4. Adverse effects. Black box warning: Due to high incidence of and fatalities associated with penicillamine-induced adverse effects, therapy must be closely monitored and patients warned to promptly report symptoms suggesting toxicity.
    1. Hypersensitivity reactions: rash, pruritus, drug fever, hematuria, antinuclear antibodies, Goodpasture's syndrome, exfoliative dermatitis, thyroiditis, and proteinuria.
    2. Bone marrow suppression and blood dyscrasias: Leukopenia, thrombocytopenia, hemolytic anemia, sideroblastic anemia, aplastic anemia, and agranulocytosis.
    3. Hepatitis and pancreatitis.
    4. Neurologic: Tinnitus, optic neuritis, peripheral motor and sensory neuropathy, and myasthenia gravis.
    5. Gastrointestinal: Anorexia, nausea, vomiting, epigastric pain, and impairment of taste.
    6. Pulmonary: Obliterative bronchiolitis, bronchial asthma, alveolitis, pulmonary hemorrhage, interstitial pneumonitis, and pulmonary fibrosis.
    7. The requirement for pyridoxine is increased, and the patient may require daily supplementation (pyridoxine).
    8. Use in pregnancy. FDA Category D (Introduction). Birth defects have been associated with use during pregnancy.
  5. Drug or laboratory interactions
    1. Penicillamine may potentiate the hematopoiesis-depressant effects of drugs such as gold salts, immunosuppressants, antimalarial agents, and phenylbutazone.
    2. Several drugs (eg, antacids and ferrous sulfate) and food can reduce GI absorption of penicillamine substantially.
    3. Penicillamine may produce a false-positive test for ketones in the urine.
  6. Dosage and method of administration
    1. Penicillamine should be taken on an empty stomach at least 1 hour before or at least 2 hours after meals and at bedtime. For patients with difficulty swallowing, penicillamine may be extemporaneously prepared as a suspension or be administered in 15-30 mL of chilled pureed fruit or fruit juice within 5 minutes of administration.
    2. The usual dose is 1-1.5 g/d (children: 20-30 mg/kg/d), administered in three or four divided doses. Initiating treatment at 25% of this dose and gradually increasing to the full dose over 2-3 weeks may minimize adverse reactions. Therefore, use a starting dose of 250 mg/d (children: 10 mg/kg/d), then increase to 500 mg/d (15 mg/kg) during week 2 and to the full dose by week 3. The maximum adult daily dose is 2 g (up to 4 g for treatment of cystinuria). In children with mild to moderate lead poisoning, a lower dose of 15 mg/kg/d has been shown to lower blood levels while minimizing adverse effects.
    3. Weekly measurement of urinary and blood concentrations of the intoxicating metal is indicated to assess the need for continued therapy. Treatment for as long as 3 months has been tolerated.