Penicillamine

Why this drug is interesting

Penicillamine occupies an odd position. It is the only oral heavy-metal chelator with a UK marketing authorisation — dimercaprol, succimer (DMSA), DMPS, Prussian blue and sodium calcium edetate return no product from an emc search (checked 6 September 2026).⁷ It is licensed specifically for "Lead poisoning in adults and children (0 to 18 years)".¹ And yet it is not the drug a UK poisons unit usually reaches for.

That gap between what is licensed and what is used is the whole point of this page. The licence is genuine and the doses are in the label; the reason practice diverges is not regulatory but pharmacological and practical, and it is worth understanding before an on-call decision is made on the basis that penicillamine is "the licensed one".

Pharmacology

Mechanism

Penicillamine is a thiol. Its sulfhydryl group binds divalent metal cations — copper, lead, mercury, zinc — forming complexes excreted in the urine. That mechanism is why the same molecule treats Wilson's disease (copper), cystinuria (by forming a soluble cysteine–penicillamine disulfide) and lead poisoning: three unrelated conditions, one chemistry.

In rheumatoid arthritis, which is its fourth and oldest indication, the mechanism is immunological rather than chelating and is not well characterised. This matters for reading the label: much of the safety section — the marrow suppression, the late dermopathy, the drug-induced lupus and myasthenia — comes from decades of chronic, high-dose use in rheumatology, not from short courses in poisoning.

Where it does and does not act

Chelators differ in the compartment they clear. In the best available comparison of the two agents UK units actually use, sodium calcium edetate mobilises lead principally from bone, while DMSA appears to act principally in the kidney, and there is no evidence that either crosses the blood–brain barrier to any major extent.³ Penicillamine has not been characterised to that standard against either. Do not assume an oral chelator clears the compartment that matters in encephalopathy.

Dosing in lead poisoning

These are the licensed UK doses, quoted from section 4.2(d) of the SmPC. They are identical in the 125 mg and 250 mg products — both labels were checked and the lead sections are word-for-word the same.¹²

Adults

"1000 mg to 1500 mg daily, in divided doses until urinary lead is stabilised at less than 0.5 mg per day."¹

Elderly

"20 mg/kg/day in divided doses until lead levels in the urine is stabilised at less than 0.5 mg per day."¹

Children 0–18

"Penicillamine should only be used in cases where blood lead levels <45 mcg/dL. A total of 15 – 20 mg/kg/day in 2 – 3 doses should be used."¹

How it is taken

Oral only. The label is specific: penicillamine "should be taken on an empty stomach at least half an hour before meals in adults and one hour before meals in paediatric patients, or on retiring".¹ It also notes that the smallest tablet is 125 mg, which "might not be suitable for very young children" — a real practical constraint in the age group most likely to have eaten lead paint.

Safety

Before the first dose

The label opens its warnings with a baseline requirement: "Full blood and platelet counts should be performed and renal function should be assessed prior to treatment with penicillamine."¹ This is not routine caution — it sets the reference point for the monitoring that follows, and two of the contraindications are conditions those tests detect.

Contraindications

• Moderate or severe renal impairment.¹ The chelate is renally excreted and the drug is nephrotoxic; this is the contraindication most likely to be relevant in a poisoned patient.
• Lupus erythematosus.¹ Penicillamine can itself induce a drug-induced lupus.
• Agranulocytosis, aplastic anaemia or severe thrombocytopenia due to penicillamine — that is, a previous haematological catastrophe on this drug.¹
• Hypersensitivity to penicillamine or excipients. The tablets also contain 96 mg lactose (250 mg strength), relevant in galactose intolerance or lactase deficiency.¹

Marrow suppression — the label gives numbers

Monitoring schedule

Urinalysis for haematuria and proteinuria weekly at first, after each dose increase, then monthly; increasing or persistent proteinuria may require withdrawal. Full blood counts weekly or fortnightly for the first eight weeks, in the week after any dose increase, then monthly.¹ Haematuria in the absence of stones or another known cause means stop immediately.¹

Interactions and cautions

NSAIDs and other nephrotoxics

May increase the risk of renal damage.¹

Antimalarials

"Penicillamine should not be used in patients who are receiving concurrently antimalarial drugs such as hydroxychloroquine phosphate, chloroquine" — similar haematological and renal toxicity, potentially synergistic.¹

Gold

Concomitant treatment should be avoided, and penicillamine used with caution in anyone who has previously reacted to gold.¹

Pyridoxine

Penicillamine increases the requirement for vitamin B6; daily pyridoxine may be given on long-term therapy, especially on a restricted diet.¹ See pyridoxine.

Pregnancy and breastfeeding

What the label does record is worth knowing before that conversation. In Wilson's disease, there have been "several cases of reversible cutis laxa in infants born to mothers taking penicillamine throughout pregnancy", set against two retrospective studies reporting "the successful delivery of 43 normal infants to 28 women receiving between 500 mg and 2000 mg of penicillamine daily", plus anecdotal reports of both congenital abnormalities and successful outcomes; where treatment continues after a risk–benefit analysis, the label advises reducing to the lowest effective dose.¹ In cystinuria, there is "one report of a severe connective tissue abnormality in the infant of a mother who received 2000 mg penicillamine daily throughout pregnancy".¹

Breastfeeding: given the lack of data and the possibility that penicillamine is transmitted in breast milk, the label restricts it to cases "considered absolutely essential by the physician".¹

In practice, lead poisoning in pregnancy is a poisons-unit decision in which the competing risks — fetal exposure to lead mobilised from maternal bone by chelation, against continued maternal and fetal poisoning if untreated — are the substance of the conversation. Call NPIS.

Do not reach for it in thallium poisoning

Longer-term effects

Mostly relevant to chronic rheumatological use rather than a course for poisoning, but they define the drug's reputation: reversible loss of taste (mineral supplements are explicitly not recommended for it), a late acquired epidermolysis bullosa / penicillamine dermopathy after months or years, breast enlargement in both sexes as a rare complication, and drug-induced lupus, myasthenia gravis and polymyositis.¹

Practical use in the ED

1. Confirm the diagnosis with a blood lead concentration, and note the units your laboratory reports. µg/dL and µmol/L are both in use and the label's paediatric threshold is written in µg/dL.
2. Call NPIS on 0344 892 0111 before choosing a chelator. Which agent, whether to chelate at all, and the endpoint are all decisions this page cannot make for you.
3. Check renal function and a full blood count before any penicillamine. The label requires it, and moderate or severe renal impairment is a contraindication.
4. Remove the source. Chelation of a patient still being exposed is treating a symptom — the UK series is, in the end, an occupational hygiene story.
5. Do not assume penicillamine because it is the licensed one. In that same UK outbreak, the fifteen patients who were chelated received oral DMSA 30 mg/kg/day or intravenous sodium calcium edetate 75 mg/kg/day — neither of which holds a UK licence.⁴

Critical appraisal

Penicillamine's UK licence for lead poisoning is a survival from an earlier era of chelation rather than a statement that it is the best available agent. The comparative literature that exists is between sodium calcium edetate and DMSA, not between either of those and penicillamine; the 2009 systematic comparison of those two concluded there were insufficient data to call either superior, with greater clinical experience for edetate in encephalopathy and DMSA a reasonable alternative where oral therapy is preferable.³ Penicillamine is largely absent from that conversation.

The honest summary is that penicillamine is the licensed answer to a question UK toxicologists usually answer another way. Knowing the licensed doses matters — they are the ones you can legally and defensibly prescribe without special arrangements — but so does knowing that the drug your poisons unit recommends will probably be an unlicensed one, and that this is normal rather than irregular in metal poisoning.

References

1. 1
   Penicillamine 250 mg film-coated tablets — Summary of Product Characteristics, Viatris. electronic Medicines Compendium, product 2713. SmPC updated 2 September 2026; fetched and parsed from the print page 6 September 2026. Source of the five licensed indications, the lead-poisoning doses in §4.2(d) for adults, elderly and children including the <45 mcg/dL paediatric restriction and the <0.5 mg/day urinary endpoint, the empty-stomach administration instruction, the §4.3 contraindications, and the §4.4 baseline testing requirement, marrow-suppression thresholds, monitoring schedule, two-hour separation from iron/digoxin/antacids, antimalarial prohibition, gold and clozapine cautions, pyridoxine requirement and the older-person toxicity statement.
2. 2
   Penicillamine 125 mg film-coated tablets — Summary of Product Characteristics, Viatris. electronic Medicines Compendium, product 2712. Checked in full against product 2713 per the check-every-product rule: the lead-poisoning sections of the two labels are identical. Cited so that the comparison is on the record rather than assumed. These two are the only penicillamine products on the emc (checked 6 September 2026).
3. 3
   Bradberry S, Vale A. A comparison of sodium calcium edetate (edetate calcium disodium) and succimer (DMSA) in the treatment of inorganic lead poisoning. Clinical Toxicology (Philadelphia) 2009;47(9):841–858. PubMed 19852620. Source of the compartment claims (edetate mobilises lead principally from bone, DMSA acts principally in the kidney, neither crosses the blood–brain barrier to any major extent) and of the conclusion that there are insufficient data to call either superior. Abstract read 6 September 2026. Note this paper does not compare either agent with penicillamine.
4. 4
   Warsi A, Pucci MR, Bradberry SM, et al. Outbreak of lead poisoning from a civilian indoor firing range in the UK. Occupational and Environmental Medicine 2024;81(3):159–162. PubMed 38302418. West Midlands Poisons Unit. Source of the 63-tested / 9-symptomatic figures, the 242 µg/dL (11.7 µmol/L) peak, the doses actually used in the UK (oral DMSA 30 mg/kg/day, IV sodium calcium edetate 75 mg/kg/day) and the stock-availability finding. Abstract read 6 September 2026.
5. 5
   Kosnett MJ, Wedeen RP, Rothenberg SJ, et al. Recommendations for medical management of adult lead exposure. Environmental Health Perspectives 2007;115(3):463–471. PubMed 17431500. Source of the exposure-removal thresholds and of the statement that chelation is not recommended for asymptomatic individuals with low blood lead concentrations. Abstract read 6 September 2026. US-focused occupational recommendations — cited for the boundary it draws, not as UK practice.
6. 6
   Hoffman RS. Thallium toxicity and the role of Prussian blue in therapy. Toxicological Reviews 2003;22(1):29–40. PubMed 14579545. Source of the evidence against penicillamine and dimercaprol in thallium poisoning, the CNS-redistribution warning specific to penicillamine, and the harm of forced potassium diuresis. Abstract read 6 September 2026.
7. 7
   electronic Medicines Compendium. medicines.org.uk/emc. Searched 6 September 2026 for dimercaprol, BAL, succimer, DMSA, Chemet, Succicaptal, unithiol, Dimaval, edetate, Ledclair, prussian blue, Radiogardase and ferric hexacyanoferrate. Every term except BAL returned a "No search results" page; BAL matched only unrelated products (Anusol preparations), which confirms the search resolves substrings rather than failing silently. The emc is an industry-hosted compendium of published SmPCs and PILs, not the MHRA register — this establishes that no SmPC is published for these agents, rather than that no marketing authorisation exists anywhere. Products 2712 and 2713 are the only penicillamine products returned.
8. 8
   National Poisons Information Service. TOXBASE · NPIS 0344 892 0111. The authoritative UK source for whether to chelate, which agent to use and the endpoint. Penicillamine holds a UK licence for lead poisoning but is not usually the agent UK poisons units recommend.