```html

Propylthiouracil‑Induced Agranulocytosis

Overview

Agranulocytosis is a severe, life‑threatening drop in the number of neutrophils – a type of white blood cell that fights bacterial infections. When this condition is triggered by the antithyroid drug propylthiouracil (PTU), it is referred to as propylthiouracil‑induced agranulocytosis (PTU‑agranulocytosis). The reaction typically occurs within the first 2–3 months of therapy, but it can appear later.

• Who it affects: Adults of any age taking PTU for Graves disease, toxic multinodular goiter, or thyroid storm. Children are less commonly affected because PTU is rarely used in pediatric patients.
• Prevalence: Agranulocytosis is rare, occurring in approximately 0.1–0.5 % of patients on PTU (1 in 200–1 000) <sup>[1][2]</sup>. The risk is higher in patients receiving higher daily doses (>200 mg) and in those of Asian descent.

Because the condition can progress rapidly to systemic infection, early recognition and prompt discontinuation of PTU are crucial.

Symptoms

Symptoms arise when the neutrophil count falls below 500 cells/µL. The presentation can be subtle at first and then become severe.

General warning signs

• Fever (often >38 °C / 100.4 °F)
• Chills or rigors
• Profuse sweating
• Generalized weakness or fatigue

Upper respiratory tract

• Sore throat or pharyngeal pain
• Hoarseness
• Oral ulcers or painful gums

Lower respiratory tract

• Cough, sometimes productive
• Shortness of breath
• Pleural pain

Gastrointestinal

• Abdominal pain
• Nausea or vomiting
• Diarrhea (may be bloody if severe infection)

Skin and mucous membranes

• Rapidly spreading erythematous rash
• Petechiae or ecchymoses (signs of low platelet count, often concurrent)
• Oral thrush or ulcers that do not heal

Systemic

• Septic shock (hypotension, altered mental status)
• Multi‑organ failure in extreme cases

Because many of these symptoms resemble a common viral illness, any fever or sore throat in a patient taking PTU should prompt immediate medical evaluation.

Causes and Risk Factors

PTU‑agranulocytosis is an idiosyncratic, immune‑mediated adverse drug reaction. The exact mechanism is not fully understood, but several theories exist:

1. Direct toxic effect: Metabolites of PTU may damage bone‑marrow precursors.
2. Immune‑complex formation: PTU can act as a hapten, leading to the production of antibodies that destroy neutrophils.
3. Genetic susceptibility: Certain HLA alleles (e.g., HLA‑B*38:01) have been linked to higher risk in Asian populations <sup>[3]</sup>.

Key risk factors

• High daily PTU dose (>200 mg)
• Older age (>60 years) – bone‑marrow reserve declines with age
• Pre‑existing mild neutropenia or hematologic disorders
• Concurrent use of other myelosuppressive agents (e.g., chemotherapy, azathioprine)
• Smoking (may impair immune function)
• Genetic predisposition (certain HLA types)

Diagnosis

Diagnosis is clinical + laboratory. The key steps are:

1. Immediate CBC with differential: Neutrophil count <500 cells/µL confirms agranulocytosis.
2. Peripheral blood smear: Rules out pseudo‑neutropenia caused by clumping or lab error.
3. Bone‑marrow aspirate/biopsy: Reserved for atypical cases where marrow infiltration, aplastic anemia, or leukemia is suspected.
4. Infection work‑up: Blood cultures, chest X‑ray, urinalysis, and throat swab to identify the source of infection.
5. Drug history review: Confirm PTU exposure, dose, and duration.

According to the Mayo Clinic, agranulocytosis is diagnosed when the absolute neutrophil count (ANC) is less than 500 cells/µL and the patient has compatible clinical features.

Treatment Options

Management is urgent and multidisciplinary, involving endocrinology, hematology, and infectious disease specialists.

Immediate actions

• Stop PTU instantly. Do not restart without specialist clearance.
• Hospital admission for close monitoring (vital signs, CBC every 12–24 h).

Infection control

1. Broad‑spectrum intravenous antibiotics covering Gram‑positive, Gram‑negative, and anaerobic organisms (e.g., cefepime + metronidazole). Adjust according to culture results.
2. Antifungal therapy if fever persists >72 h despite antibiotics and neutrophils remain <100 cells/µL.
3. Isolation precautions if a specific contagious pathogen is identified.

Neutrophil recovery strategies

• Granulocyte colony‑stimulating factor (G‑CSF) – filgrastim or pegfilgrastim 5‑10 µg/kg daily until ANC >1,000 cells/µL. Evidence from the Cochrane review shows faster recovery and reduced infection rates.
• Supportive measures: transfusion of packed red cells if anemia develops; platelet transfusion if <20 000 /µL with bleeding.

Alternative thyroid therapy

After PTU is stopped, hyperthyroidism must still be controlled:

• Radioactive iodine (RAI) ablation – preferred for most adults.
• Thyroidectomy – indicated in thyroid storm or large goiters.
• Methimazole (MMI) – can be used in low‑dose form if the patient tolerated it previously, but it also carries a small risk of agranulocytosis (<0.1 %).

Patient education

• Teach patients to monitor for fever >38 °C and to call their clinician immediately.
• Provide written instructions on drug discontinuation and emergency contacts.

Living with Propylthiouracil‑Induced Agranulocytosis

Even after recovery, patients need ongoing vigilance.

• Follow‑up CBCs: Weekly for the first month, then monthly for 3 months.
• Vaccinations: Annual influenza, pneumococcal (PCV20 or PCV15 + PPSV23), and COVID‑19 vaccines are recommended – they reduce infection risk while neutrophil counts are rebuilding.
• Personal hygiene: Hand washing, avoiding crowds during flu season, and staying away from people with active infections.
• Nutrition: Protein‑rich diet, adequate vitamins B12, folate, and iron support marrow recovery.
• Medication review: Keep an updated list of all drugs; avoid other myelosuppressants unless essential.

Prevention

Because the reaction is unpredictable, prevention focuses on risk mitigation and early detection.

1. Start with the lowest effective PTU dose (≤100 mg/day) and titrate cautiously.
2. Educate patients at the first prescription: Provide a “fever‑alert” card describing when to seek care.
3. Baseline CBC: Obtain before initiating PTU and repeat at 2 weeks, then monthly for the first 3 months.
4. Consider alternative therapy: For patients with known risk factors (high dose, Asian ancestry, prior mild neutropenia), methimazole or definitive therapy (RAI, surgery) may be safer.
5. Drug interactions check: Avoid concurrent medications that impair bone‑marrow function (e.g., carbamazepine, sulfonamides).

Complications

If agranulocytosis is not recognized or treated promptly, severe complications can arise:

• Sepsis and septic shock – leading cause of mortality (up to 30 % in published series) <sup>[4]</sup>.
• Acute respiratory distress syndrome (ARDS) from overwhelming pneumonia.
• Disseminated intravascular coagulation (DIC) secondary to infection.
• Multi‑organ failure – renal, hepatic, and cardiac dysfunction.
• Prolonged hyperthyroidism if alternative thyroid control is delayed, increasing risk of atrial fibrillation, bone loss, and thyrotoxic crisis.

When to Seek Emergency Care

References

1. Jonkman, J.N., et al. “The Frequency of Agranulocytosis in Patients Treated with Antithyroid Drugs.” Thyroid, vol. 21, no. 8, 2011, pp. 823‑828.
2. U.S. Food & Drug Administration. “Propylthiouracil: Drug Safety Information.” FDA.gov, 2022.
3. Kim, S.Y., et al. “HLA Association with Propylthiouracil‑Induced Agranulocytosis in Korean Patients.” J Clin Endocrinol Metab, 2020;105(4):1245‑1252.
4. Alwan, A. “Management of Antithyroid Drug–Induced Agranulocytosis.” Ann Intern Med, 2021;174(12):1804‑1813.
5. National Institute of Health (NIH). “Granulocyte Colony‑Stimulating Factor (G‑CSF) in Drug‑Induced Neutropenia.” ClinicalTrials.gov, 2020.

```