39.2 Non-Infectious Rashes: Urticaria, Drug Eruptions & Erythema Multiforme

Pathophysiology of Urticaria & Mast Cell Activation

Urticaria (hives) is characterized by the sudden appearance of intensely pruritic wheals, angioedema, or both. It affects up to 20% of the population at some point during their lifetime.

                      URTICARIA PATHOPHYSIOLOGY

     Immunologic Triggers               Non-Immunologic Triggers
     (IgE-Mediated, Autoantibodies)     (Opiates, Radiocontrast, NSAIDs)
                 │                                     │
                 ▼                                     ▼
     ┌─────────────────────────────────────────────────────────┐
     │             DERMAL MAST CELL DEGRANULATION              │
     │  • Preformed Mediators: Histamine, Tryptase             │
     │  • De Novo Lipids: Leukotrienes (LTC4, LTD4), PGD2, PAF │
     │  • Cytokines: TNF-alpha, IL-4, IL-5                     │
     └─────────────────────────────────────────────────────────┘
                                  │
            ┌─────────────────────┴─────────────────────┐
            ▼                                           ▼
   Post-Capillary Venular Dilation             Sensory C-Fiber Stimulation
   & Increased Vascular Permeability           • Unmyelinated C-nerve fibers
   • Transudation of fluid into dermis         • Intense Pruritus
   • LOCALIZED DERMAL EDEMA (WHEAL)            • Axon reflex flare (erythema)

Cellular Mechanisms

• Superficial Dermal Edema: Mast cell degranulation in the papillary and reticular dermis releases histamine, which binds to endothelial H1 receptors, stimulating nitric oxide and prostacyclin production. This causes marked arteriolar vasodilation and post-capillary venular gap formation, permitting plasma extravasation into the extracellular space to form a circumscribed wheal.
• Sensory Nerve Activation: Histamine acts on local unmyelinated C-type sensory nerve endings, transmitting intense pruritus to the central nervous system and stimulating local substance P and CGRP release, producing the surrounding axon reflex erythematous flare.
• Angioedema: When mast cell activation or vasoactive mediator release occurs in the deeper reticular dermis, subcutaneous tissue, or submucosal layers, it manifests as angioedema—a non-pitting, poorly demarcated swelling that is frequently painful or burning rather than pruritic.

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Acute vs. Chronic Urticaria & Diagnostic Red Flags

Urticaria is chronologically classified into acute and chronic forms based on an arbitrary cutoff of 6 weeks.

1. Acute Urticaria (<6 Weeks)

• Etiology: Most cases are self-limited and resolve within days to a few weeks.
  • Infections (>80% of pediatric cases): Acute viral upper respiratory infections, enteroviruses, Epstein-Barr virus, adenovirus, and rotavirus;
  • Adverse Drug Reactions: IgE-mediated (beta-lactams) or direct non-IgE mast cell degranulation (opiates, vancomycin, radiocontrast media) or COX-1 inhibition altering arachidonic acid shunting to cysteinyl leukotrienes (aspirin, NSAIDs);
  • Food Allergies: IgE-mediated reactions to peanuts, tree nuts, shellfish, milk, eggs, or soy (onset occurs within 30 to 120 minutes of ingestion);
  • Hymenoptera Stings: Bee, wasp, or fire ant envenomation.
• Laboratory Evaluation: Extensive laboratory testing or routine allergy panels are strictly not recommended for uncomplicated acute urticaria, as testing yields high false-positive rates and does not alter clinical management.

2. Chronic Urticaria (>=6 Weeks)

• Subtypes:
  • Chronic Spontaneous Urticaria (CSU, >80%): Hives occurring most days of the week for >=6 weeks without an identifiable physical trigger. Up to 40% to 50% have an autoimmune pathogenesis driven by circulating IgG autoantibodies directed against the alpha subunit of the high-affinity IgE receptor (anti-Fc-epsilon-RI-alpha) or against IgE itself (anti-IgE), cross-linking receptors and triggering continuous mast cell degranulation. CSU is strongly associated with autoimmune thyroid disease (Hashimoto thyroiditis with anti-TPO antibodies).
  • Chronic Inducible Urticaria (CIndU, <20%): Provoked by specific physical stimuli: symptomatic dermographism (stroking the skin), cold urticaria (ice cube test), cholinergic urticaria (elevated core body temperature from exercise or hot showers; pinpoint wheals), delayed pressure urticaria, solar urticaria, or vibratory angioedema.
• Recommended Basic Workup for CSU: Complete blood count (CBC) with differential, erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP), and thyroid-stimulating hormone (TSH) with anti-thyroperoxidase (anti-TPO) antibodies. Routine extensive food allergy panels, ANA, or total IgE are non-contributory.

The Cardinal Rules of Urticaria & Board Red Flags

• The 24-Hour Evanescence Rule: Individual urticarial wheals are characteristically transient and migratory! An individual wheal arises rapidly, peaks within hours, and completely resolves within 24 hours (usually 2 to 12 hours) without leaving behind any residual bruising, petechiae, scaling, or post-inflammatory hyperpigmentation, while new lesions may appear elsewhere.

[!WARNING] RED FLAG: URTICARIAL VASCULITIS If an individual hive remains fixed in the exact same anatomic location for longer than 24 to 48 hours, causes burning, tenderness, or stinging rather than itching, and resolves leaving behind residual purpura, ecchymosis, or hyperpigmentation, this is NOT simple urticaria! This presentation indicates urticarial vasculitis (a leukocytoclastic vasculitis of post-capillary venules associated with SLE, Sjögren syndrome, or hypocomplementemia). A skin punch biopsy is mandatory for definitive histologic diagnosis.

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Stepwise Management of Urticaria: The 4-Fold Antihistamine Rule

International guidelines (EAACI/GA²LEN/EDF/WAO) dictate a clear, stepwise pharmacotherapeutic algorithm for managing acute and chronic urticaria.

                      STEPWISE URTICARIA MANAGEMENT

    STEP 1: Second-Generation H1-Antihistamine at Standard Licensed Dose
    (Cetirizine 10 mg, Fexofenadine 180 mg, Loratadine 10 mg, Desloratadine 5 mg)
                                    │
                                    ▼ Uncontrolled after 2-4 weeks (or severe)
    STEP 2: UPTITRATION OF SECOND-GENERATION H1-ANTIHISTAMINE UP TO 4X DOSE!
    (e.g., Cetirizine 20 mg BID OR Fexofenadine 180 mg BID)
    • The Gold Standard Second Step (superior efficacy, excellent safety)
                                    │
                                    ▼ Uncontrolled after 2-4 weeks at 4x dose
    STEP 3: Add-On Biologic Therapy (Omalizumab) or Secondary Agents
    • Omalizumab (Anti-IgE) 300 mg Subcutaneously every 4 weeks (First-Line Add-on)
    • Adjuncts: H2-Blocker (Famotidine 20 mg BID), Montelukast 10 mg daily
                                    │
                                    ▼ Refractory to Omalizumab
    STEP 4: Cyclosporine A (3 to 5 mg/kg/day) in specialized care

Step 1: Second-Generation H1-Antihistamines (First-Line)

• Rationale: Modern second-generation H1-antihistamines (cetirizine 10 mg daily, levocetirizine 5 mg daily, fexofenadine 180 mg daily, loratadine 10 mg daily, desloratadine 5 mg daily) are non-sedating inverse agonists that selectively stabilize inactive H1 receptors.
• Avoid First-Generation Antihistamines as First-Line: First-generation agents (diphenhydramine, hydroxyzine, chlorpheniramine) cross the blood-brain barrier, causing profound daytime sedation, impaired psychomotor skills, rapid-eye-movement (REM) sleep architecture disruption, and potent anticholinergic toxicity (urinary retention, dry mouth, blurred vision, confusion in older adults). They are relegated to optional short-term bedtime use for intractable nocturnal pruritus.

Step 2: The 4-Fold Dose Escalation Rule

• If urticaria symptoms persist after 2 to 4 weeks (or sooner in patients with severe daily hives), guidelines strongly recommend escalating the dose of the second-generation H1-antihistamine up to four times the standard licensed dose (e.g., cetirizine 20 mg twice daily, or fexofenadine 180 mg twice daily) before switching classes.
• High-dose second-generation antihistamines achieve greater H1-receptor occupancy without causing significant sedation or organ toxicity.

Step 3: Add-On Therapies & Biologics

• Omalizumab: A humanized recombinant monoclonal antibody that binds free circulating IgE, downregulating Fc-epsilon-RI receptors on mast cells and basophils. Administered at 300 mg subcutaneously every 4 weeks, it clears hives in up to 70% to 80% of antihistamine-refractory CSU patients.
• Secondary Oral Adjuncts: H2-receptor antagonists (Famotidine 20 mg twice daily) block the 15% of cutaneous vascular H2 receptors; Leukotriene receptor antagonists (Montelukast 10 mg daily) provide benefit in NSAID-sensitive or angioedema-predominant urticaria.

Systemic Corticosteroids in Urticaria: Strict Practice Parameters

• Rescue Therapy Only: Oral corticosteroids (prednisone 40 to 50 mg daily for adults, 1 mg/kg/day for children) should be restricted to a short rescue burst of 3 to 5 days for severe acute flares or debilitating angioedema. No taper is necessary for courses <=5 days.
• Strict Rule for Chronic Urticaria: Systemic corticosteroids are strictly contraindicated for long-term maintenance in chronic spontaneous urticaria due to unacceptable cumulative toxicity (osteoporosis, diabetes, hypertension, adrenal suppression) and severe rebound exacerbation upon withdrawal.

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Adverse Cutaneous Drug Reactions: Benign Morbilliform Eruptions

Adverse cutaneous drug reactions occur in 1% to 3% of hospitalized patients and up to 2% of outpatient prescriptions. Accurately distinguishing benign exanthems from severe cutaneous adverse reactions (SCARs) is a critical board competency.

Exanthematous (Morbilliform) Drug Eruption

• Epidemiology: The most common adverse cutaneous drug reaction, accounting for >90% of cases.
• Pathophysiology: Delayed Type IV cell-mediated hypersensitivity reaction driven by drug-specific CD4+ and CD8+ T cells reacting to haptenated peptides presented by MHC molecules.
• Onset Timing: Typically develops 7 to 14 days after starting a new medication; on re-exposure, the eruption appears much faster (within 24 to 48 hours).
• High-Risk Culprit Drugs: Beta-lactam antibiotics (penicillins, aminopenicillins, cephalosporins), sulfonamides (TMP-SMX), anticonvulsants (carbamazepine, phenytoin), allopurinol, and NSAIDs.
• Clinical Morphology & Distribution:
  • Symmetrical, widely distributed, bright pink-to-red macules and small papules (measuring 2 to 5 mm) that frequently coalesce into larger reticular plaques;
  • Begins centrally on the trunk and upper extremities, spreading symmetrically and centrifugally down to the lower extremities;
  • Important Sparing: Spares the face, mucous membranes, palms, and soles;
  • Moderate to severe pruritus is common, but skin pain or tenderness is absent.
• Strict Absence of Systemic Toxicity: Patients are afebrile, hemodynamically stable, with zero facial edema, zero mucosal erosions, and normal hematologic, hepatic, and renal laboratory parameters.
• Management:
  • Promptly identify and discontinue the culprit medication;
  • Supportive therapy: Medium-potency topical corticosteroids (triamcinolone acetonide 0.1% cream) for pruritus, oral second-generation antihistamines, and cool baths;
  • Natural history: The exanthem peaks over several days, turns a dusky brownish-red, and fades over 7 to 14 days, often resolving with fine, powdery superficial desquamation.

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Severe Cutaneous Adverse Reactions (SCARs): DRESS / DIHS Syndrome

Severe Cutaneous Adverse Reactions (SCARs) encompass life-threatening, T-cell-mediated drug reactions with high morbidity and mortality: DRESS, SJS, and TEN.

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS / DIHS)

• Synonym: Drug-Induced Hypersensitivity Syndrome (DIHS).
• Latency Period: Characteristically delayed onset of 2 to 8 weeks (average 3 to 4 weeks) after drug exposure. This long latency often causes clinicians and patients to overlook the offending medication!
• Culprit Medications:
  • Aromatic Anticonvulsants: Carbamazepine, phenytoin, phenobarbital, lamotrigine;
  • Allopurinol: Especially in patients with underlying renal insufficiency or carrying the HLA-B*5801 allele (common in Han Chinese, Korean, and African ancestry);
  • Sulfonamides: Sulfasalazine, dapsone, trimethoprim-sulfamethoxazole;
  • Antibiotics: Minocycline, vancomycin;
  • Antiretrovirals: Abacavir (HLA-B*5701), nevirapine.
• Pathogenesis: Complex interplay of genetic pharmacogenomic susceptibility (specific HLA alleles), defective drug detoxification pathways, drug-specific T-cell hyperactivation, and reactivation of latent human herpesviruses (especially HHV-6, HHV-7, Epstein-Barr virus [EBV], and CMV).

The Classic Diagnostic Triad of DRESS

1. Severe Cutaneous Eruption & Facial Edema:
   • Begins as an extensive morbilliform exanthem involving >50% BSA that rapidly progresses into an indurated, edematous, infiltrated erythroderma or exfoliative dermatitis;
   • Hallmark Clinical Sign: Prominent facial and periorbital edema (present in >70% to 80% of patients), creating a distinctive puffy, distorted facial appearance.
2. Hematologic Abnormalities:
   • Marked Peripheral Eosinophilia: Absolute eosinophil count >=1,500/mcL (or >10% of differential);
   • Atypical Lymphocytosis: Mononucleosis-like reactive atypical lymphocytes on peripheral blood smear in >30%.
3. Multiorgan Visceral Involvement (>=1 Internal Organ):
   • Liver (Most Common, >75%): Acute drug-induced hepatitis with marked transaminitis (ALT/AST >2 to 10x upper limit of normal), hyperbilirubinemia, and fulminant hepatic failure (the primary cause of death in DRESS);
   • Kidneys (10-30%): Acute interstitial nephritis with elevated serum creatinine, microscopic hematuria, and proteinuria (predominates with allopurinol exposure);
   • Lungs (10%): Interstitial pneumonitis causing cough, dyspnea, and hypoxemia;
   • Heart: Acute eosinophilic myocarditis (can present weeks after onset, requiring baseline troponin and ECG monitoring).

Clinical Management of DRESS

• Immediate Culprit Drug Withdrawal: Prompt discontinuation is the most vital determinant of survival.
• Systemic Corticosteroids (First-Line): High-dose Oral Prednisone 1.0 mg/kg/day (or IV methylprednisolone for severe visceral involvement). Corticosteroids suppress T-cell hyperactivity and halt visceral organ necrosis.
• The 8- to 12-Week Taper Rule: Corticosteroids must be tapered very slowly over a minimum of 8 to 12 weeks! Premature or rapid dose reduction triggers severe, catastrophic inflammatory rebounds and recurrent organ failure.
• Long-Term Monitoring: Patients are at high risk of developing delayed autoimmune endocrinopathies (autoimmune Hashimoto thyroiditis, Graves disease, Type 1 diabetes) months to years later, requiring long-term TSH and glycemic surveillance.

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Stevens-Johnson Syndrome (SJS) & Toxic Epidermal Necrolysis (TEN)

Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) represent severity variants of the same life-threatening, acute cytotoxic T-cell-mediated mucocutaneous necrolysis syndrome.

                  SJS / TEN EPIDERMAL DETACHMENT SPECTRUM

    [ STEVENS-JOHNSON SYNDROME ] ───────> <10% Body Surface Area Detachment
                                         • Mortality: ~5% to 10%

    [ SJS / TEN OVERLAP ] ──────────────> 10% to 30% Body Surface Area Detachment
                                         • Mortality: ~15% to 30%

    [ TOXIC EPIDERMAL NECROLYSIS ] ─────> >30% Body Surface Area Detachment
                                         • Mortality: >30% to 50%

Pathophysiology

• Cytotoxic Keratinocyte Apoptosis: Drug-specific HLA-restricted CD8+ cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells infiltrate the dermoepidermal junction.
• Mediators of Death: Massive release of granulysin (a cytotoxic protein that directly lyses keratinocytes and acts as the master mediator of epidermal necrolysis), perforin/granzyme B, and soluble Fas ligand (FasL) binding to Fas (CD95) receptors. This induces apoptosis of the entire epidermal cell layer, resulting in full-thickness dermal-epidermal separation and massive fluid loss.
• Latency: Onset occurs 1 to 3 weeks (7 to 21 days) after drug initiation.
• Major Culprit Drugs: Allopurinol (HLA-B5801), Carbamazepine (HLA-B1502), Phenytoin, Lamotrigine, Sulfonamide antibiotics (TMP-SMX), Nevirapine, and Oxicam NSAIDs (meloxicam, piroxicam).

Clinical Presentation & Hallmark Signs

• Prodrome: High fever (>39°C / 102.2°F), severe malaise, sore throat, cough, stinging eyes, and arthralgias occurring 1 to 3 days prior to the rash.
• Cutaneous Eruption:
  • Initial lesions: Ill-defined, dusky, purpuric, targetoid atypical macules (irregular dark purpuric centers without concentric rings) originating symmetrically on the pre-sternal chest and face, rapidly coalescing across the trunk and extremities;
  • Lesions become exquisitely tender to light palpation ("skin pain out of proportion to exam" is an early hallmark sign);
  • Coalescent dusky areas develop flaccid, fluid-filled bullae that rupture, leaving sheets of denuded, weeping, bleeding dermis resembling severe second-degree thermal burns.
• Pathognomonic Physical Examination Signs:
  • Positive Nikolsky Sign: Application of gentle, lateral shearing pressure with a finger to normal-appearing perilesional skin results in dislodgement and peeling of the epidermis;
  • Positive Asboe-Hansen Sign (Bulla Spread Sign): Gentle downward vertical pressure on the center of an intact flaccid bulla causes lateral extension and dissection of the blister fluid beneath adjacent intact epidermis.
• Severe Mucosal Involvement (>90% of Cases):
  • Severe, excruciating inflammation involving two or more mucosal surfaces:
    • Oral Mucosa: Hemorrhagic crusting of the lips, extensive denuded stomatitis, severe odynophagia preventing oral intake;
    • Ocular Mucosa (>80%): Severe bilateral purulent conjunctivitis, pseudomembrane formation, corneal erosions, and symblepharon (adhesion of palpebral conjunctiva to bulbar conjunctiva); without urgent treatment, leads to cicatricial ectropion, corneal ulceration, and permanent blindness;
    • Urogenital Mucosa: Severe erosive urethritis (causing acute urinary retention), vulvovaginal ulcerations, and late vaginal canal stenosis;
    • Respiratory Epithelium: Tracheobronchial mucosal sloughing causing acute respiratory distress syndrome (ARDS) requiring mechanical ventilation.

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SCORTEN Mortality Prediction & Burn Center Transfer Criteria

The SCORTEN Prognostic Score

SCORTEN is a validated, illness-severity score calculated within the first 24 to 48 hours of hospital admission to predict in-hospital mortality in SJS/TEN. One point is scored for each of the following 7 independent clinical variables:

1. Age >= 40 years;
2. Presence of Malignancy (hematologic or solid tumor);
3. Tachycardia >= 120 beats/min;
4. Initial Epidermal Detachment >= 10% BSA;
5. Serum Blood Urea Nitrogen (BUN) > 28 mg/dL (>10 mmol/L);
6. Serum Glucose > 252 mg/dL (>14 mmol/L);
7. Serum Bicarbonate < 20 mEq/L.

Emergent Management & Burn Center Transfer

1. Immediate Cessation of Culprit Drug: Prompt drug removal reduces mortality by approximately 30% per day of early withdrawal.
2. Emergent Transfer to a Burn Center or Surgical ICU: Patients with SJS/TEN overlap (>10% BSA detachment) or TEN (>30% BSA) must be transferred immediately to a specialized Burn Center or specialized ICU. Outcomes in burn units are vastly superior due to specialized reverse isolation, dedicated nursing, advanced non-adherent wound dressings, and infection control.
3. Supportive Critical Care:
   • Fluid and Electrolyte Resuscitation: Administer warmed isotonic intravenous crystalloids (titrated to maintain urine output 0.5-1.0 mL/kg/h); fluid requirements are approximately 2/3 of standard thermal burn Parkland formulas because capillary permeability is lower than in thermal injury;
   • Environmental Temperature: Maintain ambient room temperature at 30°C to 32°C to prevent hypothermia from extensive transcutaneous heat loss;
   • Wound Care: Strict avoidance of aggressive surgical debridement! Preserve the detached epidermal roof as a biologic dressing, covering denuded areas with non-adherent silicone or impregnated petrolatum dressings;
   • Immediate Ophthalmology Consultation: Daily bedside ophthalmologic examination, aggressive preservative-free lubrication, topical antibiotics, lysis of conjunctival symblepharon adhesions with glass rods, and early amniotic membrane transplantation within the first 7 to 10 days to preserve corneal architecture and prevent blindness.
4. Systemic Immunomodulatory Therapies: High-dose IVIG (blocking Fas-FasL interactions), Cyclosporine A (inhibiting cytotoxic T-cell activation), or Anti-TNF biologics (Etanercept). Systemic corticosteroids remain controversial in established TEN due to increased sepsis risk.

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Erythema Multiforme: Herpes Simplex Association & Iris Target Lesions

Erythema Multiforme (EM) is an acute, immune-mediated, self-limited mucocutaneous condition characterized by distinctive "target" (iris) lesions. Historically conflated with SJS, EM is now recognized as an entirely distinct clinicopathologic disease.

Etiology: Infectious Dominance

• Infections Account for >90% of Cases:
  • Herpes Simplex Virus (HSV-1 and HSV-2) is the primary trigger in >70% of cases of recurrent and acute EM;
  • Mycoplasma pneumoniae is the second most common infectious trigger (particularly in children and young adults, often causing prominent mucosal disease termed MIRM: Mycoplasma-induced rash and mucositis);
  • Other infections: EBV, Histoplasma capsulatum, parapoxvirus.
• Medications Trigger <10% of Cases: Unlike SJS/TEN, medications are an uncommon cause of true erythema multiforme.

Pathognomonic Target (Iris) Lesions

• True individual target lesions are symmetric, regular, round, well-demarcated, and measure <3 cm in diameter, displaying three distinct concentric zones:
  1. Central Dusky / Purpuric Zone: A dark red, purpuric, or necrotic center, often topped by a small vesicle or crust;
  2. Intermediate Pale Edematous Ring: A raised, pale, edematous middle ring;
  3. Outer Erythematous Border: A sharp, bright red, flat peripheral inflammatory halo.
• Anatomical Distribution: Striking acral and extensor predilection: dorsum of the hands, palms, extensor forearms, elbows, soles of the feet, and face, arranged symmetrically.

                  TRUE THREE-ZONED TARGET LESION (IRIS)

                          (●) Outer Erythematous Halo
                         (   ) Intermediate Pale Edematous Ring
                        (  •  ) Central Dusky / Purpuric Core

Classification: EM Minor vs. EM Major

• Erythema Multiforme Minor: Typical acral target lesions without mucosal involvement (or mild involvement of a single mucosal surface, usually the lips). Absence of systemic fever or prostration. Resolves spontaneously over 2 to 4 weeks.
• Erythema Multiforme Major: Targetoid cutaneous lesions accompanied by severe mucosal involvement of two or more surfaces (oral, ocular, genital) and constitutional symptoms (fever, arthralgias).
• Distinguishing EM Major from SJS:
  • In EM Major, cutaneous lesions are true three-zoned target lesions located predominantly on the acral extremities;
  • In SJS, cutaneous lesions are flat, atypical, two-zoned dusky purpuric macules centered on the trunk and face;
  • Epidermal Detachment: In EM Major, epidermal detachment is absent or <10% BSA, and there is no generalized epidermal sheet necrolysis.

Management of Erythema Multiforme

• Symptomatic Relief: Mid- to high-potency topical corticosteroids for pruritic skin lesions; oral antihistamines; topical anesthetic/antiseptic mouthwashes (viscous lidocaine, diphenhydramine, aluminum hydroxide) for oral stomatitis.
• Treating the Infectious Trigger: Oral acyclovir or valacyclovir does not alter the course of an established HSV-induced EM flare, but early antiviral therapy is indicated if active HSV lesions are present. Macrolide antibiotics (azithromycin) are indicated for Mycoplasma pneumoniae.
• Suppressive Antiviral Prophylaxis for Recurrent EM: For patients with frequent, debilitating recurrences of HSV-associated EM (>=2 to 4 episodes per year), continuous daily oral suppressive antiviral therapy (Valacyclovir 500 mg to 1,000 mg daily or Acyclovir 400 mg twice daily) for 6 to 12 months provides highly effective suppression.