Antidyslipidemic Drugs - Detailed Overview

Background: Lipoproteins and Dyslipidemia

"Lipid-modifying drugs that predominantly lower LDL-cholesterol and/or non-HDL-cholesterol levels are the first-line approach to reduce the risk of a first or recurrent cardiovascular event." - Goldman-Cecil Medicine, 2-Volume Set

Classification of Antidyslipidemic Drugs

1. HMG-CoA Reductase Inhibitors (Statins)

Mechanism

Drugs and Intensity Classification

Pleiotropic Effects (Beyond Lipid Lowering)

• Anti-inflammatory effects (↓ CRP)
• Improved endothelial function
• Plaque stabilization
• Antithrombotic effects

Cardiovascular Outcomes Evidence

Adverse Effects

• Myopathy - the most significant concern. Ranges from myalgia (muscle pain without CK elevation) to myositis (with elevated CK) to rhabdomyolysis (severe, rare - CK >10× ULN, myoglobinuria, renal failure risk). Risk factors: high dose, CYP3A4 inhibitors (for lovastatin/simvastatin/atorvastatin), hypothyroidism, renal impairment, elderly, drug interactions.
• Hepatotoxicity - transaminase elevation; clinical hepatitis is rare. Monitoring recommended if >5× ULN.
• New-onset diabetes - small but significant increased risk (~10%); benefit of ASCVD prevention overwhelmingly outweighs this risk.
• Nocebo effect - >75-80% of statin "intolerance" symptoms in blinded trials are not due to the statin.

Drug Interactions (Important)

• CYP3A4 inhibitors (azole antifungals, macrolides, HIV protease inhibitors, amiodarone) increase plasma levels of lovastatin, simvastatin, atorvastatin → increased myopathy risk
• Gemfibrozil inhibits glucuronidation of statin lactones → increased myopathy risk (avoid with cerivastatin; caution with all statins)
• Cyclosporine, danazol increase statin levels via OATP1B1 inhibition

2. Cholesterol Absorption Inhibitor - Ezetimibe

Mechanism

Efficacy

• Reduces LDL-C by ~18-20% as monotherapy
• Added to a statin: additional ~20-25% LDL-C reduction
• Has low triglyceride-lowering effect (~9%)
• No significant effect on HDL-C

Clinical Evidence

Dosing

Adverse Effects

3. PCSK9 Inhibitors (Monoclonal Antibodies)

Mechanism

• Genetic basis: Loss-of-function PCSK9 mutations → lower LDL-C, markedly reduced ASCVD risk. Gain-of-function mutations → familial hypercholesterolemia.

Drugs

Cardiovascular Outcomes

• FOURIER trial (Evolocumab): ~15% relative risk reduction in major ASCVD events
• ODYSSEY OUTCOMES (Alirocumab): Significant MACE reduction; all-cause mortality reduction in high-risk patients

Indications (2018 AHA/ACC guidelines)

1. Established ASCVD with LDL-C ≥70 mg/dL despite maximally tolerated statin + ezetimibe
2. Familial hypercholesterolemia with LDL-C ≥70 mg/dL (secondary prevention) or ≥100 mg/dL (primary prevention)
3. Homozygous familial hypercholesterolemia

Adverse Effects

4. PCSK9 siRNA - Inclisiran

Mechanism

Advantages

• Subcutaneous injection every 6 months (after initial loading doses at 0, 3 months)
• Reduces LDL-C by 40-50%
• Sustained effects over at least 18 months
• Long dosing interval improves adherence

5. Bile Acid Sequestrants (Resins)

Mechanism

Efficacy

• Reduce LDL-C by 15-25% (dose-dependent)
• May slightly raise triglycerides - caution in hypertriglyceridemia
• Modestly raise HDL-C

Adverse Effects

• GI side effects: constipation, bloating, flatulence, nausea (major limitation)
• Drug interactions - bind concurrently administered drugs (warfarin, digoxin, thyroid hormones, thiazides, fat-soluble vitamins). Must administer other drugs 1 hour before or 4-6 hours after.
• Colesevelam has fewer GI side effects and is also FDA-approved for type 2 diabetes (lowers HbA1c ~0.5%)

Special Use

6. Fibrates (Fibric Acid Derivatives)

Mechanism

• Increases lipoprotein lipase (LPL) synthesis → ↑ TG-rich lipoprotein catabolism
• Reduces apoC-III synthesis → ↓ inhibition of LPL
• Increases apoA-I and apoA-II synthesis → ↑ HDL-C
• Modestly reduces LDL-C (mainly in mixed dyslipidemia)

Drugs and Efficacy

Cardiovascular Outcomes

Adverse Effects

• Myopathy (especially gemfibrozil + statin combination - pharmacokinetic interaction: avoid)
• Hepatotoxicity (transaminase elevation)
• Gallstones (↑ lithogenicity of bile)
• Renal: modest rise in serum creatinine (fenofibrate)

Drug Interactions

7. Niacin (Nicotinic Acid)

Mechanism

Efficacy

• ↓ TG by 20-50%
• ↑ HDL-C by 15-35% (most effective agent for raising HDL)
• ↓ LDL-C by 15-25%
• Also reduces Lp(a) by ~25-30%

Clinical Outcomes

Adverse Effects

• Flushing - prostaglandin-mediated, most common side effect; can be reduced by taking aspirin 30 minutes before, using extended-release formulation, taking at bedtime, avoiding hot beverages/alcohol.
• Hepatotoxicity - especially with immediate-release niacin at high doses
• Hyperglycemia - worsens insulin resistance
• Hyperuricemia / gout exacerbation
• GI: nausea, diarrhea
• Acanthosis nigricans (skin darkening)

8. Omega-3 Fatty Acids

Mechanism

Cardiovascular Evidence

Adverse Effects

9. Bempedoic Acid

Mechanism

• Because activation occurs only in hepatocytes, skeletal muscle is spared → lower risk of myopathy than statins.

Efficacy

• Reduces LDL-C by ~18-25% vs placebo
• Combined with ezetimibe (Nexlizet): reduces LDL-C by ~38%
• ~12% reduction in subsequent cardiovascular events

Key Role

Adverse Effects

10. Evinacumab (ANGPTL3 Inhibitor)

Mechanism

Indication

Triglyceride-Lowering Drug Efficacy Comparison

Approach to Statin Intolerance

1. Stop statin
2. Wait until symptoms resolve
3. Rechallenge with lower dose of same statin, or alternative statin
4. Titrate up as tolerated

1. Stop statin
2. Check CK, creatinine/GFR, urine myoglobin
3. Admit if CK >10× ULN with elevated creatinine or myoglobinuria
4. Evaluate predisposing factors

Blinded rechallenge studies show >75-80% of patients reporting "statin intolerance" can tolerate atorvastatin 20 mg as blinded therapy - the "nocebo effect" is a major contributor.

Treatment Algorithm (2018 AHA/ACC Guidelines)

Step 1: Lifestyle modification (diet, exercise)
         ↓
Step 2: Statin (first-line; high-intensity preferred for high/very high risk)
         ↓
Step 3: If LDL-C remains ≥70 mg/dL on maximally tolerated statin:
         Add Ezetimibe
         ↓
Step 4: If still inadequate:
         Add PCSK9 inhibitor (alirocumab or evolocumab)
         OR Inclisiran (every 6 months dosing)
         OR Bempedoic acid (especially if statin-intolerant)
         ↓
Hypertriglyceridemia (TG ≥500 mg/dL):
         Fibrate or Omega-3 FA to prevent pancreatitis
         ↓
Icosapentaenoic acid (Vascepa):
         For residual TG elevation (≥150 mg/dL) on statin at high CV risk

Special Populations

Recent Evidence (2025-2026)

• A 2025 network meta-analysis in J Cardiovasc Pharmacol (PMID 40358978) compared the efficacy of non-statin lipid-lowering therapies, showing the comparative superiority of PCSK9 inhibitors over ezetimibe and other agents for LDL-C reduction.
• A 2025 meta-analysis in Atherosclerosis (PMID 40618457) examined effects of various lipid-lowering therapies on Lp(a), finding that PCSK9 inhibitors significantly reduce Lp(a) by 20-30%, a benefit not seen with statins.
• PCSK9 inhibitors now have evidence for peripheral arterial disease reduction as well (2026 systematic review).

Prostaglandins - Lippincott Illustrated Reviews: Pharmacology

Overview

I. Role of Prostaglandins as Local Mediators

• Prostaglandins are produced in minute quantities by virtually all tissues
• They act locally on the tissues in which they are synthesized (paracrine/autocrine)
• Rapidly metabolized to inactive products at their sites of action
• Therefore, prostaglandins do not circulate in the blood in significant concentrations
• Thromboxanes and leukotrienes are related compounds synthesized from the same precursors

II. Synthesis of Prostaglandins

Step 1 - Release of Arachidonic Acid

Glucocorticoids inhibit phospholipase A2 (via lipocortin/annexin-1), reducing arachidonic acid availability - one mechanism of their powerful anti-inflammatory effect.

Step 2 - Two Major Pathways

A. Cyclooxygenase (COX) Pathway - Eicosanoids with Ring Structures

COX-1 vs COX-2

COX-2 has a larger and more flexible substrate channel than COX-1, with a larger space at the inhibitor binding site - this difference allowed the development of selective COX-2 inhibitors (celecoxib).

Biosynthetic Steps (COX Pathway)

1. Cyclooxygenase acts on arachidonic acid → forms the 5-membered ring + adds 4 oxygen atoms → unstable endoperoxide PGG₂
2. Peroxidase reduces hydroperoxy group at C-15 → PGH₂ (using glutathione as reducing agent)
3. PGH₂ is the branch point - downstream products depend on tissue-specific enzymes:

B. Lipoxygenase (LOX) Pathway

• Zileuton inhibits 5-lipoxygenase (blocks leukotriene synthesis)
• Zafirlukast, Montelukast - leukotriene receptor antagonists (used in asthma)

III. Actions of Prostaglandins

Key Functional Dichotomy: TXA₂ vs PGI₂

The net effect on platelets and blood vessels depends on the balance between TXA₂ and PGI₂.

Summary of Prostaglandin Actions by Type

Role in Pain, Fever, and Inflammation

• Pain: PGE₂ sensitizes peripheral nerve endings to bradykinin, histamine, and other inflammatory mediators → lowers threshold for nociception
• Fever: Endogenous pyrogens (cytokines) → ↑ PGE₂ in hypothalamus → elevates thermoregulatory set-point → fever. NSAIDs reverse this by blocking PGE₂.
• Inflammation: Prostaglandins promote vasodilation, vascular permeability, and leukocyte recruitment

IV. Therapeutic Uses of Prostaglandins

V. Prostaglandin Drug Classes

A. PGE₁ Analogs

1. Alprostadil (Caverject, Edex, MUSE, Prostin VR)

• Naturally produced in seminal vesicles, cavernous tissue, placenta, and ductus arteriosus
• PGE₁ maintains patency of the ductus arteriosus during fetal life
• Clinical uses:
  • Neonates with congenital heart defects - IV infusion keeps ductus arteriosus open while awaiting surgical correction
  • Erectile dysfunction - intracavernosal injection or intraurethral suppository

2. Lubiprostone (Amitiza)

• PGE₁ derivative
• Stimulates chloride channels (ClC-2) in intestinal epithelial luminal cells → ↑ intestinal fluid secretion
• Uses: Chronic idiopathic constipation, opioid-induced constipation, IBS with constipation
• Adverse effects: Nausea (most common - reduced if taken with food), diarrhea

3. Misoprostol (Cytotec)

• Synthetic PGE₁ analog (acid-stable, orally bioavailable - unlike natural PGE₁)
• Mechanism: Binds prostaglandin receptors on gastric parietal cells → ↓ gastric acid secretion + ↑ mucus and bicarbonate production
• Uses:
  • Prevention of NSAID-induced gastric ulcers (combined with NSAIDs, including diclofenac-misoprostol fixed combination)
  • Off-label obstetric use: Cervical ripening and labor induction (stimulates uterine contractions via uterine prostaglandin receptors)
• Contraindicated in pregnancy (can induce abortion)
• Adverse effects: Diarrhea, abdominal cramps

B. PGE₂ Analogs

Dinoprostone (Cervidil, Prepidil)

• Synthetic PGE₂ analog
• Uses: Cervical ripening and labor induction
• Promotes uterine smooth muscle contractions

C. PGF₂α Analogs (Prostaglandin Analogs for Glaucoma)

• Iris pigmentation (irreversible darkening of iris color - especially in hazel/green eyes)
• Eyelash changes (increased length, thickness, darkening)
• Conjunctival hyperemia
• Local irritation

D. PGI₂ (Prostacyclin) Analogs

VI. Pharmacological Inhibition of Prostaglandin Synthesis

NSAIDs - Mechanism Summary

Aspirin - Special Mechanism

Clinical Consequences of COX Inhibition

Summary Diagram of Clinical Applications

PROSTAGLANDIN ANALOGS:
├── PGE₁ (Alprostadil) ──→ Patent ductus arteriosus (neonates), Erectile dysfunction
├── PGE₁ (Lubiprostone) ──→ Constipation, IBS
├── PGE₁ (Misoprostol) ──→ Gastric ulcer prevention (anti-NSAID), Labor induction
├── PGE₂ (Dinoprostone) ──→ Cervical ripening, Labor induction
├── PGF₂α (Latanoprost, Bimatoprost, etc.) ──→ Glaucoma (↓ IOP)
└── PGI₂ (Epoprostenol, Iloprost, Treprostinil) ──→ Pulmonary arterial hypertension

PROSTAGLANDIN INHIBITORS (NSAIDs):
├── Non-selective (Ibuprofen, Naproxen) ──→ Anti-inflammatory, Analgesia, Antipyresis
├── Aspirin (irreversible) ──→ Antiplatelet, Analgesia, Antipyresis
└── COX-2 selective (Celecoxib) ──→ Anti-inflammatory with ↓ GI side effects

NSAIDs (Non-Steroidal Anti-Inflammatory Drugs)

Lippincott Illustrated Reviews: Pharmacology

I. Overview & Classification

Chemical Classes of NSAIDs

Key principle: COX-2 inhibition → anti-inflammatory and analgesic actions. COX-1 inhibition → prevention of cardiovascular events but also most adverse effects (GI, renal, platelet).

II. COX-1 vs COX-2 Selectivity

III. Mechanism of Action

Three Therapeutic Actions:

1. Anti-inflammatory - ↓ PG-mediated vasodilation, vascular permeability, leukocyte recruitment
2. Analgesic - ↓ PGE₂, which normally sensitizes nociceptors to bradykinin and histamine
3. Antipyretic - ↓ PGE₂ synthesis in hypothalamus → reset of thermoregulatory set-point → ↑ heat dissipation (vasodilation + sweating); no effect on normal body temperature

IV. Aspirin - The Prototype

Unique Mechanism: Irreversible COX Inhibition

Aspirin Dose-Dependent Effects

V. Therapeutic Uses of NSAIDs

A. Anti-inflammatory and Analgesic Uses

• Osteoarthritis, rheumatoid arthritis (RA), gout
• Headache, arthralgia, myalgia, dysmenorrhea
• Combinations with opioids for cancer pain (opioid-sparing effect)
• Salicylates: analgesic at lower doses; anti-inflammatory only at higher doses (12-20 aspirin tablets/day)

B. Antipyretic Uses

• Aspirin, ibuprofen, naproxen for fever
• ⚠ Aspirin CONTRAINDICATED in patients < 19 years with viral infections (varicella, influenza) → risk of Reye syndrome (fulminating hepatitis + cerebral edema, often fatal)
• Acetaminophen is the preferred antipyretic for children

C. Cardiovascular Applications (Aspirin)

• Aspirin irreversibly inhibits COX-1-mediated TXA₂ production in platelets
• Since platelets are anucleate (cannot synthesize new COX), the antiplatelet effect lasts the entire platelet lifespan (3-7 days)
• Low-dose aspirin (81-325 mg/day): reduces risk of MI, stroke, TIA
• Used in both primary and secondary cardiovascular prevention
• ⚠ Concomitant NSAID use may prevent aspirin from binding COX → patients should take aspirin at least 30 minutes before the NSAID

D. External/Topical Uses

• Salicylic acid (topical): acne, corns, calluses, warts
• Methyl salicylate ("oil of wintergreen"): counterirritant in arthritis creams, sports rubs
• Diclofenac gel/solution: topical treatment of osteoarthritis (knees/hands)
• Ketorolac eye drops: seasonal allergic conjunctivitis, post-ocular surgery pain/inflammation

VI. Pharmacokinetics

Aspirin

• Rapidly deacetylated by esterases → salicylate (active)
• Absorbed mainly from the upper small intestine (unionized form)
• Crosses the blood-brain barrier and placenta
• Hepatic conjugation → water-soluble metabolites → renal excretion
• At analgesic doses (<4 g/day): first-order kinetics, half-life ~3.5 hours
• At anti-inflammatory doses (>4 g/day): hepatic pathway saturates → zero-order kinetics, half-life up to 12+ hours

Low-dose aspirin decreases uric acid excretion → avoid in gout or in patients taking probenecid.

Other NSAIDs

• Well absorbed orally
• Highly protein-bound in plasma
• Metabolized by the liver (mostly to inactive metabolites)
• Exceptions with active metabolites: nabumetone, sulindac
• Excreted primarily via urine

VII. Adverse Effects

A. Gastrointestinal (Most Common)

• Take NSAIDs with food or fluids to reduce GI upset
• High-risk patients: add proton pump inhibitor (PPI) or misoprostol (PGE₁ analog - restores gastric protection)

B. Antiplatelet Effect / Bleeding

• All NSAIDs (not just aspirin) can prolong bleeding time
• Aspirin's antiplatelet effect: irreversible, lasts 3-7 days → withhold aspirin ≥1 week before surgery
• NSAIDs + anticoagulants: increased bleeding risk

C. Renal Effects

• ↓ PGE₂ and PGI₂ → ↓ renal blood flow → sodium and water retention, edema
• Can worsen heart failure, hypertension
• Blunts effects of antihypertensive medications
• May precipitate acute kidney injury in susceptible patients (renal disease, HF, volume depletion)

D. Cardiovascular Effects

• Aspirin (high COX-1 selectivity) → ↓ TXA₂ → cardioprotective
• COX-2 selective agents → ↓ endothelial PGI₂ WITHOUT reducing platelet TXA₂ → prothrombotic imbalance → ↑ risk of MI and stroke
• All NSAIDs except aspirin carry a Black Box Warning for increased cardiovascular risk
• In patients with cardiovascular disease who need an NSAID: naproxen is considered the least harmful
• NSAIDs other than aspirin: discouraged in established cardiovascular disease

E. Respiratory / Hypersensitivity

• NSAIDs block COX but NOT lipoxygenase → arachidonic acid is shunted into the leukotriene pathway → bronchoconstriction
• Aspirin-exacerbated respiratory disease (AERD) / Samter's triad: asthma + nasal polyps + NSAID sensitivity
  • NSAIDs → ↑ leukotrienes → bronchospasm, rhinorrhea, urticaria
  • Treatment: leukotriene receptor antagonists (zafirlukast, montelukast)

F. Salicylate Toxicity

• Restlessness, delirium, hallucinations, convulsions, coma
• Mixed respiratory and metabolic acidosis
• Death from respiratory failure
• Children particularly susceptible (as little as 10 g can be fatal)

G. Pregnancy

• NSAIDs should only be used if benefits outweigh risks
• Third trimester: generally AVOID - risk of premature closure of the ductus arteriosus
• Acetaminophen preferred for analgesia/antipyresis in pregnancy

VIII. Drug Interactions

IX. Selective COX-2 Inhibitor: Celecoxib

Mechanism

Therapeutic Uses

• Osteoarthritis, RA, acute pain (similar analgesic efficacy to other NSAIDs)

Pharmacokinetics

• Well absorbed orally
• Metabolized by CYP2C9 in the liver
• Half-life ~11 hours (once or twice daily dosing)
• Reduce dose in moderate hepatic impairment; avoid in severe hepatic or renal disease

Advantages over Non-selective NSAIDs

• Less GI bleeding and dyspepsia (spares COX-1-mediated gastric protection)
• However, this benefit is lost when aspirin is co-administered

Disadvantages

• ↑ Cardiovascular risk (↓ endothelial PGI₂ without affecting platelet TXA₂)
• All NSAIDs (including celecoxib) carry a cardiovascular Black Box Warning

X. Summary of NSAID Advantages and Disadvantages

XI. Acetaminophen (Paracetamol) - For Comparison

Mechanism

• Inhibits prostaglandin synthesis in the CNS → antipyretic + analgesic
• Weak peripheral COX inhibition (due to peripheral inactivation) → minimal anti-inflammatory activity
• Does not affect platelet function or bleeding time

Uses

• Fever and mild-moderate pain
• Preferred in: children with viral infections (no Reye risk), GI-sensitive patients, pregnancy (preferred analgesic), patients who don't need anti-inflammatory action

Metabolism and Toxicity

Toxicity Treatment

• N-acetylcysteine (NAC) - replenishes glutathione; most effective if given within 8-10 hours of overdose
• Acetaminophen overdose is a leading cause of acute liver failure in the developed world

Quick Comparison: NSAIDs vs Acetaminophen

Gout - Drugs for Treatment

Lippincott Illustrated Reviews: Pharmacology

I. Pathophysiology of Gout

Mechanism of Crystal-Induced Inflammation

1. Purines (from DNA, RNA catabolism) → Hypoxanthine → Xanthine → Uric acid (via xanthine oxidase)
2. Uric acid accumulates above the saturation point (>6 mg/dL) → deposits as sodium urate crystals in joints (especially the 1st MTP joint / big toe, knees, ankles, wrists, elbows) and kidneys (urate nephropathy, nephrolithiasis)
3. Neutrophils phagocytize urate crystals → crystals resist digestion → lysosomal rupture → release of hydrolytic enzymes and leukotrienes → acute inflammation
4. Colchicine interrupts this cycle by inhibiting neutrophil migration

Clinical Presentation

• Acute flares: sudden, severe pain, swelling, tenderness, warmth, and redness in the affected joint
• Triggered by: excessive alcohol, diet rich in purines (red meat, shellfish), dehydration, certain drugs (thiazide diuretics, low-dose aspirin), kidney disease, chemotherapy

Therapeutic Goal

• Inhibiting uric acid synthesis (xanthine oxidase inhibitors)
• Increasing uric acid excretion (uricosuric agents)

II. Treatment Overview

III. Treatment of Acute Gout

A. NSAIDs

• Indomethacin is the classic NSAID of choice for acute gout
• All NSAIDs are likely effective in decreasing pain and inflammation during acute attacks
• Use at maximum doses for shortest duration possible
• Avoid in patients with renal impairment (reduces renal blood flow), peptic ulcer disease, or those already on anticoagulants
• ⚠ Low-dose aspirin is contraindicated in gout - at low doses, aspirin decreases renal uric acid excretion and can worsen hyperuricemia

B. Corticosteroids

• Intra-articular corticosteroids are effective when only 1-2 joints are involved
• Systemic corticosteroids (oral prednisone) used when NSAIDs/colchicine are contraindicated or poorly tolerated

C. Colchicine (see full section below)

• Effective for acute attacks but NSAIDs have largely replaced it due to safety profile
• Must be given within 36 hours of attack onset to be effective

IV. Colchicine (Colcrys)

Mechanism of Action

1. Disrupts neutrophil cytoskeleton → ↓ neutrophil motility and migration into inflamed joints
2. Blocks phagocytosis of urate crystals by neutrophils → ↓ leukotriene and hydrolytic enzyme release
3. Blocks cell division by binding to mitotic spindles (affects rapidly dividing cells)

The anti-inflammatory activity of colchicine is specific for gout - this selectivity has diagnostic value.

Therapeutic Uses

• Acute gout: usually relieves pain within 12 hours (must be given within 36 hours of onset)
• Prophylaxis against acute gout attacks during initiation of urate-lowering therapy

Pharmacokinetics

• Oral administration, rapidly absorbed from GI tract
• Metabolized by CYP3A4 in liver and other tissues
• Undergoes enterohepatic recirculation
• High interpatient variability in elimination half-life
• Portion excreted unchanged in urine

Adverse Effects

Drug Interactions (Important)

• CYP3A4 inhibitors (clarithromycin, itraconazole) → ↑ colchicine levels → require dose adjustment
• P-glycoprotein (P-gp) inhibitors (amiodarone, verapamil) → ↑ colchicine levels → require dose adjustment
• Severe renal impairment → dose reduction required

V. Treatment of Chronic Gout (Urate-Lowering Therapy)

Key Principle:

⚠ Starting urate-lowering therapy can precipitate an acute gout attack due to rapid shifts in serum urate concentrations (crystal mobilization). Therefore, co-prescribe prophylactic low-dose colchicine, NSAIDs, or corticosteroids for at least 6 months when initiating any urate-lowering agent.

VI. Xanthine Oxidase Inhibitors - First-Line for Chronic Gout

A. Allopurinol (Zyloprim) - Preferred first-line

Mechanism

• Hypoxanthine → Xanthine, AND
• Xanthine → Uric acid

Therapeutic Uses

• First-line urate-lowering therapy for gout (preferred over febuxostat and probenecid)
• Hyperuricemia secondary to malignancy (tumor lysis syndrome - especially post-chemotherapy when large amounts of purines are released)
• Hyperuricemia due to renal disease

Pharmacokinetics

• Completely absorbed orally
• Metabolized to alloxanthine (oxypurinol) - also an active xanthine oxidase inhibitor
• Alloxanthine has a half-life of 15-18 hours → allows once-daily dosing
• Drug and active metabolite excreted in urine
• ⚠ Dose reduction required if eGFR < 30 mL/min/1.73 m²

Adverse Effects

• Generally well tolerated
• Hypersensitivity reactions (skin rashes) - most common adverse reaction; risk increased in reduced renal function
• Allopurinol hypersensitivity syndrome (rare but severe): fever, exfoliative dermatitis (Stevens-Johnson syndrome/TEN), hepatitis, renal failure
• Acute gout flares more frequent during first months of therapy → use prophylactic colchicine/NSAIDs concurrently

Drug Interactions

• Azathioprine and 6-mercaptopurine - Allopurinol inhibits xanthine oxidase, which is responsible for their metabolism → markedly ↑ toxicity → dose reduction of azathioprine/6-MP by 50-75% required

B. Febuxostat (Uloric)

Mechanism

Advantages over Allopurinol

• Less renal elimination → less dosage adjustment in renal impairment
• Lower risk of rash/hypersensitivity reactions compared to allopurinol

Disadvantages

• ⚠ Associated with greater risk of cardiovascular events (MI, stroke) compared to allopurinol
• Reserved for patients who have contraindications to, or cannot tolerate, allopurinol

VII. Uricosuric Agent

Probenecid (Generic only)

Mechanism

Use

• Second-line option for patients intolerant to xanthine oxidase inhibitors or with inadequate response
• Also used to increase serum levels of certain antibiotics (e.g., penicillins, cephalosporins) by blocking their renal tubular secretion

Limitations and Precautions

• ⚠ Avoid if creatinine clearance < 50 mL/min (inadequate urine flow to excrete the extra uric acid, risk of renal stones)
• ⚠ Low-dose aspirin antagonizes probenecid's uricosuric effect (aspirin at low doses promotes uric acid retention)
• Adequate hydration and urine alkalinization required to prevent urate stone formation
• Adverse effects: Nausea, vomiting, dermatologic reactions, rarely anemia or anaphylaxis

VIII. Recombinant Uricase

Pegloticase (Krystexxa) - Last Resort

Mechanism

Indications

• Refractory/severe gout - patients who fail standard therapies (xanthine oxidase inhibitors)
• Can rapidly lower serum urate even in very high levels

Administration

• IV infusion every 2 weeks
• Premedicate with antihistamines + corticosteroids to reduce infusion reactions

Adverse Effects

• Infusion-related reactions (most important) - flushing, chest discomfort, dyspnea
• Anaphylaxis - risk highest in patients who develop anti-drug antibodies
• Gout flares may increase during early treatment

IX. Drug Summary: Mechanism Comparison

URIC ACID OVERPRODUCTION
└── Xanthine Oxidase Inhibitors
    ├── Allopurinol (1st line) - purine analog; competitively inhibits XO
    └── Febuxostat - non-purine XO inhibitor; less renal adjustment needed

URIC ACID UNDEREXCRETION  
└── Uricosuric Agent
    └── Probenecid - blocks URAT1 in proximal tubule → ↑ renal excretion

DIRECT URIC ACID DEGRADATION
└── Recombinant uricase
    └── Pegloticase - uric acid → allantoin (refractory gout)

ACUTE ATTACK MANAGEMENT
├── NSAIDs (Indomethacin - classic choice)
├── Corticosteroids (intra-articular or systemic)
└── Colchicine - binds tubulin → ↓ neutrophil migration

X. Key Drug Interactions Summary

XI. Clinical Pearls

• Serum uric acid target: < 6 mg/dL (some guidelines target < 5 mg/dL in tophaceous gout)
• Never start urate-lowering therapy during an acute attack - wait until attack resolves, then initiate with prophylactic colchicine cover
• Naproxen preferred if NSAIDs needed in gout patients with cardiovascular disease (least cardiovascular risk)
• Febuxostat preferred over allopurinol in renal impairment (less renal adjustment); but caution for CV risk
• Pegloticase is the most powerful urate-lowering agent but is reserved for refractory cases due to infusion reactions and cost
• Dietary advice: avoid high-purine foods (red meat, organ meats, shellfish), alcohol (especially beer), high-fructose corn syrup; maintain hydration

Rheumatoid Arthritis - Drug Treatment

Lippincott Illustrated Reviews: Pharmacology

I. Pathophysiology of RA

• IL-1 and TNF-α - proinflammatory cytokines secreted by synovial macrophages
• These cytokines stimulate synovial cells to proliferate and synthesize collagenase
• Collagenase degrades articular cartilage, stimulates bone resorption, and inhibits proteoglycan synthesis
• Net result: pannus formation, erosion of bone and cartilage, joint deformity and loss of function

Diagnosis (Clinical Application 40.1)

Early diagnosis and early treatment are critical - the disease causes progressive joint destruction and loss of function if untreated.

II. Classification of Drugs Used in RA

Treatment Algorithm

DIAGNOSIS OF RA
      ↓
Start Traditional DMARD immediately
(Methotrexate preferred; alternatives: HCQ, Leflunomide, Sulfasalazine)
      ↓
Use NSAIDs / glucocorticoids as bridge therapy
      ↓
Inadequate response to methotrexate?
      ↓
Add Biologic DMARD (TNF-α inhibitor preferred) OR non-TNF biologic DMARD
OR add JAK inhibitor
      ↓
Combination: Methotrexate + Biologic DMARD most effective for remission

III. Traditional (Conventional) DMARDs

A. Methotrexate (Otrexup, Trexall) - First-Line Preferred

Mechanism

• Inhibits cytokine production
• Inhibits purine nucleotide biosynthesis → leads to immunosuppressive and anti-inflammatory effects

Key Features

• Mainstay of RA treatment - the anchor drug for most RA regimens
• Response occurs within 3-6 weeks of starting treatment
• Dosed once weekly (unlike cancer dosing) → minimizes adverse effects
• Can be combined with traditional or biologic DMARDs when monotherapy is inadequate

Adverse Effects

✅ Folic acid supplementation reduces GI and hepatic adverse effects and improves tolerability - routinely co-prescribed. ⚠ Periodic monitoring: LFTs, CBC, signs of infection ⚠ Contraindicated in pregnancy (teratogenic, abortifacient)

B. Hydroxychloroquine (Plaquenil)

Mechanism

Uses

• Early, mild RA - often used as initial therapy
• Frequently combined with methotrexate (triple therapy with sulfasalazine)
• Also used in SLE

Key Features

• Onset of effect: 6 weeks to 6 months (slow onset)
• Fewer adverse effects on liver and immune system than other DMARDs

Adverse Effects

C. Leflunomide (Arava)

Mechanism

• Actively proliferating lymphocytes depend on de novo pyrimidine synthesis → leflunomide selectively arrests these cells
• Mature non-dividing cells can use salvage pathways and are less affected

Uses

• Monotherapy when methotrexate is not tolerated or contraindicated
• Combination with methotrexate for suboptimal methotrexate response

Adverse Effects

• Headache, diarrhea, nausea (common)
• Weight loss, flu-like syndrome, skin rash, alopecia, hypokalemia
• Hepatotoxicity - not recommended in liver disease; monitor liver enzymes
• Contraindicated in pregnancy

Monitoring

D. Sulfasalazine (Azulfidine)

Mechanism

Key Features

• Onset of activity: 1-3 months
• Similar indications to leflunomide
• Used in mild-moderate RA; part of triple therapy with methotrexate + hydroxychloroquine

Adverse Effects

• GI (most common): nausea, vomiting, anorexia
• Leukopenia

E. Glucocorticoids (Symptomatic / Bridge Therapy)

• Potent anti-inflammatory (inhibit phospholipase A2, block arachidonic acid cascade, reduce cytokine production)
• Used to:
  1. Provide symptomatic relief during acute flares
  2. Bridge the gap while waiting for DMARDs to become effective (weeks to months)
• Always used at the lowest dose for the shortest duration possible to avoid long-term adverse effects (osteoporosis, adrenal suppression, hyperglycemia, Cushing syndrome, etc.)
• Intra-articular corticosteroids for 1-2 severely affected joints

IV. Biologic DMARDs

• Inadequate response to traditional DMARDs (especially methotrexate)
• Guidelines recommend adding a TNF-α inhibitor or non-TNF biologic DMARD in such cases

Class-Wide Safety Warnings (All Biologic DMARDs)

⚠ Increased risk of serious infections - TB, fungal opportunistic infections, sepsis ⚠ Screen for latent TB before starting any biologic (with TST/IGRA) ⚠ Hepatitis B reactivation risk - screen before initiation ⚠ No live vaccines during biologic therapy ⚠ Do NOT combine TNF-α inhibitors + non-TNF biologic DMARDs (severe infection risk)

A. TNF-α Inhibitors (5 agents)

TNF-α Inhibitor-Specific Adverse Effects

• Headache, nausea, rash, injection site reactions (SC agents)
• Infusion reactions with infliximab (fever, chills, pruritus, urticaria)
• Risk of lymphoma and other malignancies (Black Box Warning)
• Caution in heart failure (can cause/worsen HF)
• Reactivation of TB and hepatitis B

Combination Superiority:

B. IL-6 Receptor Antagonists

Tocilizumab (Actemra) and Sarilumab (Kevzara)

• Recombinant monoclonal antibodies that bind to IL-6 receptors, inhibiting pro-inflammatory IL-6 activity
• IL-6 drives synovitis, acute-phase response (↑ CRP), and joint destruction
• Both can be used as monotherapy (unlike most other biologics which benefit from methotrexate combination)
• Tocilizumab: IV or SC; Sarilumab: SC
• Adverse effects: Neutropenia, thrombocytopenia, elevated LFTs, GI perforation (rare), increased infection risk
• Monitoring: CBC, LFTs, lipids

C. Costimulation Blocker - Abatacept (Orencia)

Mechanism

• Route: IV infusion monthly or SC weekly
• Response takes several weeks to months
• Preferred in patients with seropositive RA (RF+, anti-CCP+)
• Adverse effects: Headache, nausea, nasopharyngitis, increased infection risk
• Do NOT combine with TNF-α inhibitors

D. Anti-CD20 Antibody - Rituximab (Rituxan)

Mechanism

• Administered as IV infusion (two doses 2 weeks apart, repeated every 6 months)
• Used in RA refractory to TNF-α inhibitors or where TNF-α inhibitors are contraindicated
• Adverse effects:
  • Infusion reactions (premedicate with corticosteroid + antihistamine + acetaminophen)
  • Progressive multifocal leukoencephalopathy (PML) (rare, caused by JC virus reactivation)
  • Hepatitis B reactivation
  • Cytopenias, infection risk

V. Targeted Synthetic DMARDs - JAK Inhibitors

Indication

• Moderate-severe established RA with inadequate response or intolerance to methotrexate and TNF-α inhibitors

Pharmacokinetics

• All metabolized primarily by CYP3A4; dose adjustments needed with potent CYP3A4 inhibitors/inducers

Adverse Effects and Monitoring

Due to long-term safety concerns, JAK inhibitors are generally reserved for patients with inadequate response or intolerance to other agents.

VI. Other Agents Used in RA (Less Common)

• Adverse effect profile
• Availability of more effective/safer agents

VII. NSAIDs in RA

• Provide symptomatic relief (pain, stiffness, swelling) but do NOT modify disease progression
• Do not prevent joint destruction or induce remission
• Used adjunctively alongside DMARDs

VIII. Summary Comparison of All RA Drug Classes

                    RHEUMATOID ARTHRITIS TREATMENT
                              │
        ┌─────────────────────┼─────────────────────┐
        │                     │                     │
   SYMPTOMATIC           TRADITIONAL            BIOLOGIC/TARGETED
  (No disease          DMARDs (1st line)          DMARDs (2nd line)
  modification)              │                      │
        │                    │              ┌────────┴────────┐
   NSAIDs              Methotrexate      TNF-α          Non-TNF
   Glucocorti-         (preferred)     Inhibitors      Biologics
   coids               HCQ             Adalimumab    IL-6R: Tocilizumab
   (bridge)            Leflunomide     Certolizumab  Costimulation:
                       Sulfasalazine   Etanercept    Abatacept
                                       Golimumab     B-cell: Rituximab
                                       Infliximab
                                                     JAK Inhibitors
                                                     (3rd line)
                                                     Tofacitinib
                                                     Baricitinib
                                                     Upadacitinib

IX. Key Drug Monitoring Requirements

X. Contraindications Summary