1. Conventional/Unfractionated Heparin and Low Molecular Weight Heparin - differences* 2. Warfarin - MOA, therapeutic uses adv effect, precaution 3. Low Molecular Weight Heparins - MOA, therapeutic uses adv effect, precaution 4. Streptokinase and Alteplase - compare and contrast 5. Anti-Platelet Drugs moa uses adv effect, precaution 6. Fibrinolytic Agents - mention, impotence in clinical use adv effect, precaution 7. Thrombolytic Drugs - enumerate, Alteplase - indications, adverse effects precaution answer in detail for 2 mbbs pharmacology refer kdt detail answer

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Here is the complete, detailed 2nd MBBS Pharmacology answer based on Katzung's Basic and Clinical Pharmacology (KDT-equivalent content):

Anticoagulants, Antiplatelet Drugs, and Thrombolytics

(2nd MBBS Pharmacology - Based on KDT / Katzung)

1. Conventional (Unfractionated) Heparin vs. Low Molecular Weight Heparin - Differences

Feature	Unfractionated Heparin (UFH)	Low Molecular Weight Heparin (LMWH)
Molecular Weight	5,000 - 30,000 Da (heterogeneous)	~5,000 Da (mean), homogeneous
Source/Preparation	Crude extract from bovine lung / porcine intestine	Derived from UFH by controlled enzymatic or chemical depolymerization
Mechanism	Inhibits thrombin (IIa), IXa, and Xa equally	Mainly inhibits Factor Xa; anti-Xa : anti-IIa ratio = 2:1 to 4:1
Route	IV or SC (not IM)	SC (IV if rapid effect needed)
Bioavailability (SC)	Low, erratic (~30%)	High, predictable (~90%)
Half-life	Short, dose-dependent (30 min - 2 hr)	Longer, ~4 hours; non-dose-dependent
Monitoring	Mandatory - aPTT (target: 1.5-2.5x baseline)	Usually not required; anti-Xa levels if needed (0.5-1.2 U/mL)
Dosing	Continuous IV infusion or 2-3x daily SC	Once or twice daily SC
Protein binding	Extensive (binds endothelial cells, macrophages, plasma proteins)	Minimal binding - more predictable response
Clearance	Saturable, dose-dependent (rapid phase + slow renal)	Renal, non-dose-dependent
Renal impairment	Dose adjustment less critical	Accumulates - monitor in CrCl <30 mL/min
HIT risk	1-4% (bovine > porcine)	Lower risk
Reversal	Protamine sulfate (1 mg per 100 U heparin)	Partial reversal by protamine (~60%)
Osteoporosis	Yes (with long-term use)	Less likely
Outpatient use	Difficult (requires hospital monitoring)	Possible - home treatment as effective as hospital UFH
Placental transfer	Does not cross placenta	Does not cross placenta
Pregnancy	Safer than warfarin; use only if clearly indicated	Preferred in pregnancy
Examples	Heparin sodium	Enoxaparin, Dalteparin, Tinzaparin

2. Warfarin - MOA, Therapeutic Uses, Adverse Effects, Precautions

Mechanism of Action

Warfarin is an oral anticoagulant that acts as a vitamin K antagonist. It inhibits the enzyme Vitamin K epoxide reductase (VKOR), blocking the regeneration of the active reduced form of Vitamin K (Vitamin KH2). Vitamin K is required as a cofactor for gamma-carboxylation of glutamate residues on clotting factors II (prothrombin), VII, IX, and X, as well as anticoagulant proteins C and S.

Key pharmacodynamic points:

Warfarin does NOT destroy existing clotting factors; it inhibits new synthesis only
Onset of action is delayed 8-12 hours and full effect takes 3-5 days (reflects degradation half-lives of existing factors)
Factor half-lives: Factor VII = 6 hr, IX = 24 hr, X = 40 hr, II = 60 hr
Transient hypercoagulable state on initiation: Protein C has a short half-life like Factor VII, so early warfarin depletes the anticoagulant Protein C before fully depleting procoagulant factors - hence UFH/LMWH must be overlapped for 5-7 days
Monitored by INR (International Normalized Ratio); target INR = 2-3 for most indications; 2.5-3.5 for mechanical heart valves

Therapeutic Uses

Prevention and treatment of deep vein thrombosis (DVT)
Prevention and treatment of pulmonary embolism (PE)
Prevention of thromboembolism in atrial fibrillation (non-valvular and valvular)
Prevention of embolism in patients with prosthetic heart valves
Secondary prevention after myocardial infarction (in some patients)
Prevention of recurrent venous thromboembolism

Adverse Effects

Bleeding - the major toxicity (GI, intracranial, genitourinary, skin). Risk increased with INR >3, elderly, concurrent NSAIDs/aspirin
Teratogenicity - crosses placenta; causes:
- Fetal warfarin syndrome (nasal hypoplasia, bone stippling, optic atrophy) - first trimester
- CNS abnormalities - second/third trimester
- Fetal hemorrhage - near delivery
- Absolutely contraindicated in pregnancy
Skin/tissue necrosis - rare; occurs in first weeks, especially in patients with hereditary Protein C deficiency. Capillary/venous thrombosis in skin due to rapid depletion of Protein C before procoagulant factors fall
Purple toe syndrome - rare cholesterol microembolism syndrome
Drug interactions - extremely numerous:
- Potentiation (increased bleeding risk): broad-spectrum antibiotics (reduce gut bacteria/Vit K), cimetidine, amiodarone, fluconazole, metronidazole, salicylates, phenylbutazone
- Inhibition (reduced anticoagulation): rifampicin, barbiturates, carbamazepine (enzyme inducers), cholestyramine

Precautions / Contraindications

Contraindicated in pregnancy (especially first trimester)
Contraindicated in patients with active bleeding, severe hypertension, bacterial endocarditis, recent neurosurgery/eye surgery
Use with caution in hepatic disease (reduced factor synthesis baseline), renal disease, alcoholism
Frequent INR monitoring mandatory, especially on initiation or dose changes
Reversal: Vitamin K1 (phytomenadione) for slow reversal; Fresh Frozen Plasma (FFP) or 4-factor PCC for immediate reversal in life-threatening bleeding
Genetic polymorphisms (CYP2C9, VKORC1) affect dosing requirements significantly

3. Low Molecular Weight Heparins (LMWH) - MOA, Therapeutic Uses, Adverse Effects, Precautions

Mechanism of Action

LMWH (e.g., enoxaparin, dalteparin, tinzaparin) are prepared from UFH by depolymerization. Their shorter chains (mean MW ~5,000 Da, ~17 saccharide units):

Still contain the critical pentasaccharide sequence that binds antithrombin, activating it
The conformational change in antithrombin produced by pentasaccharide binding is sufficient to inhibit Factor Xa
However, the chains are too short to bridge thrombin to antithrombin (requires 18+ saccharide units)
Result: Selective inhibition of Factor Xa >> Thrombin; anti-Xa : anti-IIa ratios of 2:1 to 4:1
Fondaparinux (synthetic pentasaccharide) takes this further - purely anti-Xa, no effect on thrombin at all

Therapeutic Uses

Treatment and prevention of DVT and PE (venous thromboembolism - VTE)
Treatment of acute coronary syndromes (unstable angina, NSTEMI) - e.g., enoxaparin
Prophylaxis in orthopedic surgery (hip/knee replacement), abdominal surgery
Bridging anticoagulation before/after procedures
Prophylaxis and treatment of VTE in pregnancy (preferred over warfarin)
Outpatient/home treatment of DVT (major advantage over UFH)

Adverse Effects

Bleeding - major risk, though generally lower than UFH
Heparin-Induced Thrombocytopenia (HIT) - lower incidence than UFH but can occur
Local injection site reactions - bruising, hematoma at SC injection sites
Osteoporosis - less frequent than UFH with long-term use
Accumulation in renal failure - monitor anti-Xa levels in CrCl <30 mL/min
Hypersensitivity reactions (less common than UFH)

Precautions

Monitor anti-Xa levels in renal impairment, morbid obesity, and pregnancy (dose requirements change especially in 3rd trimester)
Partial reversal only with protamine (~60% reversal; anti-Xa activity not fully reversed)
No dose adjustment needed in mild-moderate hepatic impairment
Avoid or use cautiously with other anticoagulants, NSAIDs

4. Streptokinase vs. Alteplase - Compare and Contrast

Feature	Streptokinase	Alteplase (t-PA)
Nature	Protein produced by beta-hemolytic streptococci - not an enzyme itself	Recombinant human tissue plasminogen activator (serine protease)
Mechanism	Combines with proactivator plasminogen to form an enzymatic complex -> converts remaining plasminogen to plasmin (indirect activation)	Directly activates plasminogen; preferentially binds fibrin-bound plasminogen in thrombus -> activates it to plasmin
Fibrin selectivity	Non-fibrin-selective - systemic fibrinolysis; activates both free and fibrin-bound plasminogen throughout circulation	Fibrin-selective - preferentially activates plasminogen bound to fibrin within the thrombus (theoretically limits systemic lysis)
Route	IV infusion	IV bolus + infusion
Dosing (MI)	1.5 million units IV over 60 min	15 mg bolus, then 0.75 mg/kg (max 50 mg) over 30 min, then 0.5 mg/kg (max 35 mg) over 60 min
Dosing (Stroke)	Not recommended (increased hemorrhage)	0.9 mg/kg (max 90 mg); 10% as bolus, rest over 1 hour
Antigenicity	YES - antigenic (streptococcal protein) - allergic reactions, fever	NO - non-antigenic (human protein)
Repeat dosing	Contraindicated within 6-12 months (antibody formation)	Can be repeated
Systemic fibrinogen depletion	Pronounced (systemic lytic state)	Less pronounced
Cost	Much cheaper	More expensive
Indications	AMI, PE with hemodynamic instability, DVT, iliofemoral thrombophlebitis	AMI, PE, acute ischemic stroke (within 3-4.5 hr), DVT, peripheral arterial occlusion
Specific advantage	Low cost; widely available	Fibrin-selective; approved for acute stroke; no allergy risk
Specific disadvantage	Antigenicity; not for stroke; coarser fibrinolysis	Higher cost

5. Antiplatelet Drugs - MOA, Uses, Adverse Effects, Precautions

Platelets play a central role in arterial thrombosis (white thrombus). Antiplatelet drugs target platelet activation and aggregation.

Classification

Cyclooxygenase (COX) inhibitors: Aspirin
ADP receptor (P2Y12) antagonists: Clopidogrel, Prasugrel, Ticagrelor, Ticlopidine
Glycoprotein IIb/IIIa receptor antagonists: Abciximab, Eptifibatide, Tirofiban
Phosphodiesterase inhibitors: Dipyridamole, Cilostazol
PAR-1 antagonist (thrombin receptor): Vorapaxar

A. Aspirin

MOA: Irreversibly inhibits COX-1 and COX-2 by acetylation of a serine residue. In platelets (anucleate), this permanently inhibits thromboxane A2 (TXA2) synthesis for the platelet's entire lifespan (7-10 days). TXA2 normally promotes platelet aggregation and vasoconstriction. Low-dose aspirin (75-150 mg) preferentially inhibits platelet COX-1 without fully inhibiting vascular endothelial prostacyclin (PGI2) synthesis.

Therapeutic Uses:

Secondary prevention of MI and stroke
Acute MI and acute coronary syndromes (ACS) - first-line
Unstable angina
After coronary stenting (dual antiplatelet therapy with clopidogrel)
Prevention of thromboembolism in atrial fibrillation (lower-risk patients)
Peripheral arterial disease

Adverse Effects:

GI irritation, peptic ulceration, GI bleeding
Reye syndrome in children with viral illness (aspirin contraindicated <16 years)
Prolonged bleeding time
Hypersensitivity (aspirin-exacerbated respiratory disease - bronchoconstriction)
At higher doses: salicylism (tinnitus, dizziness)

Precautions:

Avoid in children/adolescents with viral fevers
Caution with other NSAIDs (reduced antiplatelet effect)
Caution in bleeding disorders, peptic ulcer disease
Do not stop abruptly in patients on dual antiplatelet therapy after coronary stenting

B. Clopidogrel (and Thienopyridines - Ticlopidine, Prasugrel)

MOA: Prodrug; converted by hepatic CYP2C19 to active metabolite that irreversibly blocks ADP (P2Y12) receptors on platelets, preventing ADP-mediated activation and aggregation. Ticlopidine acts similarly (older, more toxic). Prasugrel is a newer thienopyridine with faster, more potent, and more consistent anti-platelet effect.

Uses:

ACS (NSTEMI, STEMI) - as part of dual antiplatelet therapy with aspirin
After percutaneous coronary intervention (PCI) / coronary stenting (DAPT)
Prevention of atherothrombotic events in peripheral vascular disease and stroke

Adverse Effects:

Bleeding
Clopidogrel: variable response due to CYP2C19 polymorphisms (poor metabolizers get reduced benefit)
Ticlopidine (now rarely used): neutropenia/agranulocytosis, TTP (thrombotic thrombocytopenic purpura)
Rash, diarrhea (GI effects)

Precautions:

Avoid omeprazole with clopidogrel (CYP2C19 inhibition reduces active metabolite)
Genetic testing for CYP2C19 status may be indicated in high-risk patients
Ticlopidine: CBC monitoring every 2 weeks for first 3 months (due to neutropenia risk)

C. Glycoprotein IIb/IIIa Inhibitors (Abciximab, Eptifibatide, Tirofiban)

MOA: Block the GPIIb/IIIa receptor (integrin alphaIIb-beta3) - the final common pathway of platelet aggregation. This receptor normally binds fibrinogen/von Willebrand factor, cross-linking platelets. Blocking it prevents aggregation regardless of the initial activating stimulus (ADP, TXA2, thrombin, collagen).

Uses: Primarily for high-risk PCI (percutaneous coronary intervention); acute coronary syndromes with planned PCI

Adverse Effects: Bleeding (major), thrombocytopenia (especially abciximab), hypersensitivity

Precautions: Reserve for high-risk interventional procedures; IV use only; monitor platelets

D. Dipyridamole and Cilostazol

MOA:

Dipyridamole: Inhibits adenosine uptake and cGMP phosphodiesterase -> increases intracellular cAMP/cGMP -> inhibits platelet function. Also a vasodilator. Minimal effect alone.
Cilostazol: Selective PDE-3 inhibitor -> increased cAMP -> vasodilation + platelet inhibition

Uses:

Dipyridamole + aspirin: secondary prevention of cerebrovascular ischemia (TIA/stroke)
Dipyridamole + warfarin: prophylaxis in patients with prosthetic heart valves
Cilostazol: intermittent claudication (peripheral arterial disease)

Adverse Effects: Dipyridamole - headache, dizziness, flushing, worsening of angina (vasodilation); Cilostazol - headache, diarrhea, palpitations; Cilostazol is contraindicated in heart failure

6. Fibrinolytic Agents - List, Importance in Clinical Use, Adverse Effects, Precautions

Classification / Enumeration

First Generation (Non-fibrin-selective):

Streptokinase
Urokinase

Second Generation (Fibrin-selective): 3. Alteplase (rt-PA, recombinant tissue plasminogen activator)

Third Generation (Modified t-PAs - longer half-life, bolus dosing): 4. Reteplase (deletion mutant of t-PA) 5. Tenecteplase (genetically engineered t-PA; single IV bolus)

Mechanism (Common Pathway)

All fibrinolytic agents ultimately convert plasminogen --> plasmin. Plasmin degrades fibrin in thrombi (and also fibrinogen, Factor V, Factor VIII). Plasmin inside a thrombus is protected from circulating alpha-2-antiplasmin, allowing local clot lysis. t-PAs preferentially activate fibrin-bound plasminogen, giving better thrombus selectivity.

Clinical Importance

Fibrinolytics have transformed the management of:

Acute STEMI - early reperfusion when primary PCI not available within 120 min
Acute ischemic stroke - alteplase within 3-4.5 hours of symptom onset is standard of care
Massive pulmonary embolism with hemodynamic instability
Severe DVT (e.g., iliofemoral thrombophlebitis, superior vena cava syndrome)
Peripheral arterial occlusion

Adverse Effects

Bleeding - most important and common
- Intracranial hemorrhage (ICH) - most feared: 0.5-1% with alteplase in stroke
- Systemic hemorrhage at venipuncture sites, retroperitoneal, GI, genitourinary
- Streptokinase causes more systemic lysis and greater bleeding risk
Allergic reactions / fever - specific to streptokinase (streptococcal protein)
Hypotension - streptokinase can cause hypotension (complement activation)
Reperfusion arrhythmias - after coronary thrombolysis
Cerebral edema and hemorrhagic transformation (in stroke)

Precautions / Contraindications

Absolute Contraindications:

Any prior intracranial hemorrhage
Active internal bleeding (excluding menses)
Known intracranial neoplasm, AV malformation, or aneurysm
Suspected aortic dissection
Recent (<3 months) ischemic stroke or serious head/facial trauma
Significant closed head injury within 3 months

Relative Contraindications:

Recent surgery (<10 days), major trauma
Prolonged/traumatic CPR
Severe uncontrolled hypertension (SBP >180, DBP >110)
Pregnancy
Recent GI or urinary tract bleeding
Diabetic hemorrhagic retinopathy
For streptokinase: prior use within 6-12 months (antibody resistance + allergy risk)

7. Thrombolytic Drugs - Enumeration + Alteplase in Detail

Enumeration of Thrombolytic Drugs

Streptokinase - 1st generation; indirect; non-fibrin-selective
Urokinase - 1st generation; direct; non-fibrin-selective
Alteplase (rt-PA) - 2nd generation; direct; fibrin-selective
Reteplase - 3rd generation; deletion mutant of t-PA; longer T1/2; bolus dosing
Tenecteplase - 3rd generation; engineered t-PA; single bolus; highest fibrin-selectivity

Alteplase - Detailed Account

Drug class: Recombinant tissue plasminogen activator (rt-PA) Nature: Human serine protease; produced by recombinant DNA technology

Mechanism of Action

Alteplase directly converts plasminogen to plasmin. It preferentially binds fibrin-bound plasminogen within a thrombus via its fibronectin finger domain and kringle-2 domain. Binding to fibrin increases its catalytic efficiency ~1000-fold. This theoretical fibrin selectivity means fibrinolysis is preferentially localized to the thrombus, minimizing systemic fibrinogenolysis (though at clinical doses, some systemic activation still occurs).

Pharmacokinetics

Half-life: 4-8 minutes (cleared rapidly by liver; must be given as bolus + infusion)
Non-antigenic (human protein - no antibody formation)
No allergy risk; can be given repeatedly

Indications (Approved)

1. Acute STEMI (Heart Attack):

Given when primary PCI not available within 120 minutes
Dose: 15 mg bolus IV, then 0.75 mg/kg over 30 min (max 50 mg), then 0.5 mg/kg over 60 min (max 35 mg)
Total maximum dose: 100 mg
Must be given with concurrent aspirin and heparin
Best results within 3 hours of symptom onset; benefit up to 12 hr

2. Acute Ischemic Stroke:

Standard of care within 3 hours of symptom onset (extended window 3-4.5 hr in selected patients)
Dose: 0.9 mg/kg (maximum 90 mg); 10% as initial IV bolus, remaining 90% infused over 60 minutes
Reduces disability even if it does not reduce mortality
Contraindicated if CT shows hemorrhage; BP must be <185/110 before and during treatment

3. Massive Pulmonary Embolism:

Indicated when associated with hemodynamic instability (hypotension, shock)
Dose: 100 mg IV over 2 hours; followed by anticoagulation with heparin

4. Catheter-directed thrombolysis: for acute peripheral arterial occlusion, DVT

Adverse Effects of Alteplase

Intracranial hemorrhage (ICH) - most feared (symptomatic ICH in ~6% of stroke patients, compared to 0.6% with placebo - but net clinical benefit still positive in eligible patients)
Systemic bleeding - at IV access sites, retroperitoneal, GI, urogenital
Angioedema - rare; occurs in ~1-5% of stroke patients; related to ACE inhibitor use
Reperfusion arrhythmias - after coronary thrombolysis (accelerated idioventricular rhythm is common and generally benign; VT/VF can occur - requires ACLS management)
Cerebral edema / hemorrhagic transformation - in stroke
No significant allergic reactions (unlike streptokinase)

Contraindications / Precautions for Alteplase

Absolute Contraindications:

Active intracranial process (hemorrhage, tumor, AVM, aneurysm)
Prior intracranial hemorrhage (any time)
Recent ischemic stroke (<3 months for cardiac indications; <3 hr for stroke use = patient already outside window)
Suspected aortic dissection
Active internal bleeding
Significant head trauma (<3 months)
Intracranial or intraspinal surgery (<3 months)
Severe uncontrolled hypertension

Specific to Stroke:

Blood pressure must be controlled to <185/110 mmHg before alteplase administration
Contraindicated if CT shows hemorrhage or large infarct (>1/3 MCA territory)
Blood glucose <50 or >400 mg/dL (exclude hypoglycemia as stroke mimic)
INR >1.7 or PT >15 sec (if on anticoagulants)
Platelets <100,000/mm3
Seizure at stroke onset (relative contraindication)

Relative Contraindications (General):

Recent major surgery (<10 days), serious trauma
Recent GI/GU bleeding (<10 days)
Prolonged or traumatic CPR
Pregnancy
Diabetic hemorrhagic retinopathy
Current anticoagulant therapy

Key Difference from Streptokinase: Alteplase has NO antigenicity, NO allergy risk, can be repeated, and is the only thrombolytic approved for acute ischemic stroke - streptokinase is actually associated with increased ICH in stroke and is contraindicated.

Sources: Katzung's Basic and Clinical Pharmacology, 16th Edition; Braunwald's Heart Disease, 12th Edition.

For your 2nd MBBS exam, the most important exam points are: (1) UFH vs LMWH differences table, (2) Warfarin mechanism with the Protein C paradox and teratogenicity, (3) Streptokinase antigenicity vs Alteplase fibrin-selectivity, (4) Aspirin irreversible COX inhibition, and (5) Alteplase being the only thrombolytic approved in acute ischemic stroke.

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