List out five drugs and five enzymes for competitive inhibitor found in a local medical shops.
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common drugs competitive enzyme inhibitors available pharmacy examples mechanisms
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Competitive Enzyme Inhibitors: 5 Drugs & 5 Enzymes Available at Local Pharmacies
Competitive inhibitors bind to the active site of an enzyme (mimicking the natural substrate), blocking substrate access. This increases the apparent Km while leaving Vmax unchanged - and the inhibition can be reversed by increasing substrate concentration.
5 Drugs That Act as Competitive Inhibitors
| # | Drug | Enzyme Inhibited | Clinical Use | Available As |
|---|---|---|---|---|
| 1 | Atorvastatin / Rosuvastatin (Statins) | HMG-CoA reductase | Lowers cholesterol | Lipitor, Crestor tablets |
| 2 | Enalapril / Lisinopril (ACE Inhibitors) | Angiotensin-converting enzyme (ACE) | Hypertension, heart failure | Envas, Lisinace tablets |
| 3 | Methotrexate | Dihydrofolate reductase (DHFR) | Cancer, rheumatoid arthritis, psoriasis | MTX tablets / injection |
| 4 | Ibuprofen / Naproxen (NSAIDs) | Cyclooxygenase (COX-1 and COX-2) | Pain, inflammation, fever | Brufen, Naprosyn tablets |
| 5 | Sildenafil (Viagra) | Phosphodiesterase-5 (PDE-5) | Erectile dysfunction, pulmonary arterial hypertension | Penegra, Suhagra tablets |
5 Enzymes Targeted by These Competitive Inhibitors
| # | Enzyme | Drug Inhibitor | Normal Substrate | Biological Role |
|---|---|---|---|---|
| 1 | HMG-CoA Reductase | Statins (atorvastatin, pravastatin) | HMG-CoA | Rate-limiting step in cholesterol biosynthesis |
| 2 | Angiotensin-Converting Enzyme (ACE) | ACE inhibitors (enalapril, lisinopril) | Angiotensin I | Converts Ang I → Ang II (raises blood pressure) |
| 3 | Dihydrofolate Reductase (DHFR) | Methotrexate | Dihydrofolate | Reduces dihydrofolate to tetrahydrofolate (needed for DNA synthesis) |
| 4 | Cyclooxygenase (COX-1 / COX-2) | NSAIDs (ibuprofen, naproxen) | Arachidonic acid | Synthesizes prostaglandins (mediators of pain and inflammation) |
| 5 | Phosphodiesterase-5 (PDE-5) | Sildenafil, tadalafil | cGMP | Breaks down cGMP in vascular smooth muscle (controls vasodilation) |
Key Pharmacology Points
- Statins are the textbook example of competitive inhibition - they are structural analogs of HMG-CoA and compete directly for the active site of HMG-CoA reductase. - Biochemistry, Lippincott Illustrated Reviews, 8th Ed, p. 189
- Methotrexate competitively inhibits DHFR and is so potent that resistance sometimes develops through gene amplification (upregulating the enzyme itself). - Goodman & Gilman's Pharmacological Basis of Therapeutics
- ACE inhibitors are cited in clinical biochemistry as a classic example of drugs acting as competitive inhibitors of a targeted enzyme. - Henry's Clinical Diagnosis and Management by Laboratory Methods
- NSAIDs like ibuprofen and naproxen are reversible competitive/mixed inhibitors of COX enzymes (unlike aspirin, which is irreversible).
- Sildenafil mimics cGMP structurally, competitively occupying PDE-5's active site, preventing cGMP breakdown and sustaining vasodilation.
Note on local availability: All five drugs above are widely stocked in pharmacies across India and most countries. Statins, ACE inhibitors, and NSAIDs are available over-the-counter or by prescription; methotrexate and sildenafil require a prescription.
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