Top 20 Mechanisms of Action!May 16th, 2020
What are “mechanisms of action”?
Mechanisms of action are the means through which medicines work. All medicines produce a desired therapeutic effect. Mechanisms of action explain how drugs achieve these desired effects.
Some drugs have more than one mechanism of action. Instead, they may achieve their therapeutic effects by multiple complementary mechanisms. However, most drugs have a single mechanism of action. For the PTCB exam, technicians will only be asked questions on mechanisms of action that affect the the top 200 drugs and medicines.
Some drug classes state the mechanism of action in its title. For example:
- ACE inhibitors block the angiotensin-converting enzyme (ACE).
- Beta-blockers work by blocking adrenergic beta receptors.
- PDE5 inhibitors block the phosphodiesterase-type 5 enzyme (for example: sildenafil [ Viagra ] ).
For other drugs, the mechanism is less obvious. For example:
- Statins work by inhibiting the HMG-CoA reductase enzyme; the rate-limiting enzyme in the mevalonate pathway of cholesterol production. Statins are effective drugs in the treatment of hypercholesterolemia. Examples of statins include atorvastatin and simvastatin.
- Loop diuretics work by inhibiting the Na+/K+/2Cl– cotransporter protein in the ascending limb of the loop of Henle. The loop of Henle is a U-shaped tubule in the kidney involved in the process by which urine is eliminated from the body. Examples of loop diuretics include furosemide and bumetanide.
How much mechanism do I need to learn?
Initially, mechanisms of action may seem complicated, but with enough time you will begin to remember them.
Remember, technicians are not expected to know mechanisms in great detail. You are only expected to know the basic mechanism of the most commonly used medicines. Take tetracyclines, for example. It is sufficient for pharmacy technicians to know they work by blocking protein synthesis inside bacterial cells.
No more detail is required than that. Otherwise you risk learning too much for the PTCB exam and material that simply will not be tested. Keep the information you learn relevant but limited. This is where effective flashcards come into play. Flashcards can help you absorb the necessary detail you need to know in a fast and concise study format.
Apply this principle across the board when studying the top 200 medicines.
Mechanisms of Action – Top 20
|Drug / Drug Class
|Mechanism of Action
|Statins work by inhibiting the HMG-CoA reductase enzyme; the rate-limiting enzyme in the mevalonate pathway of cholesterol production.
|Beta-1 adrenoceptors are found on the heart.
Beta-2 adrenoceptors are found on the lungs.
Memory tool: beta-1, 1 heart; beta-2, 2 lungs.
Some beta-blockers are selective for the heart and work to reduce the force of contraction and speed of conduction of the heart. This relieves the heart from work and oxygen demand. Beta-blockers also prolong the refractory period of the AV node, making these drugs effective in the treatment of cardiac arrhythmias.
|Beta-2 agonists are used in the treatment of asthma and COPD.
By stimulating (or “agonizing”) the beta-2 receptor, which is found in the lungs, beta-2 agonists work to cause smooth muscle relaxation – making it easier to improve air flow in the lungs.
|Corticosteroids bind to surface cell glucocorticoid receptors, which then navigate their way into the cell nucleus to alter gene expression.
Corticosteroids enhance anti-inflammatory genes and downregulate pro-inflammatory genes.
|Proteins are necessary for cells, including bacterial cells, to survive.
Tetracyclines work by inhibiting protein synthesis inside bacterial cells.
|ACE inhibitors block the angiotensin-converting enzyme – which normally converts angiotensin I into angiotensin II.
Angiotensin II is responsible for effects such as vasoconstriction (which constricts blood vessels and increases blood pressure) and releasing the hormone, aldosterone, which works to increase blood pressure further.
ACE inhibitors prevent these effects from angiotensin II and therefore they are used as antihypertensive drugs.
|NSAIDs are non-steroidal anti-inflammatory drugs.
They work by inhibiting the cyclooxygenase enzyme, or COX. There are 2 kinds of COX: COX-1 and COX-2. The therapeutic effects of NSAIDs come from COX-2 inhibition – reducing inflammation.
Therefore, NSAIDs are used to treat mild-to-moderate pain and pain related to inflammation. Aspirin also works by inhibiting COX.
|Opioids are used in the treatment of pain.
They work by acting as agonists of the mu opioid receptor.
|Antifungal Drugs Ketoconazole
|Azole antifungal drugs work by targeting ergosterol in fungal cell membranes.
By targeting ergosterol, it impairs cell membrane synthesis, cell growth, and replication – damaging fungal cells.
|Penicillins work by inhibiting enzymes responsible for linking up key elements in bacterial cell walls.
By weakening bacterial cell walls, penicillins cause these cells to swell up, break, and ultimately die. The antimicrobial activity of penicillins comes from the fact that they contain a beta-lactam ring; a 4-sided square ring in their chemical structure. Another drug class – called cephalosporins – also contain a beta-lactam ring and work in much the same way.
Examples include cefazolin, ceftriaxone, cefdinir, and cefoperazone.
|PPIs are used to treat conditions that arise from excess gastric acid production.
PPIs work to inhibit gastric acid production by blocking the “proton-pump” that feeds hydrogen ions into the stomach. PPIs irreversibly bind to the H+/K+-ATPase (aka. the proton pump) in gastric parietal cells.
|Fluoroquinolones are antibacterial drugs that work by inhibiting DNA synthesis.
As cells cannot replicate, the rate of production is reduced, and this allows the body to fight off the infection.
|Benzodiazepines are used to treat anxiety, seizures, to induce anesthesia, and insomnia.
They work by enhancing the binding of the neurotransmitter GABA to the GABA A receptor.
Once bound, it causes a “depressive” effect on neuronal synaptic transmission that lead to reduced anxiety, sleepiness, sedation, and an anticonvulsive effect.
|Antipsychotics work by a complex range of methods, but one of the most common is blocking post-synaptic D2 receptors.
D2 receptors are “dopaminergic” receptors that impact dopamine levels. D2 blockade is one of the primary ways that antipsychotic drugs reduce psychotic symptoms in affected patients.
|SSRIs are “selective serotonin reuptake inhibitors”.
Whereas antipsychotics act on dopamine receptors, SSRIs act on serotonin levels. Specifically, SSRIs work to inhibit neuronal reuptake into neuronal cells. This means more serotonin is available between neurons to increase neurotransmission.
|These 4 drugs are antagonists of the histamine, H1 type.
H1 antagonism prevents the release of histamine from granules found in mast cells. Histamine is responsible for pro-allergy effects. Hence, these drugs are used to treat allergies, hay fever, itch, and hives.
|There is also a H2 receptor and, once this is blocked (or “antagonized”), it reduces gastric acid production.
That’s why ranitidine is used in the treatment of peptic ulcer disease, dyspepsia, and GERD.
|To make clots, you need thrombin and factor Xa; two key elements in the clot forming pathway. Heparin works to inactivate factor Xa and thrombin.
There are low-molecular weight versions of heparin, too, and these drugs preferentially inhibitor factor Xa.
Examples include enoxaparin and dalteparin.
|Warfarin is also used as an anticoagulant drug.
However, warfarin works by inhibiting the enzyme vitamin K epoxide reductase – preventing the reactivation of vitamin K and the synthesis of pro-clotting factors.
|Metformin is used in the treatment of type 2 diabetes.
It works by increasing the sensitivity (or “response”) to insulin. For example, this means it suppresses glucose production by the liver, increases glucose uptake into skeletal muscle, and it suppresses glucose absorption by the intestines.
This collectively works to reduce blood sugar levels.