Antibiotics and Their Mechanisms of Action

Cephalosporins are a class of antibiotics commonly categorized into four generations based on their effectiveness against different types of bacteria.

The first generation of cephalosporins are effective against gram-positive bacteria, but less effective against gram-negative bacteria.

Second generation cephalosporins are more effective against both gram-positive and gram-negative bacteria compared to first generation, but still less effective against some resistant bacteria.

Third generation cephalosporins are effective against a wider range of gram-negative bacteria, making them a good choice for more serious infections.

Fourth generation cephalosporins are highly effective against many gram-positive and gram-negative bacteria, including some resistant strains.

Some newer cephalosporins don't fit the traditional four-generation classification and have their unique characteristics and effectiveness against bacteria.

Cephalexin is a type of antibiotic that is commonly given in oral doses of 0.25-0.5 grams, four times a day, to treat bacterial infections. The dosage can be adjusted based on the patient's weight and kidney function.

Cephalexin is primarily removed from the body through the kidneys, via filtration and secretion into the urine.

Drugs that block tubular secretion, such as probenecid, can increase the levels of cephalexin in the bloodstream.

In patients with impaired renal function, the dosage of cephalexin needs to be reduced to prevent potential buildup in the body.

Cephalosporins are a class of antibiotics that have a similar structure and mechanism of action. They effectively block the synthesis of the bacterial cell wall, leading to bacterial death.

The amount of penicillin given to newborns should be increased by 33 to 50% after the first week of life.

For newborns weighing less than 2 kilograms, the lower dose range of penicillin should be used.

After the first month of life, babies can take the same penicillin dosages as older children.

Oral penicillins, except amoxicillin, should be taken 1 to 2 hours before or after meals.

Amoxicillin, an oral penicillin, can be taken with or without food.

Probenecid can increase blood levels of penicillin by reducing its elimination from the body.

Penicillin should not be used to treat viral infections because it is effective only against bacteria.

Intramuscular injections of benzathine penicillin provide long-lasting treatment for certain bacterial infections.

A severe, life-threatening allergic reaction that can occur in response to certain medications like penicillin and cephalosporins.

The chance that someone allergic to penicillin will also be allergic to cephalosporins.

A type of beta-lactamase enzyme that can break down certain antibiotics like cephalosporins, making them ineffective.

A type of antibiotic that is effective against a wide range of bacteria, including many that are resistant to other antibiotics.

A measure of how quickly a drug is removed from the body.

An antibiotic that can enter the fluid surrounding the brain and spinal cord.

A cyclic lipopeptide produced by Streptomyces roseosporus, active against various bacterial strains, including vancomycin-resistant ones. Its mechanism involves binding to the bacterial cell membrane via calcium, disrupting its function and leading to cell death.

A bacterial cell wall component, formed through a series of enzymatic reactions, including the action of enolpyruvate transferase. Its precursor, UDP-N-acetylmuramic acid, is essential for assembling the bacterial cell wall.

A cytoplasmic enzyme involved in the initial step of producing UDP-N-acetylmuramic acid, a key component of the bacterial cell wall. It catalyzes the addition of phosphoenolpyruvate to UDP-N-acetylglucosamine.

A drug that inhibits the formation of UDP-N-acetylmuramic acid, a crucial building block of the bacterial cell wall. It acts by covalently binding to the active site of enolpyruvate transferase, blocking its function.

The ability of bacteria to resist the effects of an antibiotic. In the case of daptomycin, resistance often arises from impaired transport of the drug into the bacterial cell.

The adjusted dose of an antibiotic for a patient with renal failure is based on their creatinine clearance (Clcr), which is a measure of kidney function.

A first-generation cephalosporin antibiotic, often used for infections like skin infections, is typically given at 50% of the normal dose for a patient with a creatinine clearance of approximately 50 mL/min.

For a patient with a creatinine clearance of approximately 10 mL/min, the dose of a first-generation cephalosporin is typically reduced to 25% of the normal dose.

The recommended intravenous dose of cefazolin for adults with renal insufficiency and a creatinine clearance of approximately 50 mL/min is typically 50% of the normal dose.

A second-generation cephalosporin like cefoxitin, often used for infections like pelvic inflammatory disease, typically requires a 50-75% dose reduction for patients with a creatinine clearance of approximately 50 mL/min.

For patients with a creatinine clearance of approximately 10 mL/min, the dose of a second-generation cephalosporin like cefoxitin is typically reduced to 25% of the normal dose.

The dose of a third- or fourth-generation cephalosporin, such as ceftaroline fosamil, is typically reduced to 50% of the normal dose for patients with a creatinine clearance of approximately 50 mL/min.

Ceftriaxone, a third-generation cephalosporin, does not require a dose adjustment for patients with renal insufficiency, regardless of creatinine clearance.

For a patient with a creatinine clearance of approximately 10 mL/min, the dose of a third- or fourth-generation cephalosporin is typically reduced to 25% of the normal dose.

Ertapenem, a carbapenem antibiotic, is typically given at the normal dose for patients with renal insufficiency.

The recommended dose of imipenem for a patient with renal insufficiency and a creatinine clearance of approximately 50 mL/min is typically 75% of the normal dose.

For a patient with a creatinine clearance of approximately 10 mL/min, the dose of imipenem is typically reduced to 50% of the normal dose.

Vancomycin, a glycopeptide antibiotic, is typically given at 40% of the normal dose for patients with renal insufficiency and a creatinine clearance of approximately 50 mL/min.

For a patient with a creatinine clearance of approximately 10 mL/min, the initial dose of vancomycin is 15 mg/kg, with a loading dose, followed by 20 mg/kg/d in two doses.

The tendency of a drug to move between lipid and aqueous environments, governed by its lipid:aqueous partition coefficient. This determines how readily a drug crosses biological membranes like cell membranes, contributing to its absorption, distribution, metabolism, and excretion.

A special group of proteins that help move substances across cell membranes. These transporters are critical for the absorption, distribution, and excretion of many drugs.

A family of proteins that use energy from ATP hydrolysis to move substances across cell membranes. These transporters are important for drug resistance and excretion.

A group of transporters that use ion gradients to move substances across membranes. These carriers are crucial for the uptake of neurotransmitters in the nervous system.

The Henderson-Hasselbalch equation describes the ratio of ionized to non-ionized forms of weak acids and bases at a given pH. This ratio significantly influences how a drug moves across biological membranes.

A measure of how tightly a drug binds to a receptor. A lower Kd indicates a higher affinity.

Drugs that form weak bonds with their receptors are usually more selective. This is because they require a precise fit, and fewer receptor types will have that specific shape.

For a highly selective drug (targets a specific receptor), forming strong covalent bonds is usually avoided because it makes it less selective.

Drugs that interact through hydrophobic interactions are often highly lipid-soluble and may interact with cell membranes or receptor pockets. These interactions are usually weak.

Enzymes often show stereoselectivity, meaning they prefer one enantiomer of a drug over the other, leading to different metabolism rates.

Most chiral drugs are marketed as racemic mixtures, meaning they contain both enantiomers. This means patients may receive an ineffective dose of the drug.

Some drugs are available in both racemic and pure active forms to address issues with inactive enantiomers in racemic mixtures.

Xenon, an inert gas, surprisingly has anesthetic effects at high pressures, showing that not all pharmacologic activity relies on chemical reactions.

The movement of a drug across biological membranes, such as cell membranes, from one compartment of the body to another.

The drug's movement through aqueous channels between cells, driven by concentration differences. This means the drug follows the path of least resistance, moving from areas of high concentration to low concentration. Think of water flowing downhill.

This is the most critical factor for drug permeation as many lipid barriers exist in the body. The drug must be able to dissolve in lipids to pass through these barriers. Think of the drug needing to be 'oily' to pass through a 'fatty' membrane

These are specialized proteins that can transport drugs across membranes. They have specific binding sites for certain drugs and can move drugs against a concentration gradient.Think of a shuttle bus taking a drug from one side of a membrane to the other.

This is a type of carrier-mediated transport that requires energy (ATP) to move drugs against their concentration gradient. Think of an active transporter pushing a drug uphill, requiring energy.

This is a type of carrier-mediated transport that does not require energy and moves drugs down their concentration gradient. It is still selective and saturable but does not require energy input.

These are specialized carriers that help to expel foreign molecules from a cell. Think of a 'doorman' kicking out unwanted guests from a cell.

This is a process where a drug binds to a receptor on the cell membrane, causing a change in the cell's activity. Think of a drug 'knocking on a door' to get inside the cell.