Pharmacology

Vmax is defined as the maximum reaction rate that can be achieved with a given amount of enzyme. It is directly proportional to the enzyme concentration, representing the rate at which the enzyme is saturating with substrate. The incorrect answers provided do not accurately describe the concept of Vmax.

Km, or Michaelis constant, is a key parameter in enzyme kinetics that describes the amount of substrate required for an enzyme to reach half of its maximum velocity. This value is inversely proportional to the affinity of the enzyme for its substrate, meaning a higher Km value signifies lower affinity.

The Michaelis Menton plot typically depicts the rate of the reaction (V) on the Y axis and the substrate concentration ([S]) on the X axis, showing the relationship between substrate concentration and reaction rate.

Competitive inhibitors bind to the active site, Non-competitive inhibitors bind to an allosteric site or the active site irreversibly, Competitive inhibitors can be overcome with higher substrate concentration, Non-competitive inhibitors cannot be overcome, Competitive inhibitors increase Km and decrease potency, while both types have the same Vmax/effectiveness.

Vd stands for volume of distribution in pharmacokinetics, representing the total body amount of a drug divided by the plasma concentration of the drug. It is a crucial parameter that indicates how a drug is distributed throughout the body.

In pharmacokinetics, Cl signifies clearance, which is the elimination rate of a drug divided by its plasma concentration. It is a crucial parameter in understanding how quickly a drug is removed from the body.

The half-life (t1/2) of a drug is a crucial parameter in pharmacokinetics that indicates the time taken for the concentration of the drug in the body to decrease by 50%. It is determined by the volume of distribution (Vd) and clearance (Cl) of the drug and provides valuable insights into dosing regimens and achieving steady-state concentrations.

In pharmacology, the loading dose (LD) is the initial higher dose used to quickly achieve the desired drug concentration in the body, while the maintenance dose (MD) is the dose required to maintain that concentration over time. The formulas provided show how loading dose and maintenance dose are calculated based on volume of distribution, clearance, and bioavailability.

Drug elimination kinetics can be categorized into two main types based on the rate of elimination: zero order kinetics, where a constant amount of drug is eliminated per unit time, and first order kinetics, where a constant fraction of drug is eliminated per unit time.

Biotransformation is the process by which the body metabolizes drugs and other substances to prepare them for excretion. It predominantly occurs in the liver through Phase I (involving the CYP450 system) and Phase II (involving non-CYP450 enzymes). Therefore, the incorrect answers provided are not accurate in describing the location or process of biotransformation.

CYP450 inhibitors, by inhibiting the metabolism of lipid-soluble drugs, prevent their conversion into water-soluble metabolites for excretion. This leads to toxic accumulation and the need for lower doses to avoid adverse effects.

TI in pharmacology stands for Therapeutic Index, which represents the ratio of the median toxic/lethal dose to the median therapeutic/effective dose. It is an important measure of the safety margin of a drug.

Autonomic nicotinic Ach receptors are ligand-gated ion channels that play a crucial role in neurotransmission between neurons and neuromuscular junctions. They are not directly involved in the release of adrenaline, regulating blood sugar levels, or muscle contraction.

Muscarinic Ach Rs are G protein coupled receptors, which means they are activated by a ligand (acetylcholine) binding to the receptor, leading to a cascade of intracellular signaling events through G proteins.

GPCRs stands for G-protein coupled receptors. These receptors are involved in transmitting signals from the outside to the inside of cells, playing a crucial role in various physiological processes.

Cholinergic nerve terminals are involved in the recycling of choline and acetyl CoA to produce acetylcholine (Ach) vesicles that are released into the synaptic cleft. The enzyme acetylcholinesterase (AChE) breaks down Ach into choline and acetate.

The biosynthetic pathway for the formation of norepinephrine (NE) in adrenergic nerve terminals involves the conversion of Tyrosine to DOPA by Tyr hydroxylase, further conversion to Dopamine by Dopa decarboxylase, then to NE by Vesicular Dopamine beta hydroxylase, and finally metabolized by COMT after release from vesicles. The incorrect answers provide information on the biosynthesis pathways of serotonin, nitric oxide, and acetylcholine, unrelated to NE synthesis in adrenergic nerve terminals.

Cholinomimetics mimic the effects of Acetylcholine, act as parasympathomimetics, and are direct agonists of cholinergic receptors.

Bethanechol is a cholinomimetic drug that acts as a muscarinic agonist and is resistant to acetylcholinesterase, resulting in a long duration of action. It is primarily used to treat conditions like ileus and urinary retention.

Carbachol is a cholinomimetic drug that acts as a muscarinic/nicotinic agonist, primarily used as an ophthalmic topical medication. It works by causing the contraction of ciliary muscles, leading to pupil constriction. It is commonly used in the treatment of open-angle glaucoma.

Pilocarpine is classified as a cholinomimetic and muscarinic agonist, leading to increased secretions and constricting effects on the eye. It is specifically indicated for the emergency treatment of open-angle glaucoma.

Methacholine is not a bronchodilator but a bronchoconstrictor, and it is not a corticosteroid or antihistamine used to treat asthma symptoms.

Anticholinesterases work as indirect cholinomimetics by inhibiting acetylcholinesterase (AchE), leading to an increase in acetylcholine (Ach) action in the synapse.

Neostigmine is classified as an anticholinesterase medication with specific uses in reversing neuromuscular junction blockade, treating ileus, urinary retention, and myasthenia gravis. It does not belong to the categories of muscle relaxants, antibiotics, or antihypertensives.

Pyridostigmine is used as an anticholinesterase medication to treat myasthenia gravis by inhibiting the breakdown of acetylcholine at the neuromuscular junction.

Edrophonium is commonly used as an anticholinesterase for diagnosing myasthenia gravis due to its very short-acting nature and specific peripheral effects.

Physostigmine is primarily known as an anticholinesterase that has the ability to cross the blood-brain barrier and is used for various purposes such as treating glaucoma and as an antidote for atropine overdose/toxicity.

Echothiophate functions as an anticholinesterase, targeting the peripheral nervous system due to its charged 4* amine. It is known for its long-acting effects and is used in the treatment of glaucoma.