Half-life and linear excretion

[Benzopyrrole]

Ethanol is probably the only chemical i know that use a linear excretion and from what i understand its because only a limited amount of the enzyme that destroy ethanol into acetaldehyde is available every hour making it only able to destroy a specific amount per hour.

But now i was wondering, what makes most of chemical using a half-life excretion. What i mean by that is why is the body only able to destroy half of the amount of the chemical every half-life and not a specific amount per hour ?

 

[Deleted member 170540]

The motion of drug molecules in your body fluids is random motion, and your enzymes can metabolize a drug molecule only when the drug molecule encounters an enzyme molecule. When there's a higher concentration of the drug, there are more random collisions between the enzyme and the drug molecules, and the metabolism is faster. This metabolism rate decreases linearly when the concentration of the drug gets lower.

 

[Nagelfar]

My response is one based in its entirety on no deeper insight on my part than assumption and sourced in a personal ignorance of what the general established facts are as academia would deem them, or as would be held by those erudite with regard to the subject;

That being said I am giving my honest educated guess which seems plausible enough to me; it has to do with body weight and proportion of your metabolic homeostasis; the cycling of first pass liver cleansing has to proportionately keep levels conducive to basic running homeostasis in evolutionary / design of human machinery terms. If it were not able to level in magnitudes as thus the body would quickly diverge from its necessary equilibrium of endogenous chemicals, or so it would seem rational.

Ethanol is probably the only chemical i know that use a linear excretion and from what i understand its because only a limited amount of the enzyme that destroy ethanol into acetaldehyde is available every hour making it only able to destroy a specific amount per hour.

As for the contextual example instanced with the original post, this is interesting and I was not aware of this being so. Is this process regulated by some form of a de-ethylating enzyme (distinct from the liver's de-methylation process) or is it related to de-methylation (one part of a methyl at a time)? I would have gratitude for an simple, straight-forward elucidation of the exceptional rationale behind this mechanism.

 

[seep]

Ethanol is probably the only chemical i know that use a linear excretion

Also to some extent Dilantin, Prozac, Prilosec and salicylates (Aspirin and friends). Depends on the dose.

Etizolam and half a liter of grapefruit juice feels zero-order to me as well. It drags on...

What drugs exhibit 2nd order kinetics? This seems like it would come in handy with stimulants that overstay their welcome.

 

[seep]

As for the contextual example instanced with the original post, this is interesting and I was not aware of this being so. Is this process regulated by some form of a de-ethylating enzyme (distinct from the liver's de-methylation process) or is it related to de-methylation (one part of a methyl at a time)? I would have gratitude for an simple, straight-forward elucidation of the exceptional rationale behind this mechanism.

The enzyme in question aldehyde dehydrogenase. The body does not have enough of it to handle the legions and legions of acetaldehyde molecules that typical doses of ethanol are metabolized into, so the acetaldehyde has to wait in long lines to be converted to acetic acid (which is readily eliminated).

Medicinally, we take advantage of this metabolic sluggishness in cases or methanol and ethylene glycol poisoning. At least, some hospitals do. They bring the patient beer or whiskey in order to slow down the metabolism of methanol or ethylene glycol.