In phamacology (if I recall correctly), 1st pass clearance refers to the compound getting absorbed into the bloodstream through the stomach/intestines. In the lecture I sat on this, the example was the contrast between salicylic acid and aspirin. [Although here the driving force was almost entirely with the object of lessening salicylic acids caustic effect on the stomach lining].
When one refers to a method of drug delivery that avoids first pass clearance we normally perceive this as some sort of advantage. This is especially true with delicate molecules such as morphine. If the ether linkage in morphine is destroyed (which occurs readily by the low pH environment in the stomach), the corresponding compound is only feebly active. [Although in crazy examples, such as PPOM and the like, this may actually be deliberate in an attempt to increase the compounds bioavailability. However crazy stuff aside it is best to keep the ether linkage in-tact].
With amphetamine-like devils a completely different rationale is used. In this case the motivation is completely kinetic in origin:- IV use gives a quicker onset and shorter duration of action. Hence it is more addictive according to the drug addiction experts. They argue that the euphoric rush and edgy crash leaves the user craving more. Hence due to the increased chance of repeated administration, this method of drug delivery is considered more addictive.
Back to thread title: White Heroin => I read an review on the web compiled by DEA informants. Here they claimed that the corresponding fent analog made by employing acetic anhydride in the last step of the synthesis, has a differing phamacological profile. They claimed that although 10-fold less potent it had a duration of action that is ~twice that of regular fent. [I would offer a reference for this but the website that I got this from is currently down].
That sounds cool though, doesnt it? 10X weaker means a greatly reduced risk of a potentially lethal OD. Since it lasts twice as long there less demand for redosing. Almost as though there has been a form of compensation provided for the 10-fold drop in potency. Assuming the product was cut 9/1 and that sniffing it meant that it is no less active than IV administration, that would mean sniffing only 10mg of powder (!) If one felt that they needed more euphoria, they could always upgrade this to the corresponding alpha-methyl analogue (in accordance with negro's earlier comments regarding AMF and euphoria) White heroin indeed....[sigh]