A friend had an unforgettable experience from hiking in Madagascar: a horror called terrestrial leeches. These slug-like creeps wait patiently in trees, bushes and tall plants. They can feel you coming from some distance and they converge and drop onto you from foliage, then bite through the shirt (pants, socks) and sneak in, migrating over your skin towards the juicier body regions where they attach themselves. This is painless – in fact you are not likely to notice the leeches munching on you under the shirt as the leeches exude a potent anesthetic in their saliva. They also inject a thrombin inhibitor that suppresses the blood clotting in the wound – which unfortunately causes you to bleed profusely (though painlesly) from the bite long after the leech has got her fill + dropped off to the ground, happy and slumberous; (this is a leech version of the Thanksgiving dinner – they can live of one good fill for many months). My friend said he knew nothing about these tree leeches until he returned from the hike and found himself covered with his own blood and with some dozen of leechey hitchhikers, attached to various parts…
The leech thrombin inhibitor hirudin is medicinally useful as an anticoagulant. There has been enormous amount of medicinal chemistry and biology done on the blood coagulation cascade. At the previous company we were working on factor VIIa inhibitors (that were supposed to be safer than the anti-thrombin or anti-Xa agents), for treatment of deep vein thrombosis. The thrombosis project got shelved eventually – one reason was the difficulty with developing good orally-active compounds – but we made some pretty potent i.v. compounds. I have inadvertently found out how potent these compounds actually were: One night working in the lab, I noticed my jeans felt little heavy and sticky so I looked down and saw that the front of one trouser was completely soaked with blood, from the knee down to the sock and I could not find out where all this blood was oozing from! Eventually I noticed a tiny splinter of glass, barely 2 mm across, embedded in the knee and I realized that few hours before I was purifying some final compounds on prep-HPLC and I dropped an empty test tube (after active fraction) and I kneeled down to the floor in order to pick up the splinters – a tiny piece must have stuck to my knee then.
Here is an example of the VIIa chemical monstrosity we were making – a true embodiment of the god-awful drug design. But they sure had some long-lasting potency:
In US, the TV is now inundated with ads for Plavix. This inhibitor of platelet- aggregation is slightly more effective than aspirin in preventing heart attack (31% vs 23% risk reduction) and therefore widely prescribed as prophylactic over long periods of time. Plavix has more serious complications than aspirin – it causes prolonged bleeding. That makes the ER doctors quite unhappy as there is no available antidote for reversing the effect (like you get with the coumarine-based anticoagulants) and every mid-age weekend biker now seems to be on the drug whether they need it or not. With intracranial bleeding from head trauma, Plavix can provide a heroic and futile excersize for the entire surgery team.
Thanks to Abel Pharmboy for pointing out the story.