There have been a few different builds around Alchemist and VKF and Maelodic suggested something similar to this build a while back.
Here's my take on a poison knife fighter.
Helf Alchemist 16/Monk 3/FvS 1
32 Point Build First Lifer
Str 8 Dex 16 Con 14 Int 16 Wis 14 Chr 8
(You can increase Int but I like minimal use of tomes and GTWF requires 17 Dex)
Key Skills:
Concentration
Bluff
UMD
Heal
Move Silently
Hide
Search
APs (80):
Vistani 41
Vile Chemist 22
Ninja Assassin 13
War Soul 4
Standard Feats:
1 Improved Feint
3 Extend
6 Two Weapon Defense (Swap to Adept of Forms at 17)
9 iTWF
12 IC:P
15 GTWF
18 Master of Forms
Alchemist Feats:
4 Battalion Brew (Int to Damage)
8 Quicken
12 Simple Weapon Expertise
16 Liquid Courage
Monk Feats:
1 TWF
2 Precision
Sting of the Ninja gives us ninja poison on critical hits which we can use to build damage/vulnerability or purge for extra damage via dark exploits.
War Soul gives us Battle Trance although it keys off Wis so won't be quite as good as KtA - still, it works for the APs we have.
Vile Chemist gives Poison Weapons, Full BAB, 4 Feats, some extras and some great melee support spells.
VKF gives DPS.
Alchemist have a pretty good array of combat buffs that other classes don't have access to. The Potion Action Boosts are great if a little slow to cast so Quicken is essential. Extend is for Displacement Draught and similar. The poison imbues are actually not bad either and elemental weapon is always an option.
In particular I find the debuff/cc spells pretty good from Alchemist - at low level Glue Bomb is great.
Healing is ok via admixtures although I can see spell points being a concern on some quests. UMD is very useful here for out of combat healing.
The Reactions of Alchemists are tricky but useful once you get the hang of them and, done correctly, can make a big difference at the start of a tough fight.
Master of Forms is for Master of Flame and improved crits on 19-20. On most other builds it wouldn't be worth two feats but on this one I think its justified.
Why Half Elf? Because I love Improved Feint and the SA dice from Ninja do help. For solo runs IF is an incredibly useful panic button.
Another option is to go Human and free up two feats but the build isn't feat constrained particularly so its no big deal. I did theorycraft a human version will all the ranged feats as well as melee to make use of the thrown knife capability of VKF but it doesn't work well with monk levels (which I always thought was an oversight not to have monks be able to use throwing knives through VKF).
Currently in low mid heroics - will report back on progress.
Hap
Edit: Have swapped to Wis rather than Chr for Battle Trance - thanks adamr09!