I did a little bit more research and talked to another coder who was an instructor and this is how you are supposed to code "toxicity" when due to a drug that was properly prescribed and used:
Inpatient-code the effect first (ex. coma, vertigo, etc...) and then the E code from therapeutic use column. ****In the event that the specified effect is unknown or not documented, 796.0 is reserved for inpatient use.
Outpatient-code the effect first 9ex. coma, vertigo, etc....) and then the E code from therapeutic use column. ****In the event that the specified effect is unknow or not documented, 995.20-995.29 should be used.
In faye brown, it has a decision tree for coding adverse effects of drugs or poisoning due to drugs or medicinal or biological substances. Pretty much if the condition is due to a drug that was taken properly, you code the effect and the therapeutic E-code. If the correct medication wasn't used exactly as prescribed-code as poisoning(use poison code), add code for condition if documented and use ecode E850.x-E869.x. If the correct medication was used exactly as prescribed but was taken with alcohol and/or a drug not prescribed by the physician-code as poisoning(use poison code), add code for condition if documented and use ecode E850.x-E869.x.
You can find this info in faye brown and basic icd-9-cm coding by ahima and i'm sure it's in more books too.
Hope this helps!
Amber, CPC