I have a DUI case where the Defendat was 0 for Alcohol, but had 0.27 milligrams per milliliter of Lorazepam. I called one of my ER Doc buddies and he said no one ever does blood levels on this drug and probably a Pathologist would have to testify about the level and effect on driving. Anyone know a good expert?

Did you check with the lab? Sometimes the person doing the test can testify about effects. Sometimes.

My experience has been that a pharmacist can testify as to how the drug affects the central nervous system, the recommended dosing levels, and the required warnings. It is my understanding that no expert will be able to testify to a presumptive level of intoxication on any drug. However with evidence of side effects, evidence of the presence of the drug in the blood, and the SFST results all combined will generally make a decent case of impairment. It will depend on the presentation and the mindset of the jury at that point.

would your investigating officer need to be a D.R.E to have admissible evidence regarding the effect of the prescription drug on the defendant?

If the lab report says 0.27 milligrams per milliliter of blood you better send it back to the lab ...they need to try again. Simple arithmetic shows this is impossible.

A ml of blood is about a gram of blood.
A gram of blood has 1000 milligrams.
.27 (about a quarter) of one of those 1000 milligrams is the drug.

How is that arithmetically impossible?

therapeutic dose is normally around 20ng/ml (or so). .27 milligrams is equal to 270,000ng (nanograms). Perhaps lab report says ng/ml and not mg/ml ???

Sorry. It was 0.27 milligrams per liter.

You don't need to be a DRE to testify about your observations. Although, a DRE could testify that the officer's observations are consistent with a particular category of drugs. Then, follow up with your lab tech testifying that the drug detected in the blood is a member of the category that was called by the DRE.

We recently tried an Aggravated Assault case where the defendant's reckless driving caused SBI. No alcohol but 2 prescription meds (both CNS depressants) for which he apparently didn't have a prescription. DPS lab said one was more than a therapeutic level, defense "expert" Booker said both within therapeutic levels. The jury convicted because we had civilian witnesses to really bad driving facts pre-collision. It would have been much more difficult if they had to rely on the drugs. Do you have any bad driving facts, other witnesses, or something else that can help you here?

To the point that a pharmacist can testify; that is true but if the drug was prescribed by a physician, I suggest you talk with the Pharmacist that filled the prescription and also get copies of all information that was provided to the patient when the drug was dispensed.Unless it lists the effects, interactions with other prescribed drugs the patient is using(as on file) with the pharmacy, it will be hard to prove the patient should have been aware of the risk of driving. Also, my husband is a doctor X35 years and I have been in medical-legal and medical administration positions for nearly 39 years. Unfortunately, virtually every drug prescribed for anxiety, depression,pain, allergies, and so on; have some form of warning most falling short of saying "don't drive" but saying such things as "... is used to treat major xxxxx disorders xxxx illness so do not drive or operate heavy machinery until you know how ....will affect you". Unfortunately the individual often won't know how their driving is affected until they take their medications and drive. There are also other factors that can enhance the effect of the drug as the combined use of other prescribed drugs. Diseases and disorders for which the Pharmacist of all of the patients doctors are unaware of. Effects that often are not addressed by the Pharmacist or if the drugs were prescribed by two different physicians.
So, because of this, it is difficult to convict the driver of a criminal act. If the driver has a history of abusing legally prescribed drugs they should be treated not prosecuted. IMO.
Many of these addictions where caused by doctors prescribing pain medications or other narcotics to treat diagnosed injuries and illnesses. Some patients become addicted to these medications, some don't. Each patient responds differently. It is the failure of the doctors and pharmacists to monitor the drugs prescribed to an individual that leads to patients becoming addicted to various medications, using deadly combinations of medications, using medications longer than recommended and the like.