Drug monitoring

Question 1

______ is the bodily fluid most often used for therapeutic drug monitoring, while ____ is used for drugs of abuse screening

Answer 1

blood for TDM

urine for DOA screening

Question 2

When is therapeutic drug monitoring useful?

Answer 2

• Defined effective and toxic concentrations
• Narrow therapeutic windows
• Variable pharmacokinetics-
• Chronic dosing regimens
• Potential for drug-drug interactions
• High protein binding of drug
• Toxicity that mimics the indication for the drug
• Decreased elimination in patient
• Pregnant, infant, elderly patients
• Poor adherence or no effect seen

Question 3

When is therapeutic drug monitoring NOT useful?

Answer 3

• Drugs that are converted to active forms inside the cell
• Drugs whose pharmacological effects last much longer than their presence in blood
• Opioids

Question 4

List some drugs whose pharmacological effects last longer than their presence in blood

Answer 4

anticancer drugs
warfarin 
antiviral drugs
MAOIs
Sulbactam, clavulonic acid
Vigabatrin
Carbidopa

Question 5

Why is TDM not useful for patients prescribed opioids?

Answer 5

Phenomenon of tolerance- the levels needed for pain relief in one person could be toxic to another person

Question 6

_______ is the most common laboratory technique for therapeutic drug monitoring

Answer 6

Immunoassay

Question 7

List three methods of detection used in immunoassay for TDM

Answer 7

agglutination
fluorescence
chemiluminescence

Question 8

List classes of drugs most commonly measured in TDM

Answer 8

• antibiotics esp aminoglycosides, fluorquinolones
• anti-seizure drugs
• immunosuppressive drugs
• CV drugs esp anti-arrhythmia drugs
• psychiatric drugs esp lithium, clozapine

Question 9

When are peak and trough levels of drugs measured by TDM? Which time point is more commonly measured?

Answer 9

Most common to measure trough levels

Trough: just before next dose
Peak: 60 min after PO, 15-30 min after IV, 30-60 min after IM

Question 10

List possible causes for higher than expected drug levels

Answer 10

Overdose
Decreased clearance
Increased protein binding

Question 11

List possible causes for lower than expected drug levels

Answer 11

Decreased bioavailability
Insufficient dose
Nonadherence
Enzyme induction
Decreased protein binding

Question 12

Why might it be important to measure cocaine levels in the ED?

Answer 12

concern about MI risk

Question 13

Why might it be important to measure acetaminophen levels in the ED?

Answer 13

There is an antidote- can give N-acetylcysteine

Question 14

Most poisonings are diagnosed ______ and managed _______

Answer 14

clinically; symptomatically

Question 15

_______ is the most commonly diverted and abused pharmaceutical in the US

Answer 15

hydrocodone

Question 16

Urine screening tests for drugs of abuse are ____ but not ____

Answer 16

sensitive but not specific

Question 17

Quantitation of drugs of abuse require more sophisticated methodologies like:

Answer 17

GC, mass spec

Question 18

What are the NIDA 5?

Answer 18

Cannabinoids (THC)
Cocaine
Amphetamines
Opioids
Phencyclidine (PCP)

Question 19

List some substances that can cause a false positive screen for THC

Answer 19

ibuprofen, naproxen, sulindac, pantoprazole

Question 20

List some substances that can cause a false positive screen for opioids

Answer 20

diphenhydramine, ciprofloxacin, levofloxacin, ofloxacin, poppy seeds, quinine, rifampin, verapamil

Question 21

_____ is unique compared to other drugs of abuse in that one of its metabolites can be found in the urine long after last use

Answer 21

cannabis

Question 22

What are some methods of interference/ adulteration of drug screening immunoassays?

Answer 22

Change pH
Oxidize or reduce proteins
Change the ionic environment so antibodies don’t bind