Vancomycin is bacteriocidal. This can be used for pseudomembranous colitis, gram positive cocci, and MRSA. No absorption of it into the blood stream is possible if given orally, yet we have an oral form available. Why do we have oral capsules and oral suspensions for something that doesn’t get absorbed? Because we want it to affect the GI tract.
Must Monitor the Peak and Trough Levels
When someone is put on intravenous vancomycin, the physician will write an order that says to monitor the peak and trough blood levels. The peak will exist shortly after we give the drug intravenously. If we drew a wave, the trough would be the lowest level. After 3 doses, the patient will have their blood drawn so we could see the levels.
So when do you draw the blood?
To get the trough level, we draw the blood right before we hang the IV bag.
To get the peak level, it is not as intuitive because there’s other factors we have to keep in play. Like, how long does the infusion take to get into the body? Most antibiotics are put into a mini bag and infused over 30 minutes. Vancomycin, however, is in a larger bag that usually takes about 2 hours because if we infuse this drug too fast, they’ll get beet red, very hot, flushed and uncomfortable. Since the infusion takes about two hours and we need some time for the distribution to take place, we draw blood around 2.5 hours after the infusion has started to get the peak level.
How high do we want the peak and how low do we want the trough levels?
Usually most doctors will say we’re going to let the pharmacy analyze the blood levels. The peak blood level needs to be high enough to kill the organism. We want to be sure we’re exceeding the minimum concentration necessary to kill the organism. We also don’t want to get too high to risk toxicity. Toxicity is also associated with the trough level. This is very unusual. What we’re saying here is that we’re not allowed to give a patient their next dose until their blood level drops below a certain level. If the blood levels don’t go down far enough, we’re risking ototoxicity (hearing loss) and nephrotoxicity (kidney damage).
So the pharmacist is making sure the trough levels are low enough before the next dose is administered and that the peak is high enough that it’s killing the organism (and penetrating the lungs if it’s a respiratory infection).
Since we have to make sure the blood levels are low enough before we administer the next dose, the infection can worsen during that time. With this antibiotic, that’s a legitimate risk and that’s why we may see failure in treatment. It’s not because of resistance but because of this residual period of time.
Recap
- Bacteriocidal
- No oral absorption, but given orally to treat pseudomembranous colitis
- Use
- Penicillin allergy for gram positive cocci
- MRSA
- Pseudomembranous colitis
- Monitor Peak and Trough Blood Levels
- Adverse Reactions:
- Ototoxic
- Nephrotoxic
