Another area of concern is a critically ill patient who has a change in his or her pH. Medications that are highly bound and have high clearance rates may be affected. This is of particular concern when prescribing antibiotics that are time-dependent, such as beta-lactams.3
What happened to Mr. S? Mr. S likely experienced a drug–drug interaction that resulted in a subtherapeutic VPA level and subsequent seizure. Case reports have shown evidence that the carbapenem class of antibiotics, which includes ertapenem, interacts with VPA.7 Proposed mechanisms include a lowering of VPA serum levels due to a redistribution of the VPA onto the RBCs due to carbapenem. Other theories include the possibility that carbapenems may limit oral VPA absorption, decrease VPA enterohepatic recirculation, and increase VPA metabolism.7 Using VPA and ertapenem together is discouraged because seizures have been reported among patients receiving this combination. If it is medically necessary to administer VPA and ertapenem, closely monitor VPA levels. In Mr. S’s case, another broad-spectrum antibiotic, such as piperacillin-tazobactam, could have been used, for his diabetic foot infection.
While many medications may have high protein binding, there are few clinically important known interactions. However, our understanding of the relationship between protein binding and drug interactions may improve with additional research.
CASE CONTINUED
Under neurology’s care, lacosamide is added for treatment of Mr. S’s seizures. No more seizures are noted during the remainder of his hospitalization. Infectious disease services change his antibiotic to piperacillin-tazobactam. Mr. S continues to progress well and is discharged to a rehabilitation center 2 days later.
Related Resource
- DrugBank. www.drugbank.ca. Canadian Institutes of Health Research.
Drug Brand Names
Amiodarone • Cordarone, Pacerone
Bumetanide • Bumex
Bupivacaine • Marcaine, Sensorcaine
Buprenorphine • Belbuca, Subutex
Ceftriaxone • Rocephin
Chlordiazepoxide • Librium
Chlorpromazine • Thorazine
Clozapine • Clozaril
Cyclosporine • Gengraf, Neoral
Diazepam • Valium
Doxycycline • Acticlate, Doryx
Duloxetine • Cymbalta
Ertapenem • Invanz
Fluoxetine • Prozac, Sarafem
Furosemide • Lasix
Glargine (Insulin) • Lantus, Toujeo
Glipizide • Glucotrol
Haloperidol • Haldol
Ibuprofen • Advil, Motrin
Imipramine • Tofranil
Lacosamide • Vimpat
Lisinopril • Prinivil, Zestril
Lorazepam • Ativan
Nicardipine • Cardene
Nortriptyline • Pamelor
Paclitaxel • Abraxane, Taxol
Phenytoin • Dilantin, Phenytek
Piperacillin-tazobactam • Zosyn
Propofol • Diprivan
Sertraline • Zoloft
Tacrolimus • Prograf
Tamoxifen • Soltamox
Valproic acid • Depakene, Depakote
Verapamil • Calan, Verelan
Warfarin • Coumadin, Jantoven