SAN DIEGO — Children on warfarin should get an international normalized ratio measurement within 2-3 days of starting antibiotic therapy, since they may experience significant changes in INR value, Kathy Hinoki, R.N., reported in a poster session at an international Kawasaki disease symposium.
“I have proactively cut back on a warfarin or coumadin dose when the parent has told me the child is sick and has been started on an antibiotic,” Ms. Hinoki, a cardiology nurse with Children's Hospital Los Angeles, said in an interview.
“This prevents the lab values from getting out of whack and [lessens the] risk for bleeding.”
She noted that while pediatricians typically order antibiotic for warfarin-treated children, “they usually don't have the background about the seriousness of the warfarin-antibiotic interaction, so they probably should consult with someone who [has the expertise].”
In a 5-year study of 3,582 lab encounters in the anticoagulation clinic at Children's Hospital Los Angeles, Ms. Hinoki and her associates selected 28 children who had a stable INR on the same dose of warfarin for greater than three consecutive lab encounters prior to the initiation of antibiotic therapy.
The three most common reasons for anticoagulation were prosthetic valves, Fontan procedure, and Kawasaki disease.
The investigators measured the INR within 1-7 days after the antibiotics were started, and they calculated the percent change in INR.
Of the 28 cases, eight females and four males demonstrated INR increases of more than 20%. Of the 16 children who demonstrated either no change or a decrease in INR, 12 were males and 4 were females.
Ms. Hinoki noted that erythromycin, cefuroxime, clindamycin, levofloxacin, and doxycycline were associated with significant increases in INR, while ampicillin, cephalexin, and amoxicillin-clavulanic acid were associated with no changes in INR. Griseofulvin and azithromycin appeared to cause mild to moderate decreases in INR.
Age, ethnicity, and cardiac diagnosis appeared to have no impact on drug interactions.
“There's much more research to do, because antibiotics are constantly changing,” said Ms. Hinoki, who runs the hospital's anticoagulation program.
The symposium was sponsored by the American Heart Association.