Antithrombotic Therapy in Children: Monitoring oral anticoagulant therapy

Monitoring: Monitoring oral anticoagulant therapy in children is difficult and requires close supervision with frequent dose adjustments.1 In contrast to adults, only 10 to 20% of children can be safely monitored monthly. Reasons contributing to the need for frequent monitoring include diet, medications, primary medical problems, and age distribution.
Breast-fed infants are very sensitive to oral anticoagulants, due to the low concentrations of vitamin K in breast milk.-59 In contrast, some children are resistant to oral anticoagulants due to impaired absorption;60 requirements for total parenteral nutrition, which is routinely supplemented with vitamin K; and nutrient formulas, which are supplemented with vitamin K (55 to 110 μg/L) to protect against hemorrhagic disease of the newborn.
Most children are receiving multiple medications, both on a long-term basis to treat their primary problems or intermittently to treat acquired problems (eg, infections). These medications influence dose requirements for oral anticoagulants in a fashion similar to that of adults.52 The most commonly used medications in children that affect the INR are listed in Table 7. Most children have serious primary problems that influence the biologic effect and clearance of oral anticoagulants, as well as the risk of bleeding.
The age distribution of children requiring oral anticoagulants is skewed, with the two largest groups comprised of children <1 year of age and teenagers read buy zyrtec online. Teenagers are not necessarily compliant with their medication, and infants are a difficult group of patients to monitor due to poor venous access as well as their complicated medical problems.
The problems with monitoring oral anticoagulants in children have limited their use, even in conditions in which they are strongly indicated. Potential solutions for optimizing therapy with oral anticoagulants in children include pediatric anticoagulation clinics,1 whole blood PT/INR monitors used at home, and clinical trials to determine if lower, safer INR ranges are as efficacious.
Whole Blood Monitors for Children: Whole blood monitors use various techniques to measure the time from application of fresh samples of capillary whole blood to coagulation of the sample. The monitors include a batch-specific calibration code that converts the result into a calculated INR. There are two “point of care” monitors evaluated in the pediatric population, the CoaguChek (Boehringer Ingelheim; Mannheim, Germany) and the ProTime Microcoagulation System (International Technidyne Corp; Edison, NJ). Both monitors were shown to be acceptable and reliable for use in the outpatient laboratory and at home settings. Parents and patients undertook a formal education program prior to using the monitors. The major advantages identified by families included reduced trauma of venipunctures, minimal interruption of school and work, ease of operation, and portability.
Table 7—Commonly Used Drugs in Children That Affect Their INR Value

Drug Effect on INR
Amiodarone Increase
Aspirin Increase or no change
Amoxicillin (Amoxil) Slight increase
Cefaclor (Ceclor) Increase
Carbamazepine (Tegretol) Decrease
Phenytoin (Dilantin) Decrease
Phenobarbital Decrease
Cloxacillin Increase
Prednisone Increase
T rimethoprim-sulfamethoxazole Increase
Ranitidine Increase