Prophylactic ranitidine treatment in critically ill children--a population pharmacokinetic study

Evaluation of Intravenous Ranitidine on Gastric pH in Critically Ill Pediatric Patients

OBJECTIVE

To determine the dosing regimen of intravenous ranitidine (IVR) most likely to achieve a gastric pH of ≥4 in critically ill pediatric patients.

METHODS

A retrospective cohort study was designed and included patients younger than 19 years with gastric pH samples taken from a nasogastric tube within 24 hours after a dose of IVR in an intensive care unit. Data collection included patient demographics, clinical variables, IVR dosing, and gastric pH samples. Descriptive statistical analysis and multivariable logistic regression analysis with clustering of patients was performed to determine variables associated with odds of obtaining a pH of ≥4.

RESULTS

A total of 628 patients (1356 nasogastric samples) met study criteria (median age 1.3 years [IQR, 0.33, 5.7 years]; 53% male). The IVR dose was 0.90 ± 0.30 mg/kg per dose every 8.1 ± 2.9 hours, and 60.9% of patients (n = 383) had a pH ≥4. Patients with a pH value ≥4 had gastric pH samples taken earlier after a dose of IVR (6.7 ± 5.0 vs. 5.9 ± 4.7 hours, p < 0.001) but had no difference in IVR dose per kilogram (0.88 ± 0.31 vs. 0.88 ± 0.26, p = 0.86) or frequency of dosing (7.9 ± 3.2 vs. 7.9 ± 3.2 hours, p = 0.89). A multivariable logistic regression model identified increasing age, decreased kidney function, and decreased time to pH sample after an IVR dose with significantly greater odds of pH ≥4.

CONCLUSIONS

The IVR dosing to maintain a gastric pH ≥4 in critically ill pediatric patients should occur more frequently than every 8 hours. Gastric pH evaluation may be necessary to assess IVR efficacy.

Hemorrhagic Stress-induced Gastric Ulcer in a Healthy Toddler

A 1-year-old female toddler who was under a great amount of psychological stress presented with acute hematemesis. She had no significant medical history; she displayed lethargy and was anemic. Although blood transfusion and famotidine were administered for upper gastrointestinal bleeding (UGIB), the anemia did not improve. Thus, early endoscopy was performed under general anesthesia, revealing a gastric ulcer with exposed vessels in the supra-angular region. Cauterization via bipolar hemostatic forceps was performed on the exposed vessels, and the bleeding was controlled successfully. We diagnosed the patient with hemorrhagic stress-induced gastric ulcer due to psychological stress. Three months later, endoscopy revealed that the gastric ulcer had healed.

The enantioselective population pharmacokinetics of intravenous ketorolac in children using a stereoselective assay suitable for microanalysis†

Objective

To describe the effect of age and body size on enantiomer selective pharmacokinetic (PK) of intravenous ketorolac in children using a microanalytical assay.

Methods

Blood samples were obtained at 0, 15 and 30 min and at 1, 2, 4, 6, 8 and 12 h after a weight-dependent dose of ketorolac. Enantiomer concentration was measured using a liquid chromatography tandem mass spectrometry method. Non-linear mixed-effect modelling was used to assess PK parameters.

Key findings

Data from 11 children (1.7–15.6 years, weight 10.7–67.4 kg) were best described by a two-compartment model for R(+), S(−) and racemic ketorolac. Only weight (WT) significantly improved the goodness of fit. The final population models were CL = 1.5 × (WT/46)0.75, V1 = 8.2 × (WT/46), Q = 3.4 × (WT/46)0.75, V2 = 7.9 × (WT/46), CL = 2.98 × (WT/46), V1 = 13.2 × (WT/46), Q = 2.8 × (WT/46)0.75, V2 = 51.5 × (WT/46), and CL = 1.1 × (WT/46)0.75, V1 = 4.9 × (WT/46), Q = 1.7 × (WT/46)0.75 and V2 = 6.3 × (WT/46)for R(+), S(−) and racemic ketorolac.

Conclusions

Only body weight influenced the PK parameters for R(+) and S(−) ketorolac. Using allometric size scaling significantly affected the clearances (CL, Q) and volumes of distribution (V1, V2).

Pharmacokinetics and pharmacodynamics of famotidine and ranitidine in critically ill children

To characterize and compare acid suppression (pharmacodynamics) and pharmacokinetics of IV famotidine and ranitidine in critically ill children at risk for stress gastritis. Single-blind, randomized study in PICU patients 6 months to 18 years requiring mechanical ventilation with continuous gastric pH monitoring, randomized to IV famotidine 12 mg/m(2) or ranitidine 60 mg/m(2) when gastric pH < 4.0 >1 hour with serial blood sampling following first dose. Twenty-four children randomized to either famotidine (n = 12) or ranitidine (n = 12). Sixteen out of twenty-four completed both PK and PD study arms (7/12 famotidine; 4.7 ± 3.4 years; 9/12 ranitidine; 6.6 ± 4.7 years; p = 0.38). Time to gastric pH 4.0 and total time pH above 4.0 similar with no difference in pH at 6 and 12 hours (p > 0.2). No difference between drugs in clearance, volume of distribution and half-life (p > 0.05). Ratio of AUC pH to AUC drug concentration 0-12 hours after first dose was significantly greater for famotidine (0.06849 ± 0.01460 SD) than ranitidine (0.02453 ± 0.01448; p < 0.001) demonstrating greater potency of famotidine. pH lowering efficacy of both drugs is similar. Greater potency of famotidine may offer clinical advantage due to lower drug exposure and less frequent dosing to achieve same pH lowering effect.

A pharmacokinetic standard for babies and adults

The pharmacokinetic behavior of medicines used in humans follows largely predictable patterns across the human age range from premature babies to elderly adults. Most of the differences associated with age are in fact due to differences in size. Additional considerations are required to describe the processes of maturation of clearance processes and postnatal changes in body composition. Application of standard approaches to reporting pharmacokinetic parameters is essential for comparative human pharmacokinetic studies from babies to adults. A standardized comparison of pharmacokinetic parameters obtained in children and adults is shown for 46 drugs. Appropriate size scaling shows that children (over 2 years old) are similar to adults. Maturation changes are generally completed within the first 2 years of postnatal life; consequently babies may be considered as immature children, whereas children are just small adults.