Vancomycin continuous infusion as prophylaxis for vascular surgery.

Prosthetic graft infection is a devastating complication of vascular surgery that occurs in 3%-5% of clean prosthetic procedures. Staphylococci are the most frequently isolated pathogens, and thus surgical prophylaxis regimens often include vancomycin. However, the efficacy of these regimens in ensuring a required concentration of antibiotic is uncertain. This study aimed to determine if a continuous vancomycin infusion regimen administered perioperatively as surgical prophylaxis for vascular procedures maintained an adequate serum concentration. Thirty-four consecutive patients undergoing a vascular procedure requiring a prosthetic graft or patch were given vancomycin prophylaxis. Each patient received a loading dose calculated according to body weight 12 hours before surgery. A 24-hour continuous infusion was then started, based on calculated creatinine clearance. Serum vancomycin concentrations were checked on induction of anesthesia, 2 hours postoperatively, and at the end of the infusion. Perioperative fluid administration and blood loss were recorded. An estimated creatinine clearance was repeated on the second postoperative day. Of the 34 patients recruited, 7 did not have the anticipated procedure and 6 patients had incomplete sample collection. Twenty-one patients with complete sample collection were analyzed. The target concentration (10-25 mg/L) was achieved in 81% of all samples. All patients achieved the target concentration at 1 or more time points. The regimen employed provided appropriate concentrations at the time of intervention. No potentially toxic concentrations or adverse reactions to vancomycin were encountered. Vancomycin given as a continuous infusion delivers adequate serum concentration. Long-term graft infection rates are needed to show a clinical effect.

Population pharmacokinetics of hydroxychloroquine in patients with rheumatoid arthritis.

SUMMARY: Hydroxychloroquine (HCQ) is an antimalarial drug that is also used as a second-line treatment of rheumatoid arthritis (RA). Clinically, the use of HCQ is characterized by a long delay in the onset of action, and withdrawal of treatment is often a result of inefficacy rather than from toxicity. The slow onset of action can be attributed to the pharmacokinetics (PK) of HCQ, and wide interpatient variability is evident. Tentative relationships between concentration and effect have been made, but to date, no population PK model has been developed for HCQ. This study aimed to develop a population PK model including an estimation of the oral bioavailability of HCQ. In addition, the effects of the coadministration of methotrexate on the PK of HCQ were examined. Hydroxychloroquine blood concentration data were combined from previous pharmacokinetic studies in patients with rheumatoid arthritis. A total of 123 patients were studied, giving the data cohort from four previously published studies. Two groups of patients were included: 74 received hydroxychloroquine (HCQ) alone, and 49 received HCQ and methotrexate (MTX). All data analyses were carried out using the NONMEM program. A one-compartment PK model was supported, rather than a three-compartment model as previously published, probably because of the clustering of concentrations taken at the end of a dosing interval. The population estimate of bioavailability of 0.75 (0.07), n = 9, was consistent with literature values. The parameter values from the final model were: Cl = 9.9 +/- 0.4 L/h, V = 605 +/- 91 L, ka = 0.77 +/- 0.22 hours(-1), t(tag) = 0.44 +/- 0.02 hours. Clearance was not affected by the presence of MTX, and, hence, steady-state drug concentrations and maintenance dosage requirements were similar. A population PK model was successfully developed for HCQ.

Combination therapy with methotrexate and hydroxychloroquine for rheumatoid arthritis increases exposure to methotrexate.

OBJECTIVE: To examine the bioavailability of methotrexate (MTX) in the presence of hydroxychloroquine (HCQ), and vice versa, to determine a possible pharmacokinetic explanation for the observation that combination treatment of rheumatoid arthritis with MTX and HCQ has been shown, clinically, to be more potent than MTX used alone. METHODS: In a randomized crossover study, 10 healthy subjects received, on each of 5 dosing occasions, MTX alone as tablets or intravenous solution, HCQ alone as a tablet or oral solution, or a coadministered dose of MTX tablets with an HCQ tablet. The area under the concentration-time curve (AUC) was determined for each subject, on each dosing occasion, for each compound. RESULTS: The mean AUC for MTX was increased (p = 0.005) and the maximum MTX concentration (Cmax) decreased (p = 0.025) when MTX was coadministered with HCQ, compared to MTX administered alone. The time to reach Cmax for MTX administration, tmax, was also increased during the coadministration with HCQ (p = 0.072). The AUC of HCQ showed no significant difference (p = 0.957) between any of the dosing occasions. CONCLUSION: These results may explain the increased potency of the MTX-HCQ combination over MTX as a single agent and also the sustained effects of MTX when administered with HCQ. In addition, the reduced Cmax of MTX observed during the coadministration may explain diminution of acute liver adverse effects. Extra vigilance for MTX adverse effects during combination therapy with HCQ is recommended, especially if renal function is known to be decreased.