A phage-encoded anti-activator inhibits quorum sensing in Pseudomonas aeruginosa.

The arms race between bacteria and phages has led to the evolution of diverse anti-phage defenses, several of which are controlled by quorum-sensing pathways. In this work, we characterize a quorum-sensing anti-activator protein, Aqs1, found in Pseudomonas phage DMS3. We show that Aqs1 inhibits LasR, the master regulator of quorum sensing, and present the crystal structure of the Aqs1-LasR complex. The 69-residue Aqs1 protein also inhibits PilB, the type IV pilus assembly ATPase protein, which blocks superinfection by phages that require the pilus for infection. This study highlights the remarkable ability of small phage proteins to bind multiple host proteins and disrupt key biological pathways. As quorum sensing influences various anti-phage defenses, Aqs1 provides a mechanism by which infecting phages might simultaneously dampen multiple defenses. Because quorum-sensing systems are broadly distributed across bacteria, this mechanism of phage counter-defense may play an important role in phage-host evolutionary dynamics.

Use of a simplified nomogram to individualize digoxin dosing versus standard dosing practices in patients with heart failure.

STUDY OBJECTIVES: To compare the frequency of achieving a therapeutic serum digoxin concentration (SDC), defined as 0.5-0.9 ng/ml, by using a simplified nomogram to individualize digoxin dosing with standard dosing practices in patients with heart failure, and to characterize the relationship between genetic polymorphisms of the ABCB1 gene and SDC. DESIGN: Prospective study with a historical control group. SETTING: Outpatient care center of an urban academic medical center. PATIENTS: A total of 131 adults with heart failure due to left ventricular dysfunction who were treated with digoxin. INTERVENTION: Digoxin doses were determined either by the dosing nomogram (65 patients) or standard care (SC; 66 patients) by using historical controls who were randomly selected from a list of SDCs obtained from laboratory records and who had their digoxin doses determined by standard dosing practices. MEASUREMENTS AND MAIN RESULTS: The primary end point was the proportion of patients achieving a steady-state SDC of 0.5-0.9 ng/ml; secondary end points were mean SDC and proportion of patients achieving a steady-state SDC lower than 1.0 ng/ml. Postdistributive steady-state SDCs were measured 2-4 weeks after digoxin dosage adjustment or initiation. Therapeutic SDCs were achieved with similar frequency in both groups (38.7% in the nomogram group vs 34.5% in the SC group, p=0.65); however, more patients in the nomogram group had SDCs lower than 1.0 ng/ml than in the SC group (85.0% vs 44.9%, p<0.001). Mean daily digoxin doses were lower in the nomogram group (149 ± 67 µg vs 177 ± 74 µg, p=0.02), resulting in lower mean SDCs compared with those in the SC group (0.52 ± 0.30 ng/ml vs 1.12 ± 0.58 ng/ml, p<0.001). Patients in the pharmacogenetic substudy provided blood samples for genotyping of three common ABCB1 single nucleotide polymorphisms: C1236T (rs1128503), G2677T/A (rs2032582), and C3435T (rs1045642). SDCs were not significantly associated with ABCB1 genotypes. CONCLUSION: Our simplified digoxin dosing nomogram resulted in lower SDCs compared with standard dosing practices but achieved therapeutic SDCs with similar frequency. A greater proportion of patients dosed according to our nomogram had SDCs lower than 1.0 ng/ml, consistent with consensus guidelines. Genetic polymorphisms of the ABCB1 gene were not associated with SDC.

Delirium in a patient with toxic flecainide plasma concentrations: the role of a pharmacokinetic drug interaction with paroxetine.

OBJECTIVE: To describe a case of flecainide-induced delirium associated with a pharmacokinetic drug interaction with paroxetine. CASE SUMMARY: A 69-year-old white female presented to the emergency department with a history of confusion and paranoia over the past several days. On admission the patient was taking carvedilol 12 mg twice daily, warfarin 2 mg/day, folic acid 1 mg/day, levothyroxine 100 microg/day, pantoprazole 40 mg/day, paroxetine 40 mg/day, and flecainide 100 mg twice daily. Flecainide had been started 2 weeks prior for atrial fibrillation. Laboratory test findings on admission were notable only for a flecainide plasma concentration of 1360 microg/L (reference range 200-1000). A metabolic drug interaction between flecainide and paroxetine, which the patient had been taking for more than 5 years, was considered. Paroxetine was discontinued and the dose of flecainide was reduced to 50 mg twice daily. Her delirium resolved 3 days later. DISCUSSION: Flecainide and pharmacologically similar agents that interact with sodium channels may cause delirium in susceptible patients. A MEDLINE search (1966-January 2009) revealed one in vivo pharmacokinetic study on the interaction between flecainide, a CYP2D6 substrate, and paroxetine, a CYP2D6 inhibitor, as well as 3 case reports of flecainide-induced delirium. According to the Naranjo probability scale, flecainide was the probable cause of the patient's delirium; the Horn Drug Interaction Probability Scale indicates a possible pharmacokinetic drug interaction between flecainide and paroxetine. CONCLUSIONS: Supratherapeutic flecainide plasma concentrations may cause delirium. Because toxicity may occur when flecainide is prescribed with paroxetine and other potent CYP2D6 inhibitors, flecainide plasma concentrations should be monitored closely with commencement of CYP2D6 inhibitors.