Urine pentamidine as an indicator of lung pentamidine in patients receiving aerosol therapy

A cytotoxicity assay for evaluation of candidate anti-Pneumocystis carinii agents

A series of over 60 agents representing several different classes of compounds were evaluated for their effects on the ATP pools of Pneumocystis carinii populations derived from immunosuppressed rats. A cytotoxicity assay based on an ATP-driven bioluminescent reaction was used to determine the concentration of agent which decreased the P. carinii ATP pools by 50% versus untreated controls (IC50). A ranking system based on the IC50 value was devised for comparison of relative responses among the compounds evaluated in the cytotoxic assay and for comparison to in vivo efficacy. With few exceptions, there was a strong correlation between results from the ATP assay and the performance of the compound in vivo. Antibiotics, with the exception of trimethoprim-sulfamethoxazole (TMP-SMX), were ineffective at reducing the ATP pools and were not active clinically or in the rat model of P. carinii pneumonia. Likewise, other agents not expected to be effective, e.g., antiviral compounds, did not show activity. Standard anti-P. carinii compounds, e.g., TMP-SMX, pentamidine, and dapsone, dramatically reduced ATP levels. Analogs of the quinone and topoisomerase inhibitor groups were shown to reduce ATP concentrations and hold promise for further in vivo investigation. The cytotoxicity assay provides a rapid assessment of response, does not rely on replicating organisms, and should be useful for assessment of structure-function relationships.

Regional deposition and regional ventilation during inhalation of pentamidine

In most patients, the deposition of aerosolized pentamidine (AP) is less in the apex of the lung relative to the base. As the apex of the lung is relatively less ventilated than the base, it is possible that reduced regional ventilation may explain the inhomogeneity in regional drug deposition. The purpose of this study was to measure the relationship between regional deposition of AP and regional ventilation, and the influence of particle size and airway caliber on this relationship. Ten subjects with HIV infection who were receiving prophylaxis with AP were recruited. Using krypton (81mKr), we measured regional ventilation during treatment with AP, labeled with 99mTc. Two nebulizers were used (Respirgard II and Fisoneb) that produced particles of different size. In addition, patients were studied with and without a bronchodilator because changes in airway geometry can affect sites of particle deposition. There was no significant correlation between regional ventilation and regional particle deposition (r = 0.00, linear regression). Particle deposition in the upper lobes relative to the lower lobes was less than would be predicted by regional ventilation, by a ratio of 0.84 +/- 0.03 (mean +/- SE). Using two-way analysis of variance (ANOVA), the upper to lower zone deposition pattern was not affected by either nebulizer or by the use of albuterol. The Fisoneb had significantly more central deposition relative to the jet nebulizer (mean +/- SE, skC/P: Fisoneb 1.3 +/- 0.1, Respirgard 1.1 +/- 0.1, p = 0.005, two-way ANOVA). The use of a bronchodilator did not significantly affect the central/peripheral deposition pattern. We conclude that differences in deposition between upper and lower lung regions are not accounted for simply by differences in regional ventilation in patients undergoing prophylaxis with AP. In assessing the cause of regional inhomogeneities of pharmaceutical aerosol deposition (and in devising strategies to achieve more uniform distribution), regional ventilation should be measured directly rather than be inferred from the deposition pattern of the aerosol.

Lobar pentamidine levels and Pneumocystis carinii pneumonia following aerosolized pentamidine

Recent studies have suggested that failure of pentamidine prophylaxis against Pneumocystis carinii pneumonia (PCP) may be due to reduced deposition of pentamidine in the upper lobes. In this study, we performed bronchoalveolar lavage from the apical segment of the upper lobe and the middle lobe in 51 HIV-positive patients, all of whom were receiving prophylaxis with aerosolized pentamidine, who had presented with acute respiratory symptoms. Lavage fluid from each lobe was assayed for pentamidine using high-performance liquid chromatography (HPLC). The number of clusters of P carinii were counted after staining with a Wright-Giemsa stain. The patients were subclassified as PCP-positive (32 patients) and PCP-negative (19 patients) on the basis of the presence/absence of P carinii clusters in their BAL fluid. The concentration of pentamidine in the upper lobe compared with the middle lobe was no different (using paired Student's t tests) for either PCP-positive patients or PCP-negative patients. In comparing the positive with the negative subjects, using unpaired Student's t test, there was no difference in the concentration of pentamidine in the upper lobe or the middle lobe. For PCP-positive patients, the numbers of P carinii clusters were on average higher in the upper lobes (mean +/- SD: upper = 14.9 +/- 16.6, middle 7.5 +/- 10.8, p = 0.013, paired Student's t test), but there was no correlation between lobar P carinii cluster counts and pentamidine levels. We conclude that the absence of a relationship between cluster count and pentamidine level, the similarity in regional pentamidine levels between upper and middle lobes, as well as the similarity in pentamidine levels between the PCP-positive and PCP-negative groups indicate that the regional dose of pentamidine is not the determining factor as to whether aerosolized pentamidine prophylaxis will succeed or fail.

Exposure of health care workers to aerosolized pentamidine

In patients, urinary levels of pentamidine have been shown to reflect pulmonary deposition of aerosolized drug. Using urinary levels and air filter samples, we assessed factors responsible for health care worker (HCW) exposure. We measured serial urine samples in HCWs who administered aerosol pentamidine over an 11-month period and compared them with serial urine levels measured over 30 days in a normal volunteer in whose lungs a known amount of pentamidine (3.39 mg) had been deposited. Ambient exposure to pentamidine was determined by continuous high volume air sampling in the treatment room during routine therapy. In addition, the amount of pentamidine released by six HIV-positive subjects, performing tidal breathing with a Respirgard II nebulizer in an airtight booth, was measured by extracting air from the booth through a filter. The effect of adding noseclips, of coughing (with nebulizer shut down), and of removing the nebulizer from the patient's mouth without turning it off, were determined. Pentamidine in the urine of the normal volunteer reached a peak concentration of 9.5 ng/mg creatinine/ml and was detectable for 30 days following the exposure. In HCWs, pentamidine was detected intermittently in four of five individuals with levels as high as 18.2 ng/mg creatinine/ml. Samples of ambient treatment room air indicated small daily releases of pentamidine (0.013 +/- 0.02 mg per patient treated), but simultaneous urine levels in HCWs were negative. The data from the airtight booth revealed that removing the nebulizer from a patient's mouth without turning it off caused a 360-fold increased in pentamidine release compared to tidal breathing. Coughing resulted in a 6.9 (range 0.9-14.2)-fold increase in release, while the addition of noseclips had no significant effect. The pattern of intermittently positive urine tests and the low levels of ambient pentamidine detected in the air of the treatment room suggest that HCWs are being exposed to episodic but high concentrations of pentamidine. High level exposure is most likely to occur during treatment interruptions which are usually precipitated by coughing episodes. Because of the intermittent pattern of exposure and slow clearance of pentamidine, urine assay is useful for detecting high intermittent exposure. Random air sampling is a sensitive indicator of low level exposures but may not detect episodic high level releases.