The relationship between ritonavir plasma levels and side-effects: implications for therapeutic drug monitoring

OBJECTIVES

To assess whether the neurological or gastrointestinal adverse effects of ritonavir correlate with parameters of ritonavir systemic exposure.

METHODS

Peak (Cmax) and trough (Cmin) ritonavir plasma levels were compared in 11 patients experiencing side-effects (group A) versus 10 patients without side-effects (group B). Ritonavir was administered with the following escalation dosing scheme: 300, 400, 500 mg twice a day for 3, 4, and 5 days, respectively, then the full dose of 600 mg twice a day. Blood sampling was done in group A within 24 h of the occurrence of side-effects and in group B after at least 3 days of the full dosage regimen.

RESULTS

Both Cmax and Cmax were significantly higher (Mann-Whitney U test) in patients with side-effects. Cmax was [median (interquartile range)] 26.7 (22.7-33.3) mg/l versus 16.2 (13.4-17.0) mg/l (P = 0.001) and Cmin was 12.6 (9.1-13.9) versus 7.5 (4.9-8.6) mg/l (P = 0.002).

CONCLUSION

Patients with higher ritonavir concentrations are at a higher risk of experiencing neurological or gastrointestinal side-effects. Individualization of the dosage regimen, e.g. a downward titration of the ritonavir dose in patients with side-effects, guided by plasma level monitoring, may result in a substantial increase in the percentage of patients tolerating ritonavir without increasing the risk of treatment failure as a result of suboptimal systemic exposure.

Specific high-performance liquid chromatography assay for determination of rifabutin plasma concentration following Extrelut column extraction

A specific, precise and accurate assay for determination of rifabutin in human plasma using Extrelut column extraction was developed and validated. Rifabutin concentrations were calculated with a standard curve ranging from 5 to 800 ng ml(-1). using a split-curve approach. Chromatographic peaks were separated by means of a 5 microm Symmetry Shield RP8 using a KH2PO4 (0.05 M) buffer-acetonitrile mobile phase. Detection wavelength was set at 275 nm. Chromatography was carried out at room temperature (20-25 degrees C). The limit of quantification was 5 ng ml(-1). The recovery was over 71%. The intra-day precision of the assay was 5, 7, and 1% while the inter-day precision was 11.2, 8.1, and 5.8% at concentrations of 30, 150 and 500 ng ml(-1), respectively. The accuracy ranged from 99 to 108%. Forty of the drugs most commonly administered to HIV-positive patients were found not to interfere with the assay. The assay has been used in a comparative study of rifabutin pharmacokinetics in HIV-positive patients with or without wasting syndrome. reserved.

Penetration of clindamycin and its metabolite N-demethylclindamycin into cerebrospinal fluid following intravenous infusion of clindamycin phosphate in patients with AIDS

Clindamycin, which is usually used in combination with pyrimethamine, has been proven effective in the treatment of cerebral toxoplasmosis in human immunodeficiency virus-infected patients. However, it is not known if clindamycin achieves inhibitory concentrations at the site of infection. Also, it has been hypothesized that the activity of clindamycin against Toxoplasma gondii may be due, at least in part, to a metabolite. We evaluated the penetration of clindamycin and its major metabolite, N-demethylclindamycin (NDC), into cerebrospinal fluid (CSF) of AIDS patients undergoing lumbar puncture for diagnostic purposes. A single, 1,200-mg dose of clindamycin was administered as a 45-min intravenous infusion beginning at 1.5 or 2.5 h before CSF sampling. The concentrations of clindamycin in CSF ranged from 0.091 to 0.429 mg/liter at 1.5 h and from 0.120 to 0.283 mg/liter at 2.5 h following the beginning of the infusion. The concentrations of clindamycin in CSF were well above the 50% inhibitory concentration of 0.001 mg/liter and the parasiticidal concentration of 0.006 mg/liter. NDC was undetectable both in plasma and in CSF. Our study provides a pharmacokinetic rationale for the clinical efficacy of clindamycin in the treatment of cerebral toxoplasmosis.

Population pharmacokinetics of dapsone administered biweekly to human immunodeficiency virus-infected patients

The population pharmacokinetics of dapsone were examined in human immunodeficiency virus-infected patients receiving dapsone at a dosage of 100 mg twice weekly for the prevention of Pneumocystis carinii pneumonia. Nonlinear mixed-effect modeling was used to determine the best pharmacostatistical model for the data. A one-compartment open model with first-order absorption and elimination was used as the structural pharmacokinetic model. Several covariates were tested for their influence on pharmacokinetic parameters. Rifampin was found to increase the values of clearance/bioavailability (CL/F) and volume of distribution/ bioavailability (V/F) by approximately 70%. CL/F and V/F were 1.83 liters/h and 69.6 liters, respectively, for patients not taking rifampin. The effect of rifampin on the pharmacokinetic parameters of dapsone was appreciably less than expected on the basis of studies with healthy volunteers. Increased bilirubin levels were associated with a significant decrease in the absorption rate constant (Ka). However, this finding may be considered clinically irrelevant because the post hoc Bayesian estimates of Ka for patients with high bilirubin levels ( > 1.2 mg/dl) were at the lower bound of the values for patients with normal bilirubin levels. The value of Ka was 0.957 h-1 for a patient with a bilirubin level of 0.7 mg/dl. After inclusion of covariates in the model, the interpatient variability was 35% for CL/F, not significant for V/F, and 85% for Ka. Simulation of plasma concentration-versus-time curves indicated that the administration of 100 mg of dapsone biweekly is associated with sustained dapsone levels in the plasma of the majority of the patients. Dosage adjustments for patients concomitantly treated with rifampin may be necessary.

Pharmacokinetics of dapsone in human immunodeficiency virus-infected children

Dapsone, administered at various doses and schedules, has been proven to be a safe and effective alternative to trimethoprim-sulfamethoxazole for prevention of Pneumocystis carinii pneumonia (PCP) in adults with human immunodeficiency virus (HIV) infection. Dapsone is also recommended by the Centers for Disease Control for PCP prophylaxis in HIV-infected children. However, the suggested dosage regimen is based upon clinical experience with children with leprosy and dermatitis herpetiformis rather than pharmacokinetic and pharmacodynamic data obtained from the target patient population. In order to determine a rational dosage regimen that could be tested in clinical studies aimed at the evaluation of dapsone for the prevention of PCP in HIV-infected children, we studied the pharmacokinetics of dapsone following a 2-mg/kg of body weight oral dose in twelve HIV-positive children aged 9 months to 9 years. Plasma was collected at the following times after dapsone administration: 0, 2, 4, 6, 12, 24, 48, 72, and 96 h. The levels of dapsone in plasma were determined by high-performance liquid chromatography. Data were analyzed by noncompartmental methods. Expressed as means +/- standard deviations (ranges), the pharmacokinetic parameters were as follows: peak concentration in plasma, 1.12 +/- 0.48 (0.44 to 1.81) mg/liter; time to peak concentration in plasma, 3.8 +/- 1.3 (2 to 6) h; half-life at elimination phase, 24.2 +/- 7.1 (14.4 to 35.0) h; clearance from plasma divided by bioavailability (CL/F), 1.15 +/- 0.67 (0.37 to 2.63) ml/min/kg; and volume of distribution divided by bioavailability (V/F), 2.25 +/- 1.20 (1.00 to 4.57) liters/kg. Oral CL correlated negatively with age (r = 0.614 and P = 0.034), as did V (r = 0.631 and P = 0.028). As a consequence of the high interindividual variability in growth retardation, pharmacokinetic parameters correlated with measures of body development better than they did with age (e.g., for CL/F to height, r = 0.765 and P = 0.004, and for V/F to height, r = 0.748 and P = 0.005). Since oral CL from plasma and V were positively and highly correlated (r = 0.898 and P = 0.0001), a lower absolute F may be the cause, in part, of higher values for CL/F and V/F in smaller children. The results of this study warrant the testing of a 2-mg/kg dose of dapsone administered twice or thrice weekly to HIV-infected children. The monitoring of drug levels in plasma and dosage adjustment may be necessary for smaller children.

[Monosomy 7qter: 2 new cases of chromosomal pathology with aspecific disorders of pre- and post-natal development]

Many cases of 7q deletion associated with mental retardation and multiple malformations have been described, nevertheless it is quite different to recognize common features among these infants. In this paper the cases of two female infants with uncommon facial features and 7q deletion are described. We also try to recognize the phenotypic features of this chromosomal disorder.