Pentamidine pharmacokinetics in patients with AIDS with impaired renal function

Carboxymethyl chitosan modified lipid nanoformulations as a highly efficacious and biocompatible oral anti-leishmanial drug carrier system

Herein, carboxymethyl chitosan (CMC) grafted lipid nanoformulations were facilely prepared by thin-film hydration method as a highly efficient biocompatible anti-leishmanial carrier encapsulating amphotericin B (AmB). Nanoformulations were characterized for their physicochemical characteristics wherein TEM analysis confirmed the spherical structure, whereas FTIR analysis revealed the conjugation of CMC onto nanoformulations and confirmed the free state of AmB. Furthermore, the wettability study confirmed the presence of CMC on the surface of nanoformulations attributed to the enhanced hydrophilicity. Surface hydrophilicity additionally contributes towards consistent mucin retention ability for up to 6 h, superior mucoadhesiveness, and hence enhanced bioavailability. The proposed nanoformulations with high encapsulation and drug loading properties displayed controlled drug release in the physiological microenvironment. In vitro, antileishmanial results showed an astounding 97% inhibition in amastigote growth. Additionally, in vivo studies showed that treatment with nanoformulations significantly reduced the liver parasitic burden (93.5%) without causing any toxicity when given orally.

Pathophysiology of Drug-Induced Hypomagnesaemia

Magnesium (Mg²⁺) is the second most abundant intracellular and fourth extracellular cation found in the body and is involved in a wide range of functions in the human cell and human physiology. Its role in most of the enzyme processes (ATP-ases)-stabilisation of nucleic acids (DNA, RNA), regulation of calcium and potassium ion channels, proliferation, glucose metabolism and apoptosis-make it one of the most important cations in the cell. Three pathogenetic mechanisms are mainly implicated in the development of hypomagnesaemia: reduced food intake, decreased intestinal absorption and increased renal excretion of Mg²⁺. This review presents the function of Mg²⁺, how it is handled in the kidney and the drugs that cause hypomagnesaemia. The frequency and the number of drugs like diuretics and proton-pump inhibitors (PPIs) that are used daily in medical practice are discussed in order to prevent and treat adverse effects by providing an insight into Mg²⁺ homeostasis.

Dosing Recommendations for Pediatric Patients With Renal Impairment

A treatment gap exists for pediatric patients with renal impairment. Alterations in renal clearance and metabolism of drugs render standard dosage regimens inappropriate and may lead to drug toxicity, but these studies are not routinely conducted during drug development. The objective of this study was to examine the clinical evidence behind current renal impairment dosage recommendations for pediatric patients in a standard pediatric dosing handbook. The sources of recommendations and comparisons included the pediatric dosing handbook (Lexicomp), the U.S. Food and Drug Administration-approved manufacturer's labels, and published studies in the literature. One hundred twenty-six drugs in Lexicomp had pediatric renal dosing recommendations. Only 14% (18 of 126) of Lexicomp pediatric renal dosing recommendations referenced a pediatric clinical study, and 15% of manufacturer's labels (19 of 126) described specific dosing regimens for renally impaired pediatric patients. Forty-two products had published information on pediatric renal dosing, but 19 (45%) were case studies. When pediatric clinical studies were not referenced in Lexicomp, the renal dosing recommendations followed the adult and pediatric dosing recommendations on the manufacturer's label. Clinical evidence in pediatric patients does not exist for most renal dosing recommendations in a widely used pediatric dosing handbook, and the adult renal dosing recommendations from the manufacturer's label are currently the primary source of pediatric renal dosing information.

Systemic and Target-Site Pharmacokinetics of Antiparasitic Agents

About one-sixth of the world's population is affected by a neglected tropical disease as defined by the World Health Organization and Center for Disease Control. Parasitic diseases comprise most of the neglected tropical disease list and they are causing enormous amounts of disability, morbidity, mortality, and healthcare costs worldwide. The burden of disease of the top five parasitic diseases has been estimated to amount to a total 23 million disability-adjusted life-years. Despite the massive health and economic impact, most drugs currently used for the treatment of parasitic diseases have been developed decades ago and insufficient novel drugs are being developed. The current review provides a compilation of the systemic and target-site pharmacokinetics of established antiparasitic drugs. Knowledge of the pharmacokinetic profile of drugs allows for the examination and possibly optimization of existing dosing schemes. Many symptoms of parasitic diseases are caused by parasites residing in different host tissues. Penetration of the antiparasitic drug into these tissues, the target site of infection, is a prerequisite for a successful treatment of the disease. Therefore, for the examination and improvement of established dosing regimens, not only the plasma but also the tissue pharmacokinetics of the drug have to be considered. For the current paper, almost 7000 scientific articles were identified and screened from which 429 were reviewed in detail and 100 were included in this paper. Systemic pharmacokinetics are available for most antiparasitic drugs but in many cases, not for all the relevant patient populations and only for single- or multiple-dose administration. Systemic pharmacokinetic data in patients with organ impairment and target-site pharmacokinetic data for relevant tissues and body fluids are mostly lacking. To improve the treatment of patients with parasitic diseases, research in these areas is urgently needed.

The In Vitro Effects of Pentamidine Isethionate on Coagulation and Fibrinolysis

Pentamidine is bis-oxybenzamidine-based antiprotozoal drug. The parenteral use of pentamidine appears to affect the processes of blood coagulation and/or fibrinolysis resulting in rare but potentially life-threatening blood clot formation. Pentamidine was also found to cause disseminated intravascular coagulation syndrome. To investigate the potential underlying molecular mechanism(s) of pentamidine's effects on coagulation and fibrinolysis, we studied its effects on clotting times in normal and deficient human plasmas. Using normal plasma, pentamidine isethionate doubled the activated partial thromboplastin time at 27.5 µM, doubled the prothrombin time at 45.7 µM, and weakly doubled the thrombin time at 158.17 µM. Using plasmas deficient of factors VIIa, IXa, XIa, or XIIa, the concentrations to double the activated partial thromboplastin time were similar to that obtained using normal plasma. Pentamidine also inhibited plasmin-mediated clot lysis with half-maximal inhibitory concentration (IC50) value of ~3.6 μM. Chromogenic substrate hydrolysis assays indicated that pentamidine inhibits factor Xa and plasmin with IC50 values of 10.4 µM and 8.4 µM, respectively. Interestingly, it did not significantly inhibit thrombin, factor XIa, factor XIIIa, neutrophil elastase, or chymotrypsin at the highest concentrations tested. Michaelis-Menten kinetics and molecular modeling studies revealed that pentamidine inhibits factor Xa and plasmin in a competitive fashion. Overall, this study provides quantitative mechanistic insights into the in vitro effects of pentamidine isethionate on coagulation and fibrinolysis via the disruption of the proteolytic activity of factor Xa and plasmin.

Clinical Pharmacokinetics of Systemically Administered Antileishmanial Drugs

This review describes the pharmacokinetic properties of the systemically administered antileishmanial drugs pentavalent antimony, paromomycin, pentamidine, miltefosine and amphotericin B (AMB), including their absorption, distribution, metabolism and excretion and potential drug–drug interactions. This overview provides an understanding of their clinical pharmacokinetics, which could assist in rationalising and optimising treatment regimens, especially in combining multiple antileishmanial drugs in an attempt to increase efficacy and shorten treatment duration. Pentavalent antimony pharmacokinetics are characterised by rapid renal excretion of unchanged drug and a long terminal half-life, potentially due to intracellular conversion to trivalent antimony. Pentamidine is the only antileishmanial drug metabolised by cytochrome P450 enzymes. Paromomycin is excreted by the kidneys unchanged and is eliminated fastest of all antileishmanial drugs. Miltefosine pharmacokinetics are characterized by a long terminal half-life and extensive accumulation during treatment. AMB pharmacokinetics differ per drug formulation, with a fast renal and faecal excretion of AMB deoxylate but a much slower clearance of liposomal AMB resulting in an approximately ten-fold higher exposure. AMB and pentamidine pharmacokinetics have never been evaluated in leishmaniasis patients. Studies linking exposure to effect would be required to define target exposure levels in dose optimisation but have only been performed for miltefosine. Limited research has been conducted on exposure at the drug’s site of action, such as skin exposure in cutaneous leishmaniasis patients after systemic administration. Pharmacokinetic data on special patient populations such as HIV co-infected patients are mostly lacking. More research in these areas will help improve clinical outcomes by informed dosing and combination of drugs.

Effect of cimetidine on pentamidine induced hyperglycemia in rats

The antiprotozoal agent pentamidine, used for the treatment of Pneumocystis jirovecii pneumonia (PCP), is known to cause abnormalities in blood glucose homeostasis, such as hypoglycemia and hyperglycemia. Pentamidine has been reported to be a substrate of organic cation transporter 1 (OCT1). We investigated the combination effects of cimetidine, an OCT1 inhibitor, on the pharmacokinetics of pentamidine and on pentamidine-induced hyperglycemia. Pentamidine was infused intravenously to rats for 20 min at a dose of 7.5 or 15 mg/kg and serum samples were obtained periodically. The serum concentration of glucose did not change significantly after pentamidine infusion at 7.5mg/kg, while it increased with pentamidine at 15 mg/kg, and the maximal concentration of glucose was 167 ± 36 mg/dl, 30 min after the start of pentamidine infusion. Cimetidine (50mg/kg) enhanced the pentamidine-induced elevation of glucose concentration and the maximal concentration of glucose was 208 ± 33 mg/dl in the pentamidine 15 mg/kg treated group. Cimetidine combination significantly reduced total body clearance of pentamidine and increased pentamidine concentrations in the liver, kidneys, and lungs. A significant correlation was found between changes in serum glucose concentrations and serum concentrations of pentamidine 30 min after the start of pentamidine infusion. These results suggest that the hyperglycemic effect of pentamidine is dependent on the concentration of pentamidine and can be enhanced by cimetidine combination.

Pentamidine inhibits Coxiella burnetii growth and 23S rRNA intron splicing in vitro

Coxiella burnetii is the bacterial agent of Q fever in humans. Acute Q fever generally manifests as a flu-like illness and is typically self-resolving. In contrast, chronic Q fever usually presents with endocarditis and is often life-threatening without appropriate antimicrobial therapy. Unfortunately, available options for the successful treatment of chronic Q fever are both limited and protracted (>18 months). Pentamidine, an RNA splice inhibitor used to treat fungal and protozoal infections, was shown to reduce intracellular growth of Coxiella by ca. 73% at a concentration of 1 microM (ca. 0.6 microg/mL) compared with untreated controls, with no detectable toxic effects on host cells. Bacterial targets of pentamidine include Cbu.L1917 and Cbu.L1951, two group I introns that disrupt the 23S rRNA gene of Coxiella, as demonstrated by the drug's ability to inhibit intron RNA splicing in vitro. Since both introns are highly conserved amongst all eight genotypes of the pathogen, pentamidine is predicted to be efficacious against numerous strains of C. burnetii. To our knowledge, this is the first report describing antibacterial activity for this antifungal/antiprotozoal agent.

Structure and inhibition of human diamine oxidase

Humans have three functioning genes that encode copper-containing amine oxidases. The product of the AOC1 gene is a so-called diamine oxidase (hDAO), named for its substrate preference for diamines, particularly histamine. hDAO has been cloned and expressed in insect cells and the structure of the native enzyme determined by X-ray crystallography to a resolution of 1.8 A. The homodimeric structure has the archetypal amine oxidase fold. Two active sites, one in each subunit, are characterized by the presence of a copper ion and a topaquinone residue formed by the post-translational modification of a tyrosine. Although hDAO shares 37.9% sequence identity with another human copper amine oxidase, semicarbazide sensitive amine oxidase or vascular adhesion protein-1, its substrate binding pocket and entry channel are distinctly different in accord with the different substrate specificities. The structures of two inhibitor complexes of hDAO, berenil and pentamidine, have been refined to resolutions of 2.1 and 2.2 A, respectively. They bind noncovalently in the active-site channel. The inhibitor binding suggests that an aspartic acid residue, conserved in all diamine oxidases but absent from other amine oxidases, is responsible for the diamine specificity by interacting with the second amino group of preferred diamine substrates.

Trypanocidal drugs: mechanisms, resistance and new targets

The protozoan parasitesTrypanosoma bruceiandTrypanosoma cruziare the causative agents of African trypanosomiasis and Chagas disease, respectively. These are debilitating infections that exert a considerable health burden on some of the poorest people on the planet. Treatment of trypanosome infections is dependent on a small number of drugs that have limited efficacy and can cause severe side effects. Here, we review the properties of these drugs and describe new findings on their modes of action and the mechanisms by which resistance can arise. We further outline how a greater understanding of parasite biology is being exploited in the search for novel chemotherapeutic agents. This effort is being facilitated by new research networks that involve academic and biotechnology/pharmaceutical organisations, supported by public–private partnerships, and are bringing a new dynamism and purpose to the search for trypanocidal agents.

The clinical characteristics and antiretroviral dosing patterns of HIV-infected patients receiving dialysis

BACKGROUND

Human immunodeficiency virus (HIV)-related renal disease is the third leading cause of end-stage renal disease (ESRD) among African Americans aged 24 to 60 years. This study describes the clinical characteristics and antiretroviral dosing patterns of HIV-infected patients receiving dialysis to define the clinical needs of this growing population.

METHODS

Demographic and clinical information was collected on all HIV-infected patients incident to dialysis after January 1, 1998 until January 1, 2001 at five medical centers. The cohort was described overall and by subgroups based on hepatitis status, CD4 lymphocyte count, and use of antiretroviral therapy. Continuous and categoric variables were compared using either the Wilcoxon rank sum or Student t test and Fisher's exact or chi-square tests, as appropriate.

RESULTS

A total of 89 patients were included, 55 of whom were alive at the time of data collection. The mean age was 44.6 years (range, 22.7 to 66.9 years), 74.2% were male, and 83.2% patients were African Americans. While only 45.9% of patients undergoing renal biopsy were diagnosed with HIV-associated nephropathy (HIVAN), the majority of patients who had not undergone biopsy carried the clinical diagnosis of HIVAN (69.8%, P = 0.03). Of the cohort, 19.7% tested hepatitis B surface antigen positive, and 67.1% had reactive antibody tests for hepatitis C. Patients with hepatitis C were more likely to have experienced intravenous drug use as a risk behavior for HIV acquisition (OR 8.2; 95% CI 2.39, 27.9; P = 0.001] and to be older (OR 1.1 per year of age; 95% CI 1.02, 1.2; P = 0.01). A total of 60.7% of patients were receiving antiretroviral medication at last follow-up. Among patients alive and receiving antiretroviral medications at the time of data collection, absolute CD4+ count rose (268 vs. 339 cells/mL, P = 0.03), while among patients alive, but not receiving antiretroviral medications, absolute CD4+ count did not change (389 vs. 392 cells/mL, P = 0.11) during similar periods of follow-up. No difference was seen between initial and current HIV RNA levels for either group. Among patients receiving antiretroviral medications, there were significant variations in dosing regimens. The greatest variation was seen in the prescribing patterns of lamivudine with a 12-fold difference among patients.

CONCLUSION

The projected growth of the HIV-infected ESRD population requires a better understanding of the clinical needs of this population. The high prevalence of coinfection with hepatitis C as well as the wide variations in dosing patterns for antiretroviral medications are areas that require further investigation to minimize morbidity and mortality among this group.

Disposition of intravenous 123iodopentamidine in man

This study compared the disposition of the radiopharmaceutical [123I]iodopentamidine with that of pentamidine after intravenous infusion by measuring plasma concentrations of each using scintilation counting and high-performance liquid chromatography (HPLC), respectively. There was rapid hepatic uptake and biliary excretion of the 123I label. Distribution kinetics of the 123I label were similar to those of pentamidine, but its elimination half-life (41 +/- 27 h) was longer than that of pentamidine measured by HPLC (11 +/- 8 h). [123I]iodopentamidine distribution reflects that of pentamidine, but elimination of the radiopharmaceutical appears slower.

High-performance liquid chromatographic assay detects pentamidine metabolism by Fisher rat liver microsomes

Fisher rat liver microsomes metabolized the antimicrobial drug pentamidine to four new compounds detected by gradient elution reversed-phase high-performance liquid chromatography with variable wavelength detection. Coelution experiments with pentamidine metabolite standards determined the new peaks to be previously identified hydroxylated metabolites of pentamidine, with 1,5-bis(4'-amidinophenoxy)-3-pentanol and 1,5-di-(4'-amidinophenoxy)-2-pentanol formed in the greatest amount. The data contradict a previous report that Fisher rat liver homogenates do not metabolize pentamidine. Pentamidine and its known primary metabolites have almost identical absorption spectra; thus, pentamidine metabolism must be evaluated using gradient elution HPLC to resolve pentamidine from its metabolites. The current assay has now been used to demonstrate that Fisher and Sprague-Dawley rat, mouse, rabbit and human liver microsomes all metabolize pentamidine in vitro.

Pharmacokinetics and adverse reactions after a single dose of pentamidine in patients with Trypanosoma gambiense sleeping sickness

1. Plasma concentrations of pentamidine were measured up to 1-8 months after a single 2 h i.v. infusion of 3.0 to 4.8 mg kg-1 pentamidine isethionate in 11 patients with late stage Trypanosoma gambiense sleeping sickness. 2. Maximum plasma drug concentrations varied between 713 and 2461 nmol 1-1. After termination of infusion, a rapid distribution phase over 10 min was followed by a slower distribution phase and an elimination phase prolonged over weeks to months. 3. The 'terminal' elimination rate constant could be determined in six patients and subsequent kinetic calculations showed a three to fourfold variation in plasma clearance and 'terminal' half-life (median 1126 (range 553-2036) ml min-1 and 265 (107-446) h, respectively). The median apparent volume of distribution (Vss) was 11,850 1. Renal clearance accounted for a median of 11% of total plasma clearance, indicating that metabolism is a major route of pentamidine elimination in man. 4. Side effects were few and mild and a slight or moderate decrease in blood pressure was the most common registered adverse reaction observed in four subjects. 5. The prolonged elimination of pentamidine seems inconsistent with the present recommended dosage regimen of pentamidine for treatment of trypanosomiasis of 7 to 10 parenteral doses given once daily or every second day.

Clinical usefulness of high-pressure liquid chromatographic determination of serum pentamidine in AIDS patients

We have developed a reproducible HPLC method to determine serum pentamidine, which demonstrates good chromatographic performance, and is sensitive enough to measure therapeutic doses. Pentamidine is first extracted from serum by passage through a C-18 extraction cartridge. Potential interfering substances are then removed by washing with 100% methanol. Pentamidine is eluted from the extraction cartridge with 1-heptanesulfonic acid. The extract is chromatographed on a highly deactivated column for basic compounds in the presence of minimal concentrations of 1-heptanesulfonic acid as the pairing agent. Detection is by fluorescence. The method can determine serum pentamidine levels in the range of 15-600 ng/mL free of interference from other drugs. In monitoring pentamidine levels in AIDS patients with Pneumocystis carinii, we found that trough serum levels over 100 ng/mL were associated with toxicity (hypoglycemia or azotemia) in 100% of patients. With levels under 100 ng/mL, signs of toxicity were observed in only 29% of the patients. We conclude that dose adjustment based on serum levels reduces the incidence of toxicity and enhances pentamidine therapy.

Pentamidine-associated nephrotoxicity and hyperkalemia in patients with AIDS

The incidences of pentamidine-associated nephrotoxicity and hyperkalemia were determined from a retrospective review of records in AIDS patients using standard definitions for both toxicities. There were 37 patients, mean age 35.6 +/- 7.7 years and mean initial creatinine clearance (Clcr) 96 mL/min (1.6 mL/s). The mean pentamidine dose was 255 +/- 60 mg/d (3.87 +/- 0.33 mg/kg/d). The mean total dose was 2900 +/- 1600 mg given over 11.6 +/- 5.9 days (range 3-21 d). In 28 patients who were nephrotoxic (8 mild, 6 moderate, 14 severe), 27 episodes were possibly or probably pentamidine-associated. Total dose and days to nephrotoxicity onset were 1570 +/- 710 mg and 6.4 +/- 2.8 days (range 2-15 d), respectively. Nine patients became hyperkalemic (one required countermeasures) and all cases were pentamidine-associated. Total dose and days to hyperkalemia onset were 2510 +/- 1460 mg and 9.2 +/- 4.9 days (range 3-16 d), respectively. Mean baseline potassium increased and Clcr decreased significantly during therapy (from 4.2 to 4.9 mEq/L and from 96 to 70 mL/min, respectively). No correlation between nephrotoxicity or hyperkalemia and initial renal function was found, but significant correlations were found between the total pentamidine dose or duration and the percent of renal function remaining. AIDS patients have a high incidence of pentamidine-associated nephrotoxicity (up to 73 percent) and hyperkalemia (24 percent) with a trend to earlier onset of the former.

Pentamidine: a review

With the advent of the acquired immunodeficiency syndrome (AIDS), the therapeutic importance of pentamidine isethionate has increased greatly. This review summarizes the pharmacology, clinical experience in the treatment of Pneumocystis carinii pneumonia, and toxicity of pentamidine. Data are conflicting as to whether pentamidine is more or less effective than trimethoprim-sulfamethoxazole (TMP-SX) for the treatment of P carinii pneumonia in individuals with AIDS, but due to its toxicity and expense, it is considered as second-line therapy for P carinii pneumonia by many authorities. Hypoglycemia has been encountered in up to 27%, and nephrotoxicity in 25%, of treatment courses with pentamidine. In an attempt to circumvent the toxicities associated with parenteral administration, aerosolized delivery has been evaluated for both therapy and prevention of P carinii pneumonia. Aerosolized pentamidine, on the basis of early clinical results, convenience, and low toxicity, is being used extensively to prevent P carinii pneumonia in individuals at high risk. Relapses occur, however, and pneumothorax may be more common in those using this form of prophylaxis. Aerosolized pentamidine should not be used as sole therapy for acute P carinii pneumonia.

Acute, rapidly progressive renal failure with simultaneous use of amphotericin B and pentamidine

We report four cases of acute reversible renal failure in patients with acquired immune deficiency syndrome who received both amphotericin B (for systemic mycoses) and pentamidine isethionate (for Pneumocystis carinii pneumonia). The concurrent use of amphotericin B with either inhaled pentamidine or trimethoprim-sulfamethoxazole did not cause significant renal impairment.

Concentrations of aerosolized pentamidine in bronchoalveolar lavage, systemic absorption, and excretion

Pentamidine pulmonary pharmacokinetics were studied in 13 patients receiving once-daily inhaled therapy and 4 patients receiving low-dose intravenous treatment for Pneumocystis carinii pneumonia. Twenty-four hours after inhaled or intravenous therapy, the mean (+/- standard deviation) concentrations of pentamidine in serial bronchoalveolar specimen fluid ranged from 28.6 +/- 10 to 177.5 +/- 28 ng/ml and 6.05 +/- 2.29 to 21.4 +/- 15.7 ng/ml, respectively. Pentamidine concentrations in brochoalveolar fluid were generally higher after 2 weeks than after day 1 of therapy; however, the differences were not statistically different (P greater than 0.05). The pulmonary half-life after inhaled therapy is long; pentamidine was detectable in bronchoalveolar fluid at 33 (one patient), 69 (one patient), and 115 (one patient) days following the completion of 2 weeks of therapy. Systemic absorption of pentamidine was minimal; the mean (+/- standard deviation) plasma concentration at the completion of inhalation was 13.84 +/- 11.8 ng/ml, or 5% of the mean peak plasma concentration achieved after intravenous administration. Accumulation in the plasma did not occur with repeated inhalation as has been described with multiple intravenous dosing. Cumulative urinary excretion 24 h after the first dose was 5% of that observed with intravenous administration. These data may have importance in designing dosage regimens for the further investigation of inhaled pentamidine for treatment or prophylaxis of P. carinii pneumonia.