Drug metabolism and pharmacokinetics in malutrition

Analysis of Adverse Drug Reactions in Pediatric Patients with Epilepsy: An Intensive Pharmacovigilance Study

Epilepsy is a chronic neurological disease characterized by the presence of spontaneous seizures, with a higher incidence in the pediatric population. Anti-seizure medication (ASM) may produce adverse drug reactions (ADRs) with an elevated frequency and a high severity. Thus, the objective of the present study was to analyze, through intensive pharmacovigilance over 112 months, the ADRs produced by valproic acid (VPA), oxcarbazepine (OXC), phenytoin (PHT), and levetiracetam (LEV), among others, administered to monotherapy or polytherapy for Mexican hospitalized pediatric epilepsy patients. A total of 1034 patients were interviewed; 315 met the inclusion criteria, 211 patients presented ADRs, and 104 did not. A total of 548 ASM-ADRs were identified, and VPA, LEV, and PHT were the main culprit drugs. The most frequent ADRs were drowsiness, irritability, and thrombocytopenia, and the main systems affected were hematologic, nervous, and dermatologic. LEV and OXC caused more nonsevere ADRs, and PHT caused more severe ADRs. The risk analysis showed an association between belonging to the younger groups and polytherapy with ADR presence and between polytherapy and malnutrition with severe ADRs. In addition, most of the severe ADRs were preventable, and most of the nonsevere ADRs were nonpreventable.

Effects of starvation on the pharmacokinetics and optimal dosages of florfenicol and associated serum biochemistry in Asian seabass (Lates calcarifer)

Starvation has influence on physiology and pharmacokinetic (PK) characteristics of many drugs in land animals. However, similar PK information in fish is lacking. The current study examined the effects of starvation on fish PK, taking florfenicol (FF) in Asian seabass as an example. FF was orally administered at a single dose of 10 mg/kg into 35-day starved fish reared at 25 and 30°C and the serum FF concentration was analyzed by HPLC-FLD. At 30°C, the absorption and elimination half-lives of the starved fish were increased by 30% (from 0.44 to 0.57 h) and 55% (from 7.2 to 11.18 h), respectively. The volume of distribution, clearance, and area under the curve were changed from 1.25 to 0.71 L/kg, 0.120 to 0.044 L/kg/h, and 88 to 228 h·μg/ml, respectively. Similar starvation-induced PK changes were also observed at 25°C. The serum biochemical parameters, mainly the alanine aminotransferase, aspartate aminotransferase, and glucose levels, were significantly reduced in the starvation group. Overall, FF absorption, distribution, and elimination rates were reduced by starvation, resulting in four to five times lower optimal dosage than the non-starved fish. Drug treatment in starved fish should be treated with caution as overdosing and/or tissue residues could perceivably occur.

Effect of nutritional status on acetaminophen pharmacokinetic profile

Short-term fasting increases acetaminophen exposure in healthy subjects, whereas no effect was observed after a high-fat diet. These findings suggest the necessity of considering nutritional status when assessing the risk of acetaminophen-induced toxicity. Further role of nutrition status on pharmacokinetic profile of acetaminophen (APAP) at toxic doses are not available. Our study aims to compare the effects of nutrition status on kinetic profile of APAP in 3 different dietary conditions like - Normal diet (ND), Low protein diet (LPD) and High fat diet (HFD) groups. To investigate the pharmacokinetic profile of APAP at toxic dose, 3 groups of animals were separated after weaning and for the next 15 weeks they were fed with their respective diets (ND, LPD and HFD). Animals were dosed with APAP (300 mg/kg p.o) and blood sampling was done at different time intervals. Plasma samples were analyzed using HPLC method. Data analysis was done by Non-compartment analysis using Phoenix WinNonlin 8.3 software. LPD group show higher values of C _max, T _max, T _1/2, and AUC _0-4, AUC _0-x values compared to ND and HFD groups. Our study compared APAP pharmacokinetic profile at toxic dose in three different diet regimes.

Piperaquine Exposure Is Altered by Pregnancy, HIV, and Nutritional Status in Ugandan Women

Dihydroartemisinin-piperaquine (DHA-PQ) provides highly effective therapy and chemoprevention for malaria in pregnant African women. PQ concentrations of >10.3 ng/ml have been associated with reduced maternal parasitemia, placental malaria, and improved birth outcomes. We characterized the population pharmacokinetics (PK) of PQ in a post hoc analysis of human immunodeficiency virus (HIV)-infected and -uninfected pregnant women receiving DHA-PQ as chemoprevention every 4 or 8 weeks. The effects of covariates such as pregnancy, nutritional status (body mass index [BMI]), and efavirenz (EFV)-based antiretroviral therapy were investigated. PQ concentrations from two chemoprevention trials were pooled to create a population PK database from 274 women and 2,218 PK observations. A three-compartment model with an absorption lag best fit the data. Consistent with our prior intensive PK evaluation, pregnancy and EFV use resulted in a 72% and 61% increased PQ clearance, compared to postpartum and HIV-uninfected pregnant women, respectively. Low BMI at 28 weeks of gestation was associated with increased clearance (2% increase per unit decrease in BMI). Low-BMI women given DHA-PQ every 8 weeks had a higher prevalence of parasitemia, malaria infection, and placental malaria compared to women with higher BMIs. The reduced piperaquine exposure in women with low BMI as well as during EFV coadministration, compared to pregnant women with higher BMIs and not taking EFV, suggests that these populations could benefit from weekly instead of monthly dosing for prevention of malaria parasitemia. Simulations indicated that because of the BMI-clearance relationship, weight-based regimens would not improve protection compared to a 2,880 mg fixed-dose regimen when provided monthly. (The clinical trials described in this paper have been registered at ClinicalTrials.gov under identifiers NCT02163447 and NCT02282293.).

Severe Acute Malnutrition Results in Lower Lumefantrine Exposure in Children Treated With Artemether-Lumefantrine for Uncomplicated Malaria

Severe acute malnutrition (SAM) has been reported to be associated with increased malaria morbidity in Sub-Saharan African children and may affect the pharmacology of antimalarial drugs. This population pharmacokinetic (PK)-pharmacodynamic study included 131 SAM and 266 non-SAM children administered artemether-lumefantrine twice daily for 3 days. Lumefantrine capillary plasma concentrations were adequately described by two transit-absorption compartments followed by two distribution compartments. Allometrically scaled body weight and an enzymatic maturation effect were included in the PK model. Mid-upper arm circumference was associated with decreased absorption of lumefantrine (25.4% decreased absorption per 1 cm reduction). Risk of recurrent malaria episodes (i.e., reinfection) were characterized by an interval-censored time-to-event model with a sigmoid maximum-effect model describing the effect of lumefantrine. SAM children were at risk of underexposure to lumefantrine and an increased risk of malaria reinfection compared with well-nourished children. Research on optimized regimens should be considered for malaria treatment in malnourished children.

Mortality from adverse drug reaction-related hospitalizations in south-west Ethiopia: A cross-sectional study

WHAT IS KNOWN AND OBJECTIVE

Adverse drug reactions (ADRs) are an important cause of mortality during medical care. To our knowledge, no Ethiopian studies have reported on mortality due to ADRs in patients presenting to hospital from the community setting. The aim of this study was to determine the mortality rate attributable to ADRs in patients presenting to hospital, identify drugs implicated in the ADR-related deaths and identify factors contributing to ADR-related mortality at Jimma University Specialised Hospital (JUSH), south-west Ethiopia METHODS: This cross-sectional study included 1001 patients aged ≥18 years consecutively admitted to medical wards from May 2015 to August 2016. ADR-related mortality was determined through detailed review of medical records, laboratory tests and patient interviews followed by causality assessment by the Naranjo algorithm and expert consensus.

RESULTS

Of 1001 patients, 15, 1.5% (95% confidence interval [CI]: 0.80%-2.30%) died with an ADR. The primary suspected causes of death were drug-induced hepatotoxicity (7, 43.8%) followed by acute kidney injury (4, 25.0%). Isoniazid (6, 33.3%), pyrazinamide (3, 16.7%), efavirenz (2, 11.1%) and tenofovir (2, 11.1%) were commonly implicated drugs. The majority of ADRs (14, 93.8%) were preventable. Unadjusted bivariate comparisons suggested patients who died with ADRs were more likely to have pre-existing liver disease (40.0% vs 7.0%; 95% confidence interval [CI]: 8.1%-57.8%), a history of ADRs (40% vs 1.4%; 95% CI: 13.8%-63.4%), a lower mean (±SD) body mass index (BMI, 17.6 ± 2.1 vs 20.0 ± 2.9 kg/m² ; 95% CI = 0.9-3.9), exposure to antitubercular (46.7% vs 18.9%; 95% CI: 2.3%-53.1%) and antiretroviral (40.0% vs 7.7%; 95% CI: 7.5%-57.2%) therapies, and a higher mean number of medications (7.1 ± 3.3 vs 3.8 ± 2.1; 95% CI: 2.2-4.4) and Charlson Comorbidity Index (3.9 ± 2.9 vs 1.6 ± 1.8; 95% CI: 1.4-3.2) than surviving patients without ADRs.

WHAT IS NEW AND CONCLUSION

Fatal ADRs were common in patients presenting to hospital. The drugs implicated were mostly antitubercular and antiretroviral therapies, reflecting the high burden of HIV and tuberculosis in the study population. ADR-related deaths were significantly associated with poor nutritional status. The majority of ADR-related deaths were preventable, highlighting the need to develop a multidisciplinary approach to closely monitor patients who are prescribed antitubercular and antiretroviral therapies, particularly in patients with hepatic disease, a history of ADRs, who are malnourished and who are exposed to multiple medications.

Population Pharmacokinetics of Gentamicin in Mexican Children With Severe Malnutrition

BACKGROUND

To develop a population pharmacokinetic model of gentamicin in children with complicated severe malnutrition and to study the influence of covariates (weight and age) on pharmacokinetic indices. In addition, we use the model to perform Monte Carlo simulations to explore the efficacy of several dosage regimens.

METHODS

Twenty-six children with severe complicated malnutrition were studied. Ninety-six samples of gentamicin plasma concentrations, obtained from 0.5 to 8 hours after intravenous dosing, were analyzed. Population pharmacokinetic models were built using the program Monolix 4.2 (Lixoft, Antony, France). Monte Carlo simulations were performed to evaluate optimal dosage regimens, using the final pharmacokinetic model, based on the probability of pharmacokinetic-pharmacodynamic target attainment.

RESULTS

The concentration-time data were fitted best to 1-compartment model. The estimated population clearance was 1.1 L/h, and the volume of distribution was 2.23 L, with an interindividual variability of 47.2% and 35.6%, respectively. The final models for the clearance and volume of distribution were as follows: CL (L/h) = CL = 1.15 (age/median age) and V (L) = 2.33 (weight/median weight). In Monte Carlo simulations, gentamicin given in dosages of 7.5 to 15 mg/kg optical density was effective in achieving the pharmacodynamic target Cmax:minimal inhibitory concentration >10 for minimal inhibitory concentrations ≤2.5 mg/L, with a probability lower than 1% for Cmin >1 mg/L.

CONCLUSIONS

Based on the available evidence, an intravenous dose of 7.5 to 15 mg/kg once daily in children with complicated severe malnutrition and normal renal function ensures high probability of efficacy and low risk of nephrotoxicity, which gives further support to the recommendations issued by the World Health Organization treatment for this patient population.

Influence of malnutrition on the disposition of metronidazole in rats

The influence of dietary protein deficiency on the disposition of metronidazole and its two major metabolites was examined in male Sprague-Dawley rats fed for 4 weeks on a 23% (control-) or a 5% (low-) protein diet ad libitum. Following an intravenous bolus dose of 10 mg/kg metronidazole hydrochloride, blood samples were obtained serially for a period of 24 hr after drug administration. Serum concentration-time data were analyzed by nonlinear least-squares regression, as well as noncompartmental techniques. The average mean residence time (MRT) was significantly prolonged by 48%, while the systemic clearance (Cl) was decreased by 42% in the protein-deficient rats. Since there was no alteration in the apparent steady-state volume of distribution (V ss), the mean harmonic half-life was increased from 2.9 to 5.0 hr in the protein-deficient rats. Although the percentage of metronidazole recovered as total drug in the urine over 24 hr was not significantly different between the two groups of animals, rats on a low-protein diet excreted a significantly smaller percentage of the administered dose as unchanged metronidazole (mean ± SD, 24.6 ± 3.8 vs 36.5 ± 12%) and a larger percentage (16.7 ± 2.6 vs 8.3 ± 1.8%) as the hydroxylated metabolite. No significant difference in the partial metabolic clearance of the hydroxylated metabolite of metronidazole was seen between the two groups of animals; however, there was a significant decrease in the renal clearance of metronidazole (1.45 ± 0.68 vs 0.55 ± 0.06 ml/min/kg) in the rats fed a low-protein diet. We conclude that the decreased clearance of metronidazole in protein deficiency is a result primarily of the decreased glomerular filtration rate, decreased biliary excretion, and/or increased net tubular reabsorption of metronidazole.

Drug and nutrition interactions: not just food for thought

WHAT IS KNOWN AND OBJECTIVE

The management of drug-drug interactions - from recognition of the interaction potential, to addressing the negative consequences - are well-recognized and avoided, or rapidly addressed when identified clinically. Drug-nutrition interactions are no less important than drug-drug interactions in patient care. Unfortunately, beyond those caused by food, these interactions are less commonly recognized or identified and managed. This article will re-introduce the topic of drug-nutrition interactions to clinicians.

COMMENT

Although many clinicians are acutely aware of and vigilant for potential drug-drug interactions, most are less aware of the possibility of drug-nutrition interactions beyond classic food-drug interactions. Interaction can occur between a drug and a nutrient, multiple nutrients, food in general, specific foods or components, or nutrition status. An interaction is considered clinically significant if it alters therapeutic drug response and/or compromises nutrition status. Mechanistically the interactions may be physicochemical reactions, actions at membrane transporters or metabolizing enzymes, or an influence on physiologic function. Appreciating the many types of drug-nutrition interactions will aid the clinician and have the potential to influence patient outcome.

WHAT IS NEW AND CONCLUSION

Ongoing advances in knowledge about drug and nutrition interactions have potential to improve patient care. Drug-nutrition interactions need to be better recognized, understood on a mechanistic basis, predicted, and managed as necessary.

Drug-nutrient interactions: a broad view with implications for practice

The relevance of drug?nutrient interactions in daily practice continues to grow with the widespread use of medication. Interactions can involve a single nutrient, multiple nutrients, food in general, or nutrition status. Mechanistically, drug?nutrient interactions occur because of altered intestinal transport and metabolism, or systemic distribution, metabolism and excretion, as well as additive or antagonistic effects. Optimal patient care includes identifying, evaluating, and managing these interactions. This task can be supported by a systematic approach for categorizing interactions and rating their clinical significance. This review provides such a broad framework using recent examples, as well as some classic drug?nutrient interactions. Pertinent definitions are presented, as is a suggested approach for clinicians. This important and expanding subject will benefit tremendously from further clinician involvement.

Pharmacokinetics of intravenous and oral DA-8159, a new erectogenic, in rats with protein-calorie malnutrition

Influence of dietary protein deficiency on the pharmacokinetics of DA-8159 and one of its metabolites, DA-8164, was investigated after intravenous and oral administration of DA-8159 at a dose of 30 mg kg−1 to male Sprague-Dawley rats allowed free access to a 23% (control) or 5% (protein-calorie malnutrition, PCM) casein diet for 4 weeks. The total area under the plasma concentration-time curve from time zero to time infinity (AUC) values of DA-8164 were significantly smaller after both intravenous (87.0 vs 162 μg min mL−1) and oral (144 vs 319 μg min mL−1) administration of DA-8159 to PCM rats. This could be due to the decrease in CYP3A1/2 (50–60%) in the rats because DA-8164 was mainly formed via CYP3A1/ 2 in rats. This could be supported by significantly slower in-vitro CLint (2.04 ± 0.646 vs 3.15 ± 0.693 μL min−1 (mg protein)−1) for the formation of DA-8164 in hepatic microsomal fraction of PCM rats. After intravenous administration of DA-8159, the AUC values of DA-8159 were not significantly different between the two groups of rats although the AUC of DA-8164 was significantly smaller in PCM rats, and this may be due to the minor metabolic pathway of DA-8164 in rats. However, after oral administration of DA-8159, the AUC of DA-8159 was significantly greater in PCM rats (194 vs 122 μg min mL−1). This was not due to enhanced absorption of DA-8159 from the gastrointestinal tract in the rats but may be due to a decreased intestinal first-pass effect of DA-8159 in the rat.

Effects of protein-calorie malnutrition on the pharmacokinetics of DA-7867, a new oxazolidinone, in rats

The pharmacokinetic parameters of DA-7867, a new oxazolidinone, were compared after intravenous and oral administration at a dose of 10mg kg−1 to control rats and rats with protein-calorie malnutrition (rats with PCM). After intravenous administration of 10mg kg−1 DA-7867 to rats, metabolism of the drug was not considerable and after 14 days approximately 85.0% of the dose was recovered as unchanged drug from urine and faeces. After intravenous administration to rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity (AUC) was significantly smaller (10800 vs 6990μg min mL−1) compared with control rats. This may have been due to significantly faster total body clearance (CL, 0.930 vs 1.44mL min−1 kg−1). The faster CL in PCM rats could have been due to significantly faster non-renal clearance (0.842 vs 1.39mL min−1 kg−1 due to significantly greater gastrointestinal (including biliary) excretion; the amount of unchanged DA-7867 recovered from the entire gastrointestinal tract at 24h was significantly greater (1.19 vs 4.28% of intravenous dose)) because the renal clearance was significantly slower in PCM rats (0.0874 vs 0.0553mL min−1 kg−1). After oral administration to PCM rats, the AUC was significantly smaller compared with control rats (7900 vs 4310μgmin mL−1). This could have been due to a decrease in absorption from the gastrointestinal tract.

Effects of cysteine on metformin pharmacokinetics in rats with protein-calorie malnutrition: partial restoration of some parameters to control levels

Metformin is metabolized primarily via hepatic microsomal cytochrome P450 (CYP)2C11, CYP2D1 and CYP3A1/2 in rats. The expression and mRNA levels of hepatic CYP2C11 and CYP3A1/2 are decreased in rats with protein-calorie malnutrition (PCM), but these levels are fully or partially restored to control levels in PMC rats by oral cysteine supplementation (PCMC rats). Thus, it would be expected that the pharmacokinetic parameters of metformin in PCM rats would be returned to control levels in PCMC rats. Metformin was administered i.v. (100 mg kg−1) and orally (100 mg kg−1) to control, CC (control rats with oral cysteine supplementation), PCM and PCMC rats. The following pharmacokinetic parameters of metformin following i.v. administration were restored from levels in PCM rats to levels in control rats in PCMC rats: intrinsic clearance (0.0350, 0.0309, 0.0253 and 0.0316 mL min−1 mg−1 protein for control, CC, PCM, and PCMC rats, respectively), total area under the plasma concentration-time curve from time zero to time infinity (AUC; 4110, 4290, 5540 and 4430 μg min mL−1, respectively), and time-averaged non-renal clearance (8.12, 7.95, 5.94 and 8.17 mL min−1 kg−1, respectively). AUC values following oral administration were comparable between control and PCMC rats (1520, 1480, 2290 and 1680 μg min mL−1, respectively).

Effects of cysteine on the pharmacokinetic parameters of omeprazole in rats with protein-calorie malnutrition: partial restoration of some parameters to control levels by oral cysteine supplementation

BACKGROUND

It has been reported that omeprazole is mainly metabolized via the hepatic cytochrome (CYP) 1A1/2, 3A1/2, and 2D1, and the expressions and mRNA levels of CYP1A2, 2C11, and 3A1/2 decreased in protein-calorie malnutrition (PCM) rats compared with controls. Interestingly, the decreased CYP1A2, 2C11, and 3A1/2 in PCM rats returned fully or partially to control levels by oral cysteine supplementation (PCMC rats). Hence, it could be expected that some pharmacokinetic parameters of omeprazole might change in PCM rats and partially restore to control levels in PCMC rats. The purpose of this study is to investigate the pharmacokinetic changes of omeprazole in PCM rats and restoration of the parameters in PCMC rats to control levels.

METHODS

Omeprazole was administered intravenously (20 mg/kg) and orally (40 mg/kg) to control, PCM, and PCMC rats.

RESULTS

The following pharmacokinetic parameters were changed in PCM rats and partially returned to control levels in PCMC rats: the area under the plasma concentration-time curve (AUC; 387, 762, and 539 microg min/mL for control, PCM, and PCMC rats, respectively, after intravenous [IV] administration, and the corresponding values after oral administration: 115, 304, and 201 microg min/mL), total body clearance (51.7, 25.5, and 37.1 mL/min/kg, respectively), nonrenal clearance (51.5, 25.4, and 36.1 mL/min/kg, respectively), and in vitro intrinsic clearance (0.158, 0.118, and 0.138 mL/min/mg protein).

CONCLUSIONS

PCM was associated with significant changes in some omeprazole pharmacokinetics and the pharmacokinetic parameters restored to control levels by oral cysteine.

Effects of cysteine on the pharmacokinetics of oltipraz in rats with protein–calorie malnutrition

Effects of cysteine on the pharmacokinetics of oltipraz were investigated after iv (10 mg/kg) and oral (30 mg/kg) administration to male control, protein-calorie malnutrition (PCM), and PCM with oral cysteine supplementation (PCMC) rats. It was reported that oltipraz was mainly metabolized via hepatic CYP1A1/2, 2B1/2, 2C11, 3A1/2, and 2D1 in male rats. The expression and mRNA levels of CYP1A2, 2C11, and 3A1/2 were also reported to decrease in male PCM rats compared with controls. Interestingly, the decreased CYP isozymes in PCM rats returned fully or partially to controls by oral cysteine supplementation (PCMC rats). Hence, it would be expected that in PCM rats, some pharmacokinetic parameters of oltipraz are fully or partially returned to controls by cysteine. This was proven by the following parameters in PCMC rats: the AUC (328, 782, and 416 mug min/mL for control, PCM, and PCMC rats, respectively, after iv administration, and 223, 456, and 242 mug min/mL after oral administration), terminal half-life (130, 212, and 143 min), mean residence time (MRT) (149, 299, and 189 min), and in vitro CL(int) (0.181, 0.107, and 0.153 mL/min/mg protein) were fully returned to controls, and CL and CL(NR) values were partially returned to controls.

Effects of cysteine on the pharmacokinetics of intravenous torasemide in rats with protein−calorie malnutrition

Effects of cysteine on the pharmacokinetics of torasemide were investigated after intravenous administration at a dose of 2 mg/kg to control rats and rats with PCM and PCMC. Torasemide was reported to be mainly metabolized via hepatic CYP2C9 in humans, and human CYP2C9 and male rat CYP2C11 proteins have 77% homology. It has also been reported that in male rats with PCM, the CYP2C11 level decreased to approximately 20% of the control level, but the decreased CYP2C11 level in rats with PCM partially returned to the control level by oral cysteine supplementation (rats with PCMC). Hence, it could be expected that in rats with PCM, some pharmacokinetic parameters of torasemide could be significantly different compared with those in control rats and rats with PCMC; however, they could be not significantly different between control rats and rats with PCMC. This was proven by the following parameters; the AUC (1880, 4080, and 2290 microg x min/mL for control rats and rats with PCM and PCMC, respectively), terminal half-life (188, 277, and 139 min), MRT (154, 323, and 155 min), CL (1.06, 0.491, and 0.943 mL/min/kg), CL(NR) (0.992, 0.430, and 0.874 mL/min/kg), and in vitro intrinsic torasemide disappearance clearance, CL(int) (0.102, 0.0842, and 0.0997 mL/min/mg protein).

Pharmacokinetic changes in drugs during protein-calorie malnutrition: correlation between drug metabolism and hepatic microsomal cytochrome p450 isozymes

The rats with protein-calorie malnutrition (PCM, 5% casein diet for a period of 4-week) were reported to exhibit 60 and 80% suppression in the hepatic microsomal cytochrome P450 (CYP) 1A2 and CYP2C11 levels, respectively, and 40-50% decreases in CYP2E1 and CYP3A1/2 levels compared to control (23% casein diet for a period of 4-week) based on Western blot analysis. In addition, Northern blot analysis showed that CYP1A2, CYP2E1, CYP2C11, and CYP3A1/2 mRNAs decreased in the state of PCM as well. Hence, pharmacokinetic changes of the drugs in rats with PCM [especially the area under the plasma concentration-time curve from time zero to time infinity (AUC) changes of metabolite(s)] reported from literatures were tried to explain in terms of CYP isozyme changes in the rats. Otherwise, the time-averaged nonrenal clearance (CL NR) of parent drug was compared. Pharmacokinetic changes of the drugs in other types of malnutritional state, such as kwashiorkor and marasmus, in both human and animal models were also compared. The drugs reviewed are as follows: diuretics, antibiotics, anticancer agents, antiepileptics, antiarrythmics, analgesics, xanthines, antimalarials, and miscellaneous.

Effects of cysteine on the pharmacokinetics of intravenous clarithromycin in rats with protein-calorie malnutrition

Effects of cysteine on the pharmacokinetics of clarithromycin were investigated after intravenous administration of the drug at a dose of 20 mg/kg to control rats (4-week fed on 23% casein diet) and rats with PCM (protein-calorie malnutrition, 4-week fed on 5% casein diet) and PCMC (PCM treated with 250 mg/kg for oral cysteine twice daily during the fourth week). Clarithromycin has been reported to be metabolized via hepatic microsomal cytochrome P450 (CYP) 3A4 to 14-hydroxyclarithromycin (primary metabolite of clarithromycin) in human subjects. It has also been reported that in rats with PCM, CYP3A23 level decreased to 40-50% of control level, but decreased CYP3A23 level in rats with PCM completely returned to control level by oral cysteine supplementation (rats with PCMC). Human CYP3A4 and rat CYP3A23 proteins have 73% homology. In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity, AUC (567, 853 and 558 microg min/ml for control rats and rats with PCM and PCMC, respectively) and percentage of clarithromycin remaining after incubation with liver homogenate (69.6, 83.9 and 71.7%) were significantly greater than those in control rats and rats with PCMC. Moreover, in rats with PCM, the total body clearance, CL (35.3, 23.4 and 35.8 ml/min/kg), nonrenal clearance, CL(NR) (21.3, 15.2 and 24.1 ml/min/kg) and maximum velocity for the disappearance of clarithromycin after incubation with hepatic microsomal fraction, V(max) (351, 211 and 372 pmol/min/mg protein) were significantly slower than those in control rats and rats with PCMC. However, above mentioned each parameter was not significantly different between control rats and rats with PCMC. The above data suggested that metabolism of clarithromycin decreased significantly in rats with PCM as compared to control due to significantly decreased level of CYP3A23 in the rats. By cysteine supplementation (rats with PCMC), some pharmacokinetic parameters of clarithromycin (AUC, CL, CL(NR) and V(max)) were restored fully to control levels because CYP3A23 level was completely returned to control level in rats with PCMC.

Effects of cysteine on the pharmacokinetics of intravenous 2-(allylthio)pyrazine, a new chemoprotective agent, in rats with protein-calorie malnutrition

The effects of cysteine on the pharmacokinetics of 2-(allylthio)pyrazine (2-AP) were investigated after intravenous administration of the drug (50 mg/kg) to control (Sprague-Dawley) rats (4-week fed on 23% casein diet), and rats with protein-calorie malnutrition (PCM, 4-week fed on 5% casein diet) and PCMC (PCM with 250 mg/kg of oral cysteine, twice daily starting from the fourth week). In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity (AUC) of 2-AP was significantly smaller than that in control rats. However, in rats with PCMC, the AUC of 2-AP was significantly greater than that in control rats and rats with PCM. This could be due to significantly greater formation of M4 in rats with PCM and significantly smaller formation of M4 in rats with PCMC than that in control rats. In rats with PCMC, some pharmacokinetic parameters of 2-AP restored fully or more than the levels of control rats. For example, in rats with PCMC, the apparent volume of distribution at steady state of 2-AP (7290, 16,600, and 7050 ml/kg for control rats, and rats with PCM and PCMC, respectively), the percentage of dose excreted in 24-h urine as unchanged 2-AP (0.242, 0.727, and 0.130%), and 'the amount' excreted in 24-h urine as M4 (100, 228, and 51%) were comparable to those in control rats. However, the AUC (739, 434, and 1240 microg/min/ml) and total body clearance (67.7, 115, and 40.2 ml/min/kg) of 2-AP were significantly greater and slower, respectively, than those in control rats. This could be at least partly due to increase in S-methyltransferase activity (to form M4) in rats with PCM and greater restoration of its activity (decrease in its activity) in rats with PCMC.

Pharmacokinetics and pharmacodynamics of azosemide

Azosemide is used in the treatment of oedematous states and hypertension. The exact mechanism of action is not fully understood, but it mainly acts on both the medullary and cortical segments of the thick ascending limb of the loop of Henle. Delayed tolerance was demonstrated in humans by homeostatic mechanisms (principally an increase in aldosterone secretion and perhaps also an increase in the reabsorption of solute in the proximal tubule). After oral administration to healthy humans in the fasting state, the plasma concentration of azosemide reached its peak at 3-4 h with an absorption lag time of approximately 1 h and a terminal half-life of 2-3 h. The estimated extent of absolute oral bioavailability in humans was approximately 20.4%. After oral administration of the same dose of azosemide and furosemide, the diuretic effect was similar between the two drugs, but after intravenous administration, the effect of azosemide was 5.5-8 times greater than that in furosemide. This could be due to the considerable first-pass effect of azosemide. The protein binding to 4% human serum albumin was greater than 95% at azosemide concentrations ranging from 10 to 100 microg/ml using an equilibrium dialysis technique. The poor affinity of human tissues to azosemide was supported by the relatively small value of the apparent post-pseudodistribution volume of distribution (Vdbeta), 0.262 l/kg. Eleven metabolites (including degraded products) of azosemide including M1, glucuronide conjugates of both M1 and azosemide, thiophenemethanol, thiophencarboxylic acid and its glycine conjugate were obtained in rats. Only azosemide and its glucuronide were detected in humans. In humans, total body clearance, renal clearance and terminal half-life of azosemide were 112 ml/min, 41.6 ml/min and 2.03 h, respectively. Azosemide is actively secreted in the renal proximal tubule possibly via nonspecific organic acid secretory pathway in humans. Thus, the amount of azosemide that reaches its site of action could be significantly modified by changes in the capacity of this transport system. This capacity, in turn, could be predictably changed in disease states, resulting in decreased delivery of the diuretic to the transport site, as well as in the presence of other organic acids such as nonsteroidal anti-inflammatory drugs which could compete for active transport of azosemide. The urinary excretion rate of azosemide could be correlated well to its diuretic effects since the receptors are located in the loop of Henle. The diuretic effects of azosemide were dependent on the rate and composition of fluid replacement in rabbits; therefore, this factor should be considered in the evaluation of bioequivalence assessment.

Effects of cysteine on the pharmacokinetics of intravenous chlorzoxazone in rats with protein-calorie malnutrition

The effects of cysteine on the pharmacokinetics of chlorzoxazone (CZX) and one of its metabolites, 6-hydroxychlorzoxazone (OH-CZX), were investigated after intravenous administration of CZX, 25 mg/kg, to control rats (4-week fed on 23% casein diet) and rats with PCM (4-week fed on 5% casein diet) and PCMC (PCM with oral cysteine supplementation, 250 mg/kg, twice daily during the fourth week). In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity (AUC) of OH-CZX (436 compared with 972 microgmin/ml) and the percentages of intravenous dose of CZX excreted in 8-h urine as OH-CZX (20.2 compared with 38.5%) were significantly smaller than those in control rats. The above data indicated that the formation of OH-CZX from CZX decreased significantly in rats with PCM due to a significant decrease in chlorzoxazone-6-hydroxylase activity (328 compared with 895 pmol/min/mg protein) in the rats. The results were expected since in rats with PCM, hepatic CYP2E1 expression and its mRNA levels decreased significantly as compared to control, and CZX was metabolized to OH-CZX primarily by CYP2E1 in rats. By cysteine supplementation (rats with PCMC), some pharmacokinetic parameters restored fully (hepatic microsomal chlorzoxazone 6-hydroxylation activity based on both mg protein and nmol CYP450) or partially (total body clearance and apparent volume of distribution at steady state of CZX, and AUC, terminal half-life and 8-h urinary excretion of OH-CZX) to control levels.

Clinical pharmacokinetics of 5-fluorouracil with consideration of chronopharmacokinetics

Even though 5-fluorouracil (FU) is one of the oldest anticancer drugs, its use in cancer chemotherapy continues to increase. Fluorouracil is a pro-drug that requires intracellular activation to exert its effects. This makes it difficult to associate blood drug concentration with cell toxicity directly, although data from the literature show the existence of such a relationship. The relationship between FU pharmacokinetics and patient response has been explored extensively and reports attest a link between systemic drug exposure and response and survival. This has led to the concept of maximal tolerated exposure, and strategies to achieve this rely on pharmacokinetic follow-up and individual dose adjustment. More than 80% of the administered FU dose is eliminated by catabolism through dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme. Dihydropyrimidine dehydrogenase activity is found in most tissues but is highest in the liver. Peripheral blood mononuclear cells (PBMC) are used to monitor clinically DPD activity. A significant, but weak correlation between PBMC and liver DPD activity has been observed. The relationship between PBMC-DPD activity and FU systemic clearance is weak (r2 = 0.10); thus, simply determining PBMC-DPD is not sufficient to predict accurately FU clearance. Population pharmacokinetic analysis identified patient co-variables that influence FU clearance; drug kinetics is significantly reduced by increased age, high serum alkaline phosphatase, length of drug infusion, and low PBMC-DPD. Autoregulation of FU metabolism also is suggested; inhibition of DPD activity was observed after FU administration in both colorectal cancer patients and an animal model. Circadian rhythmicity in DPD activity is suggested from both human and animal investigations. In patients receiving protracted low dose 5-FU infusion, the circadian rhythm in FU plasma concentration peaks at 11:00h and is lowest at 23:00h, on average. The inverse relationship observed between the circadian profile of FU plasma concentration and PBMC-DP activity in these same patients suggests a link between DPD activity and FU pharmacokinetics. The impact of the biological time of drug administration was also studied with short venous infusions; clearance was 70% greater at 13:00h than at 01:00h. Similarly, peak drug concentration occurred in the first half of the night in patients receiving constant rate 5-FU infusion for 2-5d. Several studies describe wide interindividual variation in the timing of the peak and trough of the 24h rhythm in DPD activity. The rational for FU chronomodulated therapy has been the circadian rhythm in host drug tolerance, which is greatest during the night time when the proliferation of normal target tissue is least. A randomized study of chronomodulated FU therapy with maximal delivery rate at 04:00h was shown clearly to be significantly more effective and less toxic than control flat FU therapy. Future research must focus on easy-to-obtain markers of specific rhythms to individualize the chronomodulated FU delivery.

Effects of cysteine on the pharmacokinetics of intravenous phenytoin in rats with protein-calorie malnutrition

The effects of cysteine on the pharmacokinetics of phenytoin and one of its metabolites, 5-(p-hydroxyphenyl)-5-phenylhydantoin (pHPPH) were investigated after intravenous administration of phenytoin, 25 mg/kg, to control rats (4-week fed on 23% casein diet) and rats with PCM (protein-calorie malnutrition, 4-week fed on 5% casein diet) and PCMC (PCM with oral cysteine supplementation, 250 mg/kg, twice daily starting from the fourth week). In rats with PCM and PCMC, the phenytoin hydroxylation (to form pHPPH) activities were significantly smaller (164, 103 and 95.3 pmol/min per mg protein for the control rats, and rats with PCM and PCMC, respectively) than that in control rats. In rats with PCMC, the intrinsic clearance of phenytoin, CL(int) was significantly slower than those in control rats and rats with PCM (0.175, 0.131 and 0.044 ml/min). The above data suggested that the formation of pHPPH could be reduced in rats with PCM and PCMC. This was supported by significantly smaller 24-h urinary excretion of pHPPH (54.7, 35.6 and 32.5% of intravenous dose of phenytoin) in rats with PCM and PCMC than that in control rats. In rats with PCM, the maximum velocity (0.344, 0.203 and 0.196 microg/min), apparent volume of distribution in central compartment (44.4, 65.4 and 72.2 ml/kg) of phenytoin, and total area under the plasma concentration-time curve from time zero to time infinity (609, 714 and 1210 microg min/ml), renal clearance (20.5, 13.4 and 4.67 ml/min per kg) and 24-h urinary excretion (54.7, 35.6 and 32.5% of intravenous dose of phenytoin) of pHPPH were not returned to control levels by cysteine supplementation (rats with PCMC). This could be mainly due to the fact that the phenytoin hydroxylation activity in rats with PCMC was not returned to control level.

Suppression of rat hepatic cytochrome P450s by protein-calorie malnutrition: complete or partial restoration by cysteine or methionine supplementation

Pharmacokinetic profiles of therapeutic agents are altered by protein-calorie malnutrition (PCM). The current study was designed to determine the expression of hepatic cytochrome P450s in rats after protein restriction and to investigate its molecular basis. Western blot analysis revealed that rats with protein restriction for 4 weeks exhibited marked suppression in the hepatic P450 1A2, 2C11, 2E1, and 3A1/2 levels. Northern blot analysis showed that hepatic P450 1A2, 2C11, and 3A1/2 mRNAs were significantly decreased in the state of PCM. The P450 2E1 mRNA level was slightly decreased in PCM rats, suggesting the possibility that expression of P450 2E1 affected by PCM might result from the transcriptional and/or posttranscriptional regulation. PCM-induced changes in most P450 expression completely or partially returned to control levels by a week of cysteine supplementation. Cysteine also prevented decreases in P450 1A2, 2C11, 2E1, and 3A1/2 mRNA levels by PCM. Methionine was minimally active in restoring the P450 expression. A metabolic change in hepatic ethoxyresorufin dealkylase activity in PCM rats was consistent with the P450 apoprotein and mRNA levels. Although the plasma concentrations of azosemide, a loop diuretic, primarily metabolized by cytochrome P450 1A, increased in protein-deprived rats, cysteine supplementation significantly reduced the increased plasma concentrations of the drug. The altered pharmacokinetic parameters of azosemide in PCM rats returned to those of control after cysteine supplementation, corroborating the conclusion that cysteine was effective in restoring cytochrome P450 expression and metabolic activities.

Pharmacokinetics of amikacin in children with kwashiorkor

The pharmacokinetics of intravenous amikacin, administered as a mean (SD) bolus dose of 5.5 (1.2) mg/kg to children between the ages of 1 and 4 years with kwashiorkor, was studied. Although there was a tendency for the average volume of distribution to increase to the upper limit of normal, plasma elimination half-life, first order elimination-phase rate constant and clearance remained close to the reference values for adults. Despite marginal elevation of the average t1/2 beta-value, reflecting a general trend, renal impairment in respect of amikacin clearance could not be demonstrated. It was concluded that the changes in pharmacokinetic parameters found in kwashiorkor are not large enough to amend the current therapeutic regimens for amikacin in this condition.

Malnutrition and pharmacokinetics of penicillin in Ethiopian children

Penicillin was given to 104 children with different nutritional status, normal, underweight, marasmus and kwashiorkor. Penicillin was given either intravenously, intramuscularly or orally and the plasma concentration was followed at regular times after administration. There was a significantly decreased plasma clearance of penicillin in all malnourished groups compared to the normal weight-for-age group. The half-lives of penicillin were, however, not significantly different between the nutritional groups. This was explained by the fact that also the volume of distribution was decreased in the malnourished group with a net result that the half-life was unchanged. The bioavailability was decreased if penicillin was given to non-fasting individuals. The greatest difference between fasting and non-fasting was seen in the severely malnourished children with marasmus and kwashiorkor. Therefore, it is advised that, if penicillin is given orally to very sick and undernourished children, the dose should be increased and preferably be given in the fasting state.

Decreased chloramphenicol clearance in malnourished Ethiopian children

The disposition of chloramphenicol and chloramphenicol monosuccinate has been studied in thirty-four Ethiopian children of varying nutritional status. After a single intravenous dose corresponding to chloramphenicol 25 mg per kg bodyweight, the plasma clearance of chloramphenicol monosuccinate was decreased only in severely malnourished children with kwashiorkor. Seventeen % of the dose (range 0-51%) was recovered in urine as intact prodrug, indicating incomplete and variable bioavailability of chloramphenicol. Compared to underweight children, on average marasmic and kwashiorkor subjects exhibited a 2- and 3-fold increase, respectively, in the AUC of chloramphenicol. Elevated AUCs could be traced to reduced hepatic clearance of the drug. The unbound fraction both of chloramphenicol and its prodrug were slightly elevated in serum from kwashiorkor subjects. The possibility of using a single point measurement of plasma chloramphenicol as a guide to individualized dosage are discussed.

Influence of protein and calorie malnutrition on the pharmacokinetics and pharmacodynamics of bumetanide in rats

Bumetanide is a loop diuretic that is used for the treatment of edema and hypertension. The rapidly developing syndrome of extracellular fluid overload in some malnourished children has been successfully treated with furosemide, another loop diuretic, and digoxin; however, similar studies with bumetanide have not been conducted to date. Therefore, in the present study, the influence of dietary protein deficiency on the pharmacokinetics and pharmacodynamics of bumetanide was investigated after intravenous (i.v.) bolus and oral administration of bumetanide to male Sprague-Dawley rats fed on 23% (control rats) or 5% [protein and calorie malnutrition (PCM) rats] protein diet ad libitum for 4 weeks. After an i.v. dose of bumetanide, 1 mg/100 g body weight, the mean values of renal clearance and percentages of dose excreted as unchanged bumetanide in an 8-h urine sample were 166 and 154% higher, respectively, in PCM than control rats; however, nonrenal clearance (CLNR) was 28% lower. The decrease in nonrenal clearance in PCM rats might be because of the decrease in nonrenal metabolism of bumetanide in PCM rats. The urine output per 100 g of body weight was not significantly different between the two groups of rats after i.v. administration, although the amount of bumetanide excreted in the 8-h urine sample per 100 g body weight increased significantly in PCM rats. These results could be explained by the fact that the dose of bumetanide used results in urinary excretion rate of bumetanide at the plateau of the concentration-effect relationship.(ABSTRACT TRUNCATED AT 250 WORDS)

Theophylline disposition following parenteral feeding of malnourished patients

OBJECTIVE

To investigate the effect of parenteral nutrition on theophylline disposition in malnourished patients.

DESIGN

Before-after trial.

SETTING

Tertiary care center.

PATIENTS

Ten patients with historic, anthropometric, and laboratory evidence of malnutrition.

INTERVENTIONS

Patients received two 5-mg/kg intravenous infusions of theophylline separated by at least 48 hours of glucose-based parenteral nutrition providing the entire estimated nutritional requirements.

MAIN OUTCOME MEASURES

Following each theophylline administration, serum theophylline samples were collected over a 24-hour period for delineation of maximum plasma concentrations, volume of distribution, elimination rate constant, clearance, and area under the curve.

RESULTS

Peak plasma theophylline concentrations were significantly lower prior to feeding (5.3 mumol/L, 95 percent confidence interval [CI] 0.78-10.0 mumol/L, p = 0.028). Volume of distribution decreased after parenteral feeding (0.08 L/kg, 95 percent CI 0.006-0.15 L/kg, p = 0.037). The elimination rate of theophylline increased after parenteral feeding reflected by an increase in the elimination rate constant (0.06 h-1, 95 percent CI 0.01-0.10 h-1, p = 0.023).

CONCLUSIONS

This study suggests that parenteral nutrition using a glucose-based solution acutely influences theophylline disposition in malnourished patients.

Pharmacokinetics and pharmacodynamics of furosemide in protein-calorie malnutrition

The influence of dietary protein deficiency on pharmacokinetics and pharmacodynamics of furosemide was investigated after i.v. bolus (1 mg/100 g) and oral (2 mg/100 g) administration of furosemide to male Sprague-Dawley rats fed on a 23% (control) or a 5% (protein-calorie malnutrition: PCM) protein diet ad lib. for 4 weeks. After i.v. administration, the mean values of CLR, Vss, and the percentages of dose excreted in 8-hr urine as furosemide were increased 81, 31, and 61%, respectively, in PCM rats when compared with those in control rats, however, CLNR was 54% decreased in PCM rats. The decreased CLNR in PCM rats suggested the significantly decreased nonrenal metabolism of furosemide. The urine volume per g kidney after i.v. administration was not significantly different between the two groups of rats although the amount of furosemide excreted in 8-hr urine per g kidney increased significantly in PCM rats. The diuretic, natriuretic, kaliuretic, and chloruretic efficiencies reduced significantly in PCM rats after i.v. administration. After oral administration, the extent of bioavailability increased considerably from 27.6% in control rats to 47.0% in PCM rats, probably as a result of decreased gastrointestinal and hepatic first-pass metabolism. This was supported by a tissue homogenate study; the amount of furosemide remaining per g tissue after 30-min incubation of 50 micrograms of furosemide with the 9000 x g supernatant fraction of stomach (42.4 vs. 47.9 micrograms) and liver (41.4 vs. 45.9 micrograms) homogenates increased significantly in PCM rats. No significant differences in CLR and t1/2 were found between the control and the PCM rats after oral administration. The 24-hr urine volume and the amount of sodium excreted in 24-hr urine per g kidney increased significantly in PCM rats, and this might be due to a significantly increased amount of furosemide reaching the kidney excreted in urine per g kidney.

Effects of protein deficiency on lipid peroxidation in the small intestine and liver of rats

This study investigated the influence of protein restriction on lipid peroxide content (thiobarbituric acid-reactive substances) and the intracellular antioxidant defence system in the small intestine and the liver. Weanling male Sprague-Dawley rats were divided into two groups: a low-protein group fed ad lib. a diet containing 6% casein for 4 wk, and a control group fed a diet containing 22% casein but restricted to the same dietary intake as that of the low-protein group. Compared with pair-fed controls, the protein-deficient rats exhibited a decrease in glutathione content in the small intestine and the liver. Thiobarbituric acid-reactive substances were increased in the intestine only. Data on the enzymatic antioxidant defence system in the protein-deficient animals showed an increase in catalase activity in the intestine but a decrease of this activity in the liver. The activity of selenium-dependent glutathione peroxidase was decreased in the liver and remained unchanged in the intestine. Superoxide dismutase was not modified by protein deficiency in either tissue. In control rats, enzyme activities were 6-43 times higher in the liver than in the intestine. The deleterious effects of protein deficiency appeared more marked in the intestine.

Antipyrine kinetics in undernourished diabetics

In developing countries diabetics frequently suffer from varying grades of malnutrition. The combined effect of malnutrition and non-insulin dependent diabetes (NIDDM) on the drug metabolising enzyme system has been evaluated using antipyrine as a protodrug. All the patients were under treatment and their plasma glucose values were within normal limits. The AUC of antipyrine was similar in all the groups. Although none of the kinetic parameters was altered in normal diabetics, the clearance of antipyrine was decreased and its half life was prolonged, with an increase in volume of distribution, in undernourished diabetics compared to undernourished controls. The results indicate that diabetes per se may not influence antipyrine kinetics when the blood glucose is well under control, but in the presence of undernutrition, it significantly alters the disposition of the drug.

The effects of age and dietary protein restriction on the pharmacokinetics of theophylline in the rat

The influence of dietary protein levels on theophylline kinetics was examined in male Fischer 344 virgin rats of 2, 14 and 20 months of age fed for four weeks on a 23% (control) or 5% (low) protein diet ad libitum. Protein deficiency led to a significant decrease in body weight gain for the 2 month old rats (10.9% versus 26.5%). In addition, decreases in total body weight of 7.5% and 15.3% were seen for the 14 and 20 month old rats, respectively, on a low protein diet. Total proteins and albumin levels in plasma were not significantly affected by age or dietary protein levels. After intravenous administration of 10 mg/kg aminophylline, the average mean residence time (MRT) was significantly longer in 20 month old rats as compared to the younger rats, while 14 month old rats had a greater elimination rate constant than the 2 and 20 month old rats. There were significant reductions in the mean steady-state apparent volume of distribution (Vss) in the 2 and 14 month old rats on a low protein diet of 31% and 18%, respectively, while there was no difference between the diets in 20 month old rats. In addition, the Vss decreased from 0.71 L/kg to 0.57 L/kg in the 2 and 20 month old rats, respectively, on a normal protein diet. Dietary protein deficiency led to a significant reduction of total body clearance from approximately 73 to 45 ml/hr/kg in the 2 and 14 month old rats.2+p

Altered pharmacokinetics and dynamics of apomorphine in the malnourished rat: modeling of the composed relationship between concentration and heart-rate response

The impact of malnutrition on the pharmacokinetics and pharmacodynamics (change in heart rate) of apomorphine was studied in the rat. One group of rats received a low-protein diet (0.5%) ad libitum to produce prekwashiorkor. The control group received commercial food pellets. In the first experiment, the two groups received a 2 mg/kg iv bolus dose of apomorphine to determine any differences in the basic pharmacokinetic parameters. The pharmacodynamic characteristics in each group were studied at different steady-state plasma levels, achieved by iv infusions with continuous measurements of the heart rate. There was an almost twofold decrease in the plasma clearance in the malnourished rats compared with controls. A pronounced change in the pharmacodynamic response was also observed in the malnourished group. In the control group, apomorphine produced bradycardia at low concentrations and tachycardia at high concentrations, while only bradycardia was registered in the malnourished group, with maximum effects at steady-state plasma concentrations of 50 ng/ml and a return to baseline at higher concentrations. The effects in control and malnourished rats were fitted simultaneously to the sum of two Hill equations with a nonlinear regression program, and the fits were compared by means of an F test. The maximum pure tachycardia obtainable differed significantly in the prekwashiorkor group compared to the control group. These results suggest a selective down regulation/desensitization only of the receptors responsible for the tachycardia produced by apomorphine during malnutrition.

Absorption and disposition kinetics of chlorothiazide in protein-calorie malnutrition

The influence of dietary protein deficiency on the absorption and disposition kinetics of chlorothiazide was investigated in male Sprague-Dawley rats fed for 4 weeks on a 23 per cent (control) or a 5 per cent (low) protein diet ad libitum. Chlorothiazide in plasma and urine was determined by a sensitive and specific HPLC assay. Following an intravenous dose of 10 mg kg-1 chlorothiazide, there was a significant decrease in the total plasma clearance (Cl) per kg of body weight from 1.80 +/- 0.15 to 1.29 +/- 0.15 l h-1 kg-1 and apparent steady-state volume of distribution from 0.65 +/- 0.13 to 0.38 +/- 0.07 l kg-1 in the protein-deficient rats. However, no significant difference was found in the two groups of animals with respect to mean residence time (MRT) and free fraction of drug in plasma. The mean harmonic half-life was increased from 72 to 91 min in the protein-deficient rats. The urinary recovery of unchanged chlorothiazide in 48 h was essentially complete in both groups of animals. The absorption of chlorothiazide, as assessed by the mean urinary recovery of unchanged drug after oral administration, was 66 per cent and 68 per cent in normal and protein-deficient rats, respectively.

Effect of dietary protein on renal tubular clearance of drugs in humans

Diet is one of many factors that influence the pharmacokinetics of drugs. The level of protein intake has been found to significantly influence drug metabolism and glomerular filtration, both of which play an important role in the clearance of drugs. Recently, a marked change, resulting from restricted dietary protein intake, has been reported in the handling of several drugs which are reabsorbed and/or secreted by the renal tubules. In studies of healthy volunteers on protein-restricted diets the renal clearance and fractional excretion of model compounds have been altered, falling to 30% of values obtained on normal diets in the case of the weak acids oxipurinol and uric acid; the fractional excretion of the weak base cimetidine has been increased by 30%. These studies have also found that the change in the renal clearance of both acids is sustained with prolonged dietary protein-calorie restriction, and that, for oxipurinol, the magnitude of the change is directly related to the quantity of protein in the diet, the change is related specifically to the protein content in the diet (and not the total calories), the onset of change is rapid, and on a low-protein diet the renal clearance undergoes marked diurnal variation. The mechanism for the alteration in tubular function is not clear, but may be related to renal haemodynamic changes or competition for transport associated with protein intake. Regardless of the mechanism, these results have important implications for pharmacokinetic research and clinical practice.

Protein binding of salicylic and salicyluric acid in serum from malnourished children: the influence of albumin, competitive binding and non-esterified fatty acids

The serum protein binding of salicylic and salicyluric acid has been determined by ultrafiltration in 60 children after administration of oral salicylate. The children were classified according to nutritional status: well-nourished (n = 12), underweight (n = 12), marasmic (n = 17) marasmic-kwashiorkor (n = 7) and kwashiorkor (n = 12). Salicylic acid free fractions were 0.106 +/- 0.026, 0.114 +/- 0.069, 0.141 +/- 0.037, 0.285 +/- 0.279 and 0.438 +/- 0.190 in the five groups, respectively. Salicyluric acid free fractions were 0.184 +/- 0.057, 0.280 +/- 0.282, 0.236 +/- 0.114, 0.484 +/- 0.497 and 0.646 +/- 0.261, respectively. The degree of binding was dependent on serum albumin levels, ligand concentrations and non-esterified fatty acids (NEFA). The NEFA/albumin ratio ranged from 0.05 to 6.6. The fitting of a one-site Scatchard binding model to the collective data was improved when a decrease was allowed for in the number of binding sites in proportion to NEFA concentrations. Salicyluric acid binding could be fitted only when inhibition of the parent compound was included. Binding was not affected by age or sex. The major determinants of salicylate binding in sera from malnourished children have thus been identified.

INH and streptomycin in Ethiopian children with tuberculosis and different nutritional status

The plasma concentration of INH and streptomycin was followed in 45 Ethiopian children with tuberculosis. The children were grouped according to their nutritional status as normal, underweight, marasm and kwashiorkor. INH was well absorbed in all nutritional groups to give therapeutically active plasma levels. When terminal half life (t1/2) of INH was calculated for individual patients there were more children in all nutritional groups with t1/2 greater than or equal to 2 hours than less than 2 hours, indicating a slow acetylation of INH. Streptomycin was well absorbed in all nutritional groups and therapeutic levels were obtained with 20 mg/kg i.m. After 30 mg/kg i.m. of streptomycin kwashiorkor children had an increased t1/2 of streptomycin indicating a decreased renal excretion of the drug in kwashiorkor. The clinical follow-up of the children indicated that serious tuberculosis could be successfully treated with INH and streptomycin in the doses used.

Pharmacokinetics of streptomycin in Ethiopian children with tuberculosis and of different nutritional status

Fifty-six malnourished Ethiopian children with tuberculosis classified in four nutritional groups (normal, underweight, marasmus and kwashiorkor), were given streptomycin 20 or 30 mg.kg-1 i.m. The plasma concentration-time data revealed an increased apparent volume of distribution in children with kwashiorkor compared to normals. The total plasma clearance was low and did not differ between the nutritional groups. Thus, the half-life was prolonged only in kwashiorkor. The results could be explained by decreased protein binding in plasma and decreased renal clearance by glomerular filtration.

The influence of nutrition on the systemic availability of drugs. Part II: Drug metabolism and renal excretion

Plasma concentrations of an active compound vary between individuals and within a subject, even if the same drug dosage is used. These differences are related to variations of drug absorption from the gastrointestinal tract, of presystemic drug metabolism in the intestine or the liver, and of drug elimination from the systemic circulation, for instance by hepatic metabolism or renal excretion. All of these processes can be modified by nutrition. However it is necessary to emphasize the significance of the pharmaceutical formulation for variations of both drug absorption and elimination. The role of nutrition should receive adequate attention during therapeutic use of drugs as well as in drug disposition studies. Recent guidelines for the assessment of the systemic availability of drugs therefore do recommend nutrition to be controlled.

Therapeutic drug monitoring in oncology. Problems and potential in antineoplastic therapy

Therapeutic drug monitoring is now widely used in many areas of medicine. With its proliferation has come an understanding of the clinical situations in which it is likely to be of value. Factors that can limit the usefulness of therapeutic drug monitoring and situations where it is less likely to be of benefit have also been identified. At present, the routine use of therapeutic drug monitoring in antineoplastic therapy is limited to measurement of plasma methotrexate concentrations after high-dose methotrexate therapy. The lack of a more widespread application of therapeutic drug monitoring in oncology has been due to deficiencies in knowledge about the clinical pharmacology of antineoplastic agents and to factors specific to the chemotherapy of neoplasms. These factors include the broad heterogeneity of malignant neoplasms, the complexities of the drug-tumour interaction, difficulties in assessment of this interaction and the use of combinations of antineoplastic agents with cumulative efficacies and toxicities. Despite these problems, there are many areas in antineoplastic therapy where the use of therapeutic drug monitoring could prove of benefit. The prevention of the chronic pulmonary toxicity of bleomycin, the assessment of the bioavailability of oral chemotherapy, and monitoring drug disposition in the presence of hepatic or renal dysfunction are just some of the potential applications. If recent emphasis on dose as a critical factor in the success of cancer chemotherapy is substantiated, then the need to apply therapeutic drug monitoring within oncology will become more pressing.

Determinants of drug disposition in man

This article reviews some of the important determinants of variation in drug disposition such as age, gender, body weight, diet, environmental influences, drug - protein interactions, compliance, drug - drug interactions, endogenous substances, disease states, circadian variation and genetics.

The effect of dietary protein on the clearance of allopurinol and oxypurinol

A decrease in dietary protein is known to depress renal plasma flow and creatinine clearance. Using a randomized crossover design, we investigated the pharmacokinetics of allopurinol and its principal metabolite, oxypurinol, after oral administration of 600 mg of allopurinol in six normal subjects receiving a high-protein (268 g per day) or low-protein (19 g per day) diet. For allopurinol, the area under the curve of plasma concentration versus time increased by a factor of 1.45 (P less than 0.02), the renal clearance decreased by 28 per cent (P less than 0.02), and the ratio of the clearance of allopurinol to that of creatinine (fractional excretion) was unchanged between the low-protein and high-protein diets. For oxypurinol, the area under the curve increased nearly three-fold (P less than 0.02), the renal clearance decreased by 64 per cent (P less than 0.02), the fractional excretion decreased by 49 per cent (P less than 0.02), and the plasma oxypurinol half-life increased nearly threefold from 17.3 +/- 1.5 (mean +/- S.E.M.) to 49.9 +/- 2.9 hours (P less than 0.02) during the low-protein diet, as compared with the high-protein diet. We conclude that with the low-protein diet, the absorption, metabolism, and excretion of allopurinol were minimally altered but the total-body clearance of oxypurinol was greatly reduced because of a large increase in the net renal tubular reabsorption of oxypurinol.