The pharmacologic consequences of fever

Molecular Variability in Levodopa Absorption and Clinical Implications for the Management of Parkinson's Disease

Levodopa is the most widely used medication for the symptomatic treatment of Parkinson's disease and, despite being an "old" drug, is still considered the gold standard for offering symptomatic relief. The pharmacokinetic and pharmacodynamics of levodopa have been studied extensively. Our review explores the molecular mechanisms that affect the absorption of this drug, focusing on the large intra- and interindividual variability of absorption that is commonly encountered in daily clinical practice, and on the interaction with other medications. In addition, we will explore the clinical implications of levodopa absorption variability and address current and future strategies for researchers and clinicians.

The effect of the acute phase of infection on absorption of and exposure to orally administered antibiotics in non-critically ill, hospitalized patients

OBJECTIVES

During the acute phase of infection, IV antibiotics are preferred to ensure adequate systemic exposure. To assess whether adequate exposure may also be achieved with oral antibiotics, we investigated exposure to oral antibiotics and PTA during the acute phase of infection and after defervescence.

METHODS

We enrolled hospitalized, non-critically ill febrile patients treated with IV antibiotics other than amoxicillin or ciprofloxacin. The study consisted of two visits: when patients had received <24 h IV treatment; and when patients had become afebrile. On both visits, patients received one additional dose of 750 mg amoxicillin, or 500 mg ciprofloxacin, depending on the presumed infection, after which serial blood samples were obtained. The primary endpoint was the ratio of the AUC during the febrile and the afebrile phase. The AUCs were considered to be equivalent when the ratio of the mean AUCs and its 90% CI was contained within the acceptance interval of 80%-125%. The secondary endpoint was PTA.

RESULTS

Forty-four patients (15 amoxicillin, 29 ciprofloxacin) completed both study visits. The median time between the two study visits was 65.8 h (range 33.8-427.4). The ratio of the mean AUCs (study visit 1/study visit 2) was 97% (90% CI of 80%-117%) for amoxicillin and 112% (90% CI of 108%-116%) for ciprofloxacin. The PTA for amoxicillin and ciprofloxacin did not differ between the two phases and was adequate to treat common pathogens.

CONCLUSIONS

The acute phase of infection in non-critically ill febrile patients does not influence the exposure to, or PTA of, orally administered amoxicillin and ciprofloxacin. This might justify earlier IV-to-oral switching.

Systematic review: the bioavailability of orally administered antibiotics during the initial phase of a systemic infection in non-ICU patients

Background

The systemic response to an infection might influence the pharmacokinetics of antibiotics. To evaluate the desired possibility of an earlier (< 24 h) IV-to-oral switch therapy in febrile non-ICU, hospitalized patients, a systematic review was performed to assess the effect of the initial phase of a systemic infection on the bioavailability of orally administered antibiotics in such patients.

Methods

An electronic search was conducted in MEDLINE and Embase up to July 2020. Studies were selected when outcome data were collected during the initial stage of a febrile disease. Outcome data were (maximum) serum concentrations, time of achieving maximum serum concentration, and the area-under-the-plasma-concentration-time curve or bioavailability of orally administered antibiotics. Risk of bias was assessed.

Results

We identified 9 studies on 6 antibiotics. Ciprofloxacin was the most frequently studied drug. Outcomes of the studies were heterogeneous and generally had a high risk of bias. Three small studies, two on ciprofloxacin and one on clarithromycin, compared the pharmacokinetics of febrile patients with those of clinically recovered patients and suggested that bioavailability was not altered in these patients. Other studies either compared the pharmacokinetics in febrile patients with reported pharmacokinetic values from earlier studies in healthy volunteers (n = 2), or provided no comparison at all and were non-conclusive (n = 4).

Conclusion

There is a clear knowledge gap regarding the bioavailability of orally administered antibiotics in non-ICU patients during the initial phase of a systemic infection. Well-designed studies on this topic are necessary to elucidate whether patients can benefit from the advantages of an earlier IV-to-oral switch.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-05919-w.

Use of population pharmacokinetic modeling and Monte Carlo simulation to capture individual animal variability in the prediction of flunixin withdrawal times in cattle

The objective of this study was to develop a population pharmacokinetic (PK) model and predict tissue residues and the withdrawal interval (WDI) of flunixin in cattle. Data were pooled from published PK studies in which flunixin was administered through various dosage regimens to diverse populations of cattle. A set of liver data used to establish the regulatory label withdrawal time (WDT) also were used in this study. Compartmental models with first-order absorption and elimination were fitted to plasma and liver concentrations by a population PK modeling approach. Monte Carlo simulations were performed with the population mean and variabilities of PK parameters to predict liver concentrations of flunixin. The PK of flunixin was described best by a 3-compartment model with an extra liver compartment. The WDI estimated in this study with liver data only was the same as the label WDT. However, a longer WDI was estimated when both plasma and liver data were included in the population PK model. This study questions the use of small groups of healthy animals to determine WDTs for drugs intended for administration to large diverse populations. This may warrant a reevaluation of the current procedure for establishing WDT to prevent violative residues of flunixin.

Pharmacokinetics of enrofloxacin and flunixin meglumine and interactions between both drugs after intravenous co-administration in healthy and endotoxaemic rabbits

The purpose of this study was to determine the pharmacokinetics and possible interactions of enrofloxacin (ENR) and flunixin meglumine (FM) in healthy rabbits and in rabbits where endotoxaemia had been induced by administering Escherichia coli lipopolysaccharide (LPS). Six male adult New Zealand White rabbits were used for the study. In Phase I, FM (2.2 mg/kg) and ENR (5 mg/kg) were given simultaneously as a bolus intravenous (IV) injection to each healthy rabbit. After a washout period, Phase II consisted of purified LPS administered as an IV bolus injection, then FM and ENR. LPS produced statistically significant increases in some serum biochemical concentrations. After the drugs were co-administered, the kinetic parameters of FM were not significantly different in healthy compared to endotoxaemic rabbits. It is concluded that ENR and FM could be co-administered to rabbits to treat endotoxaemia as no negative interaction was observed between the pharmacokinetics of both drugs.

Influence of Escherichia coli Endotoxin-Induced Endotoxaemia on the Pharmacokinetics of Enrofloxacin after Intravenous Administration in Rabbits

The main goal of present study was to determine the effects of an Escherichia coli endotoxin-induced endotoxaemic status on disposition of enrofloxacin after a single intravenous dose (5 mg/kg) in rabbits. Septic shock was induced by the i.v. bolus administration at a single dose of E. coli lipopolysaccharide. Six adult New Zealand White rabbits were used. Concentrations of drug in plasma were determined by HPLC. The plasma pharmacokinetic values for enrofloxacin were best represented using a two-compartment open model. Total plasma clearance (Cl(T)) decreased from 2.11 (l/h/kg) in healthy animals to 1.50 (l/h/kg) in rabbits with septic shock, which is related to an increase in the AUC(0-->infinity). In endotoxaemic rabbits, volume of distribution at steady state (V(dss) = 3.61 l/kg) was significantly lower (P < 0.05) than in healthy animals (V(dss) = 4.97 l/kg). However, the elimination half-life of enrofloxacin was not affected by lipopolysaccharide administration.

Pharmacokinetics of Flunixin after Intravenous Administration in Healthy and Endotoxaemic Rabbits

The pharmacokinetics of flunixin were determined after intravenous bolus injection at a single dose (2.2 mg/kg) in healthy rabbits and diseased rabbits with Escherichia coli lipopolysaccharide-induced septic shock. Six adult New Zealand White rabbits were used. Concentrations of drug in plasma were determined by HPLC. Pharmacokinetics were best described by a two-compartment open model. In healthy rabbits, there was a high plasma clearance (0.62 L/(h kg)), and a relatively short elimination half-life (1.19 h). In endotoxaemic rabbits, total plasma clearance (0.43 L/(h kg)) was significantly lower (p<0.05), and elimination half-life (1.90 h) and AUC(0-infinity) (5.29 (microg h)/ml) were significantly higher (p<0.05) than in healthy animals. The changes of pharmacokinetics of flunixin in rabbits with septic shock could be of clinical significance, and may require monitoring of plasma flunixin levels in endotoxaemic status.

A pharmacokinetic study of amoxycillin in febrile beagle dogs following repeated administrations of endotoxin

The pharmacokinetics of amoxycillin was studied in nine male beagle dogs under healthy and febrile conditions. In Period 1, dogs received 20 mg/kg of an oral suspension of amoxycillin. Intravenous doses of saline, 2 and 20 microg/kg of endotoxin (LPS from Escherichia coli serotype) were administered to dogs (three per group) prior to administration of 20 mg/kg of amoxycillin in Period 2. Rectal temperature and behavioral changes were recorded and blood samples were collected over 12 h for pharmacokinetic analysis. Amoxycillin was assessed in plasma using liquid chromatography coupled with mass spectrometry. Plasma concentrations were analysed using a one-compartment model with lag-time for absorption using an iterative two-stage method. As compared with control groups, amoxycillin clearance decreased significantly with preliminary treatments of 2 microg/kg endotoxin (0.209 vs. 0.140 L/h kg, P < 0.05) and 20 microg/kg endotoxin (0.214 vs. 0.075 L/h kg, P < 0.05). As a result of this, the area under curve for the 2 and 20 microg/kg endotoxin groups increased significantly 100.4 vs. 149.4 microg h/mL (P < 0.05) and 99.2 vs. 277.7 microg h/mL (P < 0.05), respectively. Other drugs currently used for the treatment of fever and septic shock should be re-evaluated using a febrile animal model to avoid improper dose administration.

Influence of fever on cefazolin pharmacokinetics

The influence of fever on the pharmacokinetics of cefazolin was investigated in patients with acute febrile diseases. Nine patients were included in the study. Antibiotic serum concentrations were determined using high performance liquid chromatograpy (HPLC). An analog computer and the SIMULINK software package were used to identify the pharmacokinetic model and PCNONLIN software package to obtain the secondary parameters. In 6 patients a two-compartment pharmacokinetic model of cefazolin was observed during fever and after defervescence. In 2 patients a two-compartment model changed to a one-compartment after defervescence, and a one-compartment model was observed in one patient during both periods. Cefazolin-treated patients with a two-compartment model (6/9) had higher Cmax, mean steady state serum concentrations (Css), and area under the plasma concentration-time curve (AUC(0-->infinity)), smaller central compartment volume (V1), and lower clearance (Cl) during fever. The varying distribution of antibiotics during fever probably reflects different hemodynamic responses to fever.

Influence of fever on the pharmacokinetics of ciprofloxacin

The influence of fever on the pharmacokinetics of ciprofloxacin was investigated in seven patients with acute febrile diseases. Antibiotic serum concentrations were determined using high-performance liquid chromatograpy (HPLC). The analog computer and the Simulink software package were used to identify the pharmacokinetic model and Penoclin software package to obtain the secondary parameters. During fever, higher maximum serum concentrations (Cmax) of ciprofloxacin were observed in six out of seven patients. The result suggests that the influence of fever on the pharmacodynamics of ciprofloxacin is favorable.