CHLORAMPHENICOL IN BLOOD: SIMPLE CHEMICAL ESTIMATIONS IN PATIENTS RECEIVING MULTIPLE ANTIBIOTICS

Studies of cytochrome synthesis in rat liver

The incorporation of radioactive amino acids and of delta-amino[2,3-(3)H(2)]laevulinate into rat liver cytochromes b(5) and c and cytochrome oxidase has been examined with and without protein-synthesis inhibitors. Cycloheximide promptly inhibits labelling of both haem and protein for cytochrome c in parallel fashion. Although incorporation of (14)C-labelled amino acid into microsomal cytochrome b(5) is also rapidly inhibited, cycloheximide incompletely inhibits haem labelling of cytochrome b(5) and cytochrome a+a(3), and inhibition occurs only after repeated antibiotic injections. The possibility of apo-protein pools, or of haem exchange, with a rapidly renewed ;free' haem pool, is considered. Consistent with this model is the observation of non-enzymic haem exchange in vitro between cytochrome b(5) and methaemoglobin. Chloramphenicol, injected intravenously over 5h, results in a 20-40% decrease in incorporation of delta-amino[2,3-(3)H(2)]laevulinate into haem a+a(3) and haem of cytochromes b(5) and c. With the dosage schedule of chloramphenicol studied, amino acid labelling of total liver protein and of cytochrome c was not inhibited. Similarly, ferrochelatase activity was not decreased.

Lack of effect of paracetamol on the pharmacokinetics of chloramphenicol

The effect of oral paracetamol (1 g) on the pharmacokinetics of oral chloramphenicol (500 mg) was examined in five adult male Zimbabwean patients with normal hepatic and renal function. No significant alteration of half-life, area under the concentration-time curve or peak concentration of chloramphenicol was observed. The previously reported, potentially serious interaction between chloramphenicol and paracetamol administered intravenously was not observed with the more commonly used oral preparations.

Pharmacokinetics and bioavailability of chloramphenicol in normal and febrile goats

The effect of induced fever on the plasma concentrations and disposition kinetics of chloramphenicol (CHPC) was studied in adult goats. Fever was induced and maintained for 12 h by injecting Escherichia coli endotoxin (0.1 microgram/kg, i.v.) and repeating it at half the dose (0.05 microgram/kg) 8 h later. Pharmacokinetics of CHPC was studied in both normal (n = 6) and febrile (n = 6) animals following intravenous administration of CHPC Na-succinate (25 mg/kg). Intramuscular bioavailability of the drug was also investigated in both normal and febrile animals. Pharmacokinetics of CHPC following intravenous administration could be described by a two-compartment open model in both normal and febrile animals. In normal animals the half-life of CHPC was 73.0 +/- 4.95 min and the volume of distribution was 2.217 +/- 0.24 l/kg. These and other pharmacokinetic parameters did not differ significantly (P less than 0.05) between normal and febrile animals, except for Cop and A. Absorption of CHPC following intramuscular administration was good as indicated by its high bioavailability in both normal (83.34%) and febrile (81.98%) animals. Volume of distribution is usually expected to change when the febrile state is induced. Lack of such an effect in the present study could be due to high individual variation, or to the fact that CHPC already has a relatively large volume of distribution, which is less likely to be altered by a febrile state of short duration.

Chloramphenicol clearance in infants

Chloramphenicol clearance was evaluated over one dosing interval in 10 infants after at least 24 hours of therapy to evaluate dosage guidelines using a specific chemical assay. Serum samples were obtained prior to and at 1, 2, 4, and 6 hours after the start of a 20-minute infusion of 24 mg/kg chloramphenicol as the sodium succinate. The chemical assay used is technically simple and is specific for unesterified chloramphenicol. Peak serum concentrations ranged from 20.9 to 94.0 microgram/ml and occurred from 1 to 4 hours after infusion. Clearances ranged from 0.058 to 0.236 l./kg . hr and paralleled previously reported results using different assay methodology. The 4-hour serum chloramphenicol concentrations were significantly lower (P less than 0.05) in infants on phenobarbital. The currently recommended dose of chloramphenicol for severe infections, 100 mg/kg per day, is excessive in some infants. Widely divergent clearance rates prohibit uniform dosage guidelines so that serum level monitoring with an assay specific for chloramphenicol is essential.

Comparison of methods available for assay of chloramphenicol in clinical specimens

Eight methods for the assay of chloramphenicol in clinical samples were compared with our own modification of a plate diffusion technique using Sarcina lutea and yeast extract agar. Six of the eight methods were less sensitive than originally reported, and five of them were considered unsuitable for use in clinical microbiology practice. The remaining three methods together with the S. lutea/yeast extract modification were used to assay chloramphenicol in 20 samples of serum. Twenty samples of cerebrospinal fluid were also assayed by the S. lutea/yeast extract method. Our results indicate that only the Bacillus subtilis (sensitivity 6x0 mg/l) and the S. lutea (sensitivity 2x5 mg/l) diffusion methods are suitable for use with clinical samples in routine practice. The problems of chloramphenicol toxicity, appropriate dosage regimens, and the need for assay of the drugs are considered.

Chloramphenicol disposition in infants and children

We studied the pharmacokinetics of chloramphenicol following its intravenous administration as the sodium succinate ester to 54 infants and children. The mean "apparent t 1/2" of chloramphenicol clearance from the plasma was 5.94 hours (range 0.87 to 17.8 hours). The t 1/2 of patients who weighed less than 10 kg was significantly longer than that of those who weighed more than 10 kg (9.02 vs 4.55 hours; P less than 0.0001). There was a discrepancy between the plasma levels of chloramphenicol and total aromatic nitro compounds in four patients; these compounds were cleared at different rates. Repeated dosing (eight to 30 doses) did not produce a consistent effect on the t 1/2. The CSF concentrations of chloramphenicol in 13 patients were 67% (range 45 to 99%) of the simultaneous serum concentrations. We conclude that the marked individual variation in chloramphenicol pharmacokinetics in infants and children requires monitoring of blood concentrations during therapy.

Single injection treatment of meningococcal meningitis. 2. Long-acting chloramphenicol

A single injection of a long-acting oily preparation of chloramphenicol (Tifomycine) was compared with a five-day course of crystalline and procaine penicillin in the treatment of 131 adult patients with meningococcal meningitis. The clinical response to treatment was similar in the two groups of patients. Serial lumbar punctures showed a parallel fall in CSF cell count, protein and lactate and all posttreatment cultures were sterile. Single injection chloramphenicol treatment was cheaper and much easier to administer than penicillin. Long-acting chloramphenicol is thus an effective form of treatment for meningococcal meningitis and is likely to prove of particular value in the management of epidemics in areas with limited medical resources.

High-performance liquid chromatographic assay of chloramphenicol in serum

A new method for the analysis of serum chloramphenicol by reversed-phase, high-performance liquid chromatography (HPLC) is described. The method involves a preliminary extraction of 0.1 ml of serum with ethyl acetate containing an internal standard, chromatography with a reversed-phase C18 microparticulate column with an acetonitrile-acetate buffer mobile phase, and detection by measuring UV absorbance at 270 nm. Assay performance was compared with an existing microbiological assay. The HPLC method demonstrated both increased precision and increased sensitivity. The specificity of the HPLC method was also evaluated. The new method presents an alternative approach to the analysis of clinical specimens.

The necessity for monitoring chloramphenicol levels when treating neonatal meningitis

Chloramphenicol can be an effective agent in the treatment of ampicillin-resistant E. coli meningitis due to susceptible organisms in the premature or term infant. However, it can be used safely and effectively only if careful monitoring of serum levels is undertaken.

Drugs and children: methods for therapeutic monitoring

In this era of polypharmacy, the incidence of adverse reactions due to drug therapy has increased alarmingly since the precise effects on the metabolism of a drug given in combination with other drugs can never be predicted with certainty. Inadequate therapy due to insufficient medication or to factors which diminish absorption or enhance metabolism may be equally undesirable. The consequences to patients in terms of increased morbidity and financial cost of prolonged hospitalization may be considerable. For pediatric patients, particularly in the newborn period, these hazards may be much more dangerous. There is a need for more investigation into the validity of procedures in current use for the determination of drug levels in biologic fluids and into the interpretation of the values they produce. In addition clinical chemists and clinical pharmacologists are faced with the challenge of defining those drugs for which blood level information would be advantageous and developing rapid, sensitive, and accurate assays which can be performed by the routine clinical laboratory. The day may be not too far away when a major proportion of the workload of the clinical laboratory consists of assays primarily designed as an aid to therapy rather than diagnosis.

Chloramphenicol: an enzymological microassay

A new assay for chloramphenicol in biological fluids has been developed that offers sensitivity, specificity, precision, accuracy, economy, and ease of performance. The assay is based on the enzymological acetylation of chloramphenicol catalyzed by an R factor-mediated enzyme. [(14)C]acetyl coenzyme A serves as the donor of the labeled acetyl group, and the product, [(14)C]acetoxychloramphenicol, is separated from the labeled precursor by utilizing its preferential extraction into benzene. The product is then quantified by liquid scintillation counting. This assay measures chloramphenicol concentrations in both plasma and other biological specimens and in the presence of other antibiotics, hemolysis, or jaundice. Its rapidity and ease of performance are useful for clinical laboratories, and its sensitivity allows determinations on 10 mul of plasma.

Induction of chloramphenicol metabolism by phenobarbital

The induction of hepatic microsomal enzymes leading to more rapid metabolism of antibiotics has been demonstrated in only a few prior studies. We have studied the induction of chloramphenicol metabolism in an isolated rat liver perfusion model and in intact dogs. Using these methods, we have demonstrated that the clearance of chloramphenicol from serum is markedly increased after treatment of animals with phenobarbital. This was demonstrated to be a function of increased clearance of the drug by the liver, accompanied but not paralleled by increases in liver weight and biliary excretion by the rat liver. In intact dogs, small doses of chloramphenicol were not sufficient to demonstrate this fact, whereas a large test dose of 100 mg/kg showed markedly enhanced clearance after 1 week of oral phenobarbital administration. Prolongation of phenobarbital treatment or increased dose did not further increase the clearance, and chloramphenicol could not be demonstrated to enhance its own clearance. Human data on induction of enzymes is to date inconclusive.