Therapeutic Serum Concentrations Research Articles

Treatment of severe infections caused by penicillin-resistant pneumococci. Role of third generation cephalosporins.

Penicillin resistance occurred soon after the discovery of penicillin, first in the test tube and subsequently in patients. The prevalence of invasive pneumococcal disease has been estimated to be as high as 15-18/100,000 in the elderly population and even higher in AIDS patients, children and the very old. While prevention with pneumococcal vaccine seems the most reasonable solution, under-utilization of the vaccine and an increase in the number of immuno-compromised individuals has limited the success of this approach. Streptococcus pneumoniae is conventionally classified as penicillin-susceptible (MIC < 0.125 mg/l), penicillin-intermediate (MIC 0.125-1.0 mg/l) and penicillin-resistant (MIC > or = 2 mg/l). In many countries, penicillin resistance in pneumococci is on the increase and in some areas penicillin intermediate and resistant isolates reach 60%. As a consequence, a switch of therapy from penicillin to other agents is mandatory in infections caused by penicillin-resistant strains. Benzyl-penicillin, however, can be used for most infections caused by penicillin-intermediate and all infections caused by penicillin-sensitive strains. Third generation cephalosporins, and in particular cefotaxime, are an optional alternative, particularly in view of their low MICs against penicillin-susceptible and -intermediate and some penicillin-resistant strains, and the easily achievable therapeutic concentrations in serum, pulmonary tissues and other compartments in which pneumococcal infections occur. Third generation cephalosporins have a high safety record and can be administered to children, pregnant women and the elderly.(ABSTRACT TRUNCATED AT 250 WORDS)

Childhood Epilepsy : Current Therapeutic Recommendations.

The pharmacotherapy of epilepsy in children must account for a number of specific issues. The nature of epileptic disorders found in children differs from that in adults. For example, epilepsies of childhood are more likely to be developmentally or genetically based than those found in adults. Children also differ from adults in indications for antiepileptic drugs. Indeed, some types of childhood epilepsy do not require specific pharmacological treatment since prognosis is often excellent without therapy. This is especially true for children who are neurologically nonnal and those with benign epilepsy syndromes that have a characteristic electroclinical presentation, such as febrile seizures. In contrast, children with evidence of brain damage or those with serious epilepsy syndromes must be treated promptly.Once it has been decided that treatment is necessary, the choice of treatment should be based on a comparison of efficacy and tolerability of individual antiepileptic agents. The spectrum of toxicity is often different in younger patients from that in adults, and adverse effects that are acceptable in adults may be cause for discontinuation of therapy in children. Intellectual, cognitive and behavioural toxicity are particularly unacceptable.Establishing sustained therapeutic serum concentrations in children also requires specific attention. Rapid gastrointestinal transit times and interactions with milk and infant formulas may pose special management problems. Toxic metabolites of antiepileptic drugs are frequently produced in children. This can lead to drug hypersensitivity and other possible conditions, such as valproic acid (sodium valproate)-induced hepatotoxicity.Unless specific paediatric data are obtained, recommendations for the treatment of epilepsies in children will continue to be based on studies in adults and on anecdotal observations. Given the high prevalence and significant morbidity of childhood epilepsies, further studies of treatments are urgently needed.

Inhibition of K+ channels and stimulation of insulin secretion by the sulfonylurea, glimepiride, in relation to its membrane binding in pancreatic islets.

In isolated pancreatic islets of mice, the relationships between free glimepiride concentration and membrane binding or inhibition of ATP-sensitive K+ channels were examined. Microsomal membrane binding and K+ channel inhibition were half-maximal at 0.7 and 0.3 nmol/l glimepiride, respectively. The corresponding concentrations for glibenclamide were 0.4 and 0.6 nmol/l. Administration of glimepiride (10 nmol/l) or glibenclamide (10 nmol/l) to isolated mouse islets perifused with albumin-containing media induced a slow increase in insulin secretion. The kinetics of the secretory responses to glimepiride and glibenclamide were identical. Determination of albumin binding revealed that the free glimepiride and glibenclamide concentrations applied in our investigation were in the range of therapeutic serum concentrations of the free drugs. It is concluded that the effects of glimepiride and glibenclamide are very similar in mouse beta-cells.

AMINOGLYCOSIDE DOSING IN BURN PATIENTS USING FIRSTDOSE PHARMACOKINETICS

Burn patients have altered aminoglycoside pharmacokinetics, which often result in subtherapeutic serum concentrations when these drugs are administered by conventional dosing (CD) methods. First-dose (FD) pharmacokinetic calculations can be used in these patients to determine an appropriate dosing regimen. We reviewed our experience with FD methods (12 patients) and CD methods (14 patients). Therapeutic levels were achieved more promptly in the FD group than in the CD group (44.4 +/- 8.1 vs. 97.1 +/- 12.5 hours; p < 0.005). Therapeutic serum concentrations were achieved with the first set of steady-state levels in 11% of CD patients and in 67% of FD patients (p < 0.005). The FD group required significantly fewer dosing changes (2.1 +/- 0.3) than did the CD group (3.7 +/- 0.7, p < 0.005). These data demonstrate that aminoglycoside dosing using first-dose pharmacokinetics results in improved maintenance of therapeutic serum concentrations compared with conventional methods in burn patients.

The effect of tolbutamide on rat embryonic development in vitro.

Tolbutamide (TOLB) is a sulfonylurea used to treat non-insulin-dependent diabetes mellitus and is a suspected teratogen. However, it is not possible to discriminate between potential teratogenic effects of TOLB and malformations produced by either drug-induced hypoglycemia or the diabetic state itself. We examined the direct effect of TOLB on rat embryos cultured in a rodent whole embryo culture system. CD strain rat embryos were cultured for 48 h beginning on day 9 of gestation (plug day = day 0). Tolbutamide was added at various concentrations (90-3,600 microM). At the end of culture, viable embryos were examined for morphological score, number of somite pairs, crown-rump and head lengths, and DNA and protein content. Tolbutamide produced dose-related decreases in all endpoints at concentrations (2,250-3,600 microM) which are two to four times the human therapeutic concentration. Sera from TOLB-treated rats were adjusted to contain equal concentrations of glucose and insulin and then used for embryo culture. Serum from TOLB-treated rats had no observable effect on embryonic development. The mechanism for the embryotoxic effect of TOLB is unknown; however, the drug was previously demonstrated to alter activity of purified yeast glutathione reductase (GR). Because GR may be important for normal embryonic development, the effect of TOLB on this enzyme activity in cultured rat embryos was evaluated. Tolbutamide (2,700 microM) reduced embryonic GR activity by 35-57%. These results indicate that TOLB has a direct embryotoxic effect at levels 2 to 4 times the usual therapeutic serum concentrations on developing rodent embryos which may be mediated by GR inhibition.

Theophylline. Current thoughts on the risks and benefits of its use in asthma.

Theophylline and its derivatives have been used in the treatment of asthma for over 50 years, but since the advent of more potent bronchodilators their use has become cloaked in controversy. Their continued existence results from their undoubted usefulness in severe acute asthma, nocturnal asthma, childhood asthma and moderate to severe chronic airflow limitation, and because of habitual use by physicians in other situations. The precise mechanism of action of theophylline remains uncertain. The role of phosphodiesterase inhibition and adenosine antagonism has been reviewed and the clinical significance of the anti-inflammatory action of theophylline discussed. Theophylline has unpredictable metabolism when first administered, and continued monitoring of drug concentrations is essential. Commonly encountered adverse effects may occur at therapeutic serum concentrations, frequently necessitating drug withdrawal. The overlapping therapeutic and toxic theophylline serum ranges can lead to life-threatening adverse effects at the upper end of the therapeutic range, especially in the elderly in whom special precaution is required.

Bioavailability studies of drugs with nonlinear pharmacokinetics: II. Absolute bioavailability of intravenous phenytoin prodrug at therapeutic phenytoin serum concentrations determined by double-stable isotope technique.

Measurement of the absolute bioavailability of phenytoin (PHT) derived from test doses of phenytoin prodrug (PPD) at therapeutic PHT serum concentrations is complicated by two problems: 1) the area under the serum concentration versus time curve (AUC) produced by a given size of test dose will vary directly with background PHT serum concentration due to the nonlinear pharmacokinetic properties of PHT; 2) PPD is more water soluble than PHT, making renal excretion of PPD more likely. The authors describe a double-stable isotope method that obviates these two problems. Using only six subjects, the authors were able to demonstrate bioequivalence of PHT derived from intravenous PPD with intravenous PHT by current FDA standards for AUC ratio of test/reference formulation (90% confidence intervals between 0.80 and 1.20; ratio > or = 0.80 in > or = 80% of subjects; statistical power to detect a difference of 0.20 with a probability of 0.80).

Single-Dose Pharmacokinetics of Intraperitoneal Ofloxacin in Patients on Continuous Ambulatory Peritoneal Dialysis

The present study examines the pharmacokinetics of ofloxacin given in a single dose of 200 mg intraperitoneally (ip) in the first bag of three 2-L 8-hour exchanges. Ofloxacin was measured using high-pressure liquid chromatography (HPLC) in the serum and peritoneal effluent over 24 hours. Six patients without and 3 patients with peritonitis were studied. Ofloxacin given ip was almost completely absorbed after an 8-hour dwell, and this was not affected by peritonitis. The time required to reach peak serum concentration was longer than that reported previously following oral administration. Elimination half-life (T1/2) of ofloxacin was markedly prolonged compared to patients with normal renal function. Peritoneal clearance accounted for only one-tenth of total serum clearance. Peritonitis appeared to shorten the T1/2 of ofloxacin, but this was mainly due to an increase in total serum clearance rather than a change in peritoneal clearance. Peritoneal drug concentration > 0.5 mg/L was reached in the second and third exchange by the second hour. No side effects from ip ofloxacin were observed. We concluded that ofloxacin given in a single dose of 200 mg is safe and provides adequate therapeutic serum and peritoneal concentration for more than 24 hours in patients on continuous ambulatory peritoneal dialysis (CAPD) with 8-hour exchanges.

Valproate as a loading treatment in acute mania.

Evidence from earlier studies indicates that the antimanic action of valproate becomes most apparent within 1-4 days of achieving serum concentrations 50 micrograms/ml, that valproate can be orally loaded with achievement of therapeutic serum concentrations within the first several days of treatment, there is a rapid onset of response, and minimal side effects. To provide further data on the safety and efficacy of valproate oral loading in the treatment of acute mania, we evaluated 13 consecutive patients with acute manic syndromes who received valproate initiated at a dosage of 20 mg/kg/day. In most cases, valproate was added to other psychotropics. All 13 patients received at least 5 full days of valproate maintained at or above 20 mg/kg/day, and valproate serum concentrations were 50 micrograms/ml (mean +/- SD = 88 + 25) by the second or third day of treatment. Ten (77%) patients displayed a moderate or marked response. Side effects were infrequent and minor. Consistent with our earlier study, these findings suggest that valproate can be safely administered via a loading dose of 20 mg/kg/day to patients with acute mania, including those on other psychotropics, and that it may produce a rapid response with minimal side effects.

Selective decontamination in bone marrow transplant recipients.

Patients undergoing bone marrow transplantation become immunocompromised for various reasons. Deep granulocytopenia, induced by conditioning (chemotherapy and total body irradiation), renders the patient at risk for serious bacterial and fungal infections. Our strategy for prevention of these infections by selective decontamination (SD) is the result of more than 15 years of clinical experience and research. The combination of antibiotics, used as standard SD (neomycin, polymyxin B, pipemidic acid and amphotericin B), with the application of local antimicrobial agents eliminates aerobic Gram-negative rods, Staphylococcus aureus and Candida spp. from the mucosal surfaces of the digestive tract, while the majority of the anaerobic flora persist and support colonization resistance (CR). The antibiotics used either are not resorbed or do not yield therapeutic serum concentrations. Antibiotics which induce therapeutic serum concentrations, such as ciprofloxacin and cotrimoxazole, are only used for SD on a limited scale. When Gram-negative rods persist despite intake of the standard regimen, ciprofloxacin is given until these persisting rods are eliminated. If the patients cannot swallow the oral regimen, i.v. cotrimoxazole is given temporarily. Streptococcal infections are prevented by the i.v. administration of penicillin for 14 days starting on the first day after cytotoxic treatment (conditioning for bone marrow transplantation). The combination of SD and systemic prophylaxis has been shown to be adequate; the major problem then remaining is a relatively mild catheter-associated infection with coagulase-negative staphylococci.

Absorption of valproic acid from the gastrointestinal tract of the piglet.

Valproic acid is a commonly used drug for the treatment of epilepsy. Since valproic acid can only be given orally, its absorption from the gastrointestinal (GI) tract especially in patients with short bowel syndrome (SBS) and in neonates is important. The specific sites of absorption for valproic acid in the small intestine and colon have not been investigated. It is currently unknown whether these patients are able to absorb oral valproic acid sufficiently to maintain a therapeutic serum concentration. The primary objectives of the study were to: (a) determine the relative absorption of valproic acid from specific sites in the GI tract; and (b) investigate the influence of intestinal development on valproic acid absorption using the newborn piglet as a model. Two groups were studied: Group I included 5 piglets 18-21 days of age, and Group II included 5 piglets 1-3 days of age. A valproic acid solution was simultaneously perfused through 5 partitioned segments of the gastrointestinal tract: the duodenum, jejunum, ileum, right colon and left colon. Tritiated [3H] polyethylene glycol was co-administered to monitor water movement across the GI mucosa. Following steady state, samples were collected from each segment, and analyzed by a specific enzyme-mediated immunoassay. The absorption rates (micrograms/min/cm) of valproic acid in Group I were as follows: 9.96 +/- 2.8 duodenum; 11.28 +/- 2.79, jejunum; 9.42 +/- 3.34, ileum; 10.88 +/- 3.35, right colon; 10.96 +/- 2.92, left colon.(ABSTRACT TRUNCATED AT 250 WORDS)

Cefotaxime and metabolite disposition in two pediatric continuous ambulatory peritoneal dialysis patients.

To characterize the pharmacokinetics of cefotaxime and desacetylcefotaxime in pediatric patients undergoing continuous ambulatory peritoneal dialysis (CAPD) after intraperitoneal administration of cefotaxime. Case series. Ambulatory children from Children's Hospital nephrology clinic, Columbus, Ohio. Two adolescents without peritonitis. A single intraperitoneal dose of cefotaxime 500 mg per 1 L dianeal was given during CAPD. Cefotaxime and desacetyl-cefotaxime were measured in plasma, urine, and dialysate by HPLC. Maximum plasma concentration (Cmax) of cefotaxime was 11.94 and 13.08 mg/L and that of desacetylcefotaxime 5.73 and 5.33 mg/L. Time to reach maximum concentration (Tmax) of cefotaxime was 2.22 and 4.08 h, and that of desacetylcefotaxime was 5.33 and 5.73 h after instillation of the intraperitoneal cefotaxime dose. Systemic absorption of cefotaxime was 56.6 and 64.8 percent. Total clearance of cefotaxime was 62 and 79 mL/min/1.73 m2. Nonrenal clearance accounted for nearly 95 percent; renal and CAPD clearance contributed approximately 5 percent of the total clearance. Renal and CAPD clearance measurements of desacetylcefotaxime were similar to those for cefotaxime. Cefotaxime half-life was 1.83 and 2.49 h and desacetylcefotaxime half-life was 8.14 and 11.0 h. Cefotaxime was well absorbed and therapeutic serum concentrations were achieved after intraperitoneal administration. Renal and CAPD clearances for cefotaxime and desacetylcefotaxime were low. Cefotaxime nonrenal clearance was unaffected. Further studies are needed to establish appropriate intraperitoneal dosing guidelines of cefotaxime in pediatric CAPD patients.

Regulation of B Cell Function by Lobenzarit, A Novel Disease‐Modifying Antirheumatic Drug

Lobenzarit (disodium 4-chloro-2,2'-iminodibenzoate [CCA]) is a novel disease-modifying drug for the treatment of rheumatoid arthritis (RA). Although its clinical efficacy has been demonstrated, its mechanism of action remains unclear. We therefore examined the effects of CCA on in vitro IgM and IgM rheumatoid factor (IgM-RF) production by human B cells. IgM and IgM-RF production was induced from highly purified B cells from 8 healthy donors by stimulation with Staphylococcus aureus Cowan 1 (SAC) plus factors generated from mitogen-activated T cells (TCF) or with immobilized anti-CD3-activated CD4+ T cells. CCA suppressed the production of IgM-RF as well as IgM at concentrations of 25-50 micrograms/ml (therapeutic serum concentrations of the drug), although the IgM-RF production induced by SAC plus TCF was suppressed at lower concentrations of CCA (1-3 micrograms/ml). Whereas CCA suppressed interleukin-2 (IL-2) production by anti-CD3-activated CD4+ T cells, its suppressive effects on B cells were not overcome by addition of IL-2 or TCF. CCA did not inhibit the initial stages of B cell activation in either culture system, but rather, suppressed the maturation of previously activated B cells. Cell cycle analysis by acridine orange staining indicated that CCA-mediated inhibition of B cell responsiveness induced by anti-CD3-activated CD4+ T cells was the result of a block at the G1-S interphase. These results indicate that CCA suppresses the production of IgM and IgM-RF by directly inhibiting activated B cells. Thus, one of the actions of CCA in RA may be the suppression of the function of activated B cells.

Comparing the anticonvulsive effects of dapsone on amygdala-kindled seizures and hippocampal-kindled seizures in rats.

Dapsone, an antileprosy drug, was administered to rats with amygdala (AM)-kindled seizures or hippocampal (HIPP)-kindled seizures to elucidate its anticonvulsive efficacy. Adult male Wistar rats were subjected to kindling stimulations 2 weeks after electrode-implantation. The subjects were tested once a day for 7 successive days after inducing three generalized (stage 5) seizures to study the effects of dapsone. Dapsone had an inhibitory effect on stage 5 seizures at 12.50 mg/kg in the AM-kindled rats and at 6.25 mg/kg and 9.375 mg/kg in the HIPP-kindled rats. Thus, there was a distinct difference in the effective dose for generalized seizures between the AM-kindled rats and the HIPP-kindled rats. The inhibitory action of dapsone on stage 5 seizures may be due mainly to the elevation of the afterdischarge-triggering threshold at the stimulation site of the AM or HIPP. Such inhibitory action appears prominently at serum concentrations of about 13 micrograms/ml in AM-kindled rats and about 6 micrograms/ml in HIPP-kindled rats. The level of 6 micrograms/ml almost equals the therapeutic serum concentration of dapsone used in the treatment of leprosy.

Febrile Seizures: A Revisit to an Old Problem

Febrile seizures are a common clinical problem occurring in about 3% of children. They recur in about 30% to 40% of patients, particularly in those whose initial seizure occurs before one year of age. There is very little risk of epilepsy, neurological deficit or mental retardation to justify long term phenobarbitone therapy. Intermittent prophylactic therapy with oral or rectal diazepam at time of subsequent fever, has been found to be useful. Emphasis should be placed on parental counselling and education.

Effects of single and repeated doses of theophylline on aspects of performance, electrophysiology and subjective assessments in healthy human subjects

The effects of both single and repeated doses of theophylline were evaluated on a battery of nine performance tests, the EEG, the EMG and on subjective assessments of mood and side-effects. The subjects were 20 healthy adults who participated in both phases of this randomized, double-blind, placebo controlled, crossover study. The single dose of 400 mg and the repeated doses of 300 mg b.d. for 4 weeks were intended to attain therapeutic serum concentrations. The Sternberg Additive Factors Method for assessing information processing revealed enhanced performance in both phases of this study, while the Horizontal Addition Test showed improved performance in the single dose phase only. The remaining seven performance tests failed to show significant differences between theophylline and placebo. Single doses of theophylline did not significantly alter mood, but marked adverse effects were encountered in the repeated dose phase, possibly related to unpleasant side-effects. Both EEG and EMG findings indicative of stimulation were associated with a single dose of theophylline, but substantial tolerance developed during 4 weeks of therapy. These findings demonstrate CNS stimulation by both single and repeated doses of theophylline with the occurrence of adverse side-effects during repeated administrations.

Effect of individualized pharmacokinetic dosing on patient outcome

To study the effect of individualized pharmacokinetic dosing of aminoglycosides on patient outcome. Prospective, randomized study. Tertiary care hospital. Ninety-five patients with documented Gram-negative infections received 97 courses of aminoglycoside therapy. Patients were randomized between pharmacokinetic dose adjustment and monitoring or traditional physician-directed techniques. Patients were stratified by severity of underlying illness before randomization. Sixty-two courses of treatment were satisfactorily completed. Patients in the severely ill group (eight kinetic, eight traditional) had significantly (p less than .05) better survival (7 kinetic, 3 traditional) when managed with pharmacokinetic consultation. The kinetic arm received greater doses (156 +/- 59 mg/dose; 2.4 +/- 0.6 mg/kg) than the traditional arm (81 +/- 27 mg/dose; 1.5 +/- 0.6 mg/kg) (p less than .001). In addition, the dose per day (mg/kg) was greater in the kinetic arm (4.1 +/- 1.5) than the traditional arm (3.2 +/- 1.3) (p less than .001). The improved survival was achieved by attaining therapeutic peak serum concentrations earlier in the course of the infection and by administering more total aminoglycoside without increasing toxicity. We conclude that pharmacokinetic management of aminoglycoside dosing may improve the outcome of severely ill patients.

Individualizing Amikacin Regimens

Amikacin's pharmacokinetics and dosage requirements were studied in 98 patients receiving treatment for gram-negative infections. A wide interpatient variation in the kinetic parameters of the drug occurred in all patients and in patients who had normal serum creatinine levels or normal creatinine clearance. The half-life ranged from 0.7 to 14.4 h in 74 patients who had normal serum creatinine levels and from 0.7 to 7.2 h in 37 patients who had normal creatinine clearance. The necessary daily dose to obtain therapeutic serum concentrations ranged from 1.25 to 57 mg/kg in patients with normal serum creatinine levels and from 10 to 57 mg/kg in patients with normal creatinine clearance. In four patients (4%), a significant change in baseline serum creatinine level (greater than 0.5 mg/dl) occurred during or after treatment, which may have been amikacin-associated toxicity. Overt ototoxicity occurred in one patient. The method of individualizing dosage regimens provided a clinically useful means of rapidly attaining therapeutic peak and trough serum concentrations.

Kinetic study of serum gentamicin concentrations in baboons after single-dose administration

Summary This study establishes preliminary pharmacokinetic data on the use of gentamicin sulfate administered im to baboons. Serum concentrations ≥ 12 μg/ml are generally agreed to cause toxicosis in human beings. On the basis of preliminary test results suggesting that the manufacturer's recommended dosage for dogs of 4.4 mg/kg of body weight caused potentially toxic serum concentrations, a dosage of 3 mg/kg was chosen to conduct a single-dose kinetic study in 6 baboons. Using a single-compartment model, the gentamicin serum half-life for im administration of 3 mg of gentamicin/kg was 1.58 hours, and serum concentrations remained below the potentially toxic concentrations reported for human beings. We suggest that a dosage of 3 mg/kg is safer than a dosage of 4.4 mg/kg administered im to baboons. Minimal inhibitory concentrations for 2 Pseudomonas aeruginosa isolates were ≤ 1 μg/ml. On the basis of our measured elimination half-life of 1.58 hours, it is reasonable to suppose that dosing q 24 h will be inadequate to maintain therapeutic serum concentrations. We calculate that serum concentrations will remain at or above our measured minimal inhibitory concentration for P aeruginosa (1 μg/ml) for 100% of the treatment time if the animal is dosed q 6 h, 78% for dosing q 8 h, and 52% for dosing q 12 h. Therefore, we suggest 3 mg/kg, q 8 h or q 6 h as appropriate dosing schedules for the use of gentamicin sulfate administered im to baboons.

Cognitive functions of epileptic patients on monotherapy with phenobarbitone and healthy controls

Quantitative measurements have indicated that heredity, cerebral damage, psycho-social aspects, ictal and inter-ictal phenomena and antiepileptic drugs may interfere in the cognitive dysfunction of epileptic patients. In the present study objective methods included immediate and late recall and recognition of pictures, Stroop test and auditory selection. Twenty patients with symptomatic localized epilepsy aged 17-52 years (27 +/- 10, mean +/- sd) were compared to age and socially matched healthy controls. Patients were on therapeutic serum concentrations (25 +/- 12 mu/ml) of phenobarbitone and had active epilepsy with 1.94 generalized tonic-clonic, 0.85 simple partial and 6.28 complex partial seizures monthly (means). Patients performed worse than controls in all 6 tests (p less than 0.05 to p less than 0.001), indicating a generalized cognitive deficit related to seizures and/or barbiturate therapy. We suggest further studies should be carried out in populations with uniform monotherapeutic regimens and epileptic syndromes in order to isolate factors related to the cognitive dysfunction of epileptic patients.