Pharmacokinetics of SUN 1165, a new antiarrhythmic agent,in renal dysfunction

Summary The pharmacokinetics of a new Class I antiarrhythmic agent, SUN 1165, has been studied in 32 patients with varying degrees of renal impairment following a single oral dose of 50 mg.The apparent volume of distribution at steady state was 1.48 1 · kg^–1, the absorption rate constant was 2.2 h^–1, and plasma protein binding was 26.8% in subjects with normal renal function.These variables were not altered with renal impairment. More than 60% of SUN 1165 given orally was excreted unchanged via the kidney, both by tubular secretion and glomerular filtration.The elimination rate constant, the apparent total body clearance and the apparent renal clearance were linearly correlated with the endogenous creatinine clearance. The half-time of elimination was 3.4 h in normal subjects and it was prolonged to 23.7 h in severe renal failure (creatinine clearance below 20 ml · min^–1 · 1.48 m^–2).Dosage adjustment of SUN 1165 is necessary in renal failure.     

Pharmacokinetics and tissue concentrations of ceftazidime in burn patients

Summary The pharmacokinetics and tissue concentrations of ceftazidime have been investigated in 8 patients with severe burns (20–80% of body surface area) undergoing skin transplantation 2 to 21 days after injury. Two prophylactic doses of ceftazidime were administered as 1 g i.v. bolus injections with an 8 h interval. Blood, urine, burn blister fluid and tissue were frequently sampled and drug concentrations were analyzed by HPLC. The kinetics of ceftazidime was the same after each dose.In these patients the pharmacokinetics of ceftazidime was greatly altered from that in other patients and there was much interindividual variation. The mean ceftazidime elimination half-life, apparent volume of distribution and total clearance were: 2.7 h, 30.91 (0.38 l·kg^–1) and 139 ml·min^–1, respectively. A linear correlation was found between creatinine clearance and the renal clearance of the ceftazidime, the mean values being 108 and 95 ml·min^–1, respectively. No correlation was found between creatinine clearance and the total clearance of ceftazidime. The mean percentage urine recovery was 69% of the dose. Tissue and burn blister fluid concentrations were above the MIC, and ranged from 40.0 to 3.1 mg·kg^–1. A substantial increase in the apparent volume of distribution and non-renal clearance of ceftazidime was observed, probably due to increased capillary permeability and drug loss through the wound surface replacement of prior to surgery and subsequently to lost and blood fluid.     

Kinetics of morphine in patients with renal failure

Summary The kinetics of morphine and its glucuronidated metabolites were investigated in seven patients with advanced renal failure. The terminal elimination half life of morphine varied between 1.5 and 4.0 h (mean 2.4 h), the volume of distribution between 2.5 and 6.3 l·kg^–1 (mean 4.4 l·kg^–1) and the total plasma clearance between 13.3 and 31.3 l·min^–1·kg^–1 (mean 21.1 l·kg^–1). There were no statistically significant differences between the pharmacokinetic data in the uraemic patients and in a control group of cancer patients with normal kidney function. The concentrations of the glucuronidated metabolites rapidly rose to levels above those of morphine. The elimination half-life of M3G varied between 14.5 and 118.8 h (mean 49.6 h) in the renal failure patients, which is distinctly different from the 2.4 to 6.7 h (mean 4.0 h) found in patients with normal kidney function. There was a significant correlation between the half-life of M3G and renal function estimated as serum urea. Thus, the metabolism of morphine in patients with kidney disease is not significantly impaired. The clinical importance of the high concentrations of glucuronides in uraemic patients is not known.     

The effect of renal impairment on the pharmacokinetics of oxcarbazepine and its metabolites

We have studied the effect of renal impairment on the pharmacokinetics of oxcarbazepine, its active monohydroxy-metabolite (which predominates in plasma), their glucuronides, and the inactive dihydroxy-metabolite after a single oral dose of oxcarbazepine (300 mg). Six subjects with normal renal function and 20 patients with various degrees of renal impairment participated.The mean areas under the plasma concentration-time curves of oxcarbazepine and its monohydroxy-metabolite were 2–2.5-times higher in patients with severe renal impairment (CL_CR<10 ml·min^–1) than in healthy subjects. The apparent elimination half-life of the monohydroxy-metabolite [19 (SD 3) h] in these patients was about twice that in healthy subjects.The effect of renal impairment on the plasma concentrations of glucuronides was more marked. The renal clearances of the unconjugated monohydroxy-metabolite and its glucuronides (the main compounds recovered in urine) correlated well with creatinine clearance.The maximum target dose in patients with slight renal impairment (CL_CR>30 ml·min^–1) should not be changed. In patients with moderate renal impairment (CL_CR10–30 ml·min^–1) it should be reduced by 50%. In patients with severe renal impairment (CL_CR<10 ml·min^–1), the glucuronides of oxcarbazepine and its monohydroxy-metabolite are likely to accumulate during repeated administration, and dosage adjustment of oxcarbazepine in these patients could not be proposed from this single administration study.     

The pharmacokinetics of theophylline and enprofylline in patients with liver cirrhosis and in patients with chronic renal disease

Summary We have studied the pharmacokinetics of theophylline and enprofylline in patients with liver cirrhosis, patients with chronic renal failure, and healthy subjects, and have assessed the predictive value of routine tests of liver function and renal function (creatinine clearance) for theophylline and enprofylline total body clearances.Theophylline clearance was significantly decreased in the patients with liver cirrhosis compared with both the patients with renal failure and the healthy subjects (the mean values in the three groups were 24, 47, and 46 ml·h^–1·kg^–1 respectively.Enprofylline clearance was significantly decreased in the patients with chronic renal failure, compared with both the patients with liver cirrhosis and the healthy subjects (the values in the three groups were 64, 250, and 289 ml·h^–1·kg^–1 respectively.There was a strong correlation between creatinine clearance and enprofylline clearance, while there was only a poor correlation between the liver function tests and theophylline clearance.It appears that in various clinical situations enprofylline elimination can be predicted more precisely than theophylline elimination, which may make the drug safer in clinical practice.     

Effect of renal insufficiency on the pharmacokinetics of cyclophosphamide and some of its metabolites

Summary Cyclophosphamide pharmacokinetics were studied in seven patients with moderate to severe renal insufficiency (creatinine clearances 0–51 ml · min^–1), and compared with a matched control group of patients with normal renal function. The mean half-life of cyclophosphamide following intravenous administration in the normal group was 8.21±2.33 (SD) h whilst that in renal failure was 10.15±1.80 h: these were significantly different. The total body clearance in the normal control group was 58.6±10.9 ml·kg^–1h^–1 which was significantly larger than in renal failure where it was 48.8±10.9 ml·kg^–1h^–1. V_d , V_{d ss} and V_c were not significantly different between the two groups. A linear relationship exists between , the first order disposition rate constant and endogenous creatinine clearance since this drug shows a relatively small degree of compartmentalisation. The plasma half-life of phosphoramide mustard, a cytotoxic metabolite of cyclophosphamide, shows a parallel and significant increase in renal failure with the parent compound. The t_1/2 in normal patients was 8.33±2.0 h, whilst in the renal failure group it was 13.37±4.23 h. Total alkylating activity as measured by the nitrobenzylpyridine reaction showed a significant increase in renal failure. This data suggests that in pharmacokinetic terms it may not be necessary to alter the dose of cyclophosphamide until there is severe renal impairment. Further studies correlating the efficacy and toxicity of the drug with its pharmacokinetics in renal failure are necessary.     

Effect of age on the pharmacokinetics of vinpocetine (Cavinton) and apovincaminic acid

Summary The pharmacokinetics of vinpocetine and its main metabolite, apovincaminic acid (AVA), were studied in the aged. Vinpocetine was eliminated with a mean half-life of 2.12±0.51 h. Total plasma clearance (CL) and distribution coefficient () of the parent drug were 2.2±0.9 l · kg^–1 · h^–1 and 6.7±3.7 l · kg^–1, respectively. The CL and of vinpocetine differed significantly from young subjects but the elimination half-life was not altered. Significant changes in the elimination half-life and plasma clearance of AVA were found, perhaps because of the physiological decrease in renal function.     

Steady-state levels of pefloxacin and its metabolites in patients with severe renal impairment

Summary Twenty patients (aged 26–70 years) with severely impaired renal function received pefloxacin twice daily for 5 days as 12 mg·kg^–1 administered as a 1 h i.v. infusion, or 800 mg administered as tablets.On Day 5 the minimal and maximal plasma concentrations were 5.9 and 11.5 mg·l^–1 respectively, after the infusion, and 8.0 and 10.4 mg·l^–1, respectively, after oral administration. The steady-state level of the N-desmethyl metabolite ranged from 0.9 (infusion) to 1.2 mg·l^–1 (oral route), and that of the N-oxide metabolite ranged from 6.2 (infusion) to 9.0 mg·l^–1 (oral route). The minimal concentration of unchanged drug was related to the age of the patients (infusion), but the N-oxide concentration was influenced by the degree of renal impairment (both routes).The pefloxacin levels were similar to those achieved in healthy subjects, but reduced renal function leads accumulation of its biotransformation products, especially of the N-oxide metabolite which lacks antibacterial activity.     

Clofibrate disposition in renal failure and acute and chronic liver disease

Summary The disposition of clofibrate over 96 hours was observed following single oral dose in six patients with acute viral hepatitis, six patients with liver cirrhosis, seven patients with renal insufficiency, and six control subjects. No parameter of the disposition of CPIB (active form of clofibrate) was significantly altered in acute hepatitis. In liver cirrhosis, the mean plasma half-life was unchanged compared to controls (20.9 vs. 17.5 h), but plasma clearance of the non-protein bound drug was reduced (115 vs. 243 ml×min^–1), plasma protein binding was reduced (92.8 vs. 97.2 percent), and the apparent volume of distribution was increased (0.20 vs. 0.141×kg^–1). In renal insufficiency plasma half-life was prolonged 2 to 6-fold, depending on the degree of renal impairment. Total plasma clearance (3.4 vs. 7.1 ml×min^–1) and plasma clearance of the unbound drug (81 vs. 243 ml×min^–1 were reduced in patients with renal failure, the clearance of the unbound drug being inversely correlated with the serum creatinine concentration. Renal failure was also associated with decreased protein binding and an increased volume of distribution of CPIB, and with reduced urinary excretion of CPIB and its glucuronide metabolite. The dose of clofibrate should be halved in patients with cirrhosis. In renal insufficiency, the dose should be adjusted according to the individual serum creatinine level: only 10 to 15% of the usual weekly dose should be given in complete renal failure.     

Single-dose kinetics of primidone in acute viral hepatitis

Summary The pharmacokinetics of primidone (PRM) after oral administration of a single 500 mg dose was studied in 7 patients with acute viral hepatitis and 7 healthy control subjects. The elimination half-life and the apparent clearance of unchanged PRM in the patients were 18.0±3.1 h and 42±14 ml·h^–1·kg^–1, respectively (mean ± SD) and did not differ significantly from the values in the controls (half-life 17.0±2.4 h; clearance 35±8 ml·h^–1·kg^–1). The metabolite phenylethylmalonamide (PEMA) was detected in the serum of all normal subjects within 2–24 h. By contrast, serum levels of this metabolite were undetectable (<2 umol/l) in all but one of the patients. Serum levels of phenobarbital (PB) remained below the limit of detection (<2 µmol/l) in all subjects. The findings indicate that accumulation of PRM with its attendant toxicity is unlikely to occur in epileptic patients who develop acute viral hepatitis, despite evidence that the metabolism of the drug is affected by this condition. The possibility of impaired conversion to PB and its implications are discussed.     

Polymorphic 2-hydroxylation of desipramine

Summary We have studied the clearance of monomethylaminoantipyrine (MMAAP), the pharmacologically active form of metamizol, in 46 patients in surgical intensive care with different degrees of renal dysfunction.In 23 patients without any renal impairment, mean clearance was 2.8 ml·min^–1·kg^–1. Twentyone patients with acute renal impairment had a significantly reduced clearance of MMAAP (0.83 ml·min^–1·kg^–1). There was also reduced clearance in four patients with septic shock (1.0 ml·min^–1·kg^–1).Kinetics of the metabolites of MMAAP (N-formylaminoantipyrine (FAAP), aminoantipyrine (AAP), and its secondary product N-acetylaminoantipyrine (AcAAP)) were calculated. FAAP and AcAAP showed delayed invasion, which can be explained by reduced hepatic metabolic activity. The product of N-demethylation, AAP, was not significantly altered.The delayed elimination of monomethylaminoantipyrine can be explained by reduced hepatic function in parallel with acute renal failure due to disturbed cardiovascular function caused by septic shock. This may also lead to disturbed hepatic macro- and microperfusion associated with altered oxygen supply and oxygen consumption.     

Pharmacokinetics of a single oral dose of hydroflumethiazide in health and in cardiac failure

Summary The pharmacokinetics of hydroflumethiazide (HFT) were investigated after single oral doses of 6 µmoles/ per kg body weight in five healthy subjects and in nine patients with moderate cardiac failure. HFT was excreted in urine together with 2,4-disulfamyl-5-trifluoromethylaniline (DTA), which was also present in the blood after administration of HFT. HFT and DTA were determined by TLC and spectrofluorodensitometry. Mean cumulative urinary excretion of HFT was 46.5 and 47.5 per cent of the dose both in healthy subjects and in patients. Distribution half-life (t1/2) was about 2 h in both groups of subjects, while biological half-life (t1/2) ranged from 12.4 to 26.9 h (mean 16.6) in healthy subjects, and from 6.3 to 13.7 h (mean 9.6) in patients. Mean renal clearance was 0.33 and 0.211 · h^–1 · kg^–1 in normal subjects and patients, respectively, and was almost equal to the total body clearance. HFT had a large apparent volume of distribution (V), with mean values of 6.4 and 3.11 · kg^–1 in normal subjects and patients. Mean cumulative urinary excretion of DTA was 1.8 and 1.9 per cent in healthy subjects and patients with cardiac failure. The apparent half-life of DTA, determined from urinary excretion rate in eleven subjects, ranged from 16 to 56 h but half-lives in three others were more than 100 h. The results indicate that HFT is partly metabolized in the body to DTA, and DTA and HFT are excreted in urine. The half-life of DTA was longer than that of the parent drug. The apparent volume of distribution, clearance and biological half-life of HFT were lower in patients with cardiac failure than in healthy subjects.     

Relationship between renal function and disposition of oral cefixime

Summary The pharmacokinetics of cefixime following a single oral dose of 200 mg have been investigated in 6 normal subjects and in 22 patients with various degrees of renal insufficiency. Serum and urine samples were collected between 0 and 72 h and were subjected to two methods of analysis: bioassay and HPLC.There was a linear relationship between the two sets of results from 228 samples. This result suggests that none of the metabolites, which may accumulte in uraemic patients, has antibacterial activity.In normal subjects, the peak serum level (C_max) was 2.50 g·ml^–1 at 2.83 h (t_max); the apparent elimination half-life (t_1/2) was 3.73 h; the apparent total body clearance (CL·f^–1) was 154 ml·min^–1, the mean renal clearance (CL_R) was 39.1 ml·min^–1 and the apparent fraction of the dose recovered in 24 h urine was 0.22.In uraemic patients, C_max and t_max were slightly increased and t_1/2 was increased to 12–14 h in patients with an endogenous creatinine clearance below 20 ml·min^–1. The apparent volume of distribution was decreased. Apparent total and renal clearances were lower in proportion to the degree of renal insufficiency. Linear relationships were found between CL/f, CL_R and creatinine clearance (CL_CR).The findings suggest that the dose of cefixime needs to be reduced only in patients with severe renal failure.     

The pharmacokinetics of nifurtimox in chronic renal failure

Summary The pharmacokinetics of nifurtimox, a drug used in the treatment of Trypanosoma cruzi infections, has been studied in seven patients with chronic renal failure undergoing haemodialysis, and in seven healthy subjects.Each subject took nifurtimox 15 mg·kg^–1 orally and blood samples were obtained for 10 h after administration. Nifurtimox in serum was analyzed by HPLC.The patients with chronic renal failure had a higher C_max than the control subjects due to a change in systemic availability. An alternative explanation would be that both the distribution volume and the clearance had changed.The mean half-life in the patients with chronic renal failure was similar to that in the healthy subjects.     

First dose and steady-state pharmacokinetics of oxcarbazepine and its 10-hydroxy metabolite

Summary The pharmacokinetics of oxcarbazepine (a new anticonvulsant which is a congener of carbamazepine) and of its 10-hydroxy metabolite were studied at the outset of therapy in 8 adult epileptics comedicated with other anticonvulsants. The pharmacokinetic study was repeated under steady-state conditions after 3 months of drug intake in 6 of these subjects.The plasma elimination half-life of oxcarbazepine appeared to lie in the range 1.0–2.5 h, and that of its 10-hydroxy metabolite averaged 8.4 h. The apparent oral clearance of the parent drug (averaging 2.51·kg^–1·h^–1) was high enough to suggest substantial presystemic elimination. The oral clearance fell after 3 months of drug intake, but the half-lives of the drug and metabolite showed no statistically significant change over this time. Steady-state plasma levels of both drug and metabolite were linearly related to drug dose, metabolite levels averaging 9 times those of the parent substance.     

Influence of usual intake of dietary caffeine on single-dose kinetics of theophylline in healthy human subjects

Summary The influence of usual multiple ingestions of dietary caffeine on oral single-dose pharmacokinetics of theophylline has been investigated in 6 healthy male subjects. The subjects consumed 2 to 7 cups of regular instant coffee during the 24 h study period.Their mean serum concentrations of caffeine varied from 1.2 to 3.1 mg/l. After their usual intake of dietary caffeine, the serum concentrations of theophylline from 3 to 24 h after administration were significantly higher than after deprivation of dietary caffeine. The apparent elimination of theophylline half-life was prolonged from 6.3 (0.61) h (mean with (SEM)) to 8.3 (0.47) h (32% increase, P<0.01) and the total body clearance was reduced from 55.0 (1.31) ml·h^–1·kg^–1 to 42.5 (2.63) ml·h^–1·kg^–1 (23% decrase, P<0.001). Saturation of theophylline metabolism and/or competition between theophylline and caffeine metabolism in addition to theophylline derived from caffeine may be the cause of the delayed elimination of theophylline.The present study has indicated that a significant reduction in theophylline metabolism may be caused by a conventional intake of dietary caffeine. In bronchodilator therapy with theophylline, therefore, the daily consumption of caffeine should be taken into consideration.     

Pharmacokinetics of xamoterol after intravenous and oral administration to patients with chronic heart failure

Summary The pharmacokinetics of xamoterol, a -adrenergic partial agonist under clinical evaluation for the treatment of mild to moderate heart failure, have been studied in 8 cardiac failure patients (NYHA Class II) of mean age 62 years.After i.v. dosing, the elimination half-life was 7.4±0.4 h, the total body clearance was 228±30 ml·min^–1 and the volume of distribution at steady-state was 56±91. 72.5±4.3% of the dose was recovered unchanged in urine. After the oral dose, the absolute bioavailability of xamoterol was shown to be 5.9%. Peak plasma concentrations occurred 1 to 2.5 h after the oral dose. The apparent elimination half-life was significantly longer after oral doses (16±2 h) compared to that observed after an intravenous dose. Renal clearance of xamoterol exceeded glomerular filtration rate as measured by creatinine clearance.The pharmacokinetics of xamoterol in cardiac failure patients with good renal function (creatinine clearance >90 ml·min^–1) were similar to published data in young healthy male volunteers.     

Lack of relationship between tolbutamide metabolism and debrisoquine oxidation phenotype

Summary The oxidative metabolism of tolbutamide was studied in 13 healthy subjects of known debrisoquine phenotype. Three were poor (PM) and ten were extensive (EM) metabolisers of debrisoquine.The mean values for total plasma clearance, elimination half-life, and metabolic clearance were 0.26 ml·min^–1·kg^–1, 3.4 h, and 0.17 ml·min^–1. kg^–1 in PM subjects and 0.22 ml·min^–1·kg^–1, 4.3 h and 0.15 ml·min^–1·kg^–1 in EM subjects. Total urinary recovery (% of dose) and ratio of hydroxy- to carboxytolbutamide were 69.4% and 0.219 respectively in PM subjects and 70.9% and 0.226 in EM subjects. There were no statistically significant differences between EM and PM metabolisers for any of these parameters. In addition there was no correlation between the debrisoquine metabolic ratio and tolbutamide urinary metabolite recovery or plasma clearance.These data indicate that hydroxylation of debrisoquine and tolbutamide are not catalyzed by the same enzyme.The ratio of hydroxy- to carboxytolbutamide in our subjects, and in other recent studies, suggests that some previous publications were inaccurate and their conclusions about the genetic control of tolbutamide metabolism were incorrect.     

Influence of renal failure on the kinetics of zimeldine and norzimelidine

Summary The kinetics of zimeldine (Z) and its demethylated metabolite, norzimelidine (NZ), were determined after administration of a single 200 mg oral dose of Z to 6 healthy volunteers (Group I), and to patients with mild (Group II) and severe renal failure (Group III). Z and NZ concentrations were assayed by HPLC in serial plasma and urine samples over 6 days following the dose. In Group I Z was rapidly absorbed and metabolized into NZ, and then the plasma concentrations declined with apparent elimination half-lives of 8.4 h and 24.9 h for Z and NZ respectively, whilst the renal clearance of both compounds was low, Z 15.7 ml/min and NZ 33.0 ml/min. The plasma level of Z differed little between Groups I and III, but the area under the curve was significantly higher in Group III than in Group I subjects (AUC_0–144=17.3 and 6.8 µmol·l^–1·h, respectively). Severe renal failure did not affect the peak plasma concentration of NZ but it did significantly increase peak time, apparent elimination half-life, and the area under the plasma concentration curve. A significant inverse relationship was found between renal clearance of NZ and plasma creatinine. Since NZ is as pharmacologically potent as Z, the results suggest that the dose of Z should be reduced in patients with severe renal insufficiency.     

Pharmacokinetics of intranasal,intramuscular and intravenous glucagon in healthy subjects and diabetic patients

Summary The pharmacokinetics of intranasal, an intravenous infusion, and intramuscular glucagon has been studied in 5 healthy subjects and 11 patients with insulin-dependent diabetes mellitus.After infusion the elimination half-life was significantly longer in diabetics (11.9 vs 6.6 min) and the apparent volume of distribution was twice as high in diabetics (0.19 vs 0.37 l·kg^–1). The metabolic clearance rates were the same in the two groups (18.9 and 21.3 ml·min^–1·kg^–1 in controls and in diabetics) and were about twice those previously reported.After 1 mg intranasally the C_max of immunoractive glucagon (IRG) was similar in diabetic and in healthy subjects. Administration of a higher dose (2 mg) to diabetic patients produced a higher plasma level, although not proportionately so. The AUC after 1 mg was also similar in controls and in diabetics. The elimination half-life in both groups was similar to the value found after IV infusion; it was significantly shorter in controls (5.5 min) than in diabetics (13.8 min). In both groups, mean C_max was significantly lower than after IM glucagon, the relative bioavailability of 1 mg intranasally vs IM injection being less than 30%.After IM administration, the C_max and AUC of IRG in controls and in diabetic patients, were identical. The apparent elimination half-life was also similar in the two groups, and was three- to four-times longer (28.6 and 31.4 min) than after infusion or intranasal administration, possibly because estimation of the t_1/2 was affected by slow release of the hormone from the site of injection.