Single-dose pharmacokinetics of cefpirome in patients with renal impairment.

The pharmacokinetic parameters of cefpirome (HR 810) were examined in 22 patients with different degrees of renal impairment. HPLC was used to analyze samples of blood and urine for cefpirome; and enzymatic assay of creatinine in serum and urine was used to assess kidney function. Creatinine clearance correlated linearly with both total and renal clearance of cefpirome. The loss of kidney function resulted in a decreased renal clearance, whereas the volume of distribution remained the same. This result led to an increase in the terminal half-life of the drug, from 2 hours in healthy subjects to 14 1/2 hours in patients with uremia. This increase also resulted in a prolonged high serum concentration well above the minimum inhibitory concentration. The following dosages are thus recommended: (1) creatinine clearance greater than 50 ml/min: normal daily dose, (2) creatinine clearance from 20 to 50 ml/min: 50% of normal daily dose, and (3) creatinine clearance less than 20 ml/min: 25% of normal daily dose. An initial loading dose of 1 gm, independent of renal function, is advised. Cefpirome was safe and well tolerated.

Single-dose pharmacokinetics of cefpirome in patients receiving hemodialysis and in patients treated by continuous ambulatory peritoneal dialysis.

Cefpirome is eliminated primarily by renal excretion, compelling dosage reduction in kidney failure. We studied the elimination kinetics after intravenous administration of 1 gm cefpirome in patients undergoing hemodialysis (n = 9) and after intravenous (n = 6) or intraperitoneal administration (n = 6) of 1 gm cefpirome in subjects treated by continuous ambulatory peritoneal dialysis (CAPD). Four hours of hemodialysis removed 48% +/- 9% of the drug present in the body at the start of hemodialysis. Consequently, a supplementary dose equal to 50% of the daily dose recommended in end stage renal disease (ESRD) should be administered after each hemodialysis treatment. In patients receiving CAPD, therapeutic levels in both serum and dialysate were reached after intravenous and intraperitoneal administration. The bioavailability after intraperitoneal administration was 84%. After systemic administration, the elimination of cefpirome in the dialysate was negligible. Consequently, systemic dosage of cefpirome in patients receiving CAPD and in patients with ESRD should be identical.

Ofloxacin pharmacokinetics in chronic renal failure and dialysis.

Data on the pharmacokinetics of ofloxacin in chronic renal failure, in patients who were not dialysed or were receiving haemodialysis or continuous ambulatory peritoneal dialysis (CAPD), are reviewed. In addition, a large pool of data obtained in patients with a wide range of renal dysfunction is provided. The good absorption of ofloxacin after oral administration is not influenced by renal failure. Total plasma clearance (CL) is largely dependent on renal elimination of the drug, and renal clearance (CLR) and urinary recovery are reduced in parallel with reductions in renal function. Consequently, the serum half-life progressively increases when creatinine clearance decreases. Although there is wide variation in the published absolute values for the CL and CLR of ofloxacin, all studies show a similar pattern in the pharmacokinetic behaviour of the drug in chronic renal failure. A proposed protocol for ofloxacin dosage adjustment in chronic renal failure is reported which differs slightly but significantly from that recommended by the manufacturer. This new dosage regimen was derived from the pharmacokinetic results after single and multiple oral administration of the drug to patients with chronic renal failure. Since no clinically relevant losses of ofloxacin occur during haemodialysis or continuous ambulatory peritoneal dialysis (CAPD), the same protocol should be followed in these patients as in undialysed patients with terminal chronic renal failure.

Multiple-dose pharmacokinetics of ofloxacin, a new broad-spectrum antimicrobial agent.

Twelve healthy male volunteers received 14 oral doses of ofloxacin (300 mg each), and the concentrations of the unchanged drug were measured at various times in serum and urine over a period of 15 days. Serum and urine ofloxacin concentrations were determined in specific assays using high-pressure liquid chromatography (HPLC); urine levels were also determined by means of a microbiological assay. A washout period of 72 hours followed the first and 14th doses, allowing comparison of serum pharmacokinetics at the beginning and end of the multiple-dose regimen. Doses 2 to 14 were administered at 12-hour intervals. Maximum serum concentration (Cmax), concentration at 12 hours after dosing (C12), and area under the serum concentration-time curve (0 to 72 hours) were all 1.3 to 1.7 times greater after the 14th dose than after the initial dose. A 1.6-fold increase in C12 was already evident after the third dose; C12 remained more or less constant thereafter. Thus it is concluded that ofloxacin rapidly attained steady-state serum levels under a multiple-dose regimen, at levels only slightly above those following a single dose. High serum Cmax levels (4.6 and 5.9 micrograms/ml after the first and 14th doses, respectively) and long serum half-lives (6.0 and 7.3 hours after the first and last doses, respectively) indicated long-lasting, clinically relevant serum ofloxacin concentrations after oral administration. Serum ofloxacin levels 24 hours after the last dose were in the range of 0.3 to 0.7 microgram/ml, above the minimal inhibitory concentration (MIC90) for most bacterial strains. Cumulative urinary recovery remained high throughout the study. After 14 doses of ofloxacin (total, 4.2 gm), 88% of the unchanged drug was recovered in the urine; urinary concentrations remained above 1 microgram/ml, far above the MIC90 for most bacterial strains, for at least 108 hours after the final dose. High renal clearance values relative to total clearance (98%) confirmed the importance of the renal elimination route. Determinations of ofloxacin in urine using a microbiological assay were in close agreement with the HPLC determinations for all samples obtained throughout the study. Thus no detectable appearance of active metabolites occurred under the multiple-dose regimen. Ofloxacin was well tolerated; mild, probably drug-induced side effects were reported by three subjects, but they did not require any countermeasures.

Dose linearity and other pharmacokinetics of cefodizime after single-dose intravenous administration.

Pharmacokinetics of cefodizime, a broad-spectrum cephalosporin antibiotic, were determined after intravenous (IV) administration of single doses of 1.0, 1.5, and 2.0 gm to 12 healthy male volunteers in an open study. In a separate pilot study, data were obtained after IV administration of 0.5 gm of cefodizime to six healthy male volunteers. Determinations of cefodizime in serum and urine using a microbiological assay agreed with determinations using high-pressure liquid chromatography (HPLC), which specifically measures the unchanged drug. Active metabolites of cefodizime were not detected. After IV administration of 1.0, 1.5, and 2.0 gm of cefodizime, initial mean serum concentrations were 215, 322, and 394 mg/L, respectively (HPLC determinations). A linear response to dosage was shown (coefficient of correlation r = .89), as was the case for area under the serum concentration-time curve to infinity, AUC infinity (r = .82), and 48-hour urinary recovery of cefodizime (r = .94). In all cases, the corresponding values obtained after the 0.5-gm dose showed that the linearity extended to this dose. The kinetics of single-dose administration of cefodizime corresponded to a two-compartment open model with an apparent steady-state volume of distribution of about 40 L. Volume of distribution, terminal elimination half-life, serum and renal clearance, and percent urinary recovery were not dose dependent. Cefodizime combined a long terminal elimination half-life (mean, 2.5 hours) with a high urinary recovery (80%). After IV administration of cefodizime, urinary concentrations of the unchanged drug remained above 5 micrograms/ml for at least 24 hours after drug administration and were dose dependent. Mean values for the 1.0-gm and 2.0-gm doses were, respectively, approximately 12 mg/L and 30 mg/L, several times the minimal inhibitory concentrations (MIC90) for most clinically relevant bacteria. These results suggest that once- or twice-daily IV dosing with cefodizime (depending on the dose regimen) would be suitable for clinical use. The drug was safe and well tolerated.

The effect of food on the pharmacokinetics of ofloxacin.

After oral administration of a single dose of ofloxacin (300 mg), with and without a standard breakfast, to 12 healthy male volunteers in an open, randomized crossover study, concentrations of the unchanged drug were estimated at various times in serum and urine, over 28 hours and 48 hours, respectively. Each dose was followed by a wash-out period of 1 week. Ofloxacin concentrations were determined using high pressure liquid chromatography (HPLC): parallel determinations using a microbiological assay were in close agreement. Maximum serum concentrations (Cmax) of ofloxacin, after fasting and with breakfast, respectively, were 3.7 and 3.1 micrograms/ml (HPLC, median values). The corresponding areas under the serum concentration-time curves (AUC0-28) were 29.9 and 24.5 micrograms/ml. The lower values of Cmax and AUC0-28 found after food intake were statistically significant (p less than 0.05) but not clinically relevant when compared to the fasting values. Time to reach Cmax and terminal elimination half-life (t1/2 beta) were not significantly affected by food intake: t1/2 beta was calculated as 5.3 and 5.9 hours (HPLC, median values), fasting and with breakfast, respectively. Urinary recovery (after 48 hours: 72% and 74%, respectively) was also not significantly affected by food intake, and urinary concentrations of ofloxacin remained far above 1 microgram/ml, i.e. above the minimum inhibitory concentration (MIC90) for most bacterial strains, for at least 48 hours after drug administration. General tolerability was good; no side-effects were reported.

Relative bioavailability of ofloxacin tablets in comparison to oral solution.

Single oral doses of solution and tablet preparations of 300 mg ofloxacin were given to 13 healthy male volunteers in an open, randomized crossover study. Concentrations of the unchanged drug were monitored at various times in serum and urine, over 28 hours and 48 hours, respectively. Each dose was followed by a 1-week washout period. Drug concentrations were measured both by a specific high pressure liquid chromatography (HPLC) method and a microbiological assay. A linear distribution independent regression analysis for method comparisons was calculated and good agreement between the two methods was found. Medians of maximum serum concentrations (Cmax) of ofloxacin after oral solution and tablet form were 5.0 mg/l and 3.5 mg/l, respectively. The times to maximal serum concentration (tmax) were 0.5 hr and 1.0 hr, respectively. The lower Cmax and later tmax after the tablet form were both statistically (p less than 0.05) different when compared to the corresponding values after the oral solution. However, the areas under the serum concentration-time curves (AUC0-28), as also the urinary recoveries did not differ significantly, showing that only the speed of absorption, but not the bioavailability of the tablet is changed in comparison to the oral solution form. Long-lasting, clinically relevant urine concentrations of ofloxacin were observed after both forms until the last collecting fraction (36 to 48 hours after medication). General tolerability was good; no side-effects were reported.

Absence of interaction between ofloxacin and phenprocoumon.

The effect of ofloxacin on steady-state phenprocoumon pharmacodynamics was investigated in 7 healthy male volunteers taking daily sub-therapeutic doses of phenprocoumon. Ofloxacin 200 mg once daily for 7 days did not alter the anti-coagulant response (Quick values) to phenprocoumon after a stabilization phase of 2 weeks. Mean Quick values during the steady-state phase before and during ofloxacin administration were 54% and 52%, respectively. In vitro studies with concentrations of 0 to 100 mg ofloxacin/1 added to plasma also failed to show any interaction. The results indicate, therefore, that ofloxacin does not interfere with vitamin K-dependent coagulation cascade, as seen after other antibiotics.

Absence of crystalluria and estimation of renal parameters after oral and intravenous ofloxacin as compared to placebo in healthy volunteers.

An open placebo-controlled study on eleven healthy male volunteers was carried out to investigate renal tolerance and the possibility of crystalluria after oral and intravenous administration of ofloxacin. Subjects received single doses of 200 and 400 mg ofloxacin orally, 200 mg ofloxacin intravenously, or placebo. Urine was collected in several fractions on each study day and the urine volume, excretion of ofloxacin, and excretion of creatinine, alanine aminopeptidase, N-acetyl-beta-D-glucosaminidase, and gamma-glutamyltransferase were calculated in each fraction collected. Furthermore, the urine was investigated microscopically to determine whether ofloxacin crystals were present. Serum creatinine and creatinine clearance were also calculated. No relevant changes in creatinine clearance were observed and no drug crystals were found in the urine which indicates that renal tolerance was good. There were no differences in ofloxacin recovery after oral or intravenous administration, confirming that absolute bioavailability of the oral form is excellent.

Serum selenium levels in diuretic-treated hypertensives: a double-blind trial of piretanide against hydrochlorothiazide plus amiloride.

In a double-blind parallel group study carried out on 47 patients with mild to moderate essential hypertension, the effects of 6 mg piretanide once or twice daily on serum selenium levels were compared with 50 mg hydrochlorothiazide plus 5 mg amiloride before treatment and after 6 and 12 weeks of treatment. Serum levels of the trace element, selenium, over a treatment period of 12 weeks remained unchanged in all three treatment groups, indicating that the selenium homeostasis is not disturbed during a treatment period of three months with either piretanide or a potassium sparer/thiazide-diuretic combination.

Dose linearity and relative bioavailability testing of oxilofrine, a sympathicomimetic drug, in healthy volunteers.

Single oral doses of 16, 32 and 64 mg oxilofrine as dragées as well as 16mg as drops were given to 12 healthy male volunteers in an open Latin-square design with one week interval between dosing days. Concentrations of unchanged drug were monitored in plasma over 24 hours, in urine concentrations of free and total oxilofrine were monitored over 36 hours. Drug concentrations were measured by a specific high pressure liquid chromatography method with electrochemical detection. Medians of maximum plasma concentrations (Cmax) of oxilofrine were 9.1 ng/ml, 11.4 ng/ml, 31.4 ng/ml and 122.9 ng/ml for 16 mg drops, 16, 32, and 64 mg dragées, respectively. The times to maximum plasma concentration (tmax) were between 0.7 and 1.7 h, respectively. The values for areas under the plasma concentration-time curve (AUC0-24) were 12.8, 17.7, 61.0 and 268.2 ng/ml.h for the four treatments. The results show that both Cmax- and AUC0-24-values increase faster with increasing dosing than a linear first-pass would suggest and give evidence for a saturable first-pass metabolism. There is also evidence for an enterohepatic circulation. About 50% of the administered dose is found in the urine, urinary recovery shows a dose-linear dependency. General tolerability was good; no side-effects were reported.

Absolute bioavailability of glimepiride (Amaryl) after oral administration.

Twelve healthy fasting male volunteers received a single 1.0 mg dose of glimepiride either as an intravenous injection over one minute or as a tablet. Blood and urine samples were taken before drug administration and afterwards for up to 24 hours (blood) and 48 hours (urine) to determine serum and urinary concentrations of glimepiride and its hydroxy- and carboxy-metabolites (M1 and M2). There were no statistically significant differences between mean serum pharmacokinetic parameters for the oral and intravenous formulations either with glimepiride or M1. Mean urinary recovery of M1 plus M2 was 50% of the dose for the glimepiride tablet and 51% for the intravenous injection. The absolute bioavailability of the tablet formulation was 107% (AUDC(glimepiride)), 109% (AUDC(M1)) and 97% (urinary recovery). The tablet formulation of glimepiride is completely bioavailable and was safe and well tolerated in healthy volunteers.

Dose linearity assessment of glimepiride (Amaryl) tablets in healthy volunteers.

Twelve healthy fasting male volunteers received glimepiride in 1, 2, 4 or 8 mg single oral doses. On the days when glimepiride was taken, the subjects were given a standardised carbohydrate diet (18 bread exchange units) and drank 125 ml of water hourly. Blood and urine samples were taken before drug administration and afterwards for up to 36 hours (blood) and 48 hours (urine) to determine serum and urinary concentrations of glimepiride and its hydroxy- and carboxy-metabolites (M1 and M2). The areas under the curve for glimepiride after oral doses of 1 to 8 mg and the urinary recovery of its metabolites M1 and M2 were dose linear. All confidence intervals were well contained within the bioequivalence range of 80-125%. There was a statistically significant difference for Cmax values of glimepiride between doses after dose normalisation. A dose-dependent increase for Cmax was nevertheless clearly observed with a correlation coefficient of r=0.90. The pharmacokinetics of glimepiride are dose linear in the dose range 1 to 8 mg, and glimepiride was safe and well tolerated in healthy volunteers.

Pharmacokinetics of levofloxacin in comparison to the racemic mixture of ofloxacin in man.

After oral administration of a single dose of 200 mg of levofloxacin and 400 mg racemic mixture of ofloxacin to 6 healthy male volunteers in a double-blind, randomised cross-over study, concentrations of the unchanged isomers were determined at various times in serum and urine, over 28 hours and 48 hours, respectively. Each dosing was followed by a wash-out period of one week. Ofloxacin concentrations were determined using an enantioselective and a non-enantioselective high pressure liquid chromatography (HPLC) assay. The two measurements obtained were compared by linear distribution independent regression, and were found to be equivalent. Maximum serum concentration (Cmax) of levofloxacin after the administration of 200 mg of the levo-isomer was 2.42 mg/l (chiral derivatization HPLC, mean values); the corresponding area under the serum concentration-time curve (AUC0-28) was 17.0 mg x h/l. The corresponding Cmax values after the administration of 400 mg (+/-)-isomer (chiral derivatization HPLC and reversed phased HPLC, mean values) were 2.05 mg/l, 1.98 mg/l and 4.41 mg/l for (-)-, (+)- and (+/-) isomer, respectively. The AUCS0-28 were 17.0, 14.6 and 32.7 mg x h/l, respectively. The pharmacokinetics of the (-)- and (+)-isomer were shown to be almost equal. In serum and urine no reracemisation of the (-)-isomer to a racemic mixture was observed. General tolerability was good; no side effects were reported.

Pharmacokinetics and pharmacodynamics of the hydroxymetabolite of glimepiride (Amaryl) after intravenous administration.

Glimepiride is a new sulphonylurea which is eliminated by the formation of a hydroxy-metabolite (hydroxy-gli) and a carboxymetabolite (carboxy-gli). Animal studies have shown hydroxy-gli to exhibit some hypoglycaemic effects while carboxy-gli does not appear to have any pharmacological activity. Pharmacokinetic and pharmacodynamic effects of hydroxy-gli were assessed in humans. 12 healthy male volunteers received an intravenous injection of hydroxy-gli (1.5 mg) or placebo in a single blind, randomised, cross-over study. Samples were collected for up to 24 hours (blood) or 48 hours (urine) following administration of hydroxy-gli or placebo. Hydroxy-gli significantly decreased the minimum serum concentration (Cmin) of glucose by 12% and the average serum glucose concentration over the first four hours of treatment (Cavg0-4) by 9% compared with placebo (P < or = 0.05). In addition, maximum serum C-peptide concentration (Cmax) and Cavg0-4 were both increased by 7% after hydroxy-gli (p < or = 0.05). Serum insulin concentrations (Cmax and Cavg0-4) increased by 4% but the differences from placebo were not statistically significant. No adverse events were reported during the study. In conclusion, the hydroxymetabolite of glimepiride shows pharmacological activity in human subjects.