Influence of Post-Harvest Circulatory Rinse on Tenderness and Objective Color of Cow Striploin Steaks

ObjectivesWhole muscle cuts from cows are often less tender than cuts from young fed beef due to increased collagen cross-linking associated with animal age. The injection of a rinse solution through the carotid artery following exsanguination has been shown to improve tenderness. The objective of this study was to compare the effect of a post-harvest rinse of an isotonic solution through the circulatory system on tenderness of steaks from cows.Materials and MethodsCows (n = 28) were randomly assigned to carcass treatments. The carcass treatments consisted of non-rinsed control (n = 14) and a rinsed (n = 14) treatment, where a chilled isotonic solution (MPSC, Inc., St. Paul, MN) was rinsed through the carotid artery and veins following exsanguination. The isotonic solution consisted of water, glucose, maltose and phosphates. Both control and rinsed treatments were electrically stimulated. At 2 d postmortem, strip loins were removed from one side of each carcass. Strip loins were fabricated into 2.54 cm steaks at 3 d postmortem and objective color measurements (L*, a* and b*) were recorded on a single steak after a 30-min bloom period. Steaks were vacuum packaged and aged at 4°C for 7, 14, and 21 d. Following aging, steaks were frozen (–20°C) for future analysis. Warner-Bratzler Shear Force (WBSF) was used to measure tenderness. Frozen steaks were thawed at 4°C for 24 h before cooking. Internal temperature was monitored on all steaks using a digital thermometer that was placed in the center of each steak. Steaks were cooked on an electric clamshell grill to an internal temperature of 71°C. Peak cook temperature was recorded for each steak. Following cooking, steaks were cooled at 4°C and allowed to equilibrate to room temperature (20°C). Six cores (1.27 cm) were removed from each steak and sheared perpendicular to the muscle fiber orientation. The peak force was recorded for each core and the average calculated for each steak. Data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Shear force data were analyzed as a repeated measure with time and treatment as fixed variables. Color data were analyzed as a completely randomized design using treatment as the fixed variable. Statistical significance was considered at an α of P < 0.05 and trends at 0.05 ≤ P < 0.10.ResultsThere was no interaction (P = 0.6068) between treatment and postmortem aging day. Steaks from the rinsed treatment were more tender (P = 0.0005), than steaks in the control treatment (3.51 ± 0.168 kg vs. 4.41 ± 0.174 kg, respectively). Postmortem aging influenced (P = 0.0310) tenderness. Steaks aged 7 d were less tender (P = 0.0087) than steaks aged for 21 d (4.18 ± 0.155 kg vs. 3.72 ± 0.156 kg, respectively), while 14 d steaks did not differ (P > 0.05) from those aged 7 or 21 d. Objective color was not impacted by rinse treatment (P > 0.05).ConclusionThese data suggest that the application of a post-harvest rinse with an isotonic solution through the circulatory system improves the tenderness of cow steaks but does not influence objective color.

Effects of Low-Stress Weaning on Calf Growth Performance and Carcass Characteristics

ObjectivesThe objective of this study was to compare the influence of two low stress weaning methods with conventional weaning on post-weaning performance and carcass characteristics of beef steers.Materials and MethodsAngus × Simmental crossbred steer calves (n = 90) from a single source were stratified by body weight and dam age into three groups; one treatment was randomly assigned to each group: ABRUPT (calves isolated from dams on the day of weaning), FENCE (calves separated from dams via a barbed wire fence for 7 d prior to completely weaning), and NOSE (nose-flap inserted and calves remained with dams for 7 d prior to completely weaning). At d +7 post-weaning calves were transported to a commercial feedlot where they received standard step-up and finishing rations typical for a Northern Plains feedlot. To understand the influence of each weaning method on haptoglobin (an acute-phase protein), blood samples were collected via coccygeal venipuncture at d –7 (PreTreat), 0 (Weaning), and +7 (PostWean) from a subsample of calves (n = 10 per treatment) and analyzed using a bovine haptoglobin ELISA kit. Body weights (BW) were recorded on study d –34 (PreWean), –7 (PreTreat), 0 (Weaning), 7 (PostWean), 32 (Receiving), 175 (Ultrasound), and 253 (Final) and average daily gains (ADG) were calculated between each time period. On d 175 post-weaning BW were recorded, and ultrasound fat thickness and intramuscular fat were determined and utilized to project marketing dates. Carcass measurements were recorded at the time of harvest and included hot carcass weight, 12th rib backfat, ribeye area, USDA Yield Grade and Quality Grade, and marbling score. Haptoglobin, BW, and ADG data were analyzed as repeated measures using the ante-dependence covariance structure in the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) for effects of weaning treatment, day, and their interaction; birth weight was included as a covariate for ADG and BW. Carcass traits were analyzed for the effect of weaning treatment using the MIXED procedure. Separation of least-squares means was performed using LSD with a Tukey’s adjustment and assuming an α level of 0.05.ResultsWeaning method interacted (P < 0.0001) with time period for ADG and BW. Calf BW increased in all treatments until the PostWean period, wherein BW decreased (P < 0.0001) in ABRUPT and NOSE and was maintained (P > 0.05) in FENCE. From the Receiving to Final time periods BW increased similarly (P > 0.05) for all treatments. Calf ADG was greater (P < 0.01) in calves in the NOSE treatment at Weaning than ABRUPT or FENCE. In the PostWean period, the FENCE calves had ADG that was not different (P > 0.05) than zero but was greater (P < 0.0001) than the negative ADG of ABRUPT and NOSE calves. During the Receiving period ADG was greater (P < 0.05) for ABRUPT compared to NOSE and FENCE. Time influenced (P < 0.001) haptoglobin concentration. No difference in haptoglobin was observed between the PreTreat and Weaning or PostWean periods; however, haptoglobin concentration was greater (P < 0.001) at PostWean compared to Weaning. Weaning method did not influence (P > 0.05) carcass measurements.ConclusionCollectively these data suggest low stress weaning methods do not significantly improve post-weaning growth performance or carcass merit compared to calves weaned using conventional methods.

Influence of Beef Production System Technology on Calpain-1 Autolysis and Troponin-T Degradation

ObjectivesBeef production systems utilize implants and β-agonists to improve beef cattle feed efficiency and promote muscle growth. Warner-Bratzler shear force values can be greater in strip loin steaks from cattle treated with implants or β-agonists. Calpain-1 degrades myofibrillar proteins post-mortem, thus altering calpain-1 activation or autolysis which can influence meat tenderness and proteolysis. The objective of this study was to determine the impact beef production system technologies on calpain-1 autolysis and troponin-T degradation as an indicator of tenderness formation and postmortem proteolysis.Materials and MethodsFrom a larger study, beef striploins (n = 16, n = 4/treatment) from cattle finished utilizing four different production systems were collected for analysis: 1) no antibiotics (NA; receiving no technology); 2) non-hormone treated cattle (NHTC; fed 300 mg monensin and 90 mg tylosin during the finishing phase); 3) implant (IMPL; same technologies as NHTC and administered a series of three implants including a low- potency calf implant [36 mg zeranol], a moderate-potency initial feedyard implant [80 mg trenbolone acetate and 16 mg estradiol], and a high potency finishing implant [200 mg of trenbolone acetate and 20 mg estradiol]; and 4) all previous technologies plus fed a β-agonist (IMBA; same technologies as IMPL and fed 200 mg ractopamine hydrochloride per steer per d). Striploins were vacuum packaged, aged for 7 d, and frozen. Western Blots were conducted for calpain-1 autolysis and troponin-T degradation (30 kDa). Abundance of calpain-1 bands and troponin-T degradation product was normalized by a reference on each gel. Treatments were evaluated in PROC MIXED of SAS 9.2 where least squares means and SEM were computed and separated using least significant differences (PDIFF) when tests for fixed effects were significant at P < 0.05 and trending P ≤ 0.10.ResultsCalpain-1 autolysis differed (P < 0.05) in the IMPL group compared to the NHTC group for both active, 78 kDa band, and the fully autolyzed, 76 kDa band. The IMPL group had a greater percentage (P = 0.0048) of active calpain-1 and a lower percentage (P = 0.0048) of fully autolyzed calpain-1 compared to the NHTC group. Also, a trend was detected when comparing both the active, 78 kDa band, and fully autolyzed, 76 kDa band, in the IMBA and IMPL group where the IMPL group had a greater percentage (P = 0.0727) of active calpain-1 and a lower percentage (P = 0.0727) of fully autolyzed calpain-1. Production system did not influence (P > 0.05) 30 kDa troponin-T product abundance.ConclusionThese data indicate level of technology may play a role in the activation and autolysis of calpain-1 from the 80 kDa inactive form to the 78 kDa active product and finally to the 76 kDa autolyzed product. Calpain-1 autolysis was not measured; however, these data suggest calpain-1 autolysis in the IMPL group may be limited compared with NHTC and IMBA groups. Consequently, calpain-1 may remain in the 78 kDa active form in the implanted cattle, actively degrading myofibrillar proteins. However, production system did not influence troponin-T 30 kDa degradation products. Further analysis of the rate of calpain-1 autolysis and troponin-T degradation at different days of postmortem aging could provide further evidence that different beef production technologies impact calpain-1 autolysis and postmortem proteolysis.

Influence of Postmortem Aging and Storage Conditions on Tenderness of Grain and Grass Finished Bison Striploin Steaks

ObjectivesThe objectives of this study were to: 1) compare the influence of postmortem aging on tenderness of striploin steaks from grain- and grass-finished bison, and 2) compare the influence of freezing on tenderness of striploin steaks from grain- and grass-finished bison.Materials and MethodsBison heifers were randomly assigned to finishing treatments: Grain-finished (n = 30, backgrounded on pasture and finished for 130 d with ad libitum access to grass hay, alfalfa and a corn and dry distiller’s grain concentrate prior to slaughter) or Grass-finished (n = 30, remained on pasture until slaughter). Heifers were slaughtered at approximately 28 mo of age, and striploins were removed from both sides of the carcass posterior to the 12th rib separation and fabricated into 2.54-cm steaks. One steak was removed from each striploin (n = 60), vacuum packaged and stored fresh for 14 d at 4°C. Four additional steaks were fabricated from each striploin, aged for 4,7,14, or 21 d, vacuum packaged, and frozen for approximately 3 mo. Warner-Bratzler Shear Force (WBSF) was utilized to determine objective tenderness. Frozen steaks were thawed at 4°C for 24 h before cooking. All steaks were weighed prior to cooking to an internal temperature of 71°C. Internal temperature was monitored using a digital thermometer placed near the geometric center of each steak. After cooking, all steaks were reweighed to determine cook loss and cooled to room temperature (20°C). Five to six 1.27-cm cores were removed from each steak and sheared once perpendicular to the muscle fiber orientation and peak force was recorded. A texture analyzer with a Warner-Bratzler attachment was used to assess instrumental tenderness. An average shear force value was then calculated for each steak. For Objective 1, cook loss and shear force data were analyzed as repeated measures using the ante-dependence covariance structure in the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) for effects of finishing treatment, aging, and their interaction; peak temperature was included as a covariate. For Objective 2, shear force data were analyzed for the effects of finishing treatment, storage treatment and their interaction using the GLM procedure of SAS. For both objectives, the interaction was not significant and omitted from the final model. Separation of least-squares main effect means was performed using LSD with a Tukey’s adjustment and assuming a level of 0.05.ResultsSteaks from grain finished bison heifers had tendency to be more tender (P = 0.0552) and had less cook loss (P < 0.0001) than steaks from grass finished heifers. Tenderness of all steaks improved (P < 0.0001) with postmortem aging. Aging time also influenced cook loss (P = 0.0199). Cook loss was greater (P = 0.0133) at Day 4 than Day 7 and tended to be greater (P = 0.0561) at Day 4 than Day 21. Frozen storage improved tenderness (P < 0.0001) and increased cook loss (P < 0.0001) of bison steaks compared to fresh storage.ConclusionCollectively this data indicates postmortem aging, storage conditions, and finishing systems influence meat tenderness of bison striploin steaks. Grain-finishing resulted in reduced cook loss and tended to improved tenderness of bison steaks compared to grass-finishing. Additionally, holding bison steaks in frozen storage improved tenderness, but also increased cook loss.

Influence of maternal protein restriction in primiparous heifers during mid- and/or late-gestation on meat quality and fatty acid profile of progeny

The objective of this study was to evaluate the influence of metabolizable protein (MP) restriction in mid- and/or late-gestation on meat quality characteristics of progeny. Heifers were assigned to 2 levels of dietary protein (control [CON], 102% of MP requirements; or restricted [RES], 80% of MP requirements) at 2 stages of gestation (mid-gestation [MID] and late-gestation [LATE]) in a Balaam's Design crossover treatment structure resulting in 4 treatment combinations (CON-CON, CON-RES, RES-CON, RES-RES). A carryover effect of MID MP treatment on LATE CON indicated CON-CON steaks were more tender (P < .001) than RES CON. Mid-gestation restriction resulted in progeny with increased (P < .05) carcass water, soft tissue moisture, and decreased soft tissue fat percentage compared with progeny from dams receiving MID CON. Reduced maternal MP also differentially influenced the fatty acid profiles of progeny. Results suggest it is possible for progeny to overcome a moderate gestational MP restriction with minimal impacts on carcass composition or meat characteristics.

Effect of nursing-calf implant timing on growth performance and carcass characteristics

The objective of this study was to compare pre- and postweaning growth performance, carcass characteristics, and meat quality attributes of calves that did not receive an implant or were implanted early or late in the nursing period. Crossbred steer calves ( = 135) were stratified by birth date and birth weight and randomly assigned to the following implant treatments: control (CON; no preweaning implant), 58 d (EARLY; 36 mg zeranol, administered at an average of 58 ± 13 d of age), and 121 d (LATE; 36 mg zeranol, administered at an average 121 ± 13 d of age). After weaning, steers were blocked by initial feed yard BW to 15 pens (5 pens/treatment and 9 steers/pen). All steers were implanted on d 21 after arrival at the feed yard and again on d 108 of finishing. Steer BW and ultrasound assessment of rib eye area (uREA), rib fat thickness (uRFT), and percent intramuscular fat (uIMF) were collected when implants were administered, at weaning, and on harvest day. Carcass measurements included HCW, rib eye area (REA), 12th-rib fat thickness (FT), and marbling score. Objective color (L*, a*, and b*) was recorded, and a 3.8-cm strip loin section was removed from both sides of each carcass and portioned into 2.54-cm steaks that were aged for 3 or 14 d for analysis of cook loss and Warner-Bratzler shear force (WBSF). The remaining portion of each sample was used for analysis of moisture and crude fat. Steer BW, ADG, and G:F did not differ among treatments ( > 0.05). Steers implanted in the EARLY treatment had a greater ( < 0.05) cumulative DMI than CON but were not different from steers implanted in the LATE treatment. Ultrasound REA and uRFT (averaged across all collection days) did not differ ( > 0.05); however, steers on the CON treatment had a greater ( ≤ 0.05) percent uIMF than EARLY implanted steers, whereas steers receiving the LATE implant were intermediate and not different from the other treatments. Hot carcass weight, REA, FT, USDA yield grade, marbling score, and objective color did not differ ( > 0.05) among treatments. The proportion of steers in each USDA yield and quality grade was similar ( > 0.05) among treatments, and no differences were detected for total carcass value or price per 45.4 kg (hundredweight; > 0.05). Treatment did not influence ( > 0.05) percent cook loss, crude fat, moisture, or WBSF. In conclusion, administering a nursing implant, regardless of timing, did not influence live performance, carcass characteristics, or meat quality of steers fed in this study.

The influence of maternal energy status during midgestation on beef offspring carcass characteristics and meat quality

Research has suggested that maternal undernutrition may cause the development of a thrifty phenotype in the offspring, potentially resulting in greater adiposity and reduced muscle mass. These alterations in adipose and muscle development could have lasting impacts on offspring growth, carcass characteristics, and meat quality. However, limited research exists evaluating the impact of maternal energy status on these economically important traits of the offspring. Therefore, the objective of this study was to determine the influence of maternal energy status during midgestation on offspring carcass characteristics and meat quality. To alter maternal energy status, cows either grazed dormant, winter range (positive energy status [PES]) or were fed in a drylot at 80% of the energy requirements for BW maintenance (negative energy status [NES]) during a mean period of 102 ± 10.9 to 193 ± 10.9 d of gestation. Changes in BCS, BW, LM area (LMA), and 12th rib backfat were measured throughout midgestation. At the end of midgestation, cows in the NES group had a reduction (P ≤ 0.05) in BCS, BW, LMA, and 12th rib backfat when compared with PES dams. Cows and calves were managed similarly after midgestation through weaning and calves were managed and fed a common diet through the receiving, backgrounding, and finishing phases in the feedlot. Calves were harvested after 208 d in the feedlot, carcass characteristics were recorded, and strip loins were recovered for analysis of objective color and Warner-Bratzler shear force (WBSF). Maternal energy status had no influence on offspring HCW, dressing percent, LMA, percent KPH, marbling score, percent intramuscular fat, objective color, or WBSF (P > 0.10). Progeny of NES cows tended to have improvements in 12th rib backfat and USDA yield grade (P < 0.10). Greater ratio of marbling score to 12th rib fat thickness and ratio of percent intramuscular fat to 12th rib fat thickness (P < 0.05) were discovered in progeny from cows experiencing a NES during midgestation. These results suggest that maternal energy status during midgestation may impact fat deposition in intramuscular and subcutaneous fat depots without impacting muscle mass.

Impact of supplemental protein source offered to primiparous heifers during gestation on II. Progeny performance and carcass characteristics

A 3-yr study using primiparous crossbred beef heifers (n = 114) was conducted to determine the effects of protein supplement during late gestation on progeny performance and carcass characteristics. Pregnant heifers were stratified by heifer development system, initial BW, and AI service sire and placed in an individual feeding system. Heifers were offered meadow hay (8 to 11% CP) from early November to mid-February and provided no supplement (CON; n = 37), 0.83 kg/d (DM basis) of a dried distillers grains with solubles–based supplement (HI; n = 39), or 0.83 kg/d (DM basis) of a dried corn gluten feed–based supplement (LO; n = 38). Supplements were designed to be isonitrogenous (28% CP) and isocaloric but to differ in RUP with HI (59% RUP) having greater levels of RUP than LO (34% RUP). After the individual feeding period, heifers were placed in a drylot for calving. All heifers were bred using a fixed-timed AI protocol and pairs were moved to a commercial ranch in the Nebraska Sandhills for summer grazing. Calf weaning BW did not differ (P = 0.14) based on maternal diet. However, feedlot entry BW was greater (P = 0.03) for HI compared with CON calves. Average daily gain during the initial feedlot phase tended (P = 0.10) to be greatest for calves born to CON dams and lowest for calves born to LO dams. However, overall ADG was similar (P = 0.50) for the entire feedlot period. Residual feed intake during the reimplant and total feeding period was improved in calves born to supplemented dams in yr 2 and 3 compared with calves born to CON dams. There was no difference in final BW among treatments (P = 0.71). Hot carcass weight was similar (P = 0.72) among treatments; however, steers had greater (P < 0.01) HCW than heifers. Furthermore, percent empty body fat and 12th rib fat thickness were lowest (P = 0.05 and P = 0.04) for calves born to LO dams. Tenderness measured by Warner-Bratzler shear force was increased (P = 0.03) in longissimus samples from calves from CON dams compared to calves from LO dams. Similarly, crude fat levels tended to be greater (P = 0.07) for calves from CON dams compared with calves from LO dams. Based on these data, providing RUP supplements, similar to those used in this study, to primiparous heifers in late gestation consuming ad libitum grass hay resulted in increased initial feedlot BW for HI compared to CON calves, improved feed efficiency, and altered carcass characteristics in calves born to supplemented compared with CON dams.

The influence of growth stage on carcass composition and factors associated with marbling development in beef cattle

Subcutaneous fat and marbling both increase in beef cattle during the feeding phase but are antagonistic in regard to their contribution to beef carcass value. The objective of this study was to determine whether cellular factors associated with marbling development change with growth stage throughout the feeding period and whether they are correlated to marbling relative to carcass composition. Twenty-four steers of known origin with the cytosine and thymine (CT) leptin genotype were allotted to 3 harvest groups. Six steers per harvest group were harvested at the following predetermined points: 35 d on feed (early feeding period, EF), average live weight of 464 kg (middle feeding period, MF), and 1.17-cm 12th-rib subcutaneous fat thickness (late feeding period, LF). Longissmus muscle samples were collected within 30 min postmortem and snap frozen for real-time PCR and Western blot analysis of lipoprotein lipase, adenosine monophosphate-activated protein kinase α (AMPKα), stearoyl-coenzyme A desaturase (SCD), PPARγ, C/EBP-β, and myostatin. Carcass data were recorded, and LM samples were collected and aged 2, 7, 14, and 21 d postmortem for Warner-Bratzler shear force determination. Carcass composition was estimated by dissection of the 9-10-11 rib section and subsequent proximate analysis of the soft tissue. Intramuscular fat content of the LM increased linearly throughout the feeding period, giving additional support to marbling as an early developing tissue. Expression of AMPKα was found to be downregulated, whereas SCD expression was upregulated in the LF group relative to the first 2 harvest groups. Additionally, SCD and PPARγ were downregulated in the EF group relative to the latter 2 harvest groups. These changes in gene expression resulted in a linear increase in only PPARγ protein abundance, whereas myostatin tended to increase quadratically. A correlation was found between intramuscular fat and PPARγ abundance. This gives further evidence of the importance of adipocyte hyperplasia in increasing marbling. Targeting and increasing PPARγ expression may serve as a mechanism to increase marbling deposition. Last, LF steaks were more tender than MF or EF steaks, indicating improved tenderness with increased days on feed.

Oral flecainide pharmacokinetics in patients with impaired renal function

The pharmacokinetics of flecainide acetate were studied in 20 patients with varying degrees of renal impairment following a single oral dose. The patients were divided into two groups, on the basis of renal creatinine clearance (CLCR), for statistical and kinetic analysis. Patients with a CLCR between 4 and 41 mL/min/m2 were designated group 1 and those below 4 mL/min/m2 or unmeasurable because of lack of urine output were designated group 2. In both groups peak plasma flecainide concentrations, time to peak concentrations, and apparent volume of distribution (Vd) were similar to those reported in healthy subjects with normal renal function. The mean flecainide plasma elimination half-lives from both groups 1 and 2 were longer than those previously reported by several investigators in normal subjects. Nine patients in group 1 and seven patients in group 2 had half-lives within the range reported in healthy subjects. Therefore, CLCR alone is not a good predictor of plasma elimination half-life following a single oral dose of flecainide. Although renal clearance of flecainide is significantly reduced in end-stage renal disease (ESRD), total plasma clearance of flecainide (CLflec) was not reduced to the same degree, although there was a significant, modest correlation with CLCR. Less than 1% of the administered oral dose of flecainide was removed during hemodialysis. The relationship between dosage and plasma elimination half-life in patients with ESRD needs further study to evaluate possible dose-dependent kinetics.

Neurologic outcome and blood glucose levels during out-of-hospital cardiopulmonary resuscitation

We examined the interrelations of outcome, time elapsed during cardiopulmonary resuscitation (CPR), and blood glucose levels drawn from 83 patients with out-of-hospital cardiac arrest. Levels rose significantly during CPR. Although slope and intercept of regression lines differed for those dying in the field and those admitted, regression lines were similar for those who awoke and never awoke after admission. These results suggest that the previously reported association between poor neurologic recovery and high blood glucose level on admission after cardiac arrest is best explained by prolonged CPR, leading to both higher rise of blood glucose and worse neurologic outcome.

Ketoconazole kinetics in chronic peritoneal dialysis

The kinetics of oral ketoconazole in serum and peritoneal fluid were studied in six patients with renal failure receiving peritoneal dialysis. A dose of 400 mg ketoconazole resulted in a maximum blood concentration of 2.3 +/- 1.7 microgram/ml (mean +/- SD), which occurred 3.3 +/- 1.6 hours after dosing. The serum t1/2 was 2.4 +/- 0.8 hours. Peritoneal clearance values were less than 1 ml/min, and peritoneal penetration reached 3.4% of the serum concentration by 5 hours. Protein binding studies were also performed. Compared with healthy controls, patients receiving peritoneal dialysis have significantly less ketoconazole serum protein binding. Fifty to eighty percent of the drug is protein bound in the peritoneal fluid, and the unbound concentration is in the same range as that in the serum of healthy individuals with "therapeutic" total ketoconazole levels of 1 to 2 micrograms/ml.

Synergism at clinically attainable concentrations of aminoglycoside and beta-lactam antibiotics

We evaluated the in vitro synergistic activity at clinically attainable concentrations of combinations of aminoglycoside and beta-lactam antibiotics against 30 gentamicin-resistant clinical isolates of gram-negative bacilli. All 56 pairs of 4 aminoglycosides and 14 beta-lactams were evaluated. Combinations with amikacin demonstrated inhibitory synergistic activity in 29% of the assays, as compared with 22% for netilmicin (P = 0.018), 17% for gentamicin (P less than 0.001), and 13% for tobramycin (P less than 0.001). Among the beta-lactams, combinations with cefoperazone, ceftriaxone, or cefpiramide (SM-1652) demonstrated inhibitory synergistic activity most often (39, 38, and 35% of the assays, respectively) and with ceforanide, cefsulodin, and imipenem least often (less than or equal to 8% each). The most active combination was amikacin and ceftriaxone, with which 67% of the assays demonstrated inhibitory synergism. Isolates with high-level resistance to either antibiotic in a combination were unlikely to be inhibited synergistically by the combination. Further, combinations generally demonstrated little synergistic activity against isolates highly susceptible to beta-lactams.

Cefonicid kinetics in subjects with normal and impaired renal function

Cefonicid is a cephalosporin with a longer t1/2 than currently available cephalosporins. Cefonicid kinetics after an intravenous dose of 7.5 mg/kg were followed in four groups of subjects: group 1, four subjects with normal creatinine clearance (Clcr greater than 80 ml/min); group II, seven subjects with mild renal insufficiency (Clcr 50 to 80 ml/min); group III, five subjects with moderate to severe renal impairment (Clcr 8 to 49 ml/min); and group IV, five subjects with end-stage renal disease who were receiving maintenance hemodialysis (Clcr less than 8 ml/ml). Cefonicid volume of distribution ranged from 6.9% to 17.6% body weight but was not related to Clcr. Elimination t1/2 was 4.6 +/- 0.7 hr in group 1,6.0 +/- 2.7 hr in group II, 25.6 +/- 14.0 hr in group III, and 65.3 +/- 43.6 hr in group IV. There was a strong correlation between plasma cefonicid clearance and Clcr. Nonrenal clearance did not change with decreasing Clcr. Hemodialysis clearance calculated from plasma concentrations and recovery in dialysate was 2.5 +/- 0.9 ml/min. These kinetic parameters were used to formulate dosage regimens for patients with renal impairment.

Pharmacokinetics of ceftizoxime in patients undergoing continuous ambulatory peritoneal dialysis

The pharmacokinetics of ceftizoxime were studied in 12 patients on continuous ambulatory peritoneal dialysis. After a 3-g intravenous dose, the steady-state volume of distribution was 0.23 +/- 0.05 liter kg-1, with an elimination half-life of 9.7 +/- 5.1 h. The peritoneal clearance of ceftizoxime (2.8 +/- 0.7 ml min-1) contributed modestly to the overall serum clearance of the drug (17.1 +/- 7.4 ml min-1) and was greater than the renal clearance (0.8 +/- 0.8 ml min-1). The peritoneal concentration rose to 91 +/- 29 micrograms ml-1 at 6 h, which was 0.61 +/- 0.17 of the serum concentration. A 3-g intravenous dose of ceftizoxime given every 48 h would result in adequate activity against most susceptible organisms, but more frequent dosing may be necessary for less susceptible organisms.

Gentamicin and tobramycin Kinetics

Eighty-two hospitalized adult patients were randomized to treatment with gentamicin or tobramycin. Serum levels were compared to computer-derived mathematically predicted levels to evaluate predictability of gentamicin and tobramycin serum levels. When comparable dosages were used mean peak gentamicin levels (4.87 micrograms/ml) did not differ from those after tobramycin (4.31 micrograms/ml). Seventy-three percent of patients had peak levels after gentamicin greater than 4.0 micrograms/ml compared to 46% after tobramycin. Factors purported to influence predictability of aminoglycoside serum levels were examined. In 46 of 74 patients whose actual body weight was 10 to 35 kg less than estimated ideal body weight levels after both drugs were lower than predicted. Serum levels were also lower than predicted in 7 of 11 patients with ascites, 6 of 7 patients receiving carbenicillin therapy, and 17 of 29 patients who had pneumonia. Neither hematocrit nor temperature appeared to influence predictability of serum levels. A comparison of methods used to obtain computer-derived predicted levels showed that ideal body weight provided the most accurate prediction. Differences between predicted and measured levels were established when calculations were based on actual body weight (P = 0.009) or on surface area (P = 0.003 for peak and 0.023 for trough levels).

Effect of hemodialysis on the pharmacokinetics of theophylline in chronic renal failure

We studied theophylline elimination in 8 patients with chronic renal failure to determine the effect of hemodialysis on the pharmacokinetics of theophylline. Each subject was studied twice, once on a nondialysis day and again during dialysis. Total body theophylline clearance on the nondialysis day was similar to that reported for patients with normal renal function (57.4 +/- 27.2 ml/kg/h). Hemodialysis accelerated theophylline elimination and shortened serum theophylline half-life in all patients (nondialysis t 1/2 = 7.3 h +/- 2.3 vs. dialysis t 1/2 = 2.7 +/- 0.9 h, p less than 0.01). Dialysis clearance averaged 59.7 +/- 16.4 ml/kg/h with a fraction of drug removed of 0.4 liters in 4 h. Guidelines for theophylline management during hemodialysis are suggested.

Sotalol kinetics in renal insufficiency

Kinetics of sotalol, a beta adrenoceptor blocker, was studied in 20 patients with varying renal function. In subjects with creatinine clearance (Clcr) greater than or equal to 39 ml/min/m2, sotalol plasma clearance (x +/- SD) was 71 +/- 31 ml/min/m2, elimination half-life (t 1/2) was 8.1 +/- 3.4 hr, and renal clearance was 46 +/- 26 ml/min/m2. In patients with moderate renal impairment (Clcr = 8 to 38 ml/min/m2) elimination t 1/2 rose to 24.2 +/- 7.5 hr, and plasma clearance fell to 24 +/- 7 ml/min/m2. In patients receiving dialysis, elimination t 1/2 rose to 33.9 +/- 27.1 hr. Elimination t 1/2 during hemodialysis was 5.8 +/- 2.1 hr and was associated with a 56.7 +/- 21% reduction in plasma levels.

Randomized prospective evaluation of cimetidine and antacid control of gastric pH in the critically ill

One hundred forty-four critically ill patients admitted to an intensive care setting were randomly assigned to cimetidine or antacid treatament groups. Gastric pH was monitored hourly. One hundred twenty-three (85%) patients demonstrated a fall in pH to less than 4 and were considered to require prophylaxis. Prophylaxis was considered adequate if the measured pH could then be maintained at greater than or equal to 4. Fifty-eight patients received antacids alone, the average requirement being 41 cc/hour. Sixty-five patients received cimetidine. Seventeen (26%) of the cimetidine prophylaxis patients failed to raise their pH and were than placed on hourly administration of antacid with successful elevations of pH to greater than or equal to 4 in all cases on an average supplementary dose of 53 cc/hour. Risk factors, including sepsis, hypotension, head injury, respiratory failure, degree of trauma, and age, were not statistically different in the two treated groups. Using these same criteria, responders to cimetidine could not be differentiated from nonresponders. All patients were protected from significant stress bleeding while on this study. Significant complications of either treatment were minimal. Antacids offered consistent protection against gastric acidity and were 100% effective. A routine schedule of 300 mg every six hours of cimetidine was effective in only 47% of patients, and the maximum dose of cimetidine was effective in only 74% of patients. Hourly measurement of intragastric pH is required for monitoring the response to prophylaxis of stress bleeding in severely ill patients.

Pharmacological and in vitro evaluation of cyclacillin: assessment as potential single-dose therapy for treatment of Neisseria gonorrhoeae infection

The pharmacokinetic properties of cyclacillin administered as a 3.0-g oral dose, with and without progenecid, have been studied and correlated with in vitro activity of the drug against 109 isolates of Neisseria gonorrhoeae. By 8 h after dosage, levels of cyclacillin in serum declined below the minimal inhibitory concentration and the inferior antibacterial activity of cyclacillin (compared with that of amipicillin) suggest that cyclacillin is not a promising alternative to ampicillin for single-dose treatment of gonorrhea.

Cefadroxil kinetics in patients with renal insufficiency

Kinetic parameters and bioavailability of cefadroxil were studied in 20 subjects with differing renal function as measured by endogenous creatinine clearance (CCr). Two subjects were on hemodialysis. After an overnight fast, each subject ingested two 500-mg capsules of cefadroxil. The peak serum concentration was variable (12 to 57 mg/L) and correlated inversely with the CCr. All but one patient had maximum absorption within 4 hr of ingestion and in most patients the peak was reached within the 2-hr sample. Urinary recovery within 48 hr was 45% to 106% when CCr greater than 8 ml/min. Even in patients with the most severe renal failure (CCr less than 10 ml/min), urine concentrations of cefadroxil were adequate to treat susceptible bacteria. The rate of oral absorption ka, was not affected by the state of renal function and was 0.76 +/- 0.50 hr-1. The apparent distribution volume (V d ext) was 0.28 +/- 0.09 L/kg. The plasma elimination rate was dependent on CCr wih a small fraction of drug being removed by nonrenal routes. Except in advanced renal failure, tubular secretion was present since renal clearance of cefadroxil exceeded CCr. The data suggest that little drug accumulation will occur with the usual 8- to 12-hr dosing schedule except when the CCr is less than 25 ml/min.

Effects of probenecid on furosemide kinetics and natriuresis in man

Furosemide kinetics were studied in 4 normal subjects after single intravenous injections (1 mg/kg). One experiment was done after pretreatment with probenecid. The apparent volume of furosemide distribution was unchanged after probenecid (10.9 L). The mean plasma clearance fell from 155 to 85 ml/min and the mean plasma t1/2 rose from 36 to 61 min. Renal clearance of furosemide fell below 50% of control after probenecid, but the kidney remained the main route of its excretion (75% of the dose appeared in the urine). In another experiment in 4 subjects an infusion of furosemide was sustained following a loading dose to maintain a constant plasma level. After a control period, probenecid was given orally. This resulted in a decrease in renal excretion of furosemide with a simultaneous rise in its plasma concentration. Despite the rising plasma furosemide concentration, however, there was a diminution in both urine flow and the excreted fraction of filtered sodium, which suggested some reduction of diuretic action. In doses commonly used, probenecid reduces renal elimination of furosemide in man with only a mild impairment of its diuretic activity. This suggests that furosemide is eliminated predominantly by way of proximal tubular secretion and that tubular rather than plasma concentration is the main determinant of its diuretic effect.

Pharmacokinetics of amikacin in patients with normal or impaired renal function: radioenzymatic acetylation assay

The acetylating radioenzymatic assay was used for determination of levels of amikacin in serum and urine. Because of an inhibitor present in various amounts in urine, assay of amikacin in urine by this method requires added internal standards and thus is less precise than the assay in serum. Determination of the rate of plasma clearance, half-life, and volume of distribution of amikacin in 10 patients with normal renal function, four patients undergoing dialysis, and five patients with end-stage renal diseases have shown a relation of half-life (t1/2 in hr) to rate of clearance of serum creatinine (Cer) of t1/2 = 3 X Cer, the same relation as found for kanamycin and gentamicin. The apparent steady-state volume of distribution of amikacin in patients with diminished renal function is slightly, but not significantly, larger than that in normal patients; the values were 0.28 +/- 0.10 and 0.21 +/- 0.10, respectively. In normal patients, 87% of the drug is excreted by the kidney.

Assay of flucytosine and furosemide by high-pressure liquid chromatography

A high-pressure liquid chromatographic method for the analysis of flucytosine and furosemide concentrations in biological fluid is described. The separations were carried out on a pellicular cation-exchange resin eluted with an ammonium phosphate buffer. Detection of elution peaks was by UV absorption at 280 nm and fluorescence monitoring. Advantages of the method are specificity, minimal preanalysis sample workup, and small sample size.

Furosemide Concentrations in Serum and Urine, and Its Binding by Serum Proteins as Measured Fluorometrically

We describe a modification of the fluorometric method of Häussler and Hajdú [Arzneim. Forsch. 14, 704 and 709 (1964)] for assay of furosemide in either serum or urine. A 1-ml sample, acidified to pH 2, is extracted with 5 ml of diethyl ether; 4 ml of the ether is back-extracted into 1 ml of phosphate buffer (pH 7.0, 0.1 mol/liter), and finally acidified with 1 ml of dilute HCl (0.6 mol/liter). A procedure for estimating blanks in urine was derived to correct for dilution caused by diuresis. Internal standards are used, and the "effective" extraction ratio is used to correct for the effects of quenching and extraction differences. In equilibrium, 93% of the drug is bound to serum proteins; 65% is tightly bound. Erythrocytes contain less than 5% of the drug. Quantum yield of fluorescence at pH 1 is 0.0496 for furosemide and is 0.0163 for 4-chloro-5-sulfamoylanthranilic acid. Furosemide fluorescence diminishes with increasing pH, while that of 4-chloro-5-sulfamoylanthranilic acid (a degradation product) increases.