Key messageThe specific leaf area of European larch depends on branch height and canopy depth, indicating that both, the effect of hydraulic limitations and low water potentials in greater branch heights, and light availability affect specific leaf area.AbstractSpecific leaf area (SLA) is defined as the ratio between projected leaf area and needle dry mass. It often serves as parameter in ecosystem modelling as well as indicator for potential growth rate. We explore the SLA of European larch (Larix decidua) and the most important factors which have an influence on it. Data were collected from eight stands in Styria, Austria. The stands varied in age, elevation and species mixture. Four stands were pure larch stands with only minor proportions of Norway spruce (Picea abies), whereas the other four were mixed stands of larch and spruce. In each stand 15 representative sample trees were felled. The crown of each sample tree was divided into three sections of equal length and in each section a random sample of needles was taken for determining projected leaf area and dry mass of 50 needles. The mean SLA of larch was established to be 117 cm2 g−1 with a standard deviation of ±27.9 cm2 g−1. SLA varies within the crown, but neither between different mixtures nor years of observation nor social position of the trees. A mixed-effects model, with the plots as random effect, revealed that SLA of larch decreased with increasing branch height (p = 0.0012) and increased with increasing canopy depth (p = 0.029). We conclude that both the hydraulic limitations due to low water potentials in greater branch heights and light availability affect specific leaf area.

To study the absorption and disposition of clavulanic acid, ten healthy men received one intravenous and one oral dose of 125 mg clavulanic acid in combination with amoxycillin. Serum and urine concentrations were measured with high-performance liquid chromatography. The mean terminal half-lives in serum were 0.97 and 0.94 h, respectively. Total serum clearance was 248 +/- 55 ml/min X 1.73 m2. Renal clearance was 108 +/- 20 and 115 +/- 18 ml/min X 1.73 m2 after intravenous and peroral administration. Urinary recovery over 12 h was 49.4 +/- 8.7% of the intravenous and 35.7 +/- 13.0% of the oral dose. The bioavailability of the oral dose averaged 60.0 +/- 23.1% but varied considerably (range 31.4-98.8%), indicating very variable absorption from the gastrointestinal tract.

Sulphadiazine (SDZ) and trimethoprim (TMP) combined into co-trimazine has a half-life of 10 h in the adult and therefore the use of 1 dose/day has been introduced in the treatment of patients with urinary tract infections (UTI). To investigate the pharmacokinetics of cotrimazine given once daily in infants and children, 14 patients aged 3-49 months were given 0.3-0.4 ml/kg of suspension containing 41 mg SDZ and 9 mg TMP/ml. In all patients the peak plasma levels of SDZ at steady state were greater than 15 mg/l and after 12 h mostly greater than 10 (range 7-22) mg/l. The corresponding levels of TMP were 0.5 and 0.1 (range 0.11-0.48) mg/l. The concentrations in urine at 24 h were in the children about 40 mg/l of SDZ and 10 mg/l of TMP and in the infants 35 and 2 mg/l respectively. Therefore, in the treatment of infants and children with UTI, 1 dose of co-trimazine/day should give adequate plasma and urine levels.

Co-trimazine is a new drug combination especially designed for the treatment of urinary tract infections. It consists of trimethoprim (90 mg) and sulphadiazine (410 mg). When combined in vitro, the components show high activity and a high frequency of synergy against urinary tract pathogens. After oral absorption sulphadiazine has a serum half-life similar to that of trimethoprim and is excreted in active form into the urine to a much higher degree than sulphamethoxazole. The ratio of the concentrations of trimethoprim and sulphadiazine in the urine following co-trimazine is favourable for a strong synergistic action between the compounds. In cross-over studies in volunteers receiving repeated daily doses of co-trimazine, either 500 mg twice daily or 1000 mg once daily, it was found that antibacterial activity in the urine was at least as high as that provided by co-trimoxazole (2 x 960 mg) and considerably higher and more uniform than that given by nitrofurantion (3 x 50 mg).

Co-trimazine (sulphadiazine, 410 mg + trimethoprim, 90 mg) is a new drug combination developed especially for use in the treatment of urinary tract infections. In cross-over experiments in volunteers receiving daily doses of co-trimazine (2 X 500 mg and 1 X 1000 mg), co-trimoxazole (2X960 mg), or nitrofurantoin (3X50 mg), the degree of antibacterial activity of co-trimazine in the urine was at least as high as that of co-trimoxazole and much higher and more consistent than that of nitrofurantoin. In further cross-over experiments in volunteers receiving co-trimazine 2X1000 mg or co-trimoxazole 2X960 mg for four days no or only slight activity was found in the urine against a sulphonamide-resistant Group D streptococcus, but distinct synergistic activity between the components was found against four Escherichia coli strains sensitive to trimethoprim and sensitive or resistant to sulphonamides. Against three of the latter strains the degree of activity in the urine was higher after co-trimazine than after cotrimoxazole. The synergistic action of trimethoprim and sulphonamide in the urine appeared greater with the former than with the latter combination.