The knowledge about the pharmacokinetics of triamterene (TA) was limited until recently. The metabolic pathway of TA is the formation of p-hydroxytriamterene (OH-TA), which is subsequently conjugated with active sulfate to form p-hydroxytriamterene sulfuric acid ester (OH-TA-ester). The phase-II-metabolite is surprisingly pharmacologically active. TA and its metabolites were measured by a specific and sensitive tlc-method concomitantly. The i.v. kinetics of TA were determined after application of a newly developed lactic acid solution of the drug. Comparing these data with results after oral application of TA the bioavailability of TA was 52% and the extent of absorption 83%. The bioavailability of different dosage forms was correlated with in vitro tests. In liver disease the pharmacokinetics of TA are markedly altered. While in cirrhosis the hydroxylation of TA was decreased, the biliary excretion of this agent was strongly reduced in hepatitis. In renal disease the excretion of TA and OH-TA-ester was reduced according to endogenous creatinine clearance. In older patients the elimination of TA was impaired.

The reason for such differences is still unclear and, thus, the consequences of urbanization must be considered to explain diverse incidence rates. In general, the investigation of causes should be based on the use of a multivariate model that takes additional factors such as specific drug use, socioeconomic aspects, environmental aspects, education, and health care into account. There are large regional differences in the incidence of hip fracture in Germany. These differences were unexpected and do not follow a north-to-south or an east-to-west gradient. But they are of high socioeconomic importance and cannot be explained by geographic location, the age structure of the population and only to a small extent by the regulation of specific medication.

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The kinetics of triamterene and its active phase II metabolite were studied in 32 patients with various degrees of impaired renal function; the creatinine clearances ranged from 135 to 10 ml/min. The area under the plasma concentration-time curves (AUC) for triamterene were not influenced by kidney function, but the AUCs for the effective metabolite OH-TA-ester were significantly elevated in renal failure, indicating accumulation of the metabolite. Urinary recovery of triamterene and its metabolite over a 48 h collection period was significantly reduced in renal failure. This is considered to be due to delayed urinary excretion, corresponding to reduced renal clearance. The renal clearance of the native drug exceeded that of the metabolite, because of their different protein binding, 55% for triamterene and 91% for the metabolite. The latter is eliminated almost exclusively via tubular secretion and extra-renal elimination is less important. Administration of this antikaliuretic is therefore considered hazardous in patients with impaired kidney function.

The pharmacokinetics of the two enantiomers of tranylcypromine were evaluated in six healthy subjects after oral dosage of the racemate (20 mg of the sulphate) and the single enantiomers (10 mg of the sulphate) using an enantiospecific assay. Significant differences in AUC, Cmax, Xz, and CLR of the two enantiomers were observed both on administration of the racemate and of the individual enantiomers. The plasma concentrations and urinary excretion rates of (-)-tranylcypromine exceeded those of (+)-tranylcypromine. AUCs of the (-)-enantiomer [arithmetical means 197 ng ml-1 h after the racemate, 130 ng ml-' h after the enantiomer] were greater than those of the (+)-enantiomer [26 ng ml-' h after the racemate, 28 ng ml-' h after the enantiomer] (P = 0.0001). No in vivo racemisation was detected. The power of the study was insufficient to establish any enantiomer-enantiomer interaction except for a possible interaction at the level of renal clearance (P = 0.013 for both enantiomers).