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Previous work has shown that induction of a high-affinity NADPH-dependent nitrosodimethylamine demethylase (NDMAd) in liver microsomes occurs in rats due to fasting, ethanol consumption, and streptozotocin-induced diabetes. Several lines of observations suggest that this is due to the induction of specific cytochrome P-450 isozymes. Induction of P-450 species by ethanol has also been observed by other investigators. Since each of the above altered metabolic states has in common elevated levels of ketone bodies, the possible role of acetone, a known inducer of NDMAd, in the induction of the demethylase activity was investigated. Levels of endogenous acetone in fasted rats correlated (r = 0.72) with a three- to fourfold increase in NDMAd activity. However, a dose-response experiment showed endogenous levels of acetone to be capable of causing at most 40% of the induction in fasted rats. This suggests that other ketone bodies or factors may have contributed to the induction. The induction of NDMAd by ethanol was enhanced by alcohol dehydrogenase inhibitors pyrazole and acetaldehyde oxime, suggesting that ethanol, rather than its metabolites, was responsible for the induction.

Cephalothin kinetics was studied in 5 patients the day before (PREOP), during (SURG), and the day after (POSTOP) cardiopulmonary bypass surgery. The PREOP (114 ml/min) and SURG (94 ml/min) renal clearances were of the same order but both were less than POSTOP renal clearance (248 ml/min). Cephalothin total body clearance during operation was lower (p less than 0.01) than PREOP or POSTOP clearance, with decreased metabolic clearance the primary cause. There was reduction in cephalothin elimination throughout the surgical procedure, not only in the period of extracorporeal circulation, indicating that general anesthesia had a significant influence on drug disposition. The metabolite deacetylcephalothin was rapidly formed on all 3 days and its kinetic behavior paralleled that of the parent drug.

Substantial error occurs when individual saliva theophylline concentrations are used to predict serum theophylline concentrations. However, the use of saliva theophylline concentrations to determine product bioavailability has never been evaluated. Subjects in this study were 18 stable patients (20-51 yr) with a history of chronic obstructive pulmonary disease. Three preparations--a capsule (Elixophyllin 400 mg), elixir (Elixophyllin 373 mg), and tablet (Theolair 375 mg)--were administered in a randomized crossover design. Serum and saliva samples were obtained pre-dose and 0.25, 0.5, 1, 2, 4, 6, and 8 hours after theophylline administration. The saliva AUC0-infinity and serum AUC0-infinity were highly associated for the elixir (r = 0.84) tablet (r = 0.89), and capsule (r = 0.89). The bioavailability of the tablet and capsule calculated from elixir saliva and elixir serum AUC0-infinity were not significantly different (p = 0.2). The bioavailability of the tablet calculated from saliva and serum was 93% and 102%, respectively. The bioavailability of the capsule calculated from saliva and serum was 113% and 102% respectively. Our data suggests that theophylline bioavailability can be reliably estimated from saliva theophylline concentrations. However, study designs that include larger sample sizes and more frequent sampling may be necessary when determining bioavailability from saliva.

The effects of riboflavin deficiency on the metabolism of N-nitrosodimethylamine [(DMN) CAS: 62-75-9] and other nitrosamines were examined in rats. After weanling rats were put on a riboflavin-deficient diet, the development of the deficiency was monitored by the growth rate and the erythrocyte glutathione reductase activation coefficient. In the riboflavin-deficient rats, the liver microsomal NADPH-cytochrome c reductase activity was lower but the cytochrome P450 content was higher than that of the control. The metabolism of DMN was dependent on the severity of the deficiency. During mild deficiency, which was observed mainly with Sprague-Dawley rats, the microsomal DMN demethylase (DMNd) activity was elevated 30-80%, but the metabolism of N-nitrosomethylbenzylamine (CAS: 937-40-6) and three other nitrosamines was slightly decreased. Dietary restriction in the pair-fed group also caused an elevation of DMNd activity above that of the ad libitum control group due to a partial fasting effect. During severe deficiency, which was observed mainly with Wistar rats, however, the metabolism of DMN, as well as the oxidation of benzo[a]pyrene, was decreased. Preincubation with flavin adenine dinucleotide and flavin mononucleotide enhanced the DMNd activity of the microsomes from riboflavin-deficient rats but not that from control rats. The results suggest that, depending on the alterations of the monooxygenase enzyme system during the development of the deficiency, riboflavin deficiencies may have different effects on the metabolism of DMN and some other carcinogens.

Primidone (PRM) kinetics was examined in two groups of adult seizure patients: (1) 10 newly diagnosed in whom only PRM was used, the monotherapy (MT) group, and (2) nine in whom PRM was added to other antiepileptics, the combination therapy (CT) group. Time-concentration data were obtained after an initial dose of 250 mg and during subsequent steady-state periods. PRM elimination was slower (p less than 0.05) after the initial dose in MT patients (half-life (t 1/2) = 15.2 hr, apparent clearance = 35 ml/hr/kg) than in CT patients (t 1/2 = 8.3 hr, clearance = 51 ml/hr/kg). PRM metabolites, phenobarbital and phenylethylmalonamide, appeared much earlier in CT patients. Continued PRM exposure in MT patients was accompanied by an increase in apparent clearance in three of seven patients, but no change in four of seven. In four CT patients in whom other antiepileptics were withdrawn there was a decrease in apparent clearance (61.4 to 29.9 ml/hr/kg) no rates in the range of MT patients. PRM kinetics is influenced by concurrent antiepileptic drugs and by duration of PRM therapy.

In the hepatic cell Δ 9 -tetrahydrocannabinol (THC) is localized in nuclei and microsomes. The intracellular binding of THC affects hepatic drug metabolism: nuclei markedly reduce the metabolism of THC by hepatic microsomes; THC inhibits the microsomal oxidation of aminopyrine and hexobarbital, the conjugation of estradiol and p -nitrophenol and enhances the reduction of p -nitrobenzoic acid. The metabolism of THC, in vitro , is strikingly inhibited by SKF-525A but not by desipramine, nortriptyline and iprindole which are potent inhibitors of the oxidation of other drugs.

While monitoring oral aminophylline (theophylline ethylenediamine) therapy, larger doses (milligrams per kilogram) were necessary for children than for adults to achieve similar therapeutic serum levels. The mean apparent theophylline clearance (ATC) determined in 59 children was significantly higher (P (JAMA237:1453-1455, 1977)

Ageing of human skin may result from both the passage of time (intrinsic ageing) and from cumulative exposure to external influences (extrinsic ageing) such as ultraviolet radiation (UVR) which promotes wrinkle formation and loss of tissue elasticity. Whilst both ageing processes are associated with phenotypic changes in cutaneous cells, we summarize, in this chapter, related mechanisms involved, discuss on potentential treatment until now disposable, and suggest preventive measures.