The percutaneous absorption of topically applied tretinoin and its effect on endogenous concentrations of tretinoin and its metabolites after single doses or long-term use.

BACKGROUND: The percutaneous absorption of topically applied tretinoin cream and emollient cream formulations has not been comprehensively studied. OBJECTIVE: To assess tretinoin absorption and plasma levels of tretinoin and its metabolites after single and repeated topical tretinoin doses. METHODS: In study 1, 28 subjects were equally divided into four treatment groups that received a single dose of tritiated tretinoin in a 0.05% formulation of emollient cream (Renova, Retinova) or cream (Retin-A) alone or after 28 days of repeated nonradioactive doses. In study 2, subjects received single topical doses of tritiated tretinoin cream alone (n = 5) or after 1 year of nonradioactive applications (n = 4). Plasma, urine, and fecal samples were analyzed to determine absorption; plasma samples in study 1 were also analyzed for concentrations of tretinoin and its metabolites. RESULTS: Percutaneous absorption of tretinoin was approximately 2% after a single dose and after 28 days of daily application. In patients receiving long-term therapy (i.e., > 1 year), absorption averaged 1.1%. Mean plasma concentrations of tretinoin after 28 days of treatment with either tretinoin emollient cream or tretinoin cream were not significantly changed when compared with the corresponding endogenous concentrations before treatment. CONCLUSION: Minimal percutaneous absorption of tretinoin was obtained after its topical application in cream formulations. Neither single-dose nor long-term treatment with topical tretinoin formulations appeared to affect the endogenous levels of tretinoin or its metabolites.

A physiologically based pharmacokinetic model for retinoic acid and its metabolites.

BACKGROUND: A physiologically based pharmacokinetic (PBPK) model for all-trans-retinoic acid (tretinoin) was developed to provide a coherent description of tretinoin absorption, distribution metabolism, and excretion across species and routes of administration. OBJECTIVE: The goal of developing such a model is to provide a measure of internal dose that would be a biologically relevant surrogate for administered dose in assessing human teratogenic risk from topically applied tretinoin emollient cream. METHODS: The developed PBPK model included compartments for plasma, liver, gut, intestinal lumen, fat, skin, richly and slowly perfused tissues, placenta, and embryo. Tretinoin metabolism to 13-cis retinoic acid, oxidation, and glucuronidation were incorporated. Dose surrogates, including the maximum plasma concentration (Cmax) and area under the concentration-versus-time curve were calculated from the model. RESULTS: The ability of the model to predict tretinoin pharmacokinetics and to extrapolate across species and routes of administration was tested and validated. Model-derived estimates of dose surrogates demonstrated that the internal exposure to retinoids after topical treatment with 0.05% tretinoin emollient cream is minimal in comparison to that for teratogenic oral doses. The ratio of areas under the curve for total active retinoids after teratogenic oral doses in monkeys versus therapeutic topical doses in human beings, for example, was greater than 450,000 to 1. CONCLUSION: For topical application of tretinoin in human beings, detoxification via the glucuronidation pathway predominates, resulting in a much lower internal exposure to active retinoids than was inferred from total radioactivity data. The model predicts that topical application of tretinoin results in an internal exposure that is four to six orders of magnitude lower than a minimally teratogenic dose.

Plasma concentrations of midazolam in children following intranasal administration.

Nasally administered midazolam appears to be a useful method for rapidly sedating children prior to the induction of anesthesia. We determined the peak plasma concentrations after intranasal administration of midazolam and compared this to plasma concentrations achieved after intravenously administered midazolam in 18 children between the ages of 14 months and 5 yr, who underwent elective closure of an asymptomatic atrial septal or ventricular septal defect. Preanesthetic medication was at the discretion of the attending anesthesiologist. Induction of anesthesia was with halothane in N2O and O2 via mask, and tracheal intubation was performed after the administration of fentanyl or sufentanil plus pancuronium. Anesthesia was maintained with these agents, and augmented with halothane or isoflurane. As soon as arterial access was established, the patient received 0.1 mg/kg of either intranasal or intravenous midazolam. Midazolam concentrations were measured by gas chromatography-mass spectrometry. Intranasal midazolam achieved its peak plasma concentration of 72.2 +/- 27.3 ng/ml in 10.2 +/- 2 min. Ten minutes after the administration of midazolam, the mean plasma concentration in the intranasal midazolam group was 57% of the concentrations in the group receiving midazolam intravenously. These results confirm the clinical impression that intranasal administration of midazolam rapidly achieves sedative plasma concentrations in children.

Clinical pharmacokinetics of interferons.

Interferons are a family of proteins shown to be effective in the treatment of viral (condylomata, acuminata) and neoplastic (hairy cell leukaemia and AIDS-related Kaposi's sarcoma) diseases. To date, the clinical utility of the interferons has been hampered by an incomplete understanding of their mechanism of action. However, there is supporting evidence that the route of administration, i.e. the pharmacokinetic behaviour, is an important treatment variable. The pharmacokinetics of interferons have been fairly well described. The decline in serum concentrations of interferon is rapid after intravenous administration. The volume of distribution approximates 20 to 60% of bodyweight. Work in animals suggests that the catabolism of interferons falls within the natural handling of proteins. Clearance values vary (4.8 to 48 L/h) across the family of interferons and probably reflect the natural internal digestion and turnover of these proteins. Terminal elimination half-lives range from 4 to 16 hours, 1 to 2 hours and 25 to 35 minutes for alpha, beta and gamma, respectively. Intramuscular and subcutaneous administration of interferons alpha and beta results in protracted but fairly good absorption: greater than 80% for interferon-alpha and 30 to 70% for interferon-gamma. Interferon therapy is associated with adverse events which are usually mild and reversible. Temporal relationships exist between the degree and duration of adverse effects and the route of administration. Attempts to relate inducible biochemical markers, such as 2',5'-oligoadenylate synthetase activity, to dose or concentration have met with some success although alterations in these markers have not been shown to relate to clinical response.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased volume of distribution prolongs midazolam half-life.

It has recently been shown by several investigators that the half-life (t1/2) of midazolam is prolonged (greater than 7 h) in a small proportion of the population. One group has inferred that this subpopulation represents a group of slow metabolizers of midazolam to alpha-OH-midazolam. Others disagree and postulate that there is an increase in the volume of distribution (V) resulting in a prolonged t1/2. This controversy led us to report experience from 90 subjects and patients where t1/2, V, and clearance (CL) were determined by both model-dependent and -independent pharmacokinetic analysis. We found a 5.6% (5 of 90) incidence of prolonged t1/2, similar to that previously reported. V was clearly increased without a decrease in CL in the five subjects with prolonged t1/2. Thus, the prolonged t1/2 is secondary to an increase in V and not a result of alterations in CL and metabolism.

Estrogen deprivation in breast cancer. Clinical, experimental, and biological aspects.

The endocrinological and clinical effects of an LH-RH agonist, Zoladex, and an antiestrogen, Nolvadex, in patients with advanced breast cancer are outlined and their potential in the therapy of nonmalignant diseases of the breast and high-risk states is briefly discussed. Additional data are presented to indicate that new antiestrogens are now available for experimental studies that, unlike tamoxifen, do not possess partial estrogen-like activity and that show favorable antitumor properties against DMBA-induced mammary tumors and MCF-7 human breast cancer cells in culture. The lack of agonistic effects of this new class of pharmacological agents now allows a state of total estrogen deprivation to be approached, a previously unobtainable clinical goal.

Effect of cimetidine on the disposition of rimantadine in healthy subjects.

Twenty-three healthy male and female subjects received single 100-mg oral doses of rimantadine hydrochloride on two occasions in an open-label, sequential design with a 6-day washout between doses. The first dose of rimantadine was administered alone, and the second dose was administered concomitantly with cimetidine (300 mg four times a day for 6 days). Blood and urine samples were collected, and rimantadine concentrations were determined by a gas-chromatographic--mass-spectrometric method. There were no changes in the rate of absorption and the renal clearance of rimantadine when it was administered with cimetidine. Both parametric and nonparametric tests showed significant differences in the area under the concentration-time curve, apparent total clearance, and elimination rate constant between the treatments (P less than 0.01). The apparent total clearance was reduced by 18%, resulting in higher values for the area under the concentration-time curve in the presence of cimetidine. However, the wide therapeutic index of rimantadine renders these changes of little, if any, clinical consequence.

The influence of food on the pharmacokinetics and ACE inhibition of cilazapril.

1. The influence of food on the pharmacokinetics and angiotensin-converting enzyme (ACE) inhibitory effects of oral 5 mg doses of cilazapril was investigated in a two-way crossover study in 16 volunteers. 2. Plasma and urine concentrations of cilazaprilat, the active diacid metabolite of cilazapril, and plasma ACE activity were determined by a radio-enzymatic method. 3. Cmax decreased by 30% (P less than 0.05) with a delay in (t)max of 1 h (P less than 0.05) and area under curve (AUC) was decreased by 14% (P less than 0.05). The elimination rate was unaltered. 4. Onset of ACE inhibition was delayed by approximately 30 min but degree and duration were unaffected. 5. The effect of food on the bioavailability of cilazapril at this dose would not be expected to be clinically significant.

Multiple-dose pharmacokinetics of rimantadine in elderly adults.

To assess the possible effect of aging on rimantadine hydrochloride pharmacokinetics, single- and multiple-dose kinetics were determined in 18 healthy adults with ages between 51 and 79 years. Subjects ingested single 100-mg oral doses of rimantadine after an overnight fast, followed after 5 days by a dosage of 100 mg twice a day for 9.5 days. No differences were observed among the age-stratified groups in measured or derived pharmacokinetic parameters. Peak concentrations in plasma (mean +/- standard deviation) following the single- and multiple-dose regimens, respectively, were 89 +/- 25 and 417 +/- 129 ng/ml for subjects who were 50 to 60 years of age (group 1), 92 +/- 24 and 401 +/- 84 ng/ml for those 61 to 70 years of age (group 2), and 100 +/- 14 and 538 +/- 51 for those 71 to 79 years of age (group 3). The elimination half-life in plasma following multiple doses averaged 33.5 h for group 1, 32.5 h for group 2, and 38.6 h for group 3. Steady-state concentrations in nasal mucus developed by day 5 of dosing (1.5-fold higher than concentrations in plasma), and rimantadine remained detectable in secretions for 5 days after the last dose in 65% of subjects. Stepwise regression analysis suggested that changes in maximum concentration in plasma and area under the concentration-time curve at steady state may be related to creatinine clearance. The results indicate that no important differences in rimantadine multiple-dose pharmacokinetics exist among healthy elderly adults with ages between 51 and 79 years.

Pharmacokinetics of human recombinant interferon-alpha I after i.v. infusion and im injection in African green monkeys.

The pharmacokinetics of recombinant human interferon-alpha I (rHuIFN-alphaI) were studied following a single 3 X 10(6) U/kg dose administered as a 30-min intravenous (iv) infusion and as an intramuscular (im) injection to four African green monkeys using a crossover design. Concentrations of rHuIFN-alpha I in serum were determined by bioassay. Serum rHuIFN-alpha I concentrations declined rapidly following an iv infusion. The elimination half-life ranged from 1.7 to 2.0 h. The volume of distribution at steady state and the total body clearance ranged from 0.42 to 2.4 L/kg and 28 to 233 ml/min, respectively. A protracted absorption profile was seen following im injection, with a highly variable bioavailability ranging from 16 to 680%, compared with the iv infusion. The overall disposition of rHuIFN-alpha I is comparable to that of rHuIFN-alpha A and other IFNs in monkeys.

Rimantadine pharmacokinetics in healthy subjects and patients with end-stage renal failure.

The single-dose (two 100 mg doses) pharmacokinetics of rimantadine hydrochloride were compared in eight patients with end-stage renal disease who were on hemodialysis and seven age-matched healthy subjects. Plasma and urine rimantadine concentrations were determined by a GC/MS method. The plasma half-life (43.6 vs 27.5 hours) and AUC (9.9 +/- 2.1 vs 6.0 +/- 1.6 micrograms.hr/ml) were significantly (p less than 0.05) increased in the patient population. No significant differences were noted in the maximum rimantadine concentration, time of maximum concentration, or apparent volume of distribution. Urinary excretion of unchanged rimantadine accounted for 16% of the dose in the healthy subjects. Hemodialysis did not appreciably remove rimantadine. These findings suggest that rimantadine dosage may need to be reduced in patients with end-stage renal disease but supplemental doses on dialysis days are not required.

Pharmacokinetics of diazepam during multiple dosing of a 6-mg controlled-release capsule once daily.

Sixteen subjects completed a two-way crossover study designed to determine the steady-state pharmacokinetic profiles of diazepam and desmethyldiazepam following a 6-mg controlled-release (CR) capsule dosed once daily compared with those of a 2-mg diazepam tablet dosed 3 times a day. Treatment A consisted of 14 days of CR dosing followed by 10 days of tablet dosing. Treatment B was the reverse of Treatment A. Plasma concentrations of diazepam and desmethyldiazepam were determined by an electron-capture gas-liquid chromatographic method. The areas under the diazepam plasma concentration-time curve were similar for both formulations at initiation of dosing and at steady-state, indicating comparable extents of absorption. The mean ratios of the areas at steady-state were near unity--0.94 for Treatment A and 0.91 for Treatment B--implying that no changes in steady-state conditions occurred upon switching regimens in either direction. The steady-state profiles of desmethyldiazepam were also comparable for the two dosage forms. These data indicate that the CR capsule and the conventional tablet t.i.d. produce similar target concentrations of both the drug and metabolite; therefore, these two dosage forms and dosing regimens should be interchangeable.

Phase I studies of 2',3'-dideoxycytidine in severe human immunodeficiency virus infection as a single agent and alternating with zidovudine (AZT).

Five dose regimens of 2',3'-dideoxycytidine (ddC) were administered, intravenously for 2 weeks then orally for 4 or more weeks, to 20 patients with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC). ddC was well absorbed from the gut and crossed the blood-brain barrier. 10 of the 15 patients who received 0.03-0.09 mg/kg every 4 h had increases in their absolute number of T4+ T cells at week 2 (p less than 0.05), though in many these rises were not sustained. 11 of 13 evaluable patients had a fall in their serum human immunodeficiency virus (HIV)p24 antigen by week 2 of therapy (p less than 0.01); in 4 patients the p24 antigen subsequently rose to baseline while in others the decline was sustained. Dose-related toxic effects included cutaneous eruptions, fever, mouth sores, thrombocytopenia, and neutropenia. A reversible painful peripheral neuropathy developed in 10 patients after 6-14 weeks' treatment. These results suggest that ddC has activity against HIV in vivo and has a different toxicity profile from that of zidovudine (AZT). 6 patients with AIDS or ARC were given an alternating regimen of oral AZT (200 mg every 4 h for 7 days) and oral ddC (0.03 mg/kg every 4 h for 7 days). The regimen was well tolerated, and the 5 patients who completed 9 or more weeks of treatment had sustained rises in their T4+ T cells and/or falls in p24 antigen.

Relative bioavailability of rimantadine HCl tablet and syrup formulations in healthy subjects.

Twenty healthy male subjects completed an open-label randomized crossover design to assess the bioavailability of 100 mg of rimantadine HCl in tablet and syrup forms relative to an oral solution. Blood samples were drawn and rimantadine plasma concentrations were determined by a GC-MS method. The maximum plasma concentration (Cmax), the time to Cmax (tmax), the area under the plasma concentration-time curve (AUC), and k were compared among treatments using an analysis of variance and the Hauck-Anderson test for bioequivalence. The Hauck-Anderson test was satisfied when the syrup and solution were compared. The relative bioavailability of the syrup was 96%. Both Cmax and AUC were significantly (p less than 0.05) increased (23 and 17%, respectively) when the tablet was compared with the solution. The relative bioavailability of the tablet was 117%. This outcome was unusual and could not be explained. However, this was not anticipated to be of clinical consequence since the majority of the safety and efficacy of rimantadine HCl was established using a tablet.

Dose-proportional absorption of etretinate after doses of 25, 50, 75, and 100 mg.

Twelve healthy male subjects received single oral doses of etretinate, ranging from 25 to 100 mg (1 to 4 x 25-mg capsules) in an open-label, four-way randomized crossover design. Plasma concentrations of etretinate and two active metabolites were determined by a specific high-performance liquid chromatographic (HPLC) method. Analysis of variance and orthogonal contrasts were used to assess dose proportionality. Mean (+/- %CV) maximum concentrations after 25- to 100-mg doses were 133 (50), 195 (33), 261 (53), and 446 (65) ng/ml, whereas AUC0-12 values were 581 (46), 1090 (39), 1500 (52), and 2440 (63) ng.hr/ml, respectively. The test for proportionality indicated that Cmax and AUC0-12 increased proportionally with an increase in dose (P greater than 0.05).

Pharmacokinetics of rimantadine hydrochloride in patients with chronic liver disease.

Six patients with chronic liver disease and six sex-, age (+/- 5 years)-, and weight (+/- 5 kg)-matched healthy control subjects received a single dose of two 100 mg tablets rimantadine HCl. Eight additional patients with chronic liver disease who were not matched to healthy subjects received a single dose of two 100 mg tablets of rimantadine HCl. Blood and urine samples were collected and rimantadine concentrations were determined by a GCMS method. The values for maximum plasma concentration, AUC, elimination half-life, and renal clearance were not significantly different between patients and control subjects, independent of the statistical analyses (parametric and nonparametric) used. The mean apparent elimination half-life, volume of distribution, and total clearance in the matched patients with liver disease were 32 hours, 24 L/kg, and 676 ml/min, respectively. Renal clearance and the amount excreted in the urine unchanged were 63 ml/min and 10%, respectively. In conclusion, rimantadine pharmacokinetics were not appreciably altered in patients with less severe chronic liver disease.

Pharmacokinetics and antisecretory activity of trimoprostil in Heidenhain-pouch dogs.

Trimoprostil, a prostaglandin E2 analog, was evaluated to determine if there was a relationship between plasma concentrations and inhibition of histamine-stimulated gastric acid secretion in dogs prepared with Heidenhain pouches. Trimoprostil was given p.o. followed by collection (drainage) of gastric juice from the pouch to determine acid output. In addition, serial blood samples were withdrawn to determine trimoprostil plasma concentrations. Trimoprostil was absorbed rapidly and eliminated with T1/2 ranging from 25 to 37 min. Trimoprostil was effective in inhibiting acid output compared with control. The maximal response and duration of activity were dependent on the concentration-time profile of trimoprostil. Trimoprostil produced a maximum inhibition of 98% and suppressed acid output for at least 3 hr. When plasma concentrations were related to the antisecretory response using a modified Hill equation, the response was found to lag behind plasma concentrations as evidenced by hysteresis loops. The predicted plasma concentration associated with a 50% inhibition of acid secretion (IC50) ranged from 0.58 to 0.79 ng/ml.

Rimantadine pharmacokinetics after single and multiple doses.

Twenty-four healthy adult male volunteers were randomly assigned to one of two rimantadine regimens. The 12 volunteers assigned to regimen 1 orally received a single 100-mg rimantadine tablet followed 5 days later by 100 mg of rimantadine twice a day for 10 days. Volunteers assigned to regimen 2 ingested a single 100-mg rimantadine tablet followed 5 days later by 100 mg once a day for 10 days. The results of the study suggest that the pharmacokinetics of rimantadine are linear and accumulation of the drug during repetitive multiple doses is predictable.