RESUMEN
The pharmacokinetics and endocrine effects of a therapeutic dose (10 mg/day) of posatirelin (L-pyro-2-aminoadipyl-L-leucyl-L-prolinamide) were investigated in healthy elderly subjects. Posatirelin was given once daily by intramuscular injection for 7 days. Pharmacokinetic parameters were estimated using a model-independent approach. The plasma concentrations of free triiodotyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) and the circadian rhythms of prolactin and cortisol were considered as indicator variables of endocrine response to posatirelin administration. Posatirelin was well tolerated and no significant adverse effects were observed during the study. Peak plasma concentration (Cmax), time of peak plasma concentration (tmax), area under the plasma concentration-time curve from time zero to infinity (AUC0-infinity), elimination half-life (t1/2), and total clearance (CI/F) were measured after single-dose intramuscular injection (day 1) and after multiple-dose administration (day 7). There were no significant changes in these parameters after multiple-dose administration (day 7). Posatirelin induced a progressive reduction in basal TSH levels and maximum response. There were no significant changes during treatment in the time at which basal levels of FT3 and FT4 occurred, and these levels remained within the normal range throughout the study. The circadian rhythms of cortisol and prolactin were not influenced by posatirelin treatment. The pharmacokinetics of posatirelin were not time dependent, and the drug did not accumulate after multiple-dose administration. Short-term treatment with posatirelin did not induce clinically relevant endocrine consequences in healthy elderly subjects.
Asunto(s)
Fármacos del Sistema Nervioso Central/farmacocinética , Ritmo Circadiano/efectos de los fármacos , Hormonas Tiroideas/sangre , Hormona Liberadora de Tirotropina/análogos & derivados , Anciano , Anciano de 80 o más Años , Área Bajo la Curva , Femenino , Humanos , Hidrocortisona/sangre , Masculino , Tasa de Depuración Metabólica , Prolactina/sangre , Hormona Liberadora de Tirotropina/farmacocinética , Hormona Liberadora de Tirotropina/farmacologíaRESUMEN
This phase I open pharmacokinetic and metabolism study was conducted with six healthy male volunteers who were given 20 mg of (3)H-alpha-dihydroergocryptine in order to evaluate the absorption, plasma time course, and urinary and fecal elimination of total radioactivity. Rapid absorption into the general circulation occurred with an average K(01) of 0.99 plus minus 0.73/h. Peak time(T(max)) was reached in approximately 3 h with an average radioactivity concentration (C(max)) of 8.78 plus minus 5.9 ng eq h/ml. Distribution from the central compartment to the peripheral compartment occurred with a mean rate constant (K(12)) of 0.330 plus minus 0.22/h. Estimations of total clearance (CL) and volume of distribution (Vd) seem strongly affected by the low oral availability (F) of hydrogenated ergots. The rate constant (K(21)) of radioactivity washout from the tissue to the central compartment was 0.250 plus minus 0.130/h. However, plasma radioactivity declined biexponentially with an overall elimination constant (K(10)) of 0.029 to 0.146/h (i.e, half-lives of 23.9--4.75/h). Total radioactivity recovery in urine and feces was good with 82.78 plus minus 6.44% of dose eliminated in feces and 3.01 plus minus 0.65% in urine. The latter concentration was too low to detect metabolites or unchanged drug by radioactivity image scanning. However, the liquid scintillation count of silica gel that had been scraped off the thin layer chromatography (TLC) plates indicated the presence of metabolites in urine. Pharmacodynamically, both supine and standing blood pressure fell significantly within the first 8 h of dosing, yet there were no changes in heart rate. No adverse reactions were reported. In conclusion, the kinetics of (3)H-dihydroergocryptine are very similar to other ergot alkaloids in respect to extensive hepatic metabolism with an elimination half-life of 25 h.
RESUMEN
In this study the single-dose and steady-state pharmacokinetics of unchanged triflusal and its metabolite 2-hydroxy-4-trifluoromethylbenzoic acid (HTB) were studied in 12 elderly subjects treated with a single oral administration of 300 mg triflusal and repeated oral administrations of 300 mg triflusal b.i.d. for 13 days. After a single administration, unchanged triflusal is promptly absorbed (t(max) 0.75 h, C(max) 3.83 &mgr;g/mL) and rapidly depleted from the systemic circulation. Its concentration was measurable only up to 1 to 4 h after administration. The apparent terminal half-life was 0.85 h. HTB proves to be quickly generated from triflusal (t(max) 2.00 h, C(max) 39.88 &mgr;g/mL) and slowly eliminated from the body (t = 54.6 h). With the dose regimen proposed, unchanged triflusal does not accumulate in the body. Conversely, HTB plasma concentration builds up progressively toward steady-state levels of approximately 102 &mgr;g/mL after 4 to 5 d of treatment. No substantial change in peak time, elimination rate constant and half-life evaluated after single-dose treatment was observed on multiple-dose regimen for unchanged triflusal and its metabolite HTB. Therefore, our findings do not indicate a time-dependent pharmacokinetics for triflusal. There were no changes in blood pressure, heart rate or laboratory safety date, i.e., biochemical or hematological profiles.
RESUMEN
The effects of different doses of porcine calcitonin (pCT) were tested in vitro and in vivo. In vitro, pCT at a concentration ranging from 0.1 to 5 M. R. C. Units/ml induced a dose-dependent inhibition of ADP (1.2 microM) and collagen- (2 micrograms/ml) induced platelet aggregation, showing a prevalent action on the second wave of ADP-induced aggregation and causing prolongation of the lag time and reduction of both maximum aggregation and slope in collagen-induced aggregation. 45Ca uptake by platelets in the presence of the ionophore A23187 and 14C-serotonin release were also inhibited in a dose-related fashion, using concentrations ranging from 1 to 10 M. R. C. Units of pCT. The in vivo tests, performed before and after a 7-day treatment with 2 different doses of pCT (1 and 160 M. R. C. Units/daily, i. m.) confirmed the inhibitory effect of pCT on ADP- and collagen-induced platelet aggregation. It should be stressed that the effect of 1 unit was stronger than that of 160 units. It is therefore postulated that in vitro and in vivo effects of pCT on platelet functions probably depend on different mechanisms of action.
Asunto(s)
Plaquetas/efectos de los fármacos , Calcitonina/farmacología , Adulto , Anciano , Animales , Plaquetas/metabolismo , Calcitonina/administración & dosificación , Relación Dosis-Respuesta a Droga , Femenino , Humanos , Inyecciones Intramusculares , Masculino , Persona de Mediana Edad , Agregación Plaquetaria/efectos de los fármacos , PorcinosRESUMEN
45Calcium metabolism and circulating levels of iPTH (N-terminal fragment) and iCT were investigated in normocalcemic patients with multiple myeloma (12) in an attempt to ascertain early changes in calcium metabolism, which may occur before hypercalcemia develops. The same parameters were also investigated in patients with senile osteoporosis (11), corticosteroid-induced osteoporosis (6), Paget's disease (6) and controls without bone disorders (13). In the myeloma group, the exchangeable calcium pool (7,678 +/- 321 mg) was significantly higher (P less than 0.01) than in the control group (4,405 +/- 374 mg), the senile osteoporosis group (4,108 +/- 407 mg) and the corticosteroid-induced osteoporosis group (3,015 +/- 161 mg) and nearly as high as in the Paget's disease group (8,876 +/- 1,173 mg). Calcium pool turnover rate was higher in the myeloma group than in controls, as were bone anabolism and bone catabolism, although differences were not statistically significant. There were no statistically significant differences among the groups in the plasma iPTH or iCT, although the mean value of the latter was higher in the myeloma group than in controls (86 +/- 24 vs. 47 +/- 13 pg/ml). These data suggest that an increase in the exchangeable calcium pool and in turnover rate may occur early in the course of multiple myeloma, preceding the development of hypercalcemia. The role of some homeostatic mechanisms in maintaining normal plasma calcium levels in multiple myeloma despite increased bone calcium resorption is discussed.
Asunto(s)
Calcio/metabolismo , Mieloma Múltiple/metabolismo , Adulto , Anciano , Calcitonina/sangre , Calcio/sangre , Radioisótopos de Calcio , Femenino , Humanos , Cinética , Masculino , Persona de Mediana Edad , Osteoporosis/metabolismo , Hormona Paratiroidea/sangreRESUMEN
The authors reported the plasma levels and pharmacokinetic parameters of ciclopirox olamine in rabbits after i.v. and intravaginal administrations and in female patients after vaginal administration. Plasma levels of total and free ciclopirox were determined by a HPLC method. In rabbit ciclopirox showed a half-life of 2.22 h and an intravaginal bioavailability of about 2%. In female patients ciclopirox showed low intravaginal absorption; this value might explain the good local and systemic tolerability and also the penetration of drug in deep tissue.
Asunto(s)
Piridonas/farmacocinética , Administración Intravaginal , Adulto , Animales , Ciclopirox , Femenino , Semivida , Humanos , Piridonas/administración & dosificación , ConejosRESUMEN
Many clinical trials have shown the effectiveness of platelet-antiaggregant drugs in the treatment of obliterative peripheral arteriopathy, both locally and in the system, by improving the claudication symptoms and by preventing major cardiovascular events. In this study we evaluated the effectiveness of a 24-week treatment with triflusal, a comparatively new inhibitor of platelet aggregation, in patients affected by chronic peripheral arteriopathy, comparing twice-daily oral doses of 300 mg triflusal with twice-daily placebo doses. The percentages of successes (defined as a 40% increase of total walking distance over the basal control) were 63.6% in the triflusal group (35/55 patients) and 22.5% in the placebo group (14/62 patients). Patients treated with triflusal showed a more important increase in total walking distance and in pain-free walking distance over the basal values than those treated with placebo, together with an improvement of the symptomatology correlated with claudication. Moreover, in the triflusal group there was an increase in the peak-flow recorded through strain-gauge plethysmography. In conclusion, triflusal significantly increased both the distance which could be walked and the clinical symptoms, presumably by improving microperfusion.
Asunto(s)
Enfermedades Vasculares Periféricas/tratamiento farmacológico , Inhibidores de Agregación Plaquetaria/uso terapéutico , Salicilatos/uso terapéutico , Adulto , Anciano , Enfermedad Crónica , Método Doble Ciego , Femenino , Humanos , Masculino , Persona de Mediana Edad , Salicilatos/administración & dosificaciónRESUMEN
Skin microcirculation was evaluated in 117 patients with diabetic microangiopathy over a period of six months. They were divided into two groups. Group 1 (64 patients) was treated with oral defibrotide, a new profibrinolytic drug, in association with diet and oral antidiabetic drugs. Group 2 (53 patients) was treated only with diet and antidiabetic agents. The microcirculation was studied by means of laser-Doppler flowmetry transcutaneous partial pressure of oxygen and carbon dioxide pressure measurements, and evaluation of capillary filtration. After six months, patients in group 1 improved their microcirculatory parameters in association with an improvement in signs and symptoms. Moreover, 30 patients in group 1 and 36 in group 2 were followed up for eighteen months, and the authors observed that the deterioration of the microcirculatory parameters was significantly slowed in diabetics treated with defibrotide. A decrease in plasma fibrinogen during defibrotide treatment was observed in all treated patients in association with an increased fibrinolytic activity. In conclusion, it appears that defibrotide, enhancing fibrinolysis, improved the microcirculation in diabetics, preventing further, progressive deterioration.
Asunto(s)
Angiopatías Diabéticas/tratamiento farmacológico , Fibrinolíticos/uso terapéutico , Polidesoxirribonucleótidos/uso terapéutico , Adulto , Vasos Sanguíneos/diagnóstico por imagen , Angiopatías Diabéticas/sangre , Angiopatías Diabéticas/diagnóstico por imagen , Angiopatías Diabéticas/fisiopatología , Femenino , Fibrinógeno/análisis , Fibrinólisis/efectos de los fármacos , Humanos , Flujometría por Láser-Doppler , Pierna/irrigación sanguínea , Masculino , Microcirculación/efectos de los fármacos , Persona de Mediana Edad , Flujo Sanguíneo Regional/efectos de los fármacos , Piel/irrigación sanguínea , Ultrasonografía , Vasoconstricción/efectos de los fármacosRESUMEN
In order to evaluate the effect of triflusal (2-acetyloxy-4-trifluoromethyl benzoic acid), an orally active antiplatelet agent, on arteriosclerosis progression, a pilot, parallel, double-dummy, double-blind clinical trial vs acetylsalicylic acid (ASA) was carried out in patients with subclinical atherosclerotic lesions. The trial consisted of a 2-week run-in placebo phase, followed by a 12-month oral treatment with triflusal (600 mg/day) or ASA (300 mg/day). The primary variable was identified in the ultrasonic biopsy (UB) score; the secondary variables were the UB class changes of each arterial site, the rate of progression (ROP), the intima-media thickness (IMT), and the symptoms of arteriosclerosis. Data were evaluated by use of analysis of variance and Chi-square test. Forty-three patients (31 men, 12 women, mean age 62.8 +/- 8.4 SD) were randomized to triflusal (15 men, 6 women, mean age 64.3 +/- 6.7) or to ASA (16 men, 6 women, mean age 61.3 +/- 9.6). The analysis of variance on the UB score showed no difference between treatments: the patients' UB scores remained unchanged with no progression, thus indicating that no patient worsened during treatment. When all arterial sites under evaluation are considered, 86% of the sites in the triflusal group and 85% in the ASA group remained unchanged. No relevant change was recorded in vital signs and routine laboratory tests. Gastric disturbances were reported by two and three patients treated with triflusal and ASA, respectively. In conclusion, triflusal appears as effective as ASA in slowing arteriosclerosis progression.
Asunto(s)
Arteriosclerosis/tratamiento farmacológico , Inhibidores de Agregación Plaquetaria/uso terapéutico , Salicilatos/uso terapéutico , Administración Oral , Adulto , Anciano , Análisis de Varianza , Arteriosclerosis/diagnóstico por imagen , Aspirina/administración & dosificación , Aspirina/efectos adversos , Aspirina/uso terapéutico , Enfermedades de las Arterias Carótidas/diagnóstico por imagen , Enfermedades de las Arterias Carótidas/tratamiento farmacológico , Distribución de Chi-Cuadrado , Progresión de la Enfermedad , Método Doble Ciego , Femenino , Arteria Femoral/diagnóstico por imagen , Arteria Femoral/efectos de los fármacos , Humanos , Masculino , Persona de Mediana Edad , Proyectos Piloto , Placebos , Inhibidores de Agregación Plaquetaria/administración & dosificación , Inhibidores de Agregación Plaquetaria/efectos adversos , Salicilatos/administración & dosificación , Salicilatos/efectos adversos , Estómago/efectos de los fármacos , Túnica Íntima/diagnóstico por imagen , Túnica Íntima/efectos de los fármacos , Túnica Media/diagnóstico por imagen , Túnica Media/efectos de los fármacos , UltrasonografíaRESUMEN
In order to confirm the efficacy and safety of posatirelin (L-pyro-2-aminoadipyl-L-leucyl-L-prolinamide), a synthetic peptide having cholinergic, catecholaminergic and neurotrophic activities, a multicentre, double-blind, controlled study versus placebo was planned in elderly patients suffering from Alzheimer's disease and vascular dementia, according to National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) and National Institute of Neurological Disorders and Stroke/Association Internationale pour la Recherche et l'Enseignement en Neurosciences (NINDS-AIREN) criteria, respectively. The trial consisted of a 2-week run-in phase with placebo administered once a day orally, followed by a double-blind period of 3 months, with posatirelin or placebo administered once a day intramuscularly. Efficacy was assessed using the Gottfries-Bråne-Steen (GBS) Rating Scale (primary variable) and the Rey Memory Test (secondary variable). Laboratory tests, vital signs and adverse events were monitored. A total of 360 patients were randomized, the intent-to-treat sample (ITT) being made up of 357 patients and the per protocol sample (PP) of 260 patients. Both pragmatic and explanatory analyses showed significant differences between treatment groups in the GBS Rating Scale and the Rey Memory Test, with no difference in the two types of dementia. No difference between treatments was observed in safety variables, the incidence of adverse events in the posatirelin group being 7.3%. The study confirms previous results showing that treatment with posatirelin can improve cognitive and functional abilities of patients suffering from degenerative or vascular dementia.
RESUMEN
In an open-study design five healthy volunteers were first given 2500 IU sodium heparin intravenously and then, after 72 h, another injection of the same dosage of sodium heparin followed immediately by 400 mg defibrotide intravenously. In two separate experiments, prothrombin time, activated partial prothrombin time, antithrombin III, tissue plasminogen activator, its inhibitor and plasma heparin levels were measured at baseline and after 15 min in one experiment, and at baseline and after 2 h in the other experiment. The most important finding was that an interaction exists between heparin and defibrotide on haemostatic activity: activated partial prothrombin time was increased three-fold in volunteers given the defibrotide--heparin combination compared with volunteers given heparin alone. This statistically and clinically significant effect was evident 15 min after administration of defibrotide--heparin and was still present after 2 h. Possible explanations for this effect are discussed briefly.
Asunto(s)
Fibrinolíticos/farmacología , Hemostasis/efectos de los fármacos , Heparina/farmacología , Polidesoxirribonucleótidos/farmacología , Adulto , Interacciones Farmacológicas , Femenino , Humanos , Masculino , Valores de ReferenciaRESUMEN
Tetridamine (2-methyl-3-methylamino-4,5,6,7-tetrahydroindazole) is a well known analgesic and anti-inflammatory drug. Here the activity and the tolerability of a new 0.134% tetridamine formulation in rats and women, are reported. Anti-inflammatory and analgesic tests were performed in Sprague-Dawley rats with carrageenin oedema; topical application of 0.134% tetridamine solution showed a marked reduction of paw swelling (-54.4%) and pain sensibility (-81.0%). A 28 days vaginal tolerability study performed on Sprague-Dawley rats with tetridamine lavage (0.2 ml/rat/day) showed, in comparison with control group, no changes in haematology, coagulation, clinical biochemistry and in histological examinations of uterus and vagina. Clinical studies (4 open and 1 double-blind) were performed on 93 women suffering from vulvovaginitis and cervicitis by treatment of 0.134% tetridamine vaginal lavage, two times daily, for 7 days. Tetridamine lavage reduced or eliminated all inflammation symptoms like burning, leucorrhea, etc. and resulted very well tolerated. From these pharmacotoxicological and clinical results we can conclude that tetridamine vaginal lavage is a new formulation with high activity and good tolerability.
Asunto(s)
Antiinflamatorios no Esteroideos/farmacología , Indazoles/farmacología , Vulvovaginitis/tratamiento farmacológico , Adulto , Animales , Femenino , Humanos , Indazoles/administración & dosificación , Indazoles/uso terapéutico , Persona de Mediana Edad , Ratas , Ratas Sprague-Dawley , Irrigación Terapéutica , Vagina/efectos de los fármacosAsunto(s)
Adyuvantes Inmunológicos/farmacología , Infecciones Bacterianas/prevención & control , Inmunidad Innata/efectos de los fármacos , Ácido Pirrolidona Carboxílico/análogos & derivados , Tiazoles/farmacología , Virosis/prevención & control , Adyuvantes Inmunológicos/administración & dosificación , Adyuvantes Inmunológicos/uso terapéutico , Animales , Infecciones Bacterianas/inmunología , Infecciones por Coxsackievirus/inmunología , Infecciones por Coxsackievirus/patología , Enterovirus Humano B , Femenino , Virus de la Influenza A , Ratones , Ratones Endogámicos BALB C , Infecciones por Orthomyxoviridae/inmunología , Infecciones por Orthomyxoviridae/prevención & control , Ácido Pirrolidona Carboxílico/administración & dosificación , Ácido Pirrolidona Carboxílico/farmacología , Ácido Pirrolidona Carboxílico/uso terapéutico , Infecciones Estreptocócicas/inmunología , Infecciones Estreptocócicas/prevención & control , Streptococcus agalactiae , Tiazoles/administración & dosificación , Tiazoles/uso terapéutico , Tiazolidinas , Virosis/inmunologíaAsunto(s)
Calcitonina/uso terapéutico , Osteoporosis/tratamiento farmacológico , Fosfatasa Alcalina/metabolismo , Huesos/metabolismo , Huesos/patología , Calcitonina/administración & dosificación , Calcio/metabolismo , Evaluación de Medicamentos , Electrólitos/metabolismo , Humanos , Hidroxiprolina/orinaRESUMEN
In this study the bactericidal activity of Clofoctol has been evaluated by "in vitro" technique against gram-positive against gram-positive microorganisms clinically isolated. The results show that MIC of Clofoctol is very close to its bactericidal activity, which could therefore be retained as its main activity. The MBC recovered was 1-8 mcg/ml against strains of Staphylococcus aureus and 2-8 mcg/ml against Streptococcus pyogenes, while the bactericidal activity against Staphylococcus aureus, evaluated at M.B.C., was recovered after 30'.
Asunto(s)
Clorobencenos , Cresoles/farmacología , Pruebas de Sensibilidad Microbiana , Staphylococcus aureus/efectos de los fármacos , Streptococcus/efectos de los fármacosRESUMEN
An unusually prolonged case of heparin-induced severe thrombocytopenia and decompensated disseminated intravascular coagulation (DIC) is described. The patient, treated with heparin at a dosage of 25,000 units/day for 3 days and 12,500 units/day for an additional 4 days because of a clinically suspected deep venous thrombosis, developed (4 days after the discontinuation of heparin) a clinical and laboratory picture of severe DIC, manifested by subcutaneous hematomas and ecchymoses. Platelet count was 24 x 10(9)/l, fibrinogen level 89 mg/dl and fibrin-degradation products between 3,200 to 6,400 ng/ml. A thorough laboratory and instrumental evaluation failed to demonstrate any underlying disorder. No heparin-dependent aggregating factor was detected in the serum of the patient. The patient recovered spontaneously. Whereas fibrinogen and fibrin-degradation products reverted to normality within four weeks, platelet count normalization was delayed until the sixth week after heparin discontinuation.
Asunto(s)
Coagulación Intravascular Diseminada/inducido químicamente , Heparina/efectos adversos , Trombocitopenia/inducido químicamente , Anciano , Pruebas de Coagulación Sanguínea , Femenino , Hematoma/inducido químicamente , Humanos , Recuento de Plaquetas , Púrpura Trombocitopénica/inducido químicamente , Tromboflebitis/complicaciones , Tromboflebitis/tratamiento farmacológico , Factores de Tiempo , Warfarina/uso terapéuticoRESUMEN
We studied IFN inducing ability on syngenic C3H mice of a multibacterial antigenic extract consisting of different strains of following species: Staphylococcus aureus, Escherichia coli, Aerobacter aerogenes, Proteus vulgaris. A dose-dependent IFN production was demonstrated and two peaks of circulating IFN were observed few hours and two days after i.v. inoculation. Per os administration only at high doses induced evaluable levels of IFN in the circulation.
Asunto(s)
Antígenos Bacterianos/administración & dosificación , Inductores de Interferón , Animales , Enterobacter/inmunología , Escherichia coli/inmunología , Masculino , Ratones , Ratones Endogámicos C3H , Proteus vulgaris/inmunología , Staphylococcus aureus/inmunologíaRESUMEN
An in vitro approach was undertaken to investigate the metabolite profile of dihydro-alpha-ergocryptine,9,10-[9,10 ( -3 ) H(N)] in humans by comparison with two species, rat and monkey, for toxicological studies. Hepatocytes (rat and human) and microsomes (rat, monkey, and human) were used in this study, and a high-performance liquid chromatography system was developed to determine the metabolic profiles. From the two in vitro metabolizing systems it was concluded that the compound was extensively metabolized in all species, with a similar overall rate of 4.5 ng/min/mg protein in the microsomal system. The human metabolite profile in hepatocytes showed an intersubject variability that was not confirmed with microsomes. The more complex human pattern consisted of eight metabolites (based on chromatographic properties) that were produced in rats (major part) or in monkeys. Of these eight metabolites, seven were produced by rat microsomes and six by the monkey microsomes. Because of qualitative and quantitative differences, it was not possible to show that the human metabolite profile was closer to the rat's or to the monkey's. The conclusion is that all the observed metabolites in human are produced either in rats (for a major part) or in monkeys, so that these two species cover the human metabolic pattern for toxicological studies.
Asunto(s)
Dihidroergotoxina/metabolismo , Hígado/metabolismo , Adulto , Animales , Biotransformación , Células Cultivadas , Femenino , Humanos , Hígado/citología , Macaca fascicularis , Masculino , Microsomas Hepáticos/metabolismo , Persona de Mediana Edad , Ratas , Ratas Sprague-Dawley , Especificidad de la EspecieRESUMEN
The effects of acute porcine calcitonin (pCT) administration were studied in 11 healthy volunteers with no metabolic disease. Each subject was given, intramuscularly, 1 MRC unit of pCT in glycine vehicle, 160 units of pCT in gelatine vehicle, and placebo, according to a crossover design. The following parameters were studied: blood calcium, phosphorus and immunoreactive parathyroid hormone (iPTH); urine calcium, phosphorus, cyclic AMP and GMP. Both the pCT preparations produced, at the same time after administration, a hypocalcemic effect (P less than 0.01) which was not dose related, without any modification of urinary calcium excretion, implying that both doses are able to inhibit completely bone destruction. Despite the blood calcium decrease, no significant modifications in plasma iPTH levels were observed. pCT administration did not modify the urinary excretion of cyclic AMP, while it increased the urinary levels of cyclic GMP, particularly at the higher dose employed. Blood phosphorus decrease and urinary phosphate excretion increase were observed only after the administration of 160 MRC units of pCT. These observations suggest that the effects on urinary cyclic GMP and on blood and urine phosphorus are not mediated by PTH but could be the result of a direct action of calcitonin seen only when high doses are employed. In conclusion, one MRC unit of pCT is sufficient to inhibit bone resorption.