Papaverine hydrochloride in peripheral blood and the degree of penile erection

Pharmacokinetics of moxisylyte in healthy volunteers after intravenous infusion and intracavernous administration with and without a penile tourniquet

The concentration-time profiles of metabolites of moxisylyte (or thymoxamine), an alpha-blocking agent, were investigated in 18 healthy volunteers after intravenous (i.v.) and intracavernous (i.c.) administrations with and without a tourniquet. Four metabolites, unconjugated desacetylmoxisylyte (DAM), DAM glucuronide, and DAM and monodesmethylated DAM (MDAM) sulfates, were found in plasma and urine. For all metabolites, tmax was significantly increased after i.c. administrations and Cmax was significantly decreased. Maximum plasma level of unconjugated DAM was lower after i.c. administration with (1.81-fold) and without (1.26-fold) a tourniquet than after i.v. administration (43.6 +/- 19.6 ng/ml). The elimination half-life of each metabolite showed no change between the three treatments. The difference of 19 min between the mean residence times of unconjugated DAM after i.c. administration with and without a tourniquet may be compared with the difference between the mean duration of the intumescence, that is, 19 min (73 and 54 min with and without a tourniquet, respectively). Total percentages of metabolites recovered in urine were 66.2 +/- 20.9, 61.4 +/- 12.2, and 58.7 +/- 9.1% after i.v. and i.c. administrations with and without a tourniquet, respectively. In conclusion, tourniquet placed before i.c. administration increased the mean residence time of unconjugated DAM of approximately 25% and seemed to increase the efficacy of the drug in healthy volunteers.

Intracavernous pharmacotherapy: treatment for the aging erectile response

Fueled by serendipity, observation, and direct scientific investigations over the last 15 years the normal mechanisms of erection, and the pathophysiology of erectile dysfunction have been revealed. The demonstrations that vasoactive injections could produce penile erection without benefit of psychic or tactile stimuli revolutionized the diagnosis and treatment of erectile dysfunction by providing a direct test of end organ integrity or deficiency. This article reviews the clinical pharmacology of vasoactive corporal agents and outlines what has been surmised about the aging erectile response.

Papaverine topical gel for treatment of erectile dysfunction

Intracavernous injection of vasoactive substances has been shown to be an effective means of treatment of organic erectile dysfunction. However, up to 50% of men eventually discontinue treatment often because of lack of spontaneity and needle phobia. This study was done as a phase I, placebo controlled, nonblinded investigation of the safety and efficacy of a topical papaverine gel in the treatment of erectile dysfunction. Of 20 men with organic impotence 17 completed the trial and 13 of these patients had spinal cord injuries. After application of a 15% and 20% papaverine base gel to the scrotum, perineum and penis, cavernous artery diameter was significantly increased (36%, p < 0.001) as assessed by color flow Doppler ultrasound. Peak systolic flow velocity increased 26%. Only 3 of 14 patients achieved an increase in cavernous artery diameter of 75% or more and 2 of 14 had a peak systolic flow velocity of 25 cm. per second or more after application of a topical base gel. Similar findings were present when only the patients with spinal cord injury were analyzed. The effect of a papaverine base in producing flow alterations to the penis is dose-dependent. A diminution in blood pressure was present at 15 and 30 minutes after application to the forearm, and the heart rate diminished from 68 to 62 beats per minute after application to the genitalia. No patient was symptomatic. Serum papaverine levels were not elevated over pre-application values. No hepatotoxic effects were demonstrated. Full clinical erections (mean duration 38.7 minutes) were present in 3 patients but were also present with the placebo preparation (mean duration 8.0 minutes). In conclusion, topical papaverine gel appears to be safe and well tolerated after application to the genitalia, and increases blood flow to the penis with a 15% and 20% base preparation. Minimal systemic absorption occurs and, thus, effects are probably from local absorption. Topical therapy appears to augment reflex erections in the spinal cord injury patient and may be especially beneficial in this population. Further investigation is warranted at higher concentrations or in combination with different skin absorption enhancers.

Pharmacokinetics of moxisylyte in healthy volunteers after intravenous and intracavernous administration

The concentration-time profiles of metabolites of moxisylyte, an alpha-adrenergic receptor blocking agent, in the plasma of 12 healthy volunteers were investigated after intravenous (iv) and intracavernous (ic) administrations. The study was conducted in open, randomized, Latin Squares. Plasma levels of moxisylyte and its biotransformation products were assayed by a specific high-performance liquid chromatography method with fluorescence detection. Three metabolites, unconjugated desacetylmoxisylyte (DAM), conjugated DAM, and conjugated monodesmethylated DAM (MDAM), were found in plasma. After iv administration, unconjugated DAM appeared in plasma in < 5 min; the formation of this metabolite is slightly lower after ic administration (half-life, 6.08 +/- 2.33 min). Maximum plasma levels (57.2 +/- 29.4 ng/mL) and area under the curve of concentration versus time (43.3 +/- 11.4 micrograms.h/L) were significantly lower after ic administration than after iv administration (352.8 +/- 287.6 ng/mL and 152.6 +/- 0.247 micrograms.h/L, respectively). For conjugated DAM, the time to reach the maximum concentration is significantly increased after ic administration (0.9 h instead of 0.46 h) and the maximum concentration is significantly decreased (163.5 ng/mL instead of 203.4 ng/mL). The other pharmacokinetic parameters show no change between the two routes of administration. The pharmacokinetic parameters computed for MDAM are in the same range after iv and ic administrations, and there are no significant statistical differences.

Moxisylyte plasma kinetics in humans after intracavernous administration

Obtaining and sustaining an erection are common problems for the male spinal cord injury patient. Intracavernous injection of vasoactive substances offers a new treatment option but it must be approached with caution in this population. In this work, the use of an alpha-adrenergic blocking agent, moxisylyte, after intracavernous administration for complete paraplegic patients with erectile impotence is described. During this study, the pharmacokinetic profile of moxisylyte has been defined. Unchanged moxisylyte is not found in plasma, this drug is immediately metabolized after administration. Three metabolites were found in plasma: desacetylmoxisylyte (DAM), conjugated DAM, and conjugates of desmethylated DAM (MDAM). Maximum plasma levels of 72.3 ng ml-1, 301.4 ng ml-1, and 88.8 ng ml-1 are obtained 0.22 h, 0.9 h, and 2.08 h after drug administration for these three metabolites, respectively. The elimination half-lives are 0.89 h, 2.16 h, and 5.32 h and the MRT, 1.38 h, 3.23 h, and 8.45 h, respectively. No side-effects were noted, only one patient presented sleepiness. Successful erections (10 to 25 min) were obtained in all patients and no priapism was noted.