Pharmacokinetics and bioavailability of papaverine HCl following intravenous, peroral, rectal, vaginal, topical and buccal administration in beagle dogs

Non-aqueous formulations in topical ocular drug delivery - a paradigm shift?

Topical eyedrop application is the preferred route for drug delivery to anterior segment tissues; however, the challenge of overcoming the eye's anatomical and physiological barriers while minimising tissue toxicity has restricted developments in this field. Aqueous vehicles have traditionally been used, which typically require several additives and preservatives to achieve physiologically compatible and sterile eyedrops, elevating their toxicity potential. Non-aqueous vehicles have been suggested as efficient alternatives for topical drug delivery as they can address many of the limitations associated with conventional aqueous eyedrops. However, despite their obvious advantages, non-aqueous eyedrops remain poorly researched and few non-aqueous formulations are currently available in the market. This review challenges the conventional hypothesis that aqueous solubility is a prerequisite to ocular drug absorption and establishes a rationale for using non-aqueous vehicles for ocular drug delivery. Recent advances in the field have been detailed and future research prospects have been explored, pointing towards a paradigm shift in eyedrop formulation in the near future.

Ocular Distribution of Papaverine Using Non-aqueous Vehicles

Papaverine, a poorly soluble opium alkaloid, has recently been shown to reduce retinal inflammation due to which it may have therapeutic application in the management of Leber's hereditary optic neuropathy. In this study, papaverine eyedrops based on medium chain triglycerides were prepared and the effect of diethyl glycol monoethyl ether (DGME) on their ocular distribution was evaluated using an ex vivo porcine eye model. The route of drug penetration was also studied by orienting the eye to expose either only the cornea or the sclera to the formulation. Furthermore, in vivo studies were performed to confirm ocular tolerability and evaluate ocular drug distribution. Our results showed increased papaverine concentrations in the cornea and sclera in the presence of DGME but with a slight reduction in the retina-choroid (RC) drug concentration when administered via the corneal route, suggesting that DGME enhances drug accumulation in the anterior ocular tissues but with little effect on posterior drug delivery. In vivo, the papaverine eyedrop with DGME showed good ocular tolerability with the highest drug concentration being observed in the cornea (1.53 ± 0.28 μg/g of tissue), followed by the conjunctiva (0.74 ± 0.18 μg/g) and sclera (0.25 ± 0.06 μg/g), respectively. However, no drug was detected in the RC, vitreous humor or plasma. Overall, this study highlighted that DGME influences ocular distribution and accumulation of papaverine. Moreover, results suggest that for hydrophobic drugs dissolved in hydrophobic non-aqueous vehicles, transcorneal penetration via the transuveal pathway may be the predominant route for drug penetration to posterior ocular tissues. Graphical abstract.

Zaleplon loaded bi-layered chronopatch: A novel buccal chronodelivery approach to overcome circadian rhythm related sleep disorder

The aim of this study was to develop a novel buccal bi-layered chronopatch capable of eliciting pulsatile release pattern of drugs treating diseases with circadian rhythm related manifestation. Zaleplon (ZLP) was used as a model drug intended to induce sleep and to treat middle of night insomnia. The chronopatch was prepared adopting double casting technique. The first layer was composed of a controlled release patch containing ZLP-Precirol melt granules intended to release ZLP in a sustained manner to maintain sleep and to prevent early morning awakening. The second layer was composed of a fast release lyophilized buccal disc containing ZLP loaded SNEDDS (Z-SNEDDS) intended for rapid sleep induction. Pharmacokinetic parameters of ZLP from the chronopatch were compared to those of the immediate release capsule, Siesta®, as reference in Mongrel dogs using a randomized crossover design. The appearance of two peaks having two C_max and T_max proved the pulsatile release pattern. The increase in relative bioavailability of ZLP from the chronopatch was 2.63 folds. The results revealed the ability of the developed ZLP loaded bi-layered chronopatch to be a candidate for overcoming early morning awakening without middle of night dose administration.

Effect of intraurethral papaverine on penile erection in rats

OBJECTIVES

The aim of this study is to investigate erectile response to intraurethral administration of papaverine in rats.

MATERIAL AND METHODS

Male Sprague-Dawley rats were used in this study. Under urethane anesthesia, penis was exposed and intracavernous pressure (ICP) was recorded through a 23-gauge needle, which was inserted into right corpus cavernosum. Effects of intraurethral application of incremental doses of 0.2 ml papaverine gel (4-17.5 mg) on intracavernosal pressure were observed and compared with those of 0.4 mg papaverine applied into corpus cavernosum. Mean arterial blood pressure (MABP) and heart rate were also monitored.

RESULTS

The mean basal ICP was 8.9 +/- 1.8 mm Hg. Intraurethral administration of papaverine did not increase ICP at any doses used in this study. After intracavernous injection of papaverine (0.4 mg), a significant increase in the ICP occurred from resting (8.9 +/- 1.8 mm Hg) to a peak at 57.5 +/- 9.9 mm Hg and persisted for 22.3 +/- 6.7 minutes (p < 0.05). The latter application significantly decreased MABP (22.3 +/- 3.1 mm Hg; p < 0.05).

CONCLUSIONS

Intraurethral administration of papaverine does not seem to be an alternative to other erectile dysfunction treatment modalities. However, further studies on animals are necessary at higher concentrations or in combination with other mucosal enhancers to increase the effect of intraurethral administration of papaverine.

Hepatotoxicity related to intracavernous pharmacotherapy with papaverine

OBJECTIVES

To determine the incidence of hepatotoxicity related to self-administration of intracavernous papaverine or papaverine/phentolamine (bimix).

METHODS

From October 1994 through June 1996, we retrospectively reviewed the medical records of 71 consecutive patients diagnosed with organic erectile dysfunction (ED) and receiving intracavernous injection therapy. Inclusion criteria were documentation of normal baseline liver function tests (LFTs), a minimum of 6 months of follow-up that included LFTs, at least one self-injection every 2 weeks, and no other prior or concurrent treatment for ED. Thirty evaluable patients satisfied the inclusion criteria and formed group 1. Mean age was 63 years (range 40 to 77), mean follow-up was 18 months (range 6 to 32), and mean number of injections per month was 5.7 (range 3 to 12). An age-matched population of 20 patients (mean age 69 years, range 46 to 90) without ED but with similar comorbid risk factors formed the control group (group 2). All patients in group 2 had routine long-term follow-up of LFTs (mean 52 months, range 10 to 1 14).

RESULTS

Two patients (6.67%) from group 1 had elevated LFTs during treatment: one experienced a mild elevation in alanine aminotransferase and the other developed transient elevations of total bilirubin and aspartate aminotransferase 6 months after beginning therapy. Both patients reported a history of alcohol abuse. Both patients remained asymptomatic. Neither patient required discontinuation of therapy. One patient (5%) from group 2 developed an elevation of total bilirubin at a follow-up of 12 months.

CONCLUSIONS

Routine monitoring of LFTs is probably unnecessary during intracavernous pharmacotherapy. Patients with a history of alcohol abuse or liver disease, however, should be followed up more closely when papaverine is selected for intracavernous injection. In these patients, LFTs should be obtained before initiating treatment and at 6-month intervals.

Pharmacokinetics of vasoactive substances administered into the human corpus cavernosum

The pharmacokinetics of vasoactive substances injected into the corpus cavernosum for the treatment of erectile dysfunction have not been investigated to date. We measured the local intracavernous and peripheral venous concentration curves of papaverine and prostaglandin E1, and its primary metabolite 15-keto-13,14-dihydro-prostaglandin E1 in an intra-individual comparison after intracavernous injection. Papaverine was measured with high performance liquid chromatography and prostaglandin E1 was measured with a specially adapted radioimmunoassay. The results demonstrate that papaverine is slowly draining into the systemic circulation, showing slightly elevated levels in the peripheral blood 30 and 60 minutes after injection. Prostaglandin E1 shows a much faster decrease in local concentrations with no measurable increase in the periphery, probably due to the short half-time after lung passage. Measurement of the primary metabolite proves a local degradation of prostaglandin E1 in the corpus cavernosum into the biologically inactive 15-keto-13,14-dihydro-prostaglandin E1, which also shows a slight increase in the peripheral circulation due to the longer half-time of approximately 8 minutes. The data provide good explanation for the clinical finding of a markedly decreased incidence of priapism with the use of prostaglandin E1, which can be shown to be locally metabolized, compared to papaverine, which is retained in the corpus cavernosum in cases of nonvenogenic impotence.