Antiparkinsonian efficacy of a novel transdermal delivery system for (+)-PHNO in MPTP-treated squirrel monkeys.

We examined the ability of the antiparkinsonian agent (+)-4-propyl-9-hydroxynaphthoxazine (PHNO) to enter the systemic circulation in therapeutic concentrations after continuous transdermal absorption in squirrel monkeys rendered parkinsonian by MPTP. Direct subcutaneous administration of (+)-PHNO in the dose range of 2.5 to 20 micrograms/kg restored locomotor activity to levels seen in normal monkeys for approximately 1 hour. Application of transdermal patches capable of delivering, into an infinite sink, an estimated 2.6 micrograms/cm2/h of (+)-PHNO over a skin surface area of 4.78 to 19.12 cm2 also restored locomotor activity to the normal range during a 24-hour period. We suggest the use of transdermal application of PHNO as a novel drug delivery system for the improved management of Parkinson's disease.

Identification of oxidative degradates of the thrombin inhibitor, 3-(2-phenethylamino)-6-methyl-1-(2-amino-6-methyl-5-methyleneca rboxamidomethylpyridinyl)pyrazinone, using liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry.

Liquid chromatography/mass spectrometry was used to identify reaction products from a solution of 3-(2-phenethylamino)-6-methyl-1-(2-amino-6-methyl-5-methyleneca rboxamidomethylpyridinyl)pyrazinone (L-375,378) and hydrogen peroxide, a system that generates high levels of the oxidative degradates which form in the tablets and intravenous (i.v.) solutions of L-375,378. Two major hydrogen peroxide reaction products of L-375,378 (m/z 407) with m/z values of 369 and 370 were separated and identified. Both compounds were products of ring opening with elimination of three carbon atoms from the center pyrazinone ring. The structural assignments for these two products were alpha-amidinoamide and alpha-diamide compounds, respectively. In addition, five products (m/z 423) with a molecular weight 16 Da greater than that for L-375,378 were separated. Further liquid chromatography/tandem mass spectrometry experiments indicated that three of these M + 16 products were phenolic derivatives of L-375,378. Among them, the para-hydroxy compound has been verified using an authentic standard. The other two phenolic compounds were believed to be the meta- and ortho-hydroxy derivatives of L-375,378. The fourth M + 16 product was derived from hydroxylation of the methyl group on the center pyrazinone ring. The fifth M + 16 product was derived from oxidation on the aminopyridine moiety, most likely N-oxide of the pyridine ring. Other minor hydrogen peroxide reaction products were not studied in detail because they did not appear in tablets or i.v. formulations.

Improved method for rhesus monkey or rat skin preparation and cryosectioning for topical or transdermal skin distribution studies.

A method for preparing skin biopsies for cryosectioning was developed to accurately obtain samples from specific areas of the dermis, while minimizing contamination with epidermal tissue. Routine preparation of 6mm punch biopsies from freshly excised, full-thickness skin produced contraction and folding of the edges of the biopsy prior to mounting for snap-freezing and cryosectioning. Sample orientation was ruined, and cryosections were heterogeneous with respect to dermal structures and/or to dermal and epidermal layers. Biopsy artifacts were prevented by prefreezing skin over dry ice prior to taking biopsies. The biopsies were held frozen on dry ice until they were mounted on cryostat pegs with flattened, frozen OCT surfaces; then they were snap-frozen in chilled OCT in an isopentane bath cooled with liquid nitrogen. The method for determining skin level homogeneity of cryosections consisted of taking 10 mu m cryosections for histology between sections sampled for drug level analysis. The histological sections were fixed in 5% acetic acid in methanol and stained with hematoxylin and eosin to define the skin layers and structures associated with each sample for analysis. Histological sections from prefrozen skin had fewer processing artifacts, and dermal cryosections free of epidermal contamination were dramatically increased compared to the routine procedure.

Initial evaluation of transdermal timolol: serum concentrations and beta-blockade.

The serum concentrations and beta-blockade after dermal application of timolol ointment were evaluated in six healthy men (21-31 years old; 74-82 kg). Two patches (25 cm2) containing placebo and either 30 (n = 2) or 60 mg (n = 4) timolol base were randomly applied to the chest for 30 h. Serial serum concentrations of timolol were measured by a radioligand receptor assay. Bicycle ergometry, at a predetermined workload, was performed before and at 3, 8, 24, and 48 h after patch application; mean +/- SD heart rates (beats/min) at these times were 167 +/- 2, 158 +/- 7, 125 +/- 7, 120 +/- 5, and 150 +/- 5 (last 3 values: p less than 0.05 from pretreatment), and beta-blockade was evident in all subjects. Measurable serum concentrations in the therapeutic range were achieved in all subjects. The change in exercise-induced heart rate (y) was closely related to log timolol serum concentration (x) (y = -36 X - 5.3; r = -0.92; p less than 0.001). Based on the amount of timolol in the residual ointment, 50-60% of the original timolol dosage was delivered from the patch. Skin irritation under the patch compared with placebo was minimal. Further studies are warranted to assess the potential clinical utility of transdermal timolol.

The antiparkinsonian actions and pharmacokinetics of transdermal (+)-4-propyl-9-hydroxynaphthoxazine (+PHNO): preliminary results.

(+)-4-Propyl-9-hydroxynaphthoxazine (+PHNO) is a potent dopamine agonist that has been administered transdermally to four patients with Parkinson's disease and "on-off" fluctuations. Skin patches of increasing size were used to treat these patients, who also received infrequent doses of oral levodopa if required. The effect of +PHNO was measured as an increased duration of action of individual levodopa doses. The clinical effect measured in this way was directly proportional to the plasma concentrations of +PHNO achieved. The plasma concentrations of +PHNO began to rise 4-6 h after patch application and reached a steady state by 24 h. The final plasma concentration of +PHNO was proportional to the area of skin covered.

Regiospecific intestinal absorption of the HIV protease inhibitor L-735,524 in beagle dogs.

PURPOSE: To evaluate regional intestinal absorption and the feasibility of sustained release dosage form development for an HIV protease inhibitor, L-735,524, METHODS: L-735,524 free base or sulfate salt was administered orally as suspension, solution or in solid dosage forms to fasted or fed Beagle dogs. Delayed-release dosage forms with "slow" or "fast" in vitro dissolution rates were evaluated in vivo to assess plasma concentration profiles. In addition, drug was administered directly into the jejunum or colon of animals, and drug concentrations determined in portal circulation to characterize absorption from these sites. RESULTS: L-735,524 sulfate was well absorbed orally form a solution or capsule formulation if fasted animals' stomachs were preacidified with citric acid solution. A free base suspension, delivered in divided doses to fed animals, was also well absorbed. Prototype extended release dosage forms of L-735,524 produced a reduction in peak plasma levels but failed to prolong absorption and extend plasma concentrations compared to an immediate release capsule. Administration of L-735,524 sulfate solution (pH < 3) as bolus solution or by infusion into the jejunum resulted in rapid but incomplete absorption compared to oral gavage. The free base suspension (pH 6.5) delivered into jejunal or colonic regions did not produce measurable systemic plasma concentrations. CONCLUSIONS: Extended release formulations did not prolong absorption of L-735,524 in dogs. Optimal L-735,524 absorption was dependent on solubility in an acidic environment in the duodenum.