Squarticles as a lipid nanocarrier for delivering diphencyprone and minoxidil to hair follicles and human dermal papilla cells

Delivery of diphencyprone (DPCP) and minoxidil to hair follicles and related cells is important in the treatment of alopecia. Here we report the development of "squarticles," nanoparticles formed from sebum-derived lipids such as squalene and fatty esters, for use in achieving targeted drug delivery to the follicles. Two different nanosystems, nanostructured lipid carriers (NLC) and nanoemulsions (NE), were prepared. The physicochemical properties of squarticles, including size, zeta potential, drug encapsulation efficiency, and drug release, were examined. Squarticles were compared to a free control solution with respect to skin absorption, follicular accumulation, and dermal papilla cell targeting. The particle size of the NLC type was 177 nm; that of the NE type was 194 nm. Approximately 80% of DPCP and 60% of minoxidil were entrapped into squarticles. An improved drug deposition in the skin was observed in the in vitro absorption test. Compared to the free control, the squarticles reduced minoxidil penetration through the skin. This may indicate a minimized absorption into systemic circulation. Follicular uptake by squarticles was 2- and 7-fold higher for DPCP and minoxidil respectively compared to the free control. Fluorescence and confocal images of the skin confirmed a great accumulation of squarticles in the follicles and the deeper skin strata. Vascular endothelial growth factor expression in dermal papilla cells was significantly upregulated after the loading of minoxidil into the squarticles. In vitro papilla cell viability and in vivo skin irritancy tests in nude mice suggested a good tolerability of squarticles to skin. Squarticles provide a promising nanocarrier for topical delivery of DPCP and minoxidil.

Effect of Tocopheryl Polyethylene Glycol Succinate on the Percutaneous Penetration of Minoxidil from Water/Ethanol/Polyethylene Glycol 400 Solutions

We described to achieve the local retention of minoxidil which has penetrated the skin with minimization of its absorption into the general circulation and elimination of local irritation induced by propylene glycol. The effect of tocopheryl polyethylene glycol succinate (TPGS) on the penetration flux of minoxidil and its retention in the skin from topical minoxidil formulations consisting of water, alcohol, and polyethylene glycol 400 was characterized by an experimental design of ten solvent formulations in this study. Results show that the addition of TPGS was only able to improve the solubility of minoxidil in those solvent systems containing higher proportions of water and PEG 400, and the extent of improvement was also more profound with the addition of TPGS at concentrations higher than 5%. For those solvent systems containing a higher fraction of alcohol, an insignificant change in minoxidil solubility with increasing added amounts of TPGS was noted even with the tendency to decrease the solubility of minoxidil with higher amounts of TPGS. Increasing the amount of TPGS added gradually increased the flux and the corrected flux from solvent formulations with a lower solubility parameter, but decreased those from solvent systems with a higher solubility parameter. With the addition of TPGS, solvent formulation F6 (alcohol:PEG 400 of 50:50) was demonstrated to be the optimal choice by having an improved local effect and a reduced systemic effect compared to the reference of 2% Regaine((R)). Tocopheryl polyethylene glycol succinate (TPGS) was mainly retained locally in the stratum corneum, and the amount was proportional to the increase in the amount of TPGS added to these ten solvent formulations.

After-rinsing hair growth promotion of minoxidil-containing amino alpha-cyclodextrins

Triamino alpha-cyclodextrin (CD) was synthesized and the inclusion complex with Minoxidil (MXD) was prepared. alpha-CD was azidated by modifying the 6-hydroxylmethyl CD rim with sodium azide. Then, mono-, di-, tri-, and tetra-azidocyclodextrins were separated by a flash column chromatography and reduced to the corresponding amines by hydrogenation with Pd/C. The substantivities of MXD included in either 2-hydroxypropyl alpha-CD (HP alpha-CD) or triamino alpha-CD were evaluated in vitro using hairless mice skins. After applying the preparations onto the skin and rinsing it, the amount of the drug left on the skin was determined using high-performance liquid chromatography (HPLC). It was the highest when the drug was included in triamino alpha-CD. The electrostatic interaction between the protonated amino CD and the negatively charged skin would be responsible for the relatively high substantivity. The in vivo hair growth promotion effect of each preparation was investigated, where the sample application onto the clipped backs of female mice (C57BL6) and the subsequent rinsing of the backs were done once a day for 30 days. Only MXD in triamino alpha-CD had hair growth promotion effect, possibly due to the significant substantivity.

Simultaneous effects of tocopheryl polyethylene glycol succinate (TPGS) on local hair growth promotion and systemic absorption of topically applied minoxidil in a mouse model

In this study, topical minoxidil solutions supplemented with TPGS in cosolvent systems of various compositions consisting of water, alcohol, and polyethylene glycol 400 were designed to evaluate the efficacy of promoting hair growth after topical application and the safety in terms of the amount of minoxidil absorbed through the skin into the circulation using C57BL/6J mice as a model. The commercial product of 2% Regaine) was used as the positive control. The role, which sulfotransferase activity plays in hair growth with treatment using minoxidil, was determined as well. The results revealed that the addition of 0.5% TPGS was able to enhance the proliferation of hair, but an increase in the amount of TPGS to 2% led to deterioration in the enhancement of hair growth. At the higher added amount (2.0%) of TPGS, the promotion of hair growth was slightly reduced for both cosolvent formulations F1 (100% water) and F3 (100% PEG 400), whereas it was reduced to a greater extent for the cosolvent formulations F8-F10. In comparison, the influences of cosolvent compositions with TPGS amounts of 0.0 and 2.0% on the promotion of hair growth were similar. On the contrary, variability in the promotion of hair growth by different solvent formulations was minimal when the added amount of TPGS was 0.5%. In general, a relationship between hair growth and sulfotransferase activities after topical application of 2% Regaine and minoxidil formulations containing various amounts of TPGS was not demonstrated. Plasma concentrations of minoxidil with 2% Regaine were found to be greater than those of 2% minoxidil in those cosolvent formulations containing various amounts of TPGS, while showing insignificant differences among those 10 cosolvent formulations with a fixed amount of TPGS. A tendency for the plasma concentration of minoxidil to increase after the topical administration of minoxidil formulations containing the higher amount of TPGS (2%) was noted.

Effect of cholesterol and ethanol on dermal delivery from DPPC liposomes

The main objective of the present work was to compare the dermal delivery of minoxidil (Mx), a lipophilic drug from ethosomes versus classic liposomes, containing different cholesterol (CHOL) concentrations. All the systems were characterized for shape, lamellarity, particle size and entrapment efficiency percentage (EE), by transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), laser diffraction and ultracentrifugation or dialysis methods, respectively. Multilamellar vesicles (MLVs) were obtained and one to six lamellae were visualized by CLSM. The presence of ethanol in the formulations affects the particle size in terms of reducing this parameter. In addition, it was possible to appreciate the influence of CHOL on the vesicle size, because it was increased, as CHOL concentration was higher. When the EE was determined by two different methods (ultracentrifugation and dialysis methods), a clear losing of entrapped drug by the ultracentrifugation method was observed, because the strong energy transmitted to the samples disrupted vesicles. Vesicles were non-occlusively applied on rat skin and the permeation pattern of the different systems, depth into the skin and the main permeation pathway were studied by using beta-carotene as a fluorescent probe. CLSM studies showed that ethosomal systems were much more efficient at delivering the fluorescent substance into the skin in terms of quantity and depth, than either liposomes or hydroalcoholic solutions.

Rapid determination of trace amounts of minoxidil in hamster skin follicles with various formulations using narrow-bore LC/EC

A sensitive liquid chromatographic method with electrochemistry (LC/EC) was developed for the determination of trace of minoxidil in hamster skin follicles after topical administration of the ear using various formulations. The minoxidil in the sebaceous glands of the hamster ear was isolated from the skin and the follicles in different skin layers were treated with aqueous trichloroacetic acid followed by acetonitrile. The supernatant was directly injected into the LC/EC system and minoxidil was detected by oxidation at +800 mV versus Ag/AgCl using a glassy carbon electrode. The analytical recoveries were between 94.4 and 103.1% and the linearity was excellent up to 250 microg/ml with a regression coefficient (r(2)) of 0.9988. The LC/EC and the widely used radiolabeled scintillation methods agree well and both show high sensitivities. The LC/EC method is rapid and cost-effective with a detection limit of only 1 ng/ml.

Rapid determination of minoxidil in human plasma using ion-pair HPLC

A rapid, simple and sensitive ion-pair high-performance liquid chromatography (HPLC) method has been developed for quantification of minoxidil in plasma. The assay enables the measurement of minoxidil for therapeutic drug monitoring with a minimum detectable limit of 0.5 ng ml(-1). The method involves simple, one-step extraction procedure and analytical recovery was complete. The separation was performed on an analytical 150 x 4.6 mm i.d. microbondapak C18 column. The wavelength was set at 281 nm. The mobile phase was a mixture of 0.01 M sodium dihydrogen phosphate buffer and acetonitrile (60:40, v/v) containing 2.5 mM sodium dodecyl sulphate adjusted to pH 3.5 at a flow rate of 1 ml/min. The column temperature was set at 50 degrees C. The calibration curve was linear over the concentration range 2-100 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 8%.

Transdermal delivery of mixnoxidil with block copolymer nanoparticles

We evaluated the effect of hydrodynamic size of self-assembled nanoparticles on skin penetration of minoxidil in vitro and in vivo. Self-assembled 40- and 130-nm nanoparticles, both containing minoxidil, were prepared by solvent evaporation of poly(-caprolactone)-block-poly(ethyleneglycol) and were applied onto the skin of both hairy and hairless guinea pigs in the Franz diffusion cell. In hairy guinea pig skin, the permeation of the minoxidil that incorporated in 40-nm nanoparticles was 1.5-fold higher in the epidermal layer and 1.7-fold higher in the receptor solution than that of 130-nm nanoparticles. Nanoparticle size dependence on the permeation behavior of minoxidil was not observed for hairless guinea pig skin in either the epidermal layer or the receptor solution. Phospholipid liposomes and ethanol-water admixture, on the other hand, containing the same amount of minoxidil did not show differences in the amount of permeation irrespective of the existence of hair follicles. Confocal microscopy coupled with in vivo and in vitro skin permeation results demonstrated that nanoparticles containing solutes penetrated mainly via shunt routes like hair follicles, resulting in skin absorption of solutes.

Minoxidil-containing dosage forms: skin retention and after-rinsing hair-growth promotion

Three kinds of topical dosage forms of minoxidil (MXD), namely vesicles, double emulsions, and an inclusion complex with hydoxypropyl-beta-cyclodextrin (HP-beta-CD), were prepared. The skin retention of MXD in the preparations was evaluated in vitro using hairless mouse skins. After applying the preparations onto the skin and rinsing it, the amount of the drug left on the skin was determined using HPLC. Retention was the highest when the drug was encapsulated in cationic vesicles. Nonionic vehicle, the double emulsion, and HP-beta-CD left no significant amount of the drug after rinsing the skin. Thus, an ionic interaction between the cationic vehicle and negatively charged skin is likely responsible for the relatively high skin retention. In vivo hair growth-promotion effect of each dosage form was investigated, in which the sample application onto the clipped backs of female mice (C57BL6) and the subsequent rinsing of the backs were done once a day for 30 days. Only MXD in the cationic vesicles had hair growth promotion effect, possibly due to significant skin retention.

Differential inhibition of hepatic and duodenal sulfation of (-)-salbutamol and minoxidil by mefenamic acid

OBJECTIVE

The aim of this investigation was to determine whether mefenamic acid and salicylic acid inhibit the sulfation of (-)-salbutamol and minoxidil in the human liver and duodenum, and if so, to ascertain whether the 50% inhibitory concentration (IC50) estimates are different in the two tissues.

METHODS

Sulfotransferase activities were measured for 10 mM (-)-salbutamol and 5 mM minoxidil, and the concentration of 3'-phosphoadenosine-5'-phosphosulphate-[35S] was 0.4 microM.

RESULTS

The IC50 estimates for (-)-salbutamol and minoxidil sulfation of mefenamic acid were 72 +/- 5.4 nM and 1.5 +/- 0.6 microM (liver), respectively, and 161 + 23 microM and 420 +/- 18 microM (duodenum), respectively. The figures for the liver were significantly lower (P < 0.0001) than those for the duodenum. The IC50 estimates for (-)-salbutamol sulfation of salicylic acid were 93 +/- 11 microM (liver) and 705 +/- 19 microM (duodenum, P < 0.0001). Salicylic acid was a poor inhibitor of minoxidil sulfation.

CONCLUSION

The IC50 estimates for (-)-salbutamol sulfation of mefenamic acid and salicylic acid are lower than their unbound plasma concentrations after standard dosing, suggesting that mefenamic acid and salicylic acid should inhibit the hepatic sulfation of (-)-salbutamol in vivo.

Pharmacokinetics of minoxidil in patients with cirrhosis and healthy volunteers

OBJECTIVES

To determine the effect of reduced hepatic function on the pharmacokinetics of minoxidil. The pharmacokinetics of antipyrine, lorazepam, and indocyanine green were included as indicators of hepatic function.

METHODS

Eight mild cirrhotics and eight healthy subjects received antipyrine (po), lorazepam (IV), indocyanine green (IV) and minoxidil 5 mg (po). Blood and urine were sampled for up to 72 h after each drug, and drug concentrations were measured by validated HPLC methods. Blood pressure and heart rate were measured for safety.

RESULTS

For unchanged minoxidil, the serum elimination rate constant was significantly smaller and mean residence time was significantly longer in cirrhotic patients. Urinary elimination rate constant for minoxidil glucuronide was significantly smaller and fraction of dose excreted in urine was significantly higher in cirrhotic patients. Antipyrine elimination was significantly slower for cirrhotic patients. No differences were observed in lorazepam pharmacokinetic parameters.

CONCLUSION

Pharmacokinetic analysis suggests a longer dosage interval may be appropriate in patients with hepatic impairment. In the absence of multiple-dose minoxidil pharmacodynamic studies in this population, minoxidil should be used as in other populations: begin with a modest dose, and adjust the dose based on clinical response.

Sulfation of minoxidil by multiple human cytosolic sulfotransferases

Minoxidil is an antihypertensive agent and hair growth promoter that is metabolized by sulfation to the active compound, minoxidil sulfate. Thermostable phenol sulfotransferase (TS PST or P-PST) was initially thought to catalyze the reaction, and the enzyme was designated minoxidil sulfotransferase (MNX-ST). Information about human ST activities toward minoxidil would be useful in developing the capacity to predict individual responses to minoxidil based on tissue levels of STs. Therefore, human STs were studied from platelet homogenates, partially purified platelets, scalp skin high speed supernatants and COS-1 cell cDNA expressed preparations using a radiochemical enzymatic assay with minoxidil as the substrate. Studies showed the presence of TS PST, TL (thermolabile) PST and MNX-ST activities in human scalp skin. Biochemical properties and correlation studies suggested that in addition to TS PST, the TL PST activity, another ST activity or both were involved in the reaction. Partially purified human platelet TL PST tested with minoxidil and dopamine showed identical thermal stabilities and similar responses to the inhibitors 2,6-dichloro-4-nitrophenol (DCNP) and NaCl. To characterize the activity of TL PST toward minoxidil, several biochemical properties of the enzyme expressed from a human liver cDNA clone were investigated. When assayed with minoxidil and dopamine, thermal stabilities of the expressed enzyme were identical and IC50 values for the inhibitors DCNP and NaCl were similar. It was also demonstrated that cDNA encoded human liver dehydroepiandrosterone sulfotransferase and estrogen sulfotransferase contributed to the sulfation of minoxidil. The results confirm that at least four human STs contribute to minoxidil sulfation. MNX-ST activity represents a combination of ST activities. The data indicate that multiple ST activities should be taken into account in attempts to predict the regulation of minoxidil sulfation and individual responses to minoxidil.

Relationship between serum concentrations, hemodynamic effects, and cardiovascular lesions in dogs treated with minoxidil

The threshold hemodynamic changes associated with the cardiovascular (CV) toxicity of minoxidil (MNX) in the dog, characterized by subendocardial necrosis, right atrial hemorrhagic lesions, and coronary vascular medial hemorrhage and necrosis, have not been defined. To determine the relationship between serum concentration, hemodynamic effects [heart rate (HR) and mean arterial pressure (MAP)] and CV toxicity, groups of female Beagle dogs were treated with a continuous iv infusion of dextrose (control) or 0.05, 0.14, 0.43, 1.44, or 4.32 mg/kg/day of MNX for 3 days. Serum concentration of free MNX increased in a dose-related manner and reached steady state within 4 hr after the initiation of infusion. There was a time-dependent, apparently dose-related increase in HR at all doses. MAP was decreased at > or = 0.14 mg/kg/day in a time- and dose-related manner. The doses or steady-state serum concentrations of MNX that showed no significant hemodynamic effects and CV toxicity were approximately 0.05 mg/kg or 3.0 +/- 0.6 ng/ml and 0.14 mg/kg or 7.3 +/- 2.0 ng/ ml, respectively. CV toxicity occurred at a serum concentration of 16.6 +/- 1.9 ng/ml where HR was increased by 65 +/- 11 beats/min and MAP was decreased by 34 +/- 2 mm Hg. A serum concentration of 7.3 +/- 2 ng/ml of MNX that increased HR by 47 +/- 14 beats/min and decreased MAP by 17 +/- 8 mm Hg was not associated with CV toxicity. This study suggests that the threshold hemodynamic effects associated with the CV toxicity of MNX in the dog are a function of an increase in HR by at least 55 beats/min and a decrease in MAP by at least 30 mm Hg. In conclusion, the safety margin of drugs like MNX, where the mechanisms of toxicity are known to be related to their pharmacologic effects, should be based on the ratio of the pharmacokinetically and metabolically adjusted dose/serum concentration of the drug that evokes comparable pharmacologic effects in the animal model and humans rather than on the ratio of the nontoxic dose/serum concentration in animals to the efficacious dose in humans.

N-sulphation of desipramine in the rat brain

1. Amine N-sulphotransferase (NST) activity with desipramine (DMI) as substrate was assayed in vitro in various areas of the rat brain. Biosynthesis of 3'-phosphoadenosine-5'-phospho35sulphate (PAPS) from sodium 35sulphate and ATP was also measured by coupling it to the sulphation of minoxidil by minoxidil sulphotransferase (MST). 2. For the DMI-NST reaction, an apparent Km = 0.5 mM was obtained for DMI and two apparent Kms = 0.3 and 1.7 microM for PAPS, whereas in the PAPS-generating reactions, Km for sodium 35sulphate = 20 microM. 3. Both the enzyme activities were widely distributed in rat brain. The rate of NST activity was 2-3 orders of magnitude lower than that of PAPS generation. N-sulphoconjugation of DMI, which is proposed as a possible biotransformation pathway of DMI in the rat brain, could conceivably be supported adequately by the 'active sulphate' generated within the same areas of the brain.

The pharmacologic basis of the cardiovascular toxicity of minoxidil in the dog

Minoxidil (MNX), like several other vasoactive drugs, causes cardiovascular toxicity in dogs by undetermined mechanisms. We studied the mechanism of cardiovascular toxicity of MNX [an adenosine triphosphate (ATP)-sensitive potassium channel opener] by blocking its pharmacologic effects with glyburide (an ATP-sensitive potassium channel blocker) in groups of 5 female beagle dogs treated orally for 2 days with 1.0 mg/kg/day of MNX alone or with glyburide given in 5 or 6 divided doses of 300 mg/kg at 2 hr before and after each dose of MNX and at 3-6-hr intervals thereafter. A third group of 5 dogs received glyburide alone in the same dosing regimen as in the combination group. Mean arterial pressure (MAP), heart rate (HR), the pharmacokinetics of MNX, and gross and microscopic changes in the heart were evaluated. Glyburide did not influence the pharmacokinetics of MNX but prevented or markedly attenuated the MNX-induced cardiovascular lesions (right atrial hemorrhagic lesions, subendocardial necrosis, or coronary arteritis) occurred in dogs whose MNX-induced hemodynamic effects were effectively blocked by glyburide. In conclusion, the cardiovascular toxicity of MNX in dogs is not caused by a direct toxic effect of MNX on the heart but apparently is related to the exaggerated pharmacologic/profound hemodynamic effects it elicits in the dog.

Penetration of minoxidil from ethanol/propylene glycol solutions: effect of application volume and occlusion

We have previously established that the relative concentrations of propylene glycol and ethanol as a binary solvent system have a significant effect on the skin penetration of 2% solutions of minoxidil at 50 microL/cm2. The present work extends these studies and investigates the penetration of minoxidil from the different vehicle combinations as functions of application volume and occlusion. Decreasing the application volume has a variable effect which depends on vehicle composition. Penetration of minoxidil from 100% ethanol solutions decreased linearly with application volume. Generally, irrespective of the volume applied, the penetration of minoxidil increased with increasing ethanol fraction with a maximum penetration at 90% ethanol. Penetration from all the formulations was enhanced upon occluding the skin, with greatest increase evident in solutions with higher volatile fraction. Penetration of minoxidil in vivo showed trends similar to those seen in vitro.

Relative influence of ethanol and propylene glycol cosolvents on deposition of minoxidil into the skin

Minoxidil, a potent antihypertensive, is moderately effective in the treatment of hair loss when it is applied to the scalp as a 2% solution in 60% ethanol, 20% propylene glycol and 20% water. Important questions remain concerning both the mechanism of delivery and the pathway of penetration of this drug from its ternary solvent system. Since preliminary studies in our laboratory indicated that water in the formulation influenced permeation far less than the other two solvents, we examined the relative deposition and penetration influences of binary combinations of ethanol and propylene glycol. When 50 microL/cm2 of the formulations was spread over hairless mouse skin sections mounted in Franz diffusion cells, only small amounts of minoxidil were actually recovered from the receiver compartments. Nevertheless, more minoxidil penetrated the skin as the proportion of ethanol in the mixtures was increased. To determine if these in vitro results formed a representative picture of the in vivo behaviors of these vehicles, selected deposition experiments were performed on live, anesthetized mice under experimental conditions similar to those used in the diffusion cell work. The good agreement between in vivo and in vitro studies may be a result of the relatively fast partitioning of the drug into the skin as compared to its diffusion through the skin.

Influence of application time and formulation reapplication on the delivery of minoxidil through hairless mouse skin as measured in Franz diffusion cells

Relationships are drawn between the extent of topical delivery of test compounds in solution and the period of residence of their formulation on the skin. The studies were performed using in vitro diffusion cell techniques and a test formulation containing 2% 3H-minoxidil dissolved in 60% ethanol, 20% water and 20% 14C-propylene glycol. The permeation of propylene glycol was effectively halted upon cleansing the skin surface; the skin had very little reservoir capacity for this substance. However, the rate of delivery of minoxidil was only slowed but not stopped upon cleansing. The suggestion here is that a reservoir of minoxidil is formed in the skin which is capable of sustaining an appreciable input of drug even after the skin's surface is scrupulously cleaned. Assay of epidermal concentrations of these species not only confirms the existence of the minoxidil reservoir but also shows that the degree of its tissue concentration is proportional to the time of residence of the formulation on the skin surface. Reapplication of blank vehicle to the cleansed surface had little to no effect on the permeation of the minoxidil and was similarly without effect on that of propylene glycol. While it comes as no surprise that formulation residence time is an important variable in topical delivery, this study demonstrates the complexities of quantitative dependencies of delivery on residence time.

Drug and vehicle deposition from topical applications: localization of minoxidil within skin strata of the hairless mouse

The cutaneous bioavailability of topical 2% minoxidil solution was verified in live hairless mice. Minoxidil and propylene glycol deposition on the skin surface, epidermis and dermis from the single-dose in vivo study were compared with the results from previous in vitro studies. A distinct difference is apparent in the epidermis where the in vitro values are 11-22 times higher than the in vivo values for minoxidil and 8-16 times higher for propylene glycol. The differences were not as great in the dermis. Percutaneous absorption of the drug appeared to be a very small fraction of the applied dose. Similarly shaped stratum corneum and plasma concentration profiles and the relatively constant dermal profiles of minoxidil and propylene glycol open the possibility of transappendageal routes being involved in percutaneous absorption. The greater amount of drug and vehicle found in the dermis from in vitro studies can be explained by the absence of dermal clearance. The overestimation in the amount of drug found in the epidermis in vitro may also be attributable to poor dermal clearance. On the whole, the study raises questions about the use of in vitro tissue dispositions for bioavailability assessment and bioequivalence demonstration.

Drug and vehicle deposition from topical applications: use of in vitro mass balance technique with minoxidil solutions

The disposition of minoxidil and propylene glycol from topical solutions was measured by using an in vitro mass balance technique. The experimental approach included assessment of the following compartments of the skin and the diffusion cell as a function of time: (1) donor compartment; (2) hairless mouse skin surface, epidermis, and dermis; and (3) receiver compartment. Excellent mass balance was achieved for minoxidil at three doses. However, the recovery of propylene glycol depended on both application volume and time. The experiment involving the evaporation of propylene glycol and water from the propylene glycol:ethanol:water (20:60:20, v/v) mixture, which was placed in the well of a tissue culture plate at room temperature and 37 degrees C, substantiated the loss of vehicles to the air. When a thin application of 20 microL/cm2 was used, 60% of the propylene glycol was unaccounted for after 16 h. The evaporation of propylene glycol concentrated the solution to supersaturation, precipitated out the drug, and then stabilized the thermodynamic activity of the drug in the vehicle. The amount of formulation applied influences the rate of concentration and, thus, the time at which minoxidil precipitates. The precipitation limits the amount of minoxidil that can be absorbed and leads to poor percutaneous absorption of drug from the formulation.

Interaction of minoxidil with pigment in cells of the hair follicle: an example of binding without apparent biological effects

To identify minoxidil target cells in hair follicles we followed the uptake of radiolabeled drug in mouse vibrissae follicles both in vitro and in vivo. Autoradiography showed that both 3H-minoxidil and 3H-minoxidil sulfate accumulated in the differentiating epithelial matrix cells superior to the dermal papilla, a distribution similar to that of pigment. Minoxidil localized in melanocytes, melanocyte processes, and areas of greater melanin concentrations within the epithelial cells. Although uptake of minoxidil was significantly less in unpigmented follicles, the drug stimulated proliferation and differentiation of both pigmented and unpigmented follicles. Labeled minoxidil bound to Sepia melanin and was displaced with unlabeled minoxidil and other electron donor drugs. This interaction with melanin acts as a targeting mechanism of minoxidil to pigmented hair follicles but has no apparent functional significance in hair growth. This work illustrates how measurement of drugs in hair may be biased by pigmentation.

Treatment-resistant alopecia areata. Response to combination therapy with minoxidil plus anthralin

Combination therapy with 5% minoxidil plus 0.5% anthralin was used to treat 51 patients with severe treatment-resistant alopecia areata. History of a cosmetically inadequate response to one or both drugs used as a single agent was present in 50 of the 51 patients. Therapy was relatively well tolerated except by 1 patient who developed a severe irritant reaction and was dropped from the study. Mild to moderate irritant dermatitis was seen in all remaining patients. Cosmetic response was seen in 5 (11%) of 45 patients who completed the 6-month study. Cosmetic response was maintained in 4 (80%) of 5 patients who continued treatment for as long as 84 weeks. All responders had evidence of hair regrowth by week 12. The rapidity and extent of hair regrowth were greater with combination therapy than with either drug used as a single agent. Serum and 24-hour urinary minoxidil determinations showed enhanced systemic minoxidil absorption, which was probably secondary to the irritant dermatitis in some patients; however, no clinical evidence of a systemic minoxidil effect was found. These data suggest that combination therapy using drugs with probable different mechanisms of action may provide a synergistic effect in alopecia areata.

Influence of tretinoin on the percutaneous absorption of minoxidil from an aqueous topical solution

Nineteen healthy male volunteers completed a three-way, randomized, crossover study to determine the effect of the synthetic retinoid, tretinoin, on percutaneous absorption of minoxidil. Subjects received, for 20 days, twice-daily administrations of 1 ml of an aqueous 2% topical minoxidil solution either alone, with once-daily applications of a 0.05% tretinoin cream, or with once-daily applications of a vehicle control cream. When minoxidil was coadministered with tretinoin cream, minoxidil absorption was increased nearly threefold, compared with a 1.3-fold increase in absorption observed with coadministration of vehicle control cream. Transepidermal water loss measurements, which are sensitive to changes in stratum corneum function, were also significantly increased with tretinoin. No treatment-related changes in stratum corneum thickness were observed on the basis of skin biopsy analysis. The findings indicate that percutaneous minoxidil absorption is enhanced by tretinoin as a result of increased stratum corneum permeability.

Uptake kinetics and the effect of minoxidil on human keratinocyte cultures

The antihypertensive drug minoxidil (Lonolox) is rapidly taken up by human keratinocytes (HaCaT-cells). After 3 h the uptake is half of its maximum. Specific minoxidil receptors could not be found. High minoxidil concentrations (greater than 100 micrograms/ml) inhibited the incorporation of thymidine into DNA (ED50 = 263 micrograms/ml) and the incorporation of amino acids into proteins (ED50 = 251 micrograms/ml). The inhibition was reversible up to a concentration of 400 micrograms/ml. In the presence of 100 micrograms/ml minoxidil, the cell division remained active for a longer period of time and a higher cell density was achieved as opposed to the parallel control group. A prolongation of the proliferative capability of keratinocytes may be partially responsible for the positive effect of minoxidil on hair growth.

Studies on the efficacy of methyl esters of n-alkyl fatty acids as penetration enhancers

The efficacy of the methyl esters of medium chain n-alkyl fatty acids as penetration enhancers was evaluated in vitro using various animal and human skins with minoxidil as the test drug. Both methyl nonanoate and methyl caprate at a 10% concentration were found to be effective penetration enhancers for a 2% solution of minoxidil in alcohol USP. The percent of the applied radioactive dose of minoxidil penetrated after 17 h was 5-8 times greater for methyl non-anoate and methyl caprate enhanced solutions than for a 2% solution of minoxidil in alcohol USP alone or with the addition of 10% Azone, dimethylsulfoxide (DMSO) or N,N-diethyl-m-toluamide (DEET). The penetration enhancing activity of methyl caprate was effective for human, mouse, and hamster skins. Methyl caprate also enhanced the penetration of vitamin D3, erythromycin, triamcinolone acetonide, testosterone, and hydrocortisone.

Disposition of minoxidil in patients with various degrees of renal function

The disposition of minoxidil was evaluated after a 5 mg oral dose in 24 subjects with various degrees of renal function. Patients were divided into four groups based on a 24-hour ambulatory creatinine clearance (Clcr): Group I (n = 6) Clcr greater than 90 mL/min, Group II (n = 6) Clcr 50-80 mL/min, Group III (n = 5) Clcr of 30-49 mL/min, and Group IV (n = 7) Clcr less than 30 mL/min. Blood and urine samples obtained over 36 hours were analyzed for minoxidil by a high pressure liquid chromatography technique. Maximum plasma concentration (Cmax) and time to reach Cmax did not differ among the four groups. The terminal elimination half-life was prolonged in Group IV subjects (8.87 +/- 6.12 hours) (mean +/- SD) compared to those in Groups I, II and III (1.38 +/- 0.16, 1.99 +/- 0.45 and 2.42 +/- 0.53 hours, respectively). Apparent total body clearance (Clp/F) decreased as renal function declined; Clp/F = 0.82(Clcr) + 21.8, r = 0.739, P = 0.0001. Renal clearance and apparent nonrenal clearance also were significantly correlated with Clcr. The apparent volume of distribution significantly increased as renal function declined. Thus, the disposition of minoxidil is significantly delayed and dosage adjustment may be necessary in patients with renal insufficiency.

Absorption of minoxidil after topical application: effect of frequency and site of application

The effect of application site and frequency on the systemic absorption of topical minoxidil was studied in 52 normal men. Subjects received 1 ml 3% minoxidil solution applied four, six, or eight times daily to the scalp or two, four, six, or eight times daily to the chest for 14 days. Serum and urine were collected and analyzed for minoxidil. No systemic minoxidil accumulation occurred from increasing application frequency to the scalp. Trends in the chest data suggest that absorption may have been lower with the twice-daily regimen. Absorption through the scalp and chest were similar for the lower-frequency regimens; however, trends in the eight-times-a-day regimens suggest that absorption may have been somewhat greater from application to the scalp. Systemic minoxidil accumulation resulting from frequent application is unlikely. The initial dose probably saturates the skin for a period of time longer than the dosing intervals examined.

The pharmacokinetics of 2.5- to 10-mg oral doses of minoxidil in healthy volunteers

The dose proportionality of minoxidil was investigated by studying its pharmacokinetics after administration of single, oral doses of 2.5, 5.0, and 10.0 mg. The study, which was a Latin square cross-over design, was performed in 30 young, nonobese, normal subjects. Treatments were separated by a 4-day washout period. Serum and urine levels of minoxidil were determined by high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA). Supine blood pressure and pulse were monitored during each study phase. Minoxidil concentrations determined by RIA were highly correlated with concentrations determined by HPLC; only the HPLC data was used in the pharmacokinetic analyses. No significant effects were observed for dose normalized Cmax, tmax, volume of distribution, minoxidil renal clearance, or the percentage of the dose excreted as either minoxidil or minoxidil glucuronide. Significant differences in apparent oral clearance, dose normalized AUC, and terminal elimination rate constant (beta) were observed between the 2.5-mg dose and the higher doses, but no differences in these parameters between the 5.0- and 10.0-mg doses were apparent. Thus, the available data support dose-independent pharmacokinetics for minoxidil over this range of doses. Repeated measures analysis of variance detected significant time and treatment effects on supine blood pressure and pulse rate, but the effects were generally small and of little clinical significance. The results support the hypothesis that minoxidil has little effect on blood pressure in normotensive subjects.