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

Efficacy and safety of low-dose oral minoxidil in the management of androgenetic alopecia

INTRODUCTION

Treating alopecia can be challenging. The available treatments are topical minoxidil, low-dose oral minoxidil (LDOM), and 5-α reductase inhibitors like finasteride and dutasteride. Only topical minoxidil and finasteride 1 mg daily are FDA-approved, while the rest are used off-label. Recent research has suggested that oral minoxidil may be a safe and effective treatment for both female androgenetic alopecia (female AGA) and male androgenetic alopecia (male AGA).

AREAS COVERED

In this review, we explore the pharmacokinetics, mechanism of action, safety, and efficacy of oral minoxidil. Additionally, we discuss its effectiveness compared to other treatments available for female AGA and male AGA.

EXPERT OPINION

LDOM has demonstrated a favorable efficacy and safety profile in several trials. Subsequently, its use for the treatment of male AGA and female AGA is increasing. However, its use remains off-label, and through increased usage, we will get a better idea of the best dosage and monitoring guidelines. LDOM has also been used with some effectiveness in other forms of hair loss.

Safety of Low-Dose Oral Minoxidil in Patients With Hypertension and Arrhythmia: A Multicenter Study of 264 Patients

BACKGROUND AND OBJECTIVE

Systemic adverse effects (AE) are a major concern of low-dose oral minoxidil (LDOM) treatment, especially in patients with arterial hypertension or arrhythmia. The objective of this study was to evaluate the safety of LDOM in patients with hypertension or arrhythmia.

PATIENTS AND METHODS

Retrospective multicenter study of patients with hypertension or arrhythmia treated with LDOM for any type of alopecia.

RESULTS

A total of 254 patients with hypertension [176 women (69.3%) and 78 men (30.7%)] with a mean age of 56.9 years (range 19-82) were included. From them, the dose of LDOM was titrated in 128 patients, allowing the analysis of 382 doses. Patients were receiving a mean of 1.45 (range 0-5) antihypertensive drugs. Systemic AE were detected in 26 cases (6.8%) and included lightheadedness (3.1%), fluid retention (2.6%), general malaise (0.8%), tachycardia (0.8%) and headache (0.5%), leading to LDOM discontinuation in 6 cases (1.5%). Prior treatment with doxazosin (P<0.001), or with three or more antihypertensive drugs (P=0.012) was associated with a higher risk of discontinuation of LDOM.

CONCLUSIONS

LDOM treatment showed a favorable safety profile in patients with hypertension or arrhythmia, similar to general population.

Safety of Low-Dose Oral Minoxidil in Patients With Hypertension and Arrhythmia: A Multicenter Study of 264 Patients

BACKGROUND AND OBJECTIVE

Systemic adverse effects (AE) are a major concern of low-dose oral minoxidil (LDOM) treatment, especially in patients with arterial hypertension or arrhythmia. The objective of this study was to evaluate the safety of LDOM in patients with hypertension or arrhythmia.

PATIENTS AND METHODS

Retrospective multicenter study of patients with hypertension or arrhythmia treated with LDOM for any type of alopecia.

RESULTS

A total of 254 patients with hypertension [176 women (69.3%) and 78 men (30.7%)] with a mean age of 56.9 years (range 19-82) were included. From them, the dose of LDOM was titrated in 128 patients, allowing the analysis of 382 doses. Patients were receiving a mean of 1.45 (range 0-5) antihypertensive drugs. Systemic AE were detected in 26 cases (6.8%) and included lightheadedness (3.1%), fluid retention (2.6%), general malaise (0.8%), tachycardia (0.8%) and headache (0.5%), leading to LDOM discontinuation in 6 cases (1.5%). Prior treatment with doxazosin (P<0.001), or with three or more antihypertensive drugs (P=0.012) was associated with a higher risk of discontinuation of LDOM.

CONCLUSIONS

LDOM treatment showed a favorable safety profile in patients with hypertension or arrhythmia, similar to general population.

Low-Dose Oral Minoxidil for Alopecia: A Comprehensive Review

Low-dose oral minoxidil (LDOM) has demonstrated a promising safety and efficacy profile in the treatment of various hair disorders, including male androgenetic alopecia (AGA) and female-pattern hair loss (FPHL); however, it lacks FDA approval. The usual LDOM starting dose for male AGA is 1-5 mg/day, depending on physician preference and the patient's condition. For FPHL, it is 0.5-1 mg/day. The maximum dose is generally 5 mg/day. If patients respond well without major side effects, the dose may be gradually increased since the LDOM's efficacy appears to be dose-dependent. Patients may use LDOM long term if the treatment outcome is satisfactory. The common side effects of LDOM are hypertrichosis and cardiovascular symptoms. Females are more prone to hypertrichosis than males. The side effects of LDOM can be categorized as (a) dose-dependent type A side effects (hypertrichosis and cardiovascular symptoms) and (b) idiosyncratic type B side effects (pericardial effusion). Minoxidil acts via multiple pathways. Although minoxidil has a relatively short half-life of around 4 h, its hypotensive effect may last approximately 72 h. Effective treatments for alopecia are limited. Therefore, LDOM could be an important addition to the available therapies for managing some hair disorders, including AGA.

Low-dose Oral Minoxidil in the Treatment of Alopecia: Evidence and Experience-based Consensus Statement of Indian Experts

Alopecia is a highly prevalent condition worldwide including in India. There are different types of alopecia with differing etiology, presentation, and hence treatment. Androgenetic alopecia represents the most common form of hair loss affecting male as well as female population termed as male and female pattern hair loss, respectively. Several treatment options are available for the treatment of alopecia with often unsatisfactory results resulting in psychological distress among such patients. Topical minoxidil is known to be effective in the treatment of alopecia. However, oral minoxidil is not currently approved for the treatment of alopecia. This expert consensus is prepared to provide guidance to the clinicians regarding the use of oral minoxidil in the treatment of alopecia. Extensive literature review was performed to prepare the draft consensus which was then revised based on the suggestions and comments from the experts. The final draft was circulated to the experts for review and approval. This consensus document provides overview of evidence related to oral minoxidil and consensus from the experts for its use in the treatment of minoxidil.

Comparison of oral minoxidil, finasteride, and dutasteride for treating androgenetic alopecia

Background Androgenetic alopecia (AGA) is the most common cause of hair loss, often challenging to treat. While oral finasteride (1 mg/day) is an FDA-approved treatment for male AGA, oral minoxidil and oral dutasteride are not approved yet. However, clinicians have been increasingly using these two drugs off-label for hair loss. Recently, Japan and South Korea have approved oral dutasteride (0.5 mg/day) for male AGA.Efficacy and safety A probable efficacy ranking, in decreasing order, is- dutasteride 0.5 mg/day, finasteride 5 mg/day, minoxidil 5 mg/day, finasteride 1 mg/day, followed by minoxidil 0.25 mg/day. Oral minoxidil predominantly causes hypertrichosis and cardiovascular system (CVS) symptoms/signs in a dose-dependent manner, whereas oral finasteride and dutasteride are associated with sexual dysfunction and neuropsychiatric side effects.Pharmacokinetics and pharmacodynamics The average plasma half-lives of minoxidil, finasteride, and dutasteride are ∼4 hours, ∼4.5 hours, and ∼5 weeks, respectively. Minoxidil acts through multiple pathways to promote hair growth. It has been shown as a vasodilator, an anti-inflammatory agent, a Wnt/β-catenin signaling inducer, and an antiandrogen. Finasteride inhibits 5 α-reductase (5AR) type II isoenzyme, while dutasteride inhibits both type I and type II. Thus, dutasteride suppresses DHT levels more than finasteride in the serum and scalp.

The Role of Paracellular Transport in the Intestinal Absorption and Biopharmaceutical Characterization of Minoxidil

The purpose of this study was to evaluate mechanisms behind the intestinal permeability of minoxidil, with special emphasis on paracellular transport, and elucidate the suitability of minoxidil to be a reference drug for Biopharmaceutics Classification System (BCS). The permeability of minoxidil (vs. metoprolol) was evaluated in-silico, in-vitro using both the PAMPA assay and across Caco-2 cell monolayers, as well as in-vivo in rats throughout the entire intestine. The permeability was studied in conditions that represent the different segments of the small intestine: upper jejunum (pH 6.5), mid small intestine (pH 7.0), distal ileum (pH 7.5), and colon (pH 6.5). Since we aimed to investigate the paracellular transport of minoxidil, we have also examined its permeability in the presence of quercetin (250 µM), which closes the tight junctions, and sodium decanoate (10 mM), which opens the tight junctions. While metoprolol demonstrated segmental-dependent rat and PAMPA permeability, with higher permeability in higher pH regions, the permeability of minoxidil was pH-independent. Minoxidil PAMPA permeability was significantly lower than its rat permeability, indicating a potential significant role of the paracellular route. In rat intestinal perfusion studies, and across Caco-2 monolayers, tight junction modifiers significantly affected minoxidil permeability; while the presence of quercetin caused decreased permeability, the presence of sodium decanoate caused an increase in minoxidil permeability. In accordance with these in-vitro and in-vivo results, in-silico simulations indicated that approximatelly 15% of minoxidil dose is absorbed paracellularly, mainly in the proximal parts of the intestine. The results of this study indicate that paracellular transport plays a significant role in the intestinal permeability of minoxidil following oral administration. Since this permeation route may lead to higher variability in comparison to transcellular, these findings diminish the suitability of minoxidil to serve as the low/high BSC permeability class benchmark.

Development and Qualification of a Physiologically Based Pharmacokinetic Model of Finasteride and Minoxidil Following Scalp Application

In this study, we aimed to develop and qualify a PBPK model for scalp application using two drugs with marked differences in physicochemical properties and PK profiles. The parameters related to scalp physiology, drug PK, and formulations were incorporated into a Multi-Phase and Multi-Layer (MPML) Mechanistic Dermal Absorption (MechDermA) model within the Simcyp® Simulator V17. The finasteride PBPK model was linked to its effect on dihydrotestosterone (DHT) levels in plasma and scalp using an indirect response model. Predicted PK (and PD for finasteride) profiles and parameters were compared against the clinically reported data and justified by visual predictive checks and two-fold error criteria for model verification. The PBPK/PD model for finasteride reasonably demonstrated an ability to predict its respective PK and PD profiles, and parameters following scalp application under various clinical scenarios. Using the same scalp physiological input parameters, the minoxidil PBPK model was then developed and satisfactorily qualified with independent clinical datasets. Collectively, these results suggested that the established PBPK model may have broader utility for other topical formulations intended for scalp application.

Topical and oral minoxidil for hair disorders in pediatric patients: What do we know so far?

Minoxidil is a strong arterial vasodilator, first introduced as an antihypertensive medication. In dermatology, topical minoxidil (TMX) has been used for many types of alopecia. TMX is not FDA-approved in patients under 18 years old and there are no guidelines for its pediatric use. Low-dose oral minoxidil (OMX) has been used off-label for hair loss treatment in adults expecting to achieve better therapeutic compliance and greater clinical efficacy. However, little is known about TMX and OMX in pediatric population. the literature presented on TMX and OMX in children to date was reviewed. The terms "minoxidil", "child", "children", "childhood", and "infant" were used to perform a literature search in MEDLINE through PubMed. The search was limited to articles about humans and available in English. While 25 relevant articles were selected, duplicate titles were excluded. This article pointed out the use of minoxidil in several pediatric hair diseases. Even when used topically, dermatologists should be aware of potential risks of systemic absorption. In particular situations, OMX in very low doses may be considered. To date, there are no guidelines regarding the ideal dose or minimum age for using the drug topically or systemically.

Minoxidil versus placebo in the treatment of arterial wall hypertrophy in children with Williams Beuren Syndrome: a randomized controlled trial

Background

Insufficient elastin synthesis leads to vascular complications and arterial hypertension in children with Williams-Beuren syndrome. Restoring sufficient quantity of elastin should then result in prevention or inhibition of vascular malformations and improvement in arterial blood pressure.

Methods

The aim of this study was to assess the efficacy and safety of minoxidil on Intima Media Thickness (IMT) on the right common carotid artery after twelve-month treatment in patient with Williams-Beuren syndrome. We performed a randomized placebo controlled double blind trial. All participants were treated for 12 months and followed for 18 months. The principal outcome was assessed by an independent adjudication committee blinded to the allocated treatment groups.

Results

The principal outcome was available for 9 patients in the placebo group and 8 patients in the minoxidil group. After 12-month treatment, the IMT in the minoxidil group increased by 0.03 mm (95% CI -0.002, 0.06) compared with 0.01 mm (95%CI - 0.02, 0.04 mm) in the placebo group (p = 0.4). Two serious adverse events unrelated to the treatment occurred, one in the minoxidil and 1 in the placebo group. After 18 months, the IMT increased by 0.07 mm (95% CI 0.04, 0.10 mm) in the minoxidil compared with 0.01 mm (95% CI -0.02, 0.04 mm) in the placebo group (p = 0.008).

Conclusion

Our results suggest a slight increase after 12 and 18-month follow-up in IMT. More understanding of the biological changes induced by minoxidil should better explain its potential role on elastogenesis in Williams-Beuren syndrome.

Trials registration

US National Institutes of Health Clinical Trial Register (NCT00876200). Registered 3 April 2009 (retrospectively registered).

Electronic supplementary material

The online version of this article (10.1186/s12887-019-1544-1) contains supplementary material, which is available to authorized users.

Drug-Mediated Shortening of Action Potentials in LQTS2 Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Cardiomyocytes (CMs) derived from human induced pluripotent stem cells (hiPSCs) are now a well-established modality for modeling genetic disorders of the heart. This is especially so for long QT syndrome (LQTS), which is caused by perturbation of ion channel function, and can lead to fainting, malignant arrhythmias and sudden cardiac death. LQTS2 is caused by mutations in KCNH2, a gene whose protein product contributes to I_Kr (also known as HERG), which is the predominant repolarizing potassium current in CMs. β-blockers are the mainstay treatment for patients with LQTS, functioning by reducing heart rate and arrhythmogenesis. However, they are not effective in around a quarter of LQTS2 patients, in part, because they do not correct the defining feature of the condition, which is excessively prolonged QT interval. Since new therapeutics are needed, in this report, we biopsied skin fibroblasts from a patient who was both genetically and clinically diagnosed with LQTS2. By producing LQTS-hiPSC-CMs, we assessed the impact of different drugs on action potential duration (APD), which is used as an in vitro surrogate for QT interval. Not surprisingly, the patient's own β-blocker medication, propranolol, had a marginal effect on APD in the LQTS-hiPSC-CMs. However, APD could be significantly reduced by up to 19% with compounds that enhanced the I_Kr current by direct channel binding or by indirect mediation through the PPARδ/protein 14-3-3 epsilon/HERG pathway. Drug-induced enhancement of an alternative potassium current, I_KATP, also reduced APD by up to 21%. This study demonstrates the utility of LQTS-hiPSC-CMs in evaluating whether drugs can shorten APD and, importantly, shows that PPARδ agonists may form a new class of therapeutics for this condition.

Minoxidil is a potential neuroprotective drug for paclitaxel-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of cancer treatment. No medication has been shown to be effective in the treatment of CIPN. This study aims to integrate the image-based high-content screening, mouse behavior models and mechanistic cell-based assays to discover potential neuroprotective drugs. Among screened compounds, minoxidil showed the most potent neuroprotective effect against paclitaxel, with regard to neurite outgrowth of dorsal root ganglia (DRG). Minoxidil protected mice from thermal insensitivity and alleviated mechanical allodynia in paclitaxel-treated mice. The ultrastructure and quantified G-ratio of myelin integrity of sciatic nerve tissues supported the observations in mouse behavioral tests. The mechanistic study on DRG neurons suggested that minoxidil suppressed neuroinflammation and remodeled the dysregulation of intracellular calcium homeostasis provoked by paclitaxel. Importantly, minoxidil showed a synergistic anti-tumor effect with paclitaxel both in tumor xenograft models of cervical and breast cancer. Interestingly, the quantitative assays on hair length and hair growth both exhibited that minoxidil significantly improved the hair quality after chemotherapy. Since minoxidil is a drug approved by the Food and Drug Administration (FDA), the safety and biocompatibility are well documented. The immediate next step is to launch an early-stage clinical trial intending to prevent CIPN by minoxidil.

Prolonged hypotension induced by ingesting a topical minoxidil solution: analysis of minoxidil and its metabolites

Case

A 47-year-old man ingested 60 mL of a topical solution (3,000 mg minoxidil) and presented with prolonged hypotension. Treatment with dopamine hydrochloride and noradrenaline provided blood pressure control. Serum unchanged minoxidil concentrations at 4 and 16 h after ingestion were 4,994 and 33.9 ng/mL, respectively. Urine concentrations of unchanged minoxidil, minoxidil-O-glucuronide, and minoxidil-N-O-sulfate at 16 h after ingestion were 360.4, 1,953, and 104.5 ng/mL, respectively.

Outcome

The serum unchanged minoxidil concentration rapidly decreased over a short interval. However, the patient needed to receive vasopressor support for the first 4 days after being admitted to the hospital. The urine minoxidil-O-glucuronide concentration was higher than the concentrations of unchanged minoxidil and minoxidil-N-O-sulfate.

Conclusion

Although the serum concentration of unchanged minoxidil rapidly decreased, ingesting large amounts of a topical minoxidil solution can have serious and prolonged cardiovascular effects. Analyzing the minoxidil-O-glucuronide concentration in urine is useful for diagnosing minoxidil poisoning.

A non-human primate model for investigating drug-induced risk of orthostatic hypotension and sympathetic dysfunction: Preclinical correlate to a clinical test

INTRODUCTION

Drug induced orthostatic hypotension (OH) is an important clinical concern and can be an unexpected hurdle during drug development. OH is defined as an abnormal decrease in blood pressure (BP) triggered by a rapid postural change. The sympathetic nervous system is critical for controlling normal cardiovascular function and compensatory responses to changes in posture. Thus, OH can also serve as a surrogate indicator of sympathetic dysfunction. However, preclinical conscious models for investigating risk of OH and/or sympathetic dysfunction are lacking. Herein, we describe a conscious nonhuman primate (NHP) model which mimics the widely used clinical tilt table test for OH.

METHODS

Male, Cynomolgus NHPs (n = 7-8) implanted with radio-telemetry transmitters were placed in modified tilt chairs in a supine position. Subsequently, a 90° head up tilt was performed for 3 min followed by return to the supine position. BP and heart rate were continuously monitored. Test compounds were administered either intravenously or via oral gavage in a crossover design, with blood samples collected at the end of the each tilt to assess total drug concentrations.

RESULTS

Tilt responses were assessed following treatment with positive control compounds that cause sympathetic dysfunction; hexamethonium (ganglionic blocker) and prazosin (alpha-1 adrenergic receptor antagonist). Both compounds induced marked OH as evidenced by robust and sustained BP reduction in response to a head up tilt (decrease of 25-35 mmHg for hexamethonium, decrease of 21-44 mmHg for prazosin). OH incidence rates increased in a dose-dependent manner. OH incidences following treatment with minoxidil (vasodilator) were markedly lower to those observed with hexamethonium and prazosin indicating the role of sympathetic dysfunction in causing OH.

DISCUSSION

These data demonstrate that the NHP tilt test is a valuable model for investigating OH risk. This model fills an important preclinical gap for assessing such a safety concern and can be applied to programs where a sympathetic deficit and/or OH are anticipated or clinically observed.

Intestinal permeability study of minoxidil: assessment of minoxidil as a high permeability reference drug for biopharmaceutics classification

The purpose of this study was to evaluate minoxidil as a high permeability reference drug for Biopharmaceutics Classification System (BCS). The permeability of minoxidil was determined in in situ intestinal perfusion studies in rodents and permeability studies across Caco-2 cell monolayers. The permeability of minoxidil was compared with that of metoprolol, an FDA reference drug for BCS classification. In rat perfusion studies, the permeability of minoxidil was somewhat higher than that of metoprolol in the jejunum, while minoxidil showed lower permeability than metoprolol in the ileum. The permeability of minoxidil was independent of intestinal segment, while the permeability of metoprolol was region-dependent. Similarly, in mouse perfusion study, the jejunal permeability of minoxidil was 2.5-fold higher than that of metoprolol. Minoxidil and metoprolol showed similar permeability in Caco-2 study at apical pH of 6.5 and basolateral pH of 7.4. The permeability of minoxidil was independent of pH, while metoprolol showed pH-dependent transport in Caco-2 study. Minoxidil exhibited similar permeability in the absorptive direction (AP-BL) in comparison with secretory direction (BL-AP), while metoprolol had higher efflux ratio (ER > 2) at apical pH of 6.5 and basolateral pH of 7.4. No concentration-dependent transport was observed for either minoxidil or metoprolol transport in Caco-2 study. Verapamil did not alter the transport of either compounds across Caco-2 cell monolayers. The permeability of minoxidil was independent of both pH and intestinal segment in intestinal perfusion studies and Caco-2 studies. Caco-2 studies also showed no involvement of carrier mediated transport in the absorption process of minoxidil. These results suggest that minoxidil may be an acceptable reference drug for BCS high permeability classification. However, minoxidil exhibited higher jejunal permeability than metoprolol and thus to use minoxidil as a reference drug would raise the permeability criteria for BCS high permeability classification.

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%.

Clinical pharmacokinetics of vasodilators. Part I

Understanding the mechanism of action and the pharmacokinetic properties of vasodilatory drugs facilitates optimal use in clinical practice. It should be kept in mind that a drug belongs to a class but is a distinct entity, sometimes derived from a prototype to achieve a specific effect. The most common pharmacokinetic drug improvement is the development of a drug with a half-life sufficiently long to allow an adequate once-daily dosage. Developing a controlled release preparation can increase the apparent half-life of a drug. Altering the molecular structure may also increase the half-life of a prototype drug. Another desirable improvement is increasing the specificity of a drug, which may result in fewer adverse effects, or more efficacy at the target site. This is especially important for vasodilatory drugs which may be administered over decades for the treatment of hypertension, which usually does not interfere with subjective well-being. Compliance is greatly increased with once-daily dosing. Vasodilatory agents cause relaxation by either a decrease in cytoplasmic calcium, an increase in nitric oxide (NO) or by inhibiting myosin light chain kinase. They are divided into 9 classes: calcium antagonists, potassium channel openers, ACE inhibitors, angiotensin-II receptor antagonists, alpha-adrenergic and imidazole receptor antagonists, beta 1-adrenergic agonist, phosphodiesterase inhibitors, eicosanoids and NO donors. Despite chemical differences, the pharmacokinetic properties of calcium antagonists are similar. Absorption from the gastrointestinal tract is high, with all substances undergoing considerable first-pass metabolism by the liver, resulting in low bioavailability and pronounced individual variation in pharmacokinetics. Renal impairment has little effect on pharmacokinetics since renal elimination of these agents is minimal. Except for the newer drugs of the dihydropyridine type, amlodipine, felodipine, isradipine, nilvadipine, nisoldipine and nitrendipine, the half-life of calcium antagonists is short. Maintaining an effective drug concentration for the remainder of these agents requires multiple daily dosing, in some cases even with controlled release formulations. However, a coat-core preparation of nifedipine has been developed to allow once-daily administration. Adverse effects are directly correlated to the potency of the individual calcium antagonists. Treatment with the potassium channel opener minoxidil is reserved for patients with moderately severe to severe hypertension which is refractory to other treatment. Diazoxide and hydralazine are chiefly used to treat severe hypertensive emergencies, primary pulmonary and malignant hypertension and in severe preeclampsia. ACE inhibitors prevent conversion of angiotensin-I to angiotensin-II and are most effective when renin production is increased. Since ACE is identical to kininase-II, which inactivates the potent endogenous vasodilator bradykinin, ACE inhibition causes a reduction in bradykinin degradation. ACE inhibitors exert cardioprotective and cardioreparative effects by preventing and reversing cardiac fibrosis and ventricular hypertrophy in animal models. The predominant elimination pathway of most ACE inhibitors is via renal excretion. Therefore, renal impairment is associated with reduced elimination and a dosage reduction of 25 to 50% is recommended in patients with moderate to severe renal impairment. Separating angiotensin-II inhibition from bradykinin potentiation has been the goal in developing angiotensin-II receptor antagonists. The incidence of adverse effects of such an agent, losartan, is comparable to that encountered with placebo treatment, and the troublesome cough associated with ACE inhibitors is absent.

Relationship between contact time of applied dose and percutaneous absorption of minoxidil from a topical solution

Twenty-two healthy male volunteers completed a four-way, multiple-dose, randomized crossover study to determine the relationship between contact time of applied drug on the scalp and minoxidil absorption from a 2% topical solution. One milliliter of solution was applied twice daily over 150 cm2 of bald scalp to each subject for 6 days. Unabsorbed drug was washed off the scalp after 1, 2, 4, and 11.5 h of contact time in each of four treatments. Cumulative urinary excretion profiles within steady-state, 12-h dosing intervals were well described by straight lines for all treatments, indicating that systemic minoxidil elimination was rate controlled by constant, zero-order percutaneous drug absorption. The extent of minoxidil absorption, expressed as steady-state urinary excretion of unchanged minoxidil, minoxidil glucuronide, or the sum of these, increased in a disproportionate manner with increase in contact time of drug on the scalp. Relative to the amount absorbed after a contact time of 11.5 h, absorption was approximately 50% complete by 1 h and greater than 75% complete by 4 h. This suggests that minoxidil absorption from the vehicle into skin occurs rapidly relative to diffusion through skin. The rate of minoxidil absorption from vehicle into skin was characterized as nonlinear, whereas minoxidil excretion into urine was rate controlled by diffusion from one or more components of the skin which apparently serve as a reservoir, or depot, for minoxidil.

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.