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Topical lidocaine–prilocaine spray for the treatment of premature ejaculation: a proof of concept study

International Journal of Impotence Research volume 15, pages 277281 (2003) | Download Citation

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Abstract

Premature ejaculation (PE) is the most common sexual dysfunction in men. Since heightened sensitivity of the glans is implicated in PE, it seems reasonable that reducing this sensitivity could have a delaying effect on intravaginal ejaculation latency time (IVELT) without adversely affecting the sensation of ejaculation. We have developed a local anesthetic combination, in a metered-dose aerosol delivery system, that delivers lidocaine and prilocaine in base form without organic solvents. The drug can be easily removed prior to vaginal penetration, circumventing the need for a condom that most patients find undesirable. Herein, we report on a prospective open-label pilot study investigating the safety and efficacy of this novel delivery system for topical local anesthetic to the glans penis aimed at prolonging the IVELT in patients who self-reported having PE. This was an open-label prospective pilot study. The lidocaine–prilocaine (LP) aerosol delivered 7.5 mg lidocaine and 2.5 mg prilocaine, both in base form, per actuation. A total of 14 men who had been referred to urology clinics with the problem of PE were recruited. Consent was obtained from both subjects and their partners. Couples were asked to time their IVELT without treatment on one encounter, and then on five subsequent encounters were asked to apply the spray to the glans penis, leave on for 10–15 min, wipe off carefully before intercourse. The IVELT was timed with a stopwatch and then both partners were asked to rate their individual satisfaction relative to baseline without treatment. They were also asked to document any adverse events or comments. In all, 11 patients completed the study. The average IVELT increased from 1 min:24 s to 11 min:21 s (P=0.008) representing an average eight-fold increase. No subjects experienced a decrease in IVELT. The average satisfaction score for both subjects and partners was 1.0; on a scale where −1 was worse, 0 the same, +1 better and +2 much better. Topical LP spray, applied to the glans penis 15 min before intercourse, prolongs ejaculation time significantly and improves sexual satisfaction in both men with PE and their partners. The glandular numbness, noticed in only two cases, did not adversely affect the quality of the orgasm. Occasionally, a patient reported difficulty maintaining an erection while waiting the required 15 min between application of the spray and the initiation of intercourse.

Introduction

Premature ejaculation (PE) remains the most common sexual dysfunction in men.1 Although progress is being made in elucidating its causal mechanisms, the disparate variety of techniques and drugs available for its treatment has met only limited success. For instance, behavioral interventions were reported to be remarkably effective with initially satisfactory results in the vicinity of 90%;2 unfortunately, the success rates decline markedly to less than 25% at 3 y.2,3 Systemic drugs have proven to have variable levels of efficacy,4 but are plagued by side effects that are generally considered unacceptable, in the long term, in otherwise healthy men. Equally discouraging, the effect of these medications is temporary since the symptoms return upon their discontinuation. Therefore, it is evident that further avenues of treatment are an appropriate line of inquiry for PE.

The early Freudian-based causal hypothesis of PE has been revised and largely abandoned in favor of physiological facts.2 A heightened sensitivity of the glans is currently believed to be a fundamental initiating factor in PE. Therefore, it would be anticipated that reducing the sensitivity of the glans would translate into a delaying effect on intravaginal ejaculation latency time (IVELT) without adversely affecting the sensation of ejaculation. Two studies using topical local anesthetic creams have reported prolonged IVELTs, but exhibit significant drawbacks.5,6 The use of lidocaine–prilocaine (LP) cream reported by Berkovich et al6 required a 30-min application of the cream under a condom and resulted in numbness of the whole shaft of the penis. A more drastic approach to desensitization involves ‘neurotomy’ of the dorsal nerves of the penis.7 This invasive and irreversible measure is reported to be effective but has failed to gain wide support in the medical community.

We have developed a LP spray that is easy to administer, remains adherent to the skin after application and only provides anesthesia of the glans.8 The drug can be easily removed prior to vaginal penetration, circumventing the need for a condom that most patients find undesirable. Herein we report on a prospective open-label pilot study investigating the safety and efficacy of this novel delivery system for topical local anesthetic to the glans penis aimed at prolonging the IVELT in patients who self-reported having PE.

Methods

Although local anesthetics alone are incapable of penetrating intact skin, when applied to nonkeratinized membranes such as the mouth and glans penis, the onset of anesthesia is relatively quick, with good penetration. LP bases are both low melting point solids that, when combined, have a melting point below room temperature. This effect is well recognized and is known as a eutectic mixture. We have developed an aerosol formulation of the lidocaine/prilocaine combination that provides a metered dose delivery of 7.5 mg lidocaine base plus 2.5 mg of prilocaine base per metered dose actuation. No solvents are required so there is less risk of stinging on application, while the slightly oily texture provides good adherence to the glans but is easily washed off with water once the anesthetic effect is established.

The project was designed as a prospective, open-label pilot (proof-of-concept) investigation on the safety and efficacy of a new delivery form for a topical anesthetic. The study was approved by the University Ethics Review Board. Written informed consent was obtained from both patients and their partners.

Patients

In all 14 patients ages 23–70 y (mean 42), who self reported sexual dissatisfaction due to primary PE and were referred to Urology clinic, and their partners, were recruited to the study. All were heterosexual and in a stable monogamous marital relationship, not by protocol requirement but by random referral. In every instance, the patient's partners actively participated in the study. Exclusion criteria were age under 18 y and known allergy of subject or partner to amide local anesthetics. A detailed history was obtained from each patient, with particular reference to his sexual history. The onset and duration of PE, the severity of the problem and associated factors, treatments tried and their effects were documented. Current status of the problem and treatments being used were documented.

Treatment

Each patient was provided with a metered-dose aerosol canister that delivered a eutectic liquid mixture of 7.5 mg lidocaine base and 2.5 mg prilocaine base per actuation. They were instructed to apply at three to five applications (30–50 mg) directly onto the glans penis, leaving it in situ for at least 15 min. The number of applications was dependent on the size of the glans and the spray of the aerosol; patients were instructed to cover the glans completely. The drug mixture has to be removed after this period to avoid contamination of the partner.

Protocol

Subjects were provided with a diary, a stopwatch and the local anesthetic aerosol, which they were shown how to apply. They were also given report cards to enter subjective and objective information. They timed their IVELT using the stopwatch provided and rated their level of satisfaction. The first encounter was without treatment and served as the baseline. The satisfaction score without treatment was rated as a zero on a scale of −1 (worse than without treatment), 0 (same as without treatment), +1 (better) and +2 (much better). For the next five consecutive encounters, they were asked to use the spray; using at least three doses to cover the glans in a thin film of drug for about 15 min, then carefully wiping off the residual film with a warm, wet cloth and initiating intercourse in their ‘usual’ fashion. Subjects and their partners were instructed to avoid contaminating other parts of their bodies, especially their fingers, with the spray.

Both partners were asked to record, independently, their satisfaction scores along with the measured IVELT and any problems, side effects or differences that they noticed.

Results

Of the 14 patients, 11 completed the study. Two patients dropped out of the study and would not return any data. One patient, who we considered a treatment failure, found that although he was able to enjoy more prolonged foreplay, he still ejaculated before intromission or had difficulty maintaining an erection and was therefore unable to register any intravaginal time. However, he did feel that the treatment had enhanced his sexual relationship and asked to continue using the spray outside the study.

For the 11 completed patients, the average baseline IVELT increased from 1 min:24 s (standard deviation 1 : 07) to 11 min:21 s (s.d. 10 : 43) representing an average nine-fold increase over the baseline (range 1.4–18). None of the subjects experienced a decrease in IVELT scores. The average satisfaction scores were 1.0 (range 0–2) for the subjects and 1.0 (range –0.5 to 2) for their partners. The individual results are shown in Table 1.

Table 1: IVELT and satisfaction estimates by subjects (s) and their partners (p) before and during treatment with the LP spray

Statistical analysis: Using two-tailed paired test, the mean treatment IVELT (mean=11:21, s.d.= 10:43) was significantly longer than the baseline IVELT (mean=1:24, s.d.+1:07) (t=−3.3, P-value= 0.008) using an α=0.5 and an 80% power to detect a difference. The difference remained significant using the Wilcox signed rank test (z=−2.9, P-value=0.003).

Adverse events:

  1. Numbness: Two subjects and their partners reported problems related to the feeling of numbness of both the penis and the vagina. One couple felt that this occurred despite taking care to wipe off the excess with a warm cloth before penetration. One patient reported ‘burning’ on application at the first encounter, but did not have that problem subsequently.

  2. Erectile difficulty: Three subjects reported erectile difficulties trying to maintain an erection while waiting for the 15 min required by the protocol. One patient found that he could add low-dose sildenafil (25 mg) to prolong the erectile episode.

Discussion

This study was designed as a proof-of-concept only. As such, it has shown that the aerosol mixture applied to the glans penis results in a delay in the IVELT in most patients and that the treatment is largely free of significant local adverse effects. No systemic effects were reported by any patient.

PE is the most common form of sexual dysfunction in men. Two self-report studies in normal men reveal a prevalence rate of 30–40%.9,10 Masters and Johnson11 loosely define PE as a condition in which ejaculation occurs with minimal sexual stimulation prior to, upon, or shortly after vaginal penetration and before the person and/or his partner desires it. Most clinical studies evaluating the efficacy of various treatments for PE select an IVELT of less than 2 min as the criterion for defining PE.4 This rigid criteria, in our view, need to be complemented with the couple's perception of adequacy of their needs to achieve sexual satisfaction. The measurement of IVELT should be used only as a parameter to determine the efficacy of an intervention. For a study like this, however, measuring IVELT is mandatory to establish drug activity.

The ejaculatory process consists of two sequential reflexes that make up the ejaculatory mechanism.12 The afferent input is triggered by stimulation of penile touch and/or vibratory receptors and transmitted via pudendal nerves to the sacral region of the spinal cord and ultimately to the limbic system of the brain. The limbic system, which controls emotional behavior, motivational drive and visceral physiological homeostasis such as temperature, hunger and sexual reflex, communicates with cerebral cortex, cerebellum, brain stem and spinal cord via the neurotransmitters norepinephrine, dopamine, serotonin (stimulators) and gamma-aminobutyric acid (inhibitor). Afferent input from the penis causes a rise in the level of these stimulatory neurotransmitters in the limbic system, which results in activation of the sympathetic nervous system. The sympathetic nerves of the T10-L2 paraspinal sympathetic ganglia to the vas deferens, prostate, seminal vesicles and bladder neck trigger ejaculation with the discharge of seminal fluid into the posterior urethra. Urethral proprioceptive sensation of the seminal emission triggers the efferent component of the ejaculatory mechanism via the sacral spinal cord and parasympathetic nerves to the bulbocavernosus (BC) and perineal muscles causing rhythmic contractions, which propel the seminal fluid out of the urethra.

Treatments for PE can be directed at any component of this complex mechanism and include psychoanalytic therapy, behavioral therapy (‘stop–start’ and ‘squeeze’ techniques), centrally acting pharmacological therapy (suppress stimulating or increase the inhibiting neurotransmitters) and topical local anesthetics to the penis. Although sympathetic blockade with the alpha receptor antagonist phenoxybenzamine13 and dopamine 2 receptor blockade with known antipsychotic agents such as the phenothiazines14 do delay ejaculation, the frequency and severity of side effects prevent widespread use of these drugs. Interestingly, dopamine 2 receptor agonists L-dopamine and apomorphine have been shown to decrease the number of penile intromissions to achieve ejaculation. Serotonin reuptake inhibitors increase the level of serotonin in the brain, inhibiting the ejaculatory reflex center with prolonged IVELTs up to 7–10 min.15 Again, the high prevalence of side effects prevents their widespread use.

Several studies have compared the neural circuitry of PE patients with age-matched controls. The findings suggest that patients with psychogenic PE have an abnormal autonomic reflex. These abnormalities include a lower penile vibratory threshold, a shorter BC latency time, higher BC-evoked potentials, or a greater mean amplitude of dorsal nerve and glans penis somatosensory-evoked potentials.16,17,18,19 These abnormalities provide a rational basis for the use of topical local anesthetic. Dampening the sensory input from the glans penis could return these patients to baseline neurocircuitry and thus increase their IVELT.

Lidocaine/prilocaine (EMLA®,AstraZenneca) and tetracaine (Ametop®,Smith&Nephew) are used in conjunction with moisturizing creams to anesthetize intact keratinized skin, taking 30–60 min to take effect. In a phase 1 study, 11 men applied 2.5 g of EMLA® to the glans and shaft of the penis and covered it with a condom for 30 min.6 The patients were then asked to estimate their IVELT and rate their ejaculation quality on a scale of −1 to +2, where 0 was rated as no change from before. Five men estimated their average IVELTs to be 15–20 min, four men recorded IVELTs of 5–10 min. Only two men were dissatisfied: one cited numbness of the penis, even though his IVELT went to 20 min and his wife was happy; while the other reported no increase in IVELT.

Another topical agent is ‘SS Cream’ that contains nine oriental herbs. Several studies have shown efficacy of this preparation with only minimal side effects.5 The only adverse effect of this preparation is a burning sensation occurring in a minority of patients. Whether this will demand the use of a condom, to prevent vaginal contamination, has not been clarified. The encouraging results reported with the use of SS cream, of course, require large multicenter, independent trials before it gains wide acceptance. Unfortunately, no confirmatory independent studies have been published beyond the ones from the originators of the product. An additional drawback of the cream is the uniqueness of the components and the absence of a detail description of the preparation of the mixture.

This study was designed to evaluate the potential usefulness and safety of a novel local anesthetic delivery system. The aerosol used provides a thin film of pure local anesthetic made up of a combination of lidocaine (75%) and prilocaine (25%) base after the propellant (HFC 134-a) has vaporized on release from the canister. This film of liquid base local anesthetic provides penetration of nonkeratinized epithelial membranes such as the glans, but not intact keratinized skin such as the shaft of the penis. Furthermore, the slightly oily nature of this combination at room temperature ensures that the drug stays at the site until it is absorbed or easily wiped off with a damp cloth.

LP cream has been reported to be efficacious, but required the use of a condom and resulted in anesthesia of the whole penile shaft. The spray circumvents these significant drawbacks. At present, it appears that the use of the topical anesthetic needs to be continuous. We do not know whether patients’ IVELTs will improve with continued use of the spray, making continued application unnecessary. These results need additional confirmation in a controlled study and with a longer follow-up. The optimum duration of application needs to be identified, as it could be considerably less than the 15 min we asked our subjects to wait. The difficulty with application technique and contamination of the partners’ labia need to be addressed with an application device designed for the glans. As we have repeatedly emphasized this was a pilot study, a controlled randomized trial is currently underway in North America and Europe utilizing this aerosol mixture.

Conclusions

Topical LP spray applied to the glans penis 15 min before intercourse prolongs ejaculation time and improves sexual satisfaction of both men with PE and their partners. The glandular numbness did not adversely affect the quality of the orgasm, but two patients reported difficulty maintaining an erection while waiting for onset of topical anesthesia and one partner complained of vaginal numbness. This drawback may be resolved with a decreased residence time (earlier removal) of the aerosol mixture.

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  1. Department of Anesthesiology, Queen's University, Kingston, Ontario, Canada

    • R Henry
  2. Department of Urology, Queen's University, Kingston, Ontario, Canada

    • A Morales

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Correspondence to A Morales.

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DOI

https://doi.org/10.1038/sj.ijir.3901011

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