A 6-Month Trial of the Efficacy and Safety of Triptorelin Pamoate (11.25 mg) Every 3 Months in Children with Precocious Puberty: A Retrospective Comparison with Triptorelin Acetate

Gonadotrophin-releasing hormone (GnRH)-dependent central precocious puberty (CPP) is caused by the early activation of the hypothalamic-pituitary-gonadal axis [1, 2]. The principal aim of the treatment of CPP is to suppress gonadotrophin secretion and the associated secretion of gonadal sex steroids. Such suppression stabilises and reverses the symptoms of CPP, such as an increased growth velocity and increased epiphyseal maturation, and prevents the risks of early menarche and reduced adult height [3].

GnRH analogues [4, 5, 6, 7] represent the standard of care for the treatment of CPP [7]. GnRH analogues are available in depot formulations that can be injected once a month or every 3 months, and these formulations effectively suppress gonadal sex steroids in children with CPP [3, 8, 9, 10, 11, 12, 13]. Furthermore, a considerable amount of data on the use of GnRH analogues shows that pubertal development is reversed or stabilised, and growth is normalised without adversely affecting either the resumption of puberty or the final height and body mass index (BMI) [6, 14, 15, 16, 17, 18, 19, 20, 21].

Triptorelin, a synthetic GnRH analogue, is approved for use in CPP as 1-month and 3-month depot formulations (Ipsen Pharma, Paris, France) in a number of countries. Triptorelin is available as an acetate salt and a pamoate salt; the active molecule is identical in these two formulations (fig. 1). The acetate salt was used in the first formulations (daily and monthly) of triptorelin to be developed [22, 23]. Pamoate salts are widely used to enable slow-release formulations of pharmaceutical agents [24, 25, 26, 27], having physicochemical properties suitable for sustained release. Therefore, a triptorelin pamoate salt was also developed, which additionally facilitated a more consistent production. Subsequent new regulatory registrations have been obtained with triptorelin pamoate salt formulations [28].

The efficacy and safety of the triptorelin acetate 3-month formulation (11.25 mg) in patients with CPP was previously reported on [3], but the potential pharmacological effect of different pharmaceutical salts cannot be ignored [24], and it is important to assess the efficacy and safety of all formulations based on different salts. Here we report the data from a study of the 3-month formulation (11.25 mg) of triptorelin pamoate (the TP Study) and compare the results with those from the previous trial of triptorelin acetate 11.25 mg (the TA Study) [3], as both trials had a similar design.

Both studies were phase III, multicentre, single-stage, non-comparative, open-label trials. The TP Study was conducted at 18 centres in France (ClinicalTrials.gov identifier NCT00564850). The TA Study was conducted at 15 centres in Belgium, France, Italy, and Spain, and its design and results have been previously reported [3].

The studies were conducted in accordance with good clinical practice requirements. Local ethics approval and written informed consent were obtained from each patient or their parent/legal guardian before enrolment in the study and in accordance with the ethical principles stated in the Declaration of Helsinki.

Both studies recruited patients with proven CPP, and their inclusion/exclusion criteria were very similar (table 1) [3]. The only important difference between the studies was the cut-off for the luteinising hormone (LH) peak during the GnRH test, which was lower in the TP Study than in the TA Study (>5 and ≥7 IU/l, respectively) [3]. Patients were removed from the study if there was a lack of efficacy (as assessed by the investigator), if significant drug-related adverse events (AEs) occurred, or by patient request.

The planned duration of the TP Study was 8 months, including screening. Once enrolled in the TP Study, each patient underwent a 2-month screening period to confirm the diagnosis of CPP before starting treatment. The patients received an intramuscular injection of triptorelin pamoate 11.25 mg at baseline and 3 months after baseline. Clinical and biological follow-up occurred at 3 and 6 months. In addition, biological tests were performed at 1, 2, 4, and 5 months.

The design of the TA Study [3] was similar to that of the TP Study, except that the TA Study included further injections of triptorelin acetate at 6 and 9 months after baseline, and follow-up continued for 12 months [3]. For the purpose of fair comparison, the current paper only presents and compares the results of the TA Study from baseline to 6 months.

In both studies, the triptorelin concentration was measured before each injection and at each monthly visit by a validated radioimmunoassay with a limit of detection of 20 pg/ml. Likewise, follicle-stimulating hormone (FSH), LH, testosterone (boys only), and oestradiol (girls only) were measured at each monthly visit. In the TP Study, testosterone and oestradiol levels were measured by radioimmunoassay with limits of detection of 0.11 nmol/l and 9 pmol/l, respectively. FSH and LH levels were measured by fluoroimmunometric assay with a limit of detection of 0.05 IU/l. Similar assay methods were used in the TA Study [3].

The GnRH test was conducted at baseline, 3 months, and 6 months. GnRH (100 μg/m²) was intravenously injected, and LH and FSH serum levels were measured before injection as well as 20, 40, 60, and 90 min after injection. The same method was used in the TP and TA Studies [3].

In both studies, other assessments included: bone age determination by the Greulich and Pyle method [29] (at baseline and 6 months); height and weight (at baseline and 6 months) and the calculated growth velocity and BMI; pubertal stage according to the method of Tanner [30] (at baseline, 3 months, and 6 months); uterine length measurement in girls by pelvic ultrasound (at baseline, 3 months, and 6 months), and AEs (at baseline, 3 months, and 6 months).

The primary efficacy endpoint was the proportion of patients with a suppressed LH response (LH peak ≤3 IU/l) to the GnRH test 3 months after the first injection of the triptorelin 11.25-mg sustained-release formulation. Although the TA Study had a longer follow-up, the primary endpoint of both studies was the same [3]. Secondary efficacy endpoints included: change in peak LH levels and peak FSH levels after the GnRH test at 3 and 6 months; oestradiol levels ≤20 pg/ml in girls and testosterone levels ≤0.3 ng/ml in boys at each monthly visit, and triptorelin plasma concentrations at 3 and 6 months [3].

Safety assessment in both studies included clinical and biological tolerability tests as well as AEs. All AEs were recorded. The investigators determined the relatedness of AEs to study treatment.

Only data from the intention-to-treat (ITT) populations of the two studies are presented. The TP Study tested the null hypothesis that the proportion of responders to triptorelin pamoate treatment was ≤70% against the alternative hypothesis that the proportion of responders was ≥90%. A sample of 36 patients with a cut-off value fixed at 31 patients allowed rejection of the null hypothesis with a one-sided α risk of 2.2% and 85% power. Descriptive statistics were used for the percentages of children with suppressed LH response, and suppressed oestradiol and testosterone levels.

Of the 62 patients screened for the TP Study, 37 met the study entry criteria and received at least one dose of triptorelin pamoate 11.25 mg (ITT population). Of these 37 patients, 35 completed the study (ITT sensitivity group). Two patients violated the study entry criteria (both were over the weight restriction specified in the exclusion criteria) and were subsequently prematurely removed from the study but maintained as non-responders in the ITT analysis.

The patients' baseline characteristics are outlined in table 2 - the two study populations were broadly similar [3]; differences included a lower mean uterine length, height standard deviation score (SDS), and growth velocity in the TP Study.

The ITT population in the TP Study comprised 31/37 (83.8%) responders [p = 0.044; 95% confidence intervals (CI): 68.0-93.8] after 3 months as defined by the primary endpoint (table 3). Although this did not meet the primary efficacy criteria (which had to have p < 0.022 to reject the null hypothesis), it was similar (with largely overlapping 95% CI) to the 82.8% response rate previously observed in the ITT population [as opposed to the modified ITT (mITT) population reported in the original paper] of the TA Study after 3 months (53/64 responders) (table 3) [3]. At 6 months, 86.5% of the patients in the TP Study were responders (both the 3-month and 6-month data included the two patients who withdrew from the study as non-responders). All but one participant in the TP Study were girls; there were 10 boys in the TA Study. In the TA Study, the results for girls only (GnRH-stimulated LH peak ≤3 IU/l: 86.5% at 3 months and 98.1% at 6 months [3]) were similar to the results with triptorelin pamoate in the TP Study (table 3).

The assessment of GnRH-stimulated peak LH and FSH levels showed substantial reductions after 3 and 6 months of triptorelin pamoate treatment (table 3; fig. 2). The reductions were of a similar magnitude with the pamoate and with the acetate salt of triptorelin (table 3) [3]. The mean basal levels of these two hormones were also substantially suppressed after 3 and 6 months by treatment with triptorelin pamoate (basal LH reduced from 1.5 IU/l at baseline to 0.4 and 0.4 IU/l after 3 and 6 months, respectively; basal FSH reduced from 4.1 IU/l at baseline to 1.1 and 1.4 IU/l after 3 and 6 months, respectively).

At baseline in the TP Study, 22/36 girls (61.1%) had oestradiol levels ≤20 pg/ml (i.e., prepubertal levels), and this increased to 33/34 girls (97.1%) after 3 and 6 months of treatment with triptorelin pamoate. This was similar to the 34/54 (63.0%), 50/52 (96.2%), and 51/52 (98.1%) girls with oestradiol levels ≤20 pg/ml at baseline and after 3 and 6 months, respectively, in the TA Study [3].

The Tanner breast stage was stable in most girls after 3 and 6 months in both studies, and the mean uterine length was stable or reduced (table 4) [3]. The growth velocity showed signs of reduction with triptorelin pamoate; 6-18 months before baseline, the mean (±SD) growth velocity was 7.9 ± 2.8 cm/year, and this was reduced to 6.9 ± 1.7 cm/year between baseline and 6 months after starting triptorelin pamoate. The results from the TA Study showed reductions in growth velocity from 9.0 ± 2.3 cm/year at baseline to 6.9 ± 2.5 cm/year after 6 months [3].

After 3 months (before the second injection of triptorelin pamoate) and after 6 months, the mean residual plasma concentrations of triptorelin pamoate were 34 ± 18 and 30 ± 17 pg/ml, respectively. The values for triptorelin acetate in the TA Study were 53 ± 34 and 81 ± 82 pg/ml, respectively [3].

The most frequently reported AEs in the TP Study were injection site pain (two events in 2/37 patients, both related to treatment) and hot flush (two events in 2/37 patients; one related to treatment). Three of these events were mild in intensity and one (hot flush) was moderate, but all four patients recovered without sequelae. Other frequently reported AEs were vomiting (one event, unrelated to treatment), abdominal pain (four events in 4/37 patients; one event related to treatment), and epistaxis (one event in 37 patients, unrelated to treatment); all of these events were of mild intensity and all patients recovered without sequelae. The most frequent AEs reported in the TA Study were: headache (20%), rhinitis (13%), abdominal pain (9%), gastroenteritis (5%), and rash (5%) [3].

The results of the TP Study demonstrate that triptorelin pamoate 11.25 mg administered at 3-month intervals is an effective and well-tolerated treatment in patients with CPP during a 6-month trial. One question raised by the findings of the TA and TP Studies is whether the criteria for assessing the efficacy of GnRH analogue treatment in children are defined well enough to assess whether the two formulations based on different salts yield similar results. The peak LH after GnRH or GnRH analogue stimulation has generally been taken as a primary criterion for defining the efficacy of GnRH analogues. However, recent consensus guidelines have stated that regarding the different criteria available (clinical pubertal development, growth and bone age advancement, basal LH, stimulated LH, and sex steroid levels), no consensus could be reached to promote the routine use of one single criterion [7]. In addition, cut-off values such as the one used in the TP and TA Studies, although reflecting normal prepubertal responses, are somewhat arbitrary. In this context, we observed that at 3 months 83.8 and 85.5% and at 6 months 86.5 and 96.8% of the patients had suppressed LH peak levels in the ITT/mITT populations of the TP Study and the TA Study, respectively (table 3). Of note, early exclusions and dropouts were considered as treatment failure in the ITT analysis, and the rates of patients with suppressed LH peaks in the per-protocol populations were 94% at 3 and 6 months in the TP Study and 97% at 3 and 6 months in the TA Study.

Although no head-to-head comparison was made, the study designs of the TP Study and the TA Study were very similar, giving validity to this indirect comparison. However, the TA Study had a somewhat higher (7 vs. 5 IU/l) LH peak threshold for inclusion. The TA Study also had an inclusion criterion regarding uterine length. This resulted in a marginally (0.4 IU/l) higher peak LH at inclusion in the TA Study and in a higher mean uterine length in the TA Study (43.6 vs. 37.6 mm). In addition, there were differences in auxological criteria, with a somewhat higher height SDS, growth velocity, and BMI SDS in the TA Study. Whether these differences in auxological criteria reflect more ‘severe' CPP in the TA Study or random variation due to the small sample size cannot be determined. However, there was considerable overlap between the populations of the two studies, and we believe that the minor differences do not hinder a comparison between the two studies. One further difference is that the TA Study was of longer duration (12 vs. 6 months). However, general experience and the results of the TA Study indicate that the level of suppression obtained at 6 months is maintained or improved at 12 months. In all previous reports of triptorelin acetate for CPP, LH suppression at 6 months was similar to that at 12 months [3, 11, 12].

The hormonal responses to the two formulations of triptorelin were very similar, but some differences between formulations were observed, such as changes in uterine length and growth velocity. We believe any such minor numerical differences are more likely to reflect random variation in a small sample rather than genuine differences in the physiological effects of the two salt formulations. The AE profiles in the two studies were similar, and although the frequency of individual AEs was different in these populations, this may also simply reflect random variation. In general, the safety profile of triptorelin pamoate was similar to what would be expected with triptorelin acetate [3].

Triptorelin has been formulated as the pamoate salt to improve the manufacturing process and to aid in the development of slow-release formulations (a 6-month formulation of triptorelin pamoate exists and is used in the treatment of prostate cancer [31, 32]). Pamoic acid, also called embonic acid, is a naphthoic acid derivative. The salt form of pamoic acid (pamoate ion) can be used as a counter ion of a drug compound to increase its solubility in water. It has been suggested that the pamoate moiety has the potential to interact with an orphan G protein-coupled receptor, GPR35 [24, 33]. However, the physiological function of GPR35 is unknown, and the results of the current study (and data available on the use of triptorelin pamoate in other indications, including prostate cancer) suggest that the triptorelin pamoate salt does not have a safety profile different to that of the triptorelin acetate salt, and that the pamoate moiety has no specific pharmacodynamic properties in this setting. While the triptorelin pamoate salt is the formulation currently included in ongoing regulatory registrations, the development of novel methods of formulating both pamoate and acetate salts has been reported [34, 35, 36].

In conclusion, we consider from this study of triptorelin pamoate and the cross-trial comparison with triptorelin acetate that the outcomes were similar when either salt was used for the treatment of CPP. The primary efficacy endpoint was similar in each study, and the small sample size of each study likely accounts for any minor numerical variations in secondary endpoints. Although it is useful for clinicians to be aware that different salts of pharmacological agents exist, we consider that triptorelin acetate and triptorelin pamoate can be used equivalently for the management of CPP.

Anne-Marie Bertrand (Besancon, France), Claire Bouvattier (Kremlin-Bicêtre, France), Sylvie Cabrol (Paris, France), Michel Colle (Bordeaux, France), Régis Coutant (Angers, France), Sylvie Dufresne (Angers, France), Frédéric Huet (Dijon, France), Claudine Lecointre (Rouen, France), Bernard Le Luyer (Le Havre, France), Eric Mallet (Rouen, France), Marc Nicolino (Lyon, France), Marc Petrus (Tarbes, France), Catherine Pienkowski (Toulouse, France), Michel Polak (Paris, France), Rachel Reynaud (Marseille, France), Sylvie Soskin (Strasbourg, France), Pierre-François Souchon (Reims, France), Maité Tauber (Toulouse, France), Kathy Wagner (Nice, France), and Jacques Weill (Lille, France).

Both the TA Study and the TP Study were funded by Ipsen. The authors take full responsibility for the content of this paper and thank Martin Gilmour of ESP Bioscience, Crowthorne, UK (supported by Ipsen) for editorial assistance in the preparation of the manuscript.

Clinical trial identifier NCT00564850. The TP Study was conducted at 18 centres in France, and the TA Study at 15 centres in Belgium, France, Italy, and Spain. See the Appendix for the list of co-investigators.