Only human growth hormone (GH) exerts metabolic activity in man, and it was not until its isolation from human cadaveric pituitary glands by Raben and its subsequent purification in the late fifties that clinical use of the hormone became possible [1]. Since 1960, treatment of short stature in hypopituitary children has been an accepted therapy, although its use for many years was restricted to three-times weekly dosing and to the shortest children because of the limited availability of the hormone. Since the 1980s, the availability of recombinant GH has enabled larger scale use of GH therapy on a daily basis in children and has extended its use to adults with GH deficiency (GHD).
Intramuscular injections three times per week were un-physiological and inconvenient. Careful pharmacological studies showed that daily subcutaneous injections were more effective and less inconvenient for the children, and this daily format was introduced as a routine treatment regimen during the 1980s [2].
GH has a plasma half-life of 3.4 h after subcutaneous injection and ~ 20 min after intravenous injection [3]. The pulsatile and very irregular secretion of GH seen in normal people are impossible to replicate clinically, even when the GH is administered several times each day. In animal models, pulsatile administration of GH results in better growth and greater IGF-I generation than does continuous GH infusion [4] and [5]. In contrast, studies in GH deficient (GHD) humans have not revealed any biochemical or physiological differences when comparing treatment with daily subcutaneous GH injections to therapy comprised of several injections per day using the same daily total doses [6] and [7]. Likewise, continuous infusion of GH in adults with GHD has not demonstrated any clinically meaningful differences in metabolic response in circulating markers of glucose-, lipid- and amino acid-metabolism during six months of therapy when compared to daily injections [8]. Thus, a perfect physiological regimen for GH therapy has not been identified and daily subcutaneous GH injections have been preferred as the most practical mode of administration. It is recommended to administer the daily injections in the evening, since this to some extent mimics the normal pattern for GH secretion and also normalizes the excursions of lipid and amino acid metabolites [2]. The clinical significance, however, of this recommendation has never been documented.
Despite ongoing improvements in injection device design, daily subcutaneous administration of GH remains inconvenient, painful and distressing for many patients [9], leading to noncompliance, reduced efficacy and increased health care costs. Compliance is a problem in up to 75% of teenagers, and growth velocity is reduced in the children with poor compliance [9], [10] and [11]. To address this problem, a variety of long-acting formulations of GH have been developed with the hope of achieving comparable efficacy and safety using fewer total injections [12] and [13] (Table 1). Long-acting formulations of several hormone drugs, including, GnRH, testosterone, medroxyprogesterone and others are commonly used clinically. The aim of this review is to update the current state of long-acting GH formulations.
Table 1.
Only human growth hormone (GH) exerts metabolic activity in man, and it was not until its isolation from human cadaveric pituitary glands by Raben and its subsequent purification in the late fifties that clinical use of the hormone became possible [1]. Since 1960, treatment of short stature in hypopituitary children has been an accepted therapy, although its use for many years was restricted to three-times weekly dosing and to the shortest children because of the limited availability of the hormone. Since the 1980s, the availability of recombinant GH has enabled larger scale use of GH therapy on a daily basis in children and has extended its use to adults with GH deficiency (GHD).Intramuscular injections three times per week were un-physiological and inconvenient. Careful pharmacological studies showed that daily subcutaneous injections were more effective and less inconvenient for the children, and this daily format was introduced as a routine treatment regimen during the 1980s [2].GH has a plasma half-life of 3.4 h after subcutaneous injection and ~ 20 min after intravenous injection [3]. The pulsatile and very irregular secretion of GH seen in normal people are impossible to replicate clinically, even when the GH is administered several times each day. In animal models, pulsatile administration of GH results in better growth and greater IGF-I generation than does continuous GH infusion [4] and [5]. In contrast, studies in GH deficient (GHD) humans have not revealed any biochemical or physiological differences when comparing treatment with daily subcutaneous GH injections to therapy comprised of several injections per day using the same daily total doses [6] and [7]. Likewise, continuous infusion of GH in adults with GHD has not demonstrated any clinically meaningful differences in metabolic response in circulating markers of glucose-, lipid- and amino acid-metabolism during six months of therapy when compared to daily injections [8]. Thus, a perfect physiological regimen for GH therapy has not been identified and daily subcutaneous GH injections have been preferred as the most practical mode of administration. It is recommended to administer the daily injections in the evening, since this to some extent mimics the normal pattern for GH secretion and also normalizes the excursions of lipid and amino acid metabolites [2]. The clinical significance, however, of this recommendation has never been documented.Despite ongoing improvements in injection device design, daily subcutaneous administration of GH remains inconvenient, painful and distressing for many patients [9], leading to noncompliance, reduced efficacy and increased health care costs. Compliance is a problem in up to 75% of teenagers, and growth velocity is reduced in the children with poor compliance [9], [10] and [11]. To address this problem, a variety of long-acting formulations of GH have been developed with the hope of achieving comparable efficacy and safety using fewer total injections [12] and [13] (Table 1). Long-acting formulations of several hormone drugs, including, GnRH, testosterone, medroxyprogesterone and others are commonly used clinically. The aim of this review is to update the current state of long-acting GH formulations.Table 1.
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