Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.

Norprolac (Ferring)
25 microgram and 50 microgram tablets
Approved indication: hyperprolactinaemia
Australian Medicines Handbook section 16.2.1

The secretion of prolactin from the anterior pituitary is inhibited by dopamine. Dopamine agonists have therefore been used to treat hyperprolactinaemia, a condition which has several possible causes including prolactinomas in the pituitary.

Quinagolide is a selective agonist at the dopamine D2receptor. It has been approved for the treatment of idiopathic hyperprolactinaemia and prolactin secreting pituitary tumours.

Patients take quinagolide once a day. The drug is well absorbed but there is extensive first-pass metabolism. Prolactin concentrations start to fall within two hours of a dose and are suppressed for 24 hours. Most of the drug is metabolised with the metabolites being excreted in the faeces and urine. Therefore, impaired hepatic or renal function are contraindications to quinagolide.

As quinagolide has been available overseas for several years, long-term data are available. One study reported on a group of 40 patients treated for a mean of 32 months. The serum prolactin fell in all patients and the tumour size was reduced in 55% of the patients with microadenomas and 75% of the patients with macroadenomas. Hyperprolactinaemia can be a cause of infertility, but 10 of the 38 women in the study became pregnant while taking quinagolide.1

Most of the early comparative studies of quinagolide used bromocriptine. A study of 41 women found both drugs significantly reduced serum prolactin within eight weeks. Prolactin concentrations normalised in 81% of those given quinagolide and 70% of those given bromocriptine. Tolerability was higher in the women given quinagolide.2 Another study showed that 39% of patients with prolactinomas that were resistant to treatment with bromocriptine responded to quinagolide.3

Bromocriptine is no longer first-line therapy because treatment with cabergoline is more effective. Quinagolide has therefore been compared with cabergoline. In one small study patients took one of the drugs for 12 weeks then stopped. When their hyperprolactinaemia returned they took the other drug for 12 weeks. Although only nine patients completed the study, there were significant differences in the duration of efficacy and tolerability favouring cabergoline.4 A similar study stopped treating 39 patients with quinagolide after a year then, when their hyperprolactinaemia returned, treated them with cabergoline for a year. Cabergoline had a greater effect on tumour size and was better tolerated.5

The adverse effects of quinagolide include nausea, vomiting, headache and dizziness. Some of these symptoms improve after a few days of treatment. It is therefore recommended that quinagolide is taken with food at night and that treatment is introduced gradually. In some cases the dopaminergic action of quinagolide may cause an acute psychosis.

The once-daily dose and better tolerability give quinagolide an advantage over bromocriptine. Any differences between quinagolide and cabergoline are less clear. Cabergoline needs to be given less frequently and if the patient only needs one dose a week, a month's treatment will be cheaper than daily treatment with quinagolide.

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References

  1. Schultz PN, Ginsberg L, McCutcheon IE, Samaan N, Leavens M, Gagel RF. Quinagolide in the management of prolactinoma. Pituitary 2000;3:239-49.
  2. van der Heijden PF, de Wit W, Brownell J, Schoemaker J, Rolland R. CV 205-502, a new dopamine agonist, versus bromocriptine in the treatment of hyperprolactinaemia. Eur J Obstet Gynecol Reprod Biol 1991;40:111-18.
  3. Morange I, Barlier A, Pellegrini I, Brue T, Enjalbert A, Jaquet P. Prolactinomas resistant to bromocriptine: long-term efficacy of quinagolide and outcome of pregnancy. Eur J Endocrinol 1996;135:413-20.
  4. Giusti M, Porcella E, Carraro A, Cuttica M, Valenti S, Giordano G. A cross-over study with the two novel dopaminergic drugs cabergoline and quinagolide in hyperprolactinemic patients. J Endocrinol Invest 1994;17:51-7.
  5. Di Sarno A, Landi ML, Marzullo P, Di Somma C, Pivonello R, Cerbone G, et al. The effect of quinagolide and cabergoline, two selective dopamine receptor type 2 agonists, in the treatment of prolactinomas. Clin Endocrinol 2000;53:53-60.