Review of Pharmacology - 9E (2015)

Review of Pharmacology
• GnRH analogues like busurelin, goserelin, leuprolide, nafarelin, deslorelin, triptorelin
and histrelin are more potent and longer acting than natural GnRH. These drugs
stimulate gonadotropin secretion when given in a pulsatile manner whereas
inhibit the release on continued administration. Therefore, these agents can be
used in pulsatile manner for the treatment of anovulatory infertility, hypogonadotropic
hypogonadism, delayed puberty and cryptorchidism (these conditions require excess
of gonadotropins for treatment). On the other hand, if given continuously,
reduction in gonadotropin secretion is seen that is beneficial in the conditions
like precocious puberty, endometriosis, prostatic carcinoma, PCOD and uterine fibroids.
Most of these drugs are used by s.c. route whereas nafarelin and busurelin can be
used by nasal route and goserelin can be used as s.c. implant. Major disadvantage
of GnRH analogues is that there is stimulation of gonadotropin release initially
(flare up reaction) that can be dangerous in conditions like prostatic carcinoma
and endometriosis.
• Cetrorelix, ganirelix and abarelix are GnRH antagonists. These do not cause initial
flare up reaction. These are administered subcutaneously for the treatment of
uterine fibroids and endometriosis. Another use of these drugs is controlled
ovarian stimulation in in-vitro fertilization. In this process, recombinant FSH is
given to prepare the ova for ovulation induction. Constant monitoring of serum
estradiol is done and when sufficient levels are reached, GnRH antagonists are
given to prevent premature spontaneous ovulation.
• GnRH agonists as well as antagonists can cause hot flushes, loss of libido and
osteoporosis as adverse effects.
Endocrinology
LH; Leutenizing hormone, FSH;
Follicle stimulating hormone,
E; Estrogen, P; Progesterone,
T; Testosterone
238
Oxidation, organification and
coupling reactions are catalyzed
by thyroid peroxidase enzyme.
THYROID HORMONES
Thyroid gland contains follicular cells and parafollicular (C) cells. Former secretes thyroid
hormones (T 3
and T 4
) whereas the latter is responsible for the secretion of calcitonin. Thyroid
hormones are synthesized and stored in thyroid follicles in the following manner:
• Iodine is first taken up in the follicular cell with the help of Na + : I – symporter (NIS).
• After entry in the follicular cells, iodine is oxidized to form iodinium ( ) ions. These
ions combine with tyrosine residues of thyroglobulin to form mono-iodo tyrosine
(MIT) and di-iodo-tyrosine (DIT). This process is known as organification of iodine.
• DIT combines with DIT to form 3, 5, 3’, 5’ tetra-iodo-thyronine (T 4
) and with MIT to
form 3, 5, 3’ tri-iodo-thyronine (T 3
). This process is known as coupling.
• Oxidation, organification and coupling reactions are catalyzed by thyroid peroxidase
enzyme.
• After formation, T 3
and T 4
are transported to the follicles where these remain stored
as colloid. On stimulation via TSH, these hormones are released in the circulation.
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