Therapeutic considerations pregnancy & lactation Flashcards
What are the key considerations when administering drugs to pregnant animals?
Effect on pregnancy – Can drug disrupt gestation?
Effect on fetus – Risk of teratogenesis or developmental issues
Effect at birth – Can drug cause complications during parturition?
Label indication – Is drug licensed for use in pregnancy?
Risk-benefit balance – Weigh maternal treatment needs vs. fetal harm
Why is it difficult to predict plasma drug levels in pregnancy?
Absorption: Reduced abdominal space, increased gastric pH
Distribution: Increased plasma volume; high Vd drugs cross placenta more
Metabolism: Altered due to increased detoxification needs
Excretion: Changes in dam’s acid-base balance affect drug clearance
What determines if a drug crosses the placenta?
If drug is orally absorbed, it likely crosses placenta
Lipophilic drugs cross more easily
Basic drugs can be trapped in fetal compartment (ion trapping)
How should drug safety be checked before use in pregnancy?
Check data sheet
Consult the company if unclear
Consider risk-benefit analysis
If off-label use is necessary, obtain written owner consent
What are the key concerns when administering drugs during lactation?
Effect on neonate – Can drug be toxic via milk?
Effect on lactation – Can drug reduce milk production?
Drug licensing – Is drug approved for use during lactation?
Milk withdrawal times – Important for food-producing animals
New route of elimination
Metabolic status of dam
Lactation introduces new route of drug elimination, which pharmacokinetic properties influence drug transfer into milk?
Lipid-soluble drugs
Basic, non-ionised drugs
Low plasma protein-binding drugs – More free drug available for transfer
Some drugs are inactivated by milk
How can mastitis during lactation influence drug elimination?
Alters milk pH & mammary blood flow, potentially increasing drug excretion
What are the three ways hormones can control ovarian and uterine function?
Direct control – Acting on follicles (FSH, LH) or corpus luteum (PGF2α, progesterone)
Indirect control – Stimulating GnRH to influence gonadotropin release
Hypothalamic control – Using progesterone to suppress GnRH & reproductive cycles
How can we directly control follicular and luteal function with hormones?
FSH → Stimulates antral follicular growth
LH/HCG → Induces ovulation
- Stimulates final maturation of follicles, luteinisation & provides luteal support
PGF2α → Causes luteolysis, leading to CL regression
Progesterone → Maintains luteal phase, preventing ovulation (negative feedback effect on hypothalamus/pituitary)
How does GnRH influence reproductive control, and how can we manipulate it?
GnRH release stimulates FSH & LH, controlling follicular development & ovulation
Manipulation methods:
- GnRH agonists (e.g. deslorelin): Initially stimulate, then suppress GnRH receptors
- GnRH antagonists: Block GnRH, preventing gonadotropin release
How does progesterone and PGF2α affect the reproductive cycle?
Progesterone → Suppresses GnRH, preventing ovulation
- Used in synchronisation & oestrus suppression
PGF2α → Induces luteolysis, used for oestrus
- synchronization, abortion & treating persistent CL conditions
Why is it important to understand the different stages of the oestrous cycle for exogenous hormone use?
Different ovarian structures (follicles, corpus luteum) are present at different stages
Effects of hormones depend on stage of cycle
Multiple structures (CL + dominant follicle) can exist at same time
What conditions must be met for hormonal treatments to be effective?
PGF2α needs active corpus luteum to induce luteolysis
GnRH needs dominant follicle to trigger ovulation via LH surge
FSH requires growing antral follicles to recruit multiple co-dominant follicles.
What are the short-term effects of GnRH administration?
Induces ovulation by triggering LH surge
Hastens return to cyclicity (e.g. post-weaning in sows, lactational anoestrus in cows)
Used in synchronisation protocols (fixed-time AI)
Luteinises cystic ovarian structures
GnRH stimulation test – Assesses hypothalamic-gonadal axis function
What are the long-term effects of GnRH administration (e.g. deslorelin implant)?
Initial stimulation, followed by downregulation of GnRH receptors
Suppresses HPG axis, leading to:
- Infertility in male dogs (up to 6 months)
- Suppression of oestrous behaviour
What are the clinical uses of FSH?
Superovulation – Induces ovulation of multiple follicles
- Must be given early in follicular wave
- Requires repeated doses
Oestrous induction protocols (combined with progestogens)
Not effective in mares
Few FSH specific products, often use low dose ECG (FSH-like activity)
What are the clinical uses of LH?
Induce ovulation when animal is in oestrus
Treatment of prolonged pro-oestrus in bitch
Used in male dogs for libido deficiency
Limited use in cattle today
No LH specific product, use HCG (binds to LH receptor & has LH-like activity)
What are the effects of progesterone on target tissues?
Mammary enlargement
Endometrial proliferation
Sedative-like effects on behaviour
What are the clinical uses of progestogens?
Prevent oestrus in bitches & mares
Treat & prevent pseudopregnancy in dogs
Manage some male conditions (e.g. unwanted behaviour, prostatic disease)
Oestrus induction/synchronisation – Withdrawal of progestogens triggers oestrus
What formulations of progestogens are available?
Vaginal: Sponges (ewes), devices (PRID/CIDR – cows, mares)
Depot injections: Proligestone (Delvosteron) – long-term oestrus prevention in bitches
Oral: Megestrol (Ovarid) – dogs; Altrenogest (Regumate) – sows, mares
What is the function of progesterone receptor antagonists?
Blocks progesterone receptors → prevents pregnancy maintenance
Terminates pregnancy in any species
Induces parturition
Treats progesterone-driven conditions (e.g. pyometra in dogs, mammary hyperplasia in queens)
Product: Aglepristone (Alizin)
What is the effect of oestrogen on target tissues?
Development of vagina, urethra, mammary glands, uterus
What is the main use of exogenous oestrogen?
Urinary incontinence treatment in bitches (e.g. estriol (Incurin))
Not used for reproductive consideration
What are the clinical uses of PGF2α?
Terminate luteal phase to synchronise oestrus
Induce abortion or parturition
Treat chronic metritis or pyometra (if CL is present)
How do prolactin inhibitors work in reproductive control?
Prolactin supports CL function in bitches & pregnant queens
Inhibiting prolactin leads to CL regression & progesterone decline
- Only works when prolactin is supporting CL
What are the clinical uses of prolactin inhibitors?
Terminate pregnancy or end luteal phase
Treat pyometra
Reduce milk production (pseudopregnancy or post-weaning)
Induce oestrus when animal is in prolonged proestrus phase
How does melatonin regulate reproductive cycles?
Produced in response to decreasing daylight
Stimulates reproduction in short-day breeders (ewes)
Suppresses reproduction in long-day breeders (mares, cats, ferrets)
What are the clinical uses of melatonin?
Ewes: Implants at base of ear in May-June hasten cyclicity & oestrus onset
Mares, cats, ferrets: Used to suppress oestrus
What are the clinical uses of oxytocin?
Induce myometrial contractions to assist parturition (requires fully dilated cervix)
Promote uterine involution post-partum
Aid passage of retained placenta
Stimulate milk let-down in agalactic dams
(Ineffective in controlling oestrous cycle)
