Pharmacology Flashcards
What is carbimazole used for?
Hyperthyroidism
What is carbimazole’s MOA?
inhibit thyroid peroxidase resulting in less T3/T4 precursors –> decreased thyroid hormones output
What is carbimazole dosing frequency and ROA?
PO once daily
What happens to carbimazole after absorption?
Converted into active methimazole in the serum
What is carbimazole’s (or its metabolites’) half life?
Methimazole’s half-life 4-6 hour
Does carbimazole (or its metabolites) bind to plasma proteins?
No
How long does it take for carbimazole to exert its effect?
> 90% inhibition achieved within 12 hours, however clinical response may take 3-6 weeks after initiation due to thyroid stores in the body and T4’s long half life.
How is carbimazole metabolized?
CYP450 and FMO enzymes
How is carbimazole excreted?
> 90% excreted in urine as methimazole or its metabolites
What are adverse effects of carbimazole?
Rashes
Joint pains
Nausea
Jaundice
Agranulocytosis (rare)
What is levothyroxine used for?
Hypothyroidism
What is levothyroxine’s MOA?
Synthetic thyroid hormone
What can affect levothyroxine’s absorption?
Increased absorption with fasting
Erratic absorption with dietary fiber
Affected by gastric pH
What is levothyroxine’s bioavailability?
70-80%
How long does it take for levothyroxine to exert its effect?
PO: 3-5 days
IV: 6-8H
What is levothyroxine’s half-life?
7 days
Does levothyroxine bind to plasma proteins?
Yes, >99%
How is levothyroxine being metabolized?
Liver - glucuronidation, sulphation
Kidney - deiodination
How is levothyroxine being excreted?
Primarily by kidneys
What are adverse effects of levothyroxine?
Reduced appetite
Anxiety, insomnia
Hair loss
Diarrhea
Rare and serious:
Heart issues
Seizures
When is IV form of levothyroxine used?
Myxoedema coma (severe form of hypothyroidism)
Cannot use PO levothyroxine as there is reduced blood flow to GI
Can also use IV Liothyronine (synthetic T3)
What should you monitor after initiation of levothyroxine therapy?
Serum TSH every 6-8 weeks after initiation or dose titration
What does persistently elevated TSH levels indicate after levothyroxine therapy has been started?
Inadequate dosing, poor compliance, malabsorption, DDI or food-drug interaction
What is tamoxifen used for?
Breast cancer in both pre- and post- menopausal women
What is tamoxifen’s MOA?
selective estrogen receptor modulator (SERM)
competitively blocks endogenous estrogen binding to the estrogen receptor in the target tissue
Does tamoxifen have stereoisomers?
Yes
Tamoxifen exists in cis- (estrogenic) and trans- (anti-estrogenic) stereoisomers
How is tamoxifen’s absorption profile like?
Rapidly and extensively absorbed in intestine
F ~100%
Css typically reached after 3-4 weeks (max 16 weeks)
Tmax is 3-7 hours
Does tamoxifen bind to plasma protein?
> 98%
What is tamoxifen’s Vd?
50-60 L/kg
high concentrations found in tissues especially uterus (2-3 fold higher than serum) and breast (10 fold higher than serum)
How is tamoxifen metabolized?
Phase 1: hydroxylation, N-oxidation, dealkylation
Phase 2: glucuronidation, sulphation
Major pathway: N-demethylation
What is tamoxifen’s major metabolite and its half-life?
N-desmethyltamoxifen (t1/2 ~14 days)
How is N-demethylation of tamoxifen catalyzed? And what’s the consequences?
By CYP3A4
Should not take with grape gruit or CYP3A4 inhibitors
What are tamoxifen’s minor metabolites?
4-hydroxytamoxifen
4-hydroxy-N-desmethyltamoxifen (endoxifen)
Which of the tamoxifen’s metabolites has greater affinity for the estrogen receptor?
Minor metabolites
What catalyzes metabolism of tamoxifen into its minor metabolites? And what are its consequences?
CYP2D6
Do not take with diphenhydramine or inhibitors of CYP2D6
How is tamoxifen excreted?
Mainly through feces
What are side-effects of tamoxifen therapy?
Anti-estrogenic
- Hot flushes
- Menstrual irregularities
Estrogenic
- Risk of endometrial cancer
- DVT
- Vaginal bleed and discharge
- Nausea/vomiting
Overdose of tamoxifen can lead to?
Acute neurotoxicity eg. tremor, hyperreflexia, unsteady gait, dizziness
How do you treat tamoxifen overdose?
Supportive treatment
What is pembrolizumab used for?
Breast cancer
What is pembrolizumab’s MOA?
PD-1 inhibitor
Binds to PD-1 and prevents PD-L1 on tumor cells binding to it, thus allowing activation of immune response to fight the tumor cells
What type of antibody is pembrolizumab?
Humanized antibody (-zumab)
How is pembrolizumab administered?
IV infusion over 30 mins
What is pembrolizumab’s dose?
IV 200mg every 3 weeks
What is pembrolizumab’s Vd?
~7L
How is pembrolizumab metabolized?
non-specific catabolism (general protein degradation routes) into small peptides and single amino acids
How is pembrolizumab excreted?
No studies done
What is pembrolizumab’s half-life?
~27 days
When will pembrolizumab reach Css?
after ~19 weeks
What can cause slower clearance of pembrolizumab?
Cervical cancer in women
What are S/E of pembrolizumab?
Infusion-related S/Es, immune-related inflammation, joint pain, fatigue, diarrhea, nausea
What are C/I of pembrolizumab?
- On immunosuppressants or corticosteroids
- Pregnancy
- Hypersensitivity
List 4 ways to achieve androgen deprivation
- Inhibition of pituitary gonadotropin release (by using GnRH analogs)
- Inhibition of androgen synthesis
- Inhibition of androgen binding (by using androgen receptor blockers)
- Surgical extirpation of the glands (by castration and adrenalectomy)
What is leuprorelin used for?
Prostate cancer
What is leuprorelin’s MOA?
GLP-1 agonist
It is a synthetic GnRH which activates the pituitary GnRH receptors
Continuous GnRH causes negative feedback on the pituitary leading to reduced FSH and LH levels
Reduced FSH and LH levels suppresses testosterone production in the testes and causes prostate cancer cells (androgen-sensitive cells) to undergo apoptosis
What should you monitor after starting leuprorelin?
Measure PSA in first few weeks of therapy
Measure LH, FSH, and serum testosterone after 4 weeks of therapy
Reduction in levels of these substances indicates that the treatment works
How is leuprorelin administered?
SC or IM, given as single-dose long acting depot (1, 3, or 4 months interval)
What is leuprorelin’s time to Cmax and Css?
Cmax: 1-3 hours post injection
Css typically after 4 weeks
What is leuprorelin’s Vd?
~27L after IV
No data after SC or IM
Does leuprorelin binds to plasma protein?
~45% plasma protein binding (in vitro)
How is leuprorelin metabolized?
degraded proteolytically (peptidases) into inactive peptides
not metabolized in liver CYP450
What is leuprorelin’s half-life?
~ 3 hours
How is leuprorelin excreted?
<5% via urine
What are side effects of leuprorelin?
- Hot flushes (first few weeks)
- Injection site reaction
- Headache/dizziness
- Altered mood
- Hyperglycemia
- Decreased libido
What are C/I to leuprorelin?
Hypersensitivity
Pre-existing heart disease
Pts with risks for osteoporosis
What is bicalutamide used for?
Prostate cancer