Case Study Drugs Flashcards
Benzylpenicillin (Penicillin G)
B-lactam antibiotic belonging to Penicillin class of antibiotics. Works by targeting bacterial cell wall (composed of peptidoglycan which is a mesh-like structure made up of repeating units of sugar & amino acids). It interferes with 2nd stage of cell wall synthesis which is cross-linking of peptidoglycan chains facilitated by transpeptidase/PBPs which forms peptide bonds between amino acids in adjacent peptidoglycan chains. Benzylpenicillin contains a b-lactam ring and when it enters cell, it binds & inhibits activity of transpeptidase —> susceptible to osmotic pressure & lyses. It targets gram positive bacteria like Streptococcus but not gram negative due to additional outer membrane. It is susceptible to degradation by b-lactamases produced by some bacteria.
Ceftriaxone
3rd generation cephalosporin antibiotic belonging to the Cephalosporin class of antibiotics that is structurally similar to penicillins. (Same MOA as Benzylpenicillin)
Metronidazole
Used to treat bacterial & parasitic infections in different parts of body like skin, stomach, intestines.
Drug class: Nitroimidazoles.
Works by interfering with DNA in bacteria & parasites, & once inside cell it gets converted to its active form which can disrupt the structure of the pathogen’s DNA, preventing production of essential proteins.
Administered orally by tablet/liquid, topically as cream/gel/lotion, injection
Half life of 8hrs in adults
Excreted in urine but also in faeces to a lesser extent.
Tazocin
Used for severe bacterial infections like skin, abdominal, respiratory tract, gynaecological that are resistant to other antibiotics
Drug class: combo antibiotic of Piperacillin (broad spectrum penicillin) & Tazobactam (b-lactamase inhibitor)
Piperacillin works by interfering with cell wall formation and Tazobactam enhances Piperacillin’s effectiveness by inhibiting b-lactamase produced by some bacteria that can inactivate Piperacillin & other penicillins.
Administered via IV injection or infusion
Half life is 1hr & 1.2hrs respectively
Excreted in urine.
Metoclopramide
Used for gastrointestinal conditions like GERD, gastroparesis, nausea & vomiting from surgery or chemotherapy (anti-emetic properties)
Drug class: Prokinetic agents
Works by blocking dopamine receptors in brain to prevent nausea & vomiting. It’s prokinetic effects are due to its ability to increase muscle tone & peristalsis of the GI tract to help speed up the passage of food through the stomach
Administered orally as tablet/liquid, intramuscular or intravenous injections
Half life of 5-6 hrs
Excreted in urine but also faeces to a lesser extent.
Paracetamol (acetaminophen)
Acts centrally e.g. COX3 reduces fever, & acts peripherally e.g. COX2 reduces pain and inflammation.
It’s metabolised in the liver through 3 main pathways:
Glucuronidation: (50-55%) involves addition of glucuronic acid group to paracetamol catalysed by uridine 5’-diphosphoglucuronosyltransferase making it more water-soluble & easier for the body to excrete
Sulfation: (30%) similar to glucuronidation by catalysed by sulfotransferase
Oxidation: (5-15%) via cytochrome P450 enzyme specifically CYP2E1, CYP1A2 & CYP3A4 —> produces a reactive metabolite (N-acetyl-p-benzoquinoneimine) that’s highly toxic & can damage liver. Under normal circumstances it’s immediately detoxified by conjugation with glutathione, but if paracetamol is taken in large amounts, body’s glutathione reserves can be depleted, allowing NAPQI to accumulate & cause damage.
Glucuronide & sulfate conjugates, detoxified NAPQII, small amounts of unmetabolised paracetamol are excreted into urine.
N-acetylcysteine
Precursor to glutathione which is a potent anti-oxidant —> glutathione can be synthesised more, enhancing detoxification of NAPQI.
Most effective within 8 hours.
Side effects: nausea, vomiting, rash
Administered orally or intravenously.
Codeine
Prodrug that needs to be metabolised in its active form morphine in the liver by cytochrome P450 2D6 enzyme. Morphine acts on CNS to inhibit adenylate cyclase which is responsible for converting ATP into cAMP (cyclic adenosine monosphosphate) —> reduced intracellular cAMP levels (cAMP is a secondary messenger that’s involved in transmission of pain signals) —> inhibition of voltage-gated calcium channels which are crucial for transmission of signals in neurons, while simultaneously opens voltage-gated potassium channels —> inhibition of depolarisation in neurons, reducing the excitability of nerve cells. Morphine inhibits release of neurotransmitters involved in pain transmission like GABA, dopamine, substance P so there’s an overall inhibition of nociceptive neurotransmission.
Salbutamol
Bronchodilator medication used for asthma & other respiratory symptoms. It’s a type of b-2 adrenergic agonist which contains active ingredient albuterol. Works by selectively binding & activating b-2 adrenergic receptors found on smooth muscle cells in airways —> increased cAMP within smooth muscle cells —> activates protein kinase A —> inhibits phosphorylation of myosin (protein involved in smooth muscle contraction) —> induces smooth muscle relaxation in bronchioles —> dilation of airways making it easier to breathe. It also has anti-inflammatory effects like it can inhibit release of bronchoconstrictors like leukotrienes from mast cells which prevents bronchoconstriction & airway inflammation.
It can be used before exercise to prevent exercise-induced bronchoconstriction.
Administered via inhalation using inhalers or nebulisers.
Beclometasone
Corticosteroids medication used to treat asthma & other inflammatory respiratory conditions. Belongs to class of Inhaled corticosteroids. Works by entering the cells of airway epithelium & binds to intracellular corticosteroid receptors —> steroid-receptor complex —> migrates to cell nucleus where it undergoes dimerization, forming a structure that interacts with specific regions of DNA (steroid response elements) —> interaction with steroid response elements leads to modulation of gene transcription therefore inhibiting production of pro-inflammatory proteins & promoting production of anti-inflammatory proteins like lipocortin-1 —> lipocortin-1 inhibits activity of phospholipase A2 which is involved in production of inflammatory mediators like prostaglandins & leukotrienes.
It has anti-leukocytic activity (suppresses infiltration of inflammatory cells, particularly leukocytes in the airway tissues)
Theophylines
Bronchodilator used for asthma & managing its symptoms like shortness of breath, wheezing and chest tightness, COPD to improve airflow & other inflammatory respiratory conditions. It’s a type of xanthine derivative. Non-selective adenosine receptor antagonists particularly on adenosine receptors A1, A2, A3, & by antagonising adenosine receptors on mast cells, it inhibits its release of histamine leading to relaxation of smooth muscles in airways (bronchodilation). It also has anti-inflammatory effects as it acts as non-selective inhibitors of phosphodiesterase enzymes —> increases intracellular cAMP —> activates protein kinase A —> inhibits release of inflammatory mediators like TNF-a & leukotrienes —> decreased inflammation in airways
Levothyroxine
Synthetic form of thyroxine (T4) which is one of the thyroid hormones produced by the thyroid gland. It serves as a synthetic replacement for deficient T4 in those with hypothyroidism. It’s absorbed in the GI tract & enters bloodstream where levothyroxine binds to thyroid hormone receptors on cells throughout the body. Some of Levothyroxine is converted to T3 particularly in the liver and kidneys & it is the more biologically active form of the thyroid hormone.
Bendroflumethiazide
Drug class: thiazide diuretic. Used to treat hypertension & oedema. Works by inhibiting Na+/Cl- reabsorption at the early distal tubule of the kidneys via the Na-Cl cotransporter. This results in increase in excretion of sodium, chloride & water.
Side effects: hypokalaemia
It causes hypokalaemia by inhibiting sodium ion transport across the renal tubular epithelium through binding to the thiazide sensitive Na-Cl cotransporter —> increased potassium excretion via the Na-K exchange mechanism. (Loss of potassium increases serum uric acid)
Sando K
Medication that contains potassium chloride, a supplement used to treat or prevent hypokalaemia.
Spironolactone
It’s an aldosterone receptor antagonist used to treat hypertension, oedema, heart failure & aldosteronism. It acts both as a diuretic and an anti-hypertensive drug. It competitively binds to receptors at the aldosterone-dependent Na-K exchange site in the distal convoluted renal tubule. It causes increased amounts of sodium and water to be excreted while potassium is retained. Therefore it doesn’t cause hypokalaemia or hyperuricemia.
