Pre-hospital Medications Part 3

diphenhydramine is?

given by paramedics for it’s anti-histamine properties in the treatment of moderate to severe allergic reactions, including anaphylaxis

it is classified as an antihistamine but is also an

anti-motion-sickness drug

antiparkinsonian

cough suppressant

sedative

action of diphenhydramine

works by competitively blocking the effects of histamine at H1 receptor sites

prevents histamine from binding to receptor sites and exerting its effects in moderate to severe allergic reactions

also has anticholinergic properties

competitive antagonist of muscarinic receptors

pathophysiology of anaphylaxis

body responds to a foreign substance and a type 1 hypersensitivity reaction occurs

histamine is released from mast cells, which normally will increase blood flow and attract white blood cells to the area of the invading substance but in a hypersensitivity reaction, histamine (and other chemicals) is released in large quantities systemically causing anaphylaxis 

histamine functions 

histamine functions by binding to histamine receptors (H1 to H4)

histamine receptors are found on:

smooth muscle endothelial tissue 

vasodilation, increased vessel permeability, bronchoconstriction, chemotaxis causing nasal congestion and sneezing

central nervous tissue

which is responsible for the drowsiness associated with diphenhydramine as it easily crosses the blood brain barrier 

widespread histamine release causes

vasodilation

bronchoconstriction

increased capillary permeability

edema

runny nose

watery eyes

urticaria

anticholinergic effects

cholinergic neurons/receptors are part of the parasympathetic nervous system

acetylcholine is the primary neurotransmitter of the parasympathetic nervous system. they may act on nicotinic receptors or muscarinic receptors

anticholinergic medications will suppress the parasympathetic nervous system activity 

diphenhydramine side effects

drowsiness due to blockage of histamine receptors in the CNS

constipation

dry mouth

blurred vision

urinary retention

absorption of diphenhydramine

well absorbed when taken orally or by injection (IM or IV)

due to the first pass effect, 40-60% of the drug reaches systemic circulation when take orally

distribution of diphenhydramine

widely distributed to body tissues

will cross placental barrier

pregnancy class B

metabolism of diphenhydramine

metabolized in the liver with a half-life of 2.5-7 hours 

interactions of diphenhydramine

when used with CNS depressants, they will have addictive effects with regards to sedation

alchohol

anti-depressants

opioid analgesics

MAO inhibitors prolong and intensify anti-cholinergic properties of all antihistamines

increased anticholinergic effects with tricyclic antidepressants 

diphenhydramine is a first generation antihistamine?

true

second generation anti-histamines

do not cross the blood brain barrier to act on central histamine receptors and therefore do not cause drowsiness and have fewer interactions with other drugs

cetirizine (zyrtec)

loratadine (claritin)

H2 receptor antagonists can also be used to treat?

gastric issues such as GERD and peptic ulcers

ranitidine (zantac)

eemetic center lies in the?

medulla of the brain

stimulation of emetic center sends motor impulses through the vagus nerve to upper GI tract

sends impulses from spinal nerves to the diaphragm and abdominal muscles leading to vomiting

vomiting/emetic center may be stimulated by?

stimulation of the chemoreceptor trigger zone (CTZ)

certain medications, toxins, and radiation stimulate the CTZ

direct stimulation of emetic center by inner ear/vestibular system (motion sickness)

the GI tract

input from cerebral cortex to vomiting center (smells, memories)

action of dimenhydrinate

has antiemetic actions that act centrally at the CTZ to reduce nausea and vomiting

it is an anti-cholinergic and antihistamine- antiemetic effect also come from H1 receptor blocking properties 

dimenhydrinate also acts to inhibit vestibular stimulation

absorption of dimenhydrinate 

well absorbed orally IM or IV 

distribution of dimenhydrinate

widely distributed

metabolism of dimenhydrinate

metabolized by the liver and excreted in the urine

half like of dimenhydrinate 

5-8 hours

pregnancy with dimenhydrinate

can cross placental barrier and is excreted in breast milk, ise caution, as a guideline, it should be considered for severe vomiting for hyperemesis

interactions of dimenhydrinate 

may have potentiation or addictive effects when used with anticholinergic medications, antihistamines or with CNS depressants

alchohol

opioid analgesics

sedatives

anticholinergics (atropine, atrovent, tricyclic antidepressants)

MAO inhibitors intensify and prolong anticholinergic effects

antihistamines (benadryl, atarax, claritin)

ondansteron

ondansetron is also an anti-emetic used to prevent nausea and vomiting and is classified as a selective serotonin (5-HT3) receptor antagonist

it works by blocking the effects of serotonin in the GI tract (vagus nerve)

serotonin is released in response to stomach irritants to increase gastric motility and induces nausea and vomiting

serotonin syndrome

patient taking SSRI’s or SNRI’s will have increased action of serotonin in the body, and the administration of ondansetron could potentiate the effects of serotonin

patient may have a headache, agitation, confusion, tremors, hyperthermia, diarrhea, vomiting, tachycardia, hypertension, seizures, LOC

opioids

includes natural opiates and synthetic opioids which are commonly prescribed for pain management and to treat addiction

acetaminophen action

antipyretic action is believed to be a direct effect on the heat regulating centers in the hypothalamus leading to heat dissipations through vasodilation and sweating

analgesic action is through inhibition of prostaglandin synthetase in the CNS, though its action is not well understood 

absorption of acetaminophen

rapidly and completely absorbed in GI system

metabolism of acetaminophen

broken down by livere

excretion of acetaminophen

kidneys

half life of acetaminophen

1-4 hours

may be longer in overdose or liver disease

acetaminophen caution

risk of hepatotoxicity

in cases of overdose (accidental or intentional), significant hepatotoxicity may occur

risk is increased in chronic alcoholics and patients with liver disease

action of ibuprofen

inhibits prostaglandin synthesis by inhibiting COX enzymes resulting in analgesic and anti-inflammatory effects 

cyclooxygenase (COX)

is an enzyme involved in inflammation and is required for the formation of prostaglandins, which are inflammatory mediators

COX-1 is responsible for?

prostaglandins important in maintaining normal bodily functions in the GI tract, kidneys, and platelets 

COX-2 is responsible for?

synthesizing prostaglandins that are important mediators of pain, inflammation and fever

the primary actions of NSAIDs is

mostly non-selective, inhibition of COX and resultant anti-inflammatory properties

action of ketorolac

inhibits production of prostaglandins in inflamed tissue, which decreases responsiveness of pain receptors in damaged tissue