Antihistamines
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- Created by: amazingemilyjones
- Created on: 08-04-19 10:43
Antihistamines
Antihistamines
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Antihistamines
- OTC medicines used to treat:
- allergies
- reactions to insect bites or stings
- motion sickness
- nausea related to migraine
- short term treatment for sleeping difficulties
- Divided into two main groups:
- 1st generation (drowsy - cross blood-brain barrier) - chlorphenamine (Piriton), Diphenhydramine (Nytol), Promethazine (Phenargan), Buclizine (found in combination in Migraleve)
- 2nd generation (non-drowsy - do not cross blood-brain barrier) - Loratidine (Clarityn), Cetirizine, Acrivastine (Benadryl)
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How do antihistamines work?
- Histamine
- Basic amine present in most tissues. Increased concentration in lungs, skin and particularly in GI tract
- At a cellular level found mainly in mast cells and basophils
- Four types of receptors (G-protein coupled) H1, H2, H3 and H4
- Main action in humans:
- Stimulation of gastric acid secretion (H1)
- Contraction of smooth muscle, except blood vessels (H1)
- Cardiac stimulation (H2)
- Increased vascular permeability (H1)
- Stimulation of arousal in the circadian
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How do antihistamines work?
- Main pathophysiological role of histamines:
- Stimulation of gastric acid secretion (treated with H2 receptor antagonists)
- Mediatior of type 1 hypersensitivity reactions
- Allergic reaction overview
- Initial contact with allergen
- Plasma cell releases antibodies
- Antihistamines bind to receptors on mast cells
- Subsequent contact with allergen
- Histamine and other chemicals released - allergic reaction
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Seasonal Allergic Rhinitis
- Immune system caused and mistakenly identifies normally harmless substance as an intruder
- This substance is called an allergen - pollen
- Immune system responds by releasing histamine and chemical modulators that cause the typical hayfever symptoms
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Hay fever symptoms
- Rhinorrhoea
- Runny nose with a discharge that is thin, clear and watery
- Nasal congestion
- Inflammatory response to allergen that causes vasodilation and congestion
- Nasal itching
- Eye symptoms
- Eyes may be itchy and watery - result of tear duct congestion and pollen grain caught in the eye
- Sneezing
- Classic response is sneezing then rhinorrhoea then congestion
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Allergen Avoidance Advice
- Wearing wraparound sunglasses to stop pollen getting in eyes when outdoors
- Apply a small amount of petroleum gel to nasal openings to trap pollen grains
- Avoid cutting grass, playing or walking in grassy areas
- Taking a shower and changing clothes after being outdoors
- Do not keep fresh flowers in the house
- Keep car windows closed - pollen filter can be bought for air vents in cars
- Staying in doors when pollen count is high
- Vacuum regular - high-efficency particle arresting (HEPA) filter
- Damp dust
- Keep windows closed - particularly morning and evening
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When to Refer
- Wheezing
- Difficulty with breathing, possibly with a cough suggests an asthma attack
- Earache and facial pain
- Allergic rhinitis can be complicated by a secondary bacterial infection
- Purulent conjunctivitis
- More painful and discharge changes from watery to coloured and sticky
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Hayfever Treatment
- Antihistamines - Cetirizine, Loratadine, Chlorphenamine, Acrivastine
- Steroid nasal sprays - Beconase
- Sodium cromoglicate
- Decongestants
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Motion Sickness Symptoms
- Nausea and/or vomiting
- Dizziness
- Pallor
- Cold sweats
- Hypersalivation
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Motion Sickness Treatment and Referral
- Treatment with hyoscine hydrobromide
- minimum age 4 years, anti-muscarinic adverse effects, interacting medicines, short-acting (4 hours), take 30 minutes before travel - drug of choice
- Treatment with antihistamines - contraindications and adverse effects same as hyoscine hydrobromide
- Cinnarizine - minimum age 5 years, lasts up to 8 hours, take 2 hours before travel
- Promethazine - minimum age 2 years, lasts longer than 8 hours, take night before travel
- Referral
- OTC failure - continuing symptoms
- Age - under 2
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Insomnia
- Difficulty getting to sleep or staying asleep long enough to feel refreshed in the morning
- 1 in 3 people in the UK are affected - particularly common in the elderly
- May be short or long term
- Persistent insomnia can have a significant impact on quality of life potentially limiting productivity, affects mood and relationships with friends, family and colleagues
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Insomnia Causes
- Underlying medical conditions
- Biological, e.g. aging, pregnancy
- Behavioural, e.g. children
- Poor sleep hygeine
- Mental health, e.g. depression
- Psychological, e.g. stress
- Altered patterns, e.g. shifts
- Environmental noise
- Medicines
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Medications that Cause Insomnia
- Selective Serotonin Reuptake Inhibitors (SSRIs)
- Dopamine agonists
- Amphetamines
- Anticonvulsants
- Cold medicines and decongestants
- Steroids
- Beta agonists
- Theophylline
- Diuretics
- Caffeine
- Alcohol
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Sleep Hygiene
- Maintain a routine with regular bedtime and waking time
- Alcoholic and caffeine containing drinks should be avoided
- Avoid sleeping in very warm rooms
- Take daytime and not evening exercise
- No daytime naps
- No sleeping in to catch up
- No strenuous mental activity at bed time
- Associate bed with sleep, not TV or phones
- If unable to sleep - get up and do something, return to bed when tired
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Treating Insomnia and When to Refer
- Pharmacologicsl interventions
- Sedating antihistamnes - promethazine, diphenhydramine
- Referral
- Under 12
- Duration >3 weeks
- No known cause
- Previous undiagnosed medical conditions
- Symptoms suggestive of anxiety, stress or depression
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