2 Analgesics
The student should be aware of:
pain theories, especially the ‘gate theory’ of Melzack and Wall (1964)
the difference between anaesthesia and analgesia
the accumulative effect of many analgesics, which can lead to intentional or accidental overdose
the different combinations of separate analgesic compounds
the possibility of addiction to analgesics
neonatal sequelae to maternal analgesia
the appropriateness of the analgesic compound to the complaint.
BP
Paracetamol (Acetaminophen)
Proprietary
Paracetamol (Actavis UK Ltd) (refer to BNF for manufacturers and advice on trade names)
Calpol® infant suspension (McNeil Products Ltd; Pinewood Healthcare) (refer to BNF for manufacturers and advice on trade names)
Calpol® infant suspension (McNeil Products Ltd; Pinewood Healthcare) (refer to BNF for manufacturers and advice on trade names)
Group
Analgesic, non-opioid
Uses/indications
Mild to moderate pain, headache, rheumatic pain, pyrexia
Type of drug
POM, GSL (sold to the public in packs of no more than 16 tablets; pharmacists may dispense up to 32 tablets)
Presentation
Tablets, oral suspension, dispersible tablets, suppositories
Dosage
Adult: oral: 500 mg–1 g 4–6-hrly (max 4 g daily); P.R.: 0.5–1 g q.d.s.
Paediatric: oral – dose calculated on 10 mg per kg body weight
Paediatric: oral – dose calculated on 10 mg per kg body weight
Route of admin
Oral, P.R.
Contraindications
Hypersensitivity, hepatic and renal disease, alcohol dependence
Side effects
Rare, blood disorders, rashes, overdose causes liver damage, pancreatitis with prolonged use
Interactions
Anticoagulants – with prolonged use seems to enhance effect of warfarin
Cholestyramine – reduces the absorption of paracetamol
Metaclopromide – enhances the effect of paracetamol
Cholestyramine – reduces the absorption of paracetamol
Metaclopromide – enhances the effect of paracetamol
Pharmacodynamic properties
Antipyretic, peripherally acting analgesic
Fetal risk
Epidemiological studies in human pregnancy show no ill effects
Breastfeeding
Short courses only – amount secreted too small to be harmful. No controlled study data available and taken by a large number of women with no observed increase in adverse effects on breastfed infants, therefore considered safe
BP
Aspirin (Acetylsalicylic acid)
Proprietary
Aspirin (Actavis UK Ltd)
(Various generic manufacturers; see BNF for advice)
(Various generic manufacturers; see BNF for advice)
Group
Analgesic, non-opioid, NSAID
Uses/indications
Mild to moderate pain, including headache, neuralgia, rheumatic pain, transient musculoskeletal pain, pyrexia
Type of drug
GSL (sold to the public in packs of no more than 16 tablets; pharmacists may dispense up to 32 capsules/tablets), POM
Presentation
Tablets, some dispersible, suppositories
Dosage
300–900 mg 4–6-hrly to a max 4 g daily
Route of admin
Oral, P.R.
Contraindications
Hypersensitivity, clotting disorders, haemophilia, asthma, angio-oedema, urticaria, rhinitis, impaired renal or hepatic function, dehydration, gastric ulceration, pregnancy, unless in very low doses on obstetrician’s orders
Side effects
Increased bleeding time, leading to haemorrhage, i.e. antepartum, intrapartum, postpartum, delayed onset and duration of labour (low doses are not harmful)
mild and infrequent, gastric irritation/ulceration, hypersensitivity, bronchospasm and skin reactions in hypersensitive patients, haematuria, nervousness, dizziness, tinnitus, insomnia, rash
mild and infrequent, gastric irritation/ulceration, hypersensitivity, bronchospasm and skin reactions in hypersensitive patients, haematuria, nervousness, dizziness, tinnitus, insomnia, rash
Interactions
Alcohol – enhanced effect on the gut
Antacids – increased alkalinity of urine
Analgesics – concomitant admin increases side effects
Anticoagulants – increased risk of haemorrhage (potentiates antiplatelet effect)
Antiepileptics – enhanced effect of phenytoin and valproate
Corticosteroids – enhances the risk of gastrointestinal bleeding and ulceration
Metoclopramide – increases rate of absorption and therefore increased effects of aspirin
Antacids – increased alkalinity of urine
Analgesics – concomitant admin increases side effects
Anticoagulants – increased risk of haemorrhage (potentiates antiplatelet effect)
Antiepileptics – enhanced effect of phenytoin and valproate
Corticosteroids – enhances the risk of gastrointestinal bleeding and ulceration
Metoclopramide – increases rate of absorption and therefore increased effects of aspirin
Pharmacodynamic properties
Aspirin is an analgesic, antipyretic, anti-inflammatory that inhibits the synthesis of prostaglandins
Fetal risk
Low-dose aspirin is not thought to have harmful effects; in high doses closure of PDA in utero, persistent pulmonary hypertension, possible reduction in the amount of amniotic fluid (Bubimschi and Weiner, 2010) not recommended after 34 weeks’ gestation, kernicterus in jaundiced neonates; is also reported to be linked with fetal growth deficiency and a purpuric rash in neonates, with depression of the platelet function
Breastfeeding
Potentially Reye’s syndrome (under 16s specifically), regular high doses could cause impairment of platelet function and hypoprothrombinaemia if neonatal vitamin K stores are low
BP
Codeine phosphate
Proprietary
Codeine phosphate (Actavis UK Ltd)
Codeine phosphate (non-proprietary, see BNF for details)
Codeine phosphate (non-proprietary, see BNF for details)
Group
Analgesic, opioid – morphine salt
Uses/indications
Mild to moderate pain, cough suppressant
Type of drug
POM, (CD – injection)
Presentation
Tablets, syrup, ampoules (CD)
Dosage
Oral: 30–60 mg 4-hrly (max 240 mg daily); IM: 30–60 mg 4 hrly
Route of admin
Oral, IM
Contraindications
As for morphine, raised intracranial pressure
Side effects
Constipation, nausea, sedation, respiratory depression, especially cough reflex, dependence. In labour – maternal gastric stasis and increased risk of inhalation pneumonia
Interactions
As for diamorphine
Pharmacodynamic properties
Codeine is a narcotic analgesic that acts via the central nervous system
Fetal risk
First trimester: inguinal hernias, cardiac, circulatory and respiratory system defects, cleft lip and palate, although not according to Bubimschi and Weiner (2010)
second trimester: alimentary tract defects
labour: neonatal respiratory depression and withdrawal
second trimester: alimentary tract defects
labour: neonatal respiratory depression and withdrawal
Breastfeeding
Amount of active metabolites secreted too small to be harmful and limited data available on breastfeeding women, where there was no observed increase in adverse effects on breastfed infants
BP
Co-codaprin
Proprietary
Co-codaprin (non-proprietary, see BNF for details)
Group
Analgesic, aspirin compound (aspirin 400 mg + codeine phosphate 8 mg)
Uses/indications
Mild to moderate pain
Type of drug
POM
Presentation
Tablets (white)
Dosage
1–2 tablets 4–6-hrly (max 8 daily)
Route of admin
Oral
Contraindications
As for codeine and aspirin
Side effects
As for codeine and aspirin
Interactions
As for codeine and aspirin
Fetal risk
As for codeine and aspirin
Breastfeeding
Codeine is excreted in small amounts. Manufacturers recommend to avoid administration of opioids in breastfeeding; should also be avoided in view of aspirin content, although there are no controlled studies available for breastfeeding women
BP
Co-dydramol (Paracetamol 500 mg + Dihydrocodeine 10 mg)
Proprietary
Co-dydramol tablets 10/500 mg (Actavis UK Ltd)
Group
Analgesic, paracetamol and opioid compound
Uses/indications
Mild to moderate pain
Type of drug
POM, GSL
Presentation
Tablets (white)
Dosage
1–2 tablets 4–6-hrly (max 8 daily)
Route of admin
Oral
Contraindications
As for paracetamol and dihydrocodeine
Side effects
As for paracetamol and dihydrocodeine
Interactions
As for paracetamol and dihydrocodeine
Fetal risk
As for dihydrocodeine
Breastfeeding
No controlled study data available for breastfeeding and the risk of untoward effects in a breastfed infant is a possibility. The compound is considered safe, as it has been taken by a large number of women with no observed increase in adverse effects in infants
BP
Co-proxamol (Paracetamol 325 mg + Dextropropoxyphene 325 mg)
Proprietary
Distalgesic® (Dista Products Ltd) NB: No longer licensed due to safety concerns, but may be prescribed for patients who find it difficult to change (BNF 62, 2011).
Group
Analgesic, compound of paracetamol and opioid salt
Uses/indications
Mild to moderate pain
Type of drug
POM (CD), GSL
Presentation
Tablets (white marked DG)
Dosage
1–2 tablets 4–6-hrly (max 8 daily)
Route of admin
Oral
Contraindications
Alcohol abuse, hypersensitivity to either of the constituents, addictive or suicidal clients, hepatic or renal impairment, concomitant paracetamol usage
Side effects
Dizziness, sedation, nausea, vomiting, constipation, abdominal pain, headache. NB: overdose is complicated by respiratory depression, heart failure and by hepatic failure, and can cause death in 15 minutes
Interactions
CNS depressant effect of the opioid constituent enhances the effect of CNS depressants, including alcohol
Anticoagulant – effect of warfarin possibly enhanced
Anticonvulsants – altered metabolism; see above
Antidepressants – altered metabolism; see above
Anticoagulant – effect of warfarin possibly enhanced
Anticonvulsants – altered metabolism; see above
Antidepressants – altered metabolism; see above
Pharmacodynamic properties
A compound analgesic with a non-narcotic (paracetamol) for relief of pain in musculoskeletal conditions and a narcotic (dextropropoxyphene) for relief of visceral pain
Fetal risk
Not established as safe in pregnancy, withdrawal reported in neonates. Potential benefits should outweigh the possible hazards
Breastfeeding
Amount secreted too small to be harmful
BP
Co-codamol (Paracetamol 500 mg + Codeine 8 mg)
Proprietary
Co-codamol (Wockhardt UK Ltd) – paracetamol 500 mg + codeine 30 mg
Group
Analgesic, paracetamol and opioid compound
Uses/indications
Mild to moderate pain
Type of drug
POM
Presentation
Tablets, capsules, dispersible tablets
Dosage
1–2 tablets or capsules 4-hrly, max 8 daily
Route of admin
Oral
Contraindications
As for paracetamol and codeine
Side effects
As for paracetamol and codeine phosphate
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