TOPICS COVERED IN DR COLLEE

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TOPICS COVERED IN DR COLLEE’S LECTURE

1)Analgesics

2)Anti-emetics

3) Anxiolytics, hypnotics & sedatives

ANALGESICS:

OPIOIDS

Act on opioid receptors in the CNS

E.g. Strong: Morphine          Weak:  Codeine

             Pethidine              Dihyrocodiene

Main actions of opioids:     Analgesia

                           Sedation/euphoria

                              Nausea & vomiting

                           Respiratory depression

                           Antitussive

                           Pupillary constriction

                           Constipation

                           Histamine release

                           (pruritus & bronchospasm – asthmatics)

Pharmacokinetics of analgesics are very important.

E.g. Morphine

Routes of administration include p.o., i.m.,s.c., i.v.,rectally & Intrathecally.

I.V.- admin. of bolus produces rapid rise in plasma levels ( effects in10-15 mins)-  relieves patients pain quickly- great! However runs the risk of  rapid respiratory depression – not so great!

I.M./S.C. -  slower  rise in plasma levels &onset of action (effects in 30-45 mins) – less risk of respiratory depression but slower onset of pain relief – not so good!

P.O.  metabolism occurs in the liver and in the gut wall, and the bioavailabilty of morphine is 16-64%.  Therefore larger doses are needed.than other routes of admin.

Morphine can be given as PCA (patient controlled analgesia)

This consists of  a microprocessor syringe pump capable of being programmed to deliver a predetermined bolus dose of a drug i.v.

 * Remember naloxone for overdose treatment.

NSAIDS

Act primarily peripherally: inhibit prostaglandin synthesis

E.g. Aspirin  Ibuprofen Diclofenac Keterolac

Main Actions of NSAIDS:         Analgesics

                                 Anti-inflammatory

                                 Antipyretic

                                R.S. - Bronchoconstriction  (asthmatics)

                                G.I. -  Gastritis/gastric ulcers

                                             Renal – Loss of autoregulation

                                 Interstitial nephritis

                                 Papillary necrosis (long term)

                                 Haematological: Decreased platelet adhesiveness

NSAIDS and Opioids are often used in combination to reduce the doses required and therefore the side-effects.

PARACETAMOL

Main  actions:    Antipyretic

                        Analgesics

                        Not anti-inflammatory

LOCAL ANAESTETICS

E.g.   Lidocaine: Fast onset,  shorter duration of action about  90 mins

Bupivacaine:slower onset, about 30 mins longer duration of action (hrs)

Mechanism of action

Reversible block of conduction along nerve fibres.  Depress small unmyelinated fibres first and larger myelinated fibres last therefore order of block is: pain>temperature>touch>motor function.  Most are weak bases that exist mainly in a protonated form at body pH.  The drugs penetrate the nerve in non-ionized form, but once inside the axon some ionised molecules are formed and these block  Na+ channels.  This means that LA will not work when administered directly into inflamed tissues where the pH is altered.

Systemic toxicity  can result from absolute overdose or inadvertent intravascular injection.  Early signs:circumoral numbness, tingling, drowsiness, anxiety and tinnitus.  Severe cases: convulsions, coma apnoea and CV collapse.  (The addition of a vasoconstrictor reduces toxicity, but is contraindicated for injection close to end arteries)

Modes of use-

Non-specialist: infiltration; ring block; nerve block

Specialist: epidural, spinal, i.v. regional, plexus block

Assessment Of Pain

Effective pain management depends on assessment of pain, only the patient can say how much pain they are experiencing.  It can be quantified using scales e.g. 0 to 10, 0 being no pain at all and 10 being the worst pain ever.

NAUSEA AND VOMITING

Common in certain groups of patient  e.g.    patients post-op, patients receiving chemotherapy and those with increased susceptibility – children, women (especially after gynaecological surgery), travel-sickness prone.

Groups Of Drugs:

1.   Antidopamingeric drugs

Metoclopramide

Domperidone             Extra-pyramidal side-effects –     movement disorders (caution in elderly )

                                                   & oculo-gyric crisis

   Phenothiazines  e.g. Prochlorperazine (stemetil)

   2.      Anticholinergic  drugs

Atropine

Hyoscine                                     Rarely used for this purpose now

3.   Antihistamines

Cyclizine                                      Causes drowsiness.

4.         5-HT3 antagonists

Ondansetron                                Causes: constipation, headache, flushing

5.      Other drugs

Drugs classed as pro-kinetic: Cisapride & Metclopramide

Steroids – dexamethosone

* Anti-emetic agents are often used in combination to increase effectiveness

SEDATIVE, ANXIOLYTIC, HYPNOTIC DRUGS

Why are such drugs needed?

Answer: for treatment of pain, restlessness, anxiety, loneliness & depression -  for premediation (where amnesic effect is useful).  All of these are interlinked.  Before prescribing, always consider the cause e.g. confusion, hypoxia, dementia, hunger, dehydration and hypovolaemia.

Examples of drugs

Benzodiazepines: enhance GABA-mediated inhibition in CNS.

Midazolam – main i.v. benzodiazepine in clinical use

Temazepam – popular oral benzodiazepine

Adverse effects:   Drowiness

                        Impaired alertness

                        Ataxia (in elderly)

                        Respiratory depression (especially i.v.)

                        Interactions with other CNS depressants

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