Antibiotics and Analgesia/anaesthesia

Antibiotics

The side effects of most antibiotics are nausea and vomiting, gastrointestinal upset and skin irritation. However, if you notice that a patient is taking an aminoglycoside they may require a closer eye than normal. As with any antibiotic, you will want to know exactly why they are having them from an infection-control perspective. Aminoglycosides are a particular type of antibiotic, the most commonly seen are gentamicin, streptomycin and neomycin. Usually given to treat Gram-positive cocci in aerobic conditions, they inhibit the process of protein synthesis from within the bacterium. Unfortunately, the aminoglycosides are ototoxic, i.e. they damage the sensory cells of the cochlea and vestibular systems which is irreversible and will result in vertigo, ataxia and dizziness, etc.

Analgesia/anaesthesia

Possibly the most common type of medication you will come across in your medical career. Pain medication may range from simple analgesia, such as paracetamol (acetaminophen) and ibuprofen to the extreme opioids and

local anaesthetics. You may also encounter adjunct analgesia, such as amitriptyline and gabapentin.

Inhaled anaesthetics, such as nitrous oxide, halothane, isoflurane, etc., work by inhibiting synaptic transmission which peripherally block pain signals and centrally depress areas of the midbrain associated with consciousness and

the thalamus associated with analgesia. As a physiotherapist you will probably only encounter nitrous oxide, N2O, (when combined with oxygen at 1 : 1 ratio it is known as Entonox) as it is used extensively in acutely painful situations, such as childbirth or sporting injuries. The effects are extremely rapid and short-lived and the adverse effects are few: patients with pernicious anaemia (deficiency of vitamin B12) should avoid long-term use (longer than six hours) as bone marrow depression may occur. Repeated

and prolonged usage may produce amnesia.

Opioids are any substances that act in a similar way to morphine, while the term opiate is restricted to synthetic, morphine-like drugs. Opium has been used for thousands of years as a pain killer (and a recreational drug). The

morphine-like drugs are known as agonists (morphine, diamorphine (heroin) and codeine), partial agonists (buprenorphine) and antagonists (naloxone) depending upon their expression on the cell. Opioid receptors have three subtypes: μ, δ, and κ (mu, delta and kappa) which contribute to the analgesia at different levels. The opioid receptors are G-coupled receptors and the net effect is that of inhibition of pre-synaptic release of neurotransmitter, thus preventing nociception at the spinal level. While achieving analgesia, strong opioids also produce euphoria, especially if administered i.v. It is essential for all concerned to understand the importance of the side effects of morphine related drugs:

sedation;

respiratory depression;

nausea and vomiting;

peristalsis depression (resulting in constipation);

histamine release (resulting in bronchoconstriction,

hypotension and itching).

Buprenorphine is a partial agonist and is given as a sublingual tablet or as an injection as the first-pass metabolism is so extensive it is rendered inactive orally. It is slow-acting with a predictable 12-hour half-life and less

respiratory depression than morphine, hence its common usage in the community.

Fentanyl is delivered by epidural and transdermal patch. It has a short-acting half-life (2 hours) and is highly potent. Remifentanil (a variant form) is becoming increasingly popular as it is faster-acting and is associated with

more rapid recovery.

Codeine/dihydrocodeine is used for mild pain and is available to buy from pharmacies. It is a prodrug (it is metabolised into morphine) and taken as a syrup or tablets commonly combined with paracetamol. It is approximately a fifth as potent as morphine but more readily taken up when taken orally. Codeine is also used as an antitussive (suppresses coughs) in children.

Tramadol is taken orally or i.v. It is generally well absorbed and has a predictable half-life of 4–6 hours. Although it has a weak opioid action, it also has a centrallyacting action which inhibits the uptake of noradrenaline.

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