Explain the way that mild and strong analgesics prevent pain.

Mild analgesics:

Strong analgesics:

The structure of morphine and diamorphine (heroin) are shown in Table 20 of the Data Booklet. State the name of the functional group present in diamorphine that is not present in morphine.

Discuss two advantages and two disadvantages of the medical use of morphine and its derivatives.

Advantages:

Disadvantages:

Mild analgesics:

mild analgesics work by intercepting pain stimulus at source;

suppress production of prostaglandins/pain sensitizing substances / OWTTE;

Strong analgesics:

strong analgesics work directly on opioid/pain receptors in brain;

suppress transmission of pain impulses in brain/CNS / OWTTE;

ester;

Accept alkanoate/ethanoate/acetoxy.

Advantages:

Award [1 max] for any two of:

strong pain relief / strong analgesic;

sedation / OWTTE;

treatment of diarrhoea;

relieve coughing;

Disadvantages:

Award [1 max] for any two of:

addiction;

tolerance;

dependence;

constipation;

depresses respiratory drive;

Accept “criminals/drug addicts might get access to strong analgesics intended for medical use” / OWTTE.

Award [1 max] if one advantage and one disadvantage are given.

Although the question on mild and strong analgesics, (a), is a question that has been asked previously a myriad of times, few surprisingly scored all four marks. Candidates occasionally discussed types of medication rather than mode of action. For mild analgesics many did not state the fact that these analgesics work by intercepting the pain stimulus at the source itself. The suppression of the production of prostaglandins often was not alluded to. For strong analgesics the most common mistake involved candidates not referring to opioid receptors in the brain.

(b) proved no problem for candidates though some stated incorrect functional groups or classes (alcohol and carboxylic acid were common incorrect answers). Please note that to prepare new candidates for the 2016 syllabus, the markscheme was later altered to include the correct naming of functional groups following IUPAC guidelines.

In (c), most candidates scored at least one mark. For the advantage few stated the fact that morphine is a strong analgesic.