The efficacy of codeine is dependent on its demethylation to morphine. This extent of demethylation has wide inter-individual variability, making codeine's efficacy as a analgesic variable. Oxycodone is a semi-synthetic opioid and is a weak agonist on mu opioid receptors.

Codeine has been the mainstay of analgesia for patients after craniotomy for many years. Traditionally, craniotomies were not thought to be very painful procedures, hence the use of codeine, a moderately potent opioid (when compared to morphine).

However, in recent years, it has been found that up to 70% of post-craniotomy patients have moderate to severe pain and codeine did not provide adequate analgesic relief. Many studies have compared codeine to other drugs such as PCA morphine, fentanyl and tramadol, and patients on these stronger opioids generally had lower pain scores and better satisfaction.

No study has been conducted to determine the efficacy of analgesia of oral oxycodone to oral codeine.

Hence, the hypothesis is that oxycodone is more effective than codeine in providing pain relief in post-craniotomy patients.

Inclusion Criteria:

• Ages 21-70 years of age
• Planned elective craniotomy
• ASA 1-3
• GCS 15 pre and post-op
• Able to understand and use the visual analogue scale

Exclusion Criteria:

• Patients with GCS < 15 pre and/or post-op.
• Patients who are unable to quantify pain according to VAS scale.
• Patients who will be left intubated post-op.
• Contraindications and/or allergies to any of the trial drugs.
• Patients with renal and/or hepatic impairment.
• Patients with decreased respiratory reserves.
• Patients with post-op cognitive dysfunction.