Levodopa

Today my tutor explained to me why normally levodopa was prescribed together with carbidopa (Sinemet). The levodopa is prescribed for treatment of Parkinson’s disease which is due to low level of dopamine in the brain. Dopamine is responsible for movement or mobility.

Levodopa works by being converted to dopamine in the brain. However, before it is being converted to dopamine in the brain, it undergoes peripheral conversion to dopamine, thereby reducing the effectiveness of the drug while increasing the side effects such as nausea, vomiting and cardiovascular effects.

Therefore, carbidopa is prescribed in combination with the levodopa in order to prevent the levodopa being broken down before it reaches the brain. This then allows a lower dose of levodopa to be taken to avoid or minimize side effects such as nausea and vomiting.

At home I did extra study and found that the total daily dose of carbidopa should be a least 70mg. Lower dose of carbidopa may not achieve full inhibition of extracerebral dopa-decarboxylate.

Hospital prescription

I did the calculation for the hospital prescription for 3 months supplies. The following is the method I used to get to the quantities to be dispensed.

For codeine phosphate, since it is administered four times a day, hence, in a week, it is 28 tablets. Then 3 months is equivalent to 3 x 4 weeks = 12 weeks. Therefore, the total quantities to be dispensed for codeine phosphate is 12 x 28 tablets = 336 tablets.

Since the pack comes in size of 28 tablets per pack. Therefore, 12 packs of 28 tablets of codeine phosphate were dispensed.

For naproxen, twice a day administration in a week is equivalent to 14 tablets. Since the pack comes in 56-tab pack (14 x 4 weeks), therefore, 3 packs were dispensed.

For lansoprazole, once a day in a week is 7 capsules. The pack comes in 28-tab pack; therefore, 3 packs were dispensed.

Schizophrenia - chlorpromazine

I queried about chlorpromazine with my tutor and learned that chlorpromazine used as anti-depression is not very recommended. This is because there is possibility of developing adverse effects which can be irreversible.

Then we discussed more about antipsychotic drugs which some are used to treat schizophrenia. Opposite mechanism to Parkinson’s disease, schizophrenia is due to high level of dopamine or the brain is too sensitive to dopamine.

I learned that chlorpromazine associated with a wide range of side effects, e.g. extrapyramidal symptoms such as parkinsonian symptoms, dystonia, akathisia, and tardive dyskinesia. I did little research about the causes and found that dyskinesia might be due to long term treatment of L-Dopa for Parkinson’s disease besides high level of dopamine which causes involuntary movement impaired.

Then few days later, I was taught that procyclidine which is an antimuscarinic drug, is used to counter the side effects of chlorpromazine or antipsychotic drugs. From the BNF 53, procyclidine is used for Parkinsonism and drug-induced extrapyramidal symptoms, but not for tardive dyskinesia.

Breast Cancer and Prostate Cancer

I was taught by my tutor about the use of tamoxifen in the treatment of breast cancer. Tamoxifen (oestrogen inhibitor) is used to block and stop oestrogen to cancer cell. This is because the certain breast cancer cells use the oestrogen to survive. Tamoxifen can be used in both pre- and postmenopausal women.

On the other hand, aromatase inhibitor, anastrozole is used in postmenopausal women only with breast cancer. It works by inhibiting the conversion of androgen to oestrogen. This is because androgen present in the women as well and may be converted to oestrogen.

At home, I did further study on the topic and learned that diethylstilbestrol is used to treat prostate cancer in men by suppressing the effect of testosterone, hence shrinking the tumour. It can be used to treat breast cancer in women as well but higher doses are needed.

Apart from that, I also learned that gonadorelin analogue is used to treat advanced breast cancer in premenopausal women and advanced prostate cancer in men. It is known that the gonadorelin analogue causes stimulation of luteinising hormone (LH) release in the first 1 – 2 weeks before it starts depress the LH the following weeks. Therefore, it is important to administer the patient with anti-androgen before starting gonadorelin analogue, approximately 3 weeks before.

Examples of gonadorelin analogues are buserelin, goserelin, or triptorelin.

Examples of anti-androgens are cyprotene acetate, flutamide, or bicalutamide.